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The Sound of Silence...

Sound of silencePlayed on the Pelagian DCCCR, words by Andy Campbell

It’s the silence as the descent begins and the surface recedes, the silence, I didn’t expect that, I had read and talked to people about diving on closed circuit rebreathers but I couldn’t remember anyone really pointing this out… Diving is always a peaceful respite from the chaos of the surface, “me time” even when shared with others and I have always appreciated the lack of ringing phones or emails but the noise I never really appreciated how noisy we all are on open circuit scuba and now diving in silence I do.    

On each subsequent dive with the Pelagian DCCCR (Diver Controlled Closed Circuit Rebreather) this has not changed, the silence the switch from open circuit scuba (OC) to the Pelagian brings is almost mesmerising and I know that even after all those dives on OC that these and future dives on the Pelagian are and will always be that little bit more special to me for this reason.

The Pelagian DCCCR from Rebreather Lab seemed to be the natural choice when Big Blue Tech looked into the CCR world, I had seen them dived before and being manufactured a 2 hour ride from Koh Tao it would help immensely with logistics, training and maintenance but still not an easy choice to make. It wasn’t just about the location and logistics, whilst undergoing my initial tech training and instructor training the dive centre also used the Pelagian DCCCR and like most open circuit divers I looked on with growing curiosity. Any form of CCR demands respect and for good reason they have a reputation that precedes them…  Expensive, complicated, overly technical and yes “dangerous” with the obvious risks as you will see on any brief Google search. So my first question was the obvious one, “is it all worth it?” and as I encountered more and more CCR divers the answer was always a reassuring “Yes”.

Now this is not the blog where I will go into all of the intricacies and differences between a Diver Controlled CCR or Electronically Controlled CCR (nor could I), the crux of this blog is to reflect on my initial question now that I’m now in a better position to answer it for myself. So is it worth it? Quite simply “Yes, Yes and thrice Yes”… The training is tough, it should be with plenty of dark humour, a seven day course (Now available at Big Blue Tech) with quite literally a lot of up’s and down’s, the learning curve is steep almost cliff like but yes it’s all worth it, for the silence, for the enhanced marine experience (yes the marine life comes closer) and for the new understanding of diving each CCR diver will gain.

On the Pelagian DCCCR I can only speak positively, during our initial search for a CCR the options were numerous with computer controlled units as well as the Pelagian in the mix.  We looked at several different angles and different solutions raised different concerns, one of mine was could you effectively manage this whilst being able to actually enjoy the diving experience? Or would you spend the entire dive constantly checking and rechecking the PO2, gauges and loop volume.  In the end it couldn’t be simpler and in later blogs I will explain more with added input from Rebreather Lab about operating the Pelagian but it’s not over bearing and as with air, depth and time checks soon just becomes part of your diving routine with the simplest of adjustments to maintain the set point (PO2).

It’s mechanical, no software… still reassuring in a world of updates, no voting logic (bit like the UK and US to be honest) and yes you’re responsible for your own safety. Preparing the Pelagian for diving is of course more complex than a traditional scuba unit but with time becomes intuitive with check list’s that are easy to follow and the reassurance that once completed and all the boxes ticked you are ready to go.

Buoyancy, well after thousands of dives on open circuit scuba configurations and the pursuit of “perfect” buoyancy the CCCR kind of breaks your heart and then teases you before finally embracing you… No it’s not quite the same and during the initial training you wonder if something in your head is broken, you get moments of surreal stillness and then the up’s and down’s as you try to exhale to descend or inhale to ascend but it comes and just as with open circuit scuba will now see me on a tireless and immensely rewarding journey in search of perfect buoyancy (dive one on advanced open water, yea right, lol).

So watch this space for the next blog with more on the training and on my Pelagian experiences , of course if you would like more information then please don’t hesitate to contact us on This email address is being protected from spambots. You need JavaScript enabled to view it.  



Solo Diving ‘One of diving’s last taboos’ seen through the eyes of our students


Solo diving really is one of the ‘last taboos’ of diving, letting divers venture off on their own even with the correct  training and certifications is not something many dive shops will let you do.

The concept that "safe" diving only happens within the "buddy" system is ingrained right from the start; the idea that help is an arm’s length away is reassuring to the new diver. With time the flaws of the system become more evident, can the diver you have just met be trusted to actually help should your worst fears become a reality? When was the last time they or you for that matter practice air sharing and have you ever practiced this neutrally buoyant?

So the SDI solo course is not just about becoming a solo diver and roaming alone, it’s about making you a better diver, a better buddy and that’s good for everyone.

We recently had four divers all from different diving backgrounds and different skill levels, who wanted to explore the world of diving solo. Throughout this blog we have a Q & A with questions from present and past students   about what is involved in their solo diving course and got our current tech manager to answer these questions. The purpose for this blog is to give people a clearer understanding of Solo Diving. Finally we have our Big Blue Tech students write us up their personal feedback following their course about their experience.


Let’s be honest we have all gone diving and wanted to wonder off and explore the reef or spend a little more time with different marine life without the pressure to keep moving on; this is why we have certifications and courses at Big Blue Tech under SDI to allow you to go solo on some of the best  dive sites in the world.

SDI says “Being one of SDI’s most popular courses, the Solo Diver course stresses proper dive planning, personal limitations, and accident prevention, as well as the benefits, hazards, and proper procedures for diving solo. You will also learn the additional equipment that is required for solo diving including its proper usage and assembly. This is the perfect course for underwater photography and underwater video divers as well as those diving with their children or buddies that may not very experienced in scuba diving.”

Q&A - With Andy Campbell on an introduction Solo Diver SDI course

1. What is the objective of the solo diver course?

“The objective of a solo diver course is to make you a better buddy as well as a solo diver”

“There are flaws in the buddy system and those flaws are identified during the theory of the solo course… for example you may end up diving with a buddy that is very inexperienced or with a buddy that possibly won’t be able to help you should a problem occur”

“When you become a solo diver you become what we call completely independent / self-reliant you are carrying a redundant air supply with you, so if you were to have a problem with your primary tanks or your primary scuba system you’re carrying a backup”

“The best person to save you is you! It won’t involve any panic because you are already accustomed to that equipment you are using and you just switch tanks/ mask etc and then you ‘call the dive’”

2. What are the minimum requirements you need for a solo diver speciality course?

“For the solo diver course with SDI the pre-requisite is 100 logged dives prior to starting the course, but also the confidence and comfort level in diving that would make you a competent solo diver”

3. What is the structure of the solo diver speciality i.e. skills / tasks that would need to be carried out and performed?

“So for the solo speciality the skills range from being able to cope with an out of air scenario, a loss of buoyancy, free flowing LPI, replacement of the mask all of which are covered in skills dives prior to letting a student adventure into the open water on their own and the bottom line is that you need to become self-reliant.”

“We talk about flight and flight, we talk about equipment failures that you could encounter and we talk about the responsibility a diver has not only to themselves but to their buddies when they are recreational diving.”

"Planning a dive is one area that is normally a shock to the student, they are used to just jumping in and following a dive master and that won't work anymore. Gas planning and management is almost alien to most divers with an SPG being there to tell you when to go up.. Not anymore, it all changes and for most students this is a real eye opener and in some cases a shock about how little they really knew even with those 100 dives"

4. Is their course training material provided?

“YES! and for all the courses we offer we provide all the materials you need for the lectures and exams”

5. What happens if something goes wrong? Do you plan a backup procedure?

“This is basically the foundation of the solo course. You become more aware of your own environment, plan dives with a lot more detail than the average diver, check your equipment to a higher level and of course you have an added piece of equipment which is a total game changer and it is your redundant air supply. This could be sidemount / twin set or a pony tank / stage tank”

6. When would you use a solo specialty?

“In my case every time I don’t want to dive with the wife, no seriously I dive solo on parts of the dives sites few people are interested in, the sand for instance and on some dives i see nothing at all.."

“In addition to that if you are a videographer or photographer and you want that time on your own but the group wants to move on then you feel under pressure to keep moving.”

 “Solo diving is one of the last taboo’s in diving to an extent, and it doesn’t need to be. As long as you plan the dives, dive within ‘your comfort zone’, you backup equipment that you need to take and the training”

 “There is no reason why people can’t execute solo dives. People that want to go and look at very particular things, marine life for example or when videographers / photographers that want to spend a long time with a single subject then there is no reason why this certification isn’t perfect for them”

“At Big Blue all the videographers are solo divers, it’s a huge safety feature for them, they can take a pony tank to be able to work separately from other divers.”

7. Why do you carry a pony tank?

“A pony tank is a separate scuba tank which can be mounted on to the primary tank with a separate regulator; so if you were to have a problem with your primary system you have a completely separate system to go on to”

“Generally the tank is small, but has enough air in it to get you back from the deepest part of your dive safely to the surface”

8. What specific equipment would you need to have on you as a solo diver?

“You will be adding equipment such as a backup mask, the redundant air supply but there are other pieces of equipment that you will need to carry – a compass, ideally a backup computer, slates for communication and to carry the dive plan finally and one of the most important things you need is the mind-set and experience”

Student feedback following their SDI Solo Diver course

Nikki Rudd

Solo Evaluation: Becoming a solo diver is one of the greatest courses I have undertaken during my tech internship. What’s better than being taught true self-reliance? Depending on no one but myself and no more wondering where my buddy is or why they decided to spend 10 minutes checking out Shrimp! Don’t get me wrong, I enjoy diving with others and beam with pride when I find something unusual and to go ‘BAM! Bet you haven’t seen one of those before’, but the solo diver course takes an in-depth approach in improving all aspects of your diving, making you a confident, independent and safety conscious diver.

My navigation skills were tested to the mas when swimming off alone into the abyss, with poor visibility and slight current I was sure I’d end up in Koh Samui. That wouldn’t have been ideal. Without money I wouldn’t have been able to make the most of the situation by getting a Mc Donald’s, luckily  I mapped the dive site out beforehand and used both my compass and visual references to get back to the boat. All of which I was taught during my previous courses and re-examined when doing the solo course.

Most importantly, I have gained the confidence though simulated problems and various skill training. Unexpected out of air situations and equipment failures can be a diver’s worse nightmare. With back-up equipment and a redundant air supply, I no longer fear the worst and can dive comfortably knowing I’ll be alright as long as I don’t upset any of the local wildlife.

The course was great fun and Andy is a brilliant instructor. He made me feel confident and at ease, homing in on the importance of safety and following the fundamental rules of scuba diving. His constant skill testing and problem solving tricks removed the emotion and potential stress I could be faced with and have to manage on my own. I highly recommend this course to anyone who wants to take their diving standards and skill sets to the next level.

Tony Wong

Solo Evaluation: I have been diving for 7 years, when I was fun diving with my fellow DMT’s about 8 months ago I never even considered a course in solo diving; I even told my friends I would never go solo due to the safety aspect of the qualification. However, when I moved into tech diving last April I discovered that I could master technical diving and there was actually more safety involved in the planning of the dives and the execution of the dive itself.

I came to realise that my dive buddies were not able to assist me during a dive should a problem have occurred. One time I went fun diving with some DMT’s and we go to the dive site and the tank had come out of the tank strap and my buddy didn’t notice or was able to help me reposition the tank back into my BC, this is a prime example of using ‘save yourself’ skills where I stopped the group and removed my BC to fix the problem myself so we could continue the dive. On the other hand when we compare technical diving to recreational diving we assume everything will go wrong rather than hoping things will just be ‘OK’. With technical diving we do extra pre-dive checks and planning of the dives to ensure we minimise any risk of something going wrong. This to me seemed similar to what I had learned during the solo diving course.

In my opinion it’s not that my buddies are incompetent or they haven’t had as much experience diving, its just based on the fact they don’t have the same mind set to the ‘what if’s’ as I do. From open water onwards you are always taught to rely on your buddy and dive with a buddy, but in reality you generally will want to solve a problem by yourself before going to your buddy in a panic. To me, solo diving teaches you to prepare for that moment when something ‘could’ go wrong and how to maintain calm and deal with the problem yourself. As a dive instructor myself I am teaching my students to be reliant on their buddy but to also be self-reliant. Solo diving isn’t for the less confident minded people, it’s for the divers that want to make their diving the safest it could possibility be, and personally I am likely to only dive solo on dive sites I know while building up my solo dives before I venture out to new places to solo dive.

Solo diving is about learning new ways of dealing with situations and to keep practicing these skills until they become second nature to you. Don’t put yourself into an uncomfortable situation, dive within your limitations but also pride yourself in the fact you can dive alone and enjoy the wonderful marine life we have around us.

Solo diving is an essential course to do, not only does it make you a safer diver it also makes you a better buddy.

Chloe Gedmintas

This is the story of how I went from an Open Water student to Solo Diver; I promise I'll get to that, but first- a little about me. 

I've had the distinct pleasure of diving with Mr. Andy Campbell from that very first Open Water pool session, then on to my Advanced OW. Andy is the first person that said I'd be "epic" as a Divemaster, so came back after some traveling & went on to do that too. Post-DMT, also completed Nitrox & Deep Diving Specialties - and now, Solo Diver. I've learned and grew from him as a diver is truly invaluable. (It's still Andy's voice of reason in my head every time I'm faced with a decision underwater!)

When Andy suggested I do the Solo Diver course, I have to admit I was intimidated (and those that know me, know there isn't much that stands in my way) - but I've JUST gotten comfortable with taking customers out as a DM, and now you want me to throw everything I know about the buddy system and dive... by myself?!?

Doing Solo makes you a better diver; more aware, more prepared, even diving with a buddy it will make you a better buddy, and not have to rely on someone who may not be able to help in an emergency. Also the fact that I want to go on to do Videography, it makes a lot of sense to have Solo under my roster as well.

So first day was homework & lectures as per usual. We learned all about the importance of safety in Solo Diving. Safety in your gear (full redundancy is key, including carrying an extra gas supply/regs, mask, SMB & reel) and even more importantly, safety in yourself- having the self awareness and understanding to abort a dive where necessary, stop if you're not comfortable, ability to fix emergency situations before they become fatal, or even just being able to admit when you're lost. As a solo diver, the only thing you can rely on is your own gear & abilities; without it, well, you can easily become fish food. 

The next day I swallowed my fears, pulled the ol' 'fake it till you make it' confidence trick, and did a skills dive first (mask removal, gas/reg exchange to my pony bottle & back, fixing a free flowing LPI hose, etc). I was nervous, since even as a DM I still hate taking my mask off, and I had never dove with more than one tank before (no Sidemount for me) - let alone turn my own tank off underwater - oh ye, and because its Tech - do all of that with perfect buoyancy in trim, ok thanks. 

There were a lot of firsts for me, but I did them no problem. Even keeping my mask off while switching gases - no problem. Diving with a pony bottle was surprisingly an easy transition from the single back mount tank. It felt comfortable, I could reach everything; the only thing that got me was the reg hose is shorter so its the one time it goes UNDER your arm not over! (Found that out while struggling to reach my mouth to it and losing air by the second underwater- whoops!)

All in all, I felt like my work as a DM had paid off, I had nailed the skills without any issue, and was ready for my very first solo dive.

2nd dive of the day, we each prepped our own individual full dive plan before hand; including drawing the dive site on my slate, deciding when/where & which depths I'd be diving for and how long at each depth, calculating how much gas I would use at each depth, and based on my SAC rate (which is high - anyone who knows my laugh know I have big lungs!) how much air I would use. As a solo diver, I need to come up with a third of my tank unused, NOT including the emergency pony bottle.

I took my time making all of these calculations, presented the plan to Andy, and he said "you have max 45 minutes dive time. Off you go." 

And that was it. Slate in hand, I was off to get in my own gear, do my own checks, and jump off the boat. On my own, no one to tell me when it’s time to go, or where to start, just my own plan to follow. So off I went bit of a surface swim to the buoy line I knew best, and down I went. The strangest part was deflating my BC and heading down underwater by myself; not even customers to give the "OK, Let's go down" hand signal to. 

Once under & equalized, I did all my regular checks and descended down to the dive site. The first few minutes were the strangest but also the most eye-opening. I was really doing this, on my own! A few glances at my slate to triple-quadruple check my plan, and I was off to explore whatever the heck I wanted. I found that more creatures came out to play when I'm on my own, and closer. I spotted a big blue-spotted ray under a rock and instinctively banged my tank to show.... (after a look around)... oh right, no one! I got to just enjoy and experience this all on my own. SO RAD! Another highlight of the dive was sitting in a big school of barracuda for about 5 minutes - just because I could.

It was actually really nice to have a detailed dive plan written out on my wrist slate for reference, easy to keep an eye on how long I should be at each depth, when to shallow up, where to do the safety stop, etc.  When it was time to come up, I used my tech SMB & reel for the first time and came up directly in front of our boat Enzo. I came up to see Andy sitting on the top deck, I waved and with a hug grin let out a big "Wahoo! And that's it. I knew I could do this. 

Solo Diving is definitely a very different beast; but there is nothing quite like being under the water, in the quiet blue all by yourself, with this magical playground in front of you, and the freedom to explore it how YOU want to, with the only limit being yourself (and well, gas consumption). It's truly an incredible experience, and I'm so glad I pushed myself to do this "scary" tech course. I would no longer describe Solo as scary at all - just simply incredible. The confidence you gain after completing your very first solo dive, to plan, on time, and without getting lost - is an extremely proud, awesome moment. Once again, when I thought I've already learned so much, I've fallen head over fins in love with diving in a brand new way. :)

 Final words…

Agreed there is a lot to read but when completing a dive plan or procedure for a solo dive you must understand fully the expectations/ limitations/ safety and enjoyment of solo diving.

Should you want to open up your world of diving or even open up the opportunities of videography / photography in solo diving, get in touch and ask questions and be ‘that confident explorer’ 

Credit to everyone involved for this blog. Thanks to Andy Campbell for his astonishing teaching at Big Blue Tech and the newest SDI Solo Divers for their personal input and participation in the course – Nikki / Simone / Tony & Chloe. Finally Big Blue Movies for some of the pictures.

Remember to give Big Blue Tech a follow and see what course could interest you in speciality or technical diving next ‘Because it’s always more fun to join the dark side’

Congratulations again to all of Big Blue Tech’s new SDI Solo Divers

The difference between teaching and instructing

Skills-testI’ve been reading a lot of articles about modern scuba training of late, how it’s changed over the years, why it is or isn’t deemed adequate depending on what you do in the industry, who you work for and where you work in the world (intensive 3 day courses as opposed to courses covered over many weekends springs to mind). These all lead to the question of what students are really getting out of their diving course, and does it really prepare them for when things go wrong and an instructor or divemaster is not around to look out for them? Most of these articles are geared towards recreational diving, but the ideas put forth are of course directly translatable to technical diving. Frankly, I’m not going to get involved in discussions about recreational diver training. You can argue all day about the best method of air-sharing to employ in the event of an out of gas situation, or whether students should ever be knelt down to do their skills on their open water course, never to practice most of them whilst neutrally buoyant. What I am interested in is why we do skills, how they are taught, how they are rarely practiced outside of a course, and ultimately, how quickly they are forgotten.

It goes without saying that technical divers undertake a hobby that can have very serious consequences if things go wrong and are not dealt with before, or during a dive. For this reason, students on technical diving courses are faced with a very steep learning curve related to equipment, dive practices and procedures, risk management and dive/contingency planning. Foundation courses such as technical sidemount or intro to tech should provide the student with a good grounding of all of the above, and enough time to practice in order to gain a level of competency so that they can confidently go off and do those dives at that level, autonomously, and then be ready to move on to the next level and repeat the process. Otherwise, what was the point of those courses?

But how a course is taught will determine whether or not someone actually knows what they’re doing at the end of it, and whether they’re good at actually doing it or just "passed" a series of skills to fulfil the requirements for the course. This of course entirely depends on the instructor. My first few tech courses involved being told that I had to do this and that skill, a vague reason as to why, and then a couple of goes, first kneeling in the sand, then a second time neutrally buoyant, before being given a “stress test”- mask ripped off, air turned off, tangled up, all at the same time. Great fun if you’re not the type of person that can easily freak out, but ultimately pointless in my opinion. I didn’t feel that I had got to grips with the individual skills in the first place, or had the time to practice them before having it all piled on top of me. But crucially, it was never really communicated when, how, or why the need to employ an emergency procedure might be necessary on a real dive, without an instructor prompting me that I had an issue, and what I should look out for in myself and others on any dive.

So here’s my opinion on how any tech course should be run, based on how I teach my own. Your outlook may differ and I welcome any feedback and ideas on what is written below.

A tech course should never be a one-way process of being told this is how it is, this is what you need to do, and ticking a series of boxes to ensure that you as an instructor have fulfilled the skills and theory to be covered by the standards. I view my theory sessions as an exchange, and I always begin any topic by asking the student what their understanding is up to that point, and I actively encourage constructive interruptions and discussions. If I just sit and talk at someone for two hours, I can almost guarantee that they will learn nothing. They also need regular breaks. It’s long been proven that people’s attention span can rarely last longer than one hour before they start drifting off. Just because they are looking at you, does not mean they are listening! This exchange means that I go off the main topic all the time, and end up covering way more than just the specific thing that I began with.

The same goes for equipment workshops. It’s an exchange. I show the student different ways of setting up, for instance setting regs on sidemount tanks, and going through other ways of doing things, and why I do it this or that way, why I don’t do it that way- and where I am coming from (streamlining, simplicity, entanglement, over encumbured), and what really is wrong (e.g. SPGs flopping in your face!). They need to then have a go, get hands on, take it apart, change the height of this clip and see how it changes things, feed the longhose along the inside of the tank, then along the outside, understand when one method may be more appropriate than the other, set up a standard recreational cylinder for sidemount, and ultimately gain not just familiarity through doing and reptition, but also think about why they are doing what they are doing. Remember, as I previously said, you are preparing them to be able to do this stuff without you being there, and to be able to adapt based on the type of dive they may be doing or kind of equipment accessible to them at the time. Not just demonstrate that they can copy what you did during the course.

In open water, the first couple of dives is a process of assimilating everything up to that point, equipment familiarity, buoyancy and trim, finning techniques, awareness, and diving procedures. All before even thinking about introducing skills.

Each skill involves discussing what has gone wrong, or what combination of factors may have occurred that led to you having to employ the skill. How this failure or situation may be prevented or minimised, and when it is likely to happen on a dive. We also discuss human factors; eu-stress, dis-stress, and how we respond to these stressors; best case behavioural response, worst case emotional response. I would highly recommend that you read the psychological skills for diving facebook page, and specifically the articles on stress management to explain these points further. Also differences in experience and competency between buddies and the potential babysitting and risk factor implications of this. Finally, I discuss awareness, and how during a dive you need to be on constant lookout for problems with yourself or your buddy- a sudden stream of bubbles coming from your buddies 2nd stage swivel, why you are constantly having to put air in your BC. That kind of thing.

As for the skill itself, the student obviously has to learn the process first, which involves SLOW practice, whilst maintaining trim, buoyancy and awareness. Having taught a lot of recreational courses before becoming a tech instructor, I saw time and time again a student have a go at a skill for the first time and completely get it wrong. Normal obviously, there could be many reasons for this, they are nervous, they weren’t really paying attention to your demonstration, it's all a bit too much too soon, maybe you demonstrated it too fast, perhaps they are not a visual learner, or maybe they are just not the sharpest tool in the box! But 99 times out of 100 they get it wrong because they rush it. Same applies for tech. The whole point in doing a course is to learn new things. To learn new things most people need to get them wrong first, because then they will think about why they got it wrong and know what to do to get it right. It’s the perfect time and place to get things wrong. Learning through repetition is important, but also pointless if you’re in autopilot mode and just wanting to please the instructor and move on. Similarly, awareness is crucial. Lack of awareness at 12m hovering above the sand leads to a domino effect. Again I see it all the time. The student begins the skill, all good, nice and slow, then bang.. the head goes down and they suddenly stop what they’re doing because they crashed into the sand, or they complete the skill, look up and realise they’re now 3m above the sand. On a deco dive, you’re now potentially bent or have lost that all important line leading you back to your boat, or your buddy. Or all of these!

It is far better to learn good habits at a slower rate, than pick up bad habits at any time and have to unlearn them. So when first learning a skill, good buoyancy, trim and awareness are integral parts to doing that skill correctly.

Finally, once the student has gotten familiar with skills and diving procedures, and is consistently demonstrating good buoyancy, trim, awareness and an ability to think on their feet, then I will start to test their ability to prove this. One of the dives will just be a fun dive- no skills I tell them. Then at various points they or I will have realistic problems. Throughout this, I am not looking that they can robotically undertake the appropriate skill, but am looking at their stress response, their ability to be assertive and communicate effectively, show good awareness (self, global and situational), and as I’ve said a few times by now, maintain excellent buoyancy, trim and positioning. The kind of diver this produces is a world away from someone who just ran through a bunch of hoops to get that card. If it doesn’t, then they simply need more dives before I will certify them; producing a thinking diver is simply more important than just getting my certs up. Otherwise why the hell am I an instructor?

The problem with all of the above is that when someone is thinking of enrolling on a course, they are always told to do so based on the instructor’s reputation. I couldn’t agree more, but I have personal experience of instructors that are way more experienced than me, but very inconsistent and frankly lazy in their teaching approach, and/or demonstrated poor performance with their own diving abilities (bad role model behaviour). Please don’t take that as me putting people down and thinking I am amazing, far from it. I still have a hell of a lot to learn and practice, it never ends and I think humility and the ability to recongise your own limits is the only way to improve. Before the internet trolls get their keyboards at the ready, i’m not the kind of person to denigrate my peers to promote myself. But I do care about this industry and feel like I have to call out bad apples when I see them. All I am saying is that a student doing their first few tech courses doesn’t really have a point of reference as to whether they are being fed a load of crap, or whether they are really learning how to dive safely and think for themselves. Hopefully this article will give them more to consider when deciding where to do a course.

Finally, as a final thought. If you are a recreational or technical diver and don’t work in the industry, ask yourself when was the last time you practiced any of the skills you learned during your courses. Out of gas for instance? You very quickly forget, and if you start practicing but are missing something, that’s as good as just not practicing. Here at Big Blue Tech I will happily take someone out for a dive to refresh their skills, and with my own ex-students that are sticking around, I pretty much insist on it. Also, ask yourself when was the last time that you finished a diving course, and whilst sitting down with your instructor filling out the final paperwork, they asked for your feedback on how the course was taught, what was good, what was not so good, whether there was anything they could have done differently to improve your ability to learn. Vital questions in my opinion. How else are you going to improve as an instructor?

If you feel like it would be beneficial for you to go for a refresher dive with all the above considerations in mind, email This email address is being protected from spambots. You need JavaScript enabled to view it. for more information.

Richard Devanney

Decompression theory- Part III

Doppler-ultrasoundThe previous two articles on decompression theory introduced and discussed numerous processes that occur in our body as we breathe gases under pressure whilst diving. Some of it is pretty straight forward, some of it makes your brain hurt, and probably reminds you of your weird physics teacher from school that accidentally spat on you whenever they opened their mouth. But I’ll presume that if you are reading this you found it interesting enough to continue reading- and please remember that I take cash, credit cards, traveller’s checks, IOUs and favours.

After the work of Robert Workman and others in the sixties, we really thought we were getting a handle on the science of diving. But nothing is ever that straight forward, especially when it comes to science, or handles. In 1976 Dr Merrell Spencer published a report that put a rather significant spanner in the works of decompression theory. The focus of the report was the detection of so-called silent bubbles in the bloodstream of divers. They weren’t bubbles that were causing DCS, the bubbles were found in divers showing no symptoms, who had all dived well within the limits of the dive tables of the time. Prior to this, the idea of asymptomatic bubbles had been discussed (in fact as early as 1951 by Bateman and Behnke), but as it was only considered a theoretical possibility, mainstream decompression research continued to focus on all inert gases interacting with the body whilst in solution. In light of Dr Spencer’s work, the plot had thickened, curdled, boiled over the pan, hardened on the cooker and turned into a big bubbly elephant. Time to get the marigold gloves on (and step away from the absinthe).

Silent bubbles
Subsequent investigations of silent bubbles suggests that they may be permanently present in the bloodstream, even for people who have never been diving. This is due to a combination- predominantly mechanical in nature, of cavitation, micro-nucleation, and tribonucleation. Micro-nucleation relates to impurities in the blood stream that allow bubbles to latch on to (commonly joints and blood vessels)- so called “gas-seeds”. This is the reason why weight training is a bad idea before and after diving. The damage to muscles and ligaments forms ideal micro-nucleation sites. Cavitation is something that we see in boat propellers, mantis shrimps stunning their prey, and the pipes “knocking” in your central heating system. Essentially, fluids undergoing pressure changes create low pressure cavities of vapour, which at high pressures can implode and cause a shockwave. But at more intermediate pressures you are just left with a bubble. The human body (obviously) contains blood, which, under some circumstances produces localised cavitation such as in joints when limbs are contorted, or when the blood is pumping faster, such as exercise or thinking about your overdraft. Tribonucleation is the formation of bubbles between two submerged surfaces when those surfaces are suddenly pulled apart. This movement creates negative pressure, which can produce localised supersaturation. Too much of which leads to bubbles. The best non-diving example of this is when you crack your knuckles. People commonly think the cracking sound is caused by a bubble in the joint popping, but it’s actually the shock wave on surrounding synovial fluid as a bubble is formed that makes the sound.

Silent bubbles are now considered to be a completely normal consequence of diving. However, it’s very hard to correlate silent bubble size and frequency with DCS cases. Some people get bent with few or no silent bubbles, and others don’t get symptoms of DCS even though they have what is considered an excess of silent bubbles. Remember, an M-value is a definite line through a fuzzy grey area. However, as DCS is a bubble of gas in tissues or blood that creates symptoms, attempting to reduce the size and amount of any kind of bubbles is obviously going to be a good thing for a diver.

What we do know about silent bubbles, is that the body is normally very good at filtering them out. When they arrive at the lungs they get trapped in the fine capillaries, where they then diffuse out through the lung lining. However, if too many silent bubbles get trapped, this can reduce the overall efficiency of the lungs to off-gas, which can cause a bottleneck and result in slower off-gassing. The other effect that silent bubbles have is that they can cause excessive tiredness, caused by initiation of the compliment system, which is an immune system response, in this case induced by the presence of these “foreign invaders”. This process has no effect on the bubbles as they are inert. So increased fatigue after a dive may be an indication of a bad dive profile, dehydration, high ascent rate, or a combination of these.

Dual phase models
Given that we know that gases are roaming freely around our bodies as well as being dissolved in our tissues during a dive, we also know that they will be subjected to the same laws of physics as everything else, such as Boyle’s law. Therefore, some of the modern decompression algorithms have been modified to try and account for the behaviour of dissolved gases and gas in the free-state. Such algorithms are known as dual phase, or bubble models.

There are a number of different models to choose from- Varying Permeability Model (VPM), Reduced Gradient Bubble Model (RGBM), and varieties of each to choose from. They all still use the concepts of half-times and M-values for the dissolved gases, but they also try to model the size and shape of bubbles as they are subjected to differing pressures over the course of a dive. To explain how they do this involves going down the road of bubble mechanics, which is very maths oriented, so let’s not do that. But in simple terms we know that a bubble has a number of different forces acting on it. It has the external ambient pressure, the surrounding tissue pressure, and its own surface tension (known as the Laplace pressure). All of these forces are interacting in a way that will determine whether or not gas will diffuse into the bubble and make it bigger, or diffuse out and shrink it. If a bubble reaches a certain size, it is thought to have reached a so-called critical limit, which could then mean that it may turn into a symptomatic bubble. 

The entire point of these models is to keep the bubble below this critical volume. The differences between how each model does this is beyond the scope of this article, but, for example, of the two most popular ones, VPM is based on the work of Dr David Yount and stems from experiments done in a lab using gels. RGBM is the brain child of Dr Bruce Wenke, is proprietary, and is based on real diving data from the commercial diving industry. Dissolved gas models try to get the diver as close to the surface as soon as possible, where most off-gassing will take place. However, this causes a conflict with what the bubble models are trying to achieve. After ascending from the deepest part of a dive, they want to keep ambient pressure high. This has the effect of keeping the pressure inside a bubble higher than the partial pressure of the gas in the surrounding tissues, so that either bubbles will not get any bigger, or may actually shrink a little. But if too much time is spent deep then slow tissues will continue to on-gas, which means longer stops in the shallows- an important consideration on decompression dives. So dual phase models try and marry these two opposing factors into a best fit compromise. Deep stops are used, but are brief so as to minimise slow tissue on-gassing.

Ascent rates
Ascent rates affect everything I have mentioned in all of these articles, M-values, amount of supersaturation, and size and amount of silent bubbles. They vary, depending on who you learn to dive with. Whilst most recreational divers go to the deepest part of their dive first and then gradually and slowly shallow up throughout the rest of their dive, technical divers also do the deepest part of their dive first, but know that ascending too slowly from the bottom to the first decompression stop can complicate and extend their overall decompression obligation. Look at the recreational ascent rate limits: BSAC specifies an ascent rate of 15m/min, SSI is 9m/min, and we all know that PADI is 18m/min. No one seems to agree on what the ideal rate is, or even whether there is a single ideal rate. Paul Bert recommended 3m/min, Haldane recommended 1.5- 9m/min, Buhlmann said 10m/min. In 1958 the US Navy reviewed the ascent rate for Navy divers. Their scuba divers wanted a 30m/min ascent rate, but hard hat divers thought this was too fast for them in their heavy gear, so a compromise of 18m/min was set. This is probably where PADI's ascent rate comes from, which is generally considered at 18m/min to be a wee bit fast! Most PADI instructors don’t go up faster than their computers allow (9m/min). For decompression dives, common practise is that, from the bottom portion of the dive, through the deep stops to the first decompression stops, 9m/min is the maximum (and also the minimum), then, until the shallow stop at 6m the ascent rate is 3m/min. From 6m to the surface it’s 1m/min.

For recreational no-stop dives, when you start a slow, gradual ascent during the dive, this is actually very inefficient in terms of off-gassing. Why? It’s all about inducing that inert gas gradient. If I ascend very slowly as I dive along, I am also very slowly reducing ambient pressure. This doesn’t get the supersaturation going that you need in your fast tissues, so you end up doing most of your off-gassing on the surface after the dive. It also means that your slower tissues may continue to on-gas until you shallow up. Nowhere near the point of saturation, but enough to gradually have to off-gas more on the surface.

If on the other hand I ascend from the deepest part of the dive to an intermediate depth, say from 30m to 18m, and move at or close to 9m/min, I will be maximising that inert gas gradient and minimising my slow tissue on-gassing. Remember that your tissues will off-gas hallway from where they are to what the new ambient pressure is. If I’ve reduced ambient pressure more, that’s 50% of a bigger distance. The time that I spend at 18m means that I will be off-gassing more whilst still on my dive. Then I can move up to say 12m, then 9m, then do an extended safety stop. This is more of a quality of dive issue in terms of how tired you will feel afterwards, as I know that I will feel way less tired if I dive this kind of profile, than if I do a very slow ascent. But again that's as subjective as someone insisting that they feel less tired after diving on nitrox. 

The original aim of these articles was to provide an overview of decompression theory as we currently understand it, and then describe what we don’t understand. It took a long time to even cover the basics of what we do understand. What we don't understand is easy to explain... most of it. Tissue compartments and M-values are a mathematical way of trying to mimic biological processes. The human body is far too complex to be able to model accurately. Tissue compartments and M-values are a best guess, no more. Millions of people dive every year without incident, so they seem to work in some way, but we don’t know what really is right about them and what isn’t, as it’s very difficult to perform studies on divers who give subjective responses to questions about less than precisely controlled dive profiles. Controlled studies on large groups of divers of the type that might produce statistically relevant results just doesn’t happen. Moreover, a small proportion of divers go to the chamber for treatment of DCS, even having stayed within the limits imposed by their dive computer, and it's actually quite difficult to say that it was even definitely DCS! One study will come out saying that you need to slow your ascent rate in the last 10m- the biggest relative pressure change, then another will come out saying that 9m/min is more effective as long as you do a decent safety stop. Then add repetitive dives into the mix!

Albert Buhlmann’s work lives on in the form of most dive computer algorithms. Haldane used 5 tissue compartments in the 1908 Royal Navy tables, Buhlmann uses 16. If you’re diving on trimix that’s 32 compartments; 16 for N2 and 16 for He. So during a deep trimix dive there are potentially 32 different tissue compartments on-gassing at different rates that will then also off-gas at different rates, and each of them has their own M-value, which will change depending on the depth. If you're using VPM then in addition to these 32 compartments bubbles are also being modelled in terms of size and frequency at all points of a dive. A pretty complicated crap shoot all in all.

If there was one effective way to control on and off-gassing, wouldn’t there be only one set of ascent rates, one algorithm, or one dive table universally used by everyone? Look at all the different diving agencies and the tables they use. BSAC tables, PADI tables, SSI modified US Navy tables, NAUI, IANTD, ANDI. Then there’s dive computer algorithms, Suunto have their own, there’s Buhlmann, Buhlmann with gradient factors, VPM, RGBM, slab diffusion. The list goes on. I haven’t even touched on trimix diving, gradient factors, the effects of using hyperoxic mixtures to accelerate your decompression, or rebreather diving! There is a hell of a lot more to know, and whilst progress was being made in the 70s and 80s, this was because of the need to understand the effects of saturation diving in the oil and gas industry. They had a lot of money to throw at the problem. Unfortunately all the things that saturation divers used to do can now be done by ROVs, so decompression research has slowed off quite a bit since then.

Much of what we continue to learn about decompression results from technical divers doing decompression dives, with doctors and decompression researchers keeping track of their dive profiles. I suspect that by the time we will have really understood what’s happening to us on a dive, we’ll be diving in a way that means we don’t need to take inert gasses into our bodies anymore. We’ll either have figured out how to manufacture oxygen from seawater whilst diving (and be able to inflate our lungs), or will be breathing those aqueous fluids that are supersaturated with oxygen directly into our lungs, as was demonstrated by a rat in the James Cameron film the Abyss!

So I apologise that after all these words you didn't get a definitive "this is how it is" on decompression theory, but I hope you have a slightly better understanding than before.

Richard Devanney


Decompression theory- Part II

Bending goats

In the last article I began to provide an overview of our current understanding of decompression theory, and it appeared very quickly that a few paragraphs wouldn’t really do. So instead of writing one huge long piece I took the out of character sensible decision to spread it over 3 or 4 articles. Some people complained that the title was misleading, as I didn’t talk about what we don’t know about deco theory. That may be true but I’d rather lay the groundwork of what we think we do know before going into what we don’t. So, without sounding like Donald Rumsfeld with his known unknowns, and unknown unknowns, here’s part two.

Haldane goat300x237It’s probably a good idea to quickly recap to get you back in the zone, focussing on Nitrogen (N2). At the surface the partial pressure of N2 is 0.79. Our bodies are saturated with N2 at this pressure, and through the normal process of respiration, there is no net increase or decrease in the amount of it dissolved in our body tissues, they cannot hold any more at that pressure- this is what saturation means. Descending on a dive rapidly increases the ambient pressure surrounding our bodies. If we were to descend to 20m (3ATA) and stay there, eventually our tissues will be uniformly saturated at this depth, meaning that at 3ATA our tissues would eventually have a PPN2 of 2.37. We aren’t losing any N2 because the N2 entering our lungs will also be at 3ATA (PPN2 2.37 also), so there is no diffusion gradient occurring. The only way to increase the amount of N2 in our tissues would be to descend further, say, to 30m or 4ATA (or increase the percentage of N2 we breathe). This increases the partial pressure of N2 in our lungs to 3.16, so diffusion and perfusion work together to dissolve more N2 in our tissues until eventually the tissues go from 2.37 to 3.16 and become saturated at this pressure. This difference in partial pressures between the inspired gas mix and the tissue tension is known as the inert gas gradient (If that didn’t get you in the zone, don’t read any more).

If our bodies were all made of the same stuff, this would be the end of it and we’d all be decompression experts. Obviously they aren’t and we are not. We have blood, a brain, ligaments, cartilage, bone, fat, liver, kidneys, eyeballs, spleen etc. These “solutes” have different solubility’s for different gases, and are also perfused with blood at different rates. This means that our various tissues on and off-gas at differing rates. Decompression researchers have tried to model these overlapping processes since Paul Bert experimented with N2 under pressure and killed 21 dogs through rapid decompression! John Haldane (pictured.... on the left) was the first person to attempt to apply the scientific method to decompression in the early 20th Century. Haldane was a very accomplished scientist, and also pretty eccentric in work and general life. When hosting dinner parties, he would reportedly get bored, start thinking about work and wander off to his laboratory, forgetting about his guests! He is widely considered to be the father of decompression theory. It was he who developed the first dive tables in 1908, based on his research of putting goats and family members into a hyperbaric chamber (not at the same time), and recording what happened to them after being brought back to 1ATA from different simulated depths for different times- slowly, and quickly. Goats are a pretty good match with humans in terms of size and characteristics of body tissues, and they probably mowed his lawn too. His son, JBS Haldane, a well-known and accomplished geneticist in his own right, also became involved in his father’s research and was more than keen to allow himself into the chamber. He once stated that he enjoyed being a soldier in World War One, as he actively enjoyed killing people. Sometimes the scientists are as, if not more interesting than the discoveries that made them famous!

Half times
Haldane senior was the first person to try and model what happens to the body during a dive, by proposing that so-called tissue compartments be used to model different body tissues. He used 5 compartments, all having different “half times”. A half time is a general scientific term most commonly used in radioactivity. It describes the time it takes for a radioactive material to decay to half the original number of atoms. But it can also be applied to uptake of gases, and for a given tissue compartment it means the time it will take for it to become half saturated, or half de-saturated with inert gas. A tissue compartment with a 5 minute half time is known as a fast tissue compartment, and it might model the blood, whereas a 240 minute compartment is a slow tissue compartment, and may represent bone. A 5 minute compartment is so-called because on descent it will take 5 minutes for it to become 50% saturated with gas. After a further 5 minutes it will be 75% saturated, and then 87.5% after 15 minutes, then 96.88%, then 98.44%. With each cycle the compartment will become 50% more saturated compared with its previous level of saturation and full saturation. So in theory it will never be fully saturated as it is always chasing that half-way point. For practical purposes we can consider it saturated after 6 half-time periods. You can see that the greatest rate of on-gassing occurs within the first period. Then each consecutive period produces less and less additional saturation. By ascending and therefore off-gassing, the same principle applies, but in the opposite direction.

Once a tissue compartment is fully saturated, it means that the tissue tension is at the same partial pressure as the inspired gas. When saturated, the tissues physically cannot hold any more gas at that particular ambient pressure. If we ascend, we reduce ambient pressure, which will reduce the partial pressure of the inspired gas, which, in turn will produce that inert gas gradient. Though these reductions in pressure will instigate off-gassing, the concept of half-times tell us that reaching equilibrium between the tissues and lungs takes time. Because of the delay, tissue tension will be greater than the inspired partial pressure, and may also be higher than ambient pressure. This is known as supersaturation (saying it reminds me of Jim Bowen for those who would know). We need a certain amount of supersaturation in order to instigate a pressure gradient for gases to diffuse from the tissues back to the lungs.
Whilst it’s probable that during a recreational dive a fast tissue compartment may become saturated, slower compartments will not- unless you are able to do a 1,440 minute bottom time to saturate the 240 minute tissue. Now, if the tissue tension becomes higher than ambient pressure, it will become “supersaturated” during the ascent. This requires a bit of a description and a fancy table, both completely stolen from Mark Powell’s excellent book, Deco for Divers.

table final

Going through the example in Mark’s book, at 30m tissue 1 is saturated. Tissue 2, being a slower compartment is still on-gassing and has only reached a tissue tension of 2.50. As we ascend to 20m (3ATA), the inspired N2 has dropped to 2.37. Tissue 1 is supersaturated as the tissue tension is higher than ambient pressure and the inspired N2 partial pressure, so it begins to off-gas because of the inert gas gradient. Tissue 2 will also start to off-gas, but it is not yet supersaturated. As we ascend to 10m we can see that tissue 1 is still supersaturated, but now so is tissue 2, even though it was not supersaturated at the start of the ascent. Tying in half-times with supersaturation means that a tissue will go halfway between the current supersaturation level, back towards saturation. If supersaturation is low then it will be 50% of a short distance. If it is high it will go 50% of a large distance. For a 5 minute tissue compartment, if we reduce ambient pressure from 4ATA to 3ATA, then in 5 minutes the tissue will be at 3.5. But if I instead ascend from 4ATA to 2ATA, then there is a greater distance between the tissue tension and inspired gas tension. It’s off-gassing by 50% in both instances, but for the latter it’s 50% of a bigger difference. This means faster off-gassing.

Critical supersaturation and M-values
Although we need supersaturation to occur in order to be able to off-gas most effectively, each tissue has a theoretical limit of over-pressure, and this is known as critical supersaturation. Beyond a certain point, as the ambient pressure reduces sufficiently, and the gas cannot be released quickly enough from the tissue, it will come out of solution (Henry’s law remember) and create a bubble of gas, which is Decompression Sickness (DCS) and therefore a terrible inconvenience.

Haldane was clever enough to realise this principle in 1905, and he expressed this limit as a ratio between the inert gas tension and ambient pressure. He set it to 2:1, i.e. a diver could ascent from 2ATA to 1ATA without getting the mysterious malady of DCS as it was called at the time. This ratio was revised by Robert Workman, the nice uncle of decompression theory, in the 1960s. He changed it to 1.58:1, as long as we are only talking about N2. He reviewed previous decompression research from Haldane’s time onwards and realised it was pretty inadequate when it came to, you know, diving safely and stuff. He realised that faster tissue compartments could tolerate a higher level of overpressure than slow compartments, and also that all compartments could cope with greater overpressures as depth increases. He came up with an empirically derived equation to describe overpressure in different tissues at different depths, and called it an M-value. Rumour has it that the M stands for Mum-ra, as Workman was allegedly a fan of Thundercats, but it probably just means maximum.

So the variables that control whether tissue pressures stay within the M-value are depth, time at depth, and ascent rate. Greater depths mean greater inert gas gradients between our lungs and our tissues when we initially get to the maximum depth, meaning more gas can go into solution. Longer bottom times mean more time for saturation, which conversely means more time is required for off-gassing on ascent. Ascent rate can be analogised by imagining a balloon filled with air with a small hole in it, hovering with its legs crossed at 10m. If the balloon ascends slowly, the expanding air will be allowed the time to vent through the hole enough that the balloon will not increase in size. But if it ascends too fast, then the expanding air cannot escape quickly enough and the balloon will grow and eventually burst- critical supersaturation- reaching the M-value- hashtag DCS. Not quite as bad or weird as realising a balloon has legs though.

Recreational divers are largely concerned with fast tissues, and NDLs and depth limits are designed to prevent too much on-gassing of slower tissues. These limits, combined with maximum ascent rates mean that divers can make a direct ascent to the surface and stay within the M-value for the leading tissues (those closest to the M-value). But for decompression diving it does get much more complicated.

Decompression dives
Remember that Haldane came up with 5 theoretical tissue compartments? Well most dive computers now model 16, and each compartment has its own M-value, which changes linearly according to depth. A typical decompression dive on air to say 50m for 25 minutes will mean a much greater amount of on-gassing will occur compared with a no-stop dive to 40m, and now we are not just concerned with the fast tissues. On ascent, both fast, and slower tissue compartments are in danger of going over their own particular M-value at a given depth. So we need to pause to allow time for those tissue pressures to reduce; decompression stops. Whichever of the 16 compartments is getting close to the M-value will necessitate staying at a given depth to allow time for it to off-gas enough, then the ascent can continue until another tissue compartment again gets close to the limit, and so on and so on until eventually we reach the surface after conducting a series of stops for varying amounts of time on the way up. If we are diving on trimix now we are having to track 32 compartments- 16 for Helium (He), and 16 for N2. Ascent rate comes into play here too. On the deepest part of the dive, if I go up too slowly then I will be continuing to on-gas my slower tissues, which means reaching a decompression ceiling potentially sooner (depending on whether the ascent causes supersaturation), or extending my deco stops, or both. So (more on this in the last article), I need to move as fast as is allowed through the deep stops until I reach my first gas switch, so that I am minimising the amount of on-gassing of my slow tissues, but also staying within the balloon analogy for the leading tissues. Then I will need to ascend slower during the shallow stops. More on ascent rates in the last article, along with the additional complication of bubble mechanics.

The concept of M-values has been widely adopted within diving, and since Workman’s research they have been modified and tweaked by different researchers, most notably by Dr Albert Buhllman- the Fonz of decompression research. They are still an inherent component of every dive agency’s tables and different manufacturer’s dive computer algorithms.

It would be very easy to go on and on about M-values, and produce lots of graphs that show off-gassing in individual tissues, and highlight how the reduction in inert tissue pressure and ambient pressure relates to the M-value line for that tissue during an ascent. If you’re interested in that there are lots of articles on the internet that are easy to find. But as this is just an overview, I’ll leave it there. The next article will bring silent bubbles into the mix (just when you think you are getting it all).

Richard Devanney



Decompression theory

tech-diving-diffusionRecently on our Facebook page, I asked what people would like to read about regarding all things technical diving, and got a few interesting responses that will be the subject of future articles. But one request stood out from all the others, for a number of reasons. Firstly, most divers don’t really know a lot about it, mainly because it’s way too much information for someone who is just getting to grips with actually being underwater for the first time. Plus, it’s a wide-ranging and complicated subject, so where do you even start? Secondly, the scientific researchers studying it are the first to admit that they know very little about it!

The subject is decompression theory, and the question asked was “what does off-gassing actually mean, and how does it relate to safety stops and deco stops?” 

There is a common misconception within the recreational diving community that decompression theory is a well understood process. Whilst our understanding as applied to non-decompression dives within the 30m limit seem to work well for most people (DCS cases vary between 10-20 in every 100,000 dives), DCS can manifest after a dive within conservative limits. Go beyond the recreational limit and you are basically a guinea pig of decompression research.

This is a big, big topic. So in order to even just summarise it, this will have to be at least a three-part article. So here goes.

Before going into on and off-gassing, it’s probably a good idea to outline the basics of why we need to breathe underwater in the first place. The simple answer is because we need to breathe on land obviously. But why do we breathe? What exactly is happening as we do so?

Forgetting about diving for a moment, on land the air we breathe contains a mixture of roughly 21% oxygen (O2) and 79% nitrogen (N2). It’s actually 20.55% O2 and 78.08% N2 by volume, with less than 1% of the rest being comprised of Argon, Neon, Helium, Krypton, Hydrogen, Xenon, and Carbon dioxide. However, because these gases exist in the atmosphere in such small amounts, we just bundle them in with N2, and they are considered “inert”, meaning that chemically and biologically they do not react with our bodies (at the surface).

Breathing is an autonomic process, but we can override it to a degree. When we want to breathe in, the external intercostal muscles of the ribcage contract, and the internal intercostal muscles relax. This pulls the ribcage up and out, and the diaphragm down and away from the lungs. This reduces the air pressure in the lungs , so air is drawn in. The opposite happens when we breathe out, which causes air to be squeezed out of the lungs.

On inhalation, air going into the lungs mixes with gases that are already in the lungs. This means that the proportions of each gas in our lungs are slightly different to those in the atmosphere. (I realise I am saying the word “lungs” a lot). Once in the… lungs, air is transferred to the blood vessels and then the arteries, which delivers O2 to the body’s cells. The O2 is then used to make energy. As a by-product of this process, CO2 is produced, and carried back to the lungs via the veins. The N2 in the air is carried around the body as well. But as it is (mostly) inert, it is just circulated around until it reaches the lungs and is expelled along with the CO2. At the surface, the amount of N2 in the body remains constant. For anyone who has never been diving, that’s the end of the story. But as divers, this process gets more complicated as we descend underwater, and atmospheric pressure increases.

Dalton’s law and gas exchange
The gases we breathe at depth need to be at the same ambient pressure as the surrounding water, otherwise it would be impossible for us to inflate our lungs. So at 30m the pressure of the gases in our lungs is 4 times higher than at the surface, so our regulator will provide gas to us at 4 ATA (4 times the density: 4 times the air consumption). Because the pressure of the overall gas increases with depth, so does the pressure of an individual gas- the partial pressure. Discovered by, and named after John Dalton, a fascinating character, Dalton’s law of partial pressure states that:

“The total pressure exerted by a mixture of gases is the sum of the pressures that would be exerted by each gas if each occupied the same volume”

Simply stated, partial pressure is the pressure of a gas in a mixture of gases. Adding each individual pressure together will give you the total pressure. So for air at 30m (4ATA), the partial pressure of N2 is 4x 0.79= 3.16. The partial pressure of O2 is 4x 0.21= 0.84. Add those two answers together and you get 4ATA. The percentage of each gas stays the same, 79% for N2 and 21% for O2, but if the ambient pressure is higher, the partial pressure will also be higher. This is relevant because it’s how we track what’s happening with gases as they move around our bodies when we dive. We also commonly use millimetres of mercury (mmHg). Another gas law important to us is Henry’s law. But before we move on to that, let’s look again at the process of respiration in a little more detail.

The air that enters our lungs moves down the trachea, and reaches two bronchi- one entering each lung. As the air moves deeper into the lungs the bronchi split into smaller branches, called bronchioles, which continue to branch out and get smaller. This increases the surface area available for gas exchange. At the end of these branches are millions of sacks, called alveoli, the lining of which form a surface (the alveolus) that allows gases to be transferred from the lungs to the bloodstream and back. Incredibly, the average person’s lungs contains around 600 million alveoli, which, if you could lay them out on the floor (and not die) would cover a surface area of 100 square meters! The alveolus is less than 1,000th of the thickness of a human hair, and each one is surrounded by fine capillaries carrying blood from the pulmonary artery. Apart from the fact that all of this is amazing, the really amazing part is that the walls of the alveoli, along with the surrounding capillaries are only one cell thick, and comprised of so-called epithelial (flattened) cells. This means that gases coming to and from the lungs only have to cover a very small distance, which increases the speed of gas exchange and makes respiration very efficient in a normal healthy body. It takes around 1 second for blood to travel through the lung capillaries, and in this time it becomes almost 100% saturated with oxygen, and at the same time the CO2 produced during metabolism of O2 is moved back to the lungs to be breathed out.

Henry’s law, diffusion and perfusion
Remember the N2 that we have in our bodies at sea level? Most of it is dissolved in our blood and other tissues, akin to putting sugar in a cup of tea; same process, not as sweet. Oxygen is chemically bound to blood by Haemoglobin, and as we dive, it also dissolves in our blood plasma. The amount of N2 that is dissolved in our tissues is dictated by Henry’s law. Discovered by J. William Henry in 1800, Henry’s law states that:

“At a constant temperature, the amount of given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid”.

Translated into English, this means that the amount of gas that will dissolve into a fluid will increase as the partial pressure increases. So as we descend under the water and the partial pressure of gases in our lungs increases, more of this gas will dissolve in solution. However, different types of gases have different solubility, as do the different tissues of the body; another reason why deco theory is very complicated.

But how do gases get into our body tissues beyond the blood? A common question during TDI decompression procedures courses. The answer is diffusion and perfusion. Diffusion is where a fluid (gas or liquid) will, by random action of atoms, move from a high concentration gradient (of like atoms), to a low concentration gradient. A classy analogy is dropping some ink into a tank of water (pictured above). You can see over time that the ink moves outwards until the water becomes pale blue, and the ink is uniformly distributed in the tank. A crude analogy is when someone farts in an elevator- same process, harder to demonstrate in open air spaces, or in front of your mother (not pictured).

Gases dissolve into the blood in amounts determined by the interaction of Dalton’s law and Henry’s law. In the case of N2, the body is already saturated at sea level, so there is little diffusion occurring as the lungs, blood and tissues all contain equal amounts. The only significant exchange is O2 being transported to the tissues and metabolised, and CO2 being taken back to the lungs to be excreted. As deoxygenated blood travels back to the lungs the partial pressure is lower than in the alveoli (because some of the O2 has been used up by the body), so O2 diffuses into the blood. Likewise, CO2 diffuses out of the tissues (as a by-product of metabolism) and into the blood, to be taken to the lungs. The rate of gas exchange is described by Fick’s law, but there’s no need to go into that here. In essence, the lungs and bloodstream work in conjunction to ensure that the concentration gradient for O2 is such that it travels from the air to the blood, whilst CO2 will travel from blood to the air. As we descend during a dive (we'll ignore helium for now), N2 comes into play as we increase this diffusion gradient- our lungs are at ambient pressure (at the depth we are at), so the partial pressure of each gas is higher.

It is worth noting that increased partial pressure does not push gases into tissues like blowing up a tire. It’s the random action of like-atoms along a concentration gradient. This means that the rate of diffusion of a particular gas is not dependent on other gases in the tissue. So the movement of one gas is completely unaffected by the pressure gradient of another gas. This explains how O2 travels across the alveolar membrane into the blood, whist simultaneously CO2 travels the opposite way. Their movement in opposing directions is completely unaffected by each other (not necessarily true of N2 and He- Isobaric counter diffusion, but that’s for another article).

It’s all very well having gases diffuse in and out of tissues, but this happens over very small distances. So how does the entire body become affected by these gas exchanges? You’ve probably already guessed it, perfusion. Coming from the French verb “perfuser”, it means “to pour over or through”. It basically means blood flow, or the rate of blood flow. A terrible way of analogising how it works alongside diffusion is putting your rubbish out for the bin men to take. That’s the diffusion bit- you only have to walk to the front of your house to dump it. You can produce as much rubbish as you like and leave it out on the street but if they don’t come and take it, the only thing that will happen is an unpleasant increase in the aroma of your street, and the loss of use of the pavement. Yet if they come and take it regularly then there’s no backlog and your street hopefully smells pleasant. Similarly, blood moves around the body, carrying gases from the lungs (picking up your rubbish) and transporting them into smaller and smaller capillaries, until these capillaries become only 1 cell thick, which allows oxygen to get to the tissues (the rubbish tip- I told you it was a terrible analogy). During diving, N2 dissolved in the blood is also able to efficiently diffuse into tissues via the same capillaries, because the tissue is being constantly supplied by gas-rich blood. Different tissues of the body are supplied with blood at different rates. The brain, blood, heart and muscle are well supplied, whereas bone, fat and cartilage are poorly supplied. For a given tissue, if the gas tension (a consequence of high partial pressures) of the N2 in the blood is higher than the gas tension in the tissue then N2 will diffuse into the tissue- this is the process of on-gassing. This is what happens on descent and during the bottom portion of a dive. During the ascent, the tissue tension may be higher than the blood tension, which means diffusion will occur in the opposite direction, taking N2 back to the lungs, which has a still lower partial pressure of N2 for a given tissue.

Decompression theory, as it relates to actually going out and doing a dive, is all about quantifying this two-way exchange of gases, and ensuring that we do not exceed certain limits with regard to tissue tensions. How we control those limits directly relates to our allowed bottom times, maximum depth, and rate of ascent. This gets more complicated for technical diving, especially when we start going deeper, or longer, or both, using different gases such as trimix or heliox for the bottom portion of a dive, or hyperoxic mixtures to increase the rate of diffusion, or try to control the size and number of silent bubbles in the free phase in our bodies, in addition to the dissolved gas in our tissues.

This article sets the scene for the next, in which i'll take the on and off-gassing process further and talk about saturation, supersaturation, critical supersaturation, M-values, half-times and inert gas gradients.. all fancy terms, which will make more sense once I’ve written it! 

Richard Devanney

References and further reading:

Powell, M. (2008). Deco for divers, published by Aquapress. Available on Amazon.
Edmonds, C. McKenzie, B, Thomas, R. Pennefather, J. (2013), Diving medicine for scuba divers, 5th edition. 
Vorosmarti, J, & Vann, R. Physics, physiology and medicine of diving.

Understanding Narcosis

narcosisNarcosis is something that all qualified divers should be aware of, have an understanding of how it can affect them as they descend deeper, and know what to do to reduce its influence- before and during a dive. The effects of narcosis down to 30m are easily manageable for most divers, and even at 40m, as long as a student can demonstrate that they are in control, an instructor will certify them to go to this depth autonomously. Any good diver should know their limits and be able to constrain themselves within their personal comfort zone.

All recreational diving agencies impose depth limits that have been developed to minimise risk in terms of inert gas uptake, oxygen exposure, gas consumption and narcosis. Technical diving also applies limits, but they become more complicated to manage below the recreational depth limits; probably why it’s called technical diving.. Gas management is crucial, and a variety of breathing gases are utilised to minimise oxygen exposure, optimise decompression, and reduce the effect of narcosis. Beyond 40m narcosis becomes increasingly debilitating, so our exposure to it must be minimised as much as possible. This process begins before even thinking of putting your fins on; it is an inherent part of the dive planning process.

Firstly, what is narcosis? The word comes from the Greek word narke, which roughly translates as ‘numb’. You may also have heard it described as ‘rapture of the deep’, or ‘the martini effect’. The exact mechanism is not completely understood, but the dominant theory is the so-called Meyer-Overton hypothesis, which states that the narcotic effect of a gas relates to its solubility in the lipid (fat) phase. In English this means that the greater the amount of gas dissolution in certain body tissues, the greater the narcotic effect that gas will have. When gases are dissolved in nerve membranes, they cause disruption in nerve transmission, particularly in the brain. The effects on the diver are variable, but become more and more incapacitating as depth continues to increase.
By measuring the partition coefficient (differences in solubility expressed as a ratio), the Relative Narcotic Potency (RNP) can be determined for a given gas, expressed as a number. Below shows the different RNPs for numerous gases:

Helium- 4.26 (least narcotic).
Neon- 3.58
Hydrogen- 1.83
Nitrogen- 1.00
Argon- 0.43
Krypton- 0.14
Xenon- 0.039 (most narcotic).

Argon is used for drysuit inflation only. Neon is used as a breathing gas, but only in deep commercial diving, as it is very expensive. Nitrogen is cheap and abundant, and is therefore one of the biggest culprits in determining how narced you will feel, especially as most people dive on air.
However, you may have noticed that I said ‘gases’. Whilst in the recreational diving community the effect is known as nitrogen narcosis, nitrogen is not the only gas that we breathe that has a narcotic effect. In technical diving it is either called ‘inert gas narcosis’, or simply (and correctly) ‘gas narcosis’. The oxygen that we breathe in, and carbon dioxide (CO2) that we produce as a by-product of respiration also have a narcotic effect. The level of influence that each individual gas has on the level of narcosis is poorly understood, but we do know that as divers we must try to mimise any kind of build-up of CO2 at all points of a dive, and also factor oxygen in to calculations to determine the Equivalent Narcotic Depth (END) when using trimix on deeper dives (compared with air at the deepest part of a dive).

During respiration, oxygen is metabolised by the cells and CO2 is produced, dissolving in the blood until it is expelled through the lungs. CO2 is narcotic in itself, and at high partial pressures has anaesthetic properties. The reason it is not used as an anaesthetic during surgery is because highly elevated partial pressures imbalance the acidity of the blood, which has been shown to induce seizures in humans and animals. CO2 is 25 times more lipid soluble than nitrogen, which, as previously mentioned has been shown to increase narcotic potency. Moreover, CO2 is a vasodilator, which means that more CO2, N2 and O2 can be delivered to tissues, notably, the brain. This can increase the chance of both narcosis and CNS oxygen toxicity. So it goes without saying that divers should at all times be thinking about preventing the build-up of CO2.

Other factors that determine how narced you might feel include:

- Cold water
- Alcohol in the body (including hangovers)
- Tiredness
- Increased work of breathing
- Higher partial pressures of oxygen
- Fear
- Feelings of vertigo (no visual reference in blue water)
- Turbidity and bad visibility (can be related to vertigo as above)
- Task loading
- Descent rate

So we have an idea of what narcosis is, but how do we tell when we are ‘narced’, or identify it in other divers? Symptoms include feelings of euphoria, light-headedness, perceptual narrowing, altered perceptions of time, anxiety and/or paranoia, and even numbness. It’s very common for divers to go to 30, 40 or even 50m and say that they felt nothing. Some of them may be telling the truth to the best of their ability, some of them are downright lying, and some may attribute other factors as to why they didn’t quite feel themselves. Symptoms can often be very subtle, such as it taking longer than normal to read your SPG or not immediately understanding common hand signals. I occasionally get a very pleasant tingle when I hit 40m that passes through my entire body then disappears as abruptly as it appeared. Another common occurrence, mainly on deep air technical dives (50-55m) is something called narcosis amnesia. A diver will complete the dive, get back on the boat and then turn to their buddy and say “what the hell happened on that dive!?” Not ideal when you spent a thousand pounds on a tech liveaboard to dive a world war 2 battleship at 60m.

Divers that feel euphoric will usually indulge in the feeling and forget where they are and what they’re doing, which obviously includes such tasks as checking gas and runtimes! Paranoid divers on the other hand, usually obsess over their gas supply, as if fighting to stay in control. Paranoia however, is usually accompanied by anxiety, which can easily lead to panic. So don’t assume when your buddy is constantly checking their gas and asking you for yours that they are fine!

Divers that deny feeling narced are in my opinion, the most dangerous kind of diver, as this complete lack of self-awareness/sense of denial is usually accompanied by an inner belief that they can do anything, and that the laws of physics don’t apply to them. They have the potential to push beyond their limits by simply not recognising that their coordination and judgement is way slower than at the surface. If they push deeper than they have been trained to, they may suddenly find themselves (and their buddy) so overwhelmed by narcosis that they are unable to help themselves, and that’s assuming that they don’t have an issue to deal with during that portion of the dive, they are not already low on gas, and they haven’t had a CNS hit!
Regardless of any obvious symptoms, your brain is slower, your reaction times and reflexes are slower, your coordination is impaired, and your ability to problem solve is decreased. This gets worse and worse as depth is increased.

Minimising the effects of narcosis starts at the planning stage. How deep do you want to go and for how long? What are the conditions like? Cold water? Possibility of currents? Likelihood of the weather changing whilst you are underwater (bad timing with tide changes)? These are the factors that will influence your gas choice, decompression obligation (including deep stops), maximum operating depths and maximum partial pressures for oxygen and nitrogen. Technical divers have a maximum PPO2 of 1.4 on the bottom portion of a dive, and 1.6 on the decompression stops. But depending on the conditions, depth and duration of the dive, and duration of deco at high partial pressures of O2, this may be lowered to increase conservatism. For an extended range dive the maximum depth is 55m (with TDI), which gives a PPN2 of 5.13, which is pretty darn high. It is generally accepted that a partial pressure of 3.16 (30m) will be noticeable. So if you plan on going deeper than that you can use trimix with the quantity of helium being chosen to offset some of the nitrogen and keep the equivalent narcotic depth to 30m.

Other factors that can help to minimise narcosis include getting enough rest the night before a dive, being hydrated, not being hungover, and being as relaxed as possible before, and during the dive.

On deeper dives, use of a high performance regulator that reduces the work of breathing becomes critical to reducing CO2 build up. CO2 is a dense gas in relation to nitrogen and helium. This effectively means that on very deep dives the respiratory response is not effective in getting rid of enough CO2 with each breath. Little research has been done in this regard, but experiments conducted by the US Navy suggests that 30m is all that is required for the density of CO2 to be high enough that the effort required to breathe reduces effective respiratory ventilation. Devices with increased dead air spaces, such as rebreathers and full face masks also increase CO2. So exertion at depth is the last thing you want to be doing,  both in terms of increased narcosis and higher risk of hypercapnia.

At the beginning of a dive it’s a good idea to descend in a controlled manner, using some kind of shot line to give you a visual reference, and stopping for 20-30 seconds at certain points during the descent so that you can acclimatise to that level of narcosis before continuing on, rather than dropping like a stone and suddenly being hit by a wall of fuzziness!

Whilst you cannot build up a tolerance for narcosis, you can learn to cope with how it affects you. This means doing lots of dives of gradually increasing depth, and not going deeper until you are sure that you can function at that depth and deal with any issues that might arise, such as an out of gas situation or a catastrophic gas loss. If you don’t think you can… don’t do that dive.

The advice given to recreational divers if they experience narcosis and don’t like the feeling is to ascend to a shallower depth, and the feeling should go away. For some people this is true, the intensity of the narcosis will be reduced, but for many people there is a delay beforehand. For technical dives it doesn’t quite work in the same way. The amount of inert gas dissolved is greater, due to the longer bottom time, so the delay in reducing narcosis after ascending can be longer. I’ve done countless dives to 50m and felt really narced, but at a level that is manageable for me. On one occasion both myself and my buddy heard a high pitched engine noise independently in our heads at the bottom of a wreck at 55m, which wasn’t real (narcosis or CNS symptoms?). Whilst doing my deco stops I felt as narced at 12m as I did at 50, and it wasn’t until I switched to O2 at 6m that I started to feel normal again!

But perhaps the best thing you can do to minimise narcosis is to exercise good judgement and never go beyond your training and experience. You may well have been certified as an extended range diver and been to 55m during your course, but maybe you hated every second on the bottom but persevered because you really wanted the cert. If you hated it, why would you put yourself through that again? Perhaps it’s time to think about doing the TDI trimix course?

Richard Devanney, 22nd April 2015.

Technical Stress Test Dives

stress-testIn the Diving world and particularly the Technical Diving world there are many emergency skills practiced and mastered during training, only to be almost never used again. Ask yourself this; ‘If my manifold on my twinset has a catastrophic malfunction and starts rapidly losing gas while my buddy is far ahead of me and cannot see my signal, would I firstly, remember the somewhat complicated emergency procedure and secondly, have the muscle memory to act and execute the procedure under stress before it was too late? Unless you are an Instructor teaching these skills on a regular basis it is quite likely you may not remember an emergency skill if one day it was needed in a real emergency! This is why, along with a few good diving habits, attending skills practice dives on a regular basis is a strongly recommended practice.

Every year both the Divers Alert Network (DAN) and the British Sub Aqua Club (BSAC) release an Annual Diving Report highlighting diving incidents resulting in serious injury or death. Although diving is a relatively safe sport where injury or death is extremely rare, just like any sporting activity there are risks involved. The findings conclude that the main causes of diving related incidents range from the following.

1. Poor health – medically unfit divers with existing injuries or disease, unrelated medical emergencies while diving, like cardiac arrest etc.
2. Equipment problems – malfunctioning equipment leading to stress on the diver, leading to panic.
3. Environmental issues – nasty currents, swell, waves and dangerous entry/exits.

And last but not least….

4. Diver error - breathing wrong gases, not analysing gases, misusing and poor maintenance of equipment such as rebreathers, not servicing equipment, running out of gas, getting lost/entrapped etc. The list goes on.

There are a small amount of potential incidents in diving that would simply be out of our control (this is not the topic of today’s blog and will be discussed in future blogs). However, any good diver and especially any good technical diver knows that the diver themself needs to be in control of as many aspects of the dive as possible and ready to act upon any reasonably foreseeable emergency.

So with the huge amount of skills and emergency procedures learned along the way during training, it is fair to say that to be able to do all these skills effectively, and under stress, regular practice of these skills are needed. I know of at least a few qualified divers, some recreational and sorry to admit, some technical, which absolutely hate one of the most basic, yet important skills, being underwater without your mask on. And the reason for this? They have just not spent enough time underwater conditioning themselves so that not having a mask on does not bother them.

The solution? On every dive, yes every single dive they should be removing their mask and replacing it with their back up at least a few times until they are completely comfortable with it.

So what about more complex emergency skills like locating, isolating and shutting down a catastrophic gas loss on a twin set? Along with a thorough predive check, an excellent procedure that myself, and quite a lot of Tech Divers do is a full valve shutdown (not to be confused with an emergency valve shutdown), S-drill and bubble check at 5m before the descent. This is done on every dive and takes about 1-½ minutes. During this procedure all valves in turn have been shutdown and opened up as quickly as possible then the long hose is deployed and bubbles are checked. This keeps the diver aware of which way the valves should be turned in an emergency and also builds very fast muscle memory. Every now and then on the dive itself, it’s good practice to perform a simulated emergency valve shutdown while finning around. In the unlikely event the diver has this emergency for real, they can deal with it easily as they will have done it countless times before. This can be done on Twinset, Sidemount and CCR.

There are many emergency procedures learnt as you progress through Technical Dive training such as Gas Hemorrhage, Out of Gas, Loss of Buoyancy, Malfunctioning Inflator Button, Toxing Diver, Unconscious Diver Tow and Ascent, Buddy Breathing, Regulator Feathering, Loss of Visibility, Loss of Light, Lost Diver, Lost Line, Flooded Loop, Bailout and the dreaded No Mask Ascent. Then add to this, two or more of these emergencies happening at the same time, with no visibility. This is where panic can set in if you’re not adequately conditioned to deal with these emergencies. Everyone has a breaking point; the idea is to have that breaking point as high as possible.

So what can we do? If you’re not instructing regularly, a great way to keep skills fresh is to attend a skills practice dive at your local dive club. Practicing a single emergency skill after its been demonstrated to you, and you know its coming is great for learning the skill, although you need more than that to truly master the skill. Practicing multiple simultaneous emergency skills with no demonstration, no warnings, and limited or no visibility in a controlled environment is a much more realistic and effective way of boosting the breaking point and mastering the skills under stress. Donny McFadden and Richard Devanney at Big Blue Tech offer Technical Stress Test Dives for their customers, in a realistic fashion, using surprise simulated emergencies to raise the level of the breaking point in emergency situations. Donny and Rich cover all the emergency skills involved at all levels from beginner skills in TDI’s Intro to Tech, through to Advanced Wreck Diving, Advanced Technical Sidemount and all the way up to Mixed Gas Decompression Diving. In addition to this the ability to follow run times and decompression schedules whilst being task loaded with emergency procedures is essential to any competent Technical Diver. Both of us at Big Blue Tech are dedicated to producing divers of this calibre. So if you think you may need to get a bit of practice in then come in for a chat or get in touch for more information on Big Blue Tech’s Technical Stress Test Dives.

Diving inside wrecks- training, practice, patience

Wreck-divingDivers or non-divers, most people are fascinated by the idea of a shipwreck. On hearing the word, many will think of smugglers, galleons, battleships, or a famous oceanliner sunk in tragic circumstances, such as the RMS Titanic.

Reading about them or watching a documentary is about as close as most people will get to seeing one, but for divers there is the very real prospect of exploring many different kinds of wrecks in established dive sites all over the world. Diving around the outside of a wreck can be exhilarating, eerie, or even scary, but for the most part, done safely- with training. Recreational wreck diving speciality courses introduce divers to procedures for navigating around the outside of a wreck, and provide basic information on how to research or find a wreck. But with the exception of the SDI course, they are not designed to allow a diver to go inside a wreck, and this is emphasised throughout the PADI and SSI courses (even though the PADI course does include very limited penetration).

Exploring the inside of a wreck requires training, practice, and patience. They are very dangerous places to be in. Hazards include loss of orientation due to a “silt-out”, entanglement on fishing line, net or electric cables, entrapment due to collapsing structures such as a ceiling or unsecured hatch, and rapid changes to diving conditions due to encroaching bad weather during a dive.

People who scoff at these hazards are often the ones that think “that will never happen to me, I know what I’m doing”. They are usually also the divers that end up getting killed, or, even worse, lead someone else inside a wreck and get them killed.
As a TDI and SSI technical dive instructor, I see this complacent and over-confident attitude all the time. We have a very tame wreck in Koh Tao called the HTMS Sattakut. It’s an old landing craft infantry vessel, and was involved in numerous battles in World War 2. It was sunk in 2011 to act as an artificial reef, and is dived daily on the final dive of the SSI advanced adventurer or PADI advanced open water course. It’s also a daily occurrence that instructors or divemasters can be seen exiting the wreck with no torch, no guideline, little or no exposure protection, and anything from 1 to 6 students or customers following behind them. Now the Sattakut has been stripped of its engines and furniture, and it has a lot of natural daylight on the main corridors, so it’s unlikely that you will get yourself into any real trouble (apart from the potential for panic) unless you go into the lower levels. But that’s not the point. The point is that bad dive professionals are instilling into those students or customers a false sense of security that all wrecks are like this, and they may go to another wreck somewhere (with or without a dive guide), copy the same methods to penetrate, quickly find themselves in serious trouble and not have the means to deal with it.

Diving fatality reports are very sobering reading. Type the word wreck into the 2013 BSAC annual diving incident report and you will see that there are more than 50 incidents involving wrecks, many of those fatal. The most common reasons that people die when diving wrecks are due to:

  • Failure to obtain proper overhead environment training.
  • Failure to maintain a continuous guideline to open water.
  • Failure to properly manage gas supply.
  • Exceeding personal experience and training.
  • Failure to provide adequate lighting.

Let's briefly look at just one hazard of diving in an overhead environment; disorientation due to lack of visibility caused by a silt-out. The way I describe it to my wreck and advanced wreck students is to imagine visiting a ship in a maritime museum. Go inside it, down a few flights of stairs and walk along the corridors until you find a room. Now cover your eyes, spin yourself around a few times and feel your way out (you could also try it at home- go to the bathroom with your eyes closed the whole time after spinning around!). You’ll get out of the ship eventually, but it will take a long time and you’ll probably have a few bruises on your head and shins! Now imagine the same thing underwater but remember the following- you have a finite amount of gas, the ship may be on its side or upside-down, if you bang your head you could knock yourself unconcious or begin bleeding, you may be going deeper into the wreck and you may get tangled up and/or entrapped at any point. If you wish to penetrate wrecks, then these are the things you need to be trained to deal with. I make a point of showing my students on both the SDI wreck course and TDI advanced wreck course a complete silt-out. For the SDI students, I get them to stay at the exit whilst I stir up silt. Within seconds both I and my powerful canister light have completely dissapeared. For my advanced wreck students, they need to experience being inside that cloud of silt. 

Summary of advanced wreck training
In the same way that you’re probably not going to go for a dive to 30m immediately after the pool session on your open water course, you’re not going to explore the deep dark recesses of a wreck without gaining the appropriate skills and experience. Advanced wreck courses are designed to give a diver the tools that they need to minimise risk. They also teach and allow practice of skills that could save your life if, for example, you suddenly found yourself swimming through a thick cloud of silt. The TDI advanced wreck course runs through the following:

Gas management- In any overhead environment, you should calculate the amount of gas you will need, and also allow for any contingencies, such as two people having to share air from their furthest point of penetration to either the surface, or the depth of their next breathable gas (rock bottom or minimum gas), say a switch onto 50% O2 at 21m. You will also need to decide what rules to use for your gas contingencies (e.g. multiply deco gas requirements by two for a buddy team of two, x1.5 for 3 or more divers). The basic rule of thirds does not work on back-gas in a wreck, not with one person out of air and two elevated breathing rates. Go through the maths yourself, it will get you killed.
If the dive is a decompression dive you may also be carrying deco cylinders that will need to be staged securely before penetration, somewhere near the entrance point, then found and retrieved on exiting. How you carry your gas also needs to be considered. Will you be using a twinset with an isolation manifold, or independent doubles as in sidemount? Are you diving different sized cylinders to your buddy or buddies? If so turn pressures based on bar is not adequate, you need to calculate volumes. What gas mixtures will you be using- do you really want to penetrate a deep wreck on air have to deal with gas narcosis on top of everything else? If your main gas is trimix is it hypoxic? Will you need a travel gas? All of these factors are covered during the course.

Navigation and reel work- Using a reel is the primary tool for navigating your way inside and outside of a wreck. You will learn about the different types of reel and spools, how to hold them, how to reel in and out without creating a “bird’s nest” or tangling yourself up, how to lay the line and where (securely and not on sharp objects), and how to apply the different types of tie-off to secure the line without it disappearing behind an object that prevents its use on exiting (so-called line traps). You’ll also be taught how to use spools to “jump” from the main line to explore different areas of the wreck, connect a gap between two lines, or use a spool to look for a missing diver or the main line if you (hopefully never) lose it. You’ll also learn ways to mark the line using line arrows to either mark the exit or allow you to look for a missing diver. However, you should also become familiar with the inside of any wreck by progressively penetrating with each subsequent dive, and back-referencing where you are at any point. You’ll also be taught to cover your torch to look for ambient light or your buddy’s light in the event of separation from them or the line.

Team roles and positions- Wrecks can be a bit cramped inside, which usually (but not always) necessitate the buddy team diving in single file. You’ll learn about the different ways for a team to position themselves, and also who will do what during any given dive. Things would get very messy if every member of a team used a reel, so one person will take the role of the reel diver, with the other diver or divers acting as support and taking responsibility for other aspects of the dive.

Buoyancy and propulsion techniques- The way you propel yourself through the wreck will affect how much you can see; if you’re flailing around all over the place, you will reduce visibility pretty quickly and might injure yourself on any sharp bits of metal. Likewise, if your buoyancy is no good, you could be tangling yourself up in your own line or something else, you may puncture your BC, or if you float up to the ceiling be in danger of dislodging your 1st stage regulator. You could also dislodge a piece of the wreck (i.e. the ceiling) and find yourself entrapped. Effective finning techniques and buoyancy skills are fundamental to the course.

Communication- The lower levels of wrecks often go beyond the daylight zone, so simple hand communication is not always adequate. Using the torch to communicate, or in conjunction with hand signals without blinding your buddy are very important skills to learn. Once you have mastered these you can dive very efficiently without having to even stop or turn around to check your buddy is ok (global and situational awareness).

Equipment selection and use- Knowing how much and what type of equipment will make the difference between getting tangled up on every single bit of line you encounter, or finding yourself in need of some piece of equipment but not having it with you. Every dive requires slightly different equipment configurations, and you’ll understand how to choose what you will and won't need for any wreck dive you do.

Emergency procedures- So what if you did silt out the room you are in and now find yourself having to feel your way out? It can be done. It can even be done with your buddy(s) by using touch contact and holding on to that line that you so diligently laid on the way in. It can even be done if someone is suddenly out of air and you having to exit through some tight spots! You’ll learn how and practice until you get it right. You’ll even learn basic communication. Other fundamental skills to master include a lost line drill, catastrophic gas failure, loss of primary light and missing diver.

Entanglement and entrapment- Developing good self, global, and situational awareness will help you to minimise the likelihood of getting entangled or entrapped, but lines and cables have a mind of their own and in bad visibility it could happen (or in good visibility if your concentration slips). Again, you will learn effective techniques for dealing with such situations on yourself or your buddy.

The above is a lot to take in, which is why it is called advanced wreck. To undertake the advanced wreck course you must already have a wreck specialty qualification. The SDI wreck course provides a foundation to build from. However, you'll also be much better placed to successfully complete the course if you are already a technical diver to the level of decompression procedures or higher. The TDI advanced wreck course is comprised of classroom sessions, land drills and a minimum of 6 penetration dives, that allow you to understand and practice all of the above skills and techniques. It will make you more aware of the risks of wreck diving, allow you to plan and execute penetration dives, and enable you to deal with any reasonably foreseeable issues you may encounter. You will challenge yourself, you may learn a little bit about yourself, and hopefully you’ll have a lot of fun throughout as well!

Richard Devanney

If you’re interested to find out more about advanced wreck training, contact us at This email address is being protected from spambots. You need JavaScript enabled to view it.


SSI-TXRSince the beginning of time Big Blue Tech Thailand has been providing technical dive training through TDI (Technical Diving International) and BSAC (British Sub Aqua Club).  In that time hundreds of certifications have been issued to happy customers worldwide. However being a sub company of the biggest SSI recreational dive school in the world, Big Blue Diving Koh Tao, we have decided to now offer, alongside TDI and BSAC, technical dive training from SSI in the form of their XR and TXR programs!

So, on the 14th of July 2014 Big Blue Tech’s head instructors Donny McFadden and Richard Devanney teamed up with SSI Asia Pacific to cross over their instructor ratings to be able to teach SSI’s updated and streamlined XR and TXR programs.

The team consisted of TXR Instructor Trainer, Ben Reymenants from Blue Label Diving, SSI Asia Pacific Director, David Lee, Al Stewart, SSI Asia Pacific Director of Education, and Ben’s wife Simone Reymenants providing logistical support and promotion. Big Blue Tech was truly honoured to have such a wealth of experience camping out on Koh Tao for the 9 days!

The 9 days consisted of back-to-back 10 hour days jam packed with evaluation dives, Trimix dives, Technical Advanced Wreck dives, academic presentations and workshops, and lets not forget the millions of tanks needed for this operation that needed pumping each evening! The team’s equipment was diverse, utilising all the diving platforms, Twinset, Sidemount and Rebreathers. It was an extremely busy 9 days but overall the whole operation was a success with Donny and Rick crossing over to SSI XR/TXR with flying colours. Both Instructors know they have learnt and gained a huge amount and look forward to passing on the knowledge.

SSI’s XR and TXR stand for Extended Range and Technical Extended Range. These programs have been around for a while now, however very recently have been updated and streamlined, providing an even more extensive and comprehensive technical dive training program. With levels ranging from the entry level XR Nitrox course, allowing 40m depth, greater oxygen mixes and minimal decompression, through to Hypoxic Trimix allowing 100m deep mixed gas decompression training. TXR Technical Wreck is a course providing training in full penetration diving inside wrecks and/or other underwater structures.  Also available is the TXR Cave course, which has the intent to provide divers with the training necessary to independently plan and conduct cave penetration dives utilising advanced gas management techniques.

The materials look great, the standards are high, and the support from SSI in the Asia Pacific region is second to none.

With huge potential for the XR/TXR programs, Big Blue Tech Thailand is certainly very excited to have joined the SSI Technical Dive Family and is looking forward to producing many more high quality divers.  Along with our other solid agencies TDI and BSAC, our customers now have the choice of participating in SSI XR/TXR training.

Watch this space over the next couple of weeks for more info on Big Blue Tech Thailand’s new SSI XR/TXR programs.

We look forward to diving with you soon!

Sidemount Diving

sidemountTechnical Divers have many different equipment platforms available at their disposal. Back mount twinset is the traditional and most common style, utilizing two cylinders on the back and any additional tanks on the side. Rebreathers have been around for a long time and in recent years the technology has improved drastically, thus the popularity and safety as well. But one equipment configuration getting more and more popular in Technical diving is the Sidemount setup. Sidemount differs from back mount diving, with the cylinders usually tucked under the armpits and secured to the hips, this allows more freedom of movement and a much more streamlined profile in the water.

First born in the muddy cave systems of UK in the early 1960’s, sidemount equipment was quite primitive. No one was manufacturing equipment for sidemount, so the gear was always home made out of various other diving gear to suit their needs. Rather than having the bulky tanks strapped to their backs, the early sidemount divers would have the tanks on their side against the thighs, thus allowing them to squeeze through much tighter restrictions in the caves that were once thought impassable. Often they would not even have a buoyancy device or even fins.

In the 1970’s the cave divers of Florida adopted a new approach adding buoyancy in the form of a hydration pack (camel pack) strapped to the back, which they would orally inflate for buoyancy. The tanks were shifted higher to under the arms and by the hips. This suited the Florida cave diver better than the no mount system from the UK.

It wasn’t until the 1990’s when the first Sidemount harness was manufactured for sale. The Dive Rite “Transpack” harness. However most people continued to make their own DIY setups as sidemount was still only used by a small number of extreme, exploration cave divers.

In the 2000’s sidemount became very popular in the Technical Diving world and has even migrated to the Recreation diving world. Now used in all types of diving; open water, wrecks, caves, no-mount and decompression diving. Sidemount is here to stay, and some even say it’s the future of recreational diving.

Big Blue Tech has been training sidemount for some time now using the extremely bulky and cumbersome Dive Rite “Nomad” system. However we have recently upgraded to the incredibly advanced and streamlined X-Deep “Stealth 2.0”. Created in conjunction with cave diver Patrick Widmann, the X-Deep has a minimalist approach to design, every last piece of this system was well thought out and engineered. There is nothing on the unit you do not need and everything is in the right place, creating the most streamlined, well thought out, sidemount unit on the market.

Big Blue Tech Instructor Donny took the new X-Deep Stealth 2.0 on a few dives to test it out and came back grinning from ear to ear. With the unit naturally forcing you into the perfect trim position, and the tanks sitting exactly where you want them, the X-Deep takes almost no effort to dive in. The X-Deep has 16kg of lift, so is more than capable of taking multiple steel tanks for deep decompression diving or just one or two aluminium tanks for a relaxing shallow dive. The unit has intuitive rubber waist D-rings instead of steel with a floating adjustment on the waist strap allowing for perfect positioning of the aluminium tank as it starts to get positively buoyant. With this simple yet incredibly smart design feature it means with correct use your tanks will always be completely horizontal and parallel with your body. This creates little drag and makes movement through the water effortless.

Another great feature is the detachable bladder. This serves 3 purposes. #1. For extremely tight cave restrictions you can remove the bladder creating a “no-mount” system making it possible to squeeze through restrictions no bigger than you body. #2. Being detachable means you have a greater range of adjustment for the placement of the bladder. For leg heavy people you have bladder lower on the body. For head heavy the opposite, move the bladder higher. This means perfect trim is easily achieved. #3. For redundancy of buoyancy you simply attach a second bladder over the top of the first, creating backup buoyancy in the event of punctures or failures.

Another incredibly smart design feature of the bladder is the centred dump valve located at the bottom of the bladder. Allowing easy deflation with the option of either hand. Also meaning no need to roll to deflate.

With all these unique features, the X-Deep is by far the most advanced, versatile and intuitive sidemount unit on the market. It’s not hard to see that this unit has a lot of thought put into the design, and that’s why Big Blue Tech have lashed out and bought five brand new units for use during the TDI sidemount training we provide.

Prerequisites for the course are minimum age 18 years and an Open Water certification. The course can be taught on any level from recreational to Trimix. Sidemount can be taught in conjunction with a range of courses like Nitrox, Cave, Wreck and Advance Wreck courses.

So if you think sidemount is the way forward then drop us an email and lets get diving!

Angthong Marine Park

Angthong Marine Park Blog
ang-thong-marine-parkThailand is undoubtedly known as one of the most beautiful places on the planet. From the busy, culture filled streets of Bangkok, to the fresh aired, misty mountains of the north, and lets not forget the iconic white sandy beaches of the south found in so many postcards. This tropical paradise has all that and everything in between, but one place in the land of smiles that takes the prize as the most beautiful place in Thailand, is the Angthong National Marine Park. If you could imagine 42 limestone islands surrounded by Colgate white beaches, water so crystal clear you want to drink it, and not a soul in eyeshot to bother you, then you can imagine Angthong Marine Park!!

Big Blue Tech Thailand is only 4 short hours from this paradise, and guess what? That’s right! We are heading there in early July 2014 for some exploration diving with Big Blue Dive Club over 3 days/2 nights! This is a diving trip open for all divers, Recreational, Technical, and for the first time, Freedivers. If you’re not sure if this trip is for you, then go ahead, keep reading and when you’re done, give us a shout to confirm your place!

Being a national Marine park, Angthong has no bars, clubs, 711’s or motorbikes. Where the bars and clubs usually are there are mangroves. Where the roads with big franchises usually are, there are lakes, jungles and coconut trees. The 42 islands are filled with a huge variety of wildlife in the jungle and the sea. Researchers have discovered 16 species of mammals, more than 50 species of birds, 14 species of reptiles, and 5 species of amphibians. An interesting one to look out for is the Dusky Langur (leaf monkey), which comes down to the park’s HQ allowing visitors to get up and close with this cute creature. The park supports several types of forest and flora such as; dry evergreen forests that cover the large islands of Koh Wua Talap, Koh Paluai, and also Koh Saamsao. A very important plant Ang Thong Lady’s Slipper Orchid, is an endemic species found only in Mu Koh Ang Thong.

First established on the 12th November 1980. Koh Angthong is an archipelago in the Gulf of Thailand. With 42 islands in total, most of them quite close to each other, the national park offers breathtaking panorama views while boating around the islands. While all the islands are covered in lush, tropical forests, all of them are different shapes and sizes. Many of the islands consist of limestone Mountains ranging from 10 to 400 meters high. As limestone is ever changing over the centuries from weather, this has created unique caves and cliffs above water and below. All of the islands are uninhabited and undeveloped except for one.
Other than sitting on the beach taking in the sheer beauty of the islands, Angthong also offers a wide range of activities including; snorkeling the reefs, kayaking though the islands, hiking to the many spectacular viewpoints and of course DIVING!! With vast array of dive sites ranging from 10m to 25m this is a diver’s heaven. An abundance of coral, sea life, swim-through caves and if you’re lucky a whale shark or even pilot whales, is all found in the surrounding waters.
Many dive sites on Angthong are undiscovered, so the exploration aspect of diving here is truly incredible. With no buoy lines or other divers to be seen anywhere, it is quite possible that you could be the first person to be diving through one of the hundreds of swim-though caves. Last time Big Blue Tech was there, we found many un-dived sites and caves.
Koh Yippon Lek dive site has a depth of 20m suitable for all levels of divers. The name translates as “Small Japanese Island”. On the furthest north end of the park, this site has many shallow caves and swim-though. Marine life includes Squid, Cuttlefish, Banded Sea Snakes and huge Barrel coral.

Koh Wao dive site has a depth of 18m, starting at 5m near the carpeting rocks and heading out deeper to find the amazing overhangs and very tight swim-through caves. Juvenile Sweetlips can be found here as well as Blue Spotted Rays and Banded Sea Snakes.
Hin Yippon is a site not to be missed! Made up of huge boulders and dozens of swim-through caves this site is a great place to find hiding big Red Snappers and Groupers. This is a picture perfect site, perfect of underwater photographers. Max depth is 25m however most interesting features are at 18m or below.

The Big Blue Dive Club trip will leave Koh Tao on the 4th July. We will arrive in Angthong Marine Park in the afternoon with enough time for a couple of dives before checking in to our bungalows on the beach. A yummy home cooked Thai dinner will be served and then time to chill out and enjoy the peacefulness of it all. The following day will consist of two dives in the morning to some of the incredible swim-through caves followed by packing our lunch and heading off on the kayaks to explore the islands and have lunch on one of the many white beaches. The afternoon will be left up to you. Two more dives? Or maybe trekking up to the best viewpoint 500m above sea level! After a sunset night dive we will have a BBQ on the beach with a few beverages to celebrate under the stars. The next morning will be two more expletory dives hopefully finding the Pilot Whales Big Blue Tech saw last time we were there. After that one more yummy Thai lunch in this paradise then back on the boat to chill out as we cruise through the islands getting the perfect photo on the way back to Koh Tao.
Ok, convinced yet? Well if your not, this certainly will help. The price!! You get transfers to and from the park, lunch included on the ride there, 2 nights accommodation in bungalows on the beach, 8 amazing expletory dives, all equipment included, beach BBQ, kayak hire, park entry fees, unlimited water and soft drink, and possibly the best underwater photo you will ever get. All of this for only 5500 Thai Baht!!
Contact Big Blue Tech for bookings at This email address is being protected from spambots. You need JavaScript enabled to view it.

Contact us on facebook here.
Follow us on twitter here.
Or come into the Tech Shack for a chat.

Deeply shallow- May 29th 2014

Deeply shallow
Blue-Hole-trimixSeeing as the maximum depth you can achieve in the gulf of Thailand is around 55 metres, why would you bother with tech diving here? Just as most non-divers think that scuba divers breathe a tank of oxygen when diving, most recreational divers believe that tech diving is all about attaining depth.... It's not.

The deepest open circuit scuba dive ever was achieved by Nuno Gomes in 2005. In the Red Sea in Egypt he dived down to 318.25 metres. He did this for the sake of going deeper than anyone else, and his dive consisted of dropping down a line, then coming straight back up it, albeit 12 hours later! Within the tech diving community they call it soap on a rope diving. But why people do this is the same reason that people landed on the moon. To push the boundaries of what is possible. The physiological data gathered from such dives is invaluable towards gaining a greater understanding of what happens to our body on normal recreational dives. But you'd have to be a little bit crazy to want to go to 300 metres. Most tech divers aren't interested in seeing if they could get to those kinds of depths.

They're interested in doing something useful on a tech dive, i.e. having a dive objective. That may involve a task such as finding a new dive site, exploring a wreck or cave, or performing geological or biological research. Some such dives may be very deep, but the depth will always be a by-product of the objective of the dive, and you can't just get some tech gear and go as deep as you want, you have to progressively learn to use your equipment properly, and fully understand the procedures for going into decompression and diving deeper.

Koh Tao is a great place to learn how to dive, and technical diving is no different. We have some fantastic shallow dive sites for teaching the TDI intro to tech course (the first tech course), but we also have deeper dive sites for courses such as TDI decompression procedures and extended range. The point is, you begin the training in a benign environment, and then progress on to deeper and more challenging dive sites for more advanced training once you've got the skills nailed. Then if you go anywhere in the world such as the Blue hole in Darhab, Egypt, you will be well placed to undertake the additional training required to take you beyond 55 metres- you won't have to start from scratch.

But let's get back to basics. If you do the intro to tech course, you will be qualified to dive on a twinset to whatever depth you are already qualified to dive to. If you've done your deep speciality course, that would be 40 metres. However, given that you'll have 4,400 litres of air on a twinset instead of 2,200 on a single tank (at 200 bar pressure), it makes even more sense on the average dive site to go no deeper than say 30 metres, and, (if you have your nitrox speciality) to use 32% nitrox as your back gas and get a sizeable No Decompression Limit (NDL) that you can actually utilise, without having to end your dive because your air supply demanded you to. If you're a marine biologist conducting a survey of a dive site, it makes perfect sense that you would want to maximise the time allowed underwater for each survey. So from that point of view a single tank is not really much use to you... some of the most successful marine scientists are tech divers. 

So tech diving really doesn't need to be all about going as deep as you can. Whatever kind of diving you want to do, Big Blue Tech can provide the training that you need, in a progressive manner. For more information on your options for becoming qualified, send an email to Rick or Donny. The email address is at the top of our homepage.

What is Technical Diving? 24th May 2014

What is technical diving?
wreck-divingMost people that come to Koh Tao do so in order to learn how to dive. At the time of arrival they understandably know very little about what diving entails. The first diving qualification they can achieve is to become an open water diver consisting of 4 dives that will allow them to dive to a depth no greater than 18 metres.
Asking someone who's learning to dive what they know about technical diving is like asking a tramp which type of caviar is currently in vogue amongst the chattering classes.. but even a qualified fun diver may have a bit of a tumbleweed moment if you asked them. So what is technical diving then?

Simply put, technical diving is a type of scuba diving that exceeds the conventional limits of recreational diving, especially regarding depth and time at depth. Standard recreational scuba diving allows a person to dive with a single tank to a depth no greater than 40 metres, and that person can only spend a limited amount of time at any given depth beyond 12 metres, as dictated by their No Decompression Limit (NDL). Technical diving allows a diver to go deeper than 40 metres, and spend more time at the deeper depth by allowing them to go into decompression (beyond the NDL limits imposed on recreational divers). But this involves wearing specialised equipment, requires additional training, and incurs higher risks to the diver than recreational diving. To enable this kind of diving, different gases are also used, ata different points of the dive.

So why bother going beyond 40 metres, or going beyond the limits of your NDL? Many of the best dive sites around the world are pretty shallow, and if you want to see marine life then recreational diving will usually suffice. Why people tech dive can be summed up in 5 words; shipwrecks, caves, exploration, research, and salvage. Marine biologists often want to examine what lives beyond the photic zone and take samples of the marine life residing at such depths, or spend longer underwater at relatively shallow dive sites (the benefits of nitrox really come into play when you have two tanks worth of gas!). This all helps to increase our understanding of marine ecosystems. Ice diving is also often undertaken by marine biologists in Antarctica. This can be seen in the Werner Herzog documentary "Encounters at the end of the world". It's a bit of a no-brainer as to why people would want to dive shipwrecks or explore cave systems; they can be beautiful and mysterious places, and you may be uncovering a bit of history too- with caves, millions of years of history! Cave diving is one of the most dangerous yet exhilerating sports there is. By exploring virgin cave systems, divers can help geologists gain a better understanding of how they form and how they affect groundwater storage and movement. It also fulfills the inner explorer in all of us. For salvage diving, if a ship sinks and there is a chance it can be raised back to the surface, or the contents recovered, then the specialist salvage companies are called in. They may use a combination of commercial diving and technical diving to help them get the result they need. This was demonstrated in spectacular fashion with the recent raising of the Costa Concordia in the meditterranean.

Technical diving allows us to do all these things because the equipment and training enables a diver to go deeper, and stay longer at any given depth. It can be very challenging, but it can also be extremely rewarding. The best courses I ever did were tech courses, and the best dives I've ever done are tech dives- you get to see less common marine life too. Technical diving has historically always been marketed as being really macho, or really geeky. The reality is none of these. It simply makes you a more rounded diver, and gives you the option to really get the most out of your diving, whether that involves marine life or shipwrecks.

If you're interested to know more about technical diving, including where to start and the progression you can make, have a look on the Big Blue Tech website, like our page on facebook here, and get in touch with Big Blue Tech managers Rick and Donny. Their email address is at the top of the homepage. If you're already on Koh Tao, just pop in for a chat.

May 19th 2014

New Management!

Big news- Big Blue Tech is under new management! Richard Devanney (left in the photo) and Donny McFadden (the only other person in the photo) have taken over from outgoing manager James Foleher and his glamorous assistant Ian. James has decided to pursue other ventures, and Ian will be continue to teach recreational diving with Big Blue. 
So from the 25th May, Rick & Donny will be in charge of the technical diving department at Big Blue. They have both been at Big Blue for years, and have a lot of experience to bring to the role. They are very passionate about their diving, especially technical diving, and believe in trying to make every student they teach become the best diver that they possibly can.

They are not the type of people to cut corners either; every course they teach is to a very high standard, putting the safety of the student first every time. Prior to being involved in the diving industry, they both had very varied careers. Rick has worked as a metallurgist, melting steel in steel foundries (i.e. getting burnt for a living), a geologist on oil rigs all around the world, and before he came to Koh Tao was involved in sustainable energy for 7 years. Donny worked in the commercial construction industry for many years in Australia, and has for a long time been heavily involved in the music business as the lead singer/bassist of punk rock band Lamexcuse.

They are passionate and enthusiastic about their new role, and are currently busy developing a number of ideas with which to take Big Blue Tech forward. Big Blue Tech would like to thank James and Ian for the work they have done over the last few years, and wish them well in their future endeavours. 

Big Blue Tech has a pretty broad online presence, so whichever medium you use, you can like Big Blue Tech on facebook, follow us on twitter as @BBTechThailand. We're even on Instagram as.. you guessed it,  Big Blue Tech. If you're feeling old fashioned then just have a look at the Big Blue Tech website (you're on it now!). They will all be regularly updated with information on technical diving, training, expeditions and Big Blue Tech events. Also, if you live on Koh Tao join the Big Blue Dive Club on facebook. It's a group open to any dive professional and DMT on Koh Tao, aiming to provide information on the regular dive trips that Big Blue Tech will be running, open to all on a first come-first served basis. But seeing as Koh Tao is pretty small, you can also just pop in to the tech shack for a chat too!

With big things in store for us here at Big Blue Tech, we're excited for the future and invite you to come diving with us!


December 20th 2013

Big Blue DM's And DMT's Hit Tech
Finally the tech shack is no longer surrounded with just male testosterone. We are proud to welcome Molly and Carolina to the world of technical diving. Don't worry Harrison, we haven't forgotten about you!!!. These girls and guy have had three days of skills, drills and theory for the beginning level of tech. The nervous looks of 'How heavy is this going to be?' shrugged off with "It's actually not as bad as we thought". It looks like Harrison and Molly may go on to Advanced Nitrox after the party season has subsided. Unfortunately Carolina is heading back to her home country of Italy. Either way guys, job well done and we look forward to doing more with you. If you require any info on the courses we offer, don't hesitate to contact us at This email address is being protected from spambots. You need JavaScript enabled to view it.

November 7th 2013

Non Monsoon Catch Up

Well that time of the year has arrived again. Its supposed totechsupport be monsoon, meaning that Koh Tao should be quiet and the weather should be dreadful. Not this year!!!!.

Yet this doesn't stop the tech shack from having a bit of a catch-up, I say catch up but what I really mean is time to clean all the cylinders and service all the regulators before the season kicks off again. With bookings on the way, a quick turn will be required to ensure that everything is tip top and ready to roll. Its also a great time for people wanting to do any servicing courses or compressor operator courses, as we have so many great deals for anyone on the island. Even if you just want to pop in for a chat as its always good fun to watch Ian with a brush that was designed for very small people.

November 5th 2013

Iternships at Big Blue Tech

Sad times at Big Blue Tech!!!! Today one of our recent interns left for the Similians live aboard trip with Big Blue Koh Lak. Blake has been with us for around two and a half months ( however at times this has felt so much longer). Basically he started recreational diving and decided technical diving was more his cup of tea. Starting with Intro to Tech all the way to Decompression Procedures with compressor and gas blending and numerous other courses along the way. All our internships vary and can be tailored for any diver needs whether it be wrecks that float your boat or not in this case. Blake starting with no technical dives under his belt and left with around 100 in different conditions and depths. The beauty for us at Big Blue Tech is having our very own technical diving boat making all areas around us accessible. For any information regarding technical diving or internships contact James or Ian at This email address is being protected from spambots. You need JavaScript enabled to view it.

April 23rd 2013


Big Blue Tech Enjoying LifeFinally at BBT we got chance to experience what Burma has to offer and what can we say but WOW. Some absolute awesome diving with lots of small and large things to see ranging from the tiniest of nudibranches to large nurse sharks.
We were lucky enough to have 12 awesome divers who thoroughly enjoyed the trip and came back with huge smiles all round.

It has to be said it is a stunning environment for any diver to thoroughly enjoy. There was a little bit of something for every level whether it was large swim through's to small caverns and caves.The live aboard we tried out was the MV Thai Sea owned by a company based in Ranong by the name The Smiling Seahorse and is run by a fantastic couple named Franck and Camille. They offer a great trip for all levels of divers and have brilliant team of staff working with them and really do pamper to all your needs. The food even better and the chef Chewie can do wonders with a BBQ. The photo's will be following and keep your eyes peeled for the upcoming trips for the new season.

April 7th 2013

Big Blue Tech Returns To The Torpedo

Yesterday was an exciting and awesome day out for Big Blue Tech, not only did five of our resident techies get the chance to dive the 70m long Japanese vessel known as the Torpedo which on its own is impressive. But along came the newest addition to Big Blue which is Big Blue Free Diving.

After initially looking at the weather reports and conditions we all decided we were off. With a two and a half hours steam north in quite choppy conditions we arrived and shotted the wreck. Looking down the water was nice and blue and you could see the bouylines that attach to the Torpedo. The techies finalized there prep, as the the lot less bulky kit of Pepe and Flavia was placed in the water and prepared. We have to admit there was a real buzz on the boat as none of us had been in the water with these guys especially on the deep sites 50m+.
First impression of the wreck was WOW 10m visibility and lots of marine life around, even a very large NUDIBRANCH as Phil one of Big Blue's Dive Masters pointed out (which he was promptly slapped for, you can't take him anywhere without him looking for the small stuff ). Heading up for our first deco stops was when we started to see Pepe and Flavia in turns coming down to see us. Followed by at 5m the sight of bad ass Bryan doing what can only be described as the tech version of free diving ( not quite as elegant as he can be in a twinset). After this we packed up and headed South to our second deco dive of the day on the Unicorn, conditions still a little choppy but hey you cant stop us when we have a mission.
The Unicorn is cargo vessel that sits around 50m and can be a very hazardous wreck to dive with strong current and hit and miss visibility. The last few dives on this wreck we have had 10m+ visability and no currents we were looking forward to this one. First part of the decent was looking good, hardly any current and a thermocline at around 26m then it got dark or as Maxime ( our half French,half German ex student known as freman) pointed out " whoh that was black". Even so the guys enjoyed the whole challange and yet again the crazies(freedivers) were there to greet them on there deco stops.
All in all a massive success of a day. Thanks to everyone that made it happen and also for Pepe and Flavia for making our deco hangs heaps more fun. Pictures will be coming soon or check us out on Facebook These trips will be happening once a month to different wrecks and sites.

For any more information contact James or Bryan at This email address is being protected from spambots. You need JavaScript enabled to view it.

And we are LIVE

After 2 years of planning the new Big Blue Tech website is LIVE!!!!!!!!!!!!!!

Be sure to keep this page your favorite list as over the next few weeks/months/years, the guys here at BBT will be bringing you movies, pictures and blogs of some of the best Tech diving to be had in Asia!

Watch this space people, big things are coming...

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