Technical divers progress to decompression diving techniques.

Koh Tao, Thailand
Big Blue Tech celebrates the graduation of Magnus Baer from the TDI Decompression Procedures course conducted over 3 days and 4 dives. This course continues from the TDI Advanced Nitrox course and trains the diver on the skills, procedures and methods for mixed gas decompression using enriched air nitrox to accelerate the natural process of decompression.

As sport divers planned decompression is not something that we do or have been taught. The TDI Decompression Procedures course prepares you for planned staged decompression diving. With a maximum operating depth of 45m/150 feet, this course is your first step beyond the normal sport diving limits. Your TDI Instructor will provide you with valuable information and skills, among the topics covered are

• Kit set-up
• Equipment requirements
• Decompression techniques
• Decompression breathing gases
• Gas management
• Contingency planning

The TDI Decompressions Procedures course combined with the TDI Advanced Nitrox course form the foundation of all other technical courses.  After these two courses and some additional experience, the stage has been set for you to move onto additional technical levels. Some of the materials you will be using include the TDI Divers Guide to Decompression Procedures, US Navy or Buhlmann Air Decompression Tables (made of vinyl for easy in-water use and storage)

Over the 4 dives Magnus was exposed to different conditions including overhead, current, large swells, chimney formations which all concluded on a full day trip to Sail Rock, a local favourite dive site.

After a few days off Magnus will continue to his TDI Extended Range course which will take him to 55m.

Big Blue Tech - Technical Diving Thailand - Celebrates the graduation of Ash Dunn, Mark Slinn and Andy Cavell from their TDI Decompression Procedures Course conducted over the past few days off the coast of Thailand on and island called Koh Tao

The TDI Decompression Procedures course is best described by the TDI/SDI website as:

The TDI Decompression Procedures course prepares you for planned staged decompression diving. With a maximum operating depth of 45m/150 feet, this course is your first step beyond the normal sport diving limits.

This course began before the christmas break with some new skills to help train the students to a level appropriate for entering the next step. The students will start their next course, TDI Extended Range, on our Similans Islands Liveaboard in the new year.

The highlight of the course was the abundant marine life on every dive. With large 2 meter Bull and Gray Reef Sharks around us during all our dives the excitement of diving was forced back into every sense we had. The sharks at Chumphon Pinnacle Dive Site seem to disapear during some months and then come back in large numbers without warning. Sharks can be seen hunting and stalking prey but always keeping a safe distance from divers. This safety is kept in part from the prevention of shark feeding so no shark has associated food with a diver.

All of the students excelled at their skills and conduct in the water and received their certification after completing a written examination.

Below are some pictures from this event. The next open space for this course is in March 2010

Big Blue Tech completed a TDI Advanced Nitrox Course yesterday with the combined afternoon of skills which embodied both TDI Decompression Procedures and TDI Advanced Nitrox.

With the flexible curriculum offered by TDI it was possible for the training team to introduce interesting and valid skills which are appropriate for the diving ahead.

The students on the course were Mark Slinn, Andy Cavell and Ash Dunn who are all working towards a future as a technical diving instructor.

One of the signature skill introduced involves using a 3m marked line on the sea bed and having the divers wearing full technical diving gear start at the 1m mark and start fining, during fining the diver must remove one decompression cylinder without loosing control, upon reaching the end of the line the diver stops and begins backwards kicking, collecting his decompression cylinder while kicking backwards and returning to the start where the diver turns 180 degrees and moves away. The goal is to not use your hands and focus on perfect trim and balance while performing these skills.

Backwards finning can be quite difficult initially, to help this process we provide Jet Fins to our students as part of the equipment they will be using during the course to enhance the ease of learning. Here is a video to help illustrate the skill:

Additional to these skills was task loading with 8 cylinders removing and replacing each one while maintaining buoyancy. The training team felt the students really excelled and didn’t see them disturb the bottom, without being told to, during both 50 minute dives.

This would be the last dive until the after christmas as the students progress on to their Gas Blender and BSAC Instructor course.

Today Big Blue Tech celebrated the successful completion of a TDI Advanced Nitrox Course for Ash, Matt and Andy.

The students come from different backgrounds and environments. Matt is a oil and gas worker based in Kazakhstan but frequents Thailand; he completed his SDI Solo Diver course last month and has come back for more serious diving. Ash is a Divemaster Intern with Big Blue and will soon move up to join Big Blue Tech in December. Andy comes from Denmark where he is actively serving in the Danish Army as a Sergeant and this is his break before returning home for overseas deployment.

The TDI Advanced Nitrox course is based on familiarity with technical diving methods and equipment, buoyancy, oxygen handling, mixes of nitrox above 40% and extended depth to 40m. Some of the highlights of this course included some wreck diving at Japanese Gardens, some cavern diving at Green Rock and diving with Bull Sharks at Chumphon Pinnacle.

Some of the students will continue on to Decompression Procedures which teaches the methods behind decompression diving and more advanced skills while others would continue to gain experience or return home.

In addition, Christos was awarded the TDI Semi Closed Rebreather rating after completing all the skills and requirements for the rebreather and accompanied the course for more experience and training on the rebreather.

Today Big Blue Tech, a technical diving school based on Koh Tao in Thailand celebrates the graduation of Phil Elmer from his TDI Extended Range Course.

Phil arrived on Koh Tao almost a week previously and began with some technical diving fun dives as he was already certified as a TDI Decompression Procedures Diver. After a few trips Phil was ready to start his course. The TDI extended range course certifies the student to 55m and to use a variety of gas mixes and techniques for decompression diving. Phil started off in confined with a skill refresher and an introduction to how we do skills and then we were off deep diving the next day. The course took us to various locations, wrecks and conditions.

The final day was conducted by looking for new wrecks using gps and sonar from fishermen marks on our own boat. After a few sweeps and some dives we came up empty handed but it was great experience for Phil to see how wreck searches are conducted and it was a chance for Big Blue Tech to cross off an area of interest leaving only a few more search areas left.

As reported on the Big Blue Diving blog:
“Meanwhile in the deeply technical world of Deep Tech diving, ‘Canada’ (James Thornton-Allan) & his tattooed team of black hooded twin tank techie boys have been taking Navakid off for a jolly with a fish finder & a depth reader to see if they can find somewhere deep & dark to go diving. Ideally chancing upon a wreck would be a fine thing, but we’ll suffice with a ridge or a wall or a series of pinnacles. As long as its deep & its dark & its technical & it involves carrying around lots of tanks & a gimps hat it doesn’t really matter!”

Tonight the celebration will continue with a party at “Moov” which will be their last for the season.

Below are pictures from his course:

Technical diving (sometimes referred to as Tec diving) is a form of scuba diving that exceeds the scope of recreational diving (although the vast majority of technical divers dive for recreation and nothing else). Technical divers require advanced training, extensive experience, specialized equipment and often breathe breathing gases other than air or standard nitrox.

The concept and term ‘technical diving’ are both relatively recent advents,[note 1] although divers have been engaging in what is now commonly referred to as technical diving for decades. The term “technical diving” was first coined by Michael Menduno, editor of (now defunct) diving magazine AquaCorps in 1991.
Definition of ‘technical diving’

There is some level of professional disagreement as to what the term should encompass. It was not that many years ago that NITROX diving was considered “technical”; however today NITROX is not normally considered technical. Some say that technical diving is any type of SCUBA that is considered higher risk than conventional recreational diving. However, some advocate that this should include penetration diving (as opposed to open-water diving), whereas others contend that pentrating overhead environments should be regarded as a separate type of diving. Others seek to define technical diving solely by reference to the use of decompression. Certain minority views contend that certain non-specific higher risk factors should cause diving to be classed as technical diving. Even those who agree on the broad definitions of technical diving may disagree on the precise boundaries between technical and recreational diving.

PADI, the largest recreational diver training agency in North America, defines technical diving as “diving other than conventional commercial or recreational diving that takes divers beyond recreational diving limits. It is further defined as an activity that includes one or more of the following: diving beyond 40 meters/130 feet, required stage decompression, diving in an overhead environment beyond 130 linear feet from the surface, accelerated stage decompression and/or the use of multiple gas mixtures in a single dive.”

NOAA defines technical diving in this way: “Technical diving is a term used to describe all diving methods that exceed the limits imposed on depth and/or immersion time for recreational scuba diving. Technical diving often involves the use of special gas mixtures (other than compressed air) for breathing. The type of gas mixture used is determined either by the maximum depth planned for the dive, or by the length of time that the diver intends to spend underwater. While the recommended maximum depth for conventional scuba diving is 130 ft, technical divers may work in the range of 170 ft to 350 ft, sometimes even deeper. Technical diving almost always requires one or more mandatory decompression “stops” upon ascent, during which the diver may change breathing gas mixes at least once.” NOAA does not address issues relating to overhead environments in its definition.

The following table tries to set out the broad indicative parameters of what is normally regarded as technical rather than recreational diving.

Technical dives may be defined as being either dives to depths deeper than 130 feet / 40 meters or dives in an overhead environment with no direct access to the surface or natural light. Such environments may include fresh and saltwater caves and the interior of shipwrecks. In many cases, technical dives also include planned decompression carried out over a number of stages during a controlled ascent to the surface at the end of the dive.

The depth-based definition is derived from the fact that breathing regular air while experiencing pressures causes a progressively increasing amount of impairment due to nitrogen narcosis that normally becomes serious at depths of 100 feet / 30 metres or greater. Increasing pressure at depth also increases the risk of oxygen toxicity based on the partial pressure of oxygen in the breathing mixture. For this reason technical diving often includes the use of breathing mixtures other than air.

These factors increase the level of risk and training required for technical diving far beyond that required for recreational diving. This is a fairly conservative definition of technical diving.

Inability to ascend directly

Technical dives may alternatively be defined as dives where the diver cannot safely ascend directly to the surface either due to a mandatory decompression stop or a physical ceiling. This form of diving implies a much larger reliance on redundant equipment and training since the diver must stay underwater until it is safe to ascend or the diver has left the overhead environment.

Decompression stops

A diver at the end of a long or deep dive may need to do decompression stops to avoid decompression sickness, also known as the “bends”. Metabolically inert gases in the diver’s breathing gas, such as nitrogen and helium, are absorbed into body tissues when breathed under high pressure during the deep phase of the dive. These dissolved gases must slowly be released from body tissues by pausing or “doing stops” at various depths during the ascent to the surface. In recent years most technical divers have greatly increased the depth of the first stops, so as to reduce the risk of bubble formation before the [more traditional] long shallow stops. Most technical divers breathe enriched oxygen breathing gas mixtures such as nitrox during the beginning and ending portion of the dive. To avoid nitrogen narcosis while at maximum depth it is common to use trimix which adds a percentage of helium replacing nitrogen to the diver’s breathing mixture. Pure oxygen is then used during shallow decompression stops to reduce the time needed by the diver to effectively rid themselves most of remaining excess inert gas in their body tissues and reducing the risk of “the bends.” Surface intervals are usually required to prevent the residual nitrogen from building up to dangerous levels on subsequent dives.

Physical ceiling

These types of overhead diving can prevent the diver surfacing directly:

* Cave diving - diving into a cave system.
* Deep diving - diving into greater depths.
* Ice diving - diving under ice.
* Wreck diving - diving inside a shipwreck.

Extremely Limited Visibility

Technical dives in waters where the diver’s vision is severely impeded by low-light conditions, caused by silt or depth, require an elevated level of aptitude because of the knowledge and skill required to operate in such an environment, and because visibility impairments are often caused by moving water currents. The combination of low visibility and swift current make these technical dives extremely risky to all but the most skilled and well-equipped divers.[citation needed]

Gas mixes

Technical dives may also be defined by the use of hypoxic breathing gas mixtures other than air such as trimix, heliox, and heliair. This definition is derived from the fact that breathing a mixture with the same oxygen concentration as is found in air (roughly 21%) at depths greater than 180 feet / 55 meters results in a very rapidly increasing risk of severe symptoms of oxygen toxicity. The first sign of oxygen toxicity is usually a convulsion without warning. This convulsion usually results in a fatal accident, as the regulator falls out and the victim drowns. Sometimes the victim may get warning symptoms prior to the convulsion. These can include visual and auditory hallucinations, nausea, twitching (especially in the face and hands), irritibility and mood swings and dizziness. Increasing pressure due to depth also causes nitrogen to become narcotic, resulting in a reduced ability to react or think clearly (see Nitrogen narcosis). By adding helium to the breathing mix, divers can reduce these effects, as helium does not have the same narcotic properties at depth. These gas mixes can also lower the level of oxygen in the mix to reduce the danger of oxygen toxicity. Once the oxygen is reduced below 18% the mix is known as a hypoxic mix as it doesn’t contain enough oxygen to be used safely at the surface.

Nitrox is another common gas mix, and while it is not used for deep diving, it decreases the build up of nitrogen within the diver’s body by increasing the percentage of oxygen. This reduces the nitrogen percentage, as well as allowing for a greater number of multiple dives vs “standard” air. The depth limit of Nitrox is governed by the percentage of oxygen used, as there are multiple oxygen percentages available in nitrox. Further training and knowledge is required in order to safely use and understand the effects of these gases on the body in a diving situation.

“Deep air”/extended range diving

One of more divisive subjects in technical diving relates to using compressed air as a breathing gas on dives below 130 feet/40 meters. Whilst the largest technical diver training agencies still promote and teach such courses (TDI, IANTD and DSAT/PADI), there is an increasingly vocal minority (NAUI Tec, GUE, UTD) which argues that diving deeper on air is unacceptably risky, and argue that helium mixes should be used for dives beyond a certain limit (100 - 130 feet, depending upon agency). Such courses used to be referred to as “deep air” courses, but are now commonly called “extended range” courses.

Deep air proponents base the proper depth limit of air diving upon the risk of oxygen toxicity. Accordingly, they view the limit as being the depth at which partial pressure of oxygen reaches 1.4 ATA (which occurs at about 186 feet/50 metres). Helitrox/triox proponents argue that the defining risk should be nitrogen narcosis, and suggest that when the partial pressure of nitrogen reaches approximately 4.0 ATA (which occurs at about 125 feet/38 meters) helium is necessary to offset the effects of the narcosis.

DAN does not formally reject deep air diving per se, but it is keen to point out a number of additional risks which such diving involves.

Equipment

Technical divers may also use various forms of less common diving equipment to accomplish their goals. Typically technical dives involve significantly longer durations than average recreational scuba dives. As decompression stops act as a virtual overhead, preventing a diver with a problem from surfacing immediately, there is a need for redundant equipment. Technical divers usually carry at least two tanks, each with its own regulator. In the event of a failure, the second tank and regulator acts as a back-up system. Technical divers therefore increase their supply of available breathing gas by either connecting multiple high capacity diving cylinders and/or by using a rebreather. The technical diver may also carry additional cylinders, known as stage bottles, to ensure adequate breathing gas supply for decompression with a reserve for bail-out in case of failure of their primary breathing gas. The stage cylinders are normally carried using an adaptation of a sidemount configuration.

Training

Technical diving requires specialised equipment and training. There are many technical training organisations: see the Technical Diving section of List of diver training organizations. Technical Diving International (TDI), Global Underwater Explorers (GUE), International Association of Nitrox and Technical Divers (IANTD) and National Association of Underwater Instructors (NAUI) seem to be popular as of 2009. Recent entries into the market include Unified Team Diving (UTD), and Diving Science and Technology (DSAT), the technical arm of Professional Association of Diving Instructors (PADI). The Scuba Schools International (SSI) Technical Diving Program (TechXR - Technical eXtended Range) was launched in 2005.

British Sub-Aqua Club (BSAC) training has always had a technical element to its higher qualifications, however it has recently begun to introduce more technical level Skill Development Courses into all its training schemes, by introducing technical awareness into its lowest level qualification of Ocean Diver, for example, nitrox will become mandatory. It has also recently introduced trimix qualifications and continues to develop closed circuit training.

Today Big Blue Tech completed a TDI Advanced Nitrox Course for Martijn and Emily which took 2 days with 4 dives.

This course is designed to train divers how to use the basic technical diving equipment, dive to 40m and handle advanced mixes of nitrox up to pure oxygen.

This course is a non-decompression diving course giving the students the option of diving on nitrox, in twin tanks at depth.

The dives began with simple buoyancy, beginner skills and air consumption moving slowly to more advanced and complex skills challenging the divers and creating confident and comfortable tekkies.

Although moments of being attacked by fish, Emily getting caught waving at bat fish and Martijn forgetting his computer it was all relatively smooth.

This course was assisted by Christos Kardana and Andy Holdaway who are working to progress their professional skills for their upcoming examinations for further technical instructor ratings.

Our facilities manager and resident technical dive-master Christos Kardana recently conducted a technical refresher for a big blue tech client, covering key skills essential whilst technical diving. Conducted in a similar fashion to that of refresher common in the recreational diving industry, a variety of skills where demonstrated and completed.

The confidence to complete essential safety skills is paramount whilst diving in general, but even more so in the world of technical diving where you take on challenging dive environments and profiles. The sheer bulk and number of equipment necessary, combined with the effects of narcosis at depth and the ceilings imposed by decompression diving, emphasises the importance of executing these skills with efficiency and confidence. This is further exacerbated by the usual task loading of ‘mission diving’ common in the technical world of diving, whether it is search and recovery or simply adding a video camera and the pressure of capturing certain footage whilst at depth.

A standard technical refresher here at Big Blue Tech is conducted in a confined water environment – ocean or swimming pool- entailing equipment assembly, pre-dive and in water checks, followed by S-drills and key skills. Equipment assembly involves complete set-up of a technical twin set rig, as well as deco tank set-up and gas analysis, demonstrating correct use of an oxygen analyser and tank management and labelling. A short briefing is conducted covering the skill breakdown and dive signals followed by kit up and correct front stride entry into the water -right hand palm securing mask and primary regulator, with left forearm bracing left and right deco tanks. Buoyancy and bubble checks are completed followed by key technical dive skills:

S-drill: acting as receiver and donor for out of air drill, in a controlled manner while maintaining position in the water column.

Gas shutdown: completing full gas shutdown of all posts managing multiple failures, showing awareness in switching from primary to alternate air source and vice versa accordingly. Reaction to catastrophic gas loss and securing failure should be ideally achieved in less than 30 seconds.

Regulator recovery: retrieving long hose primary air source, with and without the use of alternate air source (necklace).

Staging cylinders: while maintaining buoyancy, deco cylinders are staged and received achieving competence both on the ‘fly’ and statically in the water column.

BCD removal: removing and re-donning BCD, demonstrating awareness in hose management and deco cylinder staging.

Tired diver tow: acting as donor and receiver of air source (long hose) towing a tired or unconscious diver at depth ensuring victim regulator is secure with one hand and controlling victims movement via securing manifold with other hand.

Simulated gas switch: switching to deco cylinder gas, noting depth, mix and teammate awareness while changing blend, both face-to-face and individually on the fly.

The above drills are an essential combination of skills required whilst tech diving whether in a team or solo. Through repetitive circuits during the refresher we aim to achieve correct execution whilst maintaining a high level of awareness for teammate and the environment. Additional drills can be added, depending on the divers comfort and experience such as breathing from deco cylinders staged at multiple locations at shallow depth, improving muscle memory and confidence in relation to quick gas switching.

A technical refresher in a confined environment can be of vital importance to an individual re-entering the world of technical diving, whether it be for a few fun dives or one considering further education. Furthermore, for one who will be diving and using equipment through a dive centre, it provides the perfect opportunity to test and become accustomed to a new set of kit and procedures -regardless of past experience or amount of time spent out of the water- before re-immersing yourself in the world of decompression and extended range diving.

Big Blue Tech is currently working on short skill circuit videos, which will be posted in the near future.

Big Blue Tech will be in Khao Sok National Park from May 17th to May 23rd conducting Cavern Diver Specialty courses, Cave Diving Programs and technical decompression diving in search of the sunken village.

During this time no one will be in the office to write the news. So here’s a video from our last trip by Claire Oei.

Recently the weather has changed, causing a mas exodus from the island on to dve boats to quickly get down before the next storm comes along.

With this perfect window of opportunity 2 of the technical team James and Oskar took advantage with some accelerated decompression diving at Chumphon Pinnacle.

The goal of this dive was to get down to around 50m and look for dropped treasure from uncoordinated recreational divers. Unfortunately all we found was a bout 20 weights and weight belts and a diving mask from “NANS”. This was not all that unique as people always find “NANS” masks. However it was good to get out and do some proper diving for change.

How best to shed that unwanted nitrogen we accumulate while we’re under pressure is a question we face on every single dive. But mastery of buoyancy control, some knowledge of different gas mixes and the right computer can dispel the uncertainty, says John Bantin

The human body has a great capacity to take change in its stride, provided you give it time to do so. We have all been taught that coming up from one depth to a lesser depth when there is a great pressure difference can cause decompression sickness (DCS), so we take it easy. Give our bodies time, and we can accommodate the change without ill-effect. The human body is a wonderful thing. In 30 years of diving, including 14 as a professional with thousands of dives with almost as many different divers under my belt, I have never knowingly seen anyone suffering from DCS. This must say something for both diver training worldwide and the assumptions of the physiologists who calculate our decompression tables and diving computer algorithms. Every dive is a decompression dive. On every dive you put your body under hydrostatic pressure and then take the pressure off again. Even if you are doing a dive that requires no formal deco stop, the speed at which you come up is part of your decompression schedule. I am not a physiologist but I do know that my body is extremely complicated. It’s certainly more complicated than that bottle of soda-water so often used to demonstrate the ill-effects of DCS in basic diving theory. However, I have come to trust my diving computer (and I have used a lot of different ones in my time) because it seems to work.

Pressure effects
I know that my body will absorb inert gas. I know, as I sit here and write these words, that it is saturated with nitrogen from the air at 1 bar of atmospheric pressure. I know that if I go up the Matterhorn I should take things easy until my body has produced extra red blood cells to cope with the reduced oxygen levels in the air and I have adjusted to the reduced pressure.I know that I can subject myself to the much greater pressures found under water, provided I give myself time and take the pressure off carefully afterwards. Under water, it is the inert-gas element of the air that I breathe that gets soaked up, rather than the oxygen that I can absorb or metabolise.

Keeping control
So what is the secret of this controlled ascent? Buoyancy control! A diver should be able to make himself neutrally buoyant at any time. In other words, he never sinks or floats upwards unless he wants to. This is done firstly by wearing the correct amount of weight applicable to the rest of his diving equipment, especially his suit; and secondly, by judicious use of the direct-feed control and dump-valves of either BC or drysuit. You can ascend using only the ascent-rate indicator on your computer, but an easier and more satisfying way is to give yourself some visual datum. If you are diving on a coral reef that comes up close to, or breaks, the surface, it’s easy. Just slowly follow the reef up and enjoy what you may see on the way. Remember to stay away from the reef once you reach the shallows, however, or you may get pushed over onto the top by the breaking waves. This will make picking you up by boat a little awkward, or even dangerous for you. If there is no natural datum, use the boat’s anchorline or a shotline that has been put in to mark the dive site.You should have planned your method of ascent before you went near the water, so if none of these options is available you may have to use your delayed surface-marker buoy. This open-ended bag, often sausage-shaped, can be filled with air at depth and sent to the surface, attached by a line deployed from a winder-reel or a shorter length of narrow webbing with a small weight on one end. Naturally you should not deploy it from a depth greater than the length of line or webbing available. Webbing is nicer to hold on to but can be carried only in short lengths. If you are diving in an area subject to currents, you can deploy your buoy from depth with a reel and this will clearly mark your position to your boat or surface cover from the moment you start your ascent. Seventeen years ago the British Sub-Aqua Club introduced its 88 Decompression Tables, with a mandatory stop at 6m. Many British divers complained at the time that it was impossible to stop at that depth, thus revealing a history of poor buoyancy control. When it was suggested that it was a good idea to be slightly heavy and hang on a buoy line, one group of divers from my local club were heard to say that it would not be effective because you would be going up and down with the waves! Always remember, depth is the vertical distance measured from the surface. Whatever system you use as a datum, it is nearly always best to be neutrally buoyant. Only very experienced divers have the control and discipline to come up carefully in bluewater conditions.

Nitrox and MOD
Give your body time to adjust. It’s clear that if you can reduce the amount of inert gas (the nitrogen) you breathe, you will absorb less in the first place. This is where nitrox mixes come in. By breathing less nitrogen, you subject your body to less stress. The convenient way to do this is to substitute more oxygen for nitrogen in the mix we call “air” (21% oxygen, 79% nitrogen). After all, oxygen is readily available. Nitrox is air enriched with extra O2. The only problem is that oxygen can be a hazardous gas when breathed under pressure, so as we increase the proportion of oxygen in the mix we reduce the pressure and therefore the depth at which it is safe to breathe it. This gives us the “maximum operating depth” of the mix. Some older divers like me can remember going to great depths breathing nothing other than air, but currently air is thought to have an MOD of 56m. Training agencies, ever with a mind to litigation, now usually opt for a 40m limit or even shallower, depending on a diver’s certification level. We should not lose sight of the fact that the human body has been designed or evolved primarily to breathe air with 21% O2 (nitrox 21) at sea-level. We can also damage ourselves by exposing ourselves to high levels of oxygen and higher-than-normal pressures for too long. All this is covered in the basic nitrox course. No-one should use nitrox unless they have been trained to do so. As the diver who has been breathing air at depth ascends, the pressure on him is reduced and the nitrogen absorbed by his body is passed from his tissues back into his bloodstream. It then turns back to gas in his lungs and is exhaled. He must allow sufficient time for this to happen or it will come out of solution within his tissues, causing damage. As he approaches the surface, the pressure changes get more acute. The pressure at 40m is 5 bar and the pressure at 30m is 4 bar, a ratio of 5:4 over 10m of ascent. The pressure at 10m is 2 bar but the pressure at only 5m above is still 1.5 bar, a ratio of 4:3 over only 5m. So you should be even more careful as you get nearer to the surface. Most contemporary computers now have a safety stop designed-in, and this will be displayed in the 5m to 3m zone. It’s a way for computer manufacturers to add some safety and deters users from making an impatient dash to the surface. Even though you’re off-gassing, you still have to breathe. And every inhalation during the ascent carries with it more nitrogen for you to absorb while trying to off-gas that which you have already absorbed. It’s a complex process. So what if you could find some way of reducing the amount of nitrogen going in during this stage of the dive? That would speed up the process of getting it out from your body.

Deco gas
This is where some divers will use a richer nitrox mix as a “decompression gas”. By switching to a rich nitrox mix (one with a greater percentage of oxygen and therefore less inert gas, one that would have been dangerous to use at depth)in the shallows, the pressure gradient at the lungs between the nitrogen in the body and that of the gas being inhaled is increased. This means that the offending nitrogen already absorbed is off-gassed far more quickly. Of course, the diver must have the discipline to use this gas only when he is sufficiently shallow to do so safely. Switching to the wrong gas at depth could be fatal. In fact, if a diver is prepared to carry the required number of tanks during a dive, he could break his ascent up into three parts, He could breathe air at a maximum depth of say 50m, swap to nitrox 32 at 30m, and then swap again to nitrox 50 at 18m. This would give him a lot more time at depth, combined with more manageable deco-stop times than he could otherwise safely take, and give his body time to adjust to the changes.

Trimix
Many of the recently qualified technical divers reading this will howl with derision at the idea of breathing air at 50m. They think everyone should use trimix. This is a breathing gas where both the percentage of nitrogen and oxygen have been reduced by the inclusion of a third inert gas, helium.Helium reduces the effects of that other problem many divers encounter, nitrogen narcosis, but it adds to decompression times because it is more readily absorbed by the body. If you live in an industrialised country where helium is available and you can afford it, that’s all very well. But trimix diving is a whole new ball game. Some professional divers will complain that you should not be breathing any nitrogen in the mix, that you should breathe a mix of oxygen and helium only, but then things get even more complicated, and much more expensive. Alas, if you look at a globe of our world you will notice two things. The first is that a great deal of it is blue, and the second that most of the best diving areas within the blue line lie a long way from the shores of industrialised countries. This is where most of the best diving is. Unless you think this sort of diving should be limited to an elite few who can afford to mount expensive expeditions to these places, taking all their helium with them, you are left with the option of breathing oxygen and nitrogen in the proportions best-suited to the job.These gases are available in our natural atmosphere and pure oxygen can be relatively easily generated.

Computers
Air as the bottom gas may not be ideal, but it is readily available. If we break up our dive into three sections, we can speed up our decompression, have more time available at depth, and spend less time hanging about on the way up. But how can we calculate the decompression times for this?
Enter the physiologist with his algorithm and the electronics expert with his computer. What we need is a nitrox-compatible computer that can be adjusted during the dive to calculate the exact decompression requirement needed for a particular nitrox mix at a given time.
When you change regulators, you change the pre-selected computer setting to match. Examples of computers capable of doing this are the DiveRite Nitek3 and Nitek Duo, the Apeks Quantum and Pulse, Delta P VR2, Cochran Commander and the Suunto Vytec and D9.
Examples of computers that can manage trimix dives are the Delta P VR3 and Dive Rite Nitek He.

Yesterday’s Sail Rock trip was a great success for Big Blue Tech. On top of the technical diving training we provided 14 nitrox tanks to customers from our new nitrox panel.

The day started at 6:30 with loading of gear, customers, food, drinks, nitrox and staff. After both long tails trugged out to one of our boats - Navakid - we began the almost 2 hour journey to Sail Rock. Normally this journey can be quite long and boring, however for us it was broken up with breakfast. Scrambled eggs, toast and jam served to the 30 divers.

Sail rock is a unique dive site and perfect for technical extended range diving because the dive site is extended above the surface and shaped like a cylinder. There’s unique marine life at 2m and 40m. Sail rock is mostly used for dive schools from closer islands like Pangan and Samui, only few schools from Koh Tao venture that far out.

For us, we had quite a long dive planned. This was training dive 6 for Hannah where she completed a simulated extended range dive, switching gas and moving shallower to extend her no decompression limit. The conditions were stunning, large schools of every fish throughout the dive site. From our max depth of 30m we could see clearly right down to 40-45m which was very tempting but not for today. With all skills completed and a great long dive we surfaced, filled gas, socialized with others on the boat and prepared for the real extended range dive.

For real extended range dive you must get on to your richer mix in time or you will go in to decompression diving. Albeit not a concern for us but it defeats the purpose of this dive. Here Hannah was able to switch in time and also practice her tolerance for long decompression hands on the simulated 30 minute decompression stop. One of the hardest things to instill in people is the idea that you can’t just go to the surface whenever you want.

Upon surfacing Hannah had completed dives 6 and 7 and was technically eligible to be certified as a Dsat Tec Apprentice. However she’s not stopping there, she’s moving on to Accelerated Decompression in the next few days and then on to the Trident Livaboard on the 23rd so there’s still much more training to be completed.

Our final dive site of the day was South West Pinnacle, cleverly named after the direction from Koh Tao. To all our amazement there was no thermocline to be found. The water was so clear you could see the light refraction from the surface dancing along the sand at 30m, normally you only see this effect in shallow water like a pool or a bay. This was just a fun dive. We used the rest of the nitrox to do a computer extended range dive without any skills to just give Hannah more time in technical gear and because it was better then sitting on the boat. The next training dives are accelerated decompression which require oxygen and they are more risky so we won’t be doing that until a wreck Wednesday dive.

Today unfortunately we’ll be in the hot sweaty compressor room filling the tanks from yesterday and prepping for the DSAT Gas Blender Course tomorrow as Hannah takes some time off to study for her next exam.