Thailand – Australia – United Kingdom

Archive for December, 2010

Merry Christmas

For us divers Christmas usually signifies the storage of diving equipment, the rush to buy new and exciting diving toys for summer or traveling to tropical destinations on your diving holiday. Christmas is also a chance to catch up with old friends and distant relatives to celebrate the season of giving and benevolence to each other.

This Christmas Big Blue Tech celebrates with a family dinner on Koh Tao Island bringing together friends and colleagues to create our own little tropical family this season. The Koh Tao community is particularly festive with the strong western culture decorating the island in fake snow, Christmas trees and bright lights.

In Big Blue Khao Lak a few select and lucky individuals will be enjoying Christmas dinner on-board our luxury liveaboard the Mv Pawara in the Similan Islands

With all the new toys and gadgets coming out in the diving trade shows and exhibitions it’s important to remember that experience and training is what counts. Get off the sofa and go diving whenever you can where ever you can. Practice makes perfect!

And after all those extra Christmas pounds have been piled on you can visit Impact Fitness in Mae Haad, Koh Tao to get back into shape.

From all of us at Big Blue Diving, Dive safe and Merry Christmas


Nitrox and Technical Diver Training

Sport divers discover new diving opportunities with a nitrox and intro to tech diver course.

Koh Tao, Thailand

Big Blue Tech celebrates the successful completion of a TDI Nitrox Diver and TDI Intro to Tech Diver course for  Sergey Baranov, Marina Sergacheva and Ivan Shomnikov by TDI Technical Instructor Ash Dunn and assisted by Divemaster Ian Jordan. This course was conducted over 4 days at Big Blue Tech on Koh Tao Island off the coast of Thailand in the Gulf.

The TDI Nitrox course is unique amongst other courses with the emphasis placed on knowing and understanding the theoretical formulas and physics behind mixed oxygen gas diving. As Nitrox diving is becoming easier and easier to get into, the TDI Nitrox diver course creates the foundation for technical diving insuring that the in water skills and complex dive planning is completed at a high level of proficiency. One skill we particularly like is testing the students underwater to see if they will follow their instructor beyond a determined maximum operating depth. The maximum operating depth in nitrox is the tolerable oxygen level for any given depth and divers exceeding this depth is a leading cause of accidents relating to enriched air nitrox.

The divers, who are from Russia but live in New Zealand enjoyed the training and the dive so much the enrolled in a TDI Intro to Tech course.

Technical diving has been seen in a mysterious light for many years, with participants being secretive about their actions and often showing unhealthy affection for their gear, of which there is always a lot.

To get into technical diving, previously you needed to know what you wanted to do and you had to make a huge decision right from the beginning. The step from sport diver to tech diver was a huge one, with a huge cost and learning curve to climb. Some of us were lucky and could ask for guidance from friends and club mates, some were less lucky and were given far from balanced advice.

TDI, the worlds leading Technical Diving Training agency has recently announced a new course in their range; the Intro to Tech course. We cover details such as equipment configuration for twins, how twins work, in water buoyancy skills plus more advanced dive planning considerations such as gas management as well as using tables and computers to efficiently plan a dive.

The course is an ideal way to determine whether you wish to extend your diving beyond Sport diving, or simply to improve your skills.

This course was conducted over 4 days and combined to give the divers a long dive on twinsets filled with enriched air nitrox. Their final dive was in excess of 80 minutes around some of the less frequented dives sites on Koh Tao.

Sidemount.. It’s not just for Cave Divers Anymore

For a generation, sidemount diving has been a staple for serious cave divers.But these days, more and more cavers, and even non-cavers, are wearing their bottles at their sides.

By Steve Lewis

There are probably a handful of things happening in the dive industry that we could peg as the latest and greatest idea or innovation. I’d add developments in lighting technology, dive computers, and thermal protection to my list, but surely the hottest trend right now has to be sidemount diving (wearing a totally independent cylinder and regulator system slung on each side of the diver’s body). Any technical diver old enough to remember Friends as a new television series may also remember when sidemount was a very specialized technique with a small and almost cliquish fellowship restricted to England’s Mendip Hills and North Florida’s Karst Country. Finding sidemount training and uncovering a mentor to help you progress in the technique was a lot like joining a medieval secret guild; you had to know someone, or have a solid recommendation from an existing initiate; and those outside the circle suspected witchcraft.

In the early days, gear was centered on mostly hand-sewn adaptations of the classic open water stab-jacket style BCD, a few welded bolt-snaps, and lots of bungee cord. And the application was ALL about exploring small silt passages; what a good friend of mine describes as “a mighty tight squeeze.” But that was then and this is now. Times and attitudes have changed. After all, back when NBC first aired Friends, the largest sport diving agency had branded TDI’s popular nitrox courses as too complex for the average diver and decompression diving was totally verboten. Now of course, nitrox is the usual choice for most divers regardless of which flavor C-Card they earned as an open-water diver, and most weekend charter rosters include at very least a couple of divers planning staged deco; and often a full boatload of weekend warriors all planning for a deep, long dive. These days, it seems that sidemount really has come out of the closet. To begin with, gone are the hand-wrought BCs. Mainstream manufacturers such as Armadillo, Dive Rite, Hollis, OMS and Oxycheq are producing beautifully crafted harness, butt-plate, wing combination’s specifically for sidemount diving. Cam bands – used to convert regular tanks to sidemount tanks in an instant – are in several manufacturer’s catalogs. And plenty of stores sell “regulator conversion kits” – essential an assortment of custom-sized hoses and 90 degree fittings designed to help make the transition from traditional backmounted doubles to sidemount a one-step process. Perhaps best of all, sidemount instruction is readily available and several agencies, SDI and TDI among them, offer specialty ratings and sidemount options for their existing curriculum from Intro-to-Tech to Advanced Trimix, in addition to the more traditional cavern and cave.

The real kicker perhaps is that sidemount divers are beginning to pop up on dive boats and at open-water sites. On a brilliant Saturday morning at a popular quarry in Ohio this past summer, there were a handful of “tech divers” wearing sidemount kit. On local charter boats too, sidemount divers are starting to make a showing, especially among divers who are trained to execute wreck penetration. It’s not just for cave divers anymore. Lamar Hires, head of Dive Rite and one of the early promoters of sidemount diving, files the reasons for using sidemount into two main categories – Lifestyle and Mission Specific. Let’s use Lamar’s definitions as a starting point to explore the overall features and benefits of SM diving.

The ubiquitous North Florida Cave Diver’s Rig consisting of a backplate, simple harness, wing and manifolded doubles, began to establish itself as the gold standard for technical divers sometime in the early 1990s. By the time TDI opened its doors in 1994, this kit configuration, with long hose on the right post, backup regulator and SPG on the left, and a generally minimalist approach to gear selection was what technical divers wore almost universally. But its one-size-fits-all approach and promotion as the universal solution to all dive applications, has lost some of its lustre over the years and technical divers have looked at other options with an open mind. With a sidemount configuration, the tanks are carried independently of each other and can be attached to the diver in the water or near to the water. This makes pre- and post dive prep easier on the diver’s back and knees, since the strain of one tank is about half of the strain of two. A good buddy of mine swears that diving sidemount has helped her enjoy dive trips more and use aspirin less! “There’s no way to describe how good it feels to take all my tanks off in the water, attach them to an equipment line and then walk up that boat ladder wearing nothing heavier than my harness and drysuit,” she says.

Also, the sidemount diver’s gas supply is fully redundant and carried in completely separate systems each with a first and second stage plus an spg (and usually a LP hose). This offers similar gas management options as a set of doubles (some argue more options than doubles) but the valves and first stages are within full sight at the diver’s side rather than behind her back. This obviously makes options during either simulated or real situation shutdowns very simple! There is never any guessing which first stage is giving the diver grief… real or otherwise. This alone has many SM divers arguing that theirs is the safer option in the case of a free-flowing second stage, runaway wing inflator, runaway drysuit inflator or other gas leak. Which is a stance I agree with. The final “lifestyle” benefit revolves around the easy of travel and sidemount diving. Number one: A SM harness has no heavy backplate and therefore helps keep luggage within airline baggage allowance. Number two: renting “bottles” at one’s destination is easy since standard scuba cylinders can be got ready for service as sidemount primary tanks quickly and with a minimum of fuss and very little extra gear. The addition of a couple of cam straps to the traveler’s luggage, makes conversion of almost any sized scuba cylinder the work of a few minutes; in fact standard stage bottle kits can be made to work in a pinch

Going back to the genesis of sidemount diving, we arrive at the original reason to move one’s primary cylinders from one’s back to one’s side; low ceilings and flat bedding planes. While this reality has informed the decision making of cave divers for more than a generation, more and more wreck divers feel that sidemount offers real advantages inside a wreck. The interior of most wrecks, even those intentionally sunk and cleaned out ahead of time, present special challenges because of the likelihood of entanglement with overhead cables and other debris. The possibilities of “unfriendly interaction” with all this mess are pretty high, and a staple of the traditional Advanced Wreck class is a session learning the best techniques to free oneself or a buddy from the clutches of a couple of metres of electrical wire and rotting wood caught in the traditional manifolded doubles. Not to say that entanglement in this sort of situation is a non-issue in sidemount, but if we look at it logically, there simply is not the number of potential line-traps behind the diver’s head when he is wearing sidemount kit. I also find the inherent lateral stability against the effect of roll wearing a sidemount setup is a huge benefit when scootering; but perhaps that’s a story for another day.

All this said, it is important to remember that no single kit configuration is right for ALL applications. Sidemount is not the silver bullet and is certainly not the best option always and everywhere. However, a growing number of tech and sport divers are finding SM an interesting and enjoyable way to dive in many different environments. A good workshop is a great way to learn the technique and to find out the best ways to route hoses, hang lights, and configure deco bottles, but having a very flexible alternative to the traditional tech diver’s kit for many divers is worth the extra effort.

Steve Lewis is an active instructortrainer for TDI and a strong advocate for the application of sidemount configuration for ALL open circuit divers who venture into an overhead environment. In addition to running SM courses and clinics on a regular basis, Steve is currently working on a new book about technical diving called Twelve Dialogues with Doppler.

Originally published in the Underwater JournalDownload your free copy now.

How using helium can reduce narcosis

It is becoming increasingly popular for divers to use helium based mixtures, usually called trimix, for deeper dives. The main reason for this is to reduce narcosis.

Koh Tao, Thailand

Of all the physiological factors that affect us as technical divers narcosis is the most common but also the most widely misunderstood. Narcosis occurs as we dive deeper and becomes more severe the deeper we go. It has several side effects all of which serve to impair our ability to carry out basic tasks. Narcosis was most famously described in Jacques Cousteau’s book, The Silent World, where Cousteau describes the symptoms and named it the “Rapture of the Deep.

Many divers incorrectly consider narcosis to be a black and white issue, either they are suffering from narcosis or they are not. Furthermore many divers claim that they have never suffered from narcosis. This shows a misunderstanding of the properties of narcosis and a lack of understanding of the symptoms. Those divers who claim never to have experienced narcosis have just never noticed the effects.

There are many effects of narcosis. The two most widely known are the extreme feelings of either euphoria or panic. In many ways the diver who experiences these feelings of panic and doom is lucky in that this type of narcosis is acting as a failsafe and preventing them going deeper and experiencing more narcosis. The diver who experiences euphoria is potentially at more risk as they are more likely to take risks or act dangerously. However, these two symptoms are not the only effects of narcosis.

There is a wide range of other effects. These may not always be as obvious as a feeling of overwhelming panic. Their symptoms can be much more subtle and so are not always immediately obvious. Divers suffering from narcosis often show a lack of judgement. They don’t always make the best decisions or in some cases take an inordinate amount of time to make what should be a simple decision. I once watched a diver on a wreck penetration course take several minutes deciding which of two points to use to make a tie off. Until pointed out later they didn’t realise that they had taken this long to make the decision.

Narcosis appears to affect our memory. Divers who report no other symptoms of narcosis frequently show a lack of memory of certain parts of the dive. I spoke to a diver a few years ago who had just done the same dive as me. I was on trimix and they were on air. They confessed that despite a 20 minute bottom time they couldn’t remember any specific detail of the dive.

Tasks which are easy in shallow water for some reason tend to become more difficult at depth. Loss of dexterity or motor control is a frequent symptom of narcosis. On many occasions I have seen someone send up a DSMB from 10m in just a few seconds only to have exactly the same task take several minutes at depth.

Narcosis often causes perceptual narrowing or task fixation. Divers become obsessed with completing the task they have begun, even when other tasks have obviously become a much higher priority. Divers suffering from narcosis often respond slower than they would in shallower water. These extra seconds can make a vital difference at depth.

It is interesting that many of these additional symptoms of narcosis are not noticeable unless a problem or emergency occurs. If everything is going well then the fact that tasks take a little longer is no problem, especially as both parties are likely to forget many of the details of the dive anyway. However, narcosis become much more of an issue if a problem occurs. In this case the diver now has to assess the situation, make a judgement and act on it. All three of these are things that may be affected by their levels of narcosis. This means they are much less able to deal with a problem due to their level of narcosis.

We are lucky that the vast majority of dives do not involve an incident of any kind. During the dives that go well we can tolerate the level of narcosis that we experience. It is only when dives don’t go well that that level of narcosis becomes dangerous. Unfortunately I still haven’t been able to reliably identify in advance the dives when things will go well and those when an incident will occur. Until then I will remain wary of narcosis.

Helium is considerably less narcotic then nitrogen and so if we replace some of the nitrogen with helium we are reducing the overall narcotic effect of the combined gas. This reduction in narcosis introduces a number of advantages. A clearer head allows the diver to enjoy the dive and actually remember what they see down there. There is little point in exploring a wreck if you don’t remember the experience afterwards.

In addition the reduction in narcosis removes the lack of judgement, loss of coordination and inability to resolve problems. This can give the technical diver a huge safety advantage. As they go deeper, and the risks increase, they can help to reduce those risks by reducing their level of narcosis. With trimix relatively easily available these days there is really no reason for divers to risk diving deep on air and inducing symptoms of nitrogen narcosis.

When we add helium into our breathing mix we can get a different set of gases. Commercial divers sometimes use a mixture of helium and oxygen which is known as heliox. However, cost considerations mean that, outside of the commercial world, divers will usually use a combination of oxygen, nitrogen and helium, known as trimix. In the same way that the general name nitrox can be used to describe any mixture of nitrogen and oxygen, the term trimix is used to describe any combination of oxygen, nitrogen and helium. Specific types of mixes are also given names as the characteristics of each are very different.

A trimix which has between 18 and 21 per cent oxygen is referred to as normoxic trimix. The term normoxic refers to ‘normal’ levels of oxygen. In other words, a similar level of oxygen to normal air. The helium content in normoxic trimix is likely to be between 21-45 per cent. This type of trimix is used to reduce narcosis in the 45-60m depth but does not change the oxygen levels significantly and so is limited to 60m by oxygen toxicity considerations.

For deeper dives the amount of oxygen in the mixture needs to be reduced and for this a hypoxic mixture is used. Hypoxic means a reduced level of oxygen such that the mixture will not sustain consciousness at the surface. Oxygen levels below 18 per cent are usually considered hypoxic for diving. The helium levels in a hypoxic trimix will be much higher as it is being used to reduce the amount of oxygen as well as being used to reduce the amount of nitrogen and so helium levels between 40-60 per cent are common.

In recent years it has become increasingly popular to add helium to the breathing mix for dives between 30-45m. In this case it is possible to use a weak normoxic trimix but it is also possible to have a higher level of oxygen, just as if diving nitrox, but with the addition of some helium. This would be called hyperoxic trimix, due to the higher than normal levels of oxygen, but this name is not commonly used in order to avoid confusion with hypoxic trimix. Hyper means high levels and hypo means low levels. Any trimix with a higher level of oxygen than air was originally called helitrox when NAUI launched the first training course into its use and TDI has stuck with this name. Other training agencies have used the term triox or Recreational Trimix to refer to the same thing. Helitrox will typically contain between 10-30 per cent helium.

There are, however, some downsides to use helium. These mostly stem from the physiological aspects of helium. Helium is a very small molecule and is a very light gas. Amongst other things this means that it conducts heat much faster then air. As a result, a diver using a helium based gas will feel colder than a diver using air or nitrox. For small helium percentages this is not too noticeable but as the helium percentage increases this becomes more and more noticeable and so for helium mixes above 20 per cent it is recommended that a separate suit inflation cylinder is used specifically for filling your drysuit. This suit inflation cylinder is usually worn either mounted on the side of the twinset, attached to the backplate or on the waistband. A simple first stage provides an inflator hose for suit inflation. No second stage is attached but instead an over pressure relief valve is attached in case of a problem with the first stage.

The physical propertied of helium also make decompression more complicated. This doesn’t necessarily mean that trimix decompression is longer or shorter, better or worse than nitrox, just different. The reason for this is that with trimix we are dealing with two inert gasses rather than just one. There may be times when the body is taking in one inert gas while releasing the other. In addition, the small size of the helium molecule meant that is a fast gas, in other words it on-gasses faster than nitrogen but also off-gasses faster. All of this combines to make trimix decompression more complicated than air or nitrox decompression.

When it comes to dive planning using trimix there are a number of options. It is possible to buy trimix decompression tables but there are so many possible combinations of trimix together with combinations of deco gasses that it is not a very practical option. Until recently many divers have used PC planning programs such as V-Planner, Proplanner or Decoplanner to plan their dives. These tools allow the diver to calculate a decompression schedule together with gas requirements and oxygen toxicity levels. A range of plans can be generated which can be used to cover a number of alternative scenarios as well as providing backup plans in case the dive is deeper or longer than anticipated. Together with a bottom timer this is a very easy and cost efficient way of planning trimix dives.

Increasingly we are seeing a range of dive computers that can handle trimix as well as air or nitrox. The VR3 was the first successful commercial trimix computer and this has now been joined by computers from a range of other manufacturers. Some manufacturers focus on the extreme end of the technical diving market whilst other manufacturers have produced computers aimed at those divers using normoxic trimix or helitrox. Suunto’s HeloO2 has brought trimix computers to the mass market and has done much to popularise this type of diving. These computers can be programmed with the details of your mixture together with any decompression gasses and will work out your decompression based on the combination of helium nitrogen and decompression gasses.

The last disadvantage of using trimix is the cost. There is no doubt that a trimix fill is more expensive than nitrox but when compared against the cost of the boat fees, petrol to get to the dive site, accommodation and a few drinks in the pub it becomes less significant. Many divers will happily spend £30 in the pub but would not spend the same amount on trimix. If that £30 can help you remember the dive then it seems good value and if it can help you deal with a potentially dangerous situation then it becomes incredibly good value.

SSI Twinset Specialty Course Released in Thailand

Technical dive college released another technical distinctive specialty pushing the industry forward.

Koh Tao, Thailand

Big Blue Tech is proud to announce the recent approval of SSI (Scuba Schools International) to release in January the new SSI Twinset Specialty written by our own Technical Diving Instructor Helen Artal.

The SSI Twinset Specialty fills the gap in training for people who want to utilize technical diving equipment or a twinset but don’t want to commit to the cost or responsibilities for technical diver training.

Helen who is also part of the Divecon / Divemaster internship mentor program plans to integrate the twinset specialty with other popular programs like deep diver and nitrox diver giving the students essentially more breathable gas during the deeper more enjoyable parts of the course. This comes in a line of other related courses like the TDI Intro to Tech course, Padi Tec Basics Specialty and GUE Twinset Diver course.

This course has been in a long list of many popular courses written by Big Blue Tech including the TDI Compressor Operator, SDI Sidemount Diver and now the SSI Twinset Diver Specialty.

Authoring courses can be a fun but long process of approvals and edits, however the end result is a course designed by people with experience to suite our environment and is exclusively available through Big Blue Tech.

For more information feel free to contact us for an outline or details. Good work Helen!

Scuba Equipment Service Technician Course

Manuela continues her technical diving internship to service and repair scuba diving regulators.

Koh Tao, Thailand

Big Blue Tech is happy to announce the graduation and certification of Manuela Agbaba from her SDI Equipment Service Technician and TDI O2 Service Technician Course focusing on underwater breathing regulators for scuba diving activities. This course was conducted by Ash Dunn and James Thornton-Allan on Koh Tao Island in Thailand.

All equipment used by divers underwater or in the provision of their breathing gases is fundamentally life support equipment. Scuba regulators and compressors work at extremely high pressures and use innovative engineering design techniques to function correctly.

The repair, adjustment and testing of this equipment is not intuitive even for the mechanically minded or those with formal engineering training in other disciplines. The service information, custom spare parts and special custom tools are usually difficult if not impossible to obtain outside the trade.

Only formal training in the repair and maintenance of div e equipment such as that received during these courses can ensure the continuing safe and reliable operation of life support equipment.

Although Manuela has no aspirations on becoming a scuba diving professional these skills would certainly enhance her employ-ability and skills in the scuba diving industry. Additionally Manuela is certified to conduct service and repair of her own regulator giving her access to spare kits back home and essentially saving her a great deal of money in the long run.

For those seeking specific training courses for regulators like ScubaPro, Apeks and Aqualung you can contact us to find out when these events are happening in Thailand.

Exploration diving trip discovers new caves in Koh Tao

Technical divers explored new regions of Koh Tao Island in search of dive sites.

Koh Tao, Thailand

Big Blue Tech headed out on the first day of sunshine after the monsoon on board our Mv Big Black Boat to search for new diving locations in areas that are not dived frequently or explored.

The dive gang included Ash Dunn, Dan Bolton and Manuela Agbaba along with members of the divemaster team who invited some nitrox diving customers for this unique opportunity.

The first dive revealed a region in the north that had a cavern / swimthrough which was new for these divers and enjoyed exploration into the cavern as certified cavern divers.

The second dive site was around the famous biorock where a structure with mild current is in place underwater to help spur the growth of coral and study it’s effect. Unfortunately visibility was reduced considerable since it’s located close to shore. However this crossed two dive locations off the list of searching areas.

If you would like to join our next exploration trip to discover some hidden gems on Koh Tao feel free to contact us.

Try Dive an APD Inspiration Closed Circuit Rebreather CCR

Are you an experienced leisure diver looking to try something new in the diving World? Have you been interested in diving on a Rebreather but not wanted to commit to a full course? Then a try dive on an APD Inspiration Closed Circuit Rebreather with Big Blue Tech in Koh Tao, Thailand could be the answer for you!

Koh Tao, Thailand

This experience with Big Blue Tech will introduce you to the basic theory of closed-circuit rebreather diving and the practical considerations of its use. You will also have a try dive on the closed circuit rebreather with our experienced technical Instructors.

Utilizing the APD Inspiration closed-circuit rebreather, our experienced TDI trained staff at Big Blue Tech in Koh Tao, Thailand can introduce you to the world of extended scuba diving freedom. Welcome to the World of diving with no bubbles!

Recently Big Blue Tech took 7 eager divers to experience the thrill of closed circuit diving in our deep swimming pool design specifically for diving activities.

The 3m pool was a perfect environment for trying the unit giving the divers a chance to try buoyancy differences and get their picture taken for a souvenir of their time.

A theory session was given to the students to understand how rebreathers work and also how to properly assemble and check the unit prior to diving. Rebreathers are complicated and expensive units but it only took the divers a few moments before they could control themselves underwater.

To enjoy a Closed Circuit Rebreather CCR Diver Try Dive with Big Blue Tech divers must be:-

  • 15 years or older
  • Open Water Diver or Advanced Open Water Diver or equivalent.
  • Enriched Air Diver or equivalent

The experience with Big Blue Tech in Koh Tao, Thailand includes:-

  • One theory tutorial on rebreather theory and preparation
  • One pool training dive and,

This is not a TDI certification course – it is an introduction to diving on rebreathers. If you enjoy it, then take the TDI Closed Circuit Rebreather course with Big Blue Tech in Koh Tao.

If you’d like to book your Closed Circuit Rebreather CCR Try dive with Big Blue Tech then please contact us at

You can view past events here and here

Technical diving gas blending technician course

Mixing elements of Nitrogen. Oxygen and Helium in gas form to create a safe breathable gas requires strict training.

Koh Tao, Thailand

Big Blue Tech celebrates the certification of Anton Chichvarkhin and Manu Agbaba from their BSAC and TDI Compressor Operator, Nitrox Blender and Advanced Gas Blender course conducted over a week on Koh Tao Island off the course of Thailand by BSAC and TDI technical instructor Ash Dunn.

Gas blending or gas mixing is the filling of diving cylinders with non-air breathing gases such as nitrox, trimix and heliox.

Filling cylinders with a mixture of gases has dangers for both the filler and the diver. During filling there is a risk of fire due to use of oxygen and a risk of explosion due to the use of high pressure gases. The composition of the mix must be safe for the depth and duration of the planned dive. If the concentration of oxygen is too lean the diver may lose consciousness due to hypoxia and if it is too rich the diver may suffer oxygen toxicity. The concentration of inert gases, such as nitrogen and helium, are planned and checked to avoid nitrogen narcosis and decompression sickness

here are several hazards with gas mixing:

  • cylinders are being filled with high pressure gas. If there is any damage or corrosion in the pressure vessel or valves of the cylinder, this is the occasion when they are most likely to fail structurally.
  • oxygen supports combustion; if it comes into contact with fuel and heat the three ingredients for a fire exist. Fires in the presence of high concentrations of oxygen burn more vigorously than those in air. A fire in the presence of high-pressure gas may cause cylinders to fail.
  • other high pressure equipment such as whips, compressors, gas banks and valves are being used, which can cause injury if the pressure is released
  • there are dangers of fire from the fuel and electric power supplies of the compressor
  • there are dangers of injury from the moving parts of the compressor
  • there is the possibility of asphyxiation due to the presence, in a confined space, of large volumes of gases that contain no oxygen

It is possible for gas blenders to create toxic and dangerous gas mixes for divers.[1][2] Too much or too little oxygen in the mix can be fatal for the diver. Oxygen analysers are used to measure the oxygen content of the mix. In good blending sites, the contents are analyzed in the presence of the diver who acknowledges the contents by signing a log.

It is possible that poisonous additives, such as carbon monoxide or hydrocarbon lubricants, will enter the cylinders from the diving air compressor.This is generally a problem with the compressor maintenance or location of the air input to the compressor though it can be from other sources

Poisonous additives can also get into the breathing mix if any material inside the blending valves or pipes burns, for instance when adiabatic heating occurs when decanting oxygen.

In the presence of large volumes of high-pressure oxygen, one corner of Fire Triangle exists in good measure. It is vital the other two corners are not allowed to exist.

Internally, the blending equipment and diving cylinders must be oxygen clean; all fuels and particles which could be sources of ignition must be removed.The materials chosen for use in the valves, joints and compressors must be oxygen compatible: they must not burn or degrade readily in high oxygen environments.

In gas blending, high temperatures are easily produced, by adiabatic heating, simply by decanting high-pressure gas into lower pressure pipes or cylinders.The pressure falls as the gas leaves the opened valve but then increases when the gas encounters obstructions such as a cylinder or a bend, constriction or particle in the pipe-work.

One simple way to reduce the heat of decanting is to open valves slowly. With sensitive valves, such as needle valves, the gas can slowly be allowed through the valve so that the pressure increase is slow on the low pressure side. The pipe-work, joints and valves in the blending system should be designed to minimize sharp bends and sudden constrictions. Sometimes 360 degree loops are present in the pipe-work to reduce vibration.

Spaces where gas is blended or oxygen is stored should be well ventilated to avoid high concentrations of oxygen and the risk of fire.

With nitrox there are several methods of gas mixing

  • Mixing by partial pressure: a measured pressure of oxygen is decanted into the cylinder and cylinder is “topped up” with air from the diving air compressor.
  • Pre-mix decanting: the gas supplier provides large cylinders with popular mixes such as 32% and 36%.
  • Mixing by continuous blending: measured quantities of oxygen are introduced to the compressor inlet.
  • Mixing by density (weight): oxygen is added to a partially full cylinder that is accurately weighed until the required mix is achieved.
  • Mixing by gas separation: a nitrogen permeable membrane is used to remove smaller nitrogen molecules from the mix until the required mix is achieved.

With trimix, measured pressures of oxygen and helium are decanted into a cylinder, which is “topped up” with air from the diving gas compressor, resulting in a three gas mix of oxygen, helium and nitrogen.An alternative is to first decant helium into a cylinder and then top it up with a known nitrox mix.

With heliox, measured pressures of oxygen and helium are decanted or pumped into a cylinder, resulting in a two gas mix of oxygen and helium.

With heliair, a measured pressure of helium is decanted into a cylinder, which is “topped up” with air from the diving gas compressor, resulting in a three gas mix of oxygen, helium and nitrogen.

To avoid oxygen toxicity and narcosis, the diver needs to plan the required mix to be blended and to check the proportions of oxygen and inert gases in the blended mix before diving.Generally the tolerance of each final component gas fraction should be within +/-1% of the required fraction.

When blending mixes with pressures less than 250 bar / 3600 psi, the Ideal gas law holds and simple equations can be used to calculate the pressures of each component gas needed to create the mix. Above this pressure, the composition of the final mix is difficult to predict using simple equations but needs the more complex Van der Waals equation.

Increases in temperature when filling make it difficult to accurately decant or pump a measured quantity of gas. When cylinders are filled with gas quickly, typically in 10 to 60 minutes at a dive filling station, the gas inside gets and still stays hot, which increases the pressure of the gas (corresponding to its mass). But, when the cylinder cools an hour or two later, the gas pressure falls showing the reduced volume of breathable gas available to the diver.

There are several solutions to this problem:

  • fill the cylinder to the required pressure, let the cylinder cool and measure the gas pressure and then repeat the process until the correct pressure is achieved. The cooling interval needed depends on the ambient temperature.
  • fill the cylinders in a water bath. The higher thermal conductivity of water compared to air means that heat in the cylinder is more quickly removed from the cylinder as it fills.
  • fill the cylinders with 5 to 20% more gas (as pressure readings) than required. If the overfill (in pressure while hot) is well judged, when the cylinder cools the final pressure will be within the tolerance of the required pressure.

Before a gas mix leaves the blending station and before the diver breathes from it, the fraction of oxygen in the mix should be checked. Usually electro-galvanic fuel cells are used to measure the oxygen fraction.[2][5] Helium gas analysers also exist, although they are expensive at present, which allow the Trimix diver to find out the proportion of helium in the mix.

In the United Kingdom, oxygen and helium is bought from commercial industrial and medical gas suppliers and typically delivered in 50 litre “J” cylinders at a maximum of 200 bar. In addition to the cost of the gas, charges may be made for cylinder rental and delivery.

The “cascade system” is used to decant economically from banks of storage cylinders so that the maximum possible gas is removed from the bank.This involves filling a diving cylinder by decanting from the bank cylinder with the lowest pressure that is higher than the diving cylinder’s pressure and then from the next higher pressure bank cylinder in succession until the diving cylinder is full. The system maximizes the use of low pressure bank gas and minimizes the use of high pressure bank gas.

Pneumatically powered booster pumps, such as the Haskel pump, are used to scavenge the remnants of expensive gases in nearly empty cylinders allowing low pressure gases to be pumped safely into cylinders already containing gas at higher pressure.

New Technical Diving Products for 2011

Our online shop is exploding with new cave and technical diving products for the new year.

Koh Tao, Thailand

Big Blue Tech has already started stocking some new and exciting items for the new year. These items received raving reviews from DEMA address a shift in more technically advanced products to suit the digital consumer.

New RX2 LED Slimline Canister Light

The RX2 LED debuts this week at DEMA. One of the most exciting features on the light is the switching mechanism. We have designed a rotary magnetic switch on the head; the switching is integrated into the board for stability and function. Full and half power modes are at your fingertips, no reaching for a canister switch. This allows multiple mounting options for the diver. The two previous blog entries give some ideas.

This light represents the latest in LED lighting innovation. The RX2 is the product of months of development with US-based companies and all production is made in USA. Our design team engineered the product and feature set – this light is not a “me to” product from a Chinese supplier. The LED boards are the latest in technology and RoHS compliant for European standards. The new polymer boards dissipate head better than conventional boards so we have over 93% efficiency with power consumption to light output. This means we were able to give you more light using the same battery power source as its predecessor the LUX while maintaining the 4 hour burn time at full power.

New Liquidvision XEO Trimix Computer

We owe the inspiration for the Liquivision Xeo to our customers. Whether they dive shallow reefs or deep wrecks, our customers told us what they wanted in a computer and we’re proud to give them what they’ve been hungry for… an affordable, well-made dive computer with a highly readable color OLED display.

The Liquivision Xeo is a wrist-mounted air, nitrox, and OC/CCR trimix computer that can serve divers of all levels. Designed with input from both physicians and highly-respected divers, the Xeo offers maximum readability, ergonomic comfort, and compact convenient size. It features Liquivision’s patented tap-interface, a bright full-color OLED display, user-replaceable battery, robust ceramic pressure sensor, two mounting options (high quality strap or bungee-cord), and the proven Buhlmann-GF (ZHL16C) algorithm. We’re proud to add the Xeo to the Liquivision “Dive Enlightened” series.

Brilliant design, brilliant display… brilliant under pressure.

New Liquidvision XEN Bottom Timer Computer

For two years, divers have been asking for an affordable OLED bottom timer. That day has arrived. No longer will you buy a computer only to put it in “gauge mode” right out of the box.

The Liquivision Xen is, simply put, the bottom timer that offers everything you want and nothing you don’t. Designed with functionality input from respected gauge-only divers, and with readability and ergonomic input from physicians, the Xen is the ideal gauge for everyone from the open water enthusiast to the most advanced record-setting technical and cave divers.

All this and more can be view on our online shop –