Posted by: tdisdiuk | September 15, 2014

One for all or all for one?

One of the most contentious issues amongst technical divers is the difference between the self sufficiency and team diving approaches to diving. Like a number of other issues in technical diving it seems to polarise opinions, often along agency boundaries. This often leads to exaggerated positions that can take on a similarity to religious fundamentalism.

The self sufficiency mindset is where the diver is fully self sufficient and approaches the dive with the view that they can perform the dive on their own and would be fully able to complete the dive without a buddy. The approach is summed up by the mindset that if you can’t do the dive on your own then you should not be doing the dive at all.

The other approach is team diving where strong team work and cooperation are the focus of the dive and you plan to dive with a team of divers and the team works as a well coordinated whole.

These two approaches seem to have a very different emphasis and many divers think that they are contradictory. That is you have to decide whether you have a self sufficient approach or a team based approach and that it is a choice of one or the other. Both approaches have their extremists who will go to great lengths to explain why their approach is right and the other approach is wrong.

In some areas technical diving in the UK has evolved into a culture of solo diving where many experienced technical divers dive solo. All equipment choices are made on the basis that you will be diving alone or that your buddy will be of no use. Gas planning is based on the principle that it is impossible or unlikely that your buddy will be any use in an emergency and so all procedures are based on individual action.

The team diving approach also has its extremists who focus on teamwork as the primary goal and consider self sufficiency to be sign of weak teamwork. These divers will only dive with divers who follow the exact same team procedures.

In reality these two extreme positions are not very realistic and when taken to extreme counteract the very point of the principles. This can cause significant problems as the advocates of self sufficiency can refuse to see some of the benefits of team diving whereas the advocates of team diving refuse to see any benefit in self sufficiency.

In particular the principle of self sufficiency does not mean the same thing as solo diving. For example, pioneering technical diving instructor Kevin Gurr says “Assume all dives are solo dives; do not get into the water if you feel you can’t do it without someone else to rely on.” This is a clear endorsement of the self sufficient approach and many people have taken this to be a recommendation for diving solo. However Kevin then goes on to say “This does not mean you should not dive in a team, you should. Be prepared to be separated and to have to look after your self.” Similarly those who advocate team diving do not mean that you should not be able to deal with situations on your own or need to rely on your team.

So despite initial impressions the self sufficient and team diving approaches are not as contradictory as they might at first seem. In fact they are just two sides of the same coin.

The best technical divers obviously have to have good individual skills. Building on your own level of buoyancy control, familiarity with kit and ability to deal with difficult situations are fundamental for anyone wanting to progress in technical diving. No diver who has thought about this question for more then a millisecond would ever suggest anything less. Team sports such as football, rugby or cricket are a perfect example of the team approach but players still ensure that they work on their individual skills. Players with weak individual skills would never make it into the team in the first place. Diving with someone who is not self sufficient is not team diving. If one of the team cannot deal with an emergency situation then they are going to weaken the overall team rather than strengthen it. This means that self sufficiency is clearly a prerequisite for team diving.

The self sufficiency extremists however go further than this. They claim that all divers should be self sufficient because you can never rely on a buddy to provide any assistance in an emergency. They will often cite examples of where an individual buddy has not been able or willing to provide assistance in an emergency and from this conclude that no buddy will ever be able to provide assistance. Furthermore they argue that a poor buddy might cause an incident that would not have happened had you been on your own. As such their argument is that it’s better to be completely solo and never have a buddy than to have a poor buddy. In some ways this argument has some merits in recreational diving as there are a whole range of abilities. Inexperienced or out of practice divers can certainly fit this description and many instructors and dive guides will tell you that they feel safer on their own. Certain recreational training agencies even support the concept of solo diving in the recreational area and provide training courses on self sufficiency and solo diving. However, this argument breaks down for technical diving. At this level any divers undertaking these types of dives require a higher level of skill and abilities. Divers who are unable to help their buddy are clearly operating at the limits of their own ability and so do not have enough self sufficiency to undertake that dive whether they are alone or with a buddy.

The best approach then is to aim for self sufficiency within a team environment. Each diver should have enough capacity to resolve any problems they may have and have enough spare capacity to be able to offer assistance to the other members of their team. If their buddies also have enough capacity to resolve their own problems and have enough spare capacity to be able to offer assistance to the other divers then you have a very strong team.

The strongest teams usually consist of experienced individual divers with good self sufficiency and self awareness skills that have practiced working together in a team. Training and practice are essential in order for team diving to work successfully. Each member of the team should have similar views so they are following the same general approach. In addition good teamwork only comes with practice. You can see this with national sports teams. Each player is amongst the best player in the country yet unless they train together as a team they will not be able to perform well as an effective team.

When team diving is carried out by experienced, trained divers then it is a very safe way of diving. In the case of a problem you have more options available to help out; more gas available, more chance of spotting the problem and more ideas on how to solve it. In the case of an incident, one member of the team can be initiating a rescue while the other sends up a delayed SMB and another provides a visual reference to ensure the rest of the team can maintain depth. It is when problems occur that the benefits of diving in a team become apparent.

Of course this is very easy to say. Of course this raises the question that if self sufficiency within a team environment is the goal how come it is not that common? The reason for this is that it’s not easy to develop these two aspects. The time and effort required to master your own skills to the point where you are truly self sufficient and then the additional time and effort required to maintain those skills is more than most people can commit to. We all have jobs, families, other hobbies and commitments which are all competing for our time. It is entirely feasible to be a recreational diver and just dive a few times a year on holiday or on a couple of dive club trips. However this is not the case for technical diving. If you are involved in decompression diving, trimix or rebreathers then it is essential to ensure that you put in sufficient practice to build up and maintain your skills. Some people may take to diving more easily than others but no one is born with all the skills and knowledge they need to become a technical diver. There are some people that may have more innate cricketing skills than others but if you want to play for one of the premiership teams you will need to put in a huge amount of practice in order to refine your skills and reach the level required. Once you have reached that level you then need to put in even more effort to maintain those skills.

The development of a strong team also requires time and effort. If it is difficult to ensure that a single person can dedicate the time and effort it is even more difficult to gather a groups or team to practice together. The individual commitments of each team member and the logistics of getting them together can be difficult. However the same principle applies. If you want to become a true technical diver then it requires a certain commitment in terms of time and effort.  Irrespective of how good a cricket player is and how much time they spend working on their individual skills they spend more time in team training.

It is because developing strong self sufficiency skills and teamwork require such a commitment that alternative approaches have sprung up. If individual divers and their buddies do not have the individual or team skills required they take alternative approaches to try to overcome these problems. Teamwork is made more prescriptive so that it removes the emphasis on the individual diver. Alternatively teamwork is ignored all together and divers adopt a solo diving mentality. Each of these approaches might seem easier in the short term and more appealing to those who cannot commit the time and effort to develop their individual and team skills but it is a poor solution to the problem. In the case of emergencies the lack of personal skills and self sufficiency can cause problem for you and any buddies you are loosely teamed up with. Equally the lack of team skills may cause confusion and often makes the situation worse. So even though those alternatives might seem more attractive in the short term and ma be acceptable for the majority of divers where nothing goes wrong they are a poor long term solution as they can fall apart in times of emergency.

There is no getting away from the fact that for technical diving there is a need to invest time and effort in developing your personal skills and your team skills to a higher level then is normally required for recreational diving. Playing cricket in the park with our kids, or in a pub team is great fun. In this environment you will sometimes find very good players but the level of play is nowhere near the same level as in the Premier League. As technical divers we should use Premier League cricket as our model rather than a game in the park or the occasional pub team game.

Posted by: tdisdiuk | March 21, 2014

Why do freeflows cause rapid ascents?

Fig 1

A number of recent incidents have prompted be to consider why do so many free flows lead to rapid ascents.


April 2013 13/094 (BSAC 2013)

Three divers were at 20m when one of them had a regulator free flow. All three made a fast ascent to the surface and, after a long surface interval, one if the divers had “tingles” in her fingers and one of the others had pains in his chest. Both divers were administered oxygen and, following a call to a hyperbaric chamber, all three divers were asked to attend.


This incident is taken directly from the 2013 BSAC Incident Report. Unfortunately it is not at all unusual, in fact, it is fair to say that incidents like this are amongst the most common type of diving incidents. Not all result in “tingles” and a trip to the hyperbaric chamber and a significant number are never reported. A significant number of free flows result in rapid ascents, 23% of rapid ascents in the 2013 BSAC incident report were due to regulator free flows. Another example from this report is given below.


June 2013 13/149

A buddy pair had descended down the shotline and on reaching the bottom at 32m, one of them experienced a regulator free flow. The dive was aborted and both divers made a rapid ascent to the surface. Oxygen was administered as a precaution to the diver who had experienced the free flow and advice given not to dive for twenty-four hours, do no heavy lifting and to drink plenty of water.


If you are at any of the popular inland dive site between January and April it is likely that you will see at least one free flow leading to a rapid ascent at some point during the weekend. Winter is particularly bad for this type of incident due to the low water temperature leading to increased risk of free flow. The following incident is from February 2013 when the water temperature was 5 deg C.


February 2013 13/029

An instructor and student entered the water for the student’s final qualifying dive in a quarry with very cold fresh water of 5 deg C. Shortly after the start of the dive at a depth of 4m the student’s regulator began to free flow. The free flow could not be stopped and the instructor provided her octopus and the pair made an AS ascent to the surface without further incident. The additional bubbles were noted by the surface cover and support divers swam out to offer assistance but none was required.


Although free flows may happen there is no reason why they should lead to a rapid ascent. It’s not as if you don’t have any air, quite the opposite, the demand valve is giving you plenty of air. For many recreational dives it is possible to do a controlled ascent and even a safety stop and still have air coming out of the free flowing regulator when you get the to surface. So the problem is often not a lack of air but a lack of practice and experience. Dealing with a free flowing regulator is included in the initial training of every diver training agency that I am aware of. Every diver should be capable of dealing with this situation without panicking. Yet panic is often exactly what happens resulting in a rapid ascent as they bolt for the surface.


June 2013 13/330

The casualty was part of a group conducting a deep dive. The group descended to 36m and then began viewing objects which were affected by the pressure change. During these exercises the casualty’s regulator began to free flow. The casualty was given the instructor’s regulator and the instructor switched to her alternate source. The casualty struggled to accept the regulator and couldn’t clear it, so she began to panic and swim to the surface. The instructor held the regulator in the student’s mouth but was unable to slow the ascent. On the surface the casualty was assisted out of the water and monitored for signs of DCI. The casualty mentioned that she had ‘tingles’ and so she was given oxygen. She had a consultation with the recompression chamber over the phone. It was decided that no further treatment was needed.


However, even if the diver doesn’t panic and bolt for the surface, a rapid ascent often occurs anyway. This is due to two reasons. Firstly the diver loosed focus on their buoyancy control because all they can focus on is the free flow. Secondly the free flow itself can cause the diver to become more positively buoyant and can effectively “suck” them to the surface.


June 2013 13/144

Two divers were at 34m when one of them experienced a regulator free flow. The buddy donated her octopus but had to hold it in place during a fast ascent. On shore the diver complained of ‘tingling’ in her right hand and felt a bit lightheaded and shaky. She was put on oxygen and the ‘tingling’ disappeared. Following oxygen treatment her arm felt ‘heavy’. She had carried diving equipment some way from a car park to the diving entry point and, following contact with a hyperbaric chamber, was awaiting a duty doctor to call her direct.


So what can we do to prevent a free flow from leading to a rapid ascent?


The first thing is that we can try to minimise the risk of a free flow in the first place. I have two suggestions to achieve this. The first is to ensure that your regulator is properly serviced. A recent survey carried out by the RNLI on behalf of the British Diving Safety Group revealed that amongst the highest risk group 40% of divers had not had their equipment serviced within the last year whereas within the lowest risk group 93% had had their equipment serviced within the last year. Of course it is important to get your equipment serviced properly. An incorrectly serviced regulator might actually be more prone to a free flow. This is not an excuse to not get your equipment serviced but rather is an encouragement to find a good service technician who can service the regulator properly.


The second thing we can do to try and avoid free flows is to refrain from using your regulator to inflate your DSMB in cold water. Using your alternative air source, octopus or even your main regulator and pushing the purge button to inflate a DSMB significantly increases the risk of a free flow as the incident below illustrates.


May 2013 13/074

Two divers were practising mid water DSMB deployment using the AS run from one of the diver’s first stage. Having inflated the DSMB successfully, the AS free flowed. Unable to stop it the diver switched to his buddy’s AS which was run from a pony cylinder. The buddy switched off the diver’s air supply to stop the free flow but when the supply was turned on again the regulator continued to free flow. The buddy switched off the supply and the divers made a controlled ascent including a 3 min safety stop at 6m. On the surface the buddy supported the diver whilst restoring his air supply to allow BCD inflation. The free flow did not restart as the air supply was restored. The incident was put down to cold water, which was about 5 deg C.


There are a number of other inflation techniques that can be used, such as using exhaled gas, a LP inflator hose, a CO2 cartridge or a small air cylinder, also know as a crack bottle. All of these remove the risk of purging the regulator causing a free flow and should be considered when diving in cold water.


If a free flow does occur then there are a number of steps that can be taken to ensure that it does not lead to a rapid ascent. It is possible to breathe from a free flowing regulator. The regulator should be removed partially from the mouth so that the stream of excess gas can escape and the diver can then “sip” the air from the stream of gas. This is a very easy skill to achieve as long as it has been practiced in advance. For divers using a twinset, side mount or a stage cylinder they can “feather” the valve which means turning it on and off very quickly to only provide enough gas for one breath at a time. This is a slightly more difficult skill but nothing that cannot be mastered with a few minutes practice although it may not be possible on a single cylinder. Even with a free flowing regulator there is often more than enough gas to do a controlled ascent to the surface and even carry out a safety stop.


If breathing from a free flowing regulator is too much of a challenge then the easiest thing to do is to switch to switch to your octopus. Even with one regulator free flowing the other will usually be working fine. If both of your regulators are not working or if the free flow has emptied your cylinder then you can use a pony cylinder or your buddy’s alternative air source. This also allows the buddy to turn off the first stage and so stop the free flow. In some cases turning it off and waiting a couple of seconds is all that is needed to stop the free flow. Either way turning off the first stage will stop the bubbles and reduce any buoyancy issues on the ascent.


All the time this is going on the diver and especially their buddy should be monitoring their depth to ensure they are not loosing control of their buoyancy. Don’t let your attention get focused entirely on dealing with the free flow and loose awareness of your position in the water column. Once the diver has a good supply of gas then a controlled ascent can begin.


None of these skills are particularly difficult but they will be stressful if it has been a while since they have been practiced. Practice these skills regularly and there is no reason why a free flow should result in a rapid ascent. Next time you are diving practice one or more of these skills;

  • Breathing from a free flowing regulator
  • Switching to out alternate air source
  • Switching to your pony cylinder
  • Breathing from your buddies alternate air source
  • Deploying a DSMB while your buddy is breathing from your AAS
  • Ascending while your buddy is breathing from your AAS
  • All while maintaining buoyancy control


The incident below shows that even with two free flows it is possible to successfully carry out a controlled ascent.


April 2013 13/093

Three divers were planning a dive to 30m. Two of the divers had single cylinders with primary and octopus second stages and one had an independent pony cylinder. The divers descended down the shotline but almost immediately upon arriving at the bottom of the shot, one of the diver’s primary second stage began to free flow causing her to switch to her octopus. One of her buddies noticed this and offered his octopus which she took and he tried for a short time to stop the free flow but to no avail. The diver and buddy prepared to ascend together and, in preparation, the buddy looked over to the third diver only to notice that he was having the same problem with a regulator free flow causing him to switch to his octopus. The buddy offered the third diver his pony regulator which he took. All three divers ascended close together up the shotline to the surface without incident. On reaching the surface, both the divers who had free flowing regulators had less than 30 bar remaining in their cylinders.



BSAC 2013 National diving Committee Incident Report 2013

RNLI 2014 Audience Profiling Research: Leisure Divers

Posted by: tdisdiuk | March 21, 2014

20 Years


Posted by: tdisdiuk | April 22, 2013

A survivor remembers HMS Hermes

Stan Curtis

This is Stan Curtis looking at pictures and video of the wreck of HMS Hermes from our last trip out there. Stan was one of the survivors of HMS Hermes and the last time he saw the Hermes was about 11:30 on the morning of April 9th, 1942. He was treading water in the sea off the coast of Ceylon as the Hermes sank in front of him. Stan was fascinated by the video and watched it several times. He was very grateful that divers are keeping alive the memory of this historic ship and the brave crew who served on her.



If you would like to join the next HMS Hermes trip then take a look at the Scuba Travel web page

Posted by: tdisdiuk | April 10, 2013

DDRC becomes an SDI Training Facility

DDRC                    sdi_2colorLogo

DDRC and SDI are proud to announce that DDRC will now be able to offer SDI certification for CPR, First Aid, Oxygen Admin and AED training courses. The combination of these two organsations means that divers will be able to receive training from the UK’s leading hyperbaric research and treatment charity, while receiving certification from one of the worlds leading diving agencies.

Divers taking the DDRC Diving Accident Responder Course (DARC) will be able to benefit from receiving training from world class diving doctors and trainers. They will then be able to receive certifications from SDI and gain recognition for their training. This certification can be recognised as part of their ongoing training towards Advanced Diver, Divemaster or even Open Water Instructor.

DDRC trainers recently completed a cross over course to SDI non-diving speciality instructors with SDI/TDI Instructor Trainer Mark Powell. “DDRC are the perfect candidates for the SDI non-diving speciality instructor. This unique scheme allows SDI to make use of the worlds leading experts to deliver non-diving speciality courses. Who better to train divers on what to do in a diving accident than DDRC and we are very proud to have DDRC as an SDI training facility”.

Jon Parlour, Training Officer at DDRC said “We are very happy to be working with SDI on our DARC course. We were impressed with the structure of the SDI course and material as well as their training philosophy and are hoping to be running additional SDI/TDI courses in the future”.


For details of DDRC courses contact;
Samantha Shayer
Training Coordinator
Tel: 01752 209999

For details on other TDI/SDI courses contact;
Mark Powell
TDI Instructor Trainer #8532
Tel: 07770 864327

Stephen Phillips
SDI/TDI UK Regional Office
27 Manse Road
Crossgar Co Down
N. Ireland BT30 9LY
Fax 08701288600
Phone Office 02844832992

Posted by: tdisdiuk | April 2, 2013


Letter-Logos-Horz-WHY SDI/TDI?

by Timothy Gort

So why did I choose to be a SDI/TDI instructor?

I started with my first TDI course on Semi-Closed Rebreather Drager Dolphin and moved on to Advanced Nitrox and Decompression Procedures, Trimix, Cavern and Intro-Cave, and DPV before finally completing the Gas Blender and Service Technician course.  Having experienced the variety of courses SDI/TDI has to offer, it was a natural progression for me to move onto the instructor grade.  Here are a few things I would like to say about SDI/TDI and why I choose to teach for them:

Instructor crossover

I had been thinking about this for some time and by chance met Brian Carney at the Birmingham NEC dive show.  For those of you who don’t know, Brian Carney happens to be the President of SDI/TDI worldwide.  Wow!  I mean how many agency presidents would make an appearance at a UK dive show?  In my books this proves to show how much SDI/TDI value their instructor training.  An instructor crossover generally consists of a theory session reviewing the instructor materials and the standards and procedures, an eLearning session and a practical skills circuit.  If you wish to learn more about becoming an SDI/TDI instructor in the UK feel free to contact SDI/TDI UK here or contact Mark Powell at Dive-Tech here.

UK Instructors

From my experience, SDI/TDI instructors often introduce students to other SDI/TDI instructors if they can offer a better date or location to suit the student.

Flexibility of courses

SDI/TDI courses are flexible and work around the student.  There are no set skills assigned to set dives but rather a set of standards the student must achieve.  This allows the student to maximise their potential and strengthen their weaknesses.  This allows the instructor to plan a course for YOU.  For the students, the standards do not change; they are still required to meet the criteria and earn their certification before they are awarded their c-card.

Instructor and student resources

SDI/TDI is constantly reviewing their materials so the students are taught on the most current information.  In the past month SDI/TDI have released new Decompression Procedures materials and made the theory portion of the Solo Diver course available as eLearning

Leading from the front

SDI/TDI was the first agency to offer any type of solo/self-reliant diver training with its release of Solo Diver and it’s still the only course of its type to be recognised by insurance agencies.

But not afraid to follow

As well as leading, SDI/TDI isn’t afraid of listening to its members.  When the other agencies introduced a sub-50m helium course, SDI/TDI followed with the introduction of the Helitrox course.

The current trend

There currently seems to be a trend in diving and some traditional courses appear to have been forgotten about with some students buying equipment they may not need and completing a course which they either may not need to may not be capable of.  Personally I feel that Intro to Tech is often the most overlooked course.  I would say that this course is probably the single most important course any student can take.  Intro to Tech is designed to help any diver decide if technical diving is for them, or help them to develop as a better diver at their current certification level.  Buoyancy and trim, equipment configurations, propulsion techniques (frog, flutter, back kick etc…) and gas management are some of the syllabus of this course.  If this is combined with Advanced Nitrox and either Decompression Procedures or Helitrox then the majority of divers will have earned the certifications to achieve most of their diving goals; especially here in the UK.  Regarding equipment, SDI/TDI has an open mind and as long as it is capable of doing the job it will be allowed on the course.  Any SDI/TDI instructor will be able to discuss the pros and cons of any equipment configuration questions any students may have.

For me, the learning doesn’t stop here.  I am looking forward to my Full Cave in Florida this Spring and hope to complete my Advanced Trimix soon.

So what are YOU waiting for?  Start your SDI/TDI training today and become the diver you’ve always wanted to.



rectotec is an SDI/TDI diver training facility offering all levels courses including Solo Diver and up to Advanced Nitrox and Decompression Procedures.  Located in Ipswich and the West Midlands, rectotec is able to run courses at a time and location to suit you; the theory can be done on-site, through e-learning or even at yours if you would so wish.  rectotec is also happy to work with dive shops or clubs and run courses at your location.

If you want to get in contact with Tim feel free to contact him on 07968148261 or


Posted by: tdisdiuk | March 27, 2013

Happy Birthday JEL

Happy Birthday to the Liberty ship S.S. James Eagan Layne, launched on this day in 1944. Beached in Whitsand Bay a few months later, she has been a home for fish and entertainment for divers for the last 67 years.


Posted by: tdisdiuk | March 26, 2013



SDI continues developing their eLearning platform, allowing divers to complete the academic portion of the Solo Diving certification online. In 1999 SDI (Scuba Diving International) launched its controversial Solo Diver Course, a program that taught recreational sport divers what tools and techniques would help them stay safe when diving on their own. This was something no other training agency had dared do before. Today, SDI continues to lead the industry by being the first and only certification agency to offer a Solo Diver Course online. This marks the 20th online scuba dive course offered in SDI’s eLearning classroom system.

Solo diving, once considered technical diving and discouraged by most certification agencies, is now seen by many experienced divers and some certification agencies as an acceptable practice for those divers suitably trained and experienced. Rather than relying on the traditional buddy diving safety system, solo divers are trained to be skilled in self-sufficiency and are willing to take responsibility for their own safety while diving.

The 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 photographers and underwater videographers, as well as those diving with their children or buddies who may not be very experienced in scuba diving.

Bob Halstead says, “I believe that all divers should be trained primarily as self-sufficient – solo – divers. They must learn to take personal responsibility for their actions in the water. If they are not capable of this, then they should still be in the care of an instructor. But the present hypocrisy that states that solo diving is unsafe while paying lip service to a buddy system that is so obviously failing is slowing the development of diving and increasing its danger needlessly.”

Start learning to dive solo today, because at one point or another, you will be diving alone, whether you want to or not.

If you would like more information about Solo Diving, please contact SDI World Headquarters, your regional office or your local SDI Instructor.

Posted by: tdisdiuk | March 26, 2013

Clarification on courses

TDI_Web Ad Horz FLAT

Please have a look at the following there seems to be a miss understanding as to the qualifications gained at TDI Advanced Nitrox and Decompression procedures course

Advanced Nitrox
This course examines the use of EAN-21 through 100 percent oxygen for optimal mixes to a depth of 40
metres / 130 feet. The objective of this course is to train divers in the benefits, hazards and proper procedures for
utilizing EAN-21 through 100 percent oxygen for dives not requiring staged decompression. TDI Decompression
Procedures or the Intro to Tech may be combined with this course at the discretion of the instructor.

Decompression Procedures
This course examines the theory, methods and procedures of planned stage decompression diving. This
program is designed as a stand-alone course or it may be taught in conjunction with TDI Advanced Nitrox,
Advanced Wreck, or Extended Range Course. The objective of this course is to train divers how to plan and
conduct a standard staged decompression dive not exceeding a maximum depth of 45 metres / 150 feet unless taught
in conjunction with the TDI Extended Range Course. The most common equipment requirements, equipment set-up
and decompression techniques are presented. Students are permitted to utilize enriched air nitrox (EAN) mixes or
oxygen for decompression provided the gas mix is within their current certification level
These are stand alone courses but can be combined which is usually done in the UK also we have the following course which many students decide to take instead
TDI Helitrox
The Helitrox course examines the theory, methods and procedures for planned stage decompression diving
utilizing Helium in the breathing mixture. This program is designed as a stand-alone course or it may be taught in
conjunction with TDI Advanced Nitrox at the discretion of the instructor. The objective of this course is to train
divers how to plan and conduct a standard staged decompression dive not exceeding a maximum depth of 45 metres
/ 150 feet. The most common equipment requirements, gear set-up, and decompression techniques are presented.
Students are permitted to utilize Enriched Air Nitrox and Helium mixes with no greater than 20% He content, and
up to 100% oxygen for decompression diving provided the gas mix is within their current certification level.
Breathing gas mixtures containing more than 20% Helium or less than 21% oxygen are not permitted (+/- 1%).

The Decompression and Heltriox Courses do not limit the amount of decompression as compared to many other agencies. Hope this clears up any confusion any questions please feel free to contact me at

Posted by: tdisdiuk | March 26, 2013

Important Manufacturer Warning

Important Manufacturer Warning

March 2nd, 2013.

It was in the early 2000s when we last heard of divers experiencing problems when using old oxygen cells, luckily without fatalities. Unfortunately there have been two recent fatalities where out of date oxygen cells were used.

At 3 years old most Teledyne cells used in rebreathers will not rise above 1.3 bar, no matter how much oxygen pressure you expose them to, at 2.5 years old some Teledyne cells will not rise above 1.3 , at 2 years old we heard of the odd case. At 18 months we didn’t hear of any incident of current limiting – when stored in air between dives.

This is where APD’s 18 month recommendation for replacing cells comes from.

The Teledyne cell manufacture date is printed on the label in a simple code: D9 is April 2009.

Teledyne stopped making cells for rebreathers in 2010, so even if you have a H0 cell, August 2010, the last cells produced for diving were made more than 2 ½ years ago.

Teledyne R22 and R17 cells MUST NO LONGER be used in rebreathers.

Current limited cells

An oxygen cell generates current.

By passing this current through a resistor, then measuring the potential difference across that resistor a millivolt output is obtained and it’s this mV output that the rebreather electronics measure and in turn display as an oxygen pressure by simply multiplying the cell output by a stored calibration factor for that cell.

The higher the oxygen pressure, the higher the current and subsequently the higher the mV output. However, there is a limit as to how much current the cell can physically produce and this is called the “current limit”.

Current limiting is seen in all oxygen cells regardless of age (often around 4.5 bar when new) but as the cell ages the lead anode is consumed and the cell’s ability to produce current is reduced.

It is worth remembering that the storage conditions affect the rate of decay: the higher the oxygen pressure the cell is stored in the faster the lead anode is reduced. If you store a cell in pure oxygen for instance, it will last just a few months. AP recommends storage in air.

Current limiting only becomes a problem when the maximum output of a cell is below the required setpoint and then with the voting logic on the APD rebreathers it only becomes a problem when a 2nd cell is also current limited below or just above the setpoint. The APD rebreathers use the average of the closest two cells to determine whether to add oxygen or not. For example, if you have one cell on 1.30 and one cell on 1.26 and the third cell on 1.68, the electronics assume that the PO2 is half way between the closest two, in this case 1.28 and the solenoid would open. However, if both the lower output cells are current limited then the true PO2 might be 1.68 and climbing. In this instance because one cell is more than 0.2 bar from the average of the closest two – the cell warning will be active.

The easiest way to avoid current limiting being a problem is to throw the cells away when they are 18 months old. If you use the cells past 18 months then you HAVE to check for current limiting. The problem is you have to check often during the dive as the drop off is sudden. This is easy to do – you simply have to add a bit more oxygen and prove to yourself that the display will go well above the setpoint but doing it once on a dive isn’t enough, you need to check it every 5 -7 minutes or whenever you think the solenoid activity is too frequent.

Solenoid Activity

Knowing what to expect from the solenoid at different stages of the dive is an essential part of a rebreather diver’s armoury.

During the ascent you expect the solenoid to operate a lot as the oxygen pressure naturally drops as you ascend and the machine tries to maintain setpoint.

However, at all other times the solenoid activity is MUCH less. On the descent for instance, you wouldn’t expect it to operate at all and on the bottom you expect it to operate intermittently – just replacing the oxygen you metabolise.

The APD Vision electronics have a 3 seconds delay before it decides whether to open the solenoid or not, on the Classic electronics it is 6 secs, and the duration of the opening time varies with how far the oxygen pressure is below the setpoint. If the oxygen pressure drops low enough, the solenoid will open continuously.

On the bottom with minimal depth changes the machine is only adding oxygen to replace the oxygen that you metabolise so you’re not expecting long injections and you’re not expecting injections every 3 secs, so if the solenoid starts adding gas so frequently look at the handset and find out why.

If the oxygen addition is sufficient you’ll find your buoyancy increases – again abnormal increases in buoyancy need further investigation.

Being aware of how your rebreather normally operates in all phases of the dive is an essential tool in knowing when the rebreather is operating abnormally.

What do I do if I suspect Current Limiting?

The danger is Hyperoxia – too much oxygen, so your actions do depend on how long you have been exposed to high levels of oxygen.

If you dive with old oxygen cells you HAVE to be checking for current limiting throughout the dive and be checking at least every 5 minutes.

A routine check would include:

· Add oxygen – are the cells able to go higher ?

· If they are not able to display higher, do a good… long… diluent flush

· Change to the low setpoint , by pressing and holding the centre button and see if it runs okay at that

· Remember : DO NOT CONTINUALLY SUPPRESS CELL WARNINGS. A cell warning needs further evaluation – which includes physical actions to check which cell is giving you the correct value. CELL WARNINGS MUST NOT BE IGNORED and bailout options should be seriously considered.

There is no substitute for regular monitoring of your handset display.

Martin Parker
Managing Director
Ambient Pressure Diving
Tel: 01326 563834
Fax: 01326 565945

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