Over the past 6 weeks, initially for the MAST project two divers from the Maldives have undertaken a TDI Extended range and 'Normoxic Trimix Course' to learn new skills, improve on existing skills, increase safety, and gain theoretical knowledge to extend the time or depth underwater. What is Extended Range? Extended Range has in the past been labelled as a deep air course but to discourage divers from diving deep on air, an extremely dangerous type of diving and far more so than your usual dive.

Extended range diving is a very comprehensive course teaching the theory, practical skills and equipment configuration knowledge required to extend the time underwater to hours rather than minutes and extend the depth to 55msw. It extensively guides the diver from the initial dive planning, to equipment configuration and requirements to the use of NITROX for decompression and the hazards involved in its use and finally the dives themselves. Practical skills are hard and intensive and prompts the diver to demonstrate skills such as Isolation drills on a twin set with manifold, accurate buoyancy control, navigation skills, swimming with no mask, buddy breathing for extended periods of time, removing decompression stage bottles mid water while retaining buoyancy, out of air drills at depth, equipment failure drills and multi level stepped decompression requiring gas switching on the fly and line laying skills. The theory involves calculations and the use of tables to accurately plan your dive including air requirements, mix of decompression gas, planning and taking into account the oxygen loading of the divers system and the effects of Central Nervous System Toxicity (CNS Toxicity) and Oxygen Toxicity Units (OTUs). The course Delves into the knowledge required to understand these and the historic figures James Lorrain Smith and Paul Bert who discovered many of these effects. The course bases itself of the knowledge learnt on the basic and advanced 'NITROX' courses and expects the diver to be able to plan air and dives prior to attending. Refresher lessons remind the trainees of Daltons Law - pressure, Boyles Law PV=K and other such laws describing how diving related effects occur.

A great sense of the dangers which can occur are introduced on this course and safety is established as being premium before one starts the course. I have thoroughly enjoyed it and it has showed how much more there is to learn. It has also demonstrated the need to practice practice, practice the skills which you learn until they become second nature or at least well honed.

Normoxic Trimix

This is the follow on course from the Extended range course and adds to the skills learnt to give the trainee the knowledge and practical skills required to utilise Helium in the breathing gases. Why use Helium? Helium is aimed at reducing the partial pressure of Nitrogen in the breathing mix and thus reducing the narcotic effects experienced while breathing Nitrogen at raised partial pressures.

Diving gases are always a trade off, as is everything in life. One has to think of it as one side of a set of scales. Helium while inert and non narcotic to the depths we breath it on this course is absorbed into the body tissues much faster than nitrogen. While it is absorbed fast it takes much longer to leave the system and as such increases the decompression times giving a large penalty. The minimum amount of helium is used to bring the nitrogen partial pressure to a level giving an acceptable narcotic effect. As such our mix is now made of excluding trace gases Oxygen, Helium and Nitrogen hence the name 'Trimix'. 'Normoxic Trimix' is the use of breathing mixtures with levels of Oxygen at or above normal levels i.e. 21%. The use of Oxygen partial pressures below 0.21 is explored in the 'Advanced Trimix course' which details the use of Hypoxic mixes or the use of breathing gases with levels of oxygen below 21%

Benefits and lessons learnt?

The course has been very informative giving another huge influx of practical training and theory skills. It has improved me as a diver more than any other course I can ever remember doing. It also requires the trainee to work with a buddy. If this is a buddy you regularly dive with by the time the course finishes I found that I had built up a bond with my buddy which allowed me to see if my buddy was tired, stressed, in trouble or happy. I became more intuitive about his next actions and spent more time making sure he was ok throughout the dive. It may not be every bodies cup of tea but for those wishing to progress themselves it really does improve the way you look act and think about diving in the future. Both these courses require a good level of physical fitness in order to carry the large amounts of back gas and decompression gas needed to extend the depth to 60m and the time to dives of up to several hours long. The second big issue to be aware of is that both courses place a large workload on the divers with much planning, and a type of multi-tasking underwater. Since we are not machines the approach to this is to train your mind to look at the tasks required to be performed and when they are required and to prioritise these in parallel with the dive profile being run. If items upset the balance one is required to reassess the requirements and re-prioritise. I found this to be the greatest challenge of all.