JackKit

Jack Ingle is the BSACs Technical Diving Adviser. He is a BSAC National Instructor, an IANTD Technical Instructor, a TDI Tri-mix instructor and co-author of NSAC nitrox courses.
KIT-CONFIGURATION WITH A REBREATHER
I have attended some of your presentations at the Dive Shows on equipment-rigging and like your ideas on keeping things neat and tidy and above all simple. You spoke mainly about open-circuit equipment but I have recently started to use an Inspiration rebreather. Do you have any suggestions with equipment configuration when diving a closed-circuit system
Pete Smith


Welcome to the world of closed-circuit diving, and I do understand your problem. If you remember, one of the philosophies with open-circuit kit configuration is to keep your front and chest area as clear as possible. This is far more comfortable for the diver and, more importantly, it makes it easier to get to life-saving equipment such as back-up regulators, inflators etc.
Not all closed-circuit rebreather systems are the same but the Inspiration uses front-mounted counterlungs, which means that they are worn over the divers shoulders, down in front of the diver and clipped to the harness to stop them floating up when they have gas inside.
The system is designed this way to make breathing easy. It works very well and must not be altered.
However, when I first started to use an Inspiration I felt quite cluttered and started to look at the system to see if I could ease some of the problems.
The one piece of equipment I use for all types of open-circuit diving is my harness - whether I am diving single cylinders or twinsets, it is always the same.
I decided that I would like to have the same harness on the Inspiration, as Im so used to it and know where everything is without having to think about it. It was a simple operation to fit this to the unit and still use the Inspiration wing. The only extra change I had to make to my harness was to fit two clips to my waistband to hold the counterlungs securely in place.
Fitting my harness doesnt solve the problem of a clear chest area, as the counterlungs have to be in that position, but it does make switching between open- and closed-circuit diving very easy.
Ambient Pressure, which produces the Inspiration, makes excellent products and you must be careful what you do to the system to avoid invalidating your warranty.
There is also the important question of staying within the CE standards. It would be worthwhile contacting AP if you are proposing to make any changes.
What do I look for in a scooter
Last year I was lucky enough to have a go on an underwater scooter while abroad on holiday. I am a serious technical diver and plan to buy my own scooter this year. Can you let me know what is available to buy, and the pros and cons for the various types
Jonathan Clare


Underwater scooters, technically known as DPVs (Diver Propulsion Vehicles) are becoming quite common, even on our side of the pond. You have had a go on one and seen the benefits it offers divers, the main one being the amount of distance you can cover in one dive compared to a free-swimming diver.
We dived the Andrea Doria in the USA a few years ago and one of the divers who used a DPV saw far more of this very large wreck than the rest of us.
It sounds as if you already do some serious diving and there are a number of factors you need to consider before you buy a DPV. First, make sure that the unit you buy is depth-rated for the dives you plan to carry out. Some recreational units are rated only to about 30m.
The more serious DPVs have a T-bar fitted to the rear so that the diver can straddle the scooter and rest on it. The smaller units are just pull-along systems, and these really cause aching of the shoulders and arms after a long dive.
This may not sound much but it can make the difference between a pleasant or uncomfortable dive.
Choice of options and accessories varies drastically and so does the price - more goodies, more money. There are different-sized motors, the more powerful offering more speed.
Type and power of batteries is always an important question, because the last thing you need is a power failure halfway through the dive. Some DPVs offer a gauge that reads the current battery power status throughout the dive, and I like this option.
You can have various types and numbers of lights, though remember that these are normally fed from the same battery that drives the motor.
For the more serious DPVs, the main manufacturers are Farallon and Aquazepp. Farallon is based in the USA but does have a UK distributor, which is Abyss UK. It offers a wide range of DPVs with lots of extras. Aquazepps are made in Munich, Germany and there is a wide selection of models from which to choose.
Remember finally that some of the bigger units are very heavy out of the water and will take up a lot of space on a dive boat, so you may not be the skippers favourite diver.
Its always worthwhile checking that he is happy to have a DPV on board!
Danger signs
I have been seeing and reading more and more about mixed-gas deep diving. I have also read that there are more accidents happening on these deep dives. Is trimix diving more dangerous than air diving
Darryl Proctor


Before we get into an air v trimix argument, lets look at the whole question of deeper diving and safety. In my opinion the deeper and longer you dive, the higher your chances of a problem occurring.
Deeper and longer diving means more decompression, whichever gas youre breathing. Spending longer in the water means more task-loading on diver, equipment and any other potential point of failure. So, yes, I do believe that deep diving is more dangerous than shallow recreational diving.
For many years air was our main gas source for the deeper part of a dive, which gave us all the problems inherent in a gas that contains lots of nitrogen.
Nitrogen is an inert gas that loads itself into the body tissues and to release it safely we have to carry out decompression stops. It is also a gas that is highly narcotic and so creates a big problem for deep divers.
There are various symptoms of nitrogen narcosis and Im sure youve suffered from some of them if you dive deeper than 30m - even shallower for some people.
One of the most frightening experiences you can have as a trimix diver is watching air divers perform while suffering from narcosis. Their physical movements are slowed right down and their brain cant function effectively enough to carry out the simplest task. Many cant even remember a large part of the dive once back on the surface. For me, this is the biggest problem with deep air diving and one reason - though not the only one - why more accidents are happening on deeper dives.
We solve this problem by getting rid of all or some of the nitrogen in the mix to reduce this narcotic effect. Trimix contains oxygen as our life-giving gas, a reduced amount of nitrogen and the balance gas becomes helium, which is far less narcotic than nitrogen. Helium is still an inert gas and we do need to carry out decompression, sometimes longer than air decompression.
We can do a simple calculation to find out how much nitrogen to put in the mix to have the Equivalent Narcotic Depth (END) of a shallower air dive. For example, I can dive to 80m and plan to have an END of 30m or less if I wish. The less nitrogen I put in the mix, the less narcosis I suffer, but this nitrogen is replaced with helium and the more of that I put in, the longer the decompression schedule becomes.
I find that carrying out deeper dives with my brain functioning as efficiently as possible (a challenge in my case!) is far safer than the alternative.
Your question: Is trimix diving more dangerous than air diving is not just about the type of gas used. Many divers are carrying out dives far in excess of their capabilities and before entering the water should ask themselves: Am I experienced enough to carry out this dive
Build up to the deeper dives slowly, gaining gradual experience of longer deco-stop times. Be comfortable with yourself and your equipment - you should feel relaxed and at one with the underwater world at all stages of a dive.