JackKit

Jack Ingle is the BSAC's 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.
BETWEEN DEVIL AND DEEP BLUE SEA
Youre doing a deco dive, and just as you're leaving the bottom your buddy passes out and you need to take him to the surface. How much deco do you dare blow off before you decide you have to inflate his jacket and hope the skipper sees him at the surface, otherwise youll be bent and maybe even dead
It struck me that I might face this situation some time, and would have to consider the level of surface support and how conservative my deco plan was. But still, it's a really nasty decision to make. I'm interested in your views.
Roger Harvey

I can't give you a definitive answer to this question. It's the type of scenario many divers run through to work out what they should do in an emergency. They might come up with the right thing to do, whatever that is, but will they actually do it if and when a genuine emergency arises
Picture the situation. You have completed the dive, your buddy lapses into unconsciousness, and you know that if you lift him to the surface you might both get decompression illness. If you inflate his jacket or wing to send him to the surface, he will very likely get a burst lung or at least DCI, and how do you know whether the boat will see the casualty on the surface
If you leave the casualty in the water in this unconscious state, he will very likely drown. What a situation! I cant answer it and nor will you be able to until the day it happens. Im afraid it will then be a split-second decision and it will be based on what your heart tells you needs to be done.
I realise this is not what you wanted to hear, but some questions have no pat answers. The scenario you raise should serve to make us think about our dive planning, practical skill improvement and safe diving practices, to ensure that we dont ever get into such situations.
Can I fake table-dives on my computer
A conundrum concerning my dive-planning has me perplexed. I want to be able to plan my deco-stop dives on paper but avoid bending my dive computer, which is a Suunto Solution Nitrox. Are there any tables or maybe even deco software that would let me more or less mimic on my dive computer the performance on paper Mimicking is not really that high on my wish-list, but I want to avoid bending the computer because I want to keep its dive-log capability.
Steve Orrell


That certainly is some conundrum, Steve. I can answer the question but probably not in the way you want.
Lets identify how a dive computer differs from hard-copy tables, or even decompression software. Both hard-copy and computer-generated tables assume that you will be at maximum depth for the total bottom-time you have planned and, using this information, they calculate the decompression schedule required.
When it comes to the dive itself, the diver is unlikely to be at maximum depth all the time, and the computer calculates the deco schedule for the varied depths and real time to which he is exposed. Most dive computers give a shorter decompression penalty than hard-copy tables, making it very difficult, if not impossible, to plan a deco-dive using both systems.
However, some divers do use both, to provide pre-dive planning information and a tool to give them all-important redundancy. If you use only an air or nitrox computer to calculate your deco schedule, if anything goes wrong with that instrument on the dive you wont know what decompression you should carry out.
One answer is to carry two computers. Other divers pre-plan the dive using a hard-copy table or a deco software package so that they know what schedule they will have to carry out. And many technical divers use a pre-planned deco schedule written on a slate with stop depths and run-times alongside a dive computer to calculate decompression throughout the dive and get the best of both worlds.
Computers, tables and decompression software might all use different algorithms, and even if they use the same one, various other factors can be programmed into the computer.
Finally, dont forget that a deco schedule is only a mathematical calculation and cannot take into account your personal physiology and current fitness.
My advice is, always plan your decompression schedule using a table or software package with which you are happy, and carry a computer as well.

Give me a G
I wonder if you can settle a point of information. Helium/air mixtures raise the pitch of sound, but by how much I maintain that a note at middle C (on the piano) will be raised to G, an octave and a half above. Is this correct
E Palfrey


Divers using gases under pressure certainly have a problem with their voices, should they need to use them.

Breathing helium tightens their vocal cords and makes them sound like high-pitched cartoon characters - the Chipmunks, if youre old enough to remember them!
This isnt a problem if youre using standard scuba equipment, because we dont try to talk to each other via sophisticated communication systems. I tend to shout at people through my second stage, and sometimes it works!
However, divers using full-face masks with communication systems to talk to each other, or to the surface-support team, do have this problem. Its possible to understand what the diver is saying, but quite funny listening to the squeaky voice at the other end.
This also happens in recompression chambers, where the divers communicate with the operator via communication systems.
As to the actual pitch, the octave and all the other operatic details, I wouldnt have a clue. As my music teacher told me many years ago, Im tone deaf.
However, next time Im sitting in a recompression chamber with Mr Pavarotti, Ill carry out a full-blown experiment and let you know.

Im after argon
Where do people get argon for their suit inflation Do they get it from a dive shop, and if so, which ones
Ben Field


Many technical divers use argon as a suit-inflation gas to maintain good body temperature levels. Argon is denser than air, and certainly helium, which means that it has more molecules to retain heat. It is usually carried by the diver in a separate small cylinder attached to the main set via a feed hose to the suit direct-feed.
A note of caution if youre planning to use argon: make sure that only a suit-inflator hose is attached to the cylinder.
I have seen divers using a standard regulator which has the suit-inflation hose and also still has the second stage attached. Argon is an inert gas with no oxygen content, and if it was breathed by mistake because the diver switched to the wrong second stage, the outcome would be fatal.
I add this warning because an incident occurred in the USA in which a child picked up his fathers mini diving cylinder and jumped into the swimming pool with it. It was an argon cylinder, and the child died.
Argon is supplied by gas companies such as BOC, Linde and Air Products to retail outlets such as dive stores which pump gas. Dive shops specialising in the technical diving market do keep a small quantity, but if your local shop has no argon, Im sure it would be willing to get some in if you asked.
It isnt expensive, and when diving in northern European waters anything that helps keep us warm is worthwhile.
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