Weir's The Martian.

[ka9q]

Not if it's pure hydrogen. Get rid of all that nasty wasty oxygen!

You may think you're joking, but hydrogen/oxygen mixtures (hydrox) and hydrogen/helium/oxygen (hydreliox) mixtures have been used in deep sea diving. As you descend, the O₂ concentration has to be reduced to keep the ppO₂ constant; too high, and you get oxygen toxicity.

Hydrogen has a famously wide flammability range, but it's not 0-100%; it actually tops out at around 96% in pure O₂. So as long as you're deep enough to keep the O₂ concentration well below 4%, you're safe.

[bknight]

You may think you're joking, but hydrogen/oxygen mixtures (hydrox) and hydrogen/helium/oxygen (hydreliox) mixtures have been used in deep sea diving. As you descend, the O₂ concentration has to be reduced to keep the ppO₂ constant; too high, and you get oxygen toxicity.

Hydrogen has a famously wide flammability range, but it's not 0-100%; it actually tops out at around 96% in pure O₂. So as long as you're deep enough to keep the O₂ concentration well below 4%, you're safe.

Being a former scuba instructor and having no experience with either of those mixtures, it seems likely that sufficient recovery time would be necessary to allow all the H₂ and He to evolve from tissues back to the lungs and then exhaled.  I always wondered why so many people wanted to deep dive nothing much living from 60-90 foot depth.  I guess being an instructor made me more conscious of the dangers involved.

[ka9q]

it seems likely that sufficient recovery time would be necessary to allow all the H₂ and He to evolve from tissues back to the lungs and then exhaled.

Well sure, long decompression schedules are still required. When using hydrogen at depth, during the ascent you switch to helium well before the O₂ percentage would rise to the explosive level, and the time spent decompressing would flush any residual hydrogen so there would never be an explosive mixture.

[Bryanpoprobson]

Being a former scuba instructor and having no experience with either of those mixtures, it seems likely that sufficient recovery time would be necessary to allow all the H₂ and He to evolve from tissues back to the lungs and then exhaled.  I always wondered why so many people wanted to deep dive nothing much living from 60-90 foot depth.  I guess being an instructor made me more conscious of the dangers involved.

As an instructor you will appreciate the following stories from my time as a BSAC instructor (stuff this PADI garbage )..

A guy turns up at our branch of the BSAC name of Dave, he says he is a "Level 3" qualified diver just moved to the area and would like to join our branch. OK bring your qualification record along for us to have a look at, no problems.

His diving record just looked wrong to me, no proper stamps and all signed by the same hand.. Still, without calling him a barefaced liar we inducted him into the branch. I was taking a class on high level entry techniques i.e entering the water in full gear from "say" a harbour wall. I demonstrated the correct technique from the 10M board at our pool. Dave tries it, enters the water, two fins emerge going in different directions, he comes up with his cylinder twisted 90degs on his back and his mask around his neck.. So we decide to test him, he doesn't even know the basics..

Anyway after 3 months winter pool training, we get him up to some sort of better standard and go on a real open water dive, but nobody wants to be his dive buddy! Roger, the clubs senior instructor decides to dive with him. As chance would have it, Roger gets into problems, when his demand valve (regulator) suddenly stopped functioning. Because of his lack of faith in Dave he didn't want to buddy breath with him. (This pre-dated the buddy mouthpieces that are commonplace now!). Roger decides to do a free ascent, as the clubs most experienced diver, this does not pose him a real serious problem. He gives Dave the throat sign, indicating he is having breathing problems and indicates that he is going up.

I had finished my dive and was sitting on the club boat, unaware of the dramas below. Dave in a panic has fully inflated his ABLJ (remember them ?). I was casually watching the water when Dave emerges like a Polaris missile, his fins came clean out of the water, how he never suffered a major embolism I will never know.. That was his first and last dive with the club..

and now back to "The Martian!" Sorry for the hijack.

[bknight]

As an instructor you will appreciate the following stories from my time as a BSAC instructor (stuff this PADI garbage )..

Different strokes for different folks!

A guy turns up at our branch of the BSAC name of Dave, he says he is a "Level 3" qualified diver just moved to the area and would like to join our branch. ...

I had finished my dive and was sitting on the club boat, unaware of the dramas below. Dave in a panic has fully inflated his ABLJ (remember them ?).

We had old fashioned buoyance compensators(70's)

I was casually watching the water when Dave emerges like a Polaris missile, his fins came clean out of the water, how he never suffered a major embolism I will never know.. That was his first and last dive with the club..

and now back to "The Martian!" Sorry for the hijack.

That was one of the last tests we did in open water was an emergency ascent.  The had to do it correctly to be certified.  One of the instructors was "on top" of the diver incase (s)he panicked.  I can remember "holding down" panicked divers, giving my buddy mouth pieces when necessary and slowly ascending, stern lecture, try again routine.
Ok back to Martians, again.

[Zakalwe]

  I always wondered why so many people wanted to deep dive nothing much living from 60-90 foot depth.  I guess being an instructor made me more conscious of the dangers involved.

[thread drift]
If you haven't already read this book, then I can thoroughly recommend it:
http://www.amazon.co.uk/Diving-Into-Darkness-Story-Survival/dp/0312383940

It's a terrible story of how quickly things can go fatally wrong in technical diving, but also a brilliant insight into the minds of the people that are compelled to push the envelope. As a total outsider to diving such as myself, it is also a fascinating peep into the technicalities involved.

[/thread drift]

[bknight]

[thread drift]
If you haven't already read this book, then I can thoroughly recommend it:
http://www.amazon.co.uk/Diving-Into-Darkness-Story-Survival/dp/0312383940

It's a terrible story of how quickly things can go fatally wrong in technical diving, but also a brilliant insight into the minds of the people that are compelled to push the envelope. As a total outsider to diving such as myself, it is also a fascinating peep into the technicalities involved.

[/thread drift]

If you saw the bent arm of our lead instructor, you would understand the dangers associated with diving, and that was "only the bends".  To have gasses expand in organs and tissues because of to rapid decompression was UGLY.  We had an old Navy training video that was shown to students showing the complications.  But having said that the scenery from 20' down was unbelievable well worth the time and effort to train and then dive them.
I guess the mind set to dive deep is rather akin to climbing mountains, driving/flying very fast has the same endorphins.

[Zakalwe]

If you saw the bent arm of our lead instructor, you would understand the dangers associated with diving, and that was "only the bends".  To have gasses expand in organs and tissues because of to rapid decompression was UGLY.  We had an old Navy training video that was shown to students showing the complications.  But having said that the scenery from 20' down was unbelievable well worth the time and effort to train and then dive them.

Oh, I understand them alright. A chap that I knew a few years back got badly bent after a dive at Scapa Flow. He did two heavy dives in a day and pushed his luck on his last deco. He got the bend in his spine and lost the use of his legs. Luckily he was diving in an area that has some of the best treatment centres that you will find anywhere (due to the North Sea rigs) and was airlifted to a deco tank in Aberdeen. It took him a week to regain use of his legs....a fair bit longer before he didn't need adult nappies. Not a nice experience for him at all and it affected his mental outlook quite badly. He used to live for diving and it was a massive loss for him being told never to dive again.

I guess the mind set to dive deep is rather akin to climbing mountains, driving/flying very fast has the same endorphins.

I'd agree with that. it must be the thrill of going where very few have gone before. There's only a handful of people alive that have gone deeper than 250 metres. Something like 10% of people that have dived to that depth have had no injuries and 50% of them have died. They are pretty damning statistics.

[ka9q]

I guess the mind set to dive deep is rather akin to climbing mountains, driving/flying very fast has the same endorphins.

Or maybe it's all that N₂ dissolved in body lipids...

[bknight]

I guess the mind set to dive deep is rather akin to climbing mountains, driving/flying very fast has the same endorphins.

Or maybe it's all that N₂ dissolved in body lipids...

Well something must drive them.  I personally don't have all those thrill seeking juices. A fast ride down a zip line is about as far as I go.

[twik]

I remember some of my friends coming back from a dive, all exuberantly proclaiming "It was wonderful! We didn't die!"

For some reason, that sort of endorsement never made me want to take up the sport.

[bknight]

I remember some of my friends coming back from a dive, all exuberantly proclaiming "It was wonderful! We didn't die!"

For some reason, that sort of endorsement never made me want to take up the sport.

Well I will testify it is wonderful and not because no one died.  In fact on all the dives I have been on, there were no injuries as everyone took the training to heart.  I'm not saying it wasn't a dangerous environment, but with caution the sites, animal and plant life is hard to describe, wonderful does an adequate job though.  For young people (to me that is) I would highly recommend taking the training and then dive.

[Count Zero]

I remember some of my friends coming back from a dive, all exuberantly proclaiming "It was wonderful! We didn't die!"

For some reason, that sort of endorsement never made me want to take up the sport.

"If at first you don't succeed, skydiving is not for you."

[Zakalwe]

"If at first you don't succeed, skydiving is not for you."

"Its not the fall for 10,000' that kills you...its the stopping in the last inch."

[bknight]

"If at first you don't succeed, skydiving is not for you."

"Its not the fall for 10,000' that kills you...its the stopping in the last inch."

That will leave a mark that won't be easily healed.