BSAC

 

"I am personally quite receptive to nitrogen rapture. I like it and fear it like doom. It destroys the instinct of life." Jacques-Yves Cousteau. The Silent World. p43

Narcosis will kill you because you don't notice the problem, because you are too slow recognising the problem, because your are too slow fixing the problem or maybe just because the problem does not seem to matter.

Let's start with the stories:

I was diving a 35 meter wreck with a buddy on OC Nitrox. He is a good competent tech diver. The wreck was on its side so when we made it back to the bow and exchanged signals that it was time to end the dive we were on a metal slope leading down to sand.
<me> <wind> he signalled.

<ok> I replied.
He produced a blob and started fiddling with it. It was a nice buddy self inflate. (I had one just like it hanging off my right hand wing D-ring.)

 

Fiddle. Fiddle. Turn. Twist. Rearrange. Pull. Straighten. Fiddle.

 

Finally he got it away but it had taken five minutes, I later checked for the flat bit on my computer dump, and he had slipped the best part of five meters down the side of the bow but we were on our way up. Back on the boat I asked him what the problem was. "What problem?" he replied.
It should have take maybe 45 seconds not 5 minutes. He was on Nitrox and I was on the rebreather with 20/30 trimix.

His brain was at about 30-32m and mine at 13-15 meters.

We were diving a 50m wreck out of Eastbourne. We're both on rebreathers and both on Trimix. It's a blob story again but my buddy had a new reel. He pulled out the reel and the blob separately. He tied a quick bowline onto the blob. The bowline fell apart.
Do it again. It fell apart again. He stopped. Slowly tied a bowline. This is a scoutmaster. He teaches this stuff. He knows what he is doing wrong. He told me he recited "the bunny rabbit comes..." he teaches cubs. The Bowline fell apart again. I tied it. We ascend.

He was on 20/30, his brain at 27 meters. I was on 18/40 brain at 20 meters.

I am at 60m and the rebreather gives a CELL ERROR. I do the DIL flush drill.

My buddy hears the bleeps and comes over to look. CELL ERROR again.

He signals <up> I reply <ok> and keep fiddling with the handset. I am locked into my drills.
<up> <ok>

<UP!> <ok>

I am grabbed and lifted to 55m.
I feel a fool <wipes brow> <up>. <ok> he replies.

Diving 20/26 so brain at 37 meters.

We are so careful to learn our drills and safety routines for tech diving but the weak link is always the grey stuff between the ears. I'd rather trust any piece of equipment than me because if I can think I can come up with a 'least worse' plan. If I can't think I'm dead. I won't solo dive where my END is much below 20 meters even if it does mean that I have to do a wodge of extra stops. (I know I shouldn't admit to solo on a BSAC forum but I book onto a lot of boats where I don't know anybody else and an unknown buddy who doesn't know my bail out or stuff could easily be worse than no buddy.)

On the rebreather helium is relatively cheap. I did a twelve dive trip to the outside of the outer Hebrides this year and cross filled the unit from my two 7L stages of 18/40 and 100% and went home with 90bar in each. 12 dives and the only fills I got from the boat was air for my suit bottle.

The downside of helium is the speed it gasses on. Deep stops are important and getting them right is too. We put a guy on a chopper out of Brighton when he missed 27 minutes with a rapid ascent. My friend, the scout master as it happens, picked him up from Gosport after recompression and the doctor said they saw no symptoms of DCI but recompressed him based entirely on his profile. "Thank goodness he wasn't on helium" the doctor said.
I wondered about that. Certainly missing 27 minutes of trimix deco would not be symptomless but would the mess up that lead to the rapid accent have happened? The diver could not account for it but it wasn't the suit, he flooded that to try and stop himself, the BCD, no this was a PADI instructor. No I think it was the back mounted counterlung of his Dräger semiclosed rebreather. The narcosis made him forget it and the suck down drills it needs.

Back when I was diving a nitrox twinset if I didn't write 'take photographs' on the slate below 40m it didn't happen. I'd come back with vague memories of a great dive and a deco profile that was spot on the nail but no pictures.

Perhaps I'm lucky that narcosis make me a bit of a procedure freak but as in the CELL ERROR case that isn't always good. What I see it do to everybody is that they stop multi-tasking. This is the trap. We handle the problem we're handling but in scuba they always come in droves. You can't drop accurate buoyancy control on a wall just because your BCD clips have come loose or something daft like that.

I now have two DIL cylinders for the rebreather. One contains 18/40 and the other 14/55 although I think I'll increase the helium in that one a bit next year. I have bail out tables for both of those in my pocket. I do all my diving on that. I do not dive air other than on OC in the pool.

Plus I have trained myself to use two computers and dive the most conservative but the are both set to minimum conservatism. Then I do the ascents slower than they ask for, I overrun the deeper stops and then add 20 to 50% to the shallow stop. The computers are there to give me shortest time to surface and if something really bad happens I can quote 'missed 10 minutes' from the least conservative and it's a realistic number not full of padding. I do the same drill every time, the slow ascent, the extra stops even if the computer thinks it's no stop. Worst case I'm doing the right thing by habit.

I like Helium.

Helium lets me remember a deep dive.

Helium means I get better pictures.

Helium means I will be more use to a buddy who has problems and far more use to myself if I have one.

As I said: "Helium - Because I'm worth it."

regards
NigelH