When I was first certified on nitrox a long, long time ago (!) I routinely drove from the English Midlands to the south coast for a day's diving, then drove back again. Because the diving was totally dependent on tides, this often meant beginning my 3 hour drive in time to get on a dive boat leaving at 7am. The diving day was usually done by 6pm or so, and we used to gather in a local hostelry for a meal and a drink or two, and to share some "there I was" stories. Often I wouldn't get home until 1am or later. Only two dives per day, but the first was usually to 150ft or so, often on a twinset, and the second would typically be to 70 or 80 ft. Dives were generally 60-90 minutes. So, by many people's standard quite hard core diving.
I started this regime just diving air, and on several occasions I was forced to stop the car on the way home for a couple of hours' sleep before I could continue. Rarely would I ever unload the car when I got home, but I'd leave it till the next day and hope that a potential thief would be put off by the damp dank smell!
Then I started using nitrox, and the difference was profound. I'd take down a side sling of 32% or 36% for use on the first dive when I was shallow enough. I still used my air computer so was underwater for the same time, but I felt an awful lot better when I surfaced. In those days we didn't have lifts to get out of the water on (they're almost universal now) and I was really concerned about the tremendous effort needed to haul a twinset plus a sidesling, plus a very heavy drysuit and an enormous amount of lead. There weren't always people to help, and when the sea was rough (pretty common) it was very arduous. Once I started using nitrox this became much easier.
The second dive would normally be on nitrox, ideally 36%, and despite the beer I had with my meal and the very late start for the return journey I always thereafter cleared out the car and rinsed all the gear when I got back. To me there's no question about it - nitrox makes you feel MUCH fresher after a day's hard diving.
Some comments on statements made. I don't have a problem using or having someone else use an air computer with nitrox. Why is this undesirable?
When I teach nitrox, I impress upon my students that once they're kitted up and ready to go, there's only one difference between nitrox and air diving, and that's the maximum acceptable depth. I ask people what their maximum depth is for the forthcoming dive, and I expect two answers (for 1.6 and for 1.4). If I don't get those answers I read those divers the riot act there and then! For Americans it's actually a bit easier to remember than it is for people using metric depths - for 36% the two depths are roughly 90ft and 110ft, and for 32% they're (again roughly, but pretty close and erring on the side of conservatism) 110ft and 130ft. Very easy to remember. This information must be in your HEAD when you jump into the water, not just written down somewhere and certainly
not written on the EANx label stuck to your tank, where of course it's completely inaccessible to you during the dive.
As to walls, if divers can't be relied on to remember and act on the maximum depths dictated by the mixes they're diving, AND to have the buoyancy control to make this easy and dependable, then they shouldn't be on the wall at all. In fact, they shouldn't be diving at all until they've got their skills up to an acceptable and safe level.
A couple more points having just read Jerry's excellent post. First, if you've had decent training (both formal and by example from your peers) you'll have learned long ago how to deploy and use a DSMB. I don't call them "lift bags" because they're completely different in construction and designed to do different jobs. In England most serious divers carry two DSMBs and two lift bags on every dive, with a separate reel for each. The red DSMB is for use on every ascent, the yellow DSMB is to announce to the people up top that you have a problem and (are likely to) need help, the first lift bag is to raise anything on the bottom that you decide would look good on your mantlepiece, and the second lift bag is for when you find that the first doesn't have enough lift to overcome the stiction
The advanced nitrox course is IMO badly named, because the nitrox bit of it is relatively marginal. It should instead be called "Intro Tech", as it principally covers equipment management and handling and scenarios you have probably never experienced before.
Caution needs to be employed when using lift bags (for their intended purpose). Unless you've planned a recovery dive, you probably have about the right amount of breathing gas for your dive, plus a safety margin. Once you start filling a lift bag it's remarkable how much gas it uses (you can work it out - there you are, your homework!). If you then need to resort to the second, that doubles what you use. If, as a friend of mine found, the two lift bags are still not enough you might be tempted to start using your DSMBs. He did, and just after he'd started filling his second DSMB he ran out of back gas. He was at the time on the bottom at about 270ft, quite alone, and with his next available gas 35%. That doesn't start becoming usable until around 115ft, so he had a fair way to go up before he could switch to it. He did it, skipping quite a few deco stops along the way, but then of course ran out of 35% long before he'd acquitted his (mentally recalculated) deco obligations. So up to (what depth?) so he could use his 80%. He couldn't of course send up his yellow DSMB or indeed any signalling device as he'd left them all on the bottom attached to the brass porthole he'd inadvertently left for the next diver (along with a nice present of four flotation devices and four reels). There was a fair current that day and the dive boat was tied into the wreck, so when he finally bolted for the surface, out of gas but still with 50 minutes of deco obligation, he was 3/4 of a mile away in a grey and choppy sea, clad all in black. Remarkably, because no-one was due to surface yet, the skipper happened to be looking in that direction and spotted him. By the time I surfaced the boat was back over the wreck and the chopper was on its way, and in due course it whisked him off to a chamber somewhere. Even more remarkably, he was back diving again within a month. He did something stupid on a CCR later, I heard, got away with it again, but then gave up diving. I think he took up a nice safe sport like base jumping or motorcycle racing.
Edited by peterbj7, 27 December 2009 - 08:37 PM.
