Posted by Karl on June 04, 2002 at 08:52:40:
In Reply to: Re: Yet, another Nitrox Question posted by Steve on June 03, 2002 at 22:45:55:
"Hopefully an EAN diver knows the MOD and dives accordingly."
That pretty much says it all. Nice quote, Steve.
The whole purpose of the nitrox class is to teach the additional reasonable limitations of diving with nitrox. The main limitation is MOD.
The whole purpose of nitrox diving is to add an additional safety factor to prevent N2 DCS. You still need gradual ascents, and safety stops, and you still need to stay conservatively within NDL limits, and to drink a lot of water and stay hydrated before and after your diving. THEN having done all that, nitrox will off-gass the N2 in your blood and body tissues better than air in your tanks would, so it is "safer."
EAN32 is also one more good reason not to dive deeper than 110 fsw. Its too bad that the dive manuals for OW1 and AOW teach that air is safe to 130 fsw. That may be true in the warm swimming pool-like waters of the East Coast. But not in the cold chilling waters out here in California.
Narcosis is the other good reason not to dive deeper than 110 fsw out here in California, whether on nitrox or air.
Now that my tech training is over, I have a set of benchmarks that I use when I am diving in cold water. It is not exactly DIR, but it is similar:
110 fsw on EAN32 for all typical recreational diving.
150 fsw on EAN25 for technical applications with a tech buddy, like a shipwreck go-and-see dive.
trimix beyond 150 fsw for technical applications with a tech team of 3 or more.
Nitrox is great for the shallower end of all diving, but anyone using it needs to adhere to the depth limits it imposes.
When can/will oxygen toxicity happen? The techical literature states it is possible anywhere beyond 1.2 ppO2 after varying intervals of time, and likely after 45 mins at a ppO2 of 1.6, and very likely after 2 mins at a ppO2 of 2.0 or higher.
EAN32 reaches a ppO2 of 1.2 at 91 fsw. Ox tox is unlikely at this depth, but possible given time.
Ordinary air has a ppO2 of 1.2 at 156 fsw. So ox tox is possible on a deep air dive, without nitrox.
In addition, CO2 loading from exertion before or during diving can increase the likelihood of ox tox over a shorter interval of time for any ppO2 of 1.2 or above.
The dive boats of California are a great way to see fantastic underwater vistas around here. Most of the boat captains and crew put a lot of energy into diving safety and into reminding divers of the safety rules. Mentioning the depth limits for nitrox, if your boat offers nitrox, would be a good thing to do, on every boat trip, during the orientation when the boat is outbound and the captain or divemaster is addressing all the divers.
I think it would be a good idea for dive boat captains to instruct their crew to remind anyone opting for one of the boat's nitrox tanks, or getting a nitrox fill on the boat, to limit their depth to 110 fsw. Reminders never hurt.
Having said all that, if there is a diver on your boat, and he/she is stupid and unlucky, there are a host of things that could make him/her die while on scuba.
As for me, I have always been very lucky. :)
And additional dive training, like nitrox, and/or tech, makes you smarter! :)