Sas
Contributor
Jax,
I agree with your logic on this one, as I would also carry 40% in a pony and not simply air. Emergency's do not happen often so you basically carry a pony bottle just to carry a pony so you might as well give it a second purpose; the basic nitrox cert allows for up to 40% and at least some of the courses touch on using higher % mixes in order to accelerate decompression, which I am assuming you are doing. So you are getting 2 uses out of your pony bottle.
Why would you carry 40%? What if you are diving deeper than the MOD of 40%? You dump the gas before each dive?
Why would the bottle have two uses? What is the second use besides bail out? If it is for decompression then it's not an emergency gas source, it's a deco bottle.
Even at the recreational limit of 130 you (or your out of air diver) will not be exposed to a high enough PPO for a long enough duration to lead to OXTOX. A PPO of 1.4 is extremely conservative as it is, and you will definitely be at or below a PPO of 1.4 within 1-2 minutes as you will be heading to the surface. OXTOX is cumulative and not instant at recreational depths on recreational mixes (<40%). I disagree with the flaming going on around you using 40%, a minute's exposure to a PPO of 2.0 will not likely kill you, but drowning definitely will.
Why not just use air and remove the risk associated with diving at a pp0 of 2? How do you know how long it will take before you start your ascent in an emergency?
Also I don't see flaming, a few people being narky about post counts but not about Jax's question.