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Yes. Very conservative, and another KEY point I'm not seeing above is this:
OxTox is NOT just a function of PPO2, but TIME at exposure. It's not like spending 2 minutes at 1.8 is going to cause OxTox, or even 10 minutes at 2.0 is unlikely to cause Tox. These key points are left out of basic Nitrox, and even Advanced Nitrox, and cause many people turmoil, when they feel like they must "Violate" the MOD to either make a rescue, or recover something which might put them at a very high PO2 (1.8 or 2.0 even)
My associate John Chatterton tells me that when he was becoming a commercial diver, he was put in a chamber, and dropped to a 2.0 PPO2 for 30 minutes to see if they toxed. He says, "If you toxed, you couldn't be a commercial diver. If you didn't, you were good." Obviously John didn't tox, since he was a commercial diver in NY for many years prior to the Shadow Divers days. Also, 1.6 PPO2 for Air is about 218 feet.
So... Remember this the CNS Clock for 1.6 PPO2 is 45 minutes on a single dive and for a 24 hour period. For most people, 10-15 minutes won't cause tox. Most of John's dives on the Uboat were less than 25 minutes of bottom time, at depths above 215. Brett Gilliam's record breaking dives were bounces.
If you ask me... The reason 1.6 is the MOD is because your clock ticks off very quickly at that PO2, which could greatly effect your subsequent dives, or an extended dive with longer decompression times.
For more information on CNS Ox Tox... read Steve Lewis' (Doppler) article here on SB. http://www.scubaboard.com/forums/content/357-daily-limits-cns-oxygen-toxicity.html
Absolutely right.... In the Jane Orenstein tech diver student death, Jane breathed pure O2 accidentally ( due to what many would call the negligent instructor watching her) from 100 feet to 20 feet, through the 100 to 50 foot traverse, then 50 foot stop, 40 foot stop, 30 foot stop, and then when headed for 20 feet, she blacked out and sank, with the instructor just watching her ( he was her buddy also). Point being, she was on pure O2 at 100 feet, and did not instantly die.