Howard, we are in violent agreement about estimating the risk of a seizure using the generally accepted tables for exposure. My understanding is that deco chambers have a slightly different risk scenario because you are not going to spit your mouthpiece out and drown if you have a seizure. Likewise, if you are in a chamber and suffering from DCS, the treatment plan weighs the risk and consequences of toxicity against the risk and consequences of prolonging your exposure to DCS. Is that true? If so would that play a part in a deco chamber being willing to dial the PPO2 up to 2.0?
Actually. What do you think the Exposure table leads to (tells us)? The simple explanation that is most often left out of basic nitrox courses is that - If you exceed the limits set forth on the
tables, you risk the increased danger of oxygen toxicity (seizure) hits; so it's not just black and white like the standard dogma says, "don't exceed 1.6 PPO2 - period - EVER - or you will die"
My point is. The current training method uses scare tactics to scare people from exceeding 1.6 PPO2 because of eminent (immediate) danger. In reality, there is time at that level of exposure, or even greater levels of exposure to make an educated decision as to what actions need to be accomplished, and weigh the risks and lack there of to exposure yourself to high ATA's of Oxygen Partial Pressure.
Let's say you're out of back gas for some reason, and you're at 100 feet. All you have is a bottle of 50% for deco. Do you breathe it and breathe O2 at 2ATA's, or do you blow and go up to 70' rapidly; right away so you can stay below the magic 1.6 ATA's?
Certainly there is no risk of drowning in a chamber, but what is the % of incidence in chambers where people actually do tox from oxygen? (I don't know).
When I took my rebreather training, one of the students was a hyperbaric doc, and he told me that it's extremely rare for ox tox in the chamber, and more often than not it's a hypoglycemic event (convulsion), rather than a hyperoxic event. I don't have numbers on this, so maybe someone else may know more.