Breathe Nitrox, Dive an Air Computer?

In the September Undercurrent article "Gray Around the Gills," we suggested that older divers might want to breathe Nitrox while keeping their dive computers in the air mode. That suggestion brought the following response from reader Douglas Peterson:

"Whoops. Are you sure that you want to recommend setting your computer on air while diving Nitrox? I'm sure the 'gray gills' will appreciate avoiding the bends, but they'll probably get a bit pissed off when the convulsions from CNS toxicity drown them."

Sorry, Douglas, we should have been more specific. Using the typical sport diving Nitrox mix (32% oxygen) and staying within accepted sport diving depth limits (130 fsw), Nitrox is no more toxic than breathing compressed air.

Charlie Johnson, vice president of training for American Nitrox Divers Inc., confirms that diving 32% Nitrox on a computer programmed for compressed air would result in very conservative nodecompression limits (important to older divers since age increases susceptibility to decompression sickness). He also mentions that there have been no reported incidents of central nervous system toxicity when 32% Nitrox is used within the 130-foot depth range, where the partial pressure of oxygen does not exceed 1.6, established as a safe level by the National Oceanic and Atmospheric Administration. As Johnson points out, every Nitrox diver should have learned these limits when getting certified.

For an even greater margin of safety, NOAA recommends staying within a caution zone of 1.45 PO2, which would impose a depth limit of 116 fsw with 32% Nitrox.