Nitrox workshop dings - Divers Alert Network

Rubicon Foundation Archive (http://rubicon-foundation.org)Richardson and Shreeves: Overview of PADI Enriched Air Diver Program• Within the realm of no-decompression diving with enriched air, there's little need forgreater exposure. Divers who stay within 1.4 atm and make progressively shallowerdives will not often find themselves limited by oxygen exposure, even with the existinglimits.• From a training and educational viewpoint, building in the two-hour credit wouldcomplicate the table and field use. This increases the possibility of error with little realbenefit in the majority of diving situations.Although the NOAA limits have been widely accepted within the technical, and scientificdiving communities, DSAT could not simply accept the limits on that basis alone. Of particularconcern were the old U.S. Navy limits, which are more conservative.US Navy Oxygen Limits for single exposuresPOj in atm1.0111.21.31.41.51.6Time240 min120 min80 min60 min50 min40 min30 minAnother concern was that much of the testing that led to the NOAA limits was conductedusing pure oxygen closed circuit scuba. Tests using semiclosed nitrogen/oxygen mixes suggestthat the presence of nitrogen might contribute to the onset of oxygen toxicity.On the advice of Dr. Des Gorman (pers. comm.), DSAT compared the NOAA limits againstthe existing body of manned test dives of oxygen exposure, and against the published analysis ofthose tests by Professor Kenneth Donald of the Royal Navy. Donald (1942) is widely regardedas a leading authority on hyperbaric oxygen exposure, having begun ground-breaking researchinto this field in 1942. In particular, DSAT (1992) compared the NOAA limits to Donald's dataand comments in his work.Based on Dr. Donald's findings, the NOAA limits employed in the Oxygen Exposure Tableseem reasonable and well within the limits of manned tests. In particular:1. The limit of 45 minutes at 1.6 atm seems very conservative and appropriate. Most of thepublished body of testing oxygen exposure involves PO2S greater than 1.6 atm. Thismakes extrapolating to lower PO2S difficult, but there is a significant (approximate)overlap at the range edge that supports the NOAA limits. Tests by Donald using pureoxygen at 25 fsw (PO2 1.75 atm) resulted in few cases of oxygen toxicity, and with onlyone exception, those that did occur involved underwater exercise and durations beyond45 minutes. Further, Donald reports that "The Admiralty Experimental Diving Unit wasunable to demonstrate oxygen poisoning in the range of 0 to 20 fsw." Using pureoxygen, this is the PO2 range of 1.0 to 1.6 atm. Against this data set, a shorter time limitof 45 minutes at the lower PO2S limit of 1.6 atm, certainly seems reasonable. With theemphasis on a maximum PO2 of 1.4 atm, the exposure in the DSAT table seems53