Nitrox workshop dings - Divers Alert Network

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Rubicon Foundation Archive (http://rubicon-foundation.org)Richardson and Shreeves: Overview of PADI Enriched Air Diver Programprogram. Symptoms include burning in the throat and chest, coughing and shortness of breath.Pulmonary oxygen toxicity is more of a concern in technical and commercial dives that requirelong decompression stops using pure or high amounts of oxygen (50 percent or more).Nonetheless, divers are advised to discontinue diving for a few days if symptoms areexperienced that could indicate pulmonary oxygen toxicity.Managing Oxygen ExposureThe high oxygen partial pressures experienced with enriched air must be kept within limits orthey pose serious hazards to the diver. The higher the partial pressure, the shorter you can safelybe exposed to it. Therefore, you must track your oxygen exposure with tables much as you trackyour nitrogen exposure. Oxygen exposure limits are independent of depth; they relate entirely topartial pressure. The oxygen partial pressure is .80 atm at 10 metres/33 feet using EANx 40.Using EANx 36, you have the same partial pressure at 12 metres/40 feet. Your oxygen exposurelimits are the same for both dives.The maximum oxygen partial pressure for PADI enriched air diving is 1.4 atm. 1.4 atm is therecommended maximum because it keeps you well within established oxygen limits appropriatefor recreational diving. Planning a dive within 1.4 atm partial pressure also provides for marginof error. Some evidence suggests that as oxygen partial pressure exceeds the 1.3 atm to 1.4 atmrange, the EAD concept becomes less reliable. Staying within 1.4 atm partial pressure reducesthe likelihood of problems with this. If the planned dive depth would exceed 1.4 atm, eitherswitch to an enriched air blend with less oxygen, or plan a shallower dive.The contingency oxygen partial pressure limit is 1.6 atm. PADI discourages planning diveswith a partial pressure this high because there is no room for error. Partial pressures between 1.4and 1.6 atm should be considered a margin for error only. Divers at work have had oxygentoxicity (convulsions) near 1.6 atm while at work. Exceeding safe oxygen limits poses a highrisk of oxygen toxicity.Dive Planning Tips for PADI EANxTreat the entire dive as though it were made at the deepest depth/highest partial pressure.Although NOAA limits don't specify minimum surface intervals, and there is no measurablecredit for surface interval, it's recommended that you have a surface interval of at least an hourbetween enriched air dives whenever possible, especially if you exceed more than 50 percent ofallowable exposure. This is believed to further reduce the likelihood of oxygen toxicity.Do not exceed 100 percent of allowable exposure in 24 hours. Doing so, even at loweroxygen partial pressures, puts you at risk of oxygen toxicity. It is recommended for extraconservatism that you limit your exposure to 90 percent. If your planned dives would cause youto approach or exceed oxygen exposure limits, switch to an enriched air with less oxygen and/orplan your dives to shallower depths. Maximum allowable dive time is always the shorter of theno-decompression time or remaining oxygen exposure time. Always check both.51
Rubicon Foundation Archive (http://rubicon-foundation.org)Lang (ed.): DAN Nitrox Workshop, Divers Alert Network, November 2000After a dive in which you were to accidentally exceed the contingency oxygen partialpressure limit of 1.6 atm, your oxygen exposure is considered 100 percent. It is recommendedthat you do not dive for at least 12 hours. The Oxygen Exposure Table allows you to track youraccumulating oxygen exposure when making repetitive and multilevel dives with differingoxygen partial pressures (this is sometimes called the "oxygen clock"). Because people differ intheir physiology, no table, computer or other method of measuring oxygen exposure canguarantee that oxygen toxicity will never occur, even within accepted oxygen limits. In rareinstances, oxygen toxicity has occurred within the NOAA limits. Stay well within oxygen limits.It's easy to keep your oxygen partial pressure well within 1.4 atm by using an enriched air withless oxygen and/or by limiting depth.Analysis of Oxygen Exposure Limits for DSAT Oxygen Exposure TableAgainst Existing Database of Manned Oxygen Test DivesThe PADI Enriched Air Diver course makes use of a new Diving Science and Technology(DSAT) Oxygen Exposure Table, distributed by PADI. This table is based on the commonlyaccepted National Oceanic and Atmospheric Administration (NOAA) single exposure limits:NOAA Oxygen Limits for single exposuresPO 2 in atm0.60.70.80.91.01.11.21.31.41.51.6Time720 min570 min450 min360 min300 min240 min210 min180 min150 min120 min45 minThe DSAT Oxygen Exposure Table allows the user to convert time at particular PO2S to apercent of allowable exposure. Exposure in 24 hours may not exceed 100 percent. Thismethodology makes it practical in the field to track exposure during repetitive dives, multileveldives, and when using more than one blend of enriched air.NOAA limits extend total exposures for PO2S from 1.6 atm through 1.1 atm with a minimumsurface interval of two hours between exposures. The DSAT Oxygen Exposure Table doesn'tallow this additional exposure time and limits 24-hour exposure to the single exposure limits forthe following reasons:• The PADI course emphasizes keeping PO2S below 1.4 atm, which is an appropriatelyconservative level for recreational divers. The significantly reduced time at higher PO2Sencourages this, plus maintains conservatism if 1.4 atm is exceeded.52
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Nitrox workshop dings - Divers Alert Network

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