- Equivalent air depth
In
technical diving , the equivalent air depth (EAD) is a way of expressing the narcotic effect of specificbreathing gas mixtures that containnitrogen , for examplenitrox andtrimix . [cite journal |last=Logan |first=JA |title=An evaluation of the equivalent air depth theory |journal=US Naval Experimental Diving Unit Technical Report |volume=NEDU-RR-01-61 |date=1961 |url=http://archive.rubicon-foundation.org/3835 |accessdate=2008-05-01 ] [cite journal |author=Berghage TE, McCraken TM |title=Equivalent air depth: fact or fiction |journal=Undersea Biomed Res |volume=6 |issue=4 |pages=379–84 |year=1979 |month=December |pmid=538866 |url=http://archive.rubicon-foundation.org/2835 |accessdate=2008-05-01] [cite book |title=DAN Nitrox Workshop Proceedings |author=Lang, M.A. |year=2001 |publisher=Divers Alert Network |location=Durham, NC |pages=197 |url=http://archive.rubicon-foundation.org/4855 |accessdate=2008-05-02 ]The equivalent air depth is the depth of a dive when breathing
air that would have the samepartial pressure ofnitrogen as the breathing gas in question, which has a different proportion ofnitrogen and is being breathed at a different depth. So, for example, a gas mix containing 40% nitrogen being used at 60 metres (200 feet) has an EAD of 25 metres (83 feet).The equivalent air depth can be calculated, for metric depths, as follows:
:EAD = ( ( (Fraction of N2 × ((Depth in metres / 10) + 1)) / 0.79 ) − 1) × 10
Working the earlier example, for a gas mix containing 40% nitrogen being used at 60 metres, the EAD is:
:EAD = ((0.4 × (( 60 / 10 ) + 1) / 0.79 ) − 1) × 10
:EAD = ((0.4 × 7 / 0.79 ) − 1) × 10
:EAD = ((2.8 / 0.79 ) − 1) × 10
:EAD = (3.544 − 1) × 10
:EAD = 25.44 metres
So at 60 metres on this mix, the diver would feel the same narcotic effect as a dive on air to 25 metres.
The severity of
nitrogen narcosis depends on the proportion of nitrogen in the gas mix and the depth of the dive. Nitrogen narcosis is a major factor limiting the depth of dives where air is breathed. Air consists of 79% nitrogen. Other gas mixes, such astrimix ,heliox andnitrox , contain different proportions of nitrogen.Oxygen Narcosis
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