Henrik Brautaset Aronsen subsurface at henrik.synth.no
Mon Dec 9 08:40:06 UTC 2013

```On Mon, Dec 9, 2013 at 4:49 PM, Willem Ferguson <
willemferguson at zoology.up.ac.za> wrote:

>
> There are opposite definitions for *EAD* and *END* depending on people
> and even organisations. Subsurface has choosen that *EAD means Equivalent
> Air Depth considering both oxygen and nitrogen narcotics*, while *END
> would mean Equivalent Nitrogen Depth (ignoring oxygen)*. This way, *EAD*would be a measure for the narcotic potential of a gas, while
> *END* would be more related to nitrogen absortion by tissues. So, when
> diving NITROX, *EAD* will remain the same (or almost) than real depth,
> while *END* would be the interesting depth for deco calculations.
>

Here's what we use in GUE:

If we use 1.2 as pO2 threshold, a 18/45 gas mix has a MOD of (pO2 / fO2) =
(1.2 / 0.18) = 6.7 ATA = 57 meters

The END (Equivalent Narcotic Depth) at 57 meters is (1 - fHe) x ATA = (1 -
0.45) x 6.7 = 3.7 ATA = 27 meters

The EAD (Equivalent Air Depth) at 57 meters is = ((1 - fO2) x ATA) /0.79 =
((1 - 0.18) x 6.7) / 0.79 = 6.9 ATA = 59 meters

Cheers,
Henrik
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