Discussion about EAD & END terminology

Willem Ferguson willemferguson at zoology.up.ac.za
Mon Dec 9 07:49:32 UTC 2013

I was not part of the discussion about the terms EAD and END on this 
mail list earlier this year, way before I even knew about Subsurface. I 
wish to make absolutely certain about the consensus reached at the time 
because this affects the content of the user manual.

I myself have had extensive contact with the literature of DAN, NAUI, 
TDI and IANTD. In all of this documentation EAD is the equivalent AIR 
depth, denoting the air depth that has the same nitrogen partial 
pressure as a particular nitrox mix. The N in END is NOT nitrogen, but 
NARCOTIC. END denotes the depth where the partial pressure of  total air 
is equivalent to the pressure of (oxygen+nitrogen) in a multigas mixture 
with gas(es) other than oxygen and nitrogen. This is because the 
narcotic effects of nitrogen and oxygen are considered to be the same. 
EAD stands to nitrox in the same way as END stands to trimix. EAD and 
END are shown in the Information Box on the dive profile. in Subsurface.

My personal point of view is that if there is completely conflicting use 
of terminology, then we need to get rid of the terminology because wrong 
usage and interpretation can cost lives in diving.

The following is currently in the user manual:

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.

This is an important issue, please comment.
Kind regards,

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