END calculations

[Octo-Danny]

In respnse to the question of how one may know the reative END of a certain EANox the equation is very simple:

END = (1-fo2)/0.79*(Depth+10) - 10

This gives the relative narcosis according to air e.g. if we dive on EANox 32 at 40m using the formula we see that it's simmilar to diving on air to 33.05 meters. This means we have to regar this as an air dive to 33 m' as to dive planning and both N2 narcosis.

[Dr Deco]

Dear Readers:

One should note that the above equation is for depth in meters. For the same Equivalent Nitrogen Depth in feet of seawater, we would have

[sp][sp]END = [(1 – fIo2)*(Depth + 33)/0.79] – 33

where fIo2 is the fraction of inspired oxygen (= 0.21 for air), depth is in feet (surface = zero).

Dr. Deco

[turnerjd]

Originally posted by Octo-Danny
In respnse to the question of how one may know the reative END of a certain EANox

Unfortunately, this is the formula for Equivalent Air Depth (EAD) the question raised previously was about ENarcD. I really wish certain agencies would call it EAD not END, after all, the factor of 0.79 is because AIR is 79% N2. We aren't breathing pure nitrogen normally!

There has been data both anecdotal and scientific to suggect that Oxygen is narcotic at depth. The origional question was about calculating an Equivalent Narcotic Depth for Nitrox and other mixes, taking the narcotic powers of oxygen and other mix gasses into consideration.

Jon T

[Dr Deco]

Dear Octo and John T:

I must confess ignorance as to the algorithm for the calculation of narcotic depths of oxygen…

Dr. Deco.

[Octo-Danny]

Turnerjd,

I know the formula is for EAD, but since narcotic depth is equivalent to air depth since all comparisons are made to a 78.5 (79) percent nitrogen, I allowed myself to change it from EAD to END. My appologies.

As to Narcotism by oxygen - no such thing as far as I know THOUGH most of the symptoms of CNS toxicity are very much alike Nitrogen Narcosis.

Octo

[Dr Deco]

Dear Octo:

It is very important to distinguish oxygen toxicity from the symptoms of “oxygen narcosis” (which I will assume is truly narcosis, if the chimerical effect does exist). Central Nervous System (CNS) Oxygen Toxicity is characterized by convulsions (much as if the individual had epilepsy) and a loss of consciousness. It is often, but not always, preceded by muscle twitching, or an aura of impending doom, or auditory illusions (in the water, one might hear a motor boat propeller).

These are quite different from nitrogen narcosis which is, as the name implies, mentation changes and then possibly falling asleep.

Dr Deco

[Octo-Danny]

Dear Dr. Deco,

I'm well aware of the symptoms of CNS toxicity but as published in numerous dive medicine books most of the symptoms excluding convultions, facial twiching and other spasms, the symptoms resemble those of N2 narcosis. For example tunnel vision, increase in hearing and bell sounds and knockings, euforia, nausea, increase in stress level, dizzyness and etc'

This is the main reasons why whyle tecahig nitrox courses we make sure that divers diving on 1.6 PO2 who feel such symptoms that they are probably due to CNS toxicity and not N2 narcosis (because of the law PN2 and high PO2).

[Dr Deco]

Dear Octo:

Diving with a possible oxygen partial pressure of 1.6 ATA is another matter. Here we have the increased possibility of CNS oxygen poisoning, especially when individuals are moving about and generating carbon dioxide.

When high partial pressures are used to treat patients in a hyperbaric chamber, the individuals rest and are relatively inactive (although the partial pressures here are 2.0 ATA to 2.8 ATA). The blood levels of carbon dioxide are not elevated. In the case of an active diver, the situation is different. Here we have a possible increase in CO2 that is capable of dilating the brain vasculature and triggering CNS toxicity.

You are correct in advising divers on these mixes to be aware that problems are possible.

Dr. Deco

[techdeepbluediver]

As to regard to the question on END that includes oxygen as norcotic, there are 3 different END formulas in use.
The first formula is as mentioned already in the thread and only takes into account nitrogen as narcotic. This formula is basically the same as an EAD formula.
Although oxygen has a narcotic value of 1.7 times that of nitrogen, it is normally calculated as 1 for ease of calculation and since the value would not matter that much.
Thus for an enriched air mix the END would be the actual depth you are diving to.
When diving on tri-mix, most software (like v-planner) includes both oxygen and nitrogen into the calculation for END. However, helium is 0.235 dimes as narcotic as nitrogen, thus at higher percentages (exceeding 4.25 ata) (normally 50% and up) and deeper depths (normally 250ft and deeper) the helium has a narcotic value.
An excellent book that explains all three formulas in depth with same calculations and other effects of gasses is 'The Art of Gas Blending' by Anton Swanepoel.
For more information see The Art of Gas Blending
Safe diving.