Trimix Narcosis & Calculating Your END

Posted on 07/16/09 No Comments

How narced do you want to get?

If you’re upcoming dive plans include helium you’re paying for out of your own pocket, then the question of how much nitrogen narcosis you can tolerate is a relevant one. If money were no object then, studies show, heliox would be the obvious choice. But when you’re footing the bill, determining your Equivalent Narcosis Depth, or END, is a calculation you need to make.

For those unfamiliar with the economics behind computing your END (for open-circuit), consider this example from Bill Stone, chairman and founder of Cis-Lunar Development Laboratories which specializes in the design of advanced life support systems for undersea and space exploration:

An hour long dive at 300 fsw using heliox-14 as a bottom mix would cost approximately $163 for helium costs alone, or nearly three times the estimated $64/hour costs of trimix 14/34, which would produce the same narcosis level at 300 fsw as diving on compressed air at 165 fsw.

So, how do you calculate your END? Finnish technical dive instructor Matti Anttila goes through the formulas in one of the many in-depth articles on his Tech Diver website. The article, he writes, is intended “compare different ways to calculate the equivalent narcosis depth of trimix blends and to demonstrate the differencies of different methods and their results.

The math gets pretty complicated, so we’ll leave it to you to click through and read it, but basically there are two main ways to compute END and, according to Anttila, “too many people rely on Method #1.”

Content Protected Using Blog Protector By: PcDrome.