Narcosis

[igotoofar]

I was thinking about this last night.

O2 has a toxicicity issue at ATA1.6 Max with most using ATA1.4

Does Nitrogen have a similar value? kind of a MND (Max Nitrogen Depth)
Example:
Air at 100ft would have PPN 3.16393939ATA

Many feel diving air to a depth of 100ft is a good limit.

Could one then say Trimix with 40% Nitrogen would give the same Nitrogen Narcosis at 229ft as air would at 100ft ? I understand I have simplified the #'s by not including the Helium or Oxygen in the mix with regard to their narcotic effects. But the idea is the same.

Thoughts?

[FMT]

Yes, this is the concept of "equivalent nitrogen depth."
or END. Like when the DIR people say they don't want an END over 100ft. This is where nitrox and triox and trimix come in.
T

[DRE]

One thing to keep in mind is the difference between Equivalent Narcotic Depth and Equivalent Air Depth. Although some people use them interchangeably, there is in fact a difference, depending upon how you consider the O2.
O2 is a metabolic gas, which means the body uses it to sustain life, whereas He and N2 are inert gasses. However, it is believed that O2 does play a role in narcosis; test subjects were asked to perform certain tasks at a certain depth with varying O2 contents, and higher O2 contents did not improve their ability, whereas He did make a difference. That's why to calculate the END both the N2 and O2 are considered in the calculation. Now, to figure out what kind of decompression benefit one would get using a nitrox mix, the EAD concept comes into play, where you would just consider the N2 and figure out what air depth would be equivalent to the depth you're using nitrox at.
In short, when using nitrox you're END is always the same as diving air, but your EAD will be shallower.

[Freedive WI]

I was always taught the 02 was twice as narcotic as N2, but because it get's metabolized by the body the narcotic efffect is basically a wash, which goes back to nitrox having the same narcotic properties as air.

Adding in varying amounts of helium can change your narcotic depth to whatever you want it to be- 80', 100', 130', ect. This is why trimix is sometimes called "dial-a-mix" since you can "dial" in the buzz you get by how much helium you add.

On a totally unrelated topic of narcosis theory the coolest research that I have been reading about is going on with some deep freedivers off of Australia and PNG.

Freedivers can get narked just like scuba divers, and this can happen on a sled or freeswimming. Freedivers can also get bent, and I have met at least one who did. This group of divers in Australia are getting around the narcosis and the DCS by using something called FRC diving. FRC stands for: Functional Resdiual Capacity- or, how much air you have left in your lungs after a full exhale. This is the same way that Seals and whales dive- they exhale and drop. All of the 02 is stored in the blood and there is no gas that gets pushed in and out of solution by compressing the lungs at depth. No gas exchange = no narcosis/DCS.

Of course, these people have VERY flexible rib cages and they work up to deeper dives over a period of time so that they can work into it slowly- just like you don't decide to get off the couch one day and run a marathon, they don't just drop down to 300' on the first plunge.

They are hitting depths of well over 300' in this manner and can dive again, and again, to these depths all day long. If the were to do a full inhale breathhold dive they would need to put plenty of surface interval inbetween dives or run the risk of getting bent. By doing FRC dives they can drop again as soon as the catch their breath.

Jon

[DiveCaptDean]

WOW,
These people are going to 300 and beyond with nothing in their lungs?????? Man..I cannot even imagine what kind of mind control that must take.