How fast is O2 tox?

[rigdiver]

Is there a quick onset though? Web Monkey had a great question, is it possible to help a diver in trouble that is over your MOD for a few minutes or is it too dangerous?

Think of the MOD as an electric fence. It may be on. Better one dead than two.

 

[amascuba]

Is there a quick onset though? Web Monkey had a great question, is it possible to help a diver in trouble that is over your MOD for a few minutes or is it too dangerous?

It's possible, but as the studies show that you might be able to go an extended period of time one time and the next time you may start toxing as soon as you reach your depth.

 

[Ben_ca]

On the drive home one day with my buddy we talked about this.... We talked about PO2's and MOD's and concluded that unless one of us is being dragged away in the jaws of a GWS we would/should be right on top of each other.... we dive DIR protocols so we expect each other to be really close (also diving in Monterey, often the vis is limited so we keep close) and in communication (passively or actively with our lights)....

But then again you can talk about what you would want to do in an emergency all day long but when it actually happens the actions could be totally different.

 

[Diver Dennis]

I guess it would be a judgement call if you were in that situation. Thanks.

 

[TheRedHead]

No matter what mix you're diving, unless you have a hard bottom at or above your MOD, this question would always be pertinent.

I think it is a very pertinent question, but there is no real answer to it. It's my understanding that you can tox and convulse without any warning. There are Oxtox signs learned by the acronym CONVENTID:Convulsions, Visual changes, Euphoria, Nausea, Twitching, Irritability, and Dizziness. Some of these can be experienced with narcosis, which is also present with nitrox mixtures at depth. I think it used to be practice to dive to 1.6 and at 1.6 there is a small chance of toxing. Someone like Thalassamania who has a long history with NOAA would know a lot more about the early history of Nitrox at 1.6. But beyond that, who knows?

I think you would be talking a real chance in a rescue situation - certainly not "at rest" - of toxing. For me, I try to keep my MOD within the hard bottom. I can dive air and increase my safety by making stops with a rich mixture of Nitrox while assuming an air profile.

 

[Web Monkey]

I think it is a very pertinent question, but there is no real answer to it. It's my understanding that you can tox and convulse without any warning. There are Oxtox signs learned by the acronym CONVENTID:Convulsions, Visual changes,

OK, now how about if there's a gas switch? Say you're on EAN36 @95', then switch to air and drop to 130?

Is O2 Tox still a possibility?

Terry

 

[TheRedHead]

OK, now how about if there's a gas switch? Say you're on EAN36 @95', then switch to air and drop to 130?

Is O2 Tox still a possibility?

I don't know. It is not a common practice. It hasn't appeared in any Nitrox text I've read. Surely there are some experts here.

 

[Packhorse]

OK, now how about if there's a gas switch? Say you're on EAN36 @95', then switch to air and drop to 130?

Is O2 Tox still a possibility?

Terry

I would think you would be fine assuming your cns clock time was still OK. Your PPO would drop so there would be less chance of oxtox but more risk of narcosis.

 

[jbd]

OK, now how about if there's a gas switch? Say you're on EAN36 @95', then switch to air and drop to 130?

Is O2 Tox still a possibility?

Terry

I can't remember where I read this because I have done a lot of reading lately regarding mixed gas diving but I recall seeing something to the affect that CNS ox tox can still occur once the person has been moved to a lower ppO2. Apparently there is a bit of lag time until sufficient O2 has been removed from the system.

Been pondering your intitial scenario as it poses the typical moral dilemna of all rescue situations whether on land or in the water. That being, what level of risk is the rescuer taking if they decide to attempt a rescue?

Given your scenario, can one mitigate the risk of becoming an oxtox victim while attempting to rescue the already toxing diver at 130 feet? IMO--possibly. The thinking would have to go something like this

1.) The toxing diver is dead if you do nothing
2.) A ppO2 of 1.6 is acceptable for a "resting" portion of the dive.
3.) Attempt the rescue in a resting mode i.e exhale and dump some air from the BC to descend to the toxing diver using the absolute bare minimum of finning activity to place you at the toxing divers location. As you are arriving at the toxing diver add sufficient air to the BC to stop the descent and initiate an ascent while taking hold of the toxing diver.
4.) Continue a controlled ascent to the surface with the toxing diver and hope for the best.

As noted by the other repondents regarding the studies they have read, there is an increased risk to the rescuer of becoming a victim but what the actual probability would be is very hard to say.

Very good question and indeed a thought provoking one at that.

 

[Charlie99]

Come on guys. Go back and read your nitrox course material regarding CNS toxicity tracking. In the NOAA tables there is a time limit associated with the various levels of ppO2. For example,

300 minutes max at 1.0ata ppO2
210 minutes max at 1.2ata ppO2
150 minutes max at 1.4ata ppO2
120 minutes max at 1.5ata ppO2
45 minutes max at 1.6ata ppO2

Do you really think that the next entry in this series is

0 minutes at 1.7ppO2 ?

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Personally, I'd have NO hesitation to go to a 2.0ata ppO2 for 5 minutes or less to conduct a rescue. On a practical basis, with an AL80, my gas supply sets my depth & time limit for a rescue with EAN32 rather than ppO2, and unless I have a full tank, gas supply still sets the depth-time limit for a rescue when I'm diving EAN36.