How fast is O2 tox?

[Charlie99]

http://www.diversalertnetwork.org/medical/articles/article.asp?articleid=35 is a DAN article on oxtox. Note the "exceptional exposure" tables at the bottom of the article ---- 60 minutes at 1.6ppO2, .... 30 minutes at 2.0ppO2.

I would classify a rescue as something that warrants being willing to use the "exceptional exposure" table.

Oxtox is the body's response to the ppO2 and DURATION of exposure.

 

[divingjd]

I stand corrected. CNS toxicity has a time element as well. The DAN article is a good resource, but note that it emphasizes the unpredictability of the onset of CNS toxicity, which is also the point AMASCUBA was making. While there is an interplay between ppO2 and time, they can't really say what it is. The DAN article also is pretty clear in recommending 1.6 as an absolute limit. "Above 1.6 ata is the "red light" area. Just don't do it. Yes, there is evidence that short exposures at higher levels of pO2 (oxygen partial pressure) are possible but so are convulsions." To get back to the OP's specific question, I would not make the bounce down. That one looks like too much risk of turning one fatality into two. Everybody makes their own risk assessments, that's mine.

 

[jbd]

To get back to the OP's specific question, I would not make the bounce down. That one looks like too much risk of turning one fatality into two. Everybody makes their own risk assessments, that's mine.

With this, jbd, Charlie99 and divingjd have just clearly illustrated the moral dilemna of rescue. Keep in mind that this is the kind of judgement that must be made in seconds with only the knowledge you have at that moment. That to me is the real relevance of Web Monkey's question.

 

[Web Monkey]

With this, jbd, Charlie99 and divingjd have just clearly illustrated the moral dilemna of rescue. Keep in mind that this is the kind of judgement that must be made in seconds with only the knowledge you have at that moment. That to me is the real relevance of Web Monkey's question.

Yep.

And I still don't have a real answer, except that hugely exceeding my PO2 can cause Ox Tox at some point, ranging from immediatly to never, and that a gas switch would probably help, but the time element is still unclear.

I was actually thinking about this on a wreck dive this past weekend, where I brought a mix that was optimum for my planned depth, but when on the wreck, started thinking about what if someone playing in the dirt down below had a problem.

Terry

 

[Ken abucs]

There's another factor you have to consider in this scenario, who the victim is. If it's an instabuddy on a dive boat I'll be a lot more conservative than if I'm diving with my brother.

But in practice I choose a MOD that matches the hard bottom, so this should be a non-issue.

 

[jbd]

And I still don't have a real answer,....

You don't and you do. You don't in that there is no black and white clear cut answer. You do in that you have thought about it and learned something from this and if the situation ever arises you will act in the manner that reflects your personal answer.

I was actually thinking about this on a wreck dive this past weekend, where I brought a mix that was optimum for my planned depth, but when on the wreck, started thinking about what if someone playing in the dirt down below had a problem.

Terry

This is the key---you were thinking about this. Pondering the what ifs and what solutions are available. Regarding rescue attempts you have the approaches indicated by Charlie99, jbd and divingjd. Regarding gas planning you have the suggestion of using the hard bottom for the MOD as opposed to the best mix for the target depth. All good stuff for planning your next dive.

 

[Charlie99]

I was actually thinking about this on a wreck dive this past weekend, where I brought a mix that was optimum for my planned depth, but when on the wreck, started thinking about what if someone playing in the dirt down below had a problem.

As noted above, I came to the conclusion that a short term ppO2 of 2.0ata was acceptable for a short time during a rescue (yes of even an "instabuddy" or unknown non-buddy diver).

The second half of the equation is available gas. I suppose those of you that won't violate 1.6ata ppO2 to rescue a diver also won't go past your standard "rock bottom". That is something to think about. What is your really, really, really hard rock bottom gas level for going after someone.

Whatever you choose, it's something that you should have clear in your mind well before you get into the water. It's not something you should be trying to figure out in the heat of the moment.

I have my own, rather scary, limits which are based upon immediately going after someone, followed by a 60fpm ascent with a heavily breathing panicked diver to shallow water or another gas source if available. Since I have a relatively low SAC, in most groups of divers I have the most air left at the end of a dive and therefore am most likely candidate to go off and do a rescue.

 

[TheRedHead]

Charlie made a good point about gas. And you have to consider the depth of the hard bottom. Could you rescue someone at 140 feet with narcosis?

 

[builder2000]

I had a similar conversation with my best friend and dive buddy. He experienced something very similar in the Caribbean years back with an "instant-buddy". She was following a sea turtle and dropped 40-50 ft below their dive plan. He went after her and was able to help her come up. He got mildly bent because of the rescue. Goes to show that some times making an instant decision can have both rewarding and bad consequences.

 

[BigTuna]

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.

An important rescue matter is that the toxing diver's airway could be locked closed with a spasm. If that happened, moving him to the surface could result in a lung overexpansion injury. There seem to be several options for dealing with this, such as:

- Wait until the convulsions stop before raising the victim.
- If the victim can be raised to a depth with lower PO2 such that the pressure reduction is minimal, do so and hold him there until convulsions stop.
- Interrupt the airway lock with a force applied to the chest, perhaps with a Heimlich maneuver.

Are there expert recommendations on this?