Is ppO2 change too large?

[Tomeck]

If I change from 21% oxygen to 100% oxygen at 20 feet/6 meters (from ppO2 of 0.34 to ppO2 of 1.6) or from 18/35 to 100% oxygen (from ppO2 of 0.288 to ppO2 of 1.6), is it dangerous, because ppO2 change is too large?

 

[rjack321]

What are you thinking "too large" of a ppO2 increase would do??

ppO2 of 1.6 is pretty standard accelerated deco why would you want to keep it small?

 

[Thalassamania]

No, I've done that hundreds of times. The issue is not the change per se, but rather the ppO2 in absolute terms. Breathing an increased ppO2 always has risk associated with it. The higher the ppO2 and the more active that you are the higher the level of risk. I find a ppO2 of 1.6 ATA when I am at rest at a deco stop to be acceptable ... others might while other who are less risk adverse might be willing to go to 1.8 and a few even to 2.0.

 

[LiteHedded]

i'd be more worried about the rock bottom required to get back to that 20 bottle
depending on your profile...

 

[caseybird]

I find a ppO2 of 1.6 ATA when I am at rest at a deco stop to be acceptable ... others might while other who are less risk adverse might be willing to go to 1.8 and a few even to 2.0.

Thal,
How do you judge the level of risk to be acceptable? Are you going by the statistical research results? Do you have any awareness (physical or mental) of danger or discomfort from a a high PPO2? Are you going by your personal records of high PPO2 without ill effects?
Just to make sure, I'm not trolling. I'm just trying to get some insite into how your make your decision. In my case, I don't exceed 1.2 precisely because I don't have enough of that kind of experience to make an informed judgement, so I don't challange the guideline. (while leaving a comfortable margin.)
Steve

 

[Thalassamania]

Thal,
How do you judge the level of risk to be acceptable? Are you going by the statistical research results? Do you have any awareness (physical or mental) of danger or discomfort from a a high PPO2? Are you going by your personal records of high PPO2 without ill effects?
Just to make sure, I'm not trolling. I'm just trying to get some insite into how your make your decision. In my case, I don't exceed 1.2 precisely because I don't have enough of that kind of experience to make an informed judgement, so I don't challange the guideline. (while leaving a comfortable margin.)
Steve

You ask a very real and very serious question, one that there is not, I fear, a clear answer for.

For myself, I was lucky enough to have done a number of O2 tolerance tests back when we thought they were meaningful, as a result I (foolishly, in light of what we know now) felt perfectly comfortable at 2.0, and used 2.0 as my cutoff for many years without incident. I know try to keep it to 1.6 but I will go to 1.8 under some circumstances.

 

[Blackwood]

If I change from 21% oxygen to 100% oxygen at 20 feet/6 meters (from ppO2 of 0.34 to ppO2 of 1.6) or from 18/35 to 100% oxygen (from ppO2 of 0.288 to ppO2 of 1.6), is it dangerous, because ppO2 change is too large?

Some may tell you that going from 18/35 to Oxygen invites a risk of isobaric counter diffusion (which isn't a function of increasing the PO₂ but rather decreasing the fractional content of the light gas - helium). However, whatever theory may predict, switches like that are done time and time again without ill effect.

 

[Tomeck]

Thank you for your answers!

 

[wedivebc]

i'd be more worried about the rock bottom required to get back to that 20 bottle
depending on your profile...

Huh

Some may tell you that going from 18/35 to Oxygen invites a risk of isobaric counter diffusion (which isn't a function of increasing the PO2 but rather decreasing the fractional content of the light gas - helium). However, whatever theory may predict, switches like that are done time and time again without ill effect.

I have been sniffing around looking for data on IBCD incidents and I don't know of any hit that have occurred on dives shallower than 300ft. Although the OP didn't mention a profile I am certain going from air straight to O2 would involve a dive less than 300ft.

 

[Blackwood]

I have been sniffing around looking for data on IBCD incidents and I don't know of any hit that have occurred on dives shallower than 300ft. Although the OP didn't mention a profile I am certain going from air straight to O2 would involve a dive less than 300ft.

Yah, I don't suspect it's an issue.