Quiz - Physics - Partial Pressure of Carbon Monoxide

[CosbySweater]

It's been 20 years since I took Padi's OW course, but I don't think it was mentioned at all then. It is now? I bet it's lip service at best. Rule 1 is it doesn't take much, and Rule 2 is you never know unless you test every tank.

1.5% = 15,000 ppm so for most (people and reactions vary) it'd take maybe two or three breaths to knock you out, a few minutes to die. It can get confusing trying to compare percentage points (parts per hundred) to parts per million and the comma can too easily be displaced. See Percent (%) to ppm conversion calculator | number conversion
and Carbon monoxide poisoning - Wikipedia

Lets work the problem backwards and figure out how much CO your scuba cylinder would need to contain at the surface to be lethal at a depth of 132 feet (5atm).

According to the wiki article, a CO% of 0.08%(0.0008 partial pressure CO, or PPCO) is likely lethal to a scuba diver. The wiki cites "Dizziness, nausea, and convulsions within 45 min; insensible within 2 hours" at a PPCO of 0.0008. Convulsions would be the primary risk. Note that the real accepted maximum PPCO for SCUBA breathing gas is probably MUCH lower than 0.0008, but for the sake of determining lethality lets go with 0.0008.

Working backwards, at a depth of 132 feet (or 5 atm), in order to achieve a PPCO of 0.0008 in your breathing gas, your cylinder would have to contain 0.0008/5 = 0.00016 PPCO at the surface (or 160 ppm).

Question - What is the actual accepted maximum PPCO at the surface for SCUBA breathing gas? I've never tested a cylinder for CO so I'm curious. I'd reason that it's significantly lower than 0.00016

 

[DandyDon]

There was only one other question on the entire Science of Diving test related to carbon monoxide - what are the avenues of how CO can get into the tank

And what is the official answer? I wonder if overheated compressors burning their own lubricating oil is included as I have met too many owners who didn't know.

Wow, that is a really bad test question. Makes zero sense.

It took me a few seconds to answer it in my head. Why has no one answered it yet?

Question - What is the accepted maximum % CO at the surface for SCUBA breathing gas? I've never tested a cylinder for CO so I'm curious. I'd reason that it's significantly lower than 0.016%.

I'm going to scream! You list as "I'm a fish" which is a very experienced level, but I guess that you're new to scuba? I never post in the Basic forum as a rule as I don't want to sound rude if I fail to watch my language.

It's more complicated than that. Wikipedia has another article on CO that explains it better, but it's rather lengthy. To answer your question, the maximum allowed in some developed countries is 5ppm, some 3ppm, but the US allow 10ppm. Most countries don't have regulations on it, but then those that do rarely enforce them.

 

[saxman242]

Why has no one answered it yet?

Hey, I liked my answer

 

[DandyDon]

Hey, I liked my answer

I'm sorry, I guess I missed it. Did you say A, B, C, or D?

 

[TMHeimer]

I'm a simpleton. 132' is about 5 ata. So 5 times 1.5= 7.5. If it's more complicated than that thus I'm missing something, that's the way it is.
How come no place to vote like with the first question?

 

[saxman242]

I'm sorry, I guess I missed it. Did you say A, B, C, or D?

A. 1.5%

The effect of 1.5% at the surface is basically instantaneous unconsciousness and death. At depth, the partial pressure would be equivalent to 7.5% surface, but the effect would be the same as 1.5% at the surface; immediate unconsciousness and death.


Now, I think the answer the question is looking for is 7.5%.

 

[Pedro Burrito]

I'm a simpleton. 132' is about 5 ata. So 5 times 1.5= 7.5. If it's more complicated than that thus I'm missing something, that's the way it is.
How come no place to vote like with the first question?

There was no place to vote because I screwed up the initial post. Sorry!

 

[Pedro Burrito]

Spoiler: Answer

The answer is c. 7.5%. Multiply the atmosphere at 40m (5 atm) times 1.5 to get 7.5%. It's interesting that the person who created this question, not me, used Carbon Monoxide instead of Oxygen or any other gas.

 

[CosbySweater]

I'm going to scream! You list as "I'm a fish" which is a very experienced level, but I guess that you're new to scuba? I never post in the Basic forum as a rule as I don't want to sound rude if I fail to watch my language.

It's more complicated than that. Wikipedia has another article on CO that explains it better, but it's rather lengthy. To answer your question, the maximum allowed in some developed countries is 5ppm, some 3ppm, but the US allow 10ppm. Most countries don't have regulations on it, but then those that do rarely enforce them.

Scream away but save the sass. We're all just trying to learn something here....

It was a legitimate question. From the beginning we've been taught about the dangers of CO in diving due to the increased partial pressures at depth, but I can't recall receiving any guidance on just how much is too much. Nor can I recall being taught how to analyze a cylinder for CO. The importance of testing a cylinder for CO is surely not lost on me, hence why I asked what is an acceptable maximum in the industry?

All that being said, I appreciate your answer. Somewhere between 3-10ppm. What number are you looking for when you analyze a tank? 0?

 

[saxman242]

It was a legitimate question. From the beginning we've been taught about the dangers of CO in diving due to the increased partial pressures at depth, but I can't recall receiving any guidance on just how much is too much. The importance of testing a cylinder for CO is surely not lost on me, hence why I asked what is an acceptable maximum in the industry? The question wasn't "how much CO can we get away with having in our cylinder without killing ourselves?"

While this doesn't totally answer the question, this was the data I was talking about in the link I posted on the previous page regarding ppCO, exposure times, and effect:

That would suggest a maximum partial pressure on a single tank dive would probably not want to be higher than about 0.015% to remain within the "no effect" zone.

If we go off a 132 ft/5 atm dive, that would mean a surface reading of ~.003%(30 ppm) would be about the maximum threshold for a single tank dive on air.

Or to approach it with other numbers from OSHA/WHO:

If we instead go off of the WHO 1 hour average limit for 1 hour as our single tank limit. That'd put us at 30 ppm (.003% ppCO) at depth, so a safe surface level reading to be within the WHO 1 hour average limit would be a surface level reading of no more than 6 ppm or .0006%.