any effect of the sorb on CO?

Marc T

Perhaps a chemist egeneer could answer that question?
Does the sorb could have any effect on CO accidentaly contained in the loop, because for example of a "bad" compressor?

Thanks

Marc

amaiel

I'm not a chemist, but I have (unfortunately) to say that the sorb doesn't effect on the CO. To filter the CO you need a catalyst (Monoxycon or similar) to transform the CO in CO2 and then filtering the CO2

For more info I suggest you to read this article Understanding SCUBA Compressors and Filtration - The Deco Stop

iain-hsm

Marc
No the soda lime cannot absorb CO, but what is known however is the ability of strong base limes with some anesthetic gases (using very dry lime) breaking down the anesthetic gas to carbon monoxide.

Carbon monoxide production from desflurane and six types of carbon dioxide absorbents in a patient model
C. Keijzer, R. S.Perez and J. J. de Lange
Background: Desflurane is known to produce high concentrations of carbon monoxide (CO) in desiccated sodalime or Baralyme. Desiccated absorbents without strong bases like potassium hydroxide or sodium hydroxide are reported to produce less or no CO at all. The purpose of this study is to compare the concentration of CO in an anesthesia circuit for desflurane with six different types of completely desiccated CO2 absorbents with less strong bases than sodalime.
Methods: A patient model was simulated using a circle anesthesia system connected to an artificial lung. Completely desiccated CO2 absorbent (950 g) was used in this system. A low flow anesthesia (500 ml min 1) was maintained using desflurane. For immediate quantification of CO production a portable gas chromatograph was used.
Results: Peak concentrations of CO were very high in Medisorb, and Spherasorb (13317 and 9045 p.p.m., respectively). It was lower with Loflosorb and Superia (524 and 31 p.p.m., respectively). Amsorb and lithium hydroxide produced no CO at all.
Conclusion: Medisorb and Spherasorb are capable of producing large concentrations of CO when desiccated. Loflosorb and Superia produce far less CO under the same conditions. Amsorb and lithium hydroxide should be considered safe when desiccated.

Any CO present in "bad air" should be investigated and treated only with a catalytic chemical called Hopkalite and only then if it is found to come from an outside source ie the petrol or diesel engine.

This only works in very dry air ONLY. post filtration after the air is better than minus 50C dewpoint. Only at these dry conditions will it convert the C0 molecule into C02. Even then only with a calculated surface area of chemical against a calculated chemical bed depth with a calculated "dwell time" and a possible increase of the compressors back pressure to around 200 barg from the more common 150barg will this catalytic conversion occur.

IMHO I would not reccomend using air from a compressor that is creating C0 ever this is only due to bad compressor oil, high temp, poor service and is not acceptable. Only air polluted C0 from say petrol or diesel engines should be treated. A compressor creating C0 should be junked. Iain Middlebrook

Marc T

Thanks for this interesting and very complete answer.
The initial idea was a more general self questionnemnt about the effect of diluent pollution when using a Rebreather versus on OC ( less diluent used - less pollutant in the loop and in the body)
It could be of course the contrary in case of O2 pollution with a progressive increase pollutant level inside the loop during the dive ( using industrial O2 grade is very common in France when personnal use )

jaap

If you worry about CO in your rebreather then maybe you should consider a known CO source that cannot be removed. Your own body!

Have a look at this posting for more details:
http://www.rebreatherworld.com/rebre...html#post48795

Not that I think it is any issue for 'normal' Rebreather-dives.

Marc T

Interesting link

Thanks

Marc

iain-hsm

Marc
If it is pollution from the oxygen supply I suppose another gas we should look at would be Argon rather than carbon monoxide. However as we are taking about a small volumetric amount 5% in a 1 to 1.5l/min metabolic uptake I think the lung tidal volume alone would compensate for even a 5% argon or (diluent) by volume in the bag. In a fully closed circuit oxygen rebreather using passive addition maybe be at increased risk but flushing technique prior to assent should resolve.
Industrial oxygen manufactured by synthetic zeolite PSA or VPSA plants produce around 95% oxygen with say around 5% concentrated of diluent gases the major being Argon. Oxygen for breathing normally is from a liquid fraction plant were the oxygen percentage is >99.9% and the certifiction is better but we have PSA plants for field hospitals, and oxygen generation at 95% in the military working well. 3000 Meters up a mountain in Afganistan was the exception!! Deco using high Argon concentrations is a sure way to get bent but 5% is a pretty small percentage. Iain Middlebrook

Genesis

An interesting thought process with regards to OC .vs. CC and polluted gas has come up before in other online forums, but I don't think its been talked about here...

That is that all things being equal, CO in your diluent supply is likely less dangerous on a CCR than the same PPM of CO in an OC rig.

That's simply because once the CO is in the loop, and is taken up, there's no more of it (unless you do a DIL flush) where on an OC rig you get a new "shot" of it with each breath. Since your hemoglobin has such a great affinity for CO its likely that any CO in your diluent would be immediately absorbed by the body and thus the amount in your breathing bags would almost immediately fall to essentially zero, absent a further dilution injection.

A compressor that is producing CO is usually doing so by detonation of the oil vapor in the compressor, which indicates severe overheating. Essentially ALL oil-lubricated compressors intentionally entrain some oil vapor into the air stream for top-end lubrication. Look at the plumbing on one sometime - Bauer started this years ago, and everyone has copied it - and it both works and is safe provided the temperatures are under control. There is typically a line going from the crankcase to the air intake plenum which draws a negative pressure on the crankcase, which of course contains oil vapors - this is entrained into the compressor input! Of course this oil vapor has to be removed before you breathe the product gas......

The bigger risk is entrainment of atmospheric sources. A car running upwind of the compressor's intake, if its a MODERN car, is unlikely to do it (indeed its actually kinda hard to commit suicide with a modern car by breathing the exhaust, as the CO levels are vastly lower than they used to be due to the catalytic converters) - but a lawn mower or weed whacker is a different story, as those don't have catalysts on them and produce tremendous amounts of CO. Of course the worst potential offender is a gas-driven compressor since the engine is right there!

Anyway as Ian has indicated there's basically nothing you can put in the scrubber that will help. Hopcalite won't work unless you have extremely dry gas, which of course isn't going to happen in a rebreather loop, and the 'sorb itself won't convert CO at all.

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