Do you trust your gas supplier?

[Genesis]

Okay, so that deals with CO - what about CO2? Is CO2 poisoning a risk for OC divers as a result of a bad fill (not talking about breathing techniques, or RB scrubber breakthrough etc). Should tanks be tested with a CO2 meter before diving?

CO2 is somewhat less of a problem simply because it takes much more of it to cause significant trouble. In fact, the Hopcalite in compressor filters works by converting CO to CO2.... intentionally...

 

[pufferfish]

Okay, so that deals with CO - what about CO2? Is CO2 poisoning a risk for OC divers as a result of a bad fill (not talking about breathing techniques, or RB scrubber breakthrough etc). Should tanks be tested with a CO2 meter before diving?

Sorry this is the CO thread not CO2

Generally the CO2 level is the most common reason for a fill station to fail a test. CO is reason number two and still in the 21st century 3% of scuba fill stations are failing for CO levels greater than 10 ppm.

In 1997 I think the CGA Gr. E standard for CO2 was changed from 500 to 1000 ppm as too many stations were failing. Generally though the CO2 is about 330 ppm in ambient air so it doesn't take much CO conversion to CO2 by hopcalite or 'silent combustion' to put a station over the 500 ppm mark. Still at this level assuming no other tank contaminants in a healthy diver I wouldn't anticipate any major health problems for the recreational diver heading to 5 ATA. Remember though the deeper you go the higher the effective contaminant concentration so what may be marginally safe on surface can become toxic at depth especially in an already susceptible diver (skip breathing or working hard). According to Dr. Edmonds in Diving and Subaquatic Medicine at about the 5% CO2 level distress may begin with shortness of breath. Working backwards assuming 5% at 5 ATA this would be 1% on surface which is about 10,000 ppm CO2. This is 10X the allowable amount and don't think those levels are too common in ambient air so you'd have to have some serious compressor problems or else have your intake in a cow barn to see those levels. So to answer your question I'd say no, tanks don't need to be field tested for CO2 if the fill station is getting quarterly accredited lab air analyses and passing.

CO is the one contaminant though whose concentration can quickly change in that three month interval (i.e. hopcalite too humid from inadequate filter changes) and if it does and you don't know bad things will happen down under. Testing tanks in the field for this tasteless odorless gas would seem prudent especially if quarterly testing is not being done.

 

[padiscubapro]

Sorry this is the CO thread not CO2

Generally the CO2 level is the most common reason for a fill station to fail a test. CO is reason number two and still in the 21st century 3% of scuba fill stations are failing for CO levels greater than 10 ppm.

In 1997 I think the CGA Gr. E standard for CO2 was changed from 500 to 1000 ppm as too many stations were failing. Generally though the CO2 is about 330 ppm in ambient air so it doesn't take much CO conversion to CO2 by hopcalite or 'silent combustion' to put a station over the 500 ppm mark. Still at this level assuming no other tank contaminants in a healthy diver I wouldn't anticipate any major health problems for the recreational diver heading to 5 ATA. Remember though the deeper you go the higher the effective contaminant concentration so what may be marginally safe on surface can become toxic at depth especially in an already susceptible diver (skip breathing or working hard). According to Dr. Edmonds in Diving and Subaquatic Medicine at about the 5% CO2 level distress may begin with shortness of breath. Working backwards assuming 5% at 5 ATA this would be 1% on surface which is about 10,000 ppm CO2. This is 10X the allowable amount and don't think those levels are too common in ambient air so you'd have to have some serious compressor problems or else have your intake in a cow barn to see those levels. So to answer your question I'd say no, tanks don't need to be field tested for CO2 if the fill station is getting quarterly accredited lab air analyses and passing.

CO is the one contaminant though whose concentration can quickly change in that three month interval (i.e. hopcalite too humid from inadequate filter changes) and if it does and you don't know bad things will happen down under. Testing tanks in the field for this tasteless odorless gas would seem prudent especially if quarterly testing is not being done.

Hopcalite is great at removing CO(it converts it to CO2 which is much less toxic), but is very suseptible to moisture.. Most fill stations have inadeuate water removal.. A good coalescor is necessaery.. Dew point shoud be kept in the range of -50c/f hopcalite starts losing it s effectiveness at -20c dewpoint.

My station typically runs zero co and zero co2...

 

[pufferfish]

Hopcalite is great at removing CO(it converts it to CO2 which is much less toxic), but is very suseptible to moisture.. Most fill stations have inadeuate water removal.. A good coalescor is necessaery.. Dew point shoud be kept in the range of -50c/f hopcalite starts losing it s effectiveness at -20c dewpoint.

My station typically runs zero co and zero co2...

Up here we like to see air drier than -50F else one starts to see free flows at depth with adiabatic cooling, high flow rates and cold water. I think the CSA standard requires -63F (-53C) as dewpoint.

Just curious about that zero CO2 since ambient is about 300 ppm. When do you test the air relative to the filter change? Better to run the compressor at least an hour after a filter change and prior to sampling else you get zero CO2 readings which are not relevant. If you really want to see how your system is set up and running try sampling the air just before you change the filters. If you pass at this point then you are doing things right.

 

[padiscubapro]

Up here we like to see air drier than -50F else one starts to see free flows at depth with adiabatic cooling, high flow rates and cold water. I think the CSA standard requires -63F (-53C) as dewpoint.

Just curious about that zero CO2 since ambient is about 300 ppm. When do you test the air relative to the filter change? Better to run the compressor at least an hour after a filter change and prior to sampling else you get zero CO2 readings which are not relevant. If you really want to see how your system is set up and running try sampling the air just before you change the filters. If you pass at this point then you are doing things right.

It should have read in the range og -50c or better.. zero is porbably an overstatment.. I don't know if you can get zero of anything.. its "below measurable limits"

before reaching the compressor the air passes through a bed of sofnalime (being a RB instructor plenty is always available - can't do it afterwards otherwise it will add moisture).
The amount of CO2 that sofnilime can remove is better than 140liters per kg. thats about 6.25 moles(mol=6.02x10^23) of CO2 per Kg, even at 300ppm, it takes a long time to exhaust. If my math is correct its over 16k(air in) cu ft/kg.
On a test if CO2 ever shows up it should be in miniscule amounts, and would indicate some type of combustion or other issue that has to be researched(this gives me another way to make sure nothing is up with my system). My filters are changed much more often than necessary..
My system has two custom chambers, 54 inches long by six inches in diameter(always under backpressure as you could guess how much air volume is in here alone plus it prevents channeling and keeps the chemical dry).. If I remember correctly (I calculated the amt of chemical/area a while ago) this works out to about 13 or 14 full size towers.. Considering that most shops with reasonable gas have only 2 or 3 towers, my system is overkill.. Tests are always done before media changes..

 

[JohnF]

CO2 is somewhat less of a problem simply because it takes much more of it to cause significant trouble. In fact, the Hopcalite in compressor filters works by converting CO to CO2.... intentionally...

This issue is one that's concerned me since I started diving. My solution has been to limit as much as possible the sources of my gas, but since much of my diving is done as a tourist when I can't even use my own tanks, it's pretty damned difficult.

Unfortunately it's almost impossible to regulate safe gas given the venues in which we dive and the circumstances under which it is supplied. We are almost wholely dependent on the expertise, ethics and sense of responsibility of the gas fillers and handlers. Your suggestion of an inexpensive test device makes a lot of sense for both users and suppliers.

Thanks
JohnF

 

[pufferfish]

My system has two custom chambers, 54 inches long by six inches in diameter(always under backpressure as you could guess how much air volume is in here alone plus it prevents channeling and keeps the chemical dry).. If I remember correctly (I calculated the amt of chemical/area a while ago) this works out to about 13 or 14 full size towers.. Considering that most shops with reasonable gas have only 2 or 3 towers, my system is overkill.. Tests are always done before media changes..

Wow those are big stacks and must give some real clean air but then again your intake is in New York so maybe you need them

That is interesting with the sofnalime prior to the stacks to remove the CO2. Too bad you couldn't sell fills over the Net with that system setup!