I think this was touched on a little bit over the previous 69 posts but not enough to satisfy my curiosity. If you are breathing in air that has too much carbon monoxide will you have obvious breathing difficulties? If yes, will those difficulties occur within the first few minutes of the dive? In other words, if you were to stay at a shallow depth for a few minutes would you KNOW to abort the dive? And if carbon monoxide wasn't the cause of this woman's death what other types of air contamination might be responsible for the other divers experiencing difficulty breathing? And is it possible (or HOW is it possible) for the shop that owns the tanks to have done something prior to or after getting the tanks filled, that would have contaminated the air? And finally, is there any sort of analyzer that will test for carbon monoxide AND other contaminants that would be dangerous for us to breathe at depth?
Lots of good questions there so we'll try and answer a few.
The symptoms one would experience from CO exposure is going to depend on many factors such as age, smoking status, work load, and most importantly the exposure concentration, depth, and time. Age is a big factor and young healthy divers would tolerate higher CO exposures than an older unfit diver.
At low exposure concentrations likely the first noticeable symptom would be a headache, possibly some nausea, and drop in exercise tolerance. This latter symptom was the complaint the Montreal fire fighters noticed initially when they reported problems with the quality of their breathing air subsequently found to be from CO contamination. As the CO concentration increases further, either directly or effectively by diving deeper, one would start to notice significant shortness of breath, anxiety, chest pain, etc.
If one asks the compressed breathing air laboratories what is the most common contaminant after moisture and CO2 are removed from the list it is carbon monoxide at the top of the list. Second on the list depending on which lab you speak with is non-methane hydrocarbons which are volatile compounds such as xylene, toluene, ethylbenzene, hexane, etc. all compounds which have been found in dive air.
These compounds generally do NOT produce shortness of breath but rather produce narcosis out of proportion to the depth. If one was exposed to only a pure hydrocarbon in general there would be a period of excitation (think of drinking a few beers) followed by a gradual lowering of one's level of consciousness until eventually the regulator would fall out of one's mouth and drowning would ensue due to loss of consciousness. This acute central nervous system toxicity is very different from carbon monoxide with its cardio-respiratory toxicity.
Below is an excellent real life description of a CO poisoning incident where the diver had a significant CO exposure and a hard bottom at 20 feet. Had he gone deeper he likely would have drowned. The tank gas was analyzed and showed high concentrations of CO. The reason his buddy had fewer symptoms and a lower concentration off the same compressor was that his tank still had 1500 psi of clean air in it so the CO from the faulty compressor was diluted more than the photographer whose tank only had 500 psi of air prior to the problematic fill directly off the compressor.
August 2008 Volume 18 Number 8
If you are interested in how a pure hydrocarbon exposure would present initially have a look at these commercial divers who came back to the bell with crude oil smeared on their dry suits. The vapor from this oil gave off benzene, ethyl benzene, toluene, xylene (BTEX), and other non-aromatic hydrocarbons all of which are highly narcotic. One can see the initial state of excitation, but more importantly the severe cognitive impairment (unable to put on full face mask) at concentrations well below where any significant drop in their level of consciousness was detected. These BTEX compounds can be found in compressed breathing air due to compressor and purifier dysfunction.
Diving Bell atmosphere protection with Analox Hyper Gas - YouTube
One can smell the BTEX and hydrocarbon compounds in most cases but the CO remains odorless which is why one must analyze for CO in the compressed breathing air. Always smell your breathing air prior to use, and one in the buddy pair or dive group should own a CO analyzer.