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So I have always believed without any real knowledge that a small amount of CO inhaled in a rebreather will all eventually get absorbed by hemaglobin because of the recycling effect as opposed breathing in exhause fumes in open air where you will likely expell some of the CO with every breath. Any thoughs on that?
The source doesn't matter. If there is CO in the loop, it will not be scrubbed, and every time it goes around the loop, it will have the opportunity to attach to hemoglobin in the body. I don't remember exactly the time it takes to remove it from the body, but IIRC it's fairly long, like on the order of longer than the dive.
Part of prepping a rebreather involves pre-breathing it. I alway tell my students to wait until the boat has stopped or is going slow enough upwind to avoid (what you so elequently describe as) the station wagon effect before commencing pre-breathing out of fear that residual CO in divers lungs from exhaust might linger in rebreather loop until it is completely absorbed during the dive, as opposed to OC diver breathing clean air from tank and expelling any residual CO.
Yes and although I don't know to what degree the roundy roundy action has on the absorbsion of CO logic dictates it has to be considerable. Since the accident was a result of a shore dive then CO would more likely come from the gas source (unless Fiona was a smoker) in which case would an acceptable level of CO in a tank pose a higher risk in a roundy roundy device?
You need to remember that the NIOSH Recommended Exposure Limit of 35 ppm is based upon the amount of exposure that a person could receive for 8 hours in a day, five days a week over a working lifetime without adverse health effects. But, this is at one atmosphere absolute pressure. All gases are subject to the ideal gas laws and the laws of partial pressures. At 10 meters (33 feet sea water) the partial pressure would be 2x the reading at the surface, and at 30 meters (99 feet sea water) it would be 4x the surface reading. So breathing a scuba tank with 35 ppm at 30 meters (99 feet) would be the equivalent of breathing 140 ppm at the surface. At 7 atmospheres absolute, it would be 6x the surface, or 210 ppm, which is over the Ceiling Limit established by NIOSH (200 ppm). The Ceiling Limit is the limit which cannot be exceeded without immediate problems. IDLH for CO on the surface is 1200 ppm, which is the limit which is "immediately dangerous to life and health."
