Originally Posted By: Caoimh?n P. Connell
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The current ASHRAE standard references the Canadian Exposure Guideline for Residential Indoor Air Quality for carbon monoxide (CO) as less than 11 ppm for an eight hour exposure. Older versions of ASHRAE referenced the WHO CO level of 2 ppm. I do not like the current ASHRAE CO reference, and I don?t use it. I much prefer the WHO reference, and I use that instead.
Although I would strictly disagree with James B?s comment that there is no safe level of CO, I would agree with the sentiment behind the comment, that if concentrations above 2 ppm are found in a home, the source should be understood. CO is normally found in outdoor air, it is simply a natural component of normal air; therefore, we know that there actually are safe levels of CO and the human body is quite able to handle these normal background levels.
Furthermore, Mr. Bushart?s comments are rather off-base, in that small amounts of CO cannot accumulate in the bloodstream. In fact, CO doesn?t ?accumulate? in the bloodstream at all. CO is in dynamic equilibrium with the breathable air, and exhibits an half-life of about 60 minutes (at sea level). Also, Mr. Bushart?s comment about CO displacing the oxygen in the blood is also incorrect ? quite the opposite, in fact. The primary metabolite of concern is carboxyhaemoglobin which upsets the ?cooperativity? of the normal haem molecule, resulting in MORE oxygen in the blood. CO causes oxygen to accumulate in the blood to unusually elevated levels. This is because the ?cooperativity? has been upset, and the blood cannot properly release the oxygen to where it is needed. That is why persons who experience CO poisoning exhibit flushed skin ? because of their oxygen rich blood. If Mr. B wants zero CO in his breathing air, he will have to move to Venus.
However, outdoor levels can be excessive in urban environments, and so I would also disagree with the comment that indoor levels should not exceed outdoor levels, since I have personally measured outdoor CO concentrations of 65 ppm in urban settings (indicating that 64 ppm in a building would be ?acceptable.?)
Brian is quite correct in that some chemicals will result in false readings. Similarly, human exposure to some chemicals can result in ?CO poisoning,? even in the absence of CO.
Vern- any gas company rep who stated that 25 ppm CO was OK in an house should, in my opinion, be removed from their current role until they have received proper training. I would have no hesitation to evacuate a school or a home if I measured 25 ppm sustained.
I would be happy to pursue the matter further.
Caoimh?n P. Connell
Forensic Industrial Hygienist
<SMALL> (The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)