Hello Bruce:

I own a couple of CO monitors which actually measure the concentration of CO in the air. The net result is that if the CO concentration goes from 23 ppm to 25 ppm in one second, my monitors will similarly respond and will display a reading of 23 ppm and then 25 ppm.

However, most of the CO detectors folks are using in their homes, would exhibit no change at all, and most would not even indicate an elevated condition. That’s because most CO detectors folks are using in their homes, are actually responding to a dynamic time (times) concentration curve (T * C), that mimics human blood disassociation curve for carboxyhaemoglobin (COHb).

COHb is the haemoglobin whose shape becomes altered when exposed to CO. The altered state more strongly holds oxygen, and won’t release it to the cells that need it; CO disrupts what is called blood “cooperativity.”

Many home CO meters have a strip containing an artificial haeme molecule mixture that mimics human blood – the color of the strip alters at specific time * concentrations of CO. So, for example, pursuant to that curve, 220 minutes @ 100 ppm, 45 minutes @ 300 ppm, and 15 minutes at 800 ppm, are all equivalent COHb 20% saturation points.

Although they are a great idea for homes (I have two such monitors in my home), they are virtually useless for scientific indoor air investigations.

DavidR mentioned the UL 2034 standard. If you read up on that standard, you will see an example of the set-point disassociation curves to which he was alluding.

Cheers!
Caoimhín P. Connell
Forensic Industrial Hygienist
Forensic Industrial Hygiene

(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.)

AMDG