Carbon Monoxide

Carbon Monoxide (chemical formula: CO) is a colorless and odorless gas. When carbon or organic material containing carbon is burnt, carbon dioxide (CO2) is usually produced. However, if it is incompletely combusted due to insufficient Oxygen (O2), Carbon Monoxide will be produced.

CO Toxicity

Hemoglobin is contained in red blood cells that carry inhaled Oxygen to the body’s tissues. CO has a high affinity for hemoglobin (250 times greater affinity than Oxygen). If CO is inhaled, it will prevent transport of Oxygen in blood, causing CO poisoning symptoms. The symptoms can be headache, nausea, and death in the worst case.

Carboxyhemoglobin Concentration

When CO is inhaled, it easily binds to the Hemoglobin in blood to form carboxyhemoglobin (COHb) and causes CO poisoning symptoms. The poisoning symptoms vary depending on the inhaled CO concentration and the length of exposure time. The table shows the associations between Carboxyhemoglobin levels and clinical manifestations. It is important to design a CO alarm that can give an alarm or activate a ventilation fan well before CO poisoning symptoms occur.

CO Poisoning Symptoms Associated with COHb Levels
COHbLevel(%) CO Poisoning Symptoms
>70% Death
50%~70% Coma, brain damage, seizure, and death
40%~50% Confusion, unconscious, coma, and possible death
35%~40% Vomiting, collapse
30% Drowsy
25% Headache and Nausea
20% Headache
15% Slight headache
10% None
5% None

Source: UL2034_4th edition, Standard for Single and Multiple Station Carbon Monoxide Alarms, March 2017, pp. 50; Inkster S.E. Health hazard assessment of CO poisoning associated with emissions from a portable, 5.5 Kilowatt, gasoline-powered generator. Washington, D.C.: U.S. Consumer Product Safety Commission. 2004

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