Detecting indoor CO exposure by measuring CO in exhaled breath

CO levels in exhaled breath were measured in 29 residents of flats, equipped with a flueless geiser (an instantaneous gas-fired water heater). The flats were selected because they had a geiser with a CO concentration of more than 250 parts per million in its flue gases. Small, but in some cases statistically significant increases in CO levels in exhaled breath were found in both smokers and non smokers, and after periods of cooking and dishwashing when the geisers had been used. Calculated COHb levels remained well below 2.5% for non smokers, but were generally higher for smokers.