Table 1.

Reference Carbon Monoxide levels in humans and various environmental sources

Subject/Source	CO level	Source
Non smoker	0-1.5% COHb	[10]
Smoker	Up to 14%COHb	[11,12]
Natural urban air level	1-30 ppm	[15]
Levels found in homes	0.5- 5 ppm	[42]
Cigarette Smoke	20 000-60 000 ppm	[15]
Alveolar Concentration in smoker	300-400 ppm	[15]
Car Exhaust without catalytic converter	30 000- 60 000 ppm	[15]

*Parts per million (ppm) by volume (100 ppm = 0.01% of CO in the air)

*Percent carboxyhemoglobin (%COHb) is the amount of CO bound to total haemoglobin