Table 1.

CO exposure limits.

Level	Concentration ($\mathbf{mg}/{\mathbf{m}}^3$)	Concentration (ppm)
Excellent	0–2.(9)	0–2.61(9)
Very Good	3–4.(9)	2.62–4.366(9)
Good	5–6.(9)	4.367–6.113(9)
Medium	7–9.(9)	6.114–8.733(9)
Bad	10–14.(9)	8.734–13.0(9)
Very Bad	>15	>13.1