Tomh - I think you mean specific gravity, not density. Anyway, some more CO information:
Percentage of Blood Saturation: Symptoms
1-10 None (every day exposure)
10-20 Tightness Across Forehead, possible headache.
20-30 Headache, Throbbing Temples.
30-40 Severe Headache, Weakness, Dizziness, Dimness of Vision, Nausea, Vomiting, and Collapse
40-50 Same as above but with more intensity.
50-60 Fainting, Increased Pulse and Respiration, Coma with Intermittent Convulsions.
60-70 Coma, Convulsions, Depressed Heart Action and Respiration, Possible Death.
70-80 Weak Pulse, Slowed Respiration, Death.
(Blood Saturation is not the samr as PPM)