Carbon monoxide (CO) — biological monitoring
When to suspect: Furnaces / foundries, coke ovens, blast furnaces, vehicle exhaust (mechanics, garages, toll), gas appliances, welding/cutting, firefighting; methylene-chloride strippers metabolise to CO.
Carboxyhaemoglobin (COHb) · end-exhaled CO (% · ppm)
| Level | Interpretation |
|---|---|
| < 1.5% | Non-smoker background (smokers 8–10%) |
| 3.5% | ACGIH BEI — COHb, end of shift |
| 20 ppm | ACGIH BEI — end-exhaled CO, end of shift |
Smoking is a major confounder — record status + time since last cigarette.
Biological exposure index
ACGIH BEI: COHb 3.5% + end-exhaled CO 20 ppm, both end of shift (TLV-TWA 25 ppm).
Basis: ACGIH BEI (ATSDR ToxProfile for CO).
Sample collection & preparation
- COHb: full anticoagulated (EDTA/heparin) tube, minimal air space, analyse promptly by CO-oximetry.
- Exhaled CO: breath-hold ~15–20 s then deep exhale into a CO monitor.
- Record smoking status.
Statutory basis. Factories Act 1948 sets only AIR limits (Second Schedule TWA/STEL, s.41F) and mandates the hazardous-process exam (s.41C, ≤12-monthly); it gives NO blood/urine values. The ranges below are ACGIH BEI / OSHA / clinical benchmarks (India has not adopted biological limits into law).
Reference information for occupational-health professionals — not medical advice, and not a substitute for examination by a qualified physician.
All 27 agents — toxicology & biological monitoring
MedFactory — Occupational Health Centre software for Indian factories