Worker Safety CO₂ Calculator

Safe entry levels and purge time for CO₂-enriched grow rooms. OSHA exposure limits + ventilation math.

Calculate purge time

Current room CO₂ (ppm)

Target entry CO₂ (ppm) OSHA TWA 5000; safe entry generally ≤ 1000

Outside (intake) CO₂ (ppm) Ambient atmospheric CO₂

Room volume (ft³) L × W × H

Exhaust CFM Exhaust capacity during purge

Purge time required —min From current to target ppm

Air changes during purge —ACH Equivalent room exchanges

Status — Current vs entry safety

CO₂ exposure limits

Threshold	CO₂ (ppm)	Effect
Atmospheric ambient	~420	Normal outdoor air. Plant baseline.
Indoor ambient (closed buildings)	600-1000	Typical indoor levels with people exhaling. Drowsiness possible at upper end.
Cognitive impairment threshold	~1000	Reduced focus, slower decisions. Workplace recommendation: keep below.
OSHA PEL (8h TWA)	5000	Permissible Exposure Limit time-weighted average over 8-hour shift.
OSHA STEL (15min)	30,000	Short-Term Exposure Limit; max for 15 min.
NIOSH IDLH	40,000	Immediately Dangerous to Life or Health.
Headache, dizziness	~30,000	Most people experience symptoms.
Loss of consciousness	~80,000	Within minutes; respiratory arrest risk.
Death	~100,000+	Within minutes if no rescue.

Why this matters for grow rooms

CO₂-enriched grow rooms commonly run 1000-1500 ppm during photoperiod, with some commercial cannabis operations pushing 1500+ ppm. While these levels are not acutely dangerous, they exceed cognitive-comfort thresholds and OSHA workplace recommendations for sustained exposure.

For workers entering during photoperiod (to inspect, train, water, harvest):

• Below 1000 ppm: generally fine; brief work without specific precautions
• 1000-1500 ppm: brief tasks tolerable; extended work warrants ventilation purge first
• 1500-3000 ppm: ventilate before entry; limit duration; monitor workers
• Above 3000 ppm: do not enter without purge to safe levels; or use respiratory protection if entry is essential

Common practice: shut off CO₂ injection 30-60 minutes before scheduled worker entry, run exhaust ventilation, monitor with a CO₂ meter, enter when levels are below 1000 ppm.

CO₂ generators add other hazards

Combustion-based CO₂ generators (natural gas or propane burners) produce additional combustion byproducts:

• Carbon monoxide (CO) — colorless, odorless, deadly at 100s of ppm. Improperly tuned burners produce dangerous CO levels.
• Nitrogen oxides (NOx) — respiratory irritants; burners running too hot produce them.
• Water vapor — burning fuel produces water; affects RH dynamics.
• Heat — burners add heat load to HVAC.

Always have a CO monitor in any room with combustion CO₂ generation. Periodic burner tuning is essential. Tank-based liquid CO₂ avoids these byproducts entirely.

The math

The purge model assumes well-mixed air and constant exhaust:

C(t) = C_outside + (C_initial − C_outside) × exp(−CFM × t / Volume)

Solving for time to reach target:
t = (Volume / CFM) × ln((C_initial − C_outside) / (C_target − C_outside))

This is the same exponential-decay model used for general indoor air quality. Real rooms have stratification and mixing inefficiencies; add 20-30% safety margin to calculated purge times.

Free under CC BY 4.0. Cite as "OAT Worker Safety CO₂ Calculator (openagriculturetechnology.com)". OSHA values per CFR 29 1910.1000; verify current values.