OSHA Carbon Monoxide Monitoring Requirements (2026): PEL, Limits & Compliance

OSHA sets a carbon monoxide permissible exposure limit of 50 ppm as an 8-hour time-weighted average (29 CFR 1910.1000), and requires atmospheric testing for CO before and during permit-required confined-space entry (1910.146). Where CO is a recognized hazard, the general duty clause obliges employers to monitor and control it.

This guide explains the OSHA CO limits, confined-space testing, employer responsibilities and a compliance checklist. It supports our best industrial CO monitors hub — use it to choose a compliant monitor from the CO gas monitor range.

OSHA CO permissible exposure limit (PEL)

For general industry, OSHA's CO PEL is 50 ppm as an 8-hour TWA, listed in 29 CFR 1910.1000 Table Z-1. A workplace CO monitor must therefore track time-weighted average exposure, not just instantaneous peaks, so a worker's full-shift dose stays under the limit.

CO exposure limits at a glance

OSHA's PEL is the enforceable limit; the NIOSH REL (35 ppm TWA, 200 ppm ceiling) and ACGIH TLV (25 ppm) are lower consensus targets many employers adopt as alarm setpoints. 1,200 ppm is the NIOSH IDLH — the level requiring immediate evacuation and rescue.

Confined-space CO testing (1910.146)

Permit-required confined spaces must be tested before and during entry in a set order: oxygen first, then flammable gases and vapors, then toxics such as carbon monoxide. Because CO almost never appears alone in a confined space, a 4-gas monitor (O₂, LEL, CO, H₂S) is the standard tool. See 4-gas vs single-gas and the best 4-gas monitor guide.

Does OSHA require CO monitors?

OSHA does not name a single 'you must wear a CO monitor' rule for every workplace, but the 50 ppm PEL, the confined-space standard, the powered-industrial-truck standard (1910.178) and the general duty clause together require employers to assess and control CO wherever internal-combustion engines, combustion heating or enclosed spaces create exposure. In practice, that means monitoring.

Employer responsibilities

• Exposure assessment — identify where CO is generated and who is exposed
• Monitor selection — choose instruments that track TWA and alarm below the PEL
• Bump testing & calibration — verify response before use and calibrate on schedule
• Confined-space program — test atmospheres in order before and during entry
• Records & training — keep exposure and calibration records and train workers on alarms and response

How to stay compliant — checklist

• Alarm setpoints below 50 ppm (commonly 35/200 ppm) with TWA tracking
• Bump test before each day of use; calibrate per manufacturer schedule
• 4-gas instrument for any permit-required confined-space entry
• Worn monitors on internal-combustion forklift operators and combustion-area workers
• Documented response and evacuation procedure for alarms

Need the hardware? Start with our best industrial CO monitors hub or the best CO monitor for forklifts guide.

Frequently asked questions

Does OSHA require CO monitors?

OSHA sets a 50 ppm CO PEL and, through the confined-space, powered-industrial-truck and general duty provisions, requires employers to assess and control CO where it is a recognized hazard — which in practice means monitoring.

What is the OSHA PEL for carbon monoxide?

50 ppm as an 8-hour time-weighted average, per 29 CFR 1910.1000 Table Z-1 for general industry.

What is the difference between OSHA PEL and NIOSH REL for CO?

The OSHA PEL (50 ppm TWA) is the legally enforceable limit; the NIOSH REL (35 ppm TWA, 200 ppm ceiling) is a lower recommended limit. Many employers set alarms to the stricter NIOSH value.

What is the CO IDLH?

1,200 ppm is the NIOSH Immediately Dangerous to Life or Health level for carbon monoxide — the point requiring immediate evacuation and rescue procedures.

Does OSHA require CO monitoring in confined spaces?

Yes — permit-required confined spaces (1910.146) must be tested for oxygen, flammables and toxics including CO before and during entry, typically with a 4-gas monitor.

What order do you test atmospheres in a confined space?

Oxygen first, then flammable gases and vapors, then toxic gases such as carbon monoxide and hydrogen sulfide.

Do warehouses need CO monitoring under OSHA?

Where internal-combustion forklifts or combustion heaters operate, employers must control CO to the PEL — see best CO monitor for forklifts.

How often must CO monitors be calibrated for OSHA?

OSHA expects instruments to be maintained and accurate; follow the manufacturer's schedule — commonly a daily bump test and calibration every six months or after a failed bump test.

What CO level requires evacuation?

Evacuate and follow rescue procedures at the 1,200 ppm IDLH; many programs evacuate at lower alarm setpoints. Follow your site's written procedure.

Are home CO alarms OSHA compliant for workplaces?

No — residential alarms don't track occupational TWA exposure or support bump testing and calibration. Use an industrial monitor, not a home CO alarm.

Does OSHA require CO training?

Employers must train workers on recognized hazards, including how to respond to CO alarms and evacuation procedures, under their hazard-communication and confined-space programs.

What records must employers keep for CO monitoring?

Exposure assessments, monitoring results, calibration and bump-test logs, and confined-space entry permits, per the applicable standards.

Related: industrial CO monitoring guides

• Best industrial CO monitors (hub guide)
• Best CO monitor for forklifts
• CO detector placement guide
• Carbon monoxide exposure symptoms
• Portable vs fixed CO monitors

By Steven Eaton, WC Safety Editorial · Updated June 23, 2026 · industrial gas-detection desk.