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Toolbox talk · 10 min · HazCom & Chemicals

Carbon Monoxide from Gas-Powered Equipment

Hazards: Carbon monoxide from gas and propane engines used indoors · Exposure of bystanders who are not running the machine · Incomplete combustion from a poorly maintained engine or heater · Symptoms mistaken for heat, fatigue or a long night

Why it matters

On July 13, 2023, a worker ran a gas-powered walk-behind concrete saw in a basement for about four hours with no respiratory protection and, in OSHA's words, insufficient engineering and administrative controls. He walked to a gas station for drinks, sat down on a trailer on his way back, and his coworkers found him unresponsive. He died of carbon monoxide toxicity (OSHA Summary Nr 158061.015). Eleven months later a man running a shop vacuum beside a big gas saw inside a cooler died the same way — and he was not the one operating the saw (Summary Nr 167692.015).

Key points

  • It is not just generators. Concrete saws, power trowels, cut-off saws, compactors, pressure washers, propane forklifts, burnishers and temporary heaters all burn fuel, and all of them make carbon monoxide.
  • 50 ppm, 8-hour average. That is the limit, in Table 1 to 1926.55 for construction and Table Z-1 to 1910.1000 for general industry. Controls come first: engineering or administrative, with PPE only where they cannot get you there.
  • A big room is still an enclosed room. The 2024 fatality happened in a space roughly 125 by 125 by 30 feet. An engine keeps adding CO; without exhaust the number keeps going up.
  • The bystander is exposed too. The man who died in 2024 was on a shop vacuum. Whoever shares the air shares the dose, and they usually have no idea an engine is the reason.
  • Heaters need combustion air, not just fuel. 1926.154(a)(1) requires fresh air in sufficient quantities and mechanical ventilation where natural supply is inadequate; (a)(2) requires special care in confined spaces to ensure proper combustion.
  • Headache and nausea are the alarm. They read like heat or a long night. Around a running engine, treat them as CO: outside, fresh air, medical attention, and nobody drives themselves home.

Do / Don't

Do

  • Use electric, hydraulic or pneumatic tools indoors wherever they exist.
  • Exhaust the space mechanically and put the intake where the air is clean.
  • Carry a CO monitor and know what number sends everyone out.
  • Keep engines and propane trucks tuned - a rich engine makes far more CO.

Don't

  • Count an open door, a roll-up or a box fan as ventilation.
  • Run a saw or trowel in a basement, cooler or tarped-off floor.
  • Work through a headache to finish the pour.
  • Assume the guy on the vacuum or the broom is out of it.

Quick site check

  • Which fuel-burning machines will run inside today, and for how long?
  • What is actually moving the air out, and where does the fresh air come in?
  • Who else works in that space, and do they know an engine is running?
  • Is there a CO monitor on site, and who is carrying it right now?
Discussion — ask the crew
  1. Which engines are running inside a building on this job today, and who decided that was fine?
  2. If you had a headache at 2 p.m. on a concrete pour, would you say so or finish the slab?
  3. Who is working near the saw operator, and what protects them?
  4. Do we have a CO monitor here, who carries it, and when was it last bump tested?
Refs: 29 CFR 1926.55 Table 1 - Permissible exposure limits for airborne contaminants: carbon monoxide, 50 ppm (55 mg/m3) as an 8-hour TWA; (b) requires administrative or engineering controls first · 29 CFR 1910.178(i)(1) - Control of noxious gases and fumes: CO created by powered industrial truck operations shall not exceed the levels in 1910.1000; (l)(3)(ii)(H) makes closed environments a required training topic · 29 CFR 1926.154(a) - Temporary heating devices: fresh air in sufficient quantities, mechanical ventilation where natural means are inadequate, special care in confined spaces to ensure proper combustion · OSHA Accident Search, Summary Nr 158061.015 (July 13, 2023): a gas-powered walk-behind concrete saw run for about four hours in a basement, no respiratory protection and insufficient controls; death from carbon monoxide toxicity · OSHA Accident Search, Summary Nr 167692.015 (June 17, 2024): a worker running a shop vacuum beside a large gas-powered concrete saw in an indoor cooler collapsed and died; acute carbon monoxide poisoning with cardiovascular diseaseSign-in sheet included in the printed version

Frequently asked questions

50 parts per million as an 8-hour time-weighted average. In construction it sits in Table 1 to 29 CFR 1926.55, listed as 50 ppm or 55 mg/m3; in general industry it is the same figure in Table Z-1 to 1910.1000. 1926.55(b) also fixes the order: administrative or engineering controls must be implemented first whenever feasible, and protective equipment is used only where those controls cannot achieve full compliance.

No. Any engine burning gasoline, diesel, propane or kerosene makes carbon monoxide, and the machines that kill people indoors are usually the ones nobody thinks of as a generator: walk-behind and cut-off concrete saws, ride-on and walk-behind power trowels, plate compactors, pressure washers, propane forklifts, propane and kerosene temporary heaters, and floor burnishers. Both fatal cases cited on this page involved a concrete saw, not a generator.

They do. 29 CFR 1910.178(i)(1), titled Control of noxious gases and fumes, states that concentration levels of carbon monoxide gas created by powered industrial truck operations shall not exceed the levels specified in 1910.1000. And 1910.178(l)(3)(ii)(H) makes it a required training subject: operator training has to cover closed environments and other areas where insufficient ventilation or poor vehicle maintenance could cause a buildup of carbon monoxide or diesel exhaust. A propane truck that has drifted out of tune produces far more CO than one that is maintained.

29 CFR 1926.154(a)(1): fresh air shall be supplied in sufficient quantities to maintain the health and safety of workmen, and where natural means of fresh air supply is inadequate, mechanical ventilation shall be provided. (a)(2) goes further for confined spaces - special care shall be taken to provide sufficient ventilation in order to ensure proper combustion, maintain health and safety, and limit temperature rise. A tarped-off floor with a salamander running is exactly that situation.

Not on its own. In the June 17, 2024 case, a large self-propelled gas-powered concrete saw was running inside a cooler measuring roughly 125 feet by 125 feet by 30 feet - close to half a million cubic feet. The worker who died was not the saw operator; he was running a shop vacuum nearby. An engine adds CO continuously, and without exhaust the concentration keeps climbing no matter how big the room is.

Headache, dizziness, weakness, nausea, shortness of breath, confusion. They look like heat, dehydration or a bad night, which is why they get worked through. Anyone with those symptoms around a running engine goes outside into fresh air immediately and gets medical attention - and does not drive themselves anywhere. Nothing in this talk is medical advice.

You measure it. Carbon monoxide has no color, odor or taste, so a person cannot detect it at any concentration. Direct-reading CO monitoring, either a personal instrument on the operator or a fixed monitor in the space, is the only way to know whether the ventilation you set up is actually working. In the July 13, 2023 case, OSHA's own summary records that the worker had insufficient engineering and administrative controls to keep his exposure below the permissible exposure limit.

Sources & references

Content checked against these sources — last reviewed August 28, 2026.

Results are estimates for planning purposes and do not replace a competent person's evaluation or an engineer's design. Follow the OSHA standards that apply to your work and your employer's written program.

By — Editorial team of SteelToeTools.com (published by LSEA SAS) Updated