Carbon Monoxide from Temporary Heaters & Generators

A crew fires up a propane heater to thaw a slab in a closed-up room. An hour later two of them have splitting headaches and feel sick. That's carbon monoxide — and it gives no warning of its own. By the time people feel it, the level in the air is already high.

The hazard

Carbon monoxide (CO) is a gas you can't see, smell, or taste. Anything burning fuel makes it: propane and kerosene heaters, gas generators, concrete saws, compactors, idling vehicles. In an enclosed space it builds up and takes the place of oxygen in your blood. Low levels bring headache, dizziness, and nausea that get put down to the flu or a bad night's sleep; higher levels take people off their feet before they can get themselves out. CO is about the same weight as air, so it doesn't settle at the floor or rise to the peak — it mixes in right where you're breathing.

What to do

• Keep generators, compactors, and other fuel engines outside and well away from doors, windows, and air intakes. Exhaust drifts back in.
• Running an engine in a building, an enclosure, or an excavation is a planned setup, not a quick one. It needs combustion air, its exhaust taken well clear, and the air tested for CO by a competent worker under the employer's written testing strategy. No plan, no engine.
• Run a fuel-fired heater the way its label says: rated for the space, enough combustion air, real ventilation, and the clearances it calls for. A heater built to vent outside has to actually vent outside — and never rig your own ducting on one that isn't.
• Put a CO alarm in every heated or enclosed work area, placed and checked the way its instructions say. A hardware-store alarm is built for a household emergency and can sit quiet at levels already past the workplace limit — it's a backstop, not the air test.
• If the alarm sounds or anyone shows symptoms: everyone out to fresh air, call 911, say CO is suspected. Nobody goes back in — not for tools, not to shut the heater down — until it's ventilated and re-tested. Don't improvise a rescue: going in after someone who's down is for the responders, with the breathing and rescue gear the emergency plan calls for.
• Choose electric tools and heaters inside where you can, and shut engines off rather than letting them idle.

Watch out for

• Two or more people with headache, dizziness, or drowsiness at the same time in the same area.
• Snow, ice, or debris blocking a heater or generator exhaust after a storm.
• An engine running just outside an open door or under an air intake.
• "It ran fine yesterday" — a tighter tarp, a colder start, or a blocked vent changes everything.

Talk it over

• Where's our CO alarm right now, who checked it, and is it placed the way its instructions say?
• Every engine and heater running on this site today — where is its exhaust actually going?