Carbon Monoxide – Heaters

Temporary heaters are dangerous if you don’t control the risks of explosion, fire, carbon monoxide poisoning, and lack of fresh air.

Heater exhaust is a source of carbon monoxide (CO). Even in small doses, CO can kill you. It’s a clear, colorless gas that you can’t smell or taste.

The first signs of carbon monoxide poisoning are headache and fatigue. More exposure can rapidly lead to loss of consciousness, arrested breathing, heart failure, and death. See the Safety Talk on
carbon monoxide for more information.

Temporary heaters can be fueled by
• electricity
• liquids such as fuel oil or kerosene
• propane
• natural gas.

Choose an indirect-fired heater instead of a direct-fired heater when you want to heat an enclosed
space. An indirect-fired heater vents combustion by-products outdoors while ducting heated air indoors. A direct-fired heater (such as an open flame or closed-flame heater) releases combustion
by-products into the heated area.


Electric heaters are not as common as gas or fuel fired heaters. They’re used where heated air must be free of combustion byproducts such as carbon monoxide and carbon dioxide. An electric heater is useful when working in a closed space with limited fresh air.

Liquid fuel

Liquid fuels such as oil and kerosene provide an economical source of heat. But you need a large storage tank on site for a constant supply of fuel.

Some liquid-fuelled heaters release exhaust fumes with an oily smell. This can be unpleasant for workers. A solution is to vent the combustion byproducts outdoors. This is sometimes done to
heat the air over new concrete in winter.

Propane or natural gas
Propane or natural gas heaters provide an economical supply of heat. The equipment is lightweight and easy to move around on site.

Both gases are highly flammable and explosive. You need to take precautions when storing, handling, or using these gases. [See the Safety Talk on Propane.]

Tips with Heaters
• Only workers holding a certificate may operate a construction heater.
• Do not block openings for ventilation.
• The cylinder connected to a heater must be at least 10 feet away.
• Keep the flame end of the heater pointed away from the cylinder and away from flammable materials. The heat from a burner can ignite materials well past the burner’s end.
• Make sure the heater has a supply of fresh air to operate safely and efficiently, and to prevent buildup of carbon monoxide.
• Test heated areas for the presence of carbon monoxide.
• Place the heater on firm, level surface to prevent tip-over.