•	 Carbon monoxide (chemical abbreviation: CO) is a clear,
colourless gas you can’t smell or taste.
It’s dangerous because it interferes with your body’s ability
to use oxygen. Even in small doses, carbon monoxide can
•	 The first signs are headache and fatigue. More exposure
can rapidly lead to loss of consciousness, arrested breath-
ing, heart failure, and death.
In construction the major source of carbon monoxide is
engine exhaust. Gasoline, propane, and diesel engines all
release carbon monoxide. Some types of welding may
also produce it.
Since carbon monoxide has no taste or smell, you need a gas
detector to see if it’s present. Some detectors are tubes that
change colour when carbon monoxide is in the air. These can
be used only once. Others are continuous monitors with a cell
designed to sense carbon monoxide.
Whenever possible, operate engines outdoors. Welding ma-
chines and generators, for example, can be left outside—only
the leads have to run into the building.
Never work alone in an area where carbon monoxide can ac-
When engines must be operated indoors, take these precau-
•	 Make sure the area is well ventilated. Keep doors and
windows open. Use fans to bring in fresh air if necessary.
•	 Limit running time and don’t let engines idle.
•	 Monitor carbon monoxide levels regularly to make sure
that ventilation is adequate.
•	 When necessary, use exhaust hoses or fans to draw engine
exhaust out of the work area.
•	 Keep engines well tuned. They will run cleaner and pro-
duce less carbon monoxide.
•	 When possible, use equipment that is electrically powered
rather than gasoline, diesel, or propane powered.
•	 When other controls are inadequate, workers must wear
respiratory protection. This means a supplied air respira-
tor. You need a respirator attached to an independent
supply of clean air.
Point out sources of carbon monoxide on site. Demonstrate
how to use a detector. Show how to ventilate indoor areas.
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