The hazards of working in confined spaces are often not rec-
ognized until it’s too late. For example:
•	 Four workers died from hydrogen sulphide poisoning in a
sewage holding tank.
•	 A worker was killed by carbon monoxide gas from a
gasoline-powered pump used to drain a pit.
•	 A worker was caught in a mixing tank which was inadver-
tently started while he was inside.
“Confined space” means a fully or partially enclosed space:
that is not both designed and constructed for continuous
human occupancy, and
in which atmospheric hazards may occur because of its
construction, location, or contents, or because of work
that is done in it.
In chemical and petrochemical plants, confined spaces include
tanks, vessels, pipes, sumps, and pits. Confined spaces in
heavy industrial plants can be roasters, digesters, mixers, bins,
Sewage-handling and water-treatment plants include various
kinds of confined spaces, from settling and holding tanks to
maintenance holes and wells below floor level.
In general construction, confined spaces include vaults, main-
tenance holes, tanks, and other spaces that meet the criteria of
Physical hazards such as live electrical conductors, operating
equipment, stored energy, pressurized pipes, noise, and heat
sources must be controlled in confined spaces through lock-
out and tagging. You must also control other dangers, includ-
ing those you may introduce into the space by the work
being performed. Such hazards include hazardous dusts,
chemical vapours, engine exhaust, and welding fumes.
Other spaces that don’t fall under the definition of confined
space but need to be assessed and controlled include:
trenches and excavations
These spaces must be adequately ventilated to ensure hazard-
ous materials and atmospheres are not present and do not ac-
cumulate from the work being performed. Workers have been
overcome and killed by solvent and adhesive vapours in small,
poorly ventilated rooms.