What is a harmful airborne contaminant

The following table illustrates the kinds of harmful atmospheres that may be present in a confined space, and how they may be created.

Source	Examples
Substance stored in the confined space or its by-product(s)	build-up of hydrogen sulphide in sewers and pits release of toxic substances e.g. hydrogen sulphide in tanks of decomposing organic material, especially when the material is disturbed
Work performed in the confined space	use of paints, adhesives, solvents or cleaning solutions welding or brazing with metals capable of producing toxic fumes exhaust fumes from engines used in the confined space painting or moulding glass-reinforced plastics
Entry of natural contaminants e.g. groundwater and gases into the confined space from the surrounding land, soil or strata	acid groundwater acting on limestone with the potential to produce dangerous accumulations of carbon dioxide methane released from groundwater and from decay of organic matter
Release of airborne contaminants	when sludge, slurry or other deposits are disturbed or when scale is removed residues left in tanks, vessels etc., or remaining on internal surfaces can evaporate into a gas or vapour
Manufacturing process

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