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 |
Gas detection trianing
