Confined spaces can present three kinds of atmospheric hazards:
o flammable, combustible, or explosive atmosphere
o oxygen-enriched or oxygen-deficient atmosphere
o Atmospheric contaminants.
The hazardous atmosphere may be due to existing conditions (e.g., residue in a tank,) or it may be created by the work being done inside the confined space (e.g., welding or using solvents). In some cases, removing sludge or scale can release trapped pockets of gas or vapour and create a hazardous atmosphere.
Moreover, dangerous atmospheres often exist together. For instance,
flammable, combustible or explosive atmospheres may also be toxic or cause an oxygen deficiency.

We will look at each of these hazardous atmospheres in the following lessons.