The best strategy to determine if building occupants are exposed to hazardous mould is to take air samples. It is important to note that even in rooms with visible mould growth air sampling may give very low spore counts. Two methods are widely used in sampling air for mould.

1. Impacting air on some growth media. This method is used when one is interested in determining the concentration of viable mould spores/fragments in the air.
2. Impacting air on some inert sticky surface. In this case the mould spores and other particulate are directly counted under a microscope regardless of whether the spores are viable or not.

Both methods have limitations. Therefore, whether to use the first, second or both methods depends on the type of data required, which in turn depends on the objective of the investigation.