Test strips comprising B subtilis spores or M phlei cells dried on aluminium foil (some serum-coated) were used to test sterilizing processes currently advised for safety cabinets. Exposure to formalin from a bowl, boiling excess formalin with the fan running, and ultraviolet radiation were all found to be unreliable, as was glutaraldehyde. Vaporization of 2 ml of formalin per 0·028 m3 followed by exposure for 18 hours at ambient temperatures was 100% successful, and the depolymerization of paraformaldehyde tablets with a hair drier was a simple, very effective alternative method.
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