Disinfection with gaseous formaldehyde. Third Part: Bactericidal and sporicidal effectiveness of gaseous formaldehyde and level of residues in dependence on concentration, temperature and relative humidity.

The highest rate of inactivation of Staphylococcus aureus (ATCC 6538), Streptococcus faecium (ATCC 6057) and spores of Bacillus subtilis var. niger (DSM 675) was observed at a relative humidity (RH) of 90-95%. At a RH of 60% D 0.75 mg HCHO l-1 air at 45 degrees C-values of 35 min and over 65 min were determined for S. aureus and for B. subtilis spores which decreased to D = 2.9 min and D = 20 min respectively at a RH of 90%. At 45 degrees C, an optimal formaldehyde (HCHO) concentration for the inactivation of S. aureus was within the range of 0.75 to 1.5 mg HCHO l-1 air, with D-values of 2.9 to 1.8 min respectively and for Bacillus subtilis spores from 1.5 to 3.2 mg HCHO l-1 air with D-values of 10.9 to 4.0 min respectively. The most effective bactericidal and sporicidal activity of HCHO was observed at temperatures ranging from 40 to 45 degrees C. The higher the exposure temperature the lower were the HCHO residues on 100 cm2 aluminium plates with a structured lacquer. Exposure to formaldehyde concentrations of 0.4 mg l-1 air for 60 minutes resulted in lower residual formaldehyde of 5.9, 5.6, 4.7 and 4.5 micrograms HCHO 100 cm-2 sample surface at 30, 35, 40 and 45 degrees C, respectively. In contrast, after exposures to 3.2 mg HCHO l-1 air residues of 48.5, 43.4, 35.6 and 30.6 micrograms HCHO 100 cm-2 were found at the same temperatures.