Disinfection with gaseous formaldehyde. Second Part: Influence of test materials on formaldehyde residues and the bactericidal and sporicidal effectiveness.

The pararosaniline method for the determination of formaldehyde residues on test surfaces after exposure to gaseous formaldehyde was standardized as well as the methods of collection, preparation and desorption from the samples. The analysis of residues on plates of 5 different materials yielded the following amounts of residues after 60 minutes exposure to 3.2 mg HCHO1-1 air at 45 degrees C and a relative humidity (RH) of about 90%; silicon rubber 287.2 micrograms, lacquered polyurethane foam 109.6 micrograms, lacquered aluminium 30.3 micrograms, plexiglass 13 micrograms and stainless steel 4 micrograms HCHO 100 cm-2. The residues of formaldehyde on lacquered aluminum after an HCHO exposition with condensing layer at 20 and 30 degrees C were 10(3)-fold higher than after an exposition to gaseous formaldehyde without a condensing layer at a relative humidity of about 90% and a temperature of 40 degrees C. The inactivations of S. aureus and Bacillus subtilis spores on carriers of 5 different materials were determined under the same conditions (60 min, 3.2 mg HCHO 1-1 air, 45 degrees C and a RH of about 90%). The decimal reductions showed that Staphylococcus aureus ATCC 6538 was more readily inactivated on non porous plexiglass with a D-value of 0.7 min or stainless steel D = 1.1 min than on porous silicon rubber D = 3 min. For spores of Bacillus subtilis var. niger DSM 675, D-values of 1.6 min for plexiglass, 2.3 min for stainless steel, 2.7 min for lacquered aluminium, 3.2 min for lacquered polyurethane foam and 4.1 min for silicon rubber were registered.