[Evaluation of humidifier units within the scope of room climate modification]

An analysis method was developed for detecting the biocides usually employed in German humidification units in air-conditioning plant to enable determination of air concentrations of methylisothiazalone often used in such plant (German trade names e.g. Kathon WT, Wacozid 3150, Lavisan Q). Results of measurements revealed great variations in isothiazolone concentrations in ambient indoor aerosols, the peak values being 3.4 micrograms/m3 air. The concentration of these compounds added to the water in the humidificator chambers was also measured in relation to the presence of microorganisms to find out the microbicidal action of the compounds. It was found that the isothiazolone concentrations varied greatly in course of time and that microbiology revealed in some cases a marked contamination of the water in the humidifiers with pathogens. Microbial analyses showed the presence of Legionella pneumophila and free amoeba, sometimes with very high aerobic colony counts. The measured data lead to the conclusion that it is possible that both the unsatisfactory hygienic status of many circulatory spray humidifiers and the exposure to the biocides contained in the humidifier fluids, may be responsible for some of the patterns of signs and symptoms known as "sick building" syndrome.