Detection of indoor airborne fungal contamination through examination of building heating, ventilating and air conditioning (HVAC) filters

Hernando R Perez, Purdue University

Abstract

This three phase research involved the pilot testing, laboratory development and field evaluation of a method for the quantification of viable fungal particles on heating, ventilating and air conditioning (HVAC) system filters. The primary purpose of this three phase work was to evaluate whether or not the airborne concentration of viable fungal particles calculated through the quantification of building HVAC filters is significantly associated with the average airborne viable fungal concentration as calculated through the collection of multiple single stage viable impactor samples taken at regular intervals while filters are in service. A second purpose of this research was to evaluate whether not the filter quantification method is able to differentiate, with respect to viable fungal airborne levels, between areas suspected of having significantly different concentrations. The filter quantification method involved the immersion of filter samples in 0.9% sterile saline, the shaking of the filter/saline combination, and the plating of aliquots of the shaking solution onto solid growth media. The inoculated media plates were incubated at room temperature for 96 hours at which time colonies were counted. The initial pilot phase of this research involved a comparison between complaint and non-complaint university building HVAC filters. The results of the comparison indicated a statistically significant greater number of mold spores on the complaint filters than on the non-complaint filters when the results were normalized for airflow. The second research phase involved the use of a ventilation test chamber in which test filters were loaded with aerosolized A. niger or P. chrysogenum fungal spore suspensions before being processed as described above. Fungal recovery values as high as 93% were found with this method. In some cases recovery values of greater than 100% were obtained. The third phase of this research involved the comparison of filter quantification and single stage impactor results in several buildings. A statistically significant relationship between the two sampling procedures was found at both shorter and longer term sampling periods. Also in this phase, the filter quantification method was found to be more likely than impactor sampling to differentiate between areas with respect to airborne fungal concentrations.

Degree

Ph.D.

Advisors

Zimmerman, Purdue University.

Subject Area

Occupational safety|Public health

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