Examining the mold and bacterial spore concentrations in indoor air at Opsund timber debarking and wood chipping factory

This report summarizes the implementation and the results from a monthly air-sampling campaign during the period May–September 2019 at the Opsund timber debarking and wood chipping factory. The work was performed on a contract from Borregaard in order to investigate the concentration of airborne molds, bacterial spores and total particles. The purpose of the study was to establish the concentration levels of molds and bacterial spores in indoor air and to examine whether some steps in the timber debarking and wood chipping process were greater sources for releasing microorganisms to the air. At Opsund timber debarking and wood chipping factory the logs are flushed clean for soil and stones before they are debarked and cut to wood chips. Molds and other microorganisms can follow the logs into this process and become airborne due to the mechanical debarking and wood chipping processes. Studies have also shown that fungi can grow on pollen, thus the level of airborne pollen were also monitored in order to investigate the correlation between pollen and molds concentrations. Air samples were collected inside the production hall, in the control room and at an outdoor reference point. The occurrence of mold and bacterial spores were compared with similar measurements performed during 2017. The results from the 2017 measurements led to routine changes concerning the use of dust masks in the production hall. Thus, knowledge achieved during the 2019 air sampling campaign may also result in measures to reduce the levels of fungi and other microorganisms inside the production hall. Measurements in this study showed that the concentration of airborne molds, bacterial spores and pollen were 10, 2 and 2.5 times higher in the production hall when compared to the outdoor reference point. Common guidelines are that if the concentration of molds in indoor air is two times higher than outdoors, there is probably an indoor source. Our measurements clearly indicate that the production of wood chips is a source for molds in indoor air at Opsund. Concentrations of molds, bacterial spores and pollen in the control room were lower than at the outdoor reference point and confirm that the increased levels in the production hall does not affect the control room.