Normal Range Criteria for Indoor Air Bacteria and Fungal Spores in a Subarctic Climate

Abstract

Indoor air bacteria and fingal spore levels were studied in 71 non‐complaint homes. lk data were analyzed according to the season and the higher limit of the range within which 95% of the cases fall was computed. On the basis of the data the following highest normal levels are proposed for winter: for bacteria 5000 cfulm3 and for fingal spores 500 cfulm3. The recommended levels apply in a subarctic climate for urban and suburban homes when the measurements are made using the same method as in this study. We recommend that if abnormal indoor sources are suspected, indoor samples should be taken in winter when the ground is frozen and covered with snow. At that time, the background levels are at their lowest and the abnormal indoor sources are most easily detected. lk recommended levels should not be used as an indicator of a health risk, but as an indication of abnormal indoor sources or insufficient ventilation.

Comparisons of seasonal fungal prevalence in indoor and outdoor air and in house dusts of dwellings in one Northeast American county1

“…Indoor sources in basement could be another important factor. The values derived from our study are more than three times higher than the guideline set by Miller et al ( 1988 ) or almost twice higher than the maximum set by Reponen et al ( 1990 ) in living room and bedroom air. This is probably a result of the different climatic conditions prevailing both externally, which effect the outdoor fungal airborne burden and internally, which affect the conditions prevailing within the dwelling.…”

“…These authors determined this maximum level of airborne fungi by applying a statistical formula used in biomedical research, which defines the normal range as that which encompasses 95% of the cases. Therefore 95% of the counts will fall below the value of [mean + 2Â ( standard deviation )] specified by Reponen et al (1990 ). If this formula is applied to the data obtained from our study, conducted in a more temperate climate, then the upper limit for fungi in the winter would be 1087 CFU /m 3 in living rooms, 909 CFU / m 3 in bedrooms, and 4156 CFU / m 3 in basements.…”

“…If the indoor /outdoor ratio exceeded this value then the draft proposal recommends that remedial action should be taken to identify the source of emission and methods to reduce the counts should be instigated. Reponen et al (1990) proposed a maximum level of 500 CFU / m 3 in the wintertime in subarctic climates. These authors determined this maximum level of airborne fungi by applying a statistical formula used in biomedical research, which defines the normal range as that which encompasses 95% of the cases.…”

Microbial Air Contamination in Farmhouses – Quantitative Aspects

“…According to the data on the prevalence of fungal aerosol in homes, the concentration levels of such particles are lower indoors than outdoors, excluding homes with mould problem and the winter season when a decrease of outdoor fungi levels in subarctic and temperate climates is observed [11,18,21,23]. During the frost-free seasons, outdoor air is thought to be the main source of indoor fungi.…”

The Health Protection Act, national guidelines for indoor air quality and development of the national indoor air programs in Finland.

“…Airborne concentrations of bacteria and mold were measured in various types of buildings during different seasons of the year (11)(12)(13)(14)(15)(16)(17)(18). In 1990, the first pilot studies on health effects associated with microbial exposure were started in apartment buildings and daycare centers as a part of the research program of KTL (19,20).…”