Objectives The purpose of this study was to compare different methods for calculating maximal allowable concentrations of potentially carcinogenic substances in indoor air. Benzene, tetrachloroethylene, trichloroethylene, and vinyl chloride were selected as the model substances.

Methods Estimates were used of carcinogenic potency from quantitative risk assessment, lowest observable effect levels (LOEL) from animal experiments and epidemiological studies combined with safety factors, and estimation from occupational exposure limits with safety factors. The estimates were compared with actual concentrations in buildings in Denmark.

Results Concentrations of benzene, tetrachloroethylene, trichloroethylene, and vinyl chloride of the order of 10 ppb, 20 ppb, 200 ppb, and 40 ppb, respectively, in indoor air were found to correspond to a 10-4 lifetime risk of cancer. Conclusions The estimated maximal allowable concentrations of carcinogenic compounds obtained from indoor air by quantitative risk assessment using a lifetime risk of 10-4 or using LOELs and suitable safety factors appear to be comparable and reasonable. Calculation based on occupational exposure limits and safety factors generally gives comparable or somewhat higher values. Using a lifetime risk of 10-6 for quantitative risk assessment does not seem reasonable considering the risks associated with activities of everyday life.

Key terms benzene; cancer; tetrachloroethylene; trichloroethylene; vinyl chloride