Is a quantitative risk assessment of air quality in underground parking garages possible?

Little information is available about the health risks associated with time spent in underground parking garages. The objective of this study was to determine whether it is possible to quantify the health risks associated with these garages without epidemiologic data on the subject. We followed the standard procedure for health risk assessment. We searched the literature for pollutant concentrations in the air samples of underground parking garages, the hazards associated with their inhalation, and their toxicological reference values. Conditions of occupational and user exposure were estimated by scenarios and taken into account to discuss toxicological reference values by modifying (with Haber's law) the adjustment factors for exposure frequency and duration. Risk quantification was possible for 39 pollutants. Acute exposures to CO and NO2 exceed toxicological reference values, as does chronic exposure to benzene for threshold effects. The risk of a carcinogenic effect associated with benzene may be greater than 10(-5). Excess exposure to air pollution indicators (PM and NO2) is also elevated, judging by the WHO Air Quality Guidelines, and also when comparing to levels with reported effects in epidemiologic studies. The risk associated with underground parking garages can be evaluated only in part. The information available is nonetheless sufficient to justify actions to reduce exposure. The risks associated with exposure in underground parking garages cannot be thoroughly evaluated because of inadequate knowledge of exposures and of the toxicity of pollutants. The available knowledge is nonetheless sufficient to advise that risk management measures should be taken to reduce both acute and chronic exposures.