(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

other solvents which can be found in household products and off-gassing from indoor
furnishings, the primary sources of benzene are gasoline and combustion sources.
Studies have shown that homes with attached garages have a higher range of indoor
concentrations of benzene than homes without attached garages (Adgate et al., 2004; Thomas
et al., 1993, Brown and Crump, 1998; Schlapia and Morris, 1998; Isbell et al., 1999; Phillips et
al., 2004; Tsai and Weisel, 2000 and Mann et al., 2001). Attached garages elevate indoor
levels when benzene from garage sources such as evaporative emissions from automobiles,
small engine equipment (i.e., lawnmowers, trimmers, and leaf blowers) storage containers and
infiltrate the home.
An attached garage can be thought of as a discrete emission source to a home. However, the
amount of benzene that actually enters the home will vary with the rate of infiltration from the
garage to the home and the air levels of benzene in the garage. One investigation attributed
more than 75% of benzene exposures in homes with attached garages to air entering from
attached garages (Fulger et al., 2002), with the resultant levels in the home also being
influenced by outdoor air levels and the whole house air exchange rates. Whole house air
exchange rates vary with the season and are lower in cold weather (Murray and Burmaster,
1995). From the various attached garage studies, the following factors have been found to
influence indoor benzene concentrations in homes with attached garages:
• Heating systems (forced air);
• Season in which the measurement is taken;
• Frequency and duration of parking the car in the garage;
• Emission characteristics of the car;
• Ventilation of the garage and home;
• Availability of vapor migration pathways from the garage to the living space;
• Other indoor sources and outdoor levels of benzene; and
• Amount and type of car maintenance undertaken in the garage.
A summary of indoor air studies of homes with attached garages used in this assessment is
presented in Table 7.11. Several of the studies cited above were not used in the high-end
indoor air scenario evaluation. Tsai and Weisel (2000) was not deemed representative for
purposes of understanding typical benzene exposures because an experimental gasoline, M85,
which is 85% methanol and 15% conventional gasoline, was used in the study. Phillips et al
(2004) was not used in this analysis as the authors indicated that the presence of an automobile
or other gasoline source(s) were not documented at the time of the study (personal
communication with Phillips and J. Panko, 2004). And several studies (Isbell et al., 1999 and
Schlapia and Morris, 1998, Morris 2004) conducted in Alaska are discussed separately in
Section 7.2.1.5. The remaining four studies were selected for use in deriving the estimate of the
mean concentrations in homes with attached garages.
Benzene VCCEP Submission
March 2006
111