(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

Small Engine Equipment Exposures
Use of small off-road engines in the U.S., such as lawn mowers, ATVs, snowmobiles,
chainsaws, leaf blowers and trimmers, is common. It is estimated that on average there are
more than 1.4 million snowmobile users, nearly 3 million ATV users, and more than 25 million
lawn equipment users (EPA, 1999a, b, 2000a). The EPA has been evaluating air emissions
from small, off-road engines and has drafted proposed emission control regulations.
Additionally, the State of California Air Resources Board has conducted preliminary evaporative
emission estimates for small off-road engines using their OFFROAD model, although currently,
only emissions for total hydrocarbons can be assessed, not specific compounds.
Because children and prospective parents could be exposed to benzene during the use of small
engine equipment, these potential sources of exposure were considered. However, the data
from studies which evaluated benzene exposure from small engine equipment use is very
limited and none were found to be satisfactory for quantitative exposure assessment. These
studies are presented below, but children’s exposures to benzene from use of small engine
equipment have not been quantified.
Wallace et al., 1989: This study measured VOC exposures of people performing common
activities. One personal sample of benzene was collected of a person while mowing the lawn,
yielding a concentration of 0.032 mg/m 3 .
Nilsson et al., 1987: For this study, investigators measured benzene emissions from twostroke
engine chainsaws. Emissions data were collected for various scenarios, including snow
and no-snow situations. Under snow conditions, benzene concentrations ranged from 0.3 to 1.8
mg/m 3 , and had an average of 0.7 mg/m 3 . Under no-snow conditions, benzene concentrations
ranged from 0.1 to 2.4 mg/m 3 , and had and an average of 0.6 mg/m 3 .
Bailey, 2001: In this study, benzene exposure while snowmobiling was estimated from
measurements of carbon monoxide tailpipe emissions and an empirical model for the prediction
of snowmobile drivers’ CO exposures (Snook and Davis, 1997). The basis for the Snook and
Davis model is that CO is an inert gas, such that photochemical and physical removal
processes in a plume of snowmobile exhaust should not be significant determinants of
exposure. Thus, transport processes such as diffusion and turbulence govern its dilution.
Bailey theorized that given CO’s stability, the empirical relationships between emission rates
and exposure should be applicable to any inert gas emitted from a tailpipe, such as benzene.
Using a regression analysis of benzene emission rates from snowmobiles, Bailey demonstrated
that benzene emission rates are correlated with CO emission rates and therefore calculated
benzene exposures using the Snook and Davis model. Exposure estimates were presented for
numerous scenarios, including riding behind a single snowmobile, as well as 5 th in a line of five
snowmobiles at various speeds. Such “trains” are common in snowmobile parks. For the train
scenarios, it was assumed that exposures from several snowmobiles are additive, which
discounts the role played by multiple snowmobiles in creating additional turbulence, which may
cause more rapid dispersion of exhaust. Modeled benzene exposures were estimated to range
from 0.12 mg/m 3 for a rider behind a single snowmobile to 3.5 mg/m 3 for a rider fifth in line; with
a mean estimated exposure of 1.7 mg/m 3 , depending on speed of the vehicle.
Because of the difficulty in estimating benzene exposure from emissions data collected for total
hydrocarbon or total VOC analysis, only those studies providing exposure measurements of
benzene are suitable for use in characterizing children’s potential exposures to benzene from
Benzene VCCEP Submission
March 2006
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