(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

use of small non-road engine equipment. However, the following limitations render the few
studies that provide exposure concentrations unsuitable for this exposure assessment:
• Because the studies conducted by Wallace et al., and Nilsson et al., were
conducted in the late 1980’s prior to the introduction of oxygenated and
reformulated gasoline, the benzene concentrations are likely to be higher than
exposures which would result from use of the equipment with RFG.
• In the Wallace et al., study there is only one data point available for evaluating
lawn mower exposures, thus deviations around this value are unknown.
• The Nilsson et al. study focused on occupationally exposed logging operators
who would have a significantly different usage pattern than an average
homeowner and thus, the exposures measured may overestimate that for the
general population using landscaping equipment.
• Use of 4-stroke small engine equipment is more common today than during the
years that the studies were conducted, thus exposure estimates from use of 2stroke
engines would not be representative of contemporary exposures.
• The exposure estimates made by Bailey for snowmobile use were obtained from
internal EPA memos, and thus have not been published in the scientific
literature although the information was used in the notice of proposed
rulemaking (NPR) for Control of Emissions from Nonroad Large Spark Ignition
Engines (66 Fed.Reg. 51098). External peer-review by the International
Snowmobile Manufacturers Association (ISMA) indicates that the EPA exposure
estimates are significantly overstated and that the Snook and Davis model is
invalid for predicting both CO and benzene exposures from snowmobile use
(ISMA, 2001). In comments submitted to EPA’s Air docket regarding the NPR,
ISMA submitted an analysis conducted by Sierra Research, which
demonstrated:
• The wake radius calculated based on Snook & Davis’ CO emissions
monitoring was unrealistically low in comparison to EPA’s inventory
estimates which lead to overestimates of CO exposure;
• Benzene exposures were calculated for the last person in the snowmobile
train by summing the individual exposures of a single sled following a
lead sled at variable distances. This method ignores the turbulence and
mixing that would occur as multiple sleds passed through the wake of the
lead sled and results in overestimates of benzene exposure.
EPA and the state of California are in the process of updating emissions regulations for small
off-road engines, which are being phased in during the years 2001 – 2007. EPA’s and
California’s Phase II emissions controls for small handheld and non-handheld engines are
expected to reduce hydrocarbon and NOx emissions by 59% and 74%, respectively (EPA
1999c, CARB, 2000). Thus, regulatory actions on the small off-road engine equipment, coupled
with use of oxygenated and reformulated gasoline will continue to result in lower operator
exposures.
Benzene VCCEP Submission
March 2006
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