13 individual exposure was measured directly which

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13 individual exposure was measured directly, which can lead to some uncertainty in the derived unit risk. The derivation of the unit risk was performed using health protective assumptions. That is, where uncertainties are encountered, health protective assumptions are used so as not to underestimate the risk. Also, there is an uncertainty in extrapolating from high occupational doses over extended times to lower environmental exposures for much shorter time periods. Since occupational exposures are chronic, they are different from the less frequent, intermittent exposures assessed at CCMA. This type of extrapolation may over-estimate but should not underestimate the potential risks. Risks for Individual vs. Combined Activities. This assessment estimates risks for both individual recreational activities and combined activities. Combined activities (e.g., SUV driving to reach a staging area, then motorcycling, followed by camping), are more likely to occur for users of the CCMA. Estimated risks for individual activities are likely to underestimate total risks for users of the CCMA. Risks of selected combined activities are estimated and presented in this report and show that SUV driving to a staging area, motorcycle riding or hiking/hunting and camping activities all can be significant contributors to risk during recreational visits to the CCMA. Conclusions : Asbestos air concentration data for the September 27 through 29, 2005 sampling event at the CCMA ranged from 0.00027 PCMe fibers/cc to 1.3 PCMe fibers/cc, depending upon the receptor/activity. Adult trailing OHV riders (motorcycle, ATV and SUV) were exposed to asbestos concentrations that exceeded occupational standards established by OSHA (PEL and 30-minute maximum excursion limit - for the trailing motorcyclist). Child trailing OHV riders (motorcycle, ATV and SUV) were exposed to measured asbestos air concentrations that generally exceeded adult asbestos air concentrations. Chronic exposure concentrations were calculated for the risk calculations for adults and children based on the minimum and maximum measured air concentrations of asbestos. In this memorandum, risks are calculated for both child and adult recreational exposures assuming an exposure duration of 12 years for a child and 18 and 30 year exposure duration for adults. The resulting risks are then summed for a child plus adult (18 year exposure) recreational exposure duration of 30 years at the CCMA, based on results using the IRIS unit risk only. The adult 30 year exposure duration calculations are presented as a basis for comparison to other sampling events previously conducted. These comparisons are anticipated to be presented in future reports. The estimated ELCRs for adult motorcycle trailing riders, and lead and trailing ATV and SUV riders exceeded 1E-04 (100 in a million), for maximum air concentrations, when the user is assumed to ride more than 12 days/year. The ELCRs for lead vehicle riders were often less than for trailing riders and sometimes less than 1E-06, for minimum air concentrations.
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  • Fall '17
  • CCMA, unit risk

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