Exposure estimate the following airborne asbestos

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Exposure Estimate : The following airborne asbestos inhalation exposure algorithm is based on the 1992 PTI HRA: EC = C a x ET x EF x ED AT Where, EC = Chronic Exposure Concentration (averaged over a 70-year lifetime) [f/ml] C a = Asbestos Concentration in fibers per cubic centimeter (f/ml) ET = Exposure Time in hours/day EF = Exposure Frequency in days/year ED = Exposure Duration in years AT = Averaging Time of 24 hours/day x 365 days/year x 70 years (lifetime). Asbestos exposures are estimated for adult receptors assuming 18 and 30 years of recreational exposures and for child receptors assuming 12 years of recreational exposures. These exposures are based on the assumption that an individual is exposed to airborne asbestos at the CCMA during recreational activities for a total of 30 years. This can be allocated as 12 years as a child, experiencing the child exposure levels measured at the CCMA, and 18 years as an adult, experiencing the adult exposure levels. The rationale for this allocation of years is based on the assumption that asbestos exposures are related to breathing height. A child, who starts recreating at the CCMA at age 6, will spend about 6 years at a height less than 5 feet, and another 6 years before reaching full height, which equals 12 total child years of exposure. Then as an adult, this same receptor will then spend 18 years (from age 18 to 36) at full height, experiencing adult exposure levels. Exposure assumptions appropriate for recreational users are presented in Table 3A (adult - 30 year exposure duration), Table 3B (child – 12 year exposure duration) and Table 3C (adult – 18 year exposure duration). All Chronic Exposure Concentrations estimated in this study (Tables 9 through 18 for the adult – 30 year exposure, Tables 19 through 26 for the child – 12 year exposure, and Tables 27 through 34 for the adult – 18 year exposure) were less than 4E-02 fibers/ml. Risk Calculation: The upper-bound excess lifetime cancer risks were calculated using the following equation described in EPA risk assessment guidance documents (EPA 1989) and is presented in the 1992 PTI HRA: ELCR = EC x URF Where,
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8 ELCR = Excess Lifetime Cancer Risk EC = Chronic Daily Exposure Concentration (averaged over a 70-year lifetime) [f/ml] URF = IRIS Unit Risk Factor for inhalation of asbestos [0.23 (f/ml) -1 ] and OEHHA Unit Risk Factor for inhalation of asbestos [1.9 (f/ml) -1 ]. For the 30-year exposure duration, estimated ELCRs using the IRIS inhalation unit risk for individual adult scenarios are presented in Tables 9 to 18 and summarized in Tables 4A and 4B (risk results using the OEHHA unit risk are summarized in Tables 4C and 4D). Estimated potential cancer risks for individual child scenarios are presented in Tables 19 to 26 and summarized in Tables 5A and 5B (risk results using the OEHHA unit risk are presented in Tables 5C and 5D). For the 18-year exposure duration, ELCRs based on the IRIS inhalation unit risk for adult scenarios are presented in Tables 27 through 34 and summarized in Table 6A and 6B (OEHHA unit risk results in Table 6C and 6D).
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