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Exposure Scenario and Formulas
Unless otherwise specified in the Indoor Environmental Health Assessment (IEHA), the typical exposure scenario assumptions are as follows:
Child Care Centers:
Age of children: 0-6 years
Duration of exposure (cancer only) = 6 years for children; 10 years for staff
5 days/week = 260 days/year
12 hours/day
Educational Facilities:
Age of children: 6-18 (school age)
180 days per year
8 hours/day
Duration of exposure (cancer only) = number of years in school (students); 20 years for staff
Formula: Non-Cancer
THQ = ( C x EF x IR)/ (RfD x BW x AT x 1000ug/mg )
Where:
THQ = Target Hazard Quotient
C = Contaminant Concentration (ug/m3)
EF =260 days x 12 hours/day =3120 (exposure frequency)
RfD =Chemical Specific Reference Dose for inhalation(mg/kg/day)
BW*=Body Weight kg
IR*= Inhalation Rate m3/day
AT = 365 days x 24 hours/day =8760 (averaging time, non-cancer)
* Varies with age
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Formulas: Cancer Risk
LECR= CPSi x ((C x CR x ET x EF x ED)/ (BW x AT))
Where:
LECR = Lifetime Excess Cancer Risk
CPSi = Cancer Slope Factor (inhalation pathway)
C = Contaminant Concentration in air (mg/m3)
CR* = Contact( Inhalation) Rate (m3/hour)
ET = Exposure Time (hours/day)
EF = Exposure Frequency (days/year)
ED = Exposure Duration (years)
BW* = Body Weight (kg)
AT = Averaging Time (days)
*Varies with age
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