Page:NIOSH DM DFM respirator evaluation draft.pdf/81

PF =V/Linhaled = Co/Cinhaled 73 (3) For these conditions, write a mass per unit time balance around the user's mouth and nose (i.e., total mass rate of contaminant inhaled into the user's body as a func- tion of component mass rates approaching the mouth and nose). One obtains (Cinhaled) (inhaled) = (C filler) (@filler) + C face seal) (@face seal). (4) These concentrations are related to the workplace contaminant concentration outside the respirator C. as follows Cinhaled = (Linhaled) (C), Cfilter = (filler) (C), and (5) (6) (7) Cface seal = (Lface seal)(C). From equations (3) through (7) and using the assumption that Cface al = C, one can obtain Linhaled = (filler) (@filler/Rinhaled) + (@face seal/inhaled). From flow-rate balance around the user's mouth and nose one obtains (8) Sinhaled = &filler + Qface seal" which can be substituted into equation (8) to yield Linhaled = Lfilter + (1 - Liller (face seal inhaled). (9) (10) Equation (10) can be solved by creating two equations for two sets of conditions. This will yield two equations in three unknowns: Linhaled face seal and Qinhaled Then an assumption will be used to eliminate face seal Case A is one in which a respirator is worn with a filter with essentially zero leakage (e.g., when a HEPA filter is fitted to the respirator during fit testing). In this case, equation (10) reduces to: L'inhaled = face seal/Qinhaled' (11)