All FFR models had a scent of bleach following overnight air-drying. Residual bleach remaining on FFRs is of concern given its known health effects. Hypochlorite powder, solutions, and vapor can be irritating and corrosive to the eyes, skin, and respiratory tract. For example, Nixon et al. (1975) reported that a 5.25% sodium hypochlorite solution caused severe irritation to human skin over a 4-h exposure. Other studies also reported skin irritation for long-term exposure down to a 1% solution (Eun et al., 1984; Habetes et al., 1986; Hostynek et al., 1990) . Low concentrations of bleach have been shown to trigger respiratory events in asthmatics and sensitized individuals (Medina-Ramon, 2005; Mirabelli et al., 2007) . The chlorine off-gassing measurements showed that overnight air-drying significantly reduced off-gassing; however, when the FFR was rehydrated with deionized water, an increase in offgassing was measured. This observation may be significant when viewed in light of the moisture in the exhaled breath of an individual; it gives rise to the possibility of an individual being exposed to low levels of chlorine (,0.2 p.p.m.) from a bleachdecontaminated FFR. Comparing Table 5 and data shown in Fig. 4 , a relationship between hydrophobic-ity of outer and inner respirator surface layers to offgassing concentration could not be established.