Personal Protective Equipment (PPE)
Properly fitted respirators with a HEPA filter may be effective at removing nanomaterials. Contrary to intuition, fibrous filters trap smaller and larger particles more effectively than mid-sized particles. Small particles (<100 nm) tend to make random Brownian motions due to their interaction with gas molecules. The increased motion causes the particle to “zig-zag around” and have a greater chance of hitting and sticking to the fiber filter (Luther, 2004). Intermediate-sized particles (>80 nm and < 2000 nm) can remain suspended in air for the longest time. (Bidleman, 1988; Preining, 1998; Spurny, 1998; Atkinson, 2000; UK Royal Society, 2004; Dennenkamp et al., 2002)
NIOSH certifies particulate respirators by challenging them with sodium chloride (NaCl) aerosols with a count median diameter 75 nm or dioctyl phthalate (DOP) aerosols with a count median diameter of 185 nm [42 CFR Part 84.181(g)], which have been found to be in the most penetrating particle size range (Stevens and Moyer, 1989). However, as with all respirators, the greatest factor in determining their effectiveness is not penetration through the filter, but rather the face-seal leakage bypassing the device. Due to size and mobility of nanomaterials in the air, leakage may be more prevalent although no more than expected for a gas (Aitken, 2004). Only limited data on face-seal leakage has been identified. Work done by researchers at the U.S. Army RDECOM on a headform showed that mask leakage (i.e., simulated respirator fit factor) measured using submicron aerosol challenges (0.72 μm polystyrene latex spheres) was representative of vapor challenges such as sulfur hexafluoride (SF6) and isoamyl acetate (IAA) (Gardner et al., 2004).
EPA Nanotechnology White Paper 49
PPE may not be as effective at mitigating dermal exposure. PPE is likely to be less effective against dermal exposure to nanomaterials than macro-sized particles from both human causes (e.g., touching face with contaminated fingers) and PPE penetration (Aitken, 2004). However, no studies were identified that discuss the efficiency of PPE at preventing direct penetration of nanomaterials through PPE or from failure due to human causes
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