Nanotechnology White Paper - US Environmental Protection Agency

48 EPA Nanotechnology White Paper
3.5.4.1 Engineering Controls
Engineering controls, and particularly those used for aerosol control, should generally be
effective for controlling exposures to airborne nanoscale materials (NIOSH, 2005a). Depending
on particle size, nanoparticles may diffuse rapidly and readily find leakage paths in engineering
control systems in which containment is not complete (Aitken et al., 2004). However, a welldesigned
exhaust ventilation system with a high efficiency particulate air (HEPA) filter should
effectively remove nanoparticles (Hinds, 1999). As with all filters, the filter must be properly
seated to prevent nanoparticles from bypassing the filter, decreasing the filter efficiency
(NIOSH, 2003). Aitken et al. (2004) recommends that engineering controls (e.g., enclosures,
local exhaust ventilation, fume hoods) used to control exposure to nanoparticles need to be of
similar quality and specification as those typically used for gases. However, the report also notes
that no research has been identified evaluating the effectiveness of engineering controls for
nanoparticles.
Efficient ultrafine particle control devices (e.g., soft x-ray enhanced electrostatic
precipitation systems) may have applicability to nanoparticles control (Kulkarni et al., 2002).
HEPA filters may be effective, and validation of their effectiveness is currently being studied
(NIOSH, 2005a). Magnetic filter systems in welding processes have proven effective in
capturing magnetic oxides and the use of nanostructured sorbents in smelter exhausts to prepare
ferroelectric materials may also have applicability (Biswas et al., 1998).
3.5.4.2 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 (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).