The Effects of Particle Charge on the Performance of a Filtering Facepiece

Abstract

This study quantitatively determined the effect of electrostatic charge on the performance of an electret filtering facepiece. Monodisperse challenge corn oil aerosols with uniform charges were generated using a modified vibrating orifice monodisperse aerosol generator. The aerosol size distributions and concentrations upstream and downstream of an electret filter were measured using an aerodynamic particle sizer, an Aerosizer, and a scanning mobility particle sizer. The aerosol charge was measured by using an aerosol electrometer. The tested electret filter had a packing density of about 0.08, fiber size of 3 microns, and thickness of 0.75 mm. As expected, the primary filtration mechanisms for the micrometer-sized particles are interception and impaction, especially at high face velocities, while electrostatic attraction and diffusion are the filtration mechanisms for submicrometer-sized aerosol particles. The fiber charge density was estimated to be 1.35 x 10(-5) coulomb per square meter. After treatment with isopropanol, most of fiber charges were removed, causing the 0.3-micron aerosol penetration to increase from 36 to 68%. The air resistance of the filter increased slightly after immersion in the isopropanol, probably due to the coating of impurities in isopropanol. The aerosol penetration decreased with increasing aerosol charge. The most penetrating aerosol size became larger as the aerosol charge increased, e.g., from 0.32 to 1.3 microns when the aerosol charge increased from 0 to 500 elementary charges.

Filtration characteristics of a fibrous filter pretreated with anionic surfactants for monodisperse solid aerosols

“…A higher face velocity leads to a shorter residence time associated with aerosol deposition by electrostatic attraction and diffusion. The data are consistent with the results from previous studies by Kanaoka et al (1987) and Chen and Huang (1998).…”

“…The performance characteristics of electret filters have been widely studied (Baumgartner and Löffler, 1986;Lathrache and Fissan, 1987;Fjeld and Owens, 1988;Chen and Huang, 1998;AFFCO, 1998). Several researchers have examined the capture mechanisms of electret filters (Baumgartner and Löffler, 1986;Lathrache et al, 1986;Trottier and Brown, 1990;Romay et al, 1998) and some studies (Brown, 1981;Pich et al, 1987;Lathrache and Fissan, 1987;Kanaoka et al, 1987) have developed semi-empirical and theoretical expressions for dielectrophoretic and Coulombic single-fiber efficiencies to illustrate the performance of the electret filters.…”

Penetration of 4.5nm to aerosol particles through fibrous filters

“…However, to study the impact of electrostatic charges on collection efficiency, filters were dipped in isopropanol for 5 min and dried naturally. Previous studies have shown that this process removes the electrical charge associated with the filter fibers (Chen & Huang, 1998;Chen, Lehtimaki, & Willeke, 1993;Martin & Moyer, 2000). These dipped filters, along with controls of each filter type, were then tested to determine the initial aerosol penetration for particles in the size ranging from 4.5 nm to 10 m.…”

“…Filtering facepieces are the most popular form of respirator among workers because of their lightness, better vision, and low maintenance compared with elastometric respirators (Chen & Huang, 1998). The performance of filter media has been extensively tested using non-biological particles (Chen & Huang, 1998;Chen, Lehtimaki, & Willeke, 1992;Martin & Moyer, 2000) and biological particles (McCullough, Brosseau, & Vesley, 1997;Qian, Willeke, Grinshpun, Donnelly, & Coffey, 1998;Willeke, Qian, Donnelly, Grinshpun, & Ulevicius, 1996).…”

Effect of xylene exposure on the performance of electret filter media

“…The effects of permanent static electric fields on filtration performance have been well established in the scientific literature (Ando, Takahashi, Togashi, & Okumura, 1990;Brown, 1981Brown, , 1992Brown, Wake, Chen & Huang, 1998). It is also well established that electret filter media exhibit better performance and lower pressure drop than mechanical filter media for particles in the .05-3 m particle diameter range.…”