Performance of Mechanical Filters and Respirators for Capturing Nanoparticles ―Limitations and Future Direction

Abstract

There is an increasing concern about the health hazard posed to workers exposed to inhalation of nanoparticles. Inhaling nanoparticles posses an occupational hazard due to elevated amount emitted to the atmosphere and working environment. Nanoparticles have potential toxic properties: the high particle surface area, number concentration, and surface reactivity. Inhalation, the most common route of nanoparticle exposure, has been shown to cause adverse effects on pulmonary functions and the deposited particles in the lung can be translocated to the blood system by passing through the pulmonary protection barriers. Filtration is the simplest and most common method of aerosol control. It is widely used in mechanical ventilation and respiratory protection. However, concerns have been raised regarding the effectiveness of the filters for capturing nanoparticles. This paper reviews the literature on the filtration performance of mechanical filters and respirators against nanoparticles. It includes the discussion about filtration mechanisms, theoretical models, affecting factors of the filtration efficiency, and testing protocols for respirator and filter certification.

Intermediate Air Filters for General Ventilation Applications: An Experimental Evaluation of Various Filtration Efficiency Expressions

“…This result is as expected considering the established filtration theory: Hinds (1999) and Lee and Liu (1980) determined that the effects of interception and inertial impaction increase with particles size, while the effect of Brownian diffusion decreases with particle size. Moreover, Mostofi et al (2010) and Kousaka et al (1989) noted that increasing air velocity substantially decreases the effect of diffusion, while it does not influence the effect of interception. The effect of impaction increases with air velocity, but this mechanism mainly influences particles larger than the upper particle size measured in the present experiments.…”

“…Published results are diverging, but it is indicated that the thermal rebound effect mainly affects particles of a few nanometers in size. A review of papers dedicated to the study of thermal rebound can be found in Mostofi et al (2010). However, this issue is out of the scope of the present investigation, which comprises measurement of particles sized above 14 nm.…”

“…This is most likely connected to the charge state of the test aerosols used. All four studied test aerosols were either uncharged or charged to a little extent only, which means that the dominating electrostatic force is the induced force (Romay et al 1998;Kim et al 2005) which substantially decreases with air velocity (Kousaka et al 1989;Mostofi et al 2010) and increases with particle size (Lee and Liu 1980;Hinds 1999). Thus, in the case of charged synthetic filters, the influence from air velocity was mainly observed at particle sizes where filtration was strongly depending on induced electrostatic forces.…”

Removal Efficiency of Bimodal PM2.5 and PM10 by Electret Respirators and Mechanical Engine Intake Filters

“…The media #A, #C and #E show a minimum number efficiency with higher than 95%, therefore, they could be regarded as N-95 respirator media (Mostofi et al, 2010). The curves presented in Fig.…”

“…However, electret media are commonly applied in the respirators to reduce the flow resistance to achieve a better comfort of wear. But it has been found there is high penetration occurring in both nano-sized (20-50 nm) and submicron-meter or micro-meter size range in electret filter media (Lathrache et al, 1986;Lathrache and Fissan, 1987;Mostofi et al, 2010;Rengasamy et al, 2010;Chen et al, 2014). Therefore, to evaluate respirators filters with more realistic bimodal PMs is essential.…”