What Does Respirator Certification Tell Us About Filtration of Ultrafine Particles?

Abstract

Recent interest in exposures to ultrafine particles (less than 100 nm) in both environmental and occupational settings led the authors to question whether the protocols used to certify respirator filters provide adequate attention to ultrafine aerosols. The authors reviewed the particle size distribution of challenge aerosols and evaluated the aerosol measurement method currently employed in the National Institute for Occupational Safety and Health (NIOSH) particulate respirator certification protocol for its ability to measure the contribution of ultrafine particles to filter penetration. Also considered were the differences between mechanical and electrically charged (electret) filters in light of the most penetrating particle size. It was found that the sodium chloride (NaCl) and dioctylphthalate (DOP) aerosols currently used in respirator certification tests contain a significant fraction of particles in the ultrafine region. However, the photometric method deployed in the certification test is not capable of adequately measuring light scatter of particles below approximately 100 nm in diameter. Specifically, 68% (by count) and 8% (by mass) of the challenge NaCl aerosol particles and 10% (by count) and 0.3% (by mass) of the DOP particles below 100 nm do not significantly contribute to the filter penetration measurement. In addition, the most penetrating particle size for electret filters likely occurs at 100 nm or less under test conditions similar to those used in filter certification. The authors conclude, therefore, that the existing NIOSH certification protocol may not represent a worst-case assessment for electret filters because it has limited ability to determine the contribution of ultrafine aerosols, which include the most penetrating particle size for electret filters. Possible strategies to assess ultrafine particle penetration in the certification protocol are discussed.

Exposure to Manufactured Nanostructured Particles in an Industrial Pilot Plant

“…Mask efficiencies to various airborne inert particles have been investigated in laboratories as well as under workplace conditions (Nelson et al, 2000;Bidwell and Janssen, 2004;Lee et al, 2005;Kim et al, 2007;Eninger et al, 2008). However, the number of studies regarding natural and engineered nanoparticles is limited.…”

“…However, the number of studies regarding natural and engineered nanoparticles is limited. Additionally, performance studies focusing on number concentrations are scarce (Balazy et al, 2006;Kim et al, 2007;Eninger et al, 2008).…”

Nanoparticle Filtration Performance of NIOSH-Certified Particulate Air-Purifying Filtering Facepiece Respirators: Evaluation by Light Scattering Photometric and Particle Number-Based Test Methods

“…TSI 8130 generated nanoparticles comprise ∼79% of the total number of NaCl and ∼5% of the total DOP aerosols by number that are close to their theoretically calculated values. (31) Similar to the TSI 8130 NaCl aerosols, ambient aerosols also showed ∼80% of particles in the <100 nm size range. The size range of NaCl aerosol used in the tests is within the required size distribution for NIOSH certification of N-series particulate respirators.…”

“…However, the photometric method is not sensitive to measure nanoparticles with no significant mass. (30,31) Recently, significant number concentrations of nanoparticles have been found in some nanotechnology workplaces handling nanomaterials. (32)(33)(34) For example, nanoparticle (<100 nm) number concentration was found to increase in the reactor area of carbon black production plants.…”

Approaches to safe nanotechnology: managing the health and safety concerns associated with engineered nanomaterials (withdrawn).

“…Most of the particles penetrating through the filter are measured simultaneously using a forward light scattering photometer. However, as noted in a recent review, the instrumentation used in the NIOSH certification test is not capable of measuring the light scattering of all particles less than 100 nm [Eninger et al 2008a]. …”