Evaluation of respirator filters for asbestos fibers

Our plain-English summary of Evaluation of respirator filters for asbestos fibers, by Y.S. Cheng, T.D. Holmes, B. Fan (Journal of Occupational and Environmental Hygiene, 2006).

The study

• Authors: Y.S. Cheng, T.D. Holmes, B. Fan
• Journal: Journal of Occupational and Environmental Hygiene
• Published: 2006;3(1):26-35
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Fiber aerosols are known to have different aerodynamic behaviors than spherical particles and usually carry higher electrostatic charges. We investigated the effects of flow rate and charge status of filter cartridges on the penetration of spherical and fiber aerosols. Four types of test respirator filters were selected: two for passive respirators, one for a powered respirator, and one disposable respirator. Surface charges on respirator filters were determined using a noncontact field electrostatic field meter. Penetration tests were performed for filter cartridges before and after charge neutralization. The surface charge measurements on the respirator filters showed that some filters, including those used in disposable face masks, are charged to enhance the collection efficiency. Only high-efficiency particulate air filters performed consistently for both spherical test aerosols and the three types of asbestos fibers. The surface charge potential of filter cartridges and flow rate did not appear to affect the performance of these filters. In contrast to the high-efficiency filters, the aerosol penetration performance of low-efficiency filters and face masks deteriorated when the charge potential on the filter was removed. Our data also showed that the surface charges decreased in a high-temperature, high-humidity environment and disappeared after 1 week. Deposition of spherical particles and fibers in the charged disposable facemask filter was enhanced. For charged-neutralized, low-efficiency filter cartridges, asbestos fibers may penetrate more than spherical particles with a mean particle size of 0.3 microm diameter.

In plain English

This laboratory study tested how well four respirator filters stopped asbestos fibers and a standard oil test aerosol (DEHS, about 0.3 micrometers). They were a disposable face mask (Filter A), a dust/fume/mist cartridge (Filter B), a powered-respirator HEPA filter (Filter C) and a HEPA cartridge (Filter D). Each was tested with charge-neutralized chrysotile, crocidolite and amosite fibers. Tests were run as supplied at a lower flow rate and, after an antistatic spray removed the filter's charge, at that rate and a higher one. No fibers were detected downstream of Filter D, which collected more than 99.99%. Filter C collected more than 98% in all cases but allowed up to 1.1% of fibers through. The face mask collected 94% to 97% of fibers untreated at 32 liters per minute and 74% to 80% after its charge was removed. Discharged at 85 liters per minute, it collected 55.0% of amosite, 29.4% of crocidolite and 23.5% of chrysotile. At 38°C and over 90% humidity, filter charges fell substantially within 2 days; most were gone by Day 6. The authors concluded that only the HEPA filters performed consistently. Most fiber tests were run once.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment testing how much asbestos fiber and a spherical oil test aerosol (DEHS) got through commercial respirator filters. For asbestos there were three test conditions, all using charge-neutralized fibers. At the lower flow rate, filters were tested untreated and after charge removal with an antistatic spray. At the higher flow rate, only charge-removed filters were tested.
• Who was studied: Four types of commercially available respirator filters: a 3M 8710 disposable face mask (Filter A), an MSA Type S dust/fume/mist cartridge (Filter B), an MSA Type A HEPA filter for powered respirators (Filter C), and an American Optical 57A HEPA filter (Filter D).
• Exposure: Three asbestos fibers, all charge-neutralized: ultrafine chrysotile (Calidria), UICC crocidolite and UICC amosite. The other test material was spherical DEHS oil particles with a mass median aerodynamic diameter of 0.30 micrometers. Filters B and D were tested at 16 and 42.5 L/min. Filters A and C were tested at 32 and 85 L/min.
• Main results:
  • All four filter types carried negative surface charges. Filters A and C had potentials between 800 and 1800 volts. Filters B and D had potentials of around 20 volts.
  • Filters were kept at 38°C and more than 90% relative humidity. Their surface charges fell substantially within 2 days, and most were gone by Day 6.
  • For DEHS spherical particles, the face mask (Filter A) collected 84.6% at 32 L/min and 78.2% at 85 L/min. These fell to 44.0% and 34.9% when the mask was neutralized.
  • For DEHS particles, both HEPA filters (C and D) had collection efficiencies above 99.97%.
  • For HEPA Filter D, no fibers were detected downstream. Collection was greater than 99.99% for all three asbestos fibers, regardless of charge status or flow rate.
  • For HEPA Filter C, fiber collection efficiency was above 98% in all cases.
  • Filter C showed above 99.7% efficiency for DEHS particles but allowed up to 1.1% penetration of asbestos fibers.
  • Untreated, the face mask (Filter A) collected 94% to 97% of amosite, crocidolite and chrysotile fibers at 32 L/min.
  • Filter A's fiber collection fell to 74% to 80% when the mask was neutralized with antistatic spray.
  • With both the face mask and the fibers discharged at 85 L/min, fiber deposition in Filter A was 55.0% for amosite, 29.4% for crocidolite and 23.5% for chrysotile.
  • Untreated, Filter B (dust/fume/mist) collected 91% to 99% of the three fibers at 16 L/min. This fell to 73% to 95% when the filter was neutralized. At 42.5 L/min the neutralized filter collected 97% to 98%.
• The authors' conclusion: The authors concluded that only the HEPA filters performed consistently on both the spherical test aerosol and the three asbestos fibers. The dust/mist filter and the disposable face mask performed worse when the filter's charge was removed or as the flow rate changed.
• Limitations the authors state:
  • Three replicates were run only for Filter A with amosite. All other fiber penetration measurements were a single test run.
  • The fibers tested were charge-neutralized, so the authors state the results may be considered minimum collection efficiencies. More highly charged asbestos may be collected more efficiently.
  • The study was done before the new NIOSH respirator filter regulation, so the newer filter classes were not tested. Based on the DEHS tests, the authors judged Filters C and D similar to N100 filters and Filter B similar to N95 filters.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Santa Rita mine, Joaquin Ridge near Coalinga, California

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Respirator, Deposition.

Related studies

• Workplace protection factors of HSE approved negative pressure full-facepiece dust respirators during asbestos stripping: preliminary findings — S.N. Tannahill, R.J. Willey, et al. (1990)
• Physiological and subjective responses to working in disposable protective coveralls and respirators commonly used by the asbestos abatement industry — M.K. White, T.K. Hodous, et al. (1989)
• Performance of power assisted respirators during simulated asbestos removal — M.P. Clayton, A.E. Bailey, et al. (2002)
• Health effects of respirator use at low airborne concentrations — J.H. Lange (2000)
• Lung fiber burden in the Nottingham gas mask cohort — G. Berry, F. Pooley, et al. (2009)
• Efficiency of sampling and analysis of asbestos fibers on filter media: implications for exposure assessment — D.A. Vallero, J.R. Kominsky, et al. (2009)

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