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Comparative Study
. 2015;12(10):678-85.
doi: 10.1080/15459624.2015.1043057.

Penetration of Combustion Aerosol Particles Through Filters of NIOSH-Certified Filtering Facepiece Respirators (FFRs)

Shuang Gao  1 , Jinyong Kim, Michael Yermakov, Yousef Elmashae, Xinjian He, Tiina Reponen, Sergey A Grinshpun
Affiliations
Comparative Study

Penetration of Combustion Aerosol Particles Through Filters of NIOSH-Certified Filtering Facepiece Respirators (FFRs)

Shuang Gao et al. J Occup Environ Hyg. 2015.

Abstract

Filtering facepiece respirators (FFRs) are commonly worn by first responders, first receivers, and other exposed groups to protect against exposure to airborne particles, including those originated by combustion. Most of these FFRs are NIOSH-certified (e.g., N95-type) based on the performance testing of their filters against charge-equilibrated aerosol challenges, e.g., NaCl. However, it has not been examined if the filtration data obtained with the NaCl-challenged FFR filters adequately represent the protection against real aerosol hazards such as combustion particles. A filter sample of N95 FFR mounted on a specially designed holder was challenged with NaCl particles and three combustion aerosols generated in a test chamber by burning wood, paper, and plastic. The concentrations upstream (Cup) and downstream (Cdown) of the filter were measured with a TSI P-Trak condensation particle counter and a Grimm Nanocheck particle spectrometer. Penetration was determined as (Cdown/Cup) ×100%. Four test conditions were chosen to represent inhalation flows of 15, 30, 55, and 85 L/min. Results showed that the penetration values of combustion particles were significantly higher than those of the "model" NaCl particles (p < 0.05), raising a concern about applicability of the N95 filters performance obtained with the NaCl aerosol challenge to protection against combustion particles. Aerosol type, inhalation flow rate and particle size were significant (p < 0.05) factors affecting the performance of the N95 FFR filter. In contrast to N95 filters, the penetration of combustion particles through R95 and P95 FFR filters (were tested in addition to N95) were not significantly higher than that obtained with NaCl particles. The findings were attributed to several effects, including the degradation of an N95 filter due to hydrophobic organic components generated into the air by combustion. Their interaction with fibers is anticipated to be similar to those involving "oily" particles. The findings of this study suggest that the efficiency of N95 respirator filters obtained with the NaCl aerosol challenge may not accurately predict (and rather overestimate) the filter efficiency against combustion particles.

Keywords: N95; combustion particles; filtering facepiece respirator; penetration.

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Figures

FIGURE 1.
FIGURE 1.
Experimental set-up (85Kr electrical charge equilibrator was used only when generating NaCl particles)
FIGURE 2.
FIGURE 2.
Total particle penetration values (measured using a P-Trak) for an N95 FFR filter samples challenged with three combustion aerosols (wood, paper, and plastic) and NaCl particles under different inhalation flow rates (QRespirator). [The error bars were obtained from five to six replicates; Symbols “*” and “**” indicate significant differences (“*”: p < 0.05; “**”: p < 0.01) when comparing the NaCl to the combustion particles]
FIGURE 3.
FIGURE 3.
Size-selective particle penetration values for N95 FFR filter samples challenged with three combustion particles (wood, paper, and plastic) and NaCl particles. Each point represents the average value of five to six replicates. Symbols “*” and “**” indicate significant differences (“*”: p < 0.05; “**”: p < 0.01) when comparing the NaCl to the combustion particles.
FIGURE 4.
FIGURE 4.
Total particle penetration values (result of P-Trak) for R95 and P95 FFR filter samples challenged with three combustion particles (wood, paper, and plastic) and NaCl particles under the inhalation flow rate (QRespirator) of 85 L/min.
See this image and copyright information in PMC

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