Conducting an evaluation of CBRN canister protection capabilities against emerging chemical and radiological hazards.

In the event of a chemical, biological, radiological, or nuclear (CBRN) hazard release, emergency responders rely on respiratory protection to prevent inhalation of these hazards. The National Institute for Occupational Safety and Health's (NIOSH) CBRN Statement of Standard calls for CBRN respirator canisters to be challenged with 11 different chemical test representative agents (TRAs) during certification testing, which represent hazards from 7 distinct Chemical Families; these 11 TRAs were identified during the original 2001 CBRN hazard assessment. CBRN hazards are constantly evolving in type, intent of use, and ways of dissemination. Thus, new and emerging hazards must be identified to ensure CBRN canisters continue to provide protection to emergency responders against all hazards that would most likely be used in an intentional or unintentional event. The objectives are to: (1) update the CBRN list of hazards to ensure NIOSH-approved CBRN canisters continue to provide adequate protection capabilities from newly emerging chemical and radiological hazards and (2) identify the need to update NIOSH TRAs to ensure testing conditions represent relevant hazards. These objectives were accomplished by reviewing recent hazard assessments to identify a list of chemical and radiological respiratory hazards, evaluate chemical/physical properties and filtration behavior for these hazards, group the hazards based on NIOSH's current Chemical Families, and finally compare the hazards to the current TRAs based on anticipated filtration behavior, among other criteria. Upon completion of the evaluation process, 237 hazards were identified and compared to NIOSH's current CBRN TRAs. Of these 237 hazards, 203 were able to be categorized into one of NIOSH's current seven Chemical Families. Five were identified for further evaluation. Based on reviewing key chemical/physical properties of each hazard, NIOSH's current 11 TRAs remain representative of the identified respiratory CBRN hazards to emergency responders and should continue to be used during NIOSH certification testing. Thus, NIOSH's CBRN Statement of Standard remains unchanged. The process developed standardizes a methodology for future hazard evaluations.

Inward Leakage Variability between Respirator Fit Test Panels - Part I. Deterministic Approach.

Inter-panel variability has never been investigated. The objective of this study was to determine the variability between different anthropometric panels used to determine the inward leakage (IL) of N95 filtering facepiece respirators (FFRs) and elastomeric half-mask respirators (EHRs). A total of 144 subjects, who were both experienced and non-experienced N95 FFR users, were recruited. Five N95 FFRs and five N95 EHRs were randomly selected from among those models tested previously in our laboratory. The PortaCount Pro+ (without N95-Companion) was used to measure IL of the ambient particles with a detectable size range of 0.02 to 1 µm. The Occupational Safety and Health Administration standard fit test exercises were used for this study. IL test were performed for each subject using each of the 10 respirators. Each respirator/subject combination was tested in duplicate, resulting in a total 20 IL tests for each subject. Three 35-member panels were randomly selected without replacement from the 144 study subjects stratified by the National Institute for Occupational Safety and Health bivariate panel cell for conducting statistical analyses. The geometric mean (GM) IL values for all 10 studied respirators were not significantly different among the three randomly selected 35-member panels. Passing rate was not significantly different among the three panels for all respirators combined or by each model. This was true for all IL pass/fail levels of 1%, 2%, and 5%. Using 26 or more subjects to pass the IL test, all three panels had consistent passing/failing results for pass/fail levels of 1% and 5%. Some disagreement was observed for the 2% pass/fail level. Inter-panel variability exists, but it is small relative to the other sources of variation in fit testing data. The concern about inter-panel variability and other types of variability can be alleviated by properly selecting: pass/fail level (IL 1-5%); panel size (e.g., 25 or 35); and minimum number of subjects required to pass (e.g., 26 of 35 or 23 of 35).

Protection factor for N95 filtering facepiece respirators exposed to laboratory aerosols containing different concentrations of nanoparticles.

A previous study used a PortaCount Plus to measure the ratio of particle concentrations outside (C out) to inside (C in) of filtering facepiece respirators (FFRs) worn by test subjects and calculated the total inward leakage (TIL) (C in/C out) to evaluate the reproducibility of the TIL test method between two different National Institute for Occupational Safety and Health laboratories (Laboratories 1 and 2) at the Pittsburgh Campus. The purpose of this study is to utilize the originally obtained PortaCount C out/C in ratio as a measure of protection factor (PF) and evaluate the influence of particle distribution and filter efficiency. PFs were obtained for five N95 model FFRs worn by 35 subjects for three donnings (5 models × 35 subjects × 3 donnings) for a total of 525 tests in each laboratory. The geometric mean of PFs, geometric standard deviation (GSD), and the 5th percentile values for the five N95 FFR models were calculated for the two laboratories. Filter efficiency was obtained by measuring the penetration for four models (A, B, C, and D) against Laboratory 2 aerosol using two condensation particle counters. Particle size distribution, measured using a Scanning Mobility Particle Sizer, showed a mean count median diameter (CMD) of 82 nm in Laboratory 1 and 131 nm in Laboratory 2. The smaller CMD showed relatively higher concentration of nanoparticles in Laboratory 1 than in Laboratory 2. Results showed that the PFs and 5th percentile values for two models (B and E) were larger than other three models (A, C, and D) in both laboratories. The PFs and 5th percentile values of models B and E in Laboratory 1 with a count median diameter (CMD) of 82 nm were smaller than in Laboratory 2 with a CMD of 131 nm, indicating an association between particle size distribution and PF. The three lower efficiency models (A, C, and D) showed lower PF values than the higher efficiency model B showing the influence of filter efficiency on PF value. Overall, the data show that particle size distribution and filter efficiency influence the PFs and 5th percentile values. The PFs and 5th percentile values decreased with increasing nanoparticle concentration (from CMD of 131 to 82 nm) indicating lower PFs for aerosol distribution within nanoparticle size range (<100 nm). Further studies on the relationship between particle size distribution and PF are needed to better understand the respiratory protection against nanoparticles.

Efficacy of face shields against cough aerosol droplets from a cough simulator.

Health care workers are exposed to potentially infectious airborne particles while providing routine care to coughing patients. However, much is not understood about the behavior of these aerosols and the risks they pose. We used a coughing patient simulator and a breathing worker simulator to investigate the exposure of health care workers to cough aerosol droplets, and to examine the efficacy of face shields in reducing this exposure. Our results showed that 0.9% of the initial burst of aerosol from a cough can be inhaled by a worker 46 cm (18 inches) from the patient. During testing of an influenza-laden cough aerosol with a volume median diameter (VMD) of 8.5 µm, wearing a face shield reduced the inhalational exposure of the worker by 96% in the period immediately after a cough. The face shield also reduced the surface contamination of a respirator by 97%. When a smaller cough aerosol was used (VMD = 3.4 µm), the face shield was less effective, blocking only 68% of the cough and 76% of the surface contamination. In the period from 1 to 30 minutes after a cough, during which the aerosol had dispersed throughout the room and larger particles had settled, the face shield reduced aerosol inhalation by only 23%. Increasing the distance between the patient and worker to 183 cm (72 inches) reduced the exposure to influenza that occurred immediately after a cough by 92%. Our results show that health care workers can inhale infectious airborne particles while treating a coughing patient. Face shields can substantially reduce the short-term exposure of health care workers to large infectious aerosol particles, but smaller particles can remain airborne longer and flow around the face shield more easily to be inhaled. Thus, face shields provide a useful adjunct to respiratory protection for workers caring for patients with respiratory infections. However, they cannot be used as a substitute for respiratory protection when it is needed. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following free supplemental resource: tables of the experiments performed, more detailed information about the aerosol measurement methods, photographs of the experimental setup, and summaries of the experimental data from the aerosol measurement devices, the qPCR analysis, and the VPA.].

Total inward leakage measurement of particulates for N95 filtering facepiece respirators--a comparison study.

National Institute for Occupational Safety and Health (NIOSH) certified particulate respirators need to be properly fit tested before use to ensure workers' respiratory protection. However, the effectiveness of American National Standards Institute-/Occupational Safety and Health Administration (ANSI-/OSHA)-accepted fit tests for particulate respirators in predicting actual workplace protection provided to workers is lacking. NIOSH addressed this issue by evaluating the fit of half-mask particulate filtering respirators as a component of a program designed to add total inward leakage (TIL) requirements for all respirators to Title 42 Code of Federal Regulations Part 84. Specifically, NIOSH undertook a validation study to evaluate the reproducibility of the TIL test procedure between two laboratories. A PortaCount® was used to measure the TIL of five N95 model filtering facepiece respirators (FFRs) on test subjects in two different laboratories. Concurrently, filter efficiency for four of the five N95 FFR models was measured using laboratory aerosol as well as polydisperse NaCl aerosol employed for NIOSH particulate respirator certification. Results showed that two N95 models passed the TIL tests at a rate of ~80-85% and ~86-94% in the two laboratories, respectively. However, the TIL passing rate for the other three N95 models was 0-5.7% in both laboratories combined. Good agreement (≥83%) of the TIL data between the two laboratories was obtained. The three models that had relatively lower filter efficiency for laboratory aerosol as well as for NaCl aerosol showed relatively low TIL passing rates in both laboratories. Of the four models tested for penetration, one model with relatively higher efficiency showed a higher passing rate for TIL tests in both laboratories indicating that filter efficiency might influence TIL. Further studies are needed to better understand the implications of the data in the workplace.

A quantitative assessment of the total inward leakage of NaCl aerosol representing submicron-size bioaerosol through N95 filtering facepiece respirators and surgical masks.

Respiratory protection provided by a particulate respirator is a function of particle penetration through filter media and through faceseal leakage. Faceseal leakage largely contributes to the penetration of particles through a respirator and compromises protection. When faceseal leaks arise, filter penetration is assumed to be negligible. The contribution of filter penetration and faceseal leakage to total inward leakage (TIL) of submicron-size bioaerosols is not well studied. To address this issue, TIL values for two N95 filtering facepiece respirator (FFR) models and two surgical mask (SM) models sealed to a manikin were measured at 8 L and 40 L breathing minute volumes with different artificial leak sizes. TIL values for different size (20-800 nm, electrical mobility diameter) NaCl particles representing submicron-size bioaerosols were measured using a scanning mobility particle sizer. Efficiency of filtering devices was assessed by measuring the penetration against NaCl aerosol similar to the method used for NIOSH particulate filter certification. Results showed that the most penetrating particle size (MPPS) was ∼45 nm for both N95 FFR models and one of the two SM models, and ∼350 nm for the other SM model at sealed condition with no leaks as well as with different leak sizes. TIL values increased with increasing leak sizes and breathing minute volumes. Relatively, higher efficiency N95 and SM models showed lower TIL values. Filter efficiency of FFRs and SMs influenced the TIL at different flow rates and leak sizes. Overall, the data indicate that good fitting higher-efficiency FFRs may offer higher protection against submicron-size bioaerosols.

Nanoparticle filtration performance of filtering facepiece respirators and canister/cartridge filters.

Respiratory protection offered by a particulate respirator is a function of the filter efficiency and face seal leakage. A previous study in our laboratory measured the filter penetration and total inward leakage (TIL) of 20-1000 nm size particles for N95 filtering facepiece respirators (FFRs) using a breathing manikin. The results showed relatively higher filter penetration and TIL value under different leak sizes and flow rates at the most penetrating particle size (MPPS), ∼45 nm for electrostatic FFRs,and ∼150 nm for the same FFRs after charge removal. This indicates an advantage of mechanical filters over electrostatic filters rated for similar filter efficiencies in providing respiratory protection in nanoparticle workplaces. To better understand the influence of the MPPS, the filtration performance of commonly used one N95 and one N100 FFR models, and four P100 canister/cartridge models were measured with monodisperse NaCl aerosols, and polydisperse NaCl aerosols employed in the National Institute for Occupational Safety and Health (NIOSH) certification test method. As expected, the polydisperse aerosol penetration was below 5% for the N95 FFR, and below 0.03% for the N100 FFR and P100 canister/cartridge filters. Monodisperse aerosol penetration results showed a MPPS of ∼40 nm for both the N95 and N100 FFRs. All four P100 canister/cartridge filters had a MPPS of ≥150 nm, similar to expectations for mechanical filters. The P100 canister/cartridge filters showed lower penetration values for different size nanoparticles than the N100 FFRs. The results indicate that a mechanical filter would offer a relatively higher filtration performance for nanoparticles than an electrostatic counterpart rated for the same filter efficiency. Overall, the results obtained in the study suggest that MPPS should be considered as a key factor in the development of respirator standards and recommendations for protection against nanoparticles.

A Cough Aerosol Simulator for the Study of Disease Transmission by Human Cough-Generated Aerosols.

Aerosol particles expelled during human coughs are a potential pathway for infectious disease transmission. However, the importance of airborne transmission is unclear for many diseases. To better understand the role of cough aerosol particles in the spread of disease and the efficacy of different types of protective measures, we constructed a cough aerosol simulator that produces a humanlike cough in a controlled environment. The simulated cough has a 4.2 l volume and is based on coughs recorded from influenza patients. In one configuration, the simulator produces a cough aerosol containing particles from 0.1 to 100 µm in diameter with a volume median diameter (VMD) of 8.5 µm and a geometric standard deviation (GSD) of 2.9. In a second configuration, the cough aerosol has a size range of 0.1-30 µm, a VMD of 3.4 µm, and a GSD of 2.3. The total aerosol volume expelled during each cough is 68 µl. By generating a controlled and reproducible artificial cough, the simulator allows us to test different ventilation, disinfection, and personal protection scenarios. The system can be used with live pathogens, including influenza virus, which allows isolation precautions used in the healthcare field to be tested without risk of exposure for workers or patients. The information gained from tests with the simulator will help to better understand the transmission of infectious diseases, develop improved techniques for infection control, and improve safety for healthcare workers and patients.

Dispersion and exposure to a cough-generated aerosol in a simulated medical examination room.

Few studies have quantified the dispersion of potentially infectious bioaerosols produced by patients in the health care environment and the exposure of health care workers to these particles. Controlled studies are needed to assess the spread of bioaerosols and the efficacy of different types of respiratory personal protective equipment (PPE) in preventing airborne disease transmission. An environmental chamber was equipped to simulate a patient coughing aerosol particles into a medical examination room, and a health care worker breathing while exposed to these particles. The system has three main parts: (1) a coughing simulator that expels an aerosol-laden cough through a head form; (2) a breathing simulator with a second head form that can be fitted with respiratory PPE; and (3) aerosol particle counters to measure concentrations inside and outside the PPE and at locations throughout the room. Dispersion of aerosol particles with optical diameters from 0.3 to 7.5 µm was evaluated along with the influence of breathing rate, room ventilation, and the locations of the coughing and breathing simulators. Penetration of cough aerosol particles through nine models of surgical masks and respirators placed on the breathing simulator was measured at 32 and 85 L/min flow rates and compared with the results from a standard filter tester. Results show that cough-generated aerosol particles spread rapidly throughout the room, and that within 5 min, a worker anywhere in the room would be exposed to potentially hazardous aerosols. Aerosol exposure is highest with no personal protective equipment, followed by surgical masks, and the least exposure is seen with N95 FFRs. These differences are seen regardless of breathing rate and relative position of the coughing and breathing simulators. These results provide a better understanding of the exposure of workers to cough aerosols from patients and of the relative efficacy of different types of respiratory PPE, and they will assist investigators in providing research-based recommendations for effective respiratory protection strategies in health care settings.

Detection of infectious influenza virus in cough aerosols generated in a simulated patient examination room.

BACKGROUND: The potential for aerosol transmission of infectious influenza virus (ie, in healthcare facilities) is controversial. We constructed a simulated patient examination room that contained coughing and breathing manikins to determine whether coughed influenza was infectious and assessed the effectiveness of an N95 respirator and surgical mask in blocking transmission. METHODS: National Institute for Occupational Safety and Health aerosol samplers collected size-fractionated aerosols for 60 minutes at the mouth of the breathing manikin, beside the mouth, and at 3 other locations in the room. Total recovered virus was quantitated by quantitative polymerase chain reaction and infectivity was determined by the viral plaque assay and an enhanced infectivity assay. RESULTS: Infectious influenza was recovered in all aerosol fractions (5.0% in >4 µm aerodynamic diameter, 75.5% in 1-4 µm, and 19.5% in <1 µm; n = 5). Tightly sealing a mask to the face blocked entry of 94.5% of total virus and 94.8% of infectious virus (n = 3). A tightly sealed respirator blocked 99.8% of total virus and 99.6% of infectious virus (n = 3). A poorly fitted respirator blocked 64.5% of total virus and 66.5% of infectious virus (n = 3). A mask documented to be loosely fitting by a PortaCount fit tester, to simulate how masks are worn by healthcare workers, blocked entry of 68.5% of total virus and 56.6% of infectious virus (n = 2). CONCLUSIONS: These results support a role for aerosol transmission and represent the first reported laboratory study of the efficacy of masks and respirators in blocking inhalation of influenza in aerosols. The results indicate that a poorly fitted respirator performs no better than a loosely fitting mask.