T. Nelson, NIHS Inc., Ardentown, DE; L. Alverez, St Paul, MN; R. Weber, 3M, Ardentown, MN.
If a pandemic influenza arrives, there will be a demand from the public for protective equipment to prevent infection. Respiratory protection will be used to reduce exposure from sprays, droplets, and aerosols that may contain the virus. The general public will not have access to the training, fit-testing, and experience that is required to be available to workers who use respirators on a routine basis. To estimate the level of performance that an N95 filtering facepiece could provide to novice users, groups of people who had not used a respirator previously were tested to measure the level of fit they could obtain. The only instructions they were provided were the written donning procedures that came with the respirators. The fit-tests followed the procedures listed in OSHA Standard 1910.134, Respiratory Protection. The range of fit factors measured were from 2 to 7300. There were statistically significant differences between the first and subsequent tests, indicating a learning effect. Observations indicated that the subjects’ willingness or ability to follow fitting instructions played a key role in the fit factors obtained.
L. Janssen, 3M, St. Paul, MN; T. Nelson, NIHS Inc., Ardentown, DE.
This study evaluated the workplace performance of an N95 filtering facepiece air-purifying respirator in a steel foundry. Air samples were collected inside and outside the respirators worn by workers who were properly trained and qualitatively fit-tested. For most workers, three or four pairs of air samples were collected on each of two days. Elemental iron concentrations on each sample pair were used to calculate workplace protection factors (WPFs). The geometric mean of the WPF distribution was 119, with a lower 5th percentile value of 19. Individual WPF measurements ranged from 5 to 753. Time-weighted average WPFs (WPF-TWA) were also calculated for each day for each worker. These WPFs ranged from 15 for the worker with the single WPF value of 5 to a high of 684. It is likely the WPF-TWA represents the best estimate of the protection an individual receives with daily respirator use. The distribution of WPF-TWA values had a geometric mean of 120 and a lower 5th percentile of 22. Both data treatments indicate this respirator’s performance was consistent with the assigned protection factor of 10 typically used for half-facepiece respirators. The respirator provided adequate protection as used in this study. All contaminant concentrations inside the respirator were well below the relevant occupational exposure limits.
A. Richardson, K. Hofacre, Battelle, Columbus, OH; P. Gardner, U.S. Army, Aberdeen Proving Ground, MD.
The Centers for Disease Control and Prevention recommends disposable N95, N99, or N100 filtering facepiece respirators (FFRs) as the minimum level of respiratory protection against transmission of influenza virus and other infectious biological aerosols. In the event of a pandemic outbreak, the potential exists for shortage of respirators and the need to reuse FFRs. Under these circumstances, reaerosolization of infectious aerosols from previously contaminated FFRs may be a concern for emergency responders and health care workers. A test method was developed to quantify the extent of reaerosolization due to a simulated cough through FFRs loaded with either an inert or biological aerosol. Particles reaerosolized from the FFRs were collected on filter paper for quantification using either a fluorescent or bioassay technique. Tests were performed to assess the effect of particle size, particle type, FFR design, and loading level. Test aerosols included inert polystyrene latex spheres with nominal diameters of 0.8 and 2.2 μm and the biological aerosols MS2 phage and Bg spores. The FFRs were loaded under cyclic flow conditions (2.3 L tidal volume, 37 breaths/min). The cough profile for reaerosolization had a peak flow rate of approximately 370 L/min and was repeated three times in succession. For the monodisperse inert aerosols tested, the extent of reaerosolization increased with increased particle size. The percent reaerosolization of the biological aerosols tended to be higher than that observed for the inert aerosols with similar aerodynamic mass median diameters. This was attributed to the broader size distributions of the biological aerosols.
A. Rengasamy, R. Verbofsky, R. Shaffer, NIOSH, Pittsburgh, PA.
NIOSH tests and certifies the filtration performance of N95 air-purifying respirators using polydisperse NaCl particles with a count median diameter of 0.075 ±0.020 µm and a geometric standard deviation of less than 1.86. In the certification test, a broad range of particle sizes (~95% of the particles lie in the range of 22 nm to 259 nm) is used to determine whether the respirator filter performance is at least 95% efficient. Using a different test system, a recent study showed higher than 5% penetration for particles near 50 nm and concluded that N95 respirators may not provide expected levels of protection. The aim of this study was to better understand the filtration efficiency of NIOSH-approved N95 respirators. Four models of N95 respirators were challenged with 20-nm to 400-nm size NaCl particles using a TSI 3160 fractional efficiency tester at 85 L/min flow rate. Five or more samples of each respirator model were tested, and the average particle penetrations were calculated for each model. The results showed that the most penetrating particle size (MPPS) was in the 40-nm range for all respirator models. Three manufacturers had one or more respirators with more than 5% penetration at the MPPS. However, the average penetration for each model was not statistically different from the 5% penetration expected. Particle penetration also was measured with the TSI 8130 automated filter tester used in NIOSH certification tests. The results showed that the penetration levels met the certification requirements. The difference in penetration values obtained with the NIOSH certification test system and other systems can be partially explained by differences in the measurement procedures. The TSI 8130 employs a forward light-scattering photometer to measure total particle penetration, while the TSI 3160 uses monodisperse aerosols and counts the actual number of particles.
R. Eninger, T. Honda, A. Adhikari, T. Reponen, S. Grinshpun, University of Cincinnati, Cincinnati, OH.
Use of filtering-facepiece respirators (FFRs) has increased in recent years, particularly among health care workers, nanotechnology workers, and emergency responders. These personal protection devices were commonly used in the aftermath of Sept. 11 and the 2003 SARS outbreak, as they are inexpensive, readily available, and disposable. N-type respirators are certified by NIOSH against a 300-nm mass median aerodynamic diameter aerosol for filtration efficiencies of 95% (N95), 99% (N99), and 99.97% (N100). The N95-type FFRs were recently evaluated against ultrafine particles (< 100 nm) by the University of Cincinnati group; however, no similar database is available for N99 type FFRs. We hypothesized that N99 respirators provide significantly greater filtration efficiency than N95 respirators for particles from 10 to 500 nm in diameter. This study evaluated N99 FFR filtration against NaCl nanoparticles and MS2 virus particles using a manikin-based protocol to simulate human inhalation. Face-seal leakage, which contributes to workplace respirator penetration, was not evaluated as respirators were sealed to the manikin face with a silicone sealant and leak-tested. Three N99 respirators, each from two manufacturers, were tested against two challenge aerosols at three inhalation flow rates: 30, 85, and 150 L/min. Particles of 10 to 500 nm in size were aerosolized from the NaCl and MS2 virus suspensions and measured real-time inside and outside the respirator using a wide-range particle spectrometer (WPS) to determine the respirator penetration. We observed that (1) peak particle penetration occurred at particle sizes less than 100 nm; (2) filtration efficiencies of N99 respirators were as variable as those of N95 respirators; and (3) while filtration efficiency of N99 respirators generally exceeds that of N95 at 300 nm, these efficiencies did not differ as much in the ultrafine particle size range.
S. van der Gijp, L. Steenweg, TNO Defence, Security and Safety, Rijswijk, The Netherlands.
The limiting factor for the storage time for respirator canisters, especially when the charcoals are impregnated with metal salts to react with various industrial chemicals. Several artificial aging methods are used for the evaluation of charcoal during the prototype and testing phase. Several of these alternative techniques were compared with actual storage of both chemical, biological, radiological, and nuclear (CBRN) canisters and ABEK canisters for several years under three different conditions. The breakthrough times of these aged canisters were evaluated with four different components. Additionally various material analysis were performed to study the surface structure of the charcoal, the clustering of the impregnates, metal salts, and the chemical composition of these salts. In this presentation the study of both the breakthrough experiments and the materials analysis will be discussed.
J. Parker, W. Duerr, H. Ahlers, NIOSH, Pittsburgh, PA.
The Bureau of Mines first approved filter self-rescuers for carbon monoxide (CO) more than 80 years ago. These respirators are currently approved by NIOSH and the Mine Safety Health Administration as gas masks for escape only from carbon monoxide. These units are relatively small, are carried on the user’s belt, and weigh approximately 1 kg. They have a mouthpiece and nose clip and a harness that goes around the neck. Inspired air is cooled by an integral heat exchanger, and expired air passes through a spring loaded exhalation valve. The canister section contains a catalyst that converts CO to carbon dioxide. The canister also contains a drying agent to prevent moisture from contacting the catalyst, which is degraded by water vapor. These respirators cannot be used in any atmosphere containing less than 19.5% oxygen. Filter self-rescuers are used to protect underground miners from CO generated by fire or explosions. Under a special NIOSH testing program, filter self-rescuers that have been carried by miners in their protective cases for 1.8 to 3 yr are collected and returned to NIOSH for testing against the NIOSH performance tests required for approval in Title 42, Code of Federal Regulations, part 84. The NIOSH test apparatus for CO is described, including special equipment necessary to test these units at 3000 parts per million CO, 25°C, and 95% relative humidity. Test results for 10 units are presented and compared to the minimum requirements. Maximum CO breakthrough concentrations, total penetrations of CO, inhalation and exhalation resistances, and maximum downstream temperature data for the 10 units tests are presented and discussed. The reliability of these respirators was also evaluated in this study. The test results show that the self-rescuers in the study were all in excellent condition inside their unopened protective cases and met NIOSH performance requirements.
R. Eninger, S. Grinshpun, T. Honda, T. Reponen, R. McKay, University of Cincinnati, Cincinnati, OH.
NIOSH certifies the filtration efficiency of filtering-facepiece respirators (FFRs) in accordance with Title 42, Code of Federal Regulations, part 84.181. FFRs are classified based on three filter efficiencies (labeled as 95, 99, and 100) and three classes of filtration degradation to sodium chloride or oil aerosol (N, R, and P). The filtration test is designed to be conservative by preconditioning the filters and using a charge-neutralized aerosol at the assumed most penetrating particle size (~300 nm). Performance of electret filters, however, cannot be accurately predicted by conventional mechanical theory as their fibers possess electrical charges, which modify filtration behavior. As a result, a most penetrating particle size shifts to the ultrafine range (less than 100 nm). In this study, the NIOSH filtration certification test for filtering-facepiece respirators was evaluated for its appropriateness in assessing filtration efficiency in the ultrafine particle size range. Certification requires measures of filtration efficiency by a forward light-scattering photometer. Photometers are capable of adequately measuring the light scatter of particles approximately 100 nm in size and above. Therefore, the certification test does not measure (or has very limited ability to measure) the contribution of ultrafine aerosols, which includes the most penetrating particle size for electret filters. Additionally, the information provided by the certification test does not allow evaluating how penetration varies based on particle size. We conclude that while the NIOSH filtration certification for filtering-facepiece respirators is effective at determining filtration efficiency against most workplace aerosols, it is limited to providing the performance data for particles above 100 nm.
S. Grinshpun, T. Honda, R. Eninger, University of Cincinnati, Cincinnati, OH.
In the event of a major disease outbreak caused by an airborne infectious agent or a deliberate use of an aerosolized bioagent in a terrorist attack, health care workers and the general population will need inexpensive, disposable, and efficient respiratory protection devices. Simple surgical masks may not provide adequate protection; the use of more efficient N95 respirators requires a face fit-testing and proper training that may not be feasible in a pandemic situation. A novel self-adhesive facepiece, Viramask, which uses triboelectric charged polypropylene/acrylic filter media, was recently developed by Wein Products. In this study, the new mask was first tested while sealed on a breathing manikin and challenged with particles aerosolized from NaCl and MS2 virus suspensions. The aerosol concentration was measured size-selectively in real-time outside and inside the mask to determine the penetration through its filter. Specific focus was given to the range of 10 to 500 nm, which includes viral particles that cause avian influenza, SARS, and other emerging diseases with possible airborne transmission. In addition, the Viramask was fit-tested when worn by human subjects to determine the fit factor and address the leakage aspect. The pressure drop across the mask was measured as well. Conventional N95, N99, and N100 filtering-facepiece respirators were also tested for comparison. It was found that the overall performance of the Viramask, for which the face-seal leakage issue is not as essential as for conventional facepieces, is much better than that of N95 and approximates that of N99/N100 respirators.
W. Chen, L. Wang, W. Su, Z. Wang, Tongji Medical College in Huazhong University of Science and Technology, Wuhan, China; Z. Zhuang, National Institute for Occupational Safety and Health, National Personal Protective Technology Laboratory, Pittsburgh, PA; X. Tang, Chongqin University, Chongqin, China.
Millions of workers in China rely on respirators and other personal protective equipment (PPE) to reduce the risk of injury and occupational diseases. However, there has not been a large survey of Chinese PPE users. Thus, an anthropometric survey of Chinese respirator users was conducted in 2006. A total of 2999 subjects who were born in 29 provinces were measured using traditional methods, while 350 of them were also scanned using a 3-D head scanner. In addition to height, weight, and neck circumference, 19 facial dimensions were measured using traditional methods. A stratified sampling plan was used with three age strata, two gender groups, and two regional groups. This survey included 2026 male workers and 973 female workers. The mean values of face length and face width for Chinese male workers were 117.0 mm and 147.6 mm; for Chinese females they were 109.9 mm and 140.1 mm, respectively. These mean values are significantly different from the values for the U.S. respirator users in a NIOSH study. The fit-test panels recently developed by NIOSH and representative of the current U.S. work force cover more than 95% of the Chinese subjects. But the percentages of the Chinese subjects in each cell of the NIOSH panels are different from the percentages of the U.S. work force in the corresponding cells. Thus, sample sizes for each cell of the NIOSH panels may need to be changed for Chinese or Asian workers when the NIOSH panels are incorporated into International Organization for Standardization respiratory protective device standards. Fit-test panels for the Chinese workers may also need to be developed using the data from this study.
A. Richardson, J. Middleton, C. Harto, K. Hofacre, Battelle, Columbus, OH.
A number of studies have examined the filtration efficiency of respirator filter media for nanoparticles (particles <100 nm in diameter), but fewer studies have examined the filtration efficiency of commercially available P95 and N95 filters. In this study, we examined the effect of nanoparticle loading on the filtration efficiency of four filters: two P95 and two N95 filters from three different manufacturers. The two P95 filters were found to have mechanical filter media while the two N95 filters were found to have electret media. Filters were loaded for 2 hr using a salt nanoparticle aerosol (NMAD 34 nm, σg =1.9), resulting in an estimated mass of approximately 5 mg being loaded onto the filter. These filters were then tested for initial penetration in a manner similar to that described by the NIOSH test standards for P95 and N95 filters. The effects of nanoparticle loading on overall filtration efficiency and filtration efficiency as a function of particle size will be discussed.