N95 Filtering Facepiece Respirators Research Articles

A low cost ingenious approach for ultraviolet decontamination of N95 filtering face-piece respirators to deal with dwindling supply during the COVID-19 pandemic

Introduction: COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus-2 is rapidly evolving and hospitals are facing the issue of shortage of personal protective equipment (PPE) due to stringent requirements of PPE use. For reuse of N95 filtering face-piece respirators (N95FFR), we prepared an ingenious cabinet with ultraviolet light C (UV-C) using scarce material available during the lockdown period. Materials and Methods: Since like many other microbiology laboratories in medical colleges, we did not have access to viruses, we could not test our product with them. We thus tested the efficacy of the cabinet to decontaminate material using 0.5 McFarland standard broth of Escherichia coli 25922. The broth was exposed to UV-C inside the cabinet for 15 and 30 minutes in Petri dishes, with and without lids. The broth was subcultured on nutrient agar plates, both pre and post exposure. We also could not test integrity and static charge of the respirators; we relied on CDC data on the same. Results: It was observed that there was at least 4 log reduction (99.99%) in the number of viable E. coli on exposure to UV-C for 15 as well as 30 minutes. The plates with glass lids on did not show any reduction in number of viable bacilli. The reduction in number of E. coli was taken as surrogate marker for the reduction of ssRNA viruses. Conclusions: UV-C inside an ingeniously made cabinet can be used to decontaminate N95 FFR in exceptional circumstances of reduced supply under lockdown conditions of a pandemic.

Performance of Composite Filters Assembled from Multiple Layers of Basic Filtration Media

There is a severe shortage of face masks and N95 respirators due to the current COVID-19 pandemic, particularly in countries that were not well prepared in advance. In order to help ease the supply demands of these resources, a strategy of using multiple layers of basic filtration media to construct a composite filter that can match the particle collection efficiency offered by a N95 filtering facepiece respirator (FFR) is proposed. In this study, the filtration performances of four face masks and one N95 respirator using the same test protocol (as a reference) were first compared. Composite filter samples composed of multiple layers of basic face mask and MERV13 furnace media were then constructed and the filter performance of the composite filters was investigated. As expected, the minimum particle collection efficiency of the N95 respirator media sample was higher than 95% and the efficiency of the samples from the four tested face masks varied from 71.8% to 83.6%. The Figure of Merit (FOM) values of the face mask samples were generally half that of the N95 media sample. It was found that a N95-comparable collection efficiency can be achieved by combining two/three layers of face mask media but at the expense of a higher media pressure drop. Additionally, the composite filter samples made up of three/five layers of MERV13 furnace media could approach the FOM offered by the N95 media without the increased pressure drop. It was also found that the measured collection efficiency of multiple-layered filter media was not equal to the calculated in the test particle size range. Further studies are required to identify the reason(s).

Performance Comparison of N95 and P100 Filtering Facepiece Respirators with Presence of Artificial Leakage

National Institute for Occupational Safety and Health-approved P100 filtering facepiece respirators (FFRs) have a higher filter efficiency compared to the N95 filters. However, the former typically produce higher flow resistance (Rf). Consequently, when faceseal leakage is present, the proportion of leakage airflow for P100 FFRs may exceed that of N95s, resulting in a higher total inward leakage (TIL) of the P100. In this manikin-based study, the performance of two pairs of N95 and P100 FFRs (N95-A versus P100-A; N95-B versus P100-B) were compared under five sealing conditions (fully sealed and partially sealed with one, two, or three leaks of 0.8-mm, and one 2-mm leak). Sodium chloride particles (CMD ~45 nm) were used as the challenge aerosol. Respirators were tested under three constant flows (15, 50, and 85 L/min) and three cyclic flows (mean inspiratory flow = 15, 50, and 85 L/min). Both filter penetration (Pfilter) and TIL were determined. The Rf under constant flows was recorded. Based on Pfilter, TIL, and Rf, the quality factor (qf) was calculated to compare the overall performance of N95 and P100 FFRs. For a fully sealed condition, the Pfilter was much lower for the P100 FFRs than for the N95 FFRs. When small leaks were inserted (0.8-mm and 2 × 0.8-mm), the TIL was higher for the P100 FFRs than for the N95 FFRs under the lowest tested flow (15 L/min), while for greater leaks (3 × 0.8-mm and 2-mm), the TIL of the P100 FFRs was always higher regardless of the flow. The Rf of P100 FFRs was measured twice as high as the N95. The qf values were also found higher for the N95 FFRs than for the P100 FFRs regardless of leak size and breathing flow. With the presence of artificial leakage, a P100 FFR with high-flow-resistance may not be as protective as a low-flow-resistance N95 FFR. This finding suggests that future efforts should be directed to reducing the breathing resistance when designing P100 FFRs.

Comparing mask fit and usability of traditional and nanofibre N95 filtering facepiece respirators before and after nursing procedures

The reliability of N95 filtering facepiece respirators (FFRs) depends on correct fitting. The perceived usability of FFRs is equally important because discomfort during usage may affect compliance. Body movements during nursing procedures may also increase the risk of face seal leakage. To evaluate the mask fit and usability of the best-fitting 3M N95 FFR and the nanofibre N95 FFR before and after nursing procedures. The physical properties of these FFRs were also examined. This experimental study had a one-group multiple comparison design. In total, 104 nursing students participated, and performed nursing procedures for 10 min when wearing the best-fitting 3M FFR and the nanofibre FFR. Mask fit and perceived usability of the FFRs were evaluated. More participants failed to obtain a fit factor ≥100 when using the best-fitting 3M FFR than when wearing the nanofibre FFR (33.7% vs 21.2%) after the procedures (P=0.417). The nanofibre FFR also demonstrated higher usability than the 3M FFRs in terms of facial heat, breathability, facial pressure, speech intelligibility, itchiness, difficulty of maintaining the mask in place, and comfort level (P<0.001). The nanofibre FFR was also lighter, thinner and had slightly higher bacterial filtration efficiency than the 3M FFRs. The nanofibre FFR demonstrated significantly better usability than the 3M FFRs. None of the respirators were able to provide consistent protection for the wearer, as detected by face seal leakage after performing nursing procedures. Further improvement in the prototype design is needed to increase compliance and ensure the respiratory protection of users.

The Effect on Fit of Multiple Consecutive Donning and Doffing of N95 Filtering Facepiece Respirators.

N95 filtering facepiece respirators (FFRs) are widely used in healthcare to reduce transmission of airborne infectious diseases. These respirators are generally described as single use or limited reuse devices, but cost and operational issues mean that they may be donned and doffed multiple times. There is scant research on the effect of this practice on adequacy of fit. The purpose of this study was to measure the effect on respirator fit of multiple donning and doffing of N95 FFRs. This was an experiment in which 16 women and 9 men employed by the National Institute for Occupational Health (NIOH), Johannesburg, donned their same N95 FFR six times. All 25 were trained in the correct wearing of the devices before the experiment. Four models of respirators were used: the six who did not use respirators at work (novice subjects) were issued a 3M 1860 FFR and the others used their currently supplied one. During the experiment subjects donned their respirators under the supervision of the tester. Quantitative fit testing was done in the NIOH Occupational Hygiene laboratory after each donning according to the OSHA-Accepted Fit Test Protocol using the TSI PortaCount Pro+ Model 8038 Respirator Fit Tester. During the test, fit was measured after each of seven exercises and then an overall fit factor was computed. Only individuals who achieved an initial overall fit factor of ≥100 were allowed to continue participation in the study. Median overall fit factors were calculated for the 25 subjects for each donning and changes across them was examined using Wilcoxon rank sum tests. Men and women and frequent and infrequent users were compared across the six tests. Infrequent use was defined as subjects who wore respirators ≤ once per week, and novice subjects. Two subjects (8%) had an overall fit factor <100 at fit Test 2, 6 (24%) at Test 3, and 8 (32%) at Tests 4, 5, and 6. Thirteen respirator users (52%) achieved ≥100 throughout the fit testing, so 12 had at least one failure at either Tests 2-6. Five of the 12 subjects with at least one failure showed persistent failures on all subsequent donnings. Six subjects out of 12 (50%) who failed a fit test achieved an overall fit factor >100 at a subsequent test. There was a significant difference between the median first and sixth overall fit factors (195 versus 150; P = 0.0271), but not between the second and sixth (161 versus 150; P = 0.3584). Men and women had similar overall fit factors, but infrequent users had larger average overall fit factors than frequent users after all six donnings. Forty-eight percent of study subjects failed at least one fit test after re-donning an N95 FFR. The fit test data suggest that donning practices probably accounted for the fit test failures. The 50% of subjects who produced overall fit factors ≥100 after a test of <100 supports this contention.

Quality Assurance Sampling Plans in US Stockpiles for Personal Protective Equipment.

Personal protective equipment (PPE) stockpiles in the United States were established to facilitate rapid deployment of medical assets to sites affected by public health emergencies. Large quantities of PPE were introduced into US stockpiles because of the need to protect healthcare and other professionals during these events. Because most stockpiled PPE was acquired during, or immediately following, large-scale public health events, such as pandemic influenza planning (2005-20080), SARS (2003), H1N1 (2009-10), and Ebola (2014-15), aging PPE poses a significant problem. PPE such as N95 filtering face piece respirators were not designed to be stored for long periods, and much of the currently stored PPE has exceeded its manufacturer-assigned shelf life. Given the significant investment in the procurement and storage of PPE, along with projections of consumption during public health emergencies, discarding large quantities of potentially viable PPE is not an attractive option. Although shelf-life extension programs exist for other stockpiled medical assets, no such option is currently available for stockpiled PPE. This article posits stockpile quality assurance sampling plans as a mechanism through which shelf-life extension programs for stockpiled PPE may be achieved. We discuss some of the nuances that should be considered when developing a plan tailored to stockpiles and provide basic decision tools that may be used in the context of a quality assurance program tailored to stockpiled PPE. We also explore basic information by comparing and contrasting different sample size options.

N95 filtering facepiece respirators do not reliably afford respiratory protection during chest compression: A simulation study

BackgroundN95 filtering facepiece respirators (N95 respirators) may not provide adequate protection against respiratory infections during chest compression due to inappropriate fitting. MethodsThis was a single-center simulation study performed from December 1, 2016, to December 31, 2016. Each participant underwent quantitative fit test (QNFT) of N95 respirators according to the Occupational Safety and Health Administration protocol. Adequacy of respirator fit was represented by the fit factor (FF), which is calculated as the number of ambient particles divided by the number inside the respirator. We divided all participants into the group that passed the overall fit test but failed at least one individual exercise (partially passed group [PPG]) and the group that passed all exercises (all passed group [APG]). Then, the participants performed three sessions of continuous chest compressions, each with a duration of 2 min, while undergoing real-time fit testing. The primary outcome was any failure (FF < 100) of the fit test during the three bouts of chest compression. ResultsForty-four participants passed the QNFT. Overall, 73% (n = 32) of the participants failed at least one of the three sessions of chest compression; the number of participants who failed was significantly higher in the PPG than in the APG (94% vs. 61%; p = 0.02). Approximately 18% (n = 8) of the participants experienced mask fit failures, such as strap slipping. ConclusionsEven if the participants passed the QNFT, the N95 respirator did not provide adequate protection against respiratory infections during chest compression.

User acceptance of reusable respirators in health care

BackgroundInclusion of reusable respirators, such as elastomeric half-face respirators (EHFRs) and powered air-purifying respirators (PAPRs), in hospital respiratory protection inventories may represent 1 solution to the problem of N95 respirator shortages experienced during pandemics. User acceptance of these devices is 1 potential barrier to implementing such a strategy in respiratory protection programs.MethodsTo assess user attitudes toward various respirators, health care workers enrolled in respiratory protection programs in a medical system using EHFRs, N95s, and PAPRs and completed an online questionnaire that addressed attitudes, beliefs, and respirator preferences under different risk scenarios. Responses were compared between user groups.ResultsOf 1,152 participants, 53% currently used N95s, 24% used EHFRs, and 23% used PAPRs. N95 users rated their respirators more favorably compared with EHFR and PAPR users (P < .001) regarding comfort and communication, however, EHFR users rated their respirators much more highly regarding sense of protection (P < .001). For all user groups, reusable respirators were significantly more likely (odds ratios 2.3-7.7) to be preferred over N95 filtering facepiece respirators in higher risk scenarios compared to “usual circumstance” scenarios.ConclusionsDespite somewhat less favorable ratings on comfort and communication, experienced EHFR and PAPR users still prefer reusable respirators over N95s in certain higher risk scenarios. This suggests that reusable respirators are an acceptable alternative to N95 respirators in health care and offer 1 viable solution to prevent pandemic-generated respirator shortages.

Inhalation Exposure and Respiratory Protection of Home Healthcare Workers Administering Aerosolized Medications (Simulation Study)

ABSTRACT There is little information regarding aerosol exposure from using medical nebulizers and the factors affecting the risk of exposure, especially for treatments performed in a patient’s home environment. Home healthcare workers (HHWs) are a rapidly growing work population often exposed to aerosol hazards. Thus, we designed a simulated environment to measure the aerosol inhalation exposure of an HHW administering pressure-nebulized medications. We determined the relative contributions of different factors to aerosol reduction, namely, the room air exchange rate, proximity to the patient, and patient breathing rate, in an exposure chamber simulating a patient’s bedroom. Additionally, the performance of respiratory protective devices worn by an HHW, a surgical mask and N95 filtering facepiece respirator (FFR), was evaluated using NaCl as a well-established surrogate. The particle concentration in the breathing zone of an unprotected worker ranged from 7,118 to 284,600 cm–3. The proximity to the aerosol source affected the aerosol concentration, but the influence of this factor diminished when the distance increased beyond 24 inches. For an unprotected HHW, ventilation was the most effective way to reduce exposure to nebulizer-produced medical aerosols. An increase in the air exchange rate from 0 to 5 h–1 significantly reduced the exposure; however, a further increase (to 17 h–1) produced only a small reduction in the particle concentration. Therefore, no evidence suggests that patient homes require extremely efficient ventilation to mitigate HHWs’ exposure to nebulizer-produced medications. Increasing the patient’s breathing flow rate reduced the aerosol inhalation exposure; however, this factor cannot be controlled, which weakens its practical viability. Wearing respiratory protection devices was found to be the most efficient way to reduce aerosol exposure (within the set of tested variables). As expected, an N95 FFR with a proper seal was about 20-fold more efficient than a surgical mask.

Study of the micro-climate and bacterial distribution in the deadspace of N95 filtering face respirators

It is common for people to use N95 filtering facepiece respirators (FFRs) in daily life, especially in locations where particulate matter (PM2.5) concentration is rising. Wearing N95 FFRs is helpful to reduce inhalation of PM2.5. Although N95 FFRs block at least 95% of particles from the atmosphere, the deadspace of N95 FFRs could be a warm, wet environment that may be a perfect breeding ground for bacterial growth. This work studies the micro-climate features including the temperature distribution and water vapor condensation in the deadspace of an N95 FFR using the computational fluid dynamics (CFD) method. Then, the temperature and relative humidity inside the same type of N95 FFR are experimentally measured. There is a good agreement between the simulation and experimental results. Moreover, an experiment is conducted to study the distribution of bacteria sampled from the inner surface of an N95 FFR after donning.

Relative survival of Bacillus subtilis spores loaded on filtering facepiece respirators after five decontamination methods.

This study determines the relative survival (RS) of Bacillus subtilis spores loaded on an N95 filtering facepiece respirator (FFR) after decontamination by five methods under worst‐case conditions. Relative survival was obtained by testing after decontamination and after storing the FFRs at 37°C and 95% relative humidity for 24 hours. The decontamination methods involved ethanol, bleach, ultraviolet irradiation (UVA 365 nm, UVC 254 nm), an autoclave, and a traditional electric rice cooker (TERC) that was made in Taiwan. Without decontamination, 59 ± 8% of the loaded spores survived for 24 hours. When 70% ethanol was added to the N95 FFR at a packing density of 0.23, the RS was 73 ± 5% initially and decayed to 22 ± 8% in 24 hours. Relative survival remained above 20% after 20 minutes of UVA irradiation. The other four decontamination measures achieved 99%‐100% biocidal efficacy, as measured immediately after the methods were applied to the test FFRs. Relative survival is a useful parameter for measuring sterilization or degree of disinfection. Bleach, UVC, an autoclave, and a TERC provide better biocidal efficacy than ethanol and UVA. Not only a higher filter quality but also a lower value of RS produced the most decontaminated FFR.

Comfort and exertion while using filtering facepiece respirators with exhalation valve and an active venting system among male military personnel.

This study aimed to determine if disposable filtering facepiece respirators (FFRs) that come with an exhalation valve (EV) and a novel active venting system (AVS) provided greater perceived comfort and exertion when compared to standard N95 FFRs without these features among male military personnel performing prolonged essential outdoor duties. We used a randomised open-label controlled crossover study design to compare three FFR options: (a) standard FFR; (b) FFR with EV; and (c) FFR with EV+AVS. Male military personnel aged between 18 and 20 years completed a questionnaire at the start of outdoor duty (baseline), after two hours of standardised non-strenuous outdoor duty and after 12 hours of duty divided into two-hour work-rest cycles. Participants rated the degree of discomfort, exertion and symptoms using a five-point Likert scale. The association between outcomes and types of FFR was assessed using a multivariate ordered probit mixed-effects model. For a majority of the symptoms, study participants gave FFR with EV and FFR EV+AVS significantly better scores than standard FFR. Both FFR with EV and FFR with EV+AVS had significantly less discomfort (FFR with EV+AVS: 91.1%; FFR with EV: 57.6%) and exertion (FFR with EV+AVS: 83.5%; FFR with EV: 34.4%) than standard FFR. FFR with EV+AVS also had significantly better scores for exertion (53.4%) and comfort (39.4%) when compared to FFR with EV. Usage of FFR with EV+AVS resulted in significantly reduced symptoms, discomfort and exertion when compared to FFR with EV and standard FFR.

Ultraviolet germicidal irradiation of influenza-contaminated N95 filtering facepiece respirators

Safe and effective decontamination and reuse of N95 filtering facepiece respirators (FFRs) has the potential to significantly extend FFR holdings, mitigating a potential shortage due to an influenza pandemic or other pandemic events. Ultraviolet germicidal irradiation (UVGI) has been shown to be effective for decontaminating influenza-contaminated FFRs. This study aims to build on past research by evaluating the UVGI decontamination efficiency of influenza-contaminated FFRs in the presence of soiling agents using an optimized UVGI dose. Twelve samples each of 15 N95 FFR models were contaminated with H1N1 influenza (facepiece and strap), then covered with a soiling agent-artificial saliva or artificial skin oil. For each soiling agent, 3 contaminated FFRs were treated with 1 J/cm2 UVGI for approximately 1 minute, whereas 3 other contaminated FFRs remained untreated. All contaminated surfaces were cut out and virus extracted. Viable influenza was quantified using a median tissue culture infectious dose assay. Significant reductions (≥3 log) in influenza viability for both soiling conditions were observed on facepieces from 12 of 15 FFR models and straps from 7 of 15 FFR models. These data suggest that FFR decontamination and reuse using UVGI can be effective. Implementation of a UVGI method will require careful consideration of FFR model, material type, and design.

Observed variation in N95 respirator use by nurses demonstrating isolation care

Video review and scoring was used to evaluate the behaviors of nurses wearing N95 filtering face piece respirators while providing isolation care in a simulated patient care environment. This study yielded a detailed description of behaviors related to N95 respirator use in a health care setting. Developing a more robust and systematic behavior analysis tool for use in demonstration, simulation, and clinical care would allow for improved respiratory protection of health care workers.

Size-selective Assessment of Respirator Protection against Airborne Fungi and (1→3)-β-D-glucan in Farms

(1→3)-β-D-glucan is a major component of the fungal cell wall. It is commonly used to evaluate human exposure to fungi. A personal sampling system was developed to size-selectively evaluate the workplace protection factors (WPFs) of N95 filtering facepiece respirators (FFRs) and surgical masks (SMs) against fungi. This field study was performed with human subjects wearing an N95 FFR or a SM during farming activities. The geometric means of the WPFs of N95 FFRs and SMs were 156.2 and 12.2 for the total culturable fungi, 55.4 and 9.0 for the total fungi, and 10.5 and 11.1 for (1→3)-β-D-glucan. The WPFs for N95 FFRs against fungal contaminants were mostly greater than those for SMs; however, about 4.8%–35.0% of WPFs in the spore size range > 1.8 µm were still below 10 (the assigned protection factor designated for N95 FFRs by the US Occupational Safety and Health Administration). The WPFs of N95 FFRs and SMs against culturable fungi and (1→3)-β-D-glucan increased with the particle size. The total (1→3)-β-D-glucan significantly correlated with the total fungi (r = 0.588, p < 0.001) and total culturable fungi (r = 0.463, p = 0.002), which suggests that (1→3)-β-D-glucan can be used as an indicator to assess respiratory protection against airborne fungi on agricultural farms.

The effect of facial expressions on respirators contact pressures

This study investigated the effect of four typical facial expressions (calmness, happiness, sadness and surprise) on contact characteristics between an N95 filtering facepiece respirator and a headform. The respirator model comprised two layers (an inner layer and an outer layer) and a nose clip. The headform model was comprised of a skin layer, a fatty tissue layer embedded with eight muscles, and a skull layer. Four typical facial expressions were generated by the coordinated contraction of four facial muscles. After that, the distribution of the contact pressure on the headform, as well as the contact area, were calculated. Results demonstrated that the nasal clip could help make the respirator move closer to the nose bridge while causing facial discomfort. Moreover, contact areas varied with different facial expressions, and facial expressions significantly altered contact pressures at different key areas, which may result in leakage.

Recognizing the breathing resistances of wearing respirators from respiratory and sEMG signals with artificial neural networks

This study is devoted to recognizing the breathing resistances of wearing respirators from respiratory and surface electromyography (sEMG) signals. Ten subjects were required to sit for 5 min and walk for 5 min while wearing two different models of N95 filtering facepiece respirators (FFRs) and without a respirator. We recorded the sEMG signals from the respiratory muscles of the subjects, and the respiratory amplitude is also collected. Subsequently, fifteen features of the sEMG time domain and respiratory amplitude were extracted and used as input vectors to a recognition model based on artificial neural networks (ANNs). Finally, the experimental results show that these artificial neural networks are effective for recognizing different airway resistances of wearing respirators from sEMG and respiratory signals. The results also indicate that abdominal and scalene are the primary respiratory muscles affected by using N95 FFRs. Relevance to industryRespirator manufactures and administrations can readily employ this paper's findings for recognizing the breathing resistances of wearing respirators from respiratory and surface electromyography (sEMG) signals based on artificial neural networks automatically. Observations of the present study are in support of testing only the two primary muscles (abdominal and scalene) to simplify the evaluation of the effects of the breathing resistances of wearing respirators on respiratory muscles.

Filter penetration and breathing resistance evaluation of respirators and dust masks

ABSTRACTThe primary objective of this study was to compare the filter performance of a representative selection of uncertified dust masks relative to the filter performance of a set of NIOSH-approved N95 filtering face-piece respirators (FFRs). Five different models of commercially available dust masks were selected for this study. Filter penetration of new dust masks was evaluated against a sodium chloride aerosol. Breathing resistance (BR) of new dust masks and FFRs was then measured for 120 min while challenging the dust masks and FFRs with Arizona road dust (ARD) at 25°C and 30% relative humidity. Results demonstrated that a wide range of maximum filter penetration was observed among the dust masks tested in this study (3–75% at the most penetrating particle size (p < 0.001). The breathing resistances of the unused FFRs and dust masks did not vary greatly (8–13 mm H2O) but were significantly different (p < 0.001). After dust loading there was a significant difference between the BR caused by the ARD dust layer on each FFR and dust mask. Microscopic analysis of the external layer of each dust mask and FFR suggests that different collection media in the external layer influences the development of the dust layer and therefore affects the increase in BR differently between the tested models. Two of the dust masks had penetration values < 5% and quality factors (0.26 and 0.33) comparable to those obtained for the two FFRs (0.23 and 0.31). However, the remaining three dust masks, those with penetration > 15%, had quality factors ranging between 0.04–0.15 primarily because their initial BR remained relatively high. These results indicate that some dust masks analysed during this research did not have an expected very low BR to compensate for their high penetration.

Respiratory protection provided by N95 filtering facepiece respirators and disposable medicine masks against airborne bacteria in different working environments

Objective: To determine the relative protection provided by N95 filtering facepiece respirators (FFR) and disposable medicine masks (DMM) against airborne bacteria in different working environments. Methods: The field study was performed with 12 subjects wearing an N95 filtering facepiece respirator and a disposable medicine mask for 1h, respectively. Airborne microorganisms and bacteria samples from both the external (Ce) and the inner (Ci) surface of N95 FFR and DMM are collected. The Ce: Ci ratio was used to calculate the bacterial filtering proportion. Bacterial filtering efficiency (BFE) was measured using the JWL-2A Sampler. Results: The bacterial filtration efficiency of N95 FFR and DMM were 99.93% and 91.53%, respectively. There was significant difference between the two materials (P<0.05). In summer, airborne bacterial concentration was higher than that in winter. In the same season, airborne bacterial concentration in hospital environment is higher than that in campus. The higher the airborne bacterial concentration, the greater bacterial contaminated on the external surface of the used masks. To all masks used in different working environment, bacterial contamination on the external surface was much greater than the inner surface (P<0.01). Compared to N95 FFR, DMM had slighter bacterial contamination on the external surface and greater bacterial contamination on the inner surface. However, this difference was not significant (P>0.05). The bacterial filtering proportion of N95 FFR is higher than DMM. These differences were significant in samples tested in summer (P<0.05) , but were not significant in samples tested in winter (P>0.05). Conclusion: Bacterial filtering efficiency of N95 respirator is superior to medicine mask, and this advantage become more obvious in high airborne bacterial concentration levels.

Application of direct-reading and elemental carbon analysis methods to measure mass-based penetration of carbon nanotubes through elastomeric half-face and filtering facepiece respirators.

The aim of this study was to apply a direct-reading aerosol instrument method and an elemental carbon (EC) analysis method to measure the mass-based penetration of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) through elastomeric half-mask respirators (EHRs) and filtering facepiece respirators (FFRs). For the direct-reading aerosol instrument method, two scanning mobility particle sizer/aerodynamic particle sizer systems were used to simultaneously determine the upstream (outside respirator) and downstream (inside respirator) test aerosols. For the EC analysis method, upstream and downstream CNTs were collected on filter cassettes and then analyzed using a thermal-optical technique. CNT mass penetrations were found in both methods to be within the associated efficiency requirements for each type and class of the respirator models that were tested. Generally, the penetrations of SWCNTs and MWCNTs had a similar trend with penetration being the highest for the N95 EHRs, followed by N95 FFRs, P100 EHRs, and P100 FFRs. This trend held true for both methods; however, the CNT penetration determined by the direct-reading aerosol instrument method (0.009-1.09% for SWCNTs and 0.005-0.21% for MWCNTs) was greater relative to the penetration values found through EC analysis method (0.007-0.69% for SWCNTs and 0.004-0.13% for MWCNTs). The results of this study illustrate considerations for how the methods can be used to evaluate penetration of morphologically complex materials through FFRs and EHRs.