This study investigates the effects of five decontamination methods on the filter quality (qf) of three commercially available electret masks—N95, Gauze and Spunlace nonwoven masks. Newly developed evaluation methods, the overall filter quality (qf,o) and the qf ratio were applied to evaluate the effectiveness of decontamination methods for respirators. A scanning mobility particle sizer is utilized to measure the concentration of polydispersed particles with diameter 14.6–594 nm. The penetration of particles and pressure drop (Δp) through the mask are used to determine qf and qf,o. Experimental results reveal that the most penetrating particle size (MPS) for the pre-decontaminated N95, Gauze and Spunlace masks were 118 nm, 461 nm and 279 nm, respectively, and the respective penetration rates were 2.6%, 23.2% and 70.0%. The Δp through the pretreated N95 masks was 9.2 mm H2O at the breathing flow rate of heavy-duty workers, exceeding the Δp values obtained through Gauze and Spunlace masks. Decontamination increased the sizes of the most penetrating particles, changing the qf values of all of the masks: qf fell as particle size increased because the penetration increased. Bleach increased the Δp of N95, but destroyed the Gauze mask. However, the use of an autoclave reduces the Δp values of both the N95 and the Gauze mask. Neither the rice cooker nor ethanol altered the Δp of the Gauze mask. Chemical decontamination methods reduced the qf,o values for the three electret masks. The value of qf,o for PM0.1 exceeded that for PM0.1–0.6, because particles smaller than 100 nm had lower penetration, resulting in a better qf for a given pressure drop. The values of qf,o, particularly for PM0.1, reveal that for the tested treatments and masks, physical decontamination methods are less destructive to the filter than chemical methods. Nevertheless, when purchasing new or reusing FFRs, penetration should be regarded as the priority.

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.

Background/purpose: The prevalence of musculoskeletal disorders (MSDs) was investigated among dentists in Taiwan, and risk factors for MSDs were evaluated for symptoms in different parts of the body. Materials and methods: The Nordic musculoskeletal questionnaire modified by the Taiwan Institute of Occupational Safety and Health was completed by 197 dentists (146 males and 51 females) from the members of three groups: the Association of Oral and Maxillofacial Surgeons (n Z 33), the Association of Family Dentistry (n Z 55), and the Taichung County Dental Association (n Z 109). Reported symptoms were compared by means of a Chi-square test according to various risk factors. Results: More than half of the respondents had experienced symptoms in the shoulders (75%), neck (72%), and lower back (66%) in the year before the survey. The three parts of the body with lower prevalence (13e15%) of trouble were hips/thighs/buttocks, knees, and ankles/ feet. Seven percent of respondents indicated no trouble in any part of their bodies. The prevalence of trouble in the neck increased when the number of days worked per week increased. Risk factors (p < 0.05) included working in a medical center for the shoulders; working with no more than one dental assistant, having a body height of >178 cm, and having a mean working time of >10 min/patient for the elbows; being <36 years old, having <11 years of experience, and having a mean time for forward bending or using a handpiece/scaler per patient for the wrists/hands; working 7 d/wk for the lower back and knees; having a patient load of >20 patients/d and being >35 years old for the hips/thighs/buttocks; and a having mean working time of >48 h/wk for the lower back.

This study seeks the optimal method for recovering loaded bacteria from filtering facepiece respirators (FFRs) and investigates the effects of artificial saliva (AS), artificial perspiration (AP) and storage conditions on the survival of bioaerosols and the filter performance of FFRs. Bioaerosols were generated using a Collison nebulizer in a test system and loaded on either N95 or surgical masks. Elution using centrifuge at 3500 rpm for ten min followed by vortexing for one min yielded a high relative survival (RS) rate of airborne Bacillus subtilis (BS) spores. When AS was added to the N95 FFR, the RS of BS declined during the first eight hours of storage and then increased to reach its highest value after 24 hr of storage. The worst case with the highest RS was at 37°C and 95% RH (p < 0.001). When AP was added to the N95 FFR and stored under the worst conditions, RS increased by over 100% during eight hours of storage. When AS was added to a surgical mask, the RS also increased by over 100% in eight hours of storage, but when AP was added to the surgical mask, RS immediately declined. When Escherichia coli (EC) were tested, their RS was lower than those of the BS samples. (Following loading with bacteria, the particle penetration and filter quality factor (q f ) increased (p < 0.001) but the slope of the linear regression between the pressure drop (∆p) and the flow rate through the filter was not statistically significantly changed (p = 0.233). In conclusion, AS and AP increased the survival of BS; AP was especially effective in N95 masks and AS was especially effective in surgical masks.

The use of electret N95 filtering facepiece respirators (N95FFRs) after prolonged storage or treatment can reduce the expense of buying non-expired N95 and thus enable developing and developed countries to optimize their use of limited resources to against airborne particles and diseases, such as coronavirus disease 2019 . The filtration performance of five N95FFR models following long-term storage, removal of charge using isopropanol alcohol (IPA), autoclaving, or treatment with gamma-radiation was assessed using a TSI 8130 automated filter tester. Statistically significant differences were found in the penetration (P), pressure drop (Δp) and quality factor (q f ) between non-expired and expired N95 models 3M-8210 and 3M-8511. A statistically significant linear correlation was also obtained between the N95 penetration ratio (PR) and the difference between year of manufacture and time of test (DYM). The PR of N95 was more strongly influenced by eliminating the charge (for extremely out-of-date respirators) on the electret filter than by the DYM. Sterilization by gamma irradiation increased the P into non-expired and expired N95FFR models (p < 0.05), reducing their q f . The q f of all N95FFR models, except UVEX-3200, was strongly affected by gamma irradiation, the removal of charge using IPA, autoclaving, and storage in that order. All expired models maintained acceptable filtration performance and still could be used to collect aerosol effectively, even though models 3M-8511 and 3M-1860 had been manufactured up to 13 years previously. As the COVID-19 outbreaks in 2019 and is getting worse in 2020, these data are useful in developing a global stockpiling strategy to maximize the longevity of N95FFRs for public health and healthcare workers. However, the aging of the straps and seal materials (rubbers, plastics) of the N95FFRs may affect their fit factor and effectiveness.