Effects of respirator ambient air cooling on thermophysiological responses and comfort sensations.

This investigation assessed the thermophysiological and subjective impacts of different respirator ambient air cooling options while wearing chemical and biological personal protective equipment in a warm environment (32.7 ± 0.4°C, 49.6 ± 6.5% RH). Ten volunteers participated in 90-min heat exposure trials with and without respirator (Control) wear and performed computer-generated tasks while seated. Ambient air cooling was provided to respirators modified to blow air to the forehead (FHC) or to the forehead and the breathing zone (BZC) of a full-facepiece air-purifying respirator using a low-flow (45 L·min(-1)) mini-blower. An unmodified respirator (APR) trial was also completed. The highest body temperatures (TTY) and least favorable comfort ratings were observed for the APR condition. With ambient cooling over the last 60 min of heat exposure, TTY averaged 37.4 ± 0.6°C for Control, 38.0 ± 0.4°C for APR, 37.8 ± 0.5°C for FHC, and 37.6 ± 0.7°C for BZC conditions independent of time. Both the FHC and BZC ambient air cooling conditions reduced facial skin temperatures, reduced the rise in body temperatures, and led to more favorable subjective comfort and thermal sensation ratings over time compared to the APR condition; however statistical differences among conditions were inconsistent. Independent of exposure time, average breathing apparatus comfort scores with BZC (7.2 ± 2.5) were significantly different from both Control (8.9 ± 1.4) and APR (6.5 ± 2.2) conditions when ambient cooling was activated. These findings suggest that low-flow ambient air cooling of the face under low work rate conditions and mild hyperthermia may be a practical method to minimize the thermophysiological strain and reduce perceived respirator discomfort.

Quality Assurance During a Global Pandemic: An Evaluation of Improvised Filter Materials for Healthcare Workers.

OBJECTIVE: The proliferation of improvised masks during the COVID-19 pandemic has raised questions regarding filter effectiveness and safety. We sought to compare the effectiveness of commonly used improvised filter materials against N95 industry standards. METHODS: Six different filter materials commonly used in the community were tested using both single- and multi-layer configurations with the TSI 8130 automated filter tester in accordance with National Institute for Occupational Safety and Health (NIOSH) standards for N95 respirators. RESULTS: Only three of the tested filter material configurations met N95 parameters with regard to filtration efficiency and pressure drop across the filter material-the: True-high-efficiency particulate air (HEPA) filter, four-layer MERV 13 and 14 HVAC filters. CONCLUSIONS: Many proposed filter materials for improvised masks do not meet current industry standards and may pose safety and efficacy concerns. Care should be taken when selecting materials for this critical respirator component, particularly for health care workers or others at high risk for pathogen exposure.

Unmanned assessment of respirator carbon dioxide levels: comparison of methods of measurement.

A study was performed to determine average inhaled carbon dioxide (F(I)CO2) concentrations of multiple respirators using unmanned test methods, and to compare results among test procedures to determine whether they could be used interchangeably. Respirator experiments were performed according to the National Institute for Occupational Safety and Health (NIOSH) (NF(I)CO2), standard European (ENF(I)CO2), and a modified method of the European test (BF(I)CO2) using full-facepiece air-purifying respirators and one air-purifying escape respirator. Bland-Altman statistics for determination of limits of agreement were applied to assess agreement among the various test methods. A considerable lack of agreement was found between NF(I)CO2 and ENF(I)CO2 methods and between BF(I)CO2 and NF(I)CO2 methods for average F(I)CO2. The modified EN136 method produced F(I)CO2 averages about 0.13% to 0.23% above unmodified EN136 values, but the agreement between methods was generally acceptable. These results demonstrate that NIOSH and European unmanned test methods for determining respirator average F(I)CO2 concentrations produce different results for like respirators. However, the findings suggest that the ENF(I)CO2 and BF(I)CO2 unmanned methods could be used interchangeably for quantifying respirator F(I)CO2 concentrations.

Inspiratory flow rates during hard work when breathing through different respirator inhalation and exhalation resistances.

There has been a long-standing debate regarding the adequacy of airflow rates used in respirator certification testing and whether these test flow rates underestimate actual values. This study investigated breath by breath inspiratory peak flow rate, minute ventilation, and instantaneous flow rates of eight young, healthy volunteers walking on a treadmill at 80-85% of maximal aerobic capacity until exhaustion while wearing an air-purifying respirator with one of eight combinations of inhalation and exhalation resistance. An analysis of variance was performed to identify differences among the eight conditions. Scheffe's post hoc analysis indicated which means differed. The group of conditions with the highest average value for each parameter was identified and considered to represent a worst-case scenario. Data was reported for these conditions. A Gaussian distribution was fit to the data and the 99.9% probability levels determined. The 99.9% probability level for the peak and instantaneous flow rates were 374 L/min and 336 L/min, respectively. The minute ventilation distribution was not Gaussian. Less than 1% of the recorded minute ventilations exceeded 135 L/min. Instantaneous flow rates exceeded the National Institute for Occupational Safety and Health's respirator test standards of 64, 85, and 100 L/min constant flow 91%, 87%, and 82% of the time, respectively. The recorded minute ventilations exceeded the 40 L/min minute ventilation test standard (for tests with a sinusoidal flow pattern) 100% of the time. This study showed that young, healthy respirator wearers generated peak flow rates, minute ventilations, and instantaneous flow rates that consistently exceeded current test standards. Their flow rates should be higher than those of a respirator wearer performing occupational work and could be considered upper limits. Testing respirators and respirator cartridges using a sinusoidal breathing pattern with a minute ventilation of 135 L/min (peak flow rate approximately 424 L/min) would encompass 99% of the recorded minute ventilations and 99.9% of the predicted peak and instantaneous flow rates from this study and would more accurately reflect human respiration during strenuous exercise.

Performance when breathing through different respirator inhalation and exhalation resistances during hard work.

Respirator inspiratory and expiratory breathing resistances impact ventilation and performance when studied independently. However, it is less clear as to how various combinations of inhalation and exhalation resistance affect user performance. The present study investigated the performance of 11 individuals during constant load, demanding work to exhaustion while wearing respirators with eight different combinations of inhalation and exhalation resistance. Exercise performance time, performance rating, minute volume, and peak inspiratory and expiratory airflow were recorded at the end of each test trial, and independent correlations with inhalation resistance and exhalation resistance were assessed. The combined impacts of respirator inhalation and exhalation resistances were quantified as the total external work of breathing (WOB(tot)) and correlations between the test variables and WOB(tot) were also examined. Significantly linear decreases in performance were found with increased inhalation resistances independent of exhalation resistance (R(2) = 0.99; p < 0.001) and with increased WOB(tot) (R(2) = 0.92; p < 0.001). Performance also decreased with increased exhalation resistance but no significant relationships were found. Minute volume decreased linearly with increased inhalation resistance independent of exhalation resistance (R(2) = 0.99; p < 0.001), but the linear decrease observed between minute volume and WOB(tot) was weak (R(2) = 0.36; p < 0.05). These findings suggest that WOB(tot) serves as a reliable estimate of the combined impacts of respirator inhalation and exhalation resistances on user performance during hard work, but that inhalation resistance alone serves as a better predictor of ventilation during respirator wear.

Speech intelligibility during respirator wear: influences of respirator speech diaphragm size and background noise.

This study assessed the effect of respirator speech device size on speech intelligibility and the impact of background noise on respirator communications effectiveness. Thirty-five subjects completed modified rhyme test (MRT) speech intelligibility testing procedures with and without a respirator under background noises of 40, 60, and 80 dBA. Respirator wear conditions included the use of one unmodified and three mechanical speech diaphragms modified to reduce the surface area of the vibrating inner membrane available for sound transmission. Average MRT scores decreased linearly as background noise levels increased for all conditions. Lower MRT scores were observed for all respirator speech diaphragm conditions compared to the nonrespirator condition within each noise category. Average MRT scores differed significantly between the unmodified speech diaphragm and one with a 70% reduced surface area with a 40-dBA background noise. However, MRT scores were similar between the modified and unmodified diaphragms at both the 60- and 80-dBA noise levels. These findings provide evidence that alternate designs of mechanical-type respirator speech devices can be achieved without further degradation of speech sound transmission.

Effect of differing facial characteristics on breathing resistance inside a respirator mask.

A group of subjects with a large range of facial characteristics was asked to breathe deeply while wearing a full facepiece respirator. The facial characteristics noted were head length, head depth, bizygomatic breadth, lip length, and Menton-Sellion length. External resistances to inhalation or exhalation were varied in each of the trials. The data collected were analyzed for possible correlation between facial characteristics and breathing resistance. Although respirator resistances were found to vary, no statistically significant correlation was found with anthropometric measurements.