Susan Shuhong Xu

Transient three-dimensional (3D) heat and moisture transfer simulations were conducted to analyze the thermal performances of the entire phase change material (PCM) integrated into firefighters' gloves. PCM was broken down into several segments to cover the back and palm of the hand but to avoid finger joints to keep hand functions. Parametric studies were performed to explore the effects of PCM melting temperatures, PCM locations in the glove and PCM layer thicknesses on the overall thermal performance improvement of firefighters' gloves. The study found that PCM segments could extend the time for hand skin surfaces (areas covered or not covered by PCM) to reach second-degree burn injury (60 °C) by 1.5-2 times compared to conventional firefighters' gloves without PCM. Moreover, PCM segments could help mitigate the temperature increase on hand skin and glove surface after fire exposure.

Firefighters are required to use a self-contained breathing apparatus (SCBA) for respiratory protection when engaged in a variety of firefighting duties. While the SCBA provides crucial respiratory support and protection, it is also cumbersome and heavy. Questions have arisen to address the current weight limitation listed in 42 CFR Part 84, which mandates the maximum weight of 16 kg (35.2 lbs) for an SCBA system. The objective of the overarching study is to inform a maximum comfortable SCBA weight by developing static and dynamic biomechanical models and collecting physiological burden and postural stability data to evaluate stressors for firefighting tasks. This paper presents data from the static models. Eight representative firefighting tasks (stair climb, hose carry, weighted carry, rope pull, dummy drag, hammer slam, overhaul, and hose advance) were used in the biomechanical models. Maximum comfortable SCBA weights were calculated based on three biomechanical models (abdominal extension/tension, lateral extension/tension, and abdominal rotation). This study found that the maximum comfortable weight for an SCBA was 39 lbs for the static postures of interest. Further studies with human subjects to investigate the SCBA weight limit by using physiological burden and dynamic models are underway and will provide crucial data to inform updates to the current weight limits for SCBAs allowing more features and extended durations of these devices without compromising user safety, performance, or comfort.

The National Institute for Occupational Safety and Health’s methods and requirements for air-purifying respirator breathing resistance in 42 CFR Part 84 do not include work of breathing. The International Organization for Standardization Technical Committee 94, Subcommittee 15 utilized work of breathing to evaluate airflow resistance for all classes of respiratory protective devices as part of their development of performance standards regarding respiratory protective devices. The objectives of this study were: (1) to evaluate the relationship between the International Organization for Standardization’s work of breathing measurements and the National Institute for Occupational Safety and Health’s breathing resistance test results; (2) to provide scientific bases for standard development organizations to decide if work of breathing should be adopted; and (3) to establish regression equations for manufacturers and test laboratories to estimate work of breathing measurements using breathing resistance data. A total of 43 respirators were tested for work of breathing at minute ventilation rates of 10, 35, 65, 105, and 135 liters per minute. Breathing resistance obtained at a constant flow rate of 85 liters per minute per National Institute of Occupational Safety and Health protocol was correlated to each of the parameters (total work of breathing, inhalation, and exhalation) obtained from the work of breathing tests. The ratio of work of breathing exhalation to work of breathing inhalation for all air-purifying respirators is similar to the ratio of exhalation to inhalation resistance when tested individually. The ratios were about 0.8 for filtering facepiece respirators, 0.5 for half-masks, and 0.25 for full-facepiece respirators. The National Institute for Occupational Safety and Health’s breathing resistance is close to work of breathing’s minute ventilation of 35 liters per minute, which represents the common walking/working pace in most workplaces. The work of breathing and the National Institute of Occupational Safety and Health’s breathing resistance were found to be strongly and positively correlated (r values of 0.7–0.9) at each work rate for inhalation and exhalation. In addition, linear and multiple regression models (R-squared values of 0.5–0.8) were also established to estimate work of breathing using breathing resistance. Work of breathing was correlated higher to breathing resistance for full-facepiece and half-mask elastomeric respirators than filtering facepiece respirators for inhalation. For exhalation, filtering facepiece respirators were correlated much better than full-facepiece and half-mask elastomeric respirators. Therefore, the National Institute for Occupational Safety and Health’s breathing resistance may reasonably be used to predict work of breathing for air-purifying respirators. The results could also be used by manufacturers for product development and evaluation.

Powered air-purifying respirators (PAPRs) are worn to protect workers from hazardous respiratory exposures in a wide range of workplaces, including healthcare. However, PAPRs may diminish the ability of wearers to correctly hear words spoken by others, potentially interfering with safe performance of healthcare duties. Accordingly, the impact of PAPRs during healthcare use on speech intelligibility (SI) and consequently on user safety, usability, and patient care is not well studied. The objectives of this study were to (1) determine a listener’s ability to comprehend single-syllable words spoken by a PAPR wearer; (2) determine a PAPR wearer’s ability to intelligibly hear and identify single-syllable words spoken by a PAPR wearer; (3) to assess the variability between speakers, listeners, and PAPR models; (4) to investigate the effects of PAPR design features on SI; and (5) inform a SI requirement for certifying future PAPRs for use in healthcare. This study utilized a Modified Rhyme Test to assess SI for PAPRs. The current National Institute for Occupational Safety and Health (NIOSH) methods for assessing SI are limited to the recently introduced PAPR100 respirator class and the class of respirators claiming chemical, biological, radiological, and nuclear (CBRN) protections. Four NIOSH-approved PAPRs were evaluated using four human subjects. Four experimental conditions were examined:(1) Speaker and Listener with no PAPR; (2) Speaker and Listener both wearing PAPRs; (3) Speaker with a PAPR, Listener without a PAPR; and (4) Speaker without a PAPR, Listener with a PAPR resulted in a total of 144 experiments. Statistical analysis showed that the SI performance ratings were not significantly different among the PAPR models, but experimental conditions had significant impact on SI. The pattern of SI across the conditions of the experiment also showed a significant difference depending on PAPR model. The SI performance rating for all PAPRs could meet the current NIOSH CBRN certification requirement for speech intelligibility.

Firefighting is an injury prone occupation. The self-contained breathing apparatus (SCBA) included as part of a firefighter ensemble contributes to these injuries by affecting a firefighter’s balance. The objective of this study was to establish a method to determine the maximum allowable weight that would prevent firefighter injury by using a 3-Dimensional Static Strength Prediction Program (3DSSPP). Four representative firefighting tasks (stair climb, hose carry, weighted carry, and rope pull) were used to perform the simulation. A representation of a 50^th percentile male firefighter was used in 100 simulated trials. Based on a biomechanical model, 3DSSPP calculated lower back (L4/L5) compression forces and the results were compared to the NIOSH guidelines. The maximum safe weight of an SCBA ranged from 35 to 75 lbs. for the tasks examined. Policymakers may use this study’s methods and findings to inform evaluation methods and performance requirements that will drive SCBA design improvements, ultimately reducing the risk of injury among firefighters.

An ASTM International subcommittee on Respiratory Protection, F23.65 is currently developing a consensus standard for assessing respirator fit capability (RFC) criteria of half-facepiece air-purifying particulate respirators. The objective of this study was to evaluate if the test methods being developed for half-facepiece respirators can reasonably be applied to nonpowered full-facepiece–air-purifying respirators (FF–APR). Benchmark RFC test data were collected for three families of FF–APRs (a one-size-only family, a two-size family, and a three-size family). All respirators were equipped with P100 class particulate filters. Respirators were outfitted with a sampling probe to collect an in-mask particle concentration sample in the breathing zone of the wearer. Each of the six respirator facepieces was tested on the National Institute for Occupational Safety and Health 25-subject Bivariate Panel. The RFC test assessed face seal leakage using a PortaCount fit test. Subjects followed the corresponding Occupational Safety and Health Administration-accepted fit test protocol. Two donnings per subject/respirator model combination were performed. The panel passing rate (PPR) (number or percentage of subjects in the panel achieving acceptable fit on at least one of two donnings) was determined for each respirator family at specified fit factor passing levels of 500, 1,000, and 2,000. As a reasonable expectation based on a previous analysis of alpha and beta fit test errors for various panel sizes, the selected PPR benchmark for our study was >75%. At the fit factor passing level of 500 obtained on at least one of two donnings, the PPRs for three-, two-, and one-size families were 100, 79, and 88%, respectively. As the fit factor passing criterion increased from 500 to 1,000 or 2,000, PPRs followed a decreasing trend. Each of the three tested families of FF–APRs are capable of fitting ≥75% of the intended user population at the 500 fit factor passing level obtained on at least one of two donnings. The methods presented here can be used as a reference for standards development organizations considering developing RFC test requirements.