This work aims to investigate and develop a novel phase change material (PCM)-integrated firefighters' turnout gear technology that would significantly enhance the thermal protection of firefighters' bodies from thermal burn injuries under high-heat conditions (such as in fire scenes). This work established a 3D human thermal simulation to explore the thermal protection improvements of firefighters' turnout gear by using PCM segments under flashover and hazardous conditions. This simulation study will guide future experimental design and testing effectively and save time and effort. The study found that the 3.0-mm-thick PCM segments with a melting temperature of 60°C could extend the thermal protection time for skin surface to reach second-degree burn injury (60°C) by one to three times under flashover conditions compared to the turnout gear without PCM. Moreover, thinner PCM segments, i.e., 1.0-3.0 mm thickness, could also significantly mitigate the skin surface temperature increase while avoiding the added weight on the turnout gear. The 3D modelling results can be used to develop a next-generation firefighter turnout gear technology.

Phase change material (PCM) has been widely studied for efficient thermal management. This work is the first holistic experimental research on the temperature control performance of PCM-integrated firefighters' gloves. The results showed that the thermal protection time could be extended by 2-5 times in the direct contact to hot object tests and around 1.5 times under the radiant/convective heat source tests when embedding a 1-mm-thick PCM layer in gloves. The PCM of melting point 68 °C showed the best thermal protection performance in all test conditions since it had the most efficient phase change function during the heating process. Considering the PCM location effect, the PCM with lower melting point (68 °C) showed better performance when located close to external environment (heat source) and the PCM with higher melting point (108 °C and 151 °C) showed better performance when located close to hand. The optimum PCM thickness would be in the range of 0.5-1.0 mm for both thermal protection improvement and hand dexterity purposes. In addition, the time for continuous temperature rises on the hand surface at post-heat exposure was longer when embedding PCM in firefighters’ gloves due to the stored latent heat in PCM. © 2024 The Authors

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.

In surgical settings, infectious particulate wound contamination is a recognized cause of post-operative infections. Powered air purifying respirators (PAPRs) are worn by healthcare workers for personal protection against contaminated aerosols. Healthcare infection preventionists have expressed concern about the possibility that infectious particles expelled from PAPR exhalation channels could lead to healthcare-associated disease, especially in operative settings where sterile procedural technique is essential. This study used computational fluid dynamics (CFD) modeling to simulate and visualize the distribution of particles exhaled by PAPR wearers. Using CFD simulations, the PAPR inside to outside ratio of particle concentrations was estimated. Also, the effects of particle sizes, supplied-air flow rates, and breathing work rates on outward leakage were evaluated. This simulation study reconstructed a geometrical model of a static median headform wearing a loose-fitting PAPR by capturing a 3D image. We defined a mathematical model for the headform and PAPR system and ran simulations with four particle sizes, three breathing workloads and two supplied-air flow rates (a total 24 configurations; 4×3×2=24) applied on the digital model of the headform and PAPR system. This model accounts for exhaled particles, but not ambient particles. Computed distributions of particles inside and outside the PAPR are displayed. The outward concentration leakage was low at surgical setting, e.g., it was about 9% for a particle size of 0.1 and 1 μm at light breathing and a 205 L/min supplied-air flow rate. The supplied-air flow rates, particle sizes, and breathing workloads had effects on the outward concentration leakage, as the outward concentration leakage increased as particle size decreased, breathing workload increased, and the supplied-air flow rate decreased. The CFD simulations can help to optimize the supplied-air flow rates. When the loose-fitting PAPR is used, exhaled particles with small size (below 1μm), or heavy breathing workloads, may generate a great risk to the sterile field and should be avoided.

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.