Guowen Song

Modeling the Thermal Protective Performance of Heat Resistant Garments in Flash Fire Exposures

This research developes a numerical model to predict skin burn injury resulting from heat transfer through a protective garment worn by an instrumented manikin exposed to laboratory-controlled flash fire exposures. This model incorporates characteristics of the simulated flash fire generated in the chamber and the heat-induced changes in fabric thermophysical properties. The model also accounts for clothing air layers between the garment and the manikin. The model is validated using an instrumented manikin fire test system. Results from the numerical model help contribute to a better understanding of the heat transfer process in protective garments exposed to intense flash fires, and to establishing systematic methods for engineering materials and garments to produce optimum thermal protective performance.

Analyzing stored thermal energy and thermal protective performance of clothing

Protective clothing can store large amounts of energy when exposed to thermal (heat, flame) hazards. After exposure, the stored thermal energy discharges naturally—or may be forced if the clothing is compressed suddenly—and contributes to human skin burn injuries. In this study, the stored thermal energy that develops in thermal protective clothing materials was analyzed under different conditions. A stored energy approach that accounts for the thermal energy contained in the exposed test specimen is developed. The stored energy approach measures the total energy delivered to the sensor from a combination of the energy directly transmitted during exposure and the energy stored in the fabric system that is subsequently discharged after the thermal exposure. The study examines the effects of moisture on protective performance and the influence of air gaps between the fabrics and the sensor in terms of a stored energy approach and TPP/RPP (thermal protective performance/radiant protective performance) approach. A minimum exposure time that caused a prediction of a second degree burn was introduced and its contribution to burn injury was examined. These analyses demonstrate that the stored thermal energy obtained during thermal exposure is significant for multilayer protective clothing. Stored thermal energy contributes a large part of the total energy required to cause a second degree skin burn injury. The results indicate that, in cases of thermal exposure, stored thermal energy can reduce significantly the level of protection expected from wearing protective clothing.

A novel personal cooling system (PCS) incorporated with phase change materials (PCMs) and ventilation fans: An investigation on its cooling efficiency.

Personal cooling systems (PCS) have been developed to mitigate the impact of severe heat stress for humans working in hot environments. It is still a great challenge to develop PCSs that are portable, inexpensive, and effective. We studied the performance of a new hybrid PCS incorporating both ventilation fans and phase change materials (PCMs). The cooling efficiency of the newly developed PCS was investigated on a sweating manikin in two hot conditions: hot humid (HH, 34°C, 75% RH) and hot dry (HD, 34°C, 28% RH). Four test scenarios were selected: fans off with no PCMs (i.e., Fan-off, the CONTROL), fans on with no PCMs (i.e., Fan-on), fans off with fully solidified PCMs (i.e., PCM+Fan-off), and fans on with fully solidified PCMs (i.e., PCM+Fan-on). It was found that the addition of PCMs provided a 54∼78min cooling in HH condition. In contrast, the PCMs only offered a 19-39min cooling in HD condition. In both conditions, the ventilation fans greatly enhanced the evaporative heat loss compared with Fan-off. The hybrid PCS (i.e., PCM+Fan-on) provided a continuous cooling effect during the three-hour test and the average cooling rate for the whole body was around 111 and 315W in HH and HD conditions, respectively. Overall, the new hybrid PCS may be an effective means of ameliorating symptoms of heat stress in both hot-humid and hot-dry environments.

Effects of moisture content and clothing fit on clothing apparent ‘wet’ thermal insulation: A thermal manikin study

‘Wet’ thermal insulation, defined as the thermal insulation when clothing gets partially or fully wet, is an important physical parameter to quantify clothing thermal comfort. As the water/sweat gradually occupies the intra-yarn and inter-yarn air voids of the clothing material, the clothing intrinsic thermal insulation will be diminished and, hence, contribute to the loss of total insulation. In cold conditions, a loss in total thermal insulation caused by sweating may result in an inadequate thermal insulation to keep thermal balance and eventually leads to the development of hypothermia and cold injuries. Therefore, it is imperative to investigate the effect of clothing fit and moisture content on clothing ‘wet’ insulation. In this study, the ‘wet’ thermal insulation of three two-layer clothing ensembles was determined using a Newton thermal manikin. Four levels of moisture content were added to the underwear: 100, 200, 500 and 700 g. The clothing apparent ‘wet’ thermal insulation under different testing scenarios was calculated and compared. A third-degree polynomial relationship between the reduction in ‘wet’ thermal insulation and the moisture content added to underwear was obtained. Further, it was evident that the clothing fit has a minimal effect on the apparent ‘wet’ thermal insulation. The findings may have important applications in designing and engineering functional cold weather clothing and immersion suits.

Comparison of Methods Used to Predict the Burn Injuries in Tests of Thermal Protective Fabrics

A study was conducted to compare the two methods, Henriques Burn Integral and Stoll criteria, in thermal protective performance evaluation on firefighter clothing composites exposed to various thermal hazards. The thermal hazards that the firefighter may encounter during fire fighting are low level thermal radiation and high intensity flashover fire. With the simulation of these thermal hazards in the lab, the heat flux behind exposed clothing composites are characterized with flux rise rate and peak heat flux. Comparisons were performed on the prediction differences of clothing system made using Henriques Burn integral and Stoll criteria under different conditions. The study demonstrated that in some cases less difference is predicted by the two methods, while in other cases a significant difference is observed. Several recommendations were made for the qualitative prediction of garment and fabric thermal protective performance under different situations.

Investigation of feasibility of developing intelligent firefighter-protective garments based on the utilization of a water-injection system

ABSTRACT This research develops a new approach to designing and creating a prototype of an intelligent firefighter thermal-protective garment. During a flash fire exposure, this intelligent garment will absorb a significant amount of the incident heat flux due to evaporation of the injected water, thus limiting the temperature increase and the total heat flux to the firefighters skin. A comprehensive mathematical model of heat and mass transport in the fabric layer during the flash fire exposure is suggested and numerically implemented using a finite-volume technique. A computational investigation is performed to optimize the performance of this novel garment system in terms of the activation temperature and the necessary amount of injected water.

An Empirical Analysis of Thermal Protective Performance of Fabrics Used in Protective Clothing

Fabric-based protective clothing is widely used for occupational safety of firefighters/industrial workers. The aim of this paper is to study thermal protective performance provided by fabric systems and to propose an effective model for predicting the thermal protective performance under various thermal exposures. Different fabric systems that are commonly used to manufacture thermal protective clothing were selected. Laboratory simulations of the various thermal exposures were created to evaluate the protective performance of the selected fabric systems in terms of time required to generate second-degree burns. Through the characterization of selected fabric systems in a particular thermal exposure, various factors affecting the performances were statistically analyzed. The key factors for a particular thermal exposure were recognized based on the t-test analysis. Using these key factors, the performance predictive multiple linear regression and artificial neural network (ANN) models were developed and compared. The identified best-fit ANN models provide a basic tool to study thermal protective performance of a fabric.

A novel protocol to characterize the thermal protective performance of fabrics in hot-water exposure

This study aims to introduce a novel protocol to characterize the thermal protective performance of fabrics used in firefighters’ clothing under hot-water exposure. For this, new and improved test methods were developed to evaluate the performance of a set of fabrics under exposure to hot-water splash and hot-water immersion with compression. The thermal energy transmission through the fabrics tested was thoroughly investigated, and the physical properties that affect the performance of fabrics were statistically identified. It has been found that mainly mass (hot-water) transfer occurs through fabrics in a hot-water splash; whereas, both conductive heat and mass transfer predominate in a hot-water immersion with compression. The compression applied in the exposure of hot-water immersion changes the physical properties of fabrics, thereby reducing fabrics’ performance. The structural configuration and physical properties (e.g., air permeability, thickness) of fabrics are crucial to their heat and mass transfer and therefore to overall fabric performance. This study’s findings may contribute to developing new fabric testing standards, as well as improved thermal protective clothing to provide better occupational safety and health for firefighters.

Effects of Simulated Flash Fire and Variations in Skin Model on Manikin Fire Test

An established numerical model of a manikin fire test, which has the capability of predicting heat transfer through thermally protective clothing exposed to an intense heat environment, is described in this paper. The model considers the fire characteristics simulated in a manikin chamber as well as the insulating air layers between protective garments and the skin surface. The numerical model is applied to analyze the effects of simulated flash fire and variations in a skin model on a manikin test. The study demonstrates that the heat flux measured by 122 thermal sensors over the surface of the manikin exhibits a bell-shaped Gaussian distribution for a short duration in calibration burn. A series of flash fire data with different distributions was generated statistically, and the effects on burn predictions were investigated. The results suggest that the fire distribution affects the burn predictions for 4 s of exposure. The effects of initial temperature distribution, thermal properties, as well as involvement of blood perfusion in a skin model on burn predictions are also discussed. The model predictions demonstrate that the initial temperature distribution in a skin model has a large effect on burn predictions for a one-layer garment exposed to short duration flash fire conditions.

The impact of air gap on thermal performance of protective clothing against hot water spray

The air gap size and distribution developed between clothing and a human body play a critical role in clothing performance, specifically for thermal protective clothing. Hot liquid is considered as one of the common hazards in industrial working environments. In this study, the clothing air layer entrapped between protective clothing and a manikin body was determined using three-dimensional body scanning, and the protective performance provide by the clothing was predicted using an instrumented hot water spray manikin evaluation system. The relationship between the average air gap size and overall protective performance was analyzed. The impact of clothing air gap developed along the human body on predicted burn injury was considered. In addition, the air gap distribution and its relation to skin burn injury were compared for the selected garments. In general, the results indicated that the average air gap size showed positive effects on the overall protective performance. For all body parts except the pelvis, the air gap size presented a significant relationship with the percentage of burn injury. For an individual garment, there was no significant correlation found between the air gap distribution and skin burn injury. The garment with a larger air gap size and minimal air gap changes during hot water spray provided better protective performance. The research findings could provide the technical basis for further development of high performance protective clothing.