Emiel DenHartog

Evaluating turnout composite layering strategies for reducing thermal burden in structural firefighter protective clothing systems

A modular approach for arranging the component layers used in the construction of structural firefighter turnout garments is explored as a strategy for reducing the thermal burden contributed by these protective garments to firefighter heat stress. An instrumented sweating manikin was used to measure the insulation, evaporative resistance and total heat loss through turnout systems configured to represent different layering strategies. The outer shell, moisture barrier and thermal liner layers of the structural turnout base composite were tested individually to determine each layers thermal insulation and evaporative resistance. Multiple two- and three-layer combinations were analyzed for their application in specific working conditions. This study demonstrates that the moisture barrier layer contributes the most resistance to evaporative heat loss through the turnout system, while dry heat loss is most restricted by the thermal liner component. Removal of a single inner liner layer was equally beneficial for heat loss, regardless of material properties. It shows the potential benefit of turnout design strategy that utilizes a modular or adaptive layering approach to reduce turnout-related heat strain in conditions consistent with fire protection.

Total heat loss as a predictor of physiological response in wildland firefighter gear

In most types of protective clothing heat strain is an important issue. The wildland firefighter clothing system in the USA has seen no major revision over the last decades. In this project the wildland firefighter clothing system was studied at the material and the systems level. On the sweating guarded hot plate and the sweating thermal manikin effects of different base layers (cotton and modacrylic) and meta-aramid outer layers of different fabric weights were evaluated. Then, a human subject trial was performed on a limited set of clothing systems to validate the results from materials and manikin testing. The clothing systems were composed of relevant materials for wildland firefighters with extra configurations added to explore the effects of the highest and lowest levels of protection. All measurement techniques were reverted to a calculation of the total heat loss (THL), as predicted from the hot plate and the manikin and compared to the calculated heat loss from the human subjects. The prediction of the heat strain, based on the sweating guarded hot plate only, gives a large overestimation of the actual heat loss in humans. The currently used standard in the USA that utilizes THL values has no link to actual human heat loss. The manikin showed much better comparison to the human data in absolute terms, but in general underestimated heat loss and showed worse overall correlation to the human heat loss data than the hot plate values.

Analysis of air gap volume in structural firefighter turnout suit constructions in relation to heat loss

Air layers in multi-layer firefighter clothing ensembles resist heat transfer from the body to the environment. By reducing the volume of air between clothing layers, heat loss may be improved throughout the multi-layer firefighter turnout suit clothing system, potentially leading to reduced heat strain for the wearer. This research utilized a systems-level approach to the methodology in order to measure the effects of fabric properties and garment air gap dimensions on clothing system heat loss through specially configured turnout suit constructions. One experimental configuration incorporated a tight fitting stretchable moisture barrier garment. Another construction used thermal knit underwear to represent a closer fitting thermal liner. Air gap surface area, volume, and thickness were estimated using three-dimensional body scanning. This study showed the significant impact of fabric air permeability and clothing air gap volume on heat loss through structural firefighter suits. Tested individually, the tighter fitting moisture barrier construction permitted greater heat loss in comparison to the traditional fit moisture barrier. Heat loss differences associated with moisture barrier fit were not observed when the moisture barriers were configured in the three-layer turnout clothing system. This research showed that microclimate air gap volume is strongly correlated with total heat loss. It confirmed the significant impact of clothing air layers on heat loss through firefighter turnout systems.

Maximum allowable exposure to different heat radiation levels in three types of heat protective clothing

To determine safe working conditions in emergency situations at petro-chemical plants in the Netherlands a study was performed on three protective clothing combinations (operator’s, firefighter’s and aluminized). The clothing was evaluated at four different heat radiation levels (3.0, 4.6, 6.3 and 10.0 k∙W∙m−2) in standing and walking posture with a thermal manikin RadMan™. Time till pain threshold (43°C) is set as a cut-off criterion for regular activities. Operator’s clothing did not fulfil requirements to serve as protective clothing for necessary activities at heat radiation levels above 1.5 k∙W∙m−2 as was stated earlier by Den Hartog and Heus1). With firefighter’s clothing it was possible to work almost three min up to 4.6 k∙W∙m−2. At higher heat radiation levels firefighter’s clothing gave insufficient protection and aluminized clothing should be used. Maximum working times in aluminized clothing at 6.3 k∙W∙m−2 was about five min. At levels of 10.0 k∙W∙m−2 (emergency conditions) emergency responders should move immediately to lower heat radiation levels.

Combined thermal manikin and thermal model predictions of working times in fully encapsulated impermeable suits.

This project aimed to develop guidelines for safe working times in fully encapsulated impermeable suits and incorporate these data into an existing Chemical Companion Decision Support System (CCDSS) that is used by First responders in the US and abroad. The CCDSS provides guidelines on many operational aspects of response to a hazardous materials (HazMat). This study addresses the use of a thermos-physiological model, combined with a sweating thermal manikin, to simulate the data and compared that to the experimental data.

The influence of designs of protective uniforms on firefighters’ performance during moderate physical exercises

The aim of this study was to verify whether the minor differences in the design of uniforms and their fit can be quantified in terms of their impact on firefighters’ cardiorespiratory parameters and subjective perception of these uniforms. The impact of minor design improvements compared to the existing designs of personal protective clothing (PPC) is still relatively difficult to quantify due to the lack of sensitive devices used in smart measuring methodologies; however, the perception of these slight differences is reported by PPC users. The impact of these design differences in PPC on firefighters was studied via physiological tests based on occupation-related activities in which cardiorespiratory parameters were monitored and three-dimensional (3D) silhouette scanning was performed on the firefighters. Apart from heart rate (beats/min), none of the other measured physiological parameters, for example, oxygen consumption (VO2, ml/min) demonstrated statistically significant differences when firefighters were testing uniforms: ergonomic (ER), standard (ST), bulky (BU), and reference outfit (RO), the latter being T-shirt and shorts. A statistically significant correlation was found between parameters measured via 3D body scanning and selected cross-sections of the silhouettes as well as subjective assessments of easiness of specific movement performance during the physiological test and assessment of bulkiness of the uniforms. There is a limited influence of the minor design differences between firefighters’ uniforms on the selected physiological parameters of the subjects wearing them. The outcome of the study can be utilized when performing the test on subjects and improving designs of PPC.

Impact of reinforcements on heat stress in structural firefighter turnout suits

Abstract The purpose of this research was to determine the impact of additional textile layer reinforcements on garment heat loss and the physiological comfort of the firefighter. Four structural firefighter turnouts with varying levels of ‘bulk’ were assessed. A base composite analysis was conducted and each suit was evaluated for thermal resistance, evaporative resistance, and overall total heat loss (THL) on a sweating thermal manikin. Raw resistance data were then modeled to predict the physiological responses of firefighters for each turnout suit. Base composite percentages were compared to the heat loss values and predicted physiological responses. The Light Weight suit along with the Control, demonstrated the greatest heat loss values and lowest rise in predicted core temperature. Overall, results depicted the harmful impact that bulky reinforcements may have on wearer physiological comfort as the Heavy Duty suit had significantly lower heat loss and a potentially fatal maximum predicted core temperature.

Relationship between novel design modifications and heat stress relief in structural firefighters’ protective clothing

The purpose of this study was to investigate design modifications in structural firefighter turnout suits for their ability to reduce heat stress during firefighting activities. A secondary aim of this research established a benchmark for the manikin heat loss value necessary to achieve significant improvements in physiological comfort. Eight professional firefighters participated in five simulated exercise sessions wearing a control turnout suit and one of four turnout prototypes: Single Layer, Vented, Stretch, and Revolutionary. Physiological responses (internal core body temperature, skin temperature, physiological strain, heart rate, and sweat loss) were measured when wearing each turnout suit prototype. Results demonstrated a significant increase in work time and significant reductions in heat stress (core temperature, skin temperature, and physiological strain) when participants wore the Single Layer, Vented, and Revolutionary prototypes. An estimated garment heat loss value of 150 W/m2 was determined in order to achieve a significant reduction in heat stress.

A Novel Adjustable Concept for Permeable Gas/Vapor Protective Clothing: Balancing Protection and Thermal Strain

Armed forces typically have personal protective clothing (PPC) in place to offer protection against chemical, biological, radiological and nuclear (CBRN) agents. The regular soldier is equipped with permeable CBRN-PPC. However, depending on the operational task, these PPCs pose too much thermal strain to the wearer, which results in a higher risk of uncompensable heat stress. This study investigates the possibilities of adjustable CBRN-PPC, consisting of different layers that can be worn separately or in combination with each other. This novel concept aims to achieve optimization between protection and thermal strain during operations. Two CBRN-PPC (protective) layers were obtained from two separate manufacturers: (i) a next-to-skin (NTS) and (ii) a low-burden battle dress uniform (protective BDU). In addition to these layers, a standard (non-CBRN protective) BDU (sBDU) was also made available. The effect of combining clothing layers on the levels of protection were investigated with a Man-In-Simulant Test. Finally, a mechanistic numerical model was employed to give insight into the thermal burden of the evaluated CBRN-PPC concepts. Combining layers results in substantially higher protection that is more than the sum of the individual layers. Reducing the airflow on the protective layer closest to the skin seems to play an important role in this, since combining the NTS with the sBDU also resulted in substantially higher protection. As expected, the thermal strain posed by the different clothing layer combinations decreases as the level of protection decreases. This study has shown that the concept of adjustable protection and thermal strain through multiple layers of CBRN-PPC works. Adjustable CBRN-PPC allows for optimization of the CBRN-PPC in relation to the threat level, thermal environment, and tasks at hand in an operational setting.

Effect of Clothing Layers on Mass Transfer of Methyl Salicylate Vapor Through CBRN Materials in a Cylinder Test

The testing of protective clothing materials against chemical and biological (CB) hazards is usually done at either a swatch of fabric or at the systems level. In this paper, a cylinder test method was developed in combination with a MethylSalicylate (MeS) Simulant test (variant to the MIST test) to study the effect of air-permeable and membrane clothing systems and specifically the effects of layering on protection. Three fabrics, material A air permeable absorptive, material B air impermeable, non-absorptive (membrane) and material C air permeable non-absorptive were tested on the cylinder alone and in combinations at 1 m/s and 10 m/s wind speeds. At high wind speeds, the MeS vapor penetrated all three materials and protection factors (PF) were lower than 10. At the lower wind speed much higher protection was found, PF(material A) = 36, PF(material B) = 29, PF(material C) = 2, and material B showed a significant decrease in protection with a leakage added (PF = 2), which did not occur with material A (PF = 29). When materials A and C were combined the combination of any layer to material A increased protection, especially with material A close to the cylinder: PF = 983 with material A twice, and PF = 765 with material C outside and material A inside. With material C on both layers, essentially no protection was obtained (PF = 2) and with material A outside and material C inside PF was 55, slightly higher than material A alone. In conclusion, the cylinder method provided very useful information in the development of protective clothing systems, especially at the lower wind speed of 1 m/s, and may provide a reliable quick and efficient way to obtain information on protection of air permeable absorptive fabrics. The method provides much more realistic data than current standard swatch tests on such materials and is cheaper and faster than a whole system MIST test.