Quantitative investigation of air gaps entrapped in multilayer thermal protective clothing in low‐level radiation at the moisture condition

Firefighters wearing protective clothing perspire profusely in the process of performing their duties, and sweat increases moisture in the inner layers of multilayer protective clothing. Also, the outer shell fabrics inevitably become wet. In this study, two kinds of outer shell fabrics (aramid IIIA fabric and aramid 1313 and flame-retardant viscose-blended fabric) and three kinds of thermal liner fabrics with different thicknesses were selected. Two wetness conditions were investigated to simulate the sweating in thermal liner fabric with or without the wet outer shell fabric. A modified thermal protective performance (TPP) tester was employed to explore the effects of moisture and its distribution on stored thermal energy developed in six fabric systems and on TPP under flash exposure. Pearson correlations were established to analyze the relationships of the fabric systems’ thickness and second-degree burn time, and of absorbed energy and second-degree burn time in different configurations. The statistical analysis from these obtained data indicated that the thickness of fabric systems had no significant correlation for second-degree burn time (p > 0.05), but the absorbed energy exhibited a strong relation (the lowest R2 value could reach 0.8070 and p-values were all much less than 0.05). Performance results for the wet thermal liner indicated that the negative impact on thermal protection reached the greatest degree in 15% wetness, but in some extreme situations (100% wetness), the performance was improved (the maximum increase can achieve 116.2% over performance in dry condition). However, the existing moisture in the outer shell showed a positive effect. These findings will enable the engineering of textile materials that achieve high performance protection from thermal hazards and give some guidance to firefighters during operations.

Section: Effect Of Moisture Content On Heat Flux Of Simulated Skin Inmentioning

confidence: 96%

Effect of moisture content on thermal protective performance of fabric assemblies by a stored energy approach under flash exposure

Zhang

Song

et al. 2017

“…This is because more heat energy was absorbed by moisture in the fabric systems, which corresponds with previous research indicating that the presence of moisture can improve the thermal storage capacity of fabric. 24 The specific heat of moisture was 4.2 J/g ℃ at room temperature, which is nearly two to three times that of the dry fabric. 25 The obtained curves of the second stage appeared steeper, as with more absorbing heat, the fabrics transferred heat to the simulated skin.…”

Section: Resultsmentioning

confidence: 92%

The effects of moisture on the thermal protective performance of firefighter protective clothing under medium intensity radiant exposure

Zhang

Song

Ren

et al. 2017

Current firefighter protective clothing is composed of multilayer fabric systems. The outer shell fabrics inevitably become wet in the process of firefighters performing their duties, and sweat may also increase moisture in the inner layers of protective clothing. In this study, two kinds of outer shell fabrics (aramid IIIA fabric and aramid 1313 and flame-retardant viscose-blended fabric) and two kinds of thermal liner fabrics with different thicknesses were selected. Three wetness conditions were simulated for the outer shell fabric, thermal liner fabric and both fabrics together. A modified thermal protective performance (TPP) tester was applied to assess TPP provided by these wetted fabrics; in addition, second-degree skin burn time was predicted and absorbed energy indexes were calculated. The regression method was employed to create fitting curves for absorbed energy and second-degree burn time in different configurations and the Pearson correlation was established to analyze their relationship, in which the lowest R2 value could reach 0.9122 and p-values were all much less than 0.05. Performance results for both wet conditions indicated that outer shell moisture and a thicker thermal liner have a positive and increased negative effect, respectively, on fabric TPP. When the sample S-3-D (aramid 1313 and flame-retardant viscose-blended fabric, moisture barrier and the thin thermal liner) was both wetted in the outer shell and thermal liner, its second-degree burn time was improved by 12.8% over performance in dry conditions. These findings may have important applications for the design and manufacture of optimal protective performance clothing systems.

“…On the other hand, in spite of the fact that a majority of burns are caused by steam condensation, thermal protective performance is usually evaluated with dry skin models according to thermal protection standards (e.g., ISO 13506, ASTM 1930 and ASTM 2700) (8,(16)(17)(18)(19)(20). To investigate the effect of perspired moisture on thermal protective performance, researchers have adapted these methods by using wet fabric systems (21)(22)(23)(24)(25)(26)(27)(28) or a set-up with an adjustable microclimate relative humidity between the fabric specimen and the copper calorimeter (skin model) (29,30). Within these studies, there is no clear conclusion about the effect of moisture on thermal protective performance.…”

Section: Introductionmentioning

confidence: 99%

Effect of perspired moisture and material properties on evaporative cooling and thermal protection of the clothed human body exposed to radiant heat

Guan

Psikuta

Camenzind

et al. 2018

Perspired moisture plays a crucial role in the thermal physiology and protection of the human body wearing thermal protective clothing. Until now, the role of continuous sweating on heat transfer, when simultaneously considering internal and external heat sources, has not been well-investigated. To bridge this gap, a sweating torso manikin with 12 thermal protective fabric systems and a radiant heat panel were applied to mimic firefighting. The results demonstrated how the effect of radiant heat on heat dissipation interacted with amount of perspired moisture and material properties. A dual effect of perspired moisture was demonstrated. For hydrophilic materials, sweating induced evaporative cooling but also increased radiant heat gain. For hydrophilic station uniforms, the increment of radiant heat gain due to perspired moisture was about 11% of the increase of heat dissipation. On the other hand, perspired moisture can increase evaporative cooling and decrease radiant heat gain for hydrophobic materials. In addition to fabric thermal resistance ( Rct) and evaporative resistance ( Ret), material hydrophilicity and hydrophobicity, emissivity and thickness are important when assessing metabolic heat dissipation and radiant heat gain with profuse sweating under radiant heat. The results provide experimental evidence that Rct and Ret, the general indicators of the clothing thermo-physiological effect, have limitations in characterizing thermal comfort and heat strain during active liquid sweating in radiant heat. This paper offers a more complete insight into clothing thermal characteristics and human thermal behaviors under radiant heat, contributing to the accurate evaluation of thermal stress for occupational and general individuals.