Kaoru Wakatsuki

Development of a high-density nonwoven structure to improve the stab resistance of protective clothing material

The purpose of this research was to enhance the stab resistance of protective clothing material by developing a new high-density nonwoven structure. Ice picks often injure Japanese police officers due to the strict regulation of swords in the country. Consequently, this study was designed to improve stab resistance against ice picks. Most existing anti-stab protective clothing research has focused on various fabrics impregnated with resin, an approach that brings with it problems of high cost and complicated processing. Seldom has research addressed the potential for improving stab resistance by using nonwoven structures, which exhibit better stab resistance than fabric. In this research, we prepared a series of nonwoven structures with densities ranging from about 0.14 g/cm3 to 0.46 g/cm3 by varying the number of stacked layers of Kevlar/polyester nonwoven under a hot press. We then proposed two methods for producing such hot-press nonwovens: the multilayer hot-press method and the monolayer hot-press method. Stab resistance was evaluated according to NIJ Standard-0115.00. We also investigated the relationship among nonwoven density, stab resistance, and flexural rigidity, and here we discuss the respective properties of the two proposed methods. Our results show that stab resistance and flexural rigidity increase with nonwoven density, but flexural rigidity of nonwovens prepared using the monolayer hot-press method only shows a slight change as nonwoven density increases. Though the two methods exhibit little difference in maximum load, the flexural rigidity of nonwovens prepared using the monolayer hot-press method is much lower, which contributes to superior wear comfort. Finally, we investigated the mechanism behind the stabbing process. Stabbing with an ice pick is a complicated process that involves many factors. Our findings indicate that nonwovens stop penetration primarily in two ways: nonwoven deformation and fiber fractures.

Scale Modeling of Flame Spread Over PE-Coated Electric Wires

A universal correlation between the flame spread rate and the flame length formed along the electric wire was studied experimentally based on scale modeling concept. In the first place, we studied the burning behavior of research-graded wire (i.e., controlled wire, polyethylene-coated metal thin rod) in order to examine the precise effect of the total pressure (30–100 kPa), the core material (nickel chrome, iron, copper), and the scale (e.g., diameter, coating thickness, etc.) on the spread rate. It turned out that the flame shape was not the only primary factor involved in determining the spread rate, implying that the heat transfer process in solid phase is essential to consider. The simplest 1-D heat transfer model along the core was introduced, and two kinds of non-dimensional groups (i.e., Peclet number (Pe) and one to describe the radial direction of heat transfer process: Λ) were found necessary to preserve the similarity. By introducing two length scales to represent the processes in gas and solid phases, all measured data were found to have collapsed into the single line in Pe-Λ plane, suggesting that flame spread behavior would be predictable based on their correlation. This correlation curve is justified with the spread data obtained using practical electric wire and cables (with/without sheath), confirming that scale modeling of flame spreading over the electric wire was successful.

Evaluation of Functional Underwear for Firefighter Clothing by Total Heat Loss

Synthetic textile such as polyester and poly-urethane has been used for underwear in terms of moisture release and function in underwear. However, the synthetic underwear has high risk for skin burns due to melting and shrinking by heat. Thermal protection and comfort in fire fighter protective clothing is always trading off, but fire fighters tend to use the synthetic underwear to feel comfort and function during firefighting operation without understanding of the risk for skin burns by the textile. Objective of this study is to investigate if the synthetic underwear plays a significant role in moisture and metabolic heat transfer within the fire fighter clothing by total heat loss measurement. Measurement of the total heat loss has been conducted by the ASTM F-1868 instrument (Kato-Tech, Co. Ltd., Japan). Three type of fire fighter clothing, one station wear, and five types of underwear have been used for the test. Test has been conducted for each clothing and combination of clothing. The results shows that range of total heat loss is 322.3 W/m2 to 385.3 W/m2, 857.9 W/m2, 782.3 W/m2 to 897.3 W/m2 for three fire fighter clothing, one station wear and five underwear, respectively. However, when the fabrics of fire fighter clothing, station wear and underwear were piled up, the range of total heat loss decreased to 242.1 W/m2 to 304.4 W/m2. The data indicates that the fire fighters multi-layer fabric controls the heat and moisture transfer within fire fighter clothing and no positive contribution by any types of underwear.

Editorial: New development of research on personal protective equipment (PPE) for occupational safety and health: New development of research on personal protective equipment (PPE) for occupational safety and health

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives (by-nc-nd) License. There exist various kinds of physical, chemical, and biological hazards in the workplace. To protect workers from these hazards, it is not controversial that environmental management measures to remove or reduce these harmful factors and to improve the quality of workplaces through an engineering approach are fundamental solutions. However, in reality, there are many work sites where such decisively effective measures cannot be applied. In such situations, a work management approach utilizing personal protective equipment (PPE) is considered an alternative and significant means for protecting the safety and health of workers. Recent industrial development, automation, and digitalization has led to increased safety and reduced need for personal protection at many workplaces, while there still remain a considerable number of jobs that continuously require protection and many countries where traditional work methods are prevalent. Simultaneously, the threats have changed and new types of risks have emerged due to changed processes, new chemicals and materials, and work routines. Thus, there are still several industries where the workers need to be protected from contamination within processes by utilizing PPE. So far, many types of PPE have been developed to tackle this scenario. Nevertheless, their effectiveness and usability still remain incomplete. Thus, a new breakthrough for PPE is currently required. Progress in advanced fiber materials, knitting and weaving technologies, fabric fabrication techniques, nanomaterials, and fiber composite materials technologies have been remarkable in recent years. Therefore, applying the results of these advanced technologies to the development of PPE is a highly promising approach. On the other hand, even though protection of targeted harmful factors is successfully achieved by using effective PPE, such high performance of protection is likely to entail additional workloads on workers. One of the main burdens is the thermal impact caused by evaporative resistance and thermal insulation derived from the characteristics of PPE materials. The higher the evaporative resistance and Editorial

Influence on Skin Burns by Water Absorbed Station Wear and Underwear in Firefighter Clothing

During firefighting, within firefighter clothing, underwear and station wear gets heavily wet due to firefighting water and moisture from the body. Water has higher thermal conductivity relative to air and it has been expected that heavily wet condition within the firefighter clothing makes faster skin burns. The objective of this study is how the wet condition within a firefighter clothing makes faster heat transfer from feeling pain and to being 2nd degree of skin burns relative to the dry condition in case of routine firefighting operation in a building (up to 20 kW/m2). Aramid station wear and cotton underwear, generally used by a Japanese firefighter, have been selected and cut 0.15 m x 0.15 m to attach an ISO 9151 copper sensor. A cone shape electric heater, which produces 12 kW/m2 to 20 kW/m2, was used to heat the fabrics. Scenario of fabrics are that (1) wet station wear and dry underwear, (2) wet station and wet underwear, (3) dry station wear and wet underwear, and (4) dry station wear and dry underwear. Evaluation method was by a heat transfer index (HTI) by ISO 9151. The time to rise temperature of 12 and 24 °C (HTI12 and HTI24), and heat transfer rate (dT/dt) were investigated for above four scenarios. The result shows that there was significant impact by condition of station wear, but little impact by underwear. In heat transfer rate (dT/dt) analysis, for the situation of feeling pain to the 2nd degree of skin burns (from HTI12 to HTI24), heat transfer rate was about 50% higher relative to the dry station wear condition. This result indicates that it is possible to be 2nd degree of skin burns easily as soon as a firefighter feels the pain, if he/she wears wet station wear.