Kaoru Wakatsuki

Bio: Kaoru Wakatsuki is an academic researcher from Shinshu University. The author has contributed to research in topics: Flame spread & Scale model. The author has an hindex of 4, co-authored 12 publications receiving 52 citations.

Experimental Study on Near-Limiting Burning Behavior of Thermoplastic Materials with Various Thicknesses Under Candle-Like Burning Configuration

Abstract: We studied the near-limiting behavior of various thicknesses of thermoplastic materials under a candle-like burning configuration; followed by an ISO 4589-2 protocol. The motivation for this work is to understand the sensitivity of the sample thickness on the limiting oxygen concentration in the range from 0.5 mm to 10 mm. In the first place, the effect of heating time on successive ignition was discussed. Through a simple analysis, it was suggested that a 30 s heating time, regulated in ISO 4589-2, might be insufficient to achieve a successful ignition when the specimen becomes thicker. Second, the effect of the thickness of the test specimen (PMMA, ABS) on the limiting oxygen concentration was examined. Flames formed over thicker PMMA (>4.0 mm thickness in this study) at near-limiting condition displayed a flickering motion, which then suddenly extinguished when the critical condition was achieved due to temporal acceleration of the surrounding flow. While the flame behavior with a thinner sample (<4.0 mm thickness in this study) at the limiting condition was found to be stationary, a gentle extinction was experienced as approached to the limit. This fact suggests that the key to leading extinction is different between thicker and thinner sample. Third, the temperature distribution over the 4.0 mm PMMA at the near-limiting condition was measured and a strategy to model/predict the limiting behavior is then proposed.

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

Abstract: 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

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

Abstract: 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

Abstract: 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.

Graphene Modified Multifunctional Personal Protective Clothing.

Abstract: Personal protective clothing is intended to protect the wearer from various hazards (mechanical, biological, chemical, thermal, radiological, etc.) and inhospitable environmental conditions that may cause harm or even death. There are various types of personal protective clothing, manufactured with different materials based on hazards and end user requirements. Conventional protective clothing has impediments such as high weight, bulky nature, lack of mobility, heat stress, low heat dissipation, high physical stress, diminishing dexterity, diminishing scope of vision, lack of breathability, and reduced protection against pathogens and hazards. By virtue of the superlative properties of graphene, fabrics modified with this material can be an effective means to overcome these limitations and to improve properties such as mechanical strength, antibacterial activity, flame resistance, conductivity, and UV resistance. The limitations of conventional personal protective equipment are discussed, followed by necessary measures which might be taken to improve personal protective equipment (PPE), the unique properties of graphene, methods of graphene incorporation in fabrics, and the current research status and potential of graphene-modified performance textiles relevant to PPE.

A Review of Fundamental Combustion Phenomena in Wire Fires

Abstract: Electrical wires and cables have been identified as a potential source of fire in residential buildings, nuclear power plants, aircraft, and spacecraft. This work reviews the recent understandings of the fundamental combustion processes in wire fire over the last three decades. Based on experimental studies using ideal laboratory wires, physical-based theories are proposed to describe the unique wire fire phenomena. The review emphasizes the complex role of the metallic core in the ignition, flame spread, burning, and extinction of wire fire. Moreover, the influence of wire configurations and environmental conditions, such as pressure, oxygen level, and gravity, on wire-fire behaviors are discussed in detail. Finally, the challenges and problems in both the fundamental research, using laboratory wires and numerical simulations, and the applied research, using commercial cables and empirical function approaches, are thoroughly discussed to guide future wire fire research and the design of fire-safe wire and cables.

Limiting oxygen concentration (LOC) of burning polyethylene insulated wires under external radiation

Abstract: Electrical cables and harnesses have been identified as a potential source of fire in the spacecraft cabin. Future space missions may require spacecraft cabin environments to have elevated oxygen concentrations and reduced ambient pressures which could change the wire fire behaviors. In this work, a group of experiments is conducted to measure the flammability limit of polyethylene (PE) insulated wires under varying oxygen concentration and external radiation. Wires with different insulation dimensions, core conditions (with and without copper core) and insulations (LDPE, HDPE and black LDPE) are examined. Experiments show that external radiation extends the burning limit of the wire insulation to a lower limiting oxygen concentration (LOC) in a linear manner for all wire configurations. Comparison also reveals that the copper core acts as a heat sink to reduce the wire flammability, similar to its role in the ignition of wire insulation, while different from the heat source found in flame spread over the wire insulation. It is also observed that with the external radiation, LDPE insulated wire become less flammable than HDPE and black LDPE insulated wires, in contrast to the result without external radiation. A simple theoretical analysis shows that (1) the in-depth radiation through the semi-transparent LDPE to the copper core acts as an additional cooling to weaken the external radiative heating, and (2) the easier dripping of molten LDPE reduces its flammability. The results of this work provide valuable information about the fire risk of electrical wires under variable oxygen concentration and external heating from an adjacent fire. Thus, it may be useful toward upgrading the fire safety design and standards of future space missions.

Review of heat and water vapor transfer through multilayer fabrics

Abstract: Multilayer fabrics have been widely used for cold weather clothing and thermal protective clothing. The thermal and water vapor resistances provided by multilayer fabrics are of considerable importance in determining thermal comfort of clothing. Firstly, those studies on the steady-state heat and water vapor transfer through multilayer fabrics are summarized. There are three circumstances between thermal resistance of individual layers and the total thermal resistance of multilayer fabrics, that is, additive thermal resistance of individual layers, less resistance per additional layer, and more resistance per additional layer. Secondly, an overview on unsteady-state heat and water vapor transfer through multilayer fabrics is presented. Thirdly, the models on the heat and water vapor transfer through multilayer fabrics at both steady state and unsteady state are summed up. Finally, several research themes for the future are described.

Transition from opposed flame spread to fuel regression and blow off: Effect of flow, atmosphere, and microgravity

Abstract: The spread of flames over the surface of solid combustible material in an opposed flow is different from the mass burning (or fuel regression) in a pool fire. However, the progress of a flame front over a solid fuel includes both flame spread and fuel regression, but the difference between these two processes has not been well clarified. In this work, experiments using cylindrical PMMA samples were conducted in normal gravity and in microgravity. We aim to identify the transition from opposed flame spread to fuel regression under varying conditions, including sample size, opposed flow velocity, pressure, oxygen concentration, external radiation, and gravity level. For a thick rod in normal gravity, as the opposed flow increases to 50–100 cm/s, the flame can no longer spread over the fuel surface but stay in the recirculation zone downstream of the cylinder end surface, like a pool fire flame. The flame spread first transitions to fuel regression at a critical leading-edge regression angle of α ≈ 45°, and then, flame blow-off occurs. Under large opposed flow velocity, a stable flat blue flame is formed floating above the rod end surface, because of vortex shedding. In microgravity at a low opposed flow (