Ken Matsuyama

Absorption Spectra of Smoke Emitted from Heated Nylon Fabric Measured with a Continuous-Wave Sub-Terahertz Spectrometer

The absorption spectra of smoke emitted from heated nylon fabric are studied in the sub-terahertz band. The transmission loss of 1.5-µm-wavelength light in the smoke is 50 dB/m or more. Even in such dense smoke, the loss for waves with the frequency ranging from 200 to 500 GHz is so small that absorption lines of gas molecules in the smoke can be detected in this frequency range. Spectral analysis indicates that the smoke contains molecules of toxic gas, such as HCN and CH3CN, generated due to incomplete combustion of the nylon fabric when heated to 500 °C with air.

Remote gas sensing in full-scale fire with sub-terahertz waves

A remote gas sensor based on a continuous-wave sub-terahertz spectrometer with an operation bandwidth between 200 and 500 GHz has been developed. The performance of the developed system was investigated in a full-scale fire. The measured transmission spectra of smoke show the existence of hydrogen cyanide (HCN) and water molecules, which were generated due to the combustion of a foam urethane block. The HCN content estimated from the absorption intensity agrees quite well with that obtained from the chemical analysis of gases sampled from the fire site. These results demonstrate the potential of the developed sensing system as a remote toxic gas sensor at disaster sites.

Incoherent sub-terahertz radiation source with a photomixer array for active imaging in smoky environments

We propose a sub-terahertz (THz) illuminator suitable for use with a THz camera when exploring objects within and behind smoke at the scene of a fire. The illuminator contains a photomixer array and each photomixer generates incoherent sub-THz waves from a single-mode laser light and optical noise using photomixing. The incoherency of the generated sub-THz waves enables us to raise their intensity by increasing the number of photomixers in operation, which makes it possible to realize very bright sub-THz illumination. Consequently, objects being under searched for within or behind smoke can be clearly illuminated using the illuminator and visualized by the THz camera even though they are surrounded by thick and/or high-temperature smoke. To verify our concept, we conducted active imaging with coherent and incoherent sub-THz radiation from a photomixer array utilizing reflection geometry. Although the contrast of the image was improved by increasing number of photomixers in operation on the imaging with coherent radiation, the shape of the target was degraded by the interference pattern of the illuminated sub-THz waves. The contrast of the image when using incoherent radiation was improved without obscuring the shape of the target by increasing the number of photomixers. We also confirmed that there was good visibility for active imaging using incoherent sub-THz illumination even though thick smoke was presented. These results indicate that the use of incoherent sub-THz waves and an array of photomixers should enable a sub-THz illuminator with a high level of brightness to be used for active imaging

Menthol-enhanced cytotoxicity of cigarette smoke demonstrated in two bioassay models

BackgroundCigarette smoke is harmful to human health at both cellular and genetic levels. Recently, a unique bioassay for smoke cytotoxicity using air pollution-sensitive plant cells (tobacco) has been proposed.MethodsModel plant cells (tobacco Bel-W3 cells) and human cells (alveolar epithelial A549 cells) suspended in fresh culture media were exposed to cigarette smoke sampled after lighting the tip of cigarettes (with vs. without menthol capsules) which were attached to a glass pipe connected to the cell-containing plastic tubes. Control cultures were also assessed.ResultsAfter exposing tobacco plant cells to cigarette smoke, cell death occurred in a dose-dependent manner. Cell death was significantly enhanced by mentholated smoke, while menthol alone was shown to be inert suggesting that menthol synergistically contributes to the enhancement of cell death, initiated by smoke-associated compounds. The enhanced toxicity of mentholated smoke was confirmed in human alveolar epithelial A549 cells.ConclusionsCigarette smoke cytotoxicity leading to cell death assessed in plant and human model cells was enhanced by menthol. Further research into these findings is encouraged.

Experimental Study on Fire Behavior in a Compartment Under Mechanical Ventilated Conditions: The Effects of Air Inlet Position

The purpose of this research is to understand the fire behavior expected in a mechanically ventilated compartment. To date, some experimental studies have been conducted for investigation of fire behavior under mechanical forced ventilation; however, it might be not enough to understand everything. We therefore carried out a series of experiments on fire behavior focused on the effect of air inlet position in a compartment with same size as an ISO 9705 room (width 2.4 m × length 3.6 m × height 2.4 m) under conditions of mechanical ventilation using a pool fire. In this paper, the effects of ventilation conditions such as air inlet position and flow rate were studied. We found that differences in the air inlet position and flow rate were one of the principal factors for determining the burning behavior.

Active imaging with incoherent sub-terahertz radiation from a photomixer array in a severe smoke

The imaging capability of active imaging with incoherent sub-terahertz (THz) radiation from a photomixer array in a smoky environment was investigated. The photomixer array consisted of nine uni-traveling-carrier photodiode modules, each with an integrated antenna. Incoherent sub-THz waves were generated by a photomixing scheme employing single-mode laser light and optical noise. Imaging tests on a target at a distance of 1.4 m showed that imaging with incoherent sub-THz illumination provides a clear view in heavy smoke for which the visibility was 0.22 m for visible light and 0.44 m for near-infrared light. These results indicate that active imaging with incoherent sub-THz radiation is an effective way to see through smoke.

Interaction of a Pool Fire in a Compartment with Negative Pressure Generated by Mechanical Ventilation

We have experimentally investigated a medium-size pool fire in a compartment, the dimensions of which corresponded to the ISO 9705 room. Airflow rates in ducts, pressure, mole fraction, and temperature of air in the compartment and a mass loss rate of the fuel were measured. The liquid fuel and pool diameter were ethanol and 600 mm, respectively, which rapidly increased the compartment pressure just after ignition. The compartment was ventilated at inlet and outlet ducts with natural and mechanical ventilation systems, which initially gave negative compartment pressures in the range of −2 to −85 Pa. The negative pressure was much weaker than the pressure increase, which restrained the air supply with natural ventilation and resulted in extinction due to lack of oxygen. On the other hand, the negative pressure with the stronger mechanical ventilation sustained the air supply and yielded the transition to a ventilation-controlled fire without extinction. The ventilation-controlled fire led to two kinds of oscillating flame: one was caused by poor oxygen supply, which is similar to that reported by previous studies, and the other was caused by repetition of ignition and extinction, which was attributed to the change in the flow rate and direction of fresh air at the inlet duct. This oscillation generated large pressure fluctuations but did not yield thermal energy with combustion.

Algebraic Equations for Calculating Surface Flame Spread and Burning of a Cubical-Shaped Polyurethane Foam Block

This work presents a simple algebraic method for calculating heat release rate (HRR) considering the three-dimensional flame spread and burning over a cubical-shaped polyurethane foam block. Flame spread area is calculated by flame spread velocity toward multiple directions over top and side surfaces. Burnt-out area is calculated by projected area of the burnt-out portion onto original top and side surfaces. Mass burning rate per burning area is calculated by radiation from flame to each burning surfaces. HRR is calculated by multiplying burning area with mass burning rate and heat of combustion. The calculated results were compared with experiments. In cases of the cubical shape or wide shape, HRR is predicted fairly well until peak HRR. In case of tall blocks, the calculated peak HRR was smaller than experiments due to HRR per unit area over vertical surface was under estimated.

An Experimental Study on the Smoke-Logging Phenomenon Using Sprinkler for Performance-Based Evacuation Safety Design

The purpose of this study is to investigate the descending air current of a smoke layer for smoke logging during sprinkler operation. The results could be used for performance-based evacuation safety design. Smoke layers were investigated experimentally using particle image velocimetry (PIV) and were analyzed according to the size of the fire source and the type of sprinkler head. As a result, a relationship was obtained between the mean droplet diameter, droplet velocity, and spray distribution for each sprinkler head. In addition, the descending air current of smoke was studied as a function of the fire source size and the velocity of the descending air current. It was predicted by the regression equation that the smoke layer moved to the bottom layer when the descending air current speed reached 0.6 m/s and confirmed that a stable descending air current was generated only when the fire source size exceeded 100 kW.

Experimental Study on Influence of Air Supply System Difference on Smoke Shielding Performance in Air Pressure Smoke Control

In this research, a full-scale fire experiment was conducted for the purpose of estimating the influence of differences in air supply systems on smoke shielding performance in air pressure smoke control. As a result, the following items were indicated by the experiment: 1. As smoke invades from the doorway surface even prior to the smoke shield limit time in cases where smoke shield opening door is intermediately open as generally considered in the field of air pressure smoke control, smoke shields require thrust from two orthogonal surfaces with each other. 2. In static pressure systems, smoke shielding performance is fixed in spite of the smoke shield opening door angle, and previous theoretical formulae often coincide with actual values. 3. In dynamic pressure systems, smoke shielding performance differs depending on the air supply system and the angles of the door of the smoke shield opening. There are systems where smoke shielding performance is better than in static pressure systems, and there are also systems where it is worse.