Takehiro Isei

Underground fire-fighting system by a rapid evaporation method of liquid nitrogen

Abstract A new underground fire-fighting system has been developed on the basis of a gas-liquid mixing-type nozzle which enables liquid nitrogen to form as very fine droplets and to be evaporated in the ventilation atmosphere. By using this system, it has become possible to evaporate a large quantity of liquid nitrogen in short times without any additional heat source near the fire area. Through the model gallery experiments using this system, open fires have been extinguished successfully within the restriction of a ventilation speed of up to 2 m/s. Furthermore, a satisfactory suppression effect has been proved through full-scale open-fire experiments in a timber-lined gallery. Thus, it is concluded that the newly developed fire-fighting system can be put into practice.

Visualization of shock waves generated from small charges in the air using Mach-Zehnder interferometry in conjunction with high-speed photography

The propagation and interaction of shock waves generated by exploding point charges inside an open ended rectangular glass tube (inner size 29 mm X 16.5 mm and length 248 mm) were observed using Mach-Zehnder interferometry in conjunction with high-speed photography. The shock wave velocity in the air was determined using high-speed photographic data and it was found that the shock wave velocity decreases as the radial distance from the explosion center increases. From the determined shock wave velocity data the shock mach number was calculated and the corresponding shock front peak overpressure was determined. The shock reflections from the walls of the tube were also visualized and the reflection coefficient was calculated.

Influence of airflow on sound propagation in a curved tunnel

Measurements were made to examine influences of airflow on propagation attenuation of sound in a curved tunnel. The speed of airflow varied in width direction of the cross section of tunnel, and the values were from around 1 to 3 m/s. Sound attenuation upwind was less than that downwind at high frequencies up to the receivers that are in sight of the source. The tendency agrees with sound attenuation measured in a straight tunnel with airflow [H. Imaizumi et al., J. JSSE 31, 228–239 (1992)]. Difference of the attenuation gradually became small in the same frequency region at receivers that are out of sight from the source. Numerical calculations by means of a ray tracing method were applied to propagation attenuation of sound in a curved two‐dimensional plane. Transmission losses of sound energy calculated only from reflection times of the sound rays on the inner wall were compared under each propagation condition. The transmission loss downwind was larger than upwind up to the receivers that are in sight...

A Prediction Method of Blast Vibration Based on Multi-Reflection Method for SH Wave to Allow for Geological Structure.

In order to predict blast vibration more precisely, we attempted to use the following equation described by circular frequency, that is used in the earthquake engineering field.O(ω) =G(χ)·H(ω)·S(ω)where, O(ω) is spectra of the wave motion of ground surface, G(ω) is the geometrical attenuation related energy spread during wave propagation, H(ω) is the transfer function and S(ω) is the source function.We developed a computer program for a multi-reflection method based on Haskell (1960) to get H(ω) in above equation. For S(ω), we used the equation derived by Sharpe (1942). Finally, we had reasonable results for wave motion of a point of ground surface by calculating inverse FFT of O(ω) obtained by convolution of H(ω) and S(ω) about two layers model and four layers model.

Sound energy distribution at an intersection of underground tunnels: Full scale experiments

Experiments on sound propagation in small‐scale tunnels with a branch have been carried out from the viewpoint of safe and rapid information transmission underground. The influences of intersection angles and acoustical properties of inner walls of the tunnels on sound propagation were examined in previous studies [J. Acoust. Soc. Am. 100, 2567 (1996)]. In the present work, sound propagation in a full‐scale underground tunnel with a branch is considered. The experimental tunnels are supported by iron frames and concrete lagging, and the cross sections are arch shaped with an area of 4.2 m2. Experimental results indicate influences of the intersection on propagation attenuation at a frequency of around 200 Hz. Whole tendencies of sound attenuation are also affected by relative arrangements of sound source and receivers, and sound attenuates more at the receivers, which are out of sight from the source than for those in sight. For the purpose of the sound‐field estimations, the characteristics of sound prop...

Sound energy distribution at an intersection of an underground tunnel: Additional small‐scale experiments

In studies on some interactions between sound propagation characteristics and environmental factors underground, small‐scale experiments on the sound energy distribution at an intersection of tunnels have been carried out in an anechoic room. The small‐scale tunnels were made by acrylic plates, and the original surfaces of inner walls were assumed to have an acoustically hard condition, while surfaces of the walls covered by flannel were acoustically soft. Impulsive sound was generated electrically as a sound source was applied, and propagated sounds were measured by an omnidirectional microphone. The experiments were carried out under several kinds of conditions for angles at the intersection and positions of the sound source. Influences of intersection on the sound energy distribution were indicated by comparisons between the measuring points before and behind the intersection with different angles. In addition, the influences of the acoustical characteristics of the inner walls and positions of the sou...

Study on fire proofing evaluation for underground roadways(1st Report). Full-scale Experiment on Flame Propagation Limit of Timber Linings.

In this paper, we present experimental results on the behavior of underground fires loaded with low fuel density and discuss the prevention of flame propagation along timbered roadways. A series of fullscale fire experiment has been carried out, using a 400 meter long test gallery and timber linings as a fuel installed in the gallery. The performances of fire resistant zones were tested under the condition that the quantity of combustible materials was reduced up to critical values, necessary to suppress flame propagation along timber lining. As a result, it was found that the quantity of fuel largely influenced the properties of underground fires, i. e., flame spread rate, fire zone length and fire temperature. A critical combustion condition was appeared in which any flames did not propagate on the leeward of ignition source, if the quantity of fuel became relatively low such as less than 7.5 or 10kg per unit gallery volume (m3). The effect of ventilation air velocity on the critical fuel quantity was also clarified in the experiment. Thus, we could provide fundamentals to make clear requirements for fire resistant zones in underground roadways.

Sound energy distribution at an intersection of underground tunnel: Small scale experiment

Underground spaces generally have complex networks of tunnels which include many intersections. When a disaster such as a fire and an earthquake breaks out there, correct transmission of sound information has an important role in order for people to evacuate from underground safely [Fujimiya and Miura, J. INCE Jpn. 6(5) (1982)]. From the above point of view, sound energy distribution characteristics at an intersection of a scale model tunnel were measured under several conditions. The scale model tunnel had a square cross section, and experiments were carried out under acoustically hard and soft conditions. Impulsive sound from an electrical sound source indicated high reproductivity and omnidirectional characteristics from a preliminary experiment in the anechoic room. In a case where the scale model tunnel has an orthogonal branch, it was observed that low‐frequency components were mainly propagated toward the branch, and this tendency was changed according to the angle of intersection. Furthermore, qua...

Blast sound propagation over hilly land

A blast sound propagates over a long range, because of its large sound power of sources and low‐frequency components. Blasting operations are often conducted at a hilly side and as a result, sometimes the sound of the blast influences the life environment beyond the hilly undulations. At both hilly sites with heights of up to several tens of meters and flat lands, excess attenuation of blast sound was measured at points of several hundred meters away. Frequency spectrums of excess attenuation beyond the hilly side show that (1) up to around 100 Hz, excess attenuation increases in proportion with frequency, and for more than 100 Hz, it shows mostly constant values of around 40 dB; (2) shapes of frequency spectrum of the excess attenuation show similar pattern with the ones of flat land; and (3) shielding effects of hills mainly appear at the frequency range around 100–250 Hz. From these results, the authors discuss the possibility of sound propagation modeling by extending usual models for flat land.

A Full-scale Experiment on Water Spray Zones for Suppression of Underground Open Fires.

In order to prove the practical effect of a water spray zone on suppression of the spread of underground fire, a full-scale experiment was performed in a 400 m long test gallery with a cross section of 5.4 m2.Firstly, it is clarified that a water spray method is effective when water droplets are uniformly sprayed in the gallery and the mean diameter is less than 0.4 mm. Secondly, the cooling effect of water spray is quantitatively discussed from many aspects such as heat transfer and ventilation. Finally, it is shown that the quantity of water required to suppress the spread of fire is proportional to the air velocity and the cross section of gallery and that for a strongest fire can be estimated by equation (5) in the paper.