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Volume 51 (2001)
- Issue 2 Pages 55-
- Issue 1 Pages 1-
Volume 51, Issue 2
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—In Case of Flames without Touching Tunnel Ceiling—Yasushi OKA, Hitoshi KURIOKA, Hiroomi SATOH, Osami SUGAWA2001 Volume 51 Issue 2 Pages 55-66
Published: 2001
Released on J-STAGE: May 09, 2011
JOURNAL FREE ACCESSExperiments were conducted to characterize the effects of longitudinal ventilation on flame properties in case of tunnel fire. Three types of model tunnel, having rectangular and horseshoe cross - section, were used and their aspect ratio, height to width, were ranging from 1/1 to 1/3.
Empirical model of the apparent flame height of the inclined flame in a tunnel is presented considering the aspect ratio. The empirical models on the flame tilt angle were also developed based on the balance of mass fluxes and/or forces given by the upward hot current and longitudinal ventilation flow. These models are composed and described by dimensionless heat release rate and Froude number. The values of empirical coefficients and exponents were derived from the series of experimental results.
It becomes clear that flames in a tunnel show larger tilt angle than that in unconfined spaces under the same conditions of heat release rate and wind velocity. It was also confirmed that the flames in tunnel were influenced by the aspect ratio of tunnel.View full abstractDownload PDF (942K) -
Hiroyuki TAMURA, Hiroshi TANAKA, Shintaro NOMURA, Daisuke KOZEKI, Kuni ...2001 Volume 51 Issue 2 Pages 67-74
Published: 2001
Released on J-STAGE: May 09, 2011
JOURNAL FREE ACCESSIn order to make clear the causes of false alarms in cases in which the fire detectors were installed inside and/or outside the cultural heritage old buildings, we collected the data of temperature, humidity, atmospheric pressure, wind velocity, temperature measured by the heat detectors, smoke density measured by the smoke detectors and intensity measured by the flame detectors for one year. The sensors and the detectors were installed in four old wooden houses and one old shrine.
The following factors were found to be the causes of false alarms.
Weather conditions ------ passage of an atmospheric depression, strong wind, the sunlight in the early morning, flashes of lightning and flickering of sunlight streaming through the leaves of trees
Artificial conditions ------ the smoking to prevent decay and expel insects, rays from haloid lamps and sparks of welding.View full abstractDownload PDF (642K) -
Eui-Pyeong LEE, Hideo OHTANI, Tsutomu SEKI, Hideo HASEGAWA, Shuji IMAD ...2001 Volume 51 Issue 2 Pages 75-81
Published: 2001
Released on J-STAGE: May 09, 2011
JOURNAL FREE ACCESSAccording to recent fire statistics in Japan, number of electrical fires shows tendency to increase gradually. One of main causes of electrical fire is short-circuit. The short-circuit due to thermal degradation is one main cause though there are many other causes.
The short-circuit mechanism of PVC cords at defective heat loss was studied as following two cases :
(1)Temperature of the covering rises rapidly by joule heating etc., or (2)Temperature of the covering rises slowly by thermal degradation at comparatively low temperature for a long time, then PVC cords are short-circuited.
As a result, the followings were obtained :
1) Though PVC cord is not short-circuited in the rating current (20 A) of divergence breaker when it is extended on the straight line and there is no defective heat loss at the room temperature, wound cord is short-circuited at the allowable current of PVC cord regardless of the protection equipment such as the divergence breaker.
2) When temperature of the covering of PVC cord rises rapidly to nearly melting point by joule heat, PVC cord is short-circuited in a few minutes or less by the direct contacting with electrical wires of two poles due to softening and melting of the covering. On the other hand, when PVC cord is short-circuited due to the thermal degradation of a long term, it is short-circuited by absorbed moisture on CaCl2 or by insulation failure due to the decrease in the insulation resistance of the covering.
3) HCl generated by thermal degradation process reacts with CaCO3 which is added as filling of PVC covering, and hygroscopic CaCl2 is produced. The short-circuit mechanism by absorbed moisture on CaCl2 is expected, and the generation of CaCl2 can be quantitatively measured.View full abstractDownload PDF (877K) -
—Prediction of Hot Layer Temperature and Exhaust Efficiency in a Fire Room—Yuichi WATANABE, Sanae MATSUSHIMA, Tokiyoshi YAMADA2001 Volume 51 Issue 2 Pages 83-94
Published: 2001
Released on J-STAGE: May 09, 2011
JOURNAL FREE ACCESSA series of pressurization smoke control experiments were conducted using a fire room [2. 7 m × 3. 6 m × 1. 18 m (height)] of two-fifths reduced scale model for examining air supply conditions necessary to prevent smoke efflux from a fire room. For understanding the prediction of the critical air velocity to prevent smoke backflow under pressurization smoke control, the temperature of the hot layer formed in a fire room shall be well-assessed. Therefore, the temperature of the hot layer in a fire room and the waste gas of the exhaust were measured for constructing equations for simple prediction.
In case of pressurization smoke control, the algebraic simple equation on the temperature of the hot layer in a fire room at unsteady state is proposed in consideration of the heat loss by the waste gas of the exhaust based on these experimental data.View full abstractDownload PDF (1024K) -
—Prediction of Height of Hot Layer Bottom Based on Plume Flow Rate within Intermittent Flame Region—Yuichi WATANABE, Sanae MATSUSHIMA, Tokiyoshi YAMADA2001 Volume 51 Issue 2 Pages 95-104
Published: 2001
Released on J-STAGE: May 09, 2011
JOURNAL FREE ACCESSA Series of pressurization smoke control experiments were conducted by using a fire room [2. 7m × 3. 6m × 1. 18 m (height)] of two-fifths reduced scale model for examining air supply conditions to prevent smoke efflux from a fire room. For understanding the prediction of critical air velocity to prevent smoke backflow under pressurization smoke control, the height of the hot layer bottom in a fire room shall be well-assessed. A fire source enlarged as a flame reached to a ceiling. The prediction of the height of the hot layer bottom under the flame was studied based on the fire plume entrainment within the intermittent flame region.
As a result, the height of the hot layer bottom to measure with Cooper' s N% (50%) agreed with it to be calculated by using Heskestad' s fire plume air entrainment formula.View full abstractDownload PDF (655K) -
Eui-Pyeong LEE, Hideo OHTANI, Tsutomu SEKI, Hideo HASEGAWA, Shuji IMAD ...2001 Volume 51 Issue 2 Pages 105-113
Published: 2001
Released on J-STAGE: May 09, 2011
JOURNAL FREE ACCESSIn a fire scene, there sometimes molten marks exist in blades of the attachmentplug and the receptacle. When the fire cause is investigated, these molten marks have possibilities to become a big clue. However the technique to discriminate between the primary molten marks (PMMs) which are cause of fire and the secondary ones (SMMs) which are produced in the fire, has not been established yet.
Therefore we artificially made PMMs and SMMs, and investigated how PMMs differs from SMMs. As a result, the followings were obtained.
1) Though cut fusion of two blade was made at the PMMs and the SMMs, cut fusion of single blade and melted mass of two blade were made at the SMMs.
2) DAS (Dendrite Arm Spacing) apparently differed between PMMs and SMMs. DAS of PMMs was 3. 5∼14. 0 μm, but DAS of SMMs (ambient temperature when molten marks were made : 450°C∼900°C) was 24. 5∼56. 8 μm.
3) If DAS in molten marks can be measured, the ambient temperature when molten marks were made can be estimated from the DAS, and the discrimination between PMM and SMM becomes possible.View full abstractDownload PDF (2697K)
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