Bulletin of Japan Association for Fire Science and Engineering

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The firing phenomena of polyvinyl chloride (PVC) covering cords, having the disconnected element wires, due to an abnormal heating caused by the over current in the residual wires have already been reported by authors.
However, there are different firing causes of the PVC cords, such as the thermal runaway which is produced by the largely reduced electric resistance of the PVC covering at the elevated temperature. It is very important to investigate the firing properties of the PVC cords due to high temperature deterioration since the PVC cords are often used under the condition of the elevated temperature.
In order to determine the relationship between the firing phenomena and high temperature deterioration properties of the PVC cords, some experiments and theoretical calculations are carried out using the model PVC covering which has the electrode separation of 10 mm, and is fixing with five porcelain tubes to hold the electrode separation and its configuration against the deformation at the elevated temperature.
The results obtained from present studies are shown as follows:
(1) The electric resistivity of the PVC covering is reduced to the order of 10² (Ωm) with temperature rise of about 300°C from the room temperature, and the PVC covering is changed from the electric insulator into the organic semiconductor.
(2) The thermal runaway of the PVC covering is expected from the theoretical results under the conditions of impressed voltage of AC 100V and the elevated temperature, therefore, the firing phenomena of the PVC cords according to the Kinbara's effect may be caused.
(3) The PVC covering cords, which have been thermally treated at the temperature over 200°C, may be fired by applying AC 100V at the room temperature.

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The velocity and temperature of the smoke of fire flowing through out a corridor varry at the time going by. So far, the shutting characteristics of the air shutter for fire prevention at a constant temperature have been studied. Now investigating the buoyancy effect in higher temperature, the basic data for actual design are obtained. In experiment, a side flow of smoke which has high temperature attack against the air shutter.
The results are as follows:
(1) Total stored energy in an air shutter system formed by the push, the pull and the side flow is constant, though they vary in each other.
(2) The value of the break limit ratio of push-pull flow volume, (Q₃ /Q₁ ) limit, may be expressed as follows:
i) It is influenced not only by the value of push-pull distance ratio, H/E, and side flow velocity ratio, v₀ /v₁ , but also by the one of side flow temperature ratio, T₀ /T₁ .
ii) When side flow volume, Q₀ , and side flow temperature, T₀ , are constant, the values of (Q₃ /Q₁ ) limit in the case of uniform side velocity distribution have also the same values with the case of varied ones which have large at ceiling parts and small at floor parts.

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