On the Outbreak of Fire due to Leakage of Electricity from Neon-Transformer through Planking.

Abstract

When lead wires from a neon-transformer (usually 7～15 kV leakage type) lighting neon tubes for advertisement contact through a board, electric current passes through it and the board may be heated to ignition, although the current is only of the order of several 10 mA. Fires due to this planking ignition have been reported frequently of late years.
To investigate the mechanism of this ignition, electric tension of about 15 kV from a leakage transformer was applied lengthwise to a board of about 10cm × 5cm × 5mm and the state of ignition was observed.
Burned zig-zag channels of 2～3 mm diameter, at the top of which ignition is taking place, extend from both side along the soft tissue of the wood, and when these channels are joined together, the current attains to its maximum value 22 mA, showing that the board is broken down electrically. Thus, by the heat produced in the carbonized channel, ignition begins at several points of the channel, and finally the board is destroyed.
If the board is initially drenched, vaporization of water in the board begins in the first place and when the board has been nearly dried up, channels begin to appear and extend easily through out the board.
Mechanism of the channel extension and the effect of drenching to make the board to be easily destroyed were also considered.