Abstract
The boundary lines of the burned areas were surveyed about forest fires, and following results were obtained.
1. It is very easy to stop the advancing fire at the edge situated to the windward of the fire.
2. When the fire runs up the win d-swept slope, the fire is easily put out in the windshadow of the edge, but when the edge is flat or the slope is gentle the fire may run over the fire lines and especially it often happens when there are dense, inflammable stands such as Hinoki, Akamatsu, Sugi and bushes.
3. When the wind velocity is small, and air humidity is high and the burning force becomes low it can be easily put out in the windshadow on the slope.
4. When the conditions of such elements as fuel, weather and topography are favourable, the self-extinguishing lines are also observed in forest fires.
