AbstractSome early stages of compartment fires were explored experimentally using small‐scale model fires. In particuylar, the flame spread on the compartment floor was investigated with various ventilation openings. The average flame‐spread rate was higher than that for the free‐burning condition (without a compartment),namely, 3.2 times at the maximum, and seems to depend only on the ventilation opening height and not on its width. Therefore it appears that the driving wind of the inflow air from the ventilation opening to the flame increase‐spread rate. These data were compared with the flame angle data by Quintiere. The gas temperature within the compartment and the ceiling surface temperature was also measured to assess the radiation effect on flame spread. However, the radiation heat flux was unexpectedl