A mathematical model to analyze the behaviors of the fire which take place within compartments is build up. The model compartment using in this study has an opening and the interior walls of it are covered with combustible slabs. The present model can be computed by use of an electric computer, and intends to predict behaviors of the fire mentioned as follows:

a)	whether the fire will go out soon without spreading or keep burning and grow to be a developed fire,
b)	whether "flashover"will occur or not, and what the "flashover" time is, if it occurs,
c)	how the temperature in the fire compartment will change with time, especially, what the temperature and the duration time of fully developed stage of the fire will be,
d)	how the concentration of oxygen and unburnt fuel in the indoor air will change with time,
e)	how the high temperature air discharged from the compartment through the opening will change with time, especially, how it will be in the "flashover" period.

This study has made a progress in the above problems,while the present model still has much room for improvement.

This paper represents the outline of the model and some results of the sample computations, and also refers to the limitation of the model.

* Research member, Physics and Fire Division, Building Research Institute, Ministry of construction.