小型区画を用いたバックドラフト実験 Backdraft Experiments in a Small Compartment Fire
This paper describes results of preliminary backdraft experiments in a 0.85 m high, 0.78 m wide, 1.08 m long compartment, a roughly one third scale residential room. Each surface of the compartment was made with five (for side and upper) or seven (for floor) layers of insulation board to obtain a highly insulated condition. The compartment had a small opening in the middle of the front wall to realize a low-ventilation condition. Interior wall surfaces including the ceiling were partially or fully covered with 12 mm thick wood to simulate a room fire. This wood was the fuel for the fire. A total of seventeen experiments were carried out to find backdraft occurrence conditions for the low-ventilation, highly insulated compartment, and to understand backdraft phenomena. <br>Ten of the seventeen experiments resulted in backdrafts. In this paper, one of these ten experiments, namely Experiment 13, is described in detail to show the backdraft scenario in the compartment. In Experiment 13, backdrafts occurred seven times which is the largest number among the seventeen experiments. Temperature and oxygen concentration measured at 0.15 m below the ceiling showed a very unique change shortly before and after a backdraft. From these experimental results, the backdraft scenario observed in these experiments is as follows: <br>1) Before a backdraft occurs, the compartment fire is much reduced due to the lack of oxygen in the upper layer of the compartment. <br>2) Pre-backdraft phenomena starts. In this process, pyrolyzates from the fuel (wood) accumulate in the upper layer. At the same time, as the fire dies back due to lack of oxygen, the room cools and fresh air from the outside of the compartment is drawn in and mixed into the upper layer. Thus a flammable, premixed gas which can be ignited in many ways is made. Partially burned wood and char on the side and ceiling walls can act as the igniter. This process usually takes a few minutes in the experiments. <br>3) Suddenly, a backdraft occurs. The backdraft consumes all vapor phase combustible products and oxygen in the compartment and makes a fire ball which erupts out of the compartment. After the backdraft the above mentioned pre-backdraft phenomena starts again.
日本火災学会論文集 48(1), 11-17, 1998-06-30