Abstract: In order to study how to locate the indoor low-level flame through the door slit light characteristics under the full occlusion environment, a ISO 9705 standard room was constructed, with a 90 cm×2 cm slit between the door and the floor, and a 0.5A standard wood stack fire was used to simulate the indoor low-level fire. The change of the door slit light characteristics was recorded by the outdoor video, and the change rule of door slit light characteristics and the correlation between the indoor low-level flame position and the door slit light characteristics was analyzed, coupled with the MATLAB luminance recognition and image processing technology. The results show that the geometry of the door slit light was roughly quadrilateral under a certain luminance threshold, when the flame is located in the center axis of the door, the geometry is isosceles trapezoidal, and when the flame is biased to the side, the door slit light is deflected to its opposite side. As the distance of the flame from the door increased, the angle of the quadrilateral girdle decreased, while the extension distance of the door slit light first increased and then decreased. The correlation was obtained between the indoor low-level flame position and the geometric parameters of the door slit light. The distance of the flame from the door and the extension distance of the door slit light can be characterized by the segmentation function. The study can provide a technical reference for locating the position of indoor fire after a fire accident by video.

Key words: fire investigation, video analysis, light through the door slits, fire location