As shown in the fig.7, fig.8 and fig.9, in the initial stage of combustion, the wood doesn’t give the fire and only generates a small bit of smoke. There is almost no difference between the fig.7 and the fig.8. In the middle stage of combustion the image character also isn’t obvious. Analyzing the fig.7, the fig.8 and the fig.9, the optical flows of before and after the polyurethane combustion are calculated (see table3). The changes of the optical flows between the stage of no combustion and the initial stage of combustion are not significant. But the optical flow increase with the combustion, in the middle stage of combustion, the optical flow increases to more than 0.5.Therefore, in the middle stage detecting the smoldering
(pyrolysis) wood fire with optical flow is effective.