Influences of Temperature, Relative Humidity, and Heat Sources on Ignition: A Laboratory Test

Based on the definition of ignition, the present study tested 3 factors that influence ignition probability in the laboratory. By using a weather chamber, tests were conducted with a 4 x 3 x 2 factorial arrangement in a completely randomized design. Experimental factors included temperature, relative humidity, and firebrand size. From the Daja-Shei National Forest, fine forest fuel of red pine (Pinus taiwanesis) with a diameter < 2.5 cm was collected for the tests. The results showed that larger firebrands had a higher ignition probability. Relative humidity, as an estimation of fuel moisture, also influenced ignition but it interacted with air temperature, which was used to estimate fuel temperature. Low relative humidity resulted in a higher ignition probability, but when higher temperatures occurred, moderate relative humidity also resulted in a higher ignition occurrence.