58 



that the relative humidity decreases during the warmer 

 part of the day. With a decrease of the relative hum- 

 idity, the ignition point is lowered, and the fire "burns 

 more easily. Knowing this, Mr. Chas. ¥. King, who was 

 in charge of the Light Burning operation of the Weed 

 Lumber Company in the summer of 1920, waited until late 

 afternoon before lighting the fires. The fires were 

 allowed to burn only until the next morning when they 

 were extinguished. In this way the danger from intense 

 fires was mitigated, and the precedent of controlled 

 burning during the dry season was established. The 

 trouble in this connection is that the relative hum- 

 idity of the atmosphere may be favorable at thetime 

 the fires are started, but that it is subject to fre- 

 quent and sudden changes due to warm winds, 3lt the 

 present time no scientific observations have been made 

 concerning the relation of atmospheric humidity of the 

 time of Light Burning. 



Another very important factor which may add to the 

 danger of Light Burning is wind. Regulated surface fires 

 may be fanned into fires of such intensity that they 

 may be very destructive, if not altogether uncontrollsble. 

 These winds sre more particularly prevalent in canyons 

 and ravines where they blow up the slope during the day 

 time and down during thenight. 



No one of the above factors may necessarily be the 

 source of danger in Light Burning, but a combination of 

 two or more which increases the intensity of the fire 

 and the amount of damage done. 



