On the few occasions where surface fires have occurred, it has usually been caused by exposure to another fire or from equipment working on the piles. Internal fires are much more common than surface fires and are difficult to detect and extinguish. Such fires are capable of burning for extended periods before any obvious indications of a fire are observed. Spontaneous heating is caused when heat produced by the microbial decay of wood is not readily dissipated. In some piles, the temperatures continue to rise due a number of factors.
Fires frequently occur while attempts are made to separate heated from non-heated chips.
When heated chips are exposed to sufficient air, combustion may occur. Blown wood chips or pneumatically conveyed wood chip piles are more vulnerable to spontaneous combustion since the fines are separated and stratified in such a manner that hampers heat dissipation. Deviations from requirements 3.2.3.1. This Subsection does not apply where the existing situation is approved and does not endanger life safety, or approved alternative measures to the requirements set out in this Subsection are taken to provide life safety. Surface of ground 3.2.3.2.