I have investigated several fires involving similar equipment, generally feeding trees in one end and discharging wood chips to go to the pulp and paper plant out the other. The internal mechanisms are typically powered by a 1200 HP supercharged diesel engine driving hydraulic pinch drives, chain flails, rotating chipper head and bark pusher/discharge mechanism. With that much going on, spark generation is unavoidable. The operators I have spoken with say that small fires in the refuse discharged beneath the machine are an everyday occurrence and are generally easily extinguished. Many of these machines are sold with a permanent fire suppression system built in as an option.

Fires originating in the hydraulics are another matter. A blown hydraulic hose at 2000 to 3000 PSIG pressure atomizes the hydraulic fluid which can be ignited by electrics, by the engine exhaust manifold or possibly even the supercharger. Some of the indicia of an atomized hydraulic fluid fire are a bright, generally smokeless flame (because of the effective atomization), quite often described as “dancing” (from the reaction of the jetting fluid from the broken hose). With accumulated pressure, the hydraulic fluid continues to spray for a while even when the engine is stopped. With all the combustible material present, the fire can spread quickly, be very hard to extinguish and can result in a total loss. The diesel fuel tank is another very large fire load and on occasion may BLEVE. I am aware of one instance where a chipper machine fire was repeatedly water bombed by a forest fire fighting airplane, and still smoldered for several days.

Hope this helps.

Michael A. Learmonth, B.A.Sc., M.B.A., M.Eng., J.D., LL.B., C.F.E.I., P.Eng.
Senior Associate, Giffin Koerth Forensic Engineering and Science
40 University Avenue, Suite 800
Toronto, Ontario, Canada M5J 1T1
Phone: 416-368-1700 ext. 225
Fax: 416-368-5576