As a firefighter I've fought several fires in combines. Most of the time it's started by a spark catching dust on fire. A lot of the time the following dust explosion will blow access panels several feet away. The dust will carry flames all over the inside. A small fire extinguisher is not going to slow it down at all.

I was Combining, had my oils plug rupture and a small fire started but got it out. The 9600 had plenty of hours on it before, and I was borrowing it from a friend

We have had the same thing happen.  Luckily we got it put out with a quick response from the local volunteer fire department.   Ours started at the turbo.  At any rate, we have 2 more fire extinguishers on the combine now than we had before :

I literally just watched a video of one of these same machines. There's a separator within the unit that rides on two bearings and the bearings went bad and caused a fire. However, the operator heard the noise and reacted quickly and saved the machine and the unit.