re: Danger of sawdust combustion?

Static electricity does create sparks when a discharge occurs so grounding is good. Depending on how much electric charge accumulate, the sparks are more powerful.
I have not grounded my dust collection system and I do receive a shock or 2 when I get very close the clear hose.

I always swipe the floor every time I see dust accumulating.

I have a fire extinguisher within reach. Probably is not going to help me much when disaster strikes.