Before we moved to a development, I had a large shop with nearly 200 ft. of PVC dust collector pipe with drops to all machines and none of it was grounded. I read up for almost a year before I assembled and installed the collector system and I found that; there has never been a reported fire or fire claim caused by static in a home dust dust collection system. A few fires have been reported where a nail or screw was sucked up, hit the impeller and the resulting spark started a fire in the DC bag. If you're concerned, get some copper wire and run screws thru the PVC with the wire wrapped around the head of it. If the screw protrudes into the pipe and the wire is grounded to a water pipe or to the electrical system, it should reduce the static a lot. Just my opinion coupled with experience.
WB