I have one more experience to share while on topic of grinders. I was doing some grinding (I forget it it was bench or angle grinder it happened so long ago) on a cold winter nite in my garage wearing a thick shirt. Lots of sparks. Suddenly, I started to feel nice and warm and comfortable. Then a bit hot. I looked down and my shirt was on fire. Burned a nice 5" diameter hole, no injury. I still have the evidence.