I'm not sure if this is the right place to post this but I wanted to get it out there right away. Mythtaken can move it if there's a better spot. Yesterday I spent the afternoon grinding a set of steak knives. Because I was working with such thin material (.072") I decided to do my grinding post-HT. As I was grinding the third of six knives something caught my eye at my dust collector. I am running a 2HP Pro-Point (Princess Auto but essentially the same as the Craftex from Busy Bee) with a top and bottom fabric bag. When I looked closer I realized that the damned bag was on fire at several points! I put the fire out and investigated a little but could find no cause for the bottom bag to have caught fire. I patched the holes and kept on grinding...still had three blades to go. In short order I had more fire, mostly around the top of the bag where it clamps onto the metal centre portion. The fire was quite hot, hotter than the burning bag should have been on it's own. It would appear that metal dust had collected and the sparks from the steel I was grinding had ignited the dust which burned quite hot. This is frightening because a person could have a fire smouldering in the bottom of the collector and not realize it until they shut down the machines and leave the shop. In my case with a detached shop I would have had no idea something was amiss until the shop was fully engulfed! And for you guys with a shop in the basement the prospect is even worse! I ended up dumping a bunch of water from my cooling bucket into the duct under my grinder and letting the fan suck the water in and atomize it. That appears to have done the trick with no more fire or hot spots. I went back out an hour later and took the bag off and there were no issues. Now, I'm not sure why this came to pass. I wonder if it's because I was grinding hardened steel and, perhaps, the sparks were hotter? I was mostly grinding with an 80 grit Klingspor belt and, because the material was thin and already hardened I wasn't working it particularly hard, yet here we are...a dust collector bag that looks like swiss cheese. So what's the go forward? I think it would be wise to switch up the bottom bag to a metal drum of some sort...just have to take some measurements and hopefully find some suitable fire-resistant material to form a collar between the drum and the structure of the collector. But that doesn't preclude hot sparks from igniting wood dust in the bottom of the bin (or, even scarier, aluminum dust). Maybe this is a problem more associated with grinding hardened steel, which I don't do very often, but I think some method of fogging the inlet occasionally with water would prevent the chance of fire, though it might make for what the Old Man would have called "a hellacious mess". So, thoughts? let's talk about how we can prevent burning our shops to the ground!