Whoomf! Fire When You Do Not Want It.

I did not expect this to happen, which is probably why it did happen. I was cutting wood for handles and stand and one piece started giving me some grief. Either the saw is a bit dull or that particular piece of birch was exceptionally hard (birch is amongst the hardest woods, contrary to what many books say). It smoked a bit, but not much. So I paused the work, tried a different cut when suddenly there was a lot of smoke. Like, a lot lot. In seconds, the workshop was full of it.

© Charly, all rights reserved. Click for full size.

Luckily I tend not to lose my head in emergency situations. I noticed the smoke going from the vacuum collecting dust. I have immediately unplugged it and the saw from electricity and I dragged the vac outside. The paper dust filter inside was on fire and it was impossible to put out because it was windy. I have barely managed to take it off and leave it to burn safely on the concrete pavement. The wooden dust was smoldering a bit but I have managed to scoop it out and toss it in the oven where it could burn safely.

I do not know how this could happen, I have been using this setup for about a decade by now with zero problems. Either the saw was so dull that the friction started the fire – birch is much more flammable than other woods – or a metal splinter or something somehow got in the cut and it struck a spark. Visually, the blade does not seem dull and I cannot find any damage on any of the teeth, so I am baffled.

Tomorrow I have to go and purchase a new vacuum for my shop. This one could be repaired, but it would take a really long time. I will probably not bother. But it can be easily converted now into a dedicated blower, so I shall probably do that.

I had to take a few hours rest, I was in a bit of a shock afterward.


  1. avalus says

    It might be the birchwood flaves or dust? I -think- I remember from my youth that birch was the easiest to set fire to by friction firestarter (thingie? The stone-age fiddlebow like device)

    Hopefully your were not hurt by the smoke. Iky stuff.

  2. says

    At work, we basically had the same thing happening twice.
    Once in the dust collection of a sawing machine and once in a CNC mill busy milling a wooden pattern.

    Almost every company that I know of that does wood processing on CNC machines has had a machine fire at least once. This is why we *never* let a wood milling operation run unmanned at night.

    In the case of the milling machine, the operator actually saw the milling cutter strike a spark, and was able to extinguish the fire before is was more than fist-sized. With regard to the sawing machine, (probably) the workpiece was just pushed too hard into the saw. Those filters sure did burn well. We’ve switched to a cyclone separator now. It’s much more conventient IMO; no more cleaning filters; just empty the collection bucket.

    So I would recommend you also look into a cyclone separator for your next dust collector. They need much less filtration and there is less surface area to catch fire. It’s also possible to DIY them for a small shop if you are so inclined. On youtube e.g. Mattias Wandel and Marius Hornberger have good videos about building cyclone separators.

  3. Ice Swimmer says

    I think this could have ended up a lot worse than it did. Yikes indeed.

    Either it’s friction heat or there could have been a rock, a metal shrapnel or a piece of barbed wire inside the wood, which has rubbed against the side of the saw blade (if the teeth are undamaged).

  4. Jazzlet says

    Yikes, glad you managed to get the vacuum outside and the burning filter off without further damage to the work shop and without getting burnt, but I’m not at all surprised you needed a sit down after that! Shock will do that.

  5. says

    @avalus, I think it was the birchwood in combination with a slightly blunted sawblade. When I was cutting the apple roots last year, there was some sand and small stones embedded in them and that has probably blunted the saw ever so slightly. And birchwood is indeed one of the easiest-to-ignite woods that I know of, probably the easiest to ignite in my part of the world.
    @rsmith thanks for the tips, I know Matthias Wandel but I do not watch his videos regularly. I was thinking about it, but not too much. I will look into it deeper now, that’s for sure. The problem with cyclone separators is -- the smaller and lighter the particles, the bigger the separator needs to be to separate them effectively. And my workshop is pretty crammed as it is. Even the shop vacuum that I use has to be one of the smallest ones there are.

  6. Ice Swimmer says

    Birch is both easily ignited and it has a good heating value (also, it doesn’t produce sparks while burning like spruce does). That’s why it’s the premium firewood here and firewood as a commodity is often classified as either birch logs (a bit more expensive) or miscellaneous logs (alder, softwoods, maybe also aspen or willow, a bit less expensive).

  7. says

    Glad you came out of that OK! Very dramatic!

    It’s also why you should never vacuum up any volatiles. I know you’re smarter than that, but some people aren’t. “Hey it’s a wet/dry vacuum, I can suck up this diesel fuel…”

    I left an angle grinder on the bench where it was in the stream of sparks from another angle grinder. What I didn’t notice, of course, was that I was blowing carbide/steel dust into the cooling vents of the grinder. When I started using that grinder a few minutes later, it started to scream, vibrate, and then burst into flame. Very exciting. It reminded me why I wear welding gloves when I am using hand tools.

  8. Tethys says

    It is shocking when the vacuum system starts smoldering. I’ve only had it happen once, and luckily spotted the spark as it disappeared into the sawdust filled vac and immediately caught fire in the airflow. I flew the shopvac up the stairs and dumped it outside in record time. I only destroyed the filter, and still have the vac. The hazards of wood dust? It burns real good.

Leave a Reply