Sawdust and gas appliances, an accident waiting to happen?

August 7, 201411 Comments

Since my workshop is located in the basement it makes sense that I might be a little concerned about the potential for explosions or fires due to the exposure of sawdust, woodchips & shavings to pilot lights from our gas furnace and water heater. But I’m not!

gas furnace

Am I being cavalier about the topic?…Maybe. Do I know something others should in a similar situation?…Always a possibility. So why am I bringing up this topic if it’s something that doesn’t bother me?

Because it’s a topic many of you have asked about in emails over the years, and since I’ve never written about it before I thought it was time.

water heater warning label

Let me start by saying that “YES!” Yes I am concerned about fires or explosions due to the exposure of sawdust to ANY flame source in my house. But I also know from years of experience that you’re more likely to slip and fall on the sawdust than you are to have an explosion.

dusty saw handle

This dusty saw handle sits right next to my furnace intake…

So my first piece of advice to anyone concerned with this situation is that they should be diligent about keeping their shop clean. I’m not saying their shop should be spotless (mine always has a fine layer of dust on the shelves and chips & shavings under the bench) but instead I’m suggesting they should take the time to sweep up the big piles off the floor at the end of the day or even in between heavy dust/chip-making operations such as planing or sanding.

In fact, you don’t even need a heavy-duty dust collection system for this operation. A broom and dust pan are just as effective. And this is important not only in keeping things from getting volatile, but again, it can keep you from slipping and falling (or even from it becoming a haven for unwanted critters like mice and bugs.)

The next thing I would recommend to think about is the location of the tools. Position them furthest away from the pilot lights, or orient the tools so the sawdust and chips are being expelled AWAY from the flame.

For example, my tablesaw is located next to both my gas furnace and water heater, about 3-4 feet away to be exact, and it can throw a lot of sawdust on me when I don’t have the dust collection turned on. To keep things from getting all fired up, I have the saw positioned so that when I’m making a cut, the sawdust is expelled away from the appliances instead of towards them.

I’ve done plenty of dado cutting action that throws an amazing amount of sawdust on the floor. Then because I’m in a rush to get out of the shop for whatever reason I end up leaving those piles on the floor and not cleaning them up for a day or more (sometimes up to a week) without fear of a fiery demise.

overhead air cleaner

If you find it’s the fine dust you’re most concerned about (given its tendency to land everywhere) I’d recommend using an air-cleaner of some sort. I happen to have an overhead air cleaner that works amazing at grabbing a lot of it (of course if you don’t remember to turn it on regularly, like I forget to, it doesn’t do you any good.)

This is actually the stuff I’m most worried about, but again, not for explosions or fires. Instead, I’m more concerned about it getting in my lungs.

dusty shelves

If you can’t afford an air-cleaner something as simple as a box fan with a furnace filter taped to it, or even an open window to help circulate fresh-air will make all the difference. Having decent air-flow through your shop is something we might not think a lot about, but good air-flow will actually help to keep that fine dust a little more under control.

In fact, in my first basement wood shop I had some amazing basement windows I could open wide, set a fan in and have it suck a ton of sawdust out that otherwise would have accumulated all over the shop.

There are of course obvious reasons why we want to have some sort of dust collection on our tools. But for a lot of us there’s no way we can justify a huge “whole-shop” system with drop down duct work and supply lines. But something as simple as a shop vac or a bag outfitted under an open bottom tablesaw will help to keep the sawdust and chips contained enough until you empty it.

And for sure there will be streams of sawdust flying out if you’re only using a small shop-vac, but you’d be surprised how much more would be if you weren’t!

So in closing, from my own experience, the flames on gas furnaces and water heaters aren’t as worrisome for starting fires or explosions with sawdust and chips as slipping, falling or even longterm respiratory disease is. What are your thoughts on the topic?

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Comments (11)

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  1. Pete says:

    Matt this is a great question. Fortunately I don’t have to deal with this issue in my shop. But I wouldn’t be concerned with this, for a pilot to ignite your saw dust on fire your air source would need to be nearly saturated. A pilot will burn the dust that it comes in contact with but just that. For it to continue a fire it would need a constant source. That’s not the case with dust in the air. Just keep open flame away from the rest of your wood!

  2. Daryl says:

    Matt, I also have a basement shop with a furnace and the only thing I do different is about once a month I open the service panel and blow it out with the air compressor. Although this is more about preventing furnace breakdown than fires.

    • Brian says:

      You can’t overstate the importance of keeping that dust out of the furnace. Just ask my woodworker friend about his $2300 repair bill in the middle of winter. Make sure you change those furnace filters regularly. I actually walled off my furnace and made sure to tape every duct seam with aluminum tape. It keeps dust out of the rest of the house and out of the furnace.

      • Matt says:

        That’s why I at least try to encourage folks to use a shop vac or take the time to clean up after a day in the shop. Several years ago I posted a video titled “Minimize the dust” that was filled with my own tips on keeping sawdust contained to the shop and somewhat manageable.

        http://youtu.be/w_5HqFVWKUw

  3. Marshal says:

    I work a lot with grain dust (fine particulate matter). Explosion from PM dust is equal to TNT. The dust itself is not excessively combustible. However, in suspension it is explosive. Four factors required are… Oxygen, ignition source, confined space, and high concentration of dust in suspension. Google grain dust explosions.

    Grain dust is a finer PM and the concentration is much higher if not controlled… Ie hard to see across the room. We use dust system bag houses, good old fashion housekeeping, and eliminate ignition sources.

  4. Chuck M. says:

    Matt, as Marshal hints to in his post, the confined space is the concern here. I’m sure you’ve hears of explosions at grain elevators in the Midwest from the concentrated dust in the air. As with actual flammables whose vapors are heavier than air, they concentrate at the floor where a pilot light for a hot water heater is located. An explosion would occur when the concentration of whatever is in the air reaches the LEL or “Lower Explosive Limit”. This is where there is the “right” mix of oxygen and flammable material in the air where an open flame would cause ignition. Inversely, there is also an UEL or “Upper Explosive Limit” where the concentration becomes so high that there is not enough oxygen left in respect to the flammable material and ignition can no longer occur.

    To give you an idea at where minimum ignition would occur, in a 10′ X 10′ X10′ room, a minimum concentration of 0.035 oz./cubic foot of sawdust would be necessary with an optimal ignition occurring at 1.0 oz./cubic foot. To give you an idea of what these amounts equate to … the lower concentration would equate to about 1/64″ of dust coating every surface in the 10 cubic foot room (walls, floor, and ceiling) and the optimal amount would be about 1/2″ of dust covering every surface in the same 10 cubic foot room. The minimum concentration required for ignition, when suspended in the air, would make visibility beyond 3-5 feet impossible according to the NFPA 499, Annex A 5.2.2, which classifies combustible dusts and flammables.

    • Matt says:

      While it may feel like that’s the situation in my own shop from time to time, especially when I’ve done router work and forgot to turn the dust collection on, with a little cleanup after the work is done should maintain a “safe” environment.

      • Chuck M. says:

        I hear you there … I flattened my workbench top with the router and sled method with no dust collection … me and everything else was coated with dust that took me about three hours to get “clean enough” for me to move on.

  5. John Fitz says:

    Great topic, one that is sure to resonate with any basement-shop owner. I started out with some concerns but felt comfortable based on information similar to what Chuck wrote above – the density of airborne dust needed for an explosion is pretty high.

    I was always more concerned about the issue with vapors that could be either flammable (as shown in the warning label in the picture you posted) or just plain old unhealthy. I used the same method many basement dwellers use – I put an exhaust fan in the window – but I was always very concerned about creating enough negative pressure to cause an issue with exhaust gasses from the heating equipment being drawn down the flu/chimney and into my shop area. I either opened another window in the basement for effective air supply, or (temporarily) turned off the boiler so it wouldn’t kick on while I had the fan running.

    We’ve since replaced our heating system with an enclosed high efficiency unit that draws combustion air from outside so I don’t worry about it any more, but I encourage basement shop users to consider the possible issues with vapors and the downstream effect of any measures they use to control them (like exhaust fans).

  6. Barbara P says:

    I am in the market for a new house. One that I am considering has a huge wood workshop in the basement. The seems to be a separate vacuum system, but I don’t know if or how it works. The house was built 13 years ago and has the original HVAC system. How concerned should I be about dust in the HVAC? What questions should I ask? What inspections of the HVAC should I request besides cleaning all air ducts in the house? Heart else should I ask in addition to how often they changed the air filters and cleaned all air ducts? Thanks…

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