Fire Danger?

[Darrell Jones]

My woodshop is my 2 car attached garage. I am nearing the end of a large cabinet building project that has lasted nearly a month. There is considerable sawdust on the floor but the shop is so full it is too hard to clean up until the project is done. My neighbor was over the other day and told me I should build a screen around my furnace (which is also in the garage) to keep airborn dust away from it as it could ignite the particles and explode. It is all pretty much enclosed. Draws in cold air from inside the house and I have no heat registers in the garage. You'd think my propane heater would ignite if anything was going to. Should I be concerned? Thanks.....DJ

[Anthony Whitesell]

Explode...no. It has been calculated that the static generated in our home shop DCs won't explode wood dust. Catch fire...possibly. I think I'd be worried about a chip going under the system, then catching fire, then travelling to the rest of the saw dust.

I think some screen around the bottom may be something to think about doing. I wouldn't worry about the dust, I think the larger chips pose more of a threat.

[Lori Kleinberg]

I have a similar setup except in a 3 car garage. I have been working this way for a couple 3 years and no problems,
although truth to tell I don't really make much of anything but sawdust :eek::D.
I would still be interested in this kind of information. Oh yeah, I do keep a fire extinguisher in the gara--shop.

[Jim Mackell]

My woodshop is my 2 car attached garage. I am nearing the end of a large cabinet building project that has lasted nearly a month. There is considerable sawdust on the floor but the shop is so full it is too hard to clean up until the project is done.

You'd think my propane heater would ignite if anything was going to. Should I be concerned? Thanks.....DJ


Well, the sawdust is a FIRE hazard much more so than an explosion hazard. From your description it sounds like you have a heavy fire load - lots of stuff to burn if ignition occurs for any reason.

Propane can ignite dust if the exact ratio of dust to oxygen is reached. Again, not likely.

With so much at risk in terms of your tools and projects, why not take 15 minutes every day and clean the saw dust up? Every if you only got 90%, it's a start.

[Matt Meiser]

Its certainly possible. Dust explosions are common, but usually in industrial environments. I agree that fire is a lot more likely than explosion. I will tell you that I tend to keep my shop vacuumed up pretty well, cleaning between each phase of a project, and when I switch between woodworking and welding I make sure it is spotless (both ways since the metal grinding dust would ruin a wood project.) I do know that a handfull of shavings from my dust bin make great campfire starters.

There are other benefits to a cleaner shop, like breating less dust, tracking less in the house, fewer finishing problems, etc.

[Rick Christopherson]

Your neighbor's comment about explosion from airborne dust is rooted in fact, but in an open-air environment such as your shop, it is not a concern.

A pile of sawdust laying on the floor is not very flammable, because you can't get enough oxygen into the core of the pile to burn. On the other hand, a thin layer of sawdust resting on the various surfaces in the shop is much more flammable. That's because the depth of the dust is lower, and it is easier for oxygen to be present.

But note that this is a completely different situation from airborne dust. There is what is called the Lower Explosive Limit (LEL) for any airborne material, whether it be a gas or a dust, etc. At concentrations below the LEL, the spacing between adjacent particles is too far apart for the ignition of one particle to ignite an adjacent particle. There is also an Upper Explosive Limit (UEL). When a concentration is above the UEL (such as a pile of dust on the floor) then the fuel is too rich to burn and there is not enough oxygen.

When an airborne wood dust concentration is above the LEL, the spontaneous ignition from particle to particle is extremely rapid, and it is an explosive ignition. If this occurs in a confined vessel or space, the expanding gasses will result in a violent explosion.

With that information stated, taking this back to your situation, no, you do not have to worry about an explosive situation in your garage. If your dust collector ruptured a bag and filled the garage with a cloud of dust to the point that you had a hard time seeing, then you would have a dangerous situation with a risk of an explosion that would destroy the building. However, even if you just had a small cloud of dust that surrounded the furnace, then the worst you would have is a small fireball from the localized cloud igniting, but not explosively.

With the exception of the ruptured bag example, you will not have an LEL condition in the open air of your workshop. You could have an LEL concentration inside of your dust collection system, but that is a different discussion.

[Darrell Jones]

WOW, this forum is so awesome. Thanks again everyone. I feel better and I promise to try to sweep up a bit every night.:)

[Peter Quinn]

I think it would be hard to see or breath in an environment approaching the level of airborne dust required for an explosion. I understand it is actually quite difficult to create these conditions even in a lab for testing. Fire danger from sawdust and chips is more likely and equally serious, especially if they ignite after you have left the shop.

Check out (http://billpentz.com/woodworking/cyclone/Ducting.cfm#Duct%20Pipe)

I have a few fire extinguishers in my shop and one outside the entrance fully charged, multi fuel type (electrical, grease or wood extinguishing). Hope I never need them. I am guilty of letting the cleaning go till the end of a job too, but find a decent shop vac and a few minutes of discipline each day make my environment safer for working, breathing and sleeping at night.

Not sure what a screen will do other than keep out large flying chips and bugs, but if the situation is serious enough that a screen would help, I'd make no excuses, stop and clean up a bit. Possibly if space allows a wall/door to isolate the combustion unit might help? Between my oil furnace and shop I built a stud wall covered in 5/8" fire rated sheet rock, hung an old louvered door covered in fine furnace filters to allow fresh air but keep out dust, left enough space to meet all applicable set backs from combustion and allow for service of the unit.

[Gordon Harner]

If I have read this thread correctly I'd be concerned about an entire different issue. If you need to control the dust going into you system in the garage to the burner what about fumes from gasoline or finishing materials? This is a real explosion risk. Even if we are talking about a fresh air supply for the conditioned air in the ducts this is a big hazard. I think that you should evaluate your system for these hazards.

[James Suzda]

My woodshop is my 2 car attached garage. I am nearing the end of a large cabinet building project that has lasted nearly a month. There is considerable sawdust on the floor but the shop is so full it is too hard to clean up until the project is done. My neighbor was over the other day and told me I should build a screen around my furnace (which is also in the garage) to keep airborn dust away from it as it could ignite the particles and explode. It is all pretty much enclosed. Draws in cold air from inside the house and I have no heat registers in the garage. You'd think my propane heater would ignite if anything was going to. Should I be concerned? Thanks.....DJ
I would be more concerned about the fumes from any gasoline that might drip from any vehicles parked in the garage. But, no-where in your message do you say you park anything in your garage other than your toys (tools).
When I asked my insurance man about putting a furnace in my garage the only thing I heard was a gasp and him hitting the floor! :D But, after he woke up again, he did say as long as the furnace was 2 foot off the floor it would be okay.

[Josiah Bartlett]

I caught the dust in the base of my Unisaw on fire once, after I was cutting MDF with a fairly dull blade. It filled the garage with smouldery smoke. Fortunately I noticed it before it caught flames, but I can see it being a problem. I always clean up when the dust gets thick enough that the floor changes color, now.

Some furnaces (gas ones) don't have a good draft when they light, and if something goes awry with the normal process it is possible for flash to come out the bottom of the furnace.

When I used to work in an attached garage I used to have to clean the dust out of the furnace every time I changed the filter, it would clog a little sensor oriface that determined whether the draft fan was working and it wouldn't light.