Curious -- Spark risk

Re: Curious -- Spark risk

John in NM

Sparks certainly can start fires under the right conditions, but it is pretty rare, which is why you find a lot of metal workers and even woodworkers to be pretty complacent about them.

The reason it is rare is that though the spark is hot, the actual mass of the oxidizing steel is very small, so it carries surprisingly little energy. When something burns - like wood dust on the floor - it is actually vapor coming from the solid that you see burning, basically the smoke is what ignites rather than the solid itself. This takes a fair amount of energy to start, and under most conditions grinding sparks just don't carry that much in spite of being quite hot.

Welding "sparks" (hot splatter really) is much more dangerous, as the particles are vastly bigger and carry a great deal more energy. Fires from welding are much more common than from grinding.

One should still be very aware of the potential fire danger from grinding, I don't mean to minimize that. Just explaining why so many people take it so casually.

Re: Curious -- Spark risk

Bill Howatt

I generally agree that the risk is low and John's explanation.

Nontheless, it is a possible heat source and how it behaves will depend on how may sparks land it what sort of material. So to assume that you can do a bunch of grinding and then leave the shop without a good look at the area before leaving is a mistake.

There are reports of fires being started by cut-off grinding wheels but they tend to produce more and quite likely larger glowing sparks.

Bill

I agree with both, but in the woodshop

Keith Newton

The biggest chance of starting a fire isn’t from dust, but from finishing products. Needless to say volitiles in finishing products could easily combust, but the most easily overlooked item is steel wool. As a kid my older brother showed me that he could hold his hand right in that plum of sparks without getting burned. But if you want to experiment, just lay half a pad of 0000 on something fireproof and send some of those sparks into it and watch what happens. It spreads outward and gets really hot enough to combust other things around it.

Re: Curious -- Spark risk

Sgian Dubh

"Anyone have experience with grinding sparks. Anyone had a problem?

Ah, sparks starting fires Gary. I've seen it. Different situation, but it's certainly possible. A classic case from many years ago at a place I worked involved a bench joiner thinking the horizontal belt sanding machine was a great tool for regrinding his plane blades. It did do a good job I suppose, but then the fire alarm located in the dust shed went off as the dust/ chip bins caught alight. Mass evacuation of about 200 staff from the whole complex of offices, joiners, glass workers and metal bashers as the company fire marshals tackled the blaze and the fire service rushed to our site. Needless to say, that particular joiner wasn't so highly thought of after that, ha, ha. Slainte.

sparks and heat

John K Jordan

>>>if you want to experiment, just lay half a pad of 0000 on something fireproof and send some of those sparks into it and watch what happens.

For even more excitement saturate the steel wood first with very fine aluminum powder. This is thermite, gets hot enough to weld. It makes a great science demonstration.

The worst spark throwing I know of is cutting thick steel with abrasive wheels on a chop saw. The particles are so hot and stay hot long enough to bond to other steel particles accumulating on the spark guard a foot from the cutting point. The can build up a strong steel mass: