Why dust explosions in a home woodshop are just a myth q gas station


Before getting into the details, let me set your mind at ease. There is absolutely no reasonable risk of this happening. There’s not even a remote risk. gas zombies black ops It’s so close to impossible that you’re much better off building a large metal shield over your shop, because it’s much more likely to get hit by a meteor than have a PVC-induced dust explosion. There has never, ever been a verified PVC static-caused dust explosion in a home wood shop. Not even one. Of course, you can’t really prove anything by a lack of evidence, but the fact that we have no record of it ever happening tends to back up the science of why it’s not a realistic risk. So just stop worrying about it.

First of all, we need to understand that getting dust to explode is very difficult. Researchers in the field have to work very hard to get dust clouds to ignite under very controlled lab conditions, using specially build sparking devices that don’t use static electricity at all. In fact, static discharge may often get the blame for a dust explosion just because the investigators can’t find any other reason.

Why does a dust cloud explode, anyway? Well, like most explosions, we have a material that not only burns, it burns very, very rapidly. A dust cloud takes a relatively small amount of material and vastly increases its surface area, suspending it within an oxidizer (oxygen), allowing it to all burn at once. A 2×4 may take 20 minutes to burn up and release its energy in your fireplace, but if you ignite the entire thing in a fraction of a second, the result is rather spectacular.

So, are all clouds of dust that dangerous? No, because it takes a very, very particular type of dust cloud to be flammable. The ignition has to spread across the cloud, so the particles have to be close enough, otherwise the particles right in the ignition source burn but it never gets any further. Just as the particles can’t be too far apart, they also can’t be too close together, since this removes the oxygen necessary for the rapid burn. gas vs electric stove cost So you have to get just the right "mixture" of fuel and air, just like a gasoline engine. And for dust clouds, the zone between too much and too little is extremely narrow, only a few thousandths of a pound per cubic foot.

Also, not any discharge will do. It needs to be a actual "spark", i.e. a concentrated point discharge, a diffuse discharge will not do the job. Also, it has to be a fairly "energetic" spark, a weak spark does nothing. Sparks happen when two points have a charge differential, i.e. there’s more electrical charge in one thing than the other. The spark happens when the electrons jump across the gap. To be energetic, you need a lot of electrons making the leap, so the source point needs to give up a lot of charge very quickly.

OK, then, what about sanding? Yes, now we have dust that might be the right size. But do we have the quantity? Remember, we’re now talking about a dust cloud that’s constantly being sucked away by the dust collector at high velocity. electricity 2pm lyrics To have any chance of hitting the cloud with a spark, we have to have a way of continuously replenishing the dust.

Let’s say you’re sanding a 12×12 piece of red oak. You’d have to sand off over 3/16" per minute to get that much sawdust! It’s extremely unlikely you can generate that much sawdust. electricity youtube billy elliot Maybe with a wide-belt sander, but then you’d have a much larger dust collector connected. A bigger system moves more air, so you have to make sawdust even faster. With a more typical 1000 cfm system, you’d have to sand off 3/4" per minute to generate the three pounds required! Just for fun, the next time you’re sanding, sweep up a pile and weigh it to get some notion of how much three pounds of sawdust is.

The reason the PVC gets a static charge is from the sawdust rubbing against the PVC. There’s nothing special about PVC, even metal ducts will take a charge. But metal ducts can be grounded to bleed away the charge. Just like PVC, an ungrounded metal duct will give you a static zap (ever been popped getting out of your car in the winter?). electricity in the body symptoms In fact, you’ll get a far more intense jolt from a metal duct, because metal is a conductor. When you provide the grounding path with your finger, you provide the conduit for all the electric charge stored in the entire duct because it will freely move through the metal. Conductive materials will naturally assume a balanced charge throughout their entire structure.

PVC is different, because it’s an insulator. Insulating materials have no problem with an unbalanced charge because electricity moves through them very slowly if at all. When you ground a static-charged PVC duct, you only drain the charge in the immediate vicinity of your finger, just a fraction of an inch. The rest of the charge will resist flowing to the ground point. Because of this, it’s nearly impossible to get a "spark" discharge off an insulator like PVC. In fact, I challenge you to get even a tickle off PVC. I recently pumped a couple cubic feet of sawdust through my floor sweep, putting so much static on the PVC that the hairs on my arm were standing straight up at over 6 inches away from the duct. electricity 220 volts wiring I grabbed my bandsaw’s table, touched the duct and felt … nothing.

So, if you can cause a discharge (albeit weak) on the outside, what about the inside of the duct? The situation’s a little different in there. Remember, the PVC became charged because the dust is rubbing on it. Well, that action is two-way, i.e. the dust is getting charged the same way. Not only at the same time, but the same type of charge and very near the same level. If we’re looking to make a spark, just where would that happen? Both the cloud and duct are insulators that resist discharge. There’s very little if any electrical charge difference between them. The bottom line is that even if you got a discharge (and they probably do happen), it would be even weaker and more diffuse than to a grounded point on the outside, nowhere near energetic and "spark-y" enough for ignition.

• A much more likely danger (and something has has actually been documented) is ignition in the collection bin. Sucking up something metallic which then strikes the blower impeller (fan) can create a spark that goes into the pile of sawdust. This type of ember can smolder for hours before flaring up, taking your shop with it. The simple answer? Install a fire suppression bomb, see the sidebar for details.