Reply by Steven H

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Posted on Fire extinguishers in the shop

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Steven H

1117 posts in 3515 days

#1 posted 05-13-2010 06:17 AM

This is what PocketHole69 has wrote from this thread.

1. Combustible Dust

Wood boards / chunks / pieces just burn and are easily controlled with extinguishers, or in a worst case scenario easy to get away from (run). In contrast, combustible dust in an unconfined area flashes and ignites nearby flammable surfaces, potentially setting fire to large portions (or all) of your shop. Combustible dust in confined areas (such as small rooms, dust collectors, paint booths, and tool enclosures) explodes.

Combustible dust explosions kill people. They are a top safety concern of OSHA with recent high-profile incidents such as the sugar plant explosion in Georgia. It doesn’t take much dust to do it either- as little as 1 pound floating around your shop in the air can provide the perfect fuel-to-air ratio for an explosion. The fact that many shops are in basements, utility rooms, and garages where there are ignition sources such as water heaters and furnaces nearby, as well as unshielded tools and frayed cords arcing is the perfect recipe for disaster.

Sources of combustible dust in the wood shop include sawdust, dust collectors, metal dust if you’re in to metal working, and lint / paper products.

The best defense against combustible dust is good housekeeping. Clean up after yourself and don’t let dust accumulate. Try to do your woodworking away from possible sources of ignition and open flame such as pilot lights.

Many will argue for dust collection in the shop, and a well implemented dust collection system can minimize the risk. However, dust collectors pose special hazards of their own and dust collector explosions can occur when a burning bit of sawdust gets introduced to a huge bag of floating dust inside the collector.

Most dust collector fires in industrial settings get out of hand when the dust collector ignites and explodes, and then because of bad housekeeping all the dust outside the collector, shaken up and sent airborne by the dust collector popping, gets ignited by the dust collector explosion. This one-two punch levels buildings, as the video linked below will show:

Combustible Dust: An Insidious Hazard
(Youtube, 30 minutes long. Probably more than you ever wanted to know about dust)

2. Paint / Stain spray in the air and buildup on surfaces

If you want to make something really damn hard to put out when it catches on fire, put about 10 coats of old paint or poly on it. Also spray painting creates the same hazards as combustible dust when in the air.

Use a paint booth or spray outside. Clean up your mess.

3. Metalworking

Metalworking creates metal shavings and dust. Metal shavings and dust burn when they get hot, and metal working is known to create heat.

If you have a metal fire you can’t put it out with a common Class ABC dry chemical fire extinguisher. They burn ridiculously hot so you might not even be able to approach them to drag whatever is burning out of your shop. Spraying water on metals fires usually causes an explosion because they burn so hot that they catalyze the water in to Hydrogen and Oxygen (a flammable gas and an oxidizer to accelerate combustion), causing a violent ignition.

If you work on metal with any regularity and don’t have a Class D fire extinguisher handy you’re asking for your house to be burnt down. Most municipal fire departments, and especially rural volunteer departments, are ill-equipped to handle a metal fire. At the very least you need to have a bucket of sand nearby so you can cover up and slow the combustion process and try to prevent radiant heat ignition of the rest of your shop until the fire department arrives.

4. Oily rags

Oily rags that contain oil, finishes, paint, etc. go through a process of biological and chemical decomposition that creates heat. This decomposition occurs everywhere, even in rags sitting on your workbench exposed. This is a tiny amount of heat- it normally just dissipates in the air and is not even noticed. The problem comes when they are stored in a closed container with other oily rags- the heat can’t escape. When the heat can’t escape it in turn speeds up decomposition, which in turn creates more heat, which in turn speeds up decomposition, etc. until the rags reach the auto-ignition temperature of the rags or chemicals they contain, causing them to spontaneously ignite.

The scary thing about this is you don’t have to be in your shop for it to happen- you can do your finishing, go to bed or work, and then 8 hours later while you’re sound asleep the rags can reach ignition temperature and light your house on fire. It might take days for rags to reach ignition temperature, and having your house burn down while you’re at work really sucks from what I’ve heard.

At the minimum you should store oily rags separate from other waste and remove them from your house when you’re done. Better is a metal can with a tight fitting lid that can contain a fire and starve any that might start of oxygen. Best is a OSHA approved container that is rated for storing oily rags- they really aren’t that expensive when you think about what is at risk (your home and your family)

5. Location

Where a fire starts in your home has a lot to do with if the fire department is going to be able to save your house and everything you own.

The two absolute worst places for a fire to start? The basement and the garage.

Where are many home workshops located? The basement and the garage.

When a fire starts in the basement you have about a 50/50 chance of losing your home, and even more so if your basement is below grade. Basement fires are hard to approach- heat rises so a firefighting going down a staircase to the basement is going to get cooked and may not be able to make it. Basement fires compromise the floor structure of the first level of your home, making firefighter entry in to your house a dangerous proposition. Some fire departments won’t even enter a home when there is a basement fire burning- they don’t want to see their men step on a soft spot in the floor and fall through in to an inferno.

Garage fires are dangerous for obvious reasons- people store flammable stuff in garages: paint, gas, chemicals, cars full of gas, etc. If garage fires are not quickly controlled they can quickly burn out of control, and with most garages attached to houses in the US the rest of the house is just one minimum code requirement wall away.

What can you do to minimize risk?

Those are the major threats. Here is what you can do to minimize the risk:

1. Have a fire extinguisher appropriate to the materials in your shop

You should have, as a minimum, a 5 lb. Class ABC dry chemical fire extinguisher in your shop. You should have one in the garage and kitchen too.

If you are working with metals, you should have some Class D extinguishing agent nearby.

If anyone is wondering what the fire classes are, they are:

Class A: Ordinary Combustibles (wood, paper, etc.)
Class B: Liquid Fuel Fires (paint, stain, gas, etc.)
Class C: Energized Electrical Fires (power tools, wiring shorts, etc.)
Class D: Metals Fires

Read up more on Fire Classes

2. Clean up after yourself

90% of workshop related fire threats can be negated by cleaning up after yourself. A dirty shop is not just messy, it’s unsafe. Your momma was right when she told you to clean your room.

Regularly clean up dust after working with wood products. Clean up spray booths and ventilate after spraying finishes. Take out your trash, and store oily rags properly.

3. Look around and realize what your hazards are

Do you have a pilot light nearby that could light dust next time you’re sanding? Do you have frayed cords or overloaded outlets that can arc and start a fire? Do you have exposed electrical wiring? Do you have a pile of oily rags in the corner by your wood pile?

What can you do to minimize the risk to your home and family? Everyone who’s house burnt down never thought it could happen to them, but one day everything they owned, their pictures, their memories, their pets, and sometimes even their family members were gone. Nearly every house fire I’ve been to could have been prevented. You owe it to yourself and your family to take a minute and minimize the risk of fire.

4. Install a fire alarm

Really, this is a no-brainer. You should have a fire alarm in your shop, in your kitchen, in your garage if different from your shop, and outside every bedroom on every story of your home. Central monitoring is great if you can afford it, but at the very least get one that will go off and wake you and your family up if there is a fire.

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