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There's a strong belief amoung non-technical people that home computers should not ever be left on unattended - since they are electrical devices and can go up in flames and set the room on fire.

Now it's obvious that any component inside the computer system unit can break at any moment and maybe even produce a fair share of toxic smoke. But do computers actually go up in flames that can cause a fire around them?

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I think we should distinguish between 'conflagrations' which emit a little smoke, and overheating which might cause fires by contact with something flammable.

Reputable computer hardware manufacturers use components which do not accelerate fires and are flame-retardant so far as possible.

The Underwriters Laboratories rating system requires these things, but Gnoupi is right about power supplies: don't buy very cheap "noname" power supplies: they may have been designed with no regard for safety considerations.

But, by and large, computer system unit don't go up in flames ... although there may be a few exceptional 'cases'.

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As with every electrically based device, it's not impossible, but it's extremely rare, especially with reputable name brands. Also, if a consumer is neglegent (i.e. plugging 20 devices into one outlet, never cleaning out the inside of the computer case, etc), it can increase the risk as well. –  BBlake Dec 30 '09 at 17:41
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Seems that yes, according to this answer (and some others on the same question).

In general, the parts that can actually catch on fire are batteries. It's a problem which concerns laptop, but only in some faulty cases. Check this article for more information.

For desktop computers, if there is a cause, it's the power supply. Buying very cheap "noname" power supplies is actually dangerous, because many are faulty, and not handling the power ranges they claim. Not sure if that would be enough to start a fire, but clearly enough to make sparks and shut down power in your room/house. It's a French link, but you can check the video on this page, where the tester is checking capability of some noname PSU (direct link to video).

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My wife had a hard disk drive catch fire on her once, back in the old PC days. The computer was in a sporting goods store, very close to the skate sharpener, and she could taste the metal in the air when she used it. Since then, no problems.

However, thousands of companies leave thousands of computers on 24/7 without problems, so for a computer in known good shape in a known good environment, I wouldn't worry about it.

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A modern PC? It's highly unlikely - your motherboard has temperature sensors, and will cut out if they get too high. If voltages suddenly start going off the chart, your motherboard will cut power. Your motherboard catches fire? Well, there's not much it can do about that, so it's still possible - just unlikely.

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If it's going to catch fire it's usually something 'external' that's gotten inside and been set afire by a spark or heat. For example, we had a guy bring us a computer that (for years) sat in his woodworking shop. It ate tonnes of dried sawdust over the time; one day the video card fan finally died and the heat form the GPU chipset caused the 1/4 inch of sawdust sitting on the backside of the video card to begin to smoke and smolder.

Luckily he turned it off before it actually lit on fire and brought it to us to figure out why it was smoking.

Most 'solid state' components tend to just either melt or 'pop', usually with a stink, but usually without visible flames/sparks. :)

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I've seen the end results of CRT and power supply fires before. I now recommend that unattended computer equipment be shutdown unless there's a really good reason to leave it running...

Anything that handles a significant amount of power has a possibility of catching on fire. Computers are among some of the least likely things in a house to catch fire, but why leave it running for no reason and take a chance?

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Yes, I once saw a locally-built computer melt itself completely down.

Must say it was quite an impressive sight.

Luckily I had backup and the manufacturer gave me a new one.

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Yes,

It can happen. I have had a video card shoot fire before.

Addition: The card failed with no overclocking at the time of failure. It just shut off over night and then in the morning when I found it, I opened the case to investigate. Reset the power supply, powered on, and flames shot off the video card. BFG did not question me when they went through their troubleshooting process for RMA. I was like, it shot fire out of a component on it. Haha.

Also, I have seen power supplies get very hot and burn up. Like people are saying, don't cheap out on a power supply. All the other times were technition mistakes back in the day I saw turn badly for them from connecting wires incorrectly or things not seated properly. You know something went wrong when you hear someone turn the system on and then a string of expletives following.

But to answer your question more directly, you will not normaly see computers just catch fire. Components are mostly made efficiently and safely today with tolerance and failure limits to prevent further damage and user safety. There is always exceptions, but in most cases, the component that dies just dies and computer will either give errors or just shut off.

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Was overclocking involved? –  Adam Luchjenbroers Dec 30 '09 at 11:35
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