Are holes on the inside of a microwave door a problem?

July 11, 2009 12:43 PM

The inside of my microwave door has small holes melted in it. Is it still safe?

Something melted holes in the inside of our microwave door. The largest hole is about 3mm. Here's a photo (2MB). It doesn't appear that the screen inside the door has been affected, and I haven't seen any condensation or anything inside the door. There are no holes one the outside of the door. Is the microwave still safe to use?

posted by DakotaPaul to grab bag (13 answers total)

I would assume it's fine so long as the screen mesh is intact (the mesh acts as a Faraday cage).

But new microwaves are cheap...
posted by meta_eli at 12:56 PM on July 11, 2009

I would not advise you using it.

The inside of a microwave oven is a Faraday cage. (The screen is part of the Faraday cage.) The purpose is to prevent the microwaves from escaping. A hole in the cage could permit microwaves to escape, which can be a hazard to you.

Also, that is highly abnormal and any machine that acts in one abnormal fashion could well have other abnormal behaviors which might be more hazardous.

As Meta_Eli says, microwave ovens are cheap, and the risk isn't worth it.
posted by Chocolate Pickle at 1:30 PM on July 11, 2009

Radio Shack used to carry them, a electronics repair place might still carry them, or there is, of course, online, but microwave leak detection kits are cheap and easy to use. Still, microwaves are so cheap today, it's probably not worth it to try and limp along with a damaged microwave, which will only deteriorate as it continues to age.
posted by AzraelBrown at 2:17 PM on July 11, 2009

It's the metal that's important, and that seems undisturbed. What caused the holes? Also, microwaves are about 10cm long (2.5 GHz), about two orders of magnitude longer than holes (it was overkill to begin with); I would think it's well into the "evanescent wave" regime, where the electric field outside the mesh decays exponentially.

Put a chocolate bar just outside the door. Does it melt?
posted by gensubuser at 2:19 PM on July 11, 2009

The door not only protects you from the microwaves, but also from bits of superheated food in the event of a tragic accident striking that late-night burrito.
posted by HFSH at 2:27 PM on July 11, 2009

But with no holes on the outside that would only cause difficulty in cleaning the inside of the door, I guess.
posted by HFSH at 2:29 PM on July 11, 2009

After you try gensubuser's suggestion, put a chocolate bar *inside* the microwave, after taking out the turntable, and you can actually see that the waves are on the size of 10 cm. Why? Because the peaks+troughs will melt the chocolate more, so you will have extra melted spots on the chocolate, spaced centimeters apart. That's just for fun, though, but it is by way of proving to yourself the waves are much too long to appreciably get through the tiny holes in the (hopefully intact) metal screen.

That having been said, yeah, microwaves aren't so expensive. You can pick up a used one for cheap on craigslist, and who knows what'll be growing inside your microwave door due to the cleaning problem HFSH pointed out.
posted by nat at 2:37 PM on July 11, 2009

I'm not clear on what dangers you're actually concerned about. Microwaves can't give you cancer or anything like that. The worst they can do is hurt you by heating you up before you notice it. Cataracts are possible, but at the level of exposure that's at all likely from a possibly slightly leaky microwave? Meh. Do you tend to run the thing for extended periods when you aren't nearby? Or stand with your face right by the door?
posted by molybdenumblue at 3:17 PM on July 11, 2009 [2 favorites]

The holes were probably melted by hot sizzling oil/butter/grease splattering on the plastic surface. Been there, seen that.

Gensubuser has the best homebrew microwave-detector idea, but as everyone else said, microwaves are fifty-dollar items now, so if it worries you even a little, just replace it. And be sure to really break it before disposal, or someone else will end up using it.
posted by rokusan at 4:12 PM on July 11, 2009

At one point I probably could have derived this for you, but it's been a while since I've taken E&M so I'm just going to cheat and look it up:

SE(dB) = 20 log [(λ/2)/L]

This is for SE, the attenuation (in dB) of a "slot antenna" of length L at wavelength λ. The wavelength at ~2.4GHz is about 12.5cm, or 125mm. Your hole is 3mm. The result is about 26dB. Granted that is for a solid conductive sheet, but it's in the ballpark. That's pretty severe attenuation. Even given the relatively high field strengths inside a microwave oven, there's not much coming out the other side of the hole. Plus, it's going to act like a point source so the field density is going to drop off quickly.

Provided I wasn't planning on using it as a peephole to look in at the food better (sticking my eye right up to it), I'd keep using it. The main risk of 2.4GHz RF is thermal — in other words, burning you — and in most cases you'll feel it before it can hurt you as you start to move part of your body somewhere it shouldn't be. A lot is made of microwave "radiation," sometimes to the point of hysteria, but it's not going to make your kitchen radioactive or anything.

I do not agree with the "if it worries you even a little, just replace it." If you really and honestly think there's a problem, by all means replace it, but don't do it out of some irrational fear.

The easy solution is you could always solder some wire mesh over the hole, joining it to the existing grid, or you could see if the existing wire could just be pushed back into place (if the hole was caused by dinging it with something).
posted by Kadin2048 at 8:40 PM on July 11, 2009 [2 favorites]

It's not dangerous but food particles can now get between the plastic and the mesh. These may rot & stink eventually. I'd keep using it till but would also start shopping in that slow, lazy way that lets you get the best deal.
posted by chairface at 9:02 PM on July 12, 2009

Thanks for all the responses. I don't know what caused the holes; we just moved in and the microwave was left here. It's an over-the-range microwave/hood combo, so I'm thinking the expense and time involved in replacing it aren't worth it. Just wanted to make sure that the holes wouldn't cause further damage and potentially injure someone.
posted by DakotaPaul at 1:42 PM on July 13, 2009

The holes are absolutely not a microwave leakage problem, because they are only in the plastic inner skin and have not affected the metal screen at all. The only bad thing they might even conceivably do is make the interior harder to clean. Patch them with a bit of transparent gardener's tape and you're good to go.

If you do end up getting rid of this microwave because of these holes, please don't break it. Unless you know it to be unsafe for other reasons, somebody else should be able to end up using it.
posted by flabdablet at 3:41 PM on July 13, 2009