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Comment by zhte415 | Hacker News Reader

> The astronomers were flummoxed—that is, until one of the testers, during a third attempt, opened the door of a microwave oven before the magnetron was shut off by the timer. They found that although the door shuts the magnetron off, a whiff of gigahertz radiation could escape.

I assume it is miniscule level that escapes - there is no 'lock' feature on any microwave I've seen, forcing power off before door opening - but in the future I'm going to leave a microwave a rest for a second before opening the door.

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This is tangential, but if you have an old microwave that you don't mind perhaps getting a bit dirty, you can make ball lightning in the comfort of your own home. Discovered this during my "I wonder what will happen to this when I microwave it!" phase.

1) Take a tealight. Bog standard little candle.

2) Remove the metal casing. Snip the little metal foot off the bottom end of the wick. You now have a little puck of paraffin with a wick in it.

3) Place said candle in a glass tealight holder. Ikea sell 'em for a few pence.

4) Light it. Stick it in the microwave, right in the centre, without the turntable.

5) Engage. Observe with wonder as the paraffin vapour enters a plasma state and hovers in the middle of your microwave, contained by the microwaves.

I dare say this works better in some than others, and perhaps depends on the shape of the standing wave in your microwave, and I make no guarantees as to your or your microwave's safety - but it's a really neat demo, either way.

If you try this, put a glass of water inside the microwave with the candle. You don't want the microwave to run empty, and the water will keep that from happening.

As I said, old microwave you don't care about. Glass of water would likely absorb most of the energy that would otherwise be gleefully wasted on making plasma.

Even easier is to turn half a grape to plasma in a microwave: https://www.youtube.com/watch?v=0i2lhO3bSjQ

Using a high-temperature-resistant glass sphere with an opening on one end can protect the roof of the microwave oven if it doesn't have a standing wave that would keep the plasma localized. Most glass probably can't withstand prolonged heating from the plasma, so don't run it for long.

No, it's full power, for the full duration that it takes for the door to swing from fully closed to engaging the switch that kills the microwave.

But exposure to a fraction of a second of microwaves is not dangerous, to the best of my knowledge. It just annoys astronomers and keeps microwave designers up at night.

Microwave ovens can and often do leak quite a bit of radiation during operation. If you want proof, set up your wireless router near the microwave, turn the microwave on and watch as your wireless signal just vanishes.

Considering they lasted "a few milliseconds", I would not be too concerned.

I'm not too concerned because it is microwave radiation, but a few milliseconds is more than enough for lethal doses of radiation.

It is not ionizing radiation, the primary hazard of microwave radiation is its heating effects on sensitive tissue that has poor blood circulation -- in particular it has been implicated in the development of cataracts in the eye. So to a first approximation, the few milliseconds of 1000W output is really only as hazardous as a few minutes of the typical leakage you get with the door closed (somewhere on the order of 5 mW).

By the time the door opens any appreciable amount, the microwaves will have long dissipated. It's a very short burst, so even though it's at full (and decaying) power, the total energy released is harmless.

I still would recommend stopping before opening, if only to avoid accidentally triggering the redundant failsafe switch which shorts out the power and blows the fuse.

I still would recommend stopping before opening, if only to avoid accidentally triggering the redundant failsafe switch which shorts out the power and blows the fuse.

Could you elaborate further on the design of this failsafe and what, specifically, triggers it? Do all microwave ovens have it?

It's a triply-redundant design, present in practically all ovens:

http://www.microtechfactoryservice.com/switch.html

Pretty sure your cellphone and wifi hotspot are more dangerous microwave sources than that :)

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