# Demonstrating Hidden a Danger Microwave

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The heating of water in the microwave can actually be dangerous? Watch the video and see the potential hazzards involved with this everyday activity. Water alone should never be heated in a microwave. Watch and find out why.

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## 16 Discussions

It depends how fast you turntable turns and how big the container is.
Gas will condense out of a saturated liquid if there are points of low pressure. Soundwaves travelling through a liquid do this since sound is just periods of high and low pressure. The low pressure allows gas to condense out easier. If your microwave turntable turns fast enough to cause microscopic eddies around the sides of the container (liquids dont tend to turn as a whole if you turn them, the sides will as they stick to the cup, but the centre wont move much), then it will boil. The centre of eddies are lower pressure than the surrounding fluid, just like tornados.
BUT, the smaller the cup in the centre of the turntable the less speed the sides are moving at, the less chance of eddies forming due to the different speeds in the liquid. Honestly most microwaves probably don't turn fast enough to have any effect. So.. yes in all likelihood it will happen.

The reason water superheats has little to do with the microwave oven you have, and more the container it is boiled it.
A ceramic cup, or pyrex glass, when new are near perfectly smooth down to the atomic level. Most water is to all extents "pure", unless you live a a very hard (chalk flakes in the water hard) water area. As a microwave excites the water in the cup as a whole relatively evenly, not like a pan where only the bottom of the pan conducts heat to the water, causing water to "convect" (hot water rising as it becomes less dense, making the water circulate from to top to bottom), the water can receive more energy than it needs to boil into a gas.
This is because for a bubble to form it needs a point to concentrate on. This can be a pressure wave through the liquid, like that caused when water circulates. You can test this yourself, get 2 bottles of larger and a friend. After opening your friend's larger, tap the lip of the open bottle downwards and watch as the gas in the larger is released by the soundwave travelling through the glass into the larger, and he calls you a dick for covering him in beer.
Another way gas bubbles form is on scratches and imperfections in the container walls. This is why bubbles form on the inside of open lemonade bottles, a scratch on the bottle wall allows CO2 molecules to condense (long boring explanation why, basically static electricity on a very small scale). Once a bubble forms it causes pressure changes in the surrounding solvent which then allows other bubbles to form.
In a new cup there are no microscopic scratches yet, and as the water is heated from the centre outwards, no convection currents form. So the still water can superheat. Which then explosively boils the moment you move the cup/put a spoon/milk into it.
If you have a new powerful microwave and a new cup,put a wooden chopstick in it or stir it first before heating up your tea or coffee.

"Superheated" water has been an issue in Australia for over 10 years--particularly in high-power ovens (> 2400W) where the water can exceed boiling, but the glass is still cool to the touch.

Pyrex and glass are the worst offenders. As cited elsewhere porous materials are safer, and water purity plays a major role.

Drop a sugar cube in it....JUST LIKE MYTHBUSTERS! (they used distilled water btw)

The water in question is likely distilled water (or water with very very little to no impurities in it) Water boils due to the impurities in it (part of the reason to add salt to a pot of water you want to boil, the other is to raise the boiling point so when you add food it doesn't take as long to get the water and food simmering or boiling again) So it you take distilled water, raise its temperture to the boiling level and then add an impurity( salt, suger, whatever is naturally on the spoon or whatever he added to the bottom of the spoon) you will get a flash boiling which will tend to cause very hot water to splash and shoot out of the container it was heated in.

He isn't even wearing gloves! Jeez he's just asking for it!

No no no... The minerals in tap water cause the water to boil (like the fork). Only pure water has a chance of exploding like this.

4 replies

Actually I have always heard the opposite, but I may be wrong. But the impurities in the coffee and water create a greater surface tension by the water molecules attaching to the impurities strengthening the surface tension. Since pure H2O has no impurities, the surface tension is weaker. Also some tidbits... soapy water has little to no surface tension and is also used in a cheap way to get rid of flees by rigging up a lamp over a bowl of soapy water. Pure H20 conducts no electricity.

Think of it this way. Why does adding salt to water make it boil faster. ;) I recall a mythbusters ep where they do this very thing.

tap water CAN do this.... part of the "trick" is using the glass glasses... 99.8% of ceramic mugs have tiny cracks in the glaze, in the bottom of the mugs. these cracks for a point where bubbles form... sort of like a seed crystal. and once the bubbles start, the risk of exploding water goes away. The danger is in the "hot enough to boil" water, that has not had a chance to divulge it's entrapped air. Once disturbed.. the water, which is at that point supersaturated with gas, unleashes a majority of the gas all at once, hence the explosion. good information to know, but not really sure it qualifies as an "instructable"

actually a cup of milk coffee done this to me once O.o i heated it in the microwave 8after about 3 other cups for others) and when u put in the spoon to stir it out jumped the drink :D there was only a little bit left in the bottom :( it only happened to mine tho :S