Is microwave cooking safe?


by Si14
Tags: cooking, microwave, safe
Si14
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#1
Oct29-09, 01:55 AM
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Hi everyone:

Have you ever heard anything about the effects of the microwave on body?

..
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Pythagorean
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Oct29-09, 02:50 AM
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I don't know about the food; I trust it in general, but I can tell you something about frustrated total internal reflection:

Under "ordinary conditions" it is true that the creation of an evanescent wave does not affect the conservation of energy, i.e. the evanescent wave transmits zero net energy. However, if a third medium with a higher refractive index than the second medium is placed within less than several wavelengths distance from the interface between the first medium and the second medium, the evanescent wave will be different from the one under "ordinary conditions" and it will pass energy across the second into the third medium.
When teaching us about frustrated total internal refraction, my optics teacher stated that he never got his face close to the microwave to check his food while it was running anymore.
Moonbear
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Oct29-09, 08:57 AM
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Quote Quote by Si14 View Post
Hi everyone:

Have you ever heard anything about the effects of the microwave on body?

..
Yeah, it's bad to microwave your body. Did you have a more specific question? Are you asking about eating the foods cooked in a microwave, or the shielding on microwave ovens, or something else entirely?

Si14
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#4
Oct29-09, 12:22 PM
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Is microwave cooking safe?


Quote Quote by Pythagorean View Post
I don't know about the food; I trust it in general, but I can tell you something about frustrated total internal reflection:



When teaching us about frustrated total internal refraction, my optics teacher stated that he never got his face close to the microwave to check his food while it was running anymore.
Thank you. but I didn't understand, what does it mean by 1st, 2nd and 3rd medium? Is the 3rd medium food? and the 2nd medium air? and 1st is the medium where microwave generated?
Am I correct?


Quote Quote by Moonbear View Post
Yeah, it's bad to microwave your body. Did you have a more specific question? Are you asking about eating the foods cooked in a microwave, or the shielding on microwave ovens, or something else entirely?
Thank you. Of course they have some standards for radiation dosage emitted from microwave ovens. And they can test them simply by measuring the radiation and power around and far away from ovens, BUT, how about the food which is prepared by this method? I think I read some where that some Russian groups are working on the effects of microwave cooked foods on body? Have you heard about that?
D H
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Oct29-09, 12:35 PM
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Quote Quote by Si14 View Post
Of course they have some standards for radiation dosage emitted from microwave ovens.
Of course they don't, because microwave ovens do not emit *any* ionizing radiation.
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Oct29-09, 12:50 PM
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Quote Quote by D H View Post
Of course they don't, because microwave ovens do not emit *any* ionizing radiation.
wait a minute, as far as I know, these ovens are working with high frequency waves. at those frequencies, if you stand near them, they will penetrate to your body and damage your tissues. but they damp in the air, so standing far away form them can reduce this damage. in ovens, they shield the device, that means it will absorb the waves and keeps them inside. so it minimizes the radiation dose outside the shield. But what is Ionizing radiation? you mean after bombarding the food by these waves, they will be ionized (for example hydrogen or carbon) and will radiate also?
D H
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Oct29-09, 03:01 PM
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Quote Quote by Si14 View Post
wait a minute, as far as I know, these ovens are working with high frequency waves. ... so it minimizes the radiation dose outside the shield. But what is Ionizing radiation? you mean after bombarding the food by these waves, they will be ionized (for example hydrogen or carbon) and will radiate also?
Your use of words such as "high frequency waves" and "radiation dose" makes me think that you are thinking of things like x-rays and gammas given off by radioactive elements such as uranium, radium, etc. That is not what goes on in a microwave oven. The electromagnetic radiation in a microwave is of a much lower frequency than the electromagnetic radiation that comes out of the light bulbs in your house. It is a very low frequency compared to the radiation you are familiar with. It is an extremely low frequency compared to the damaging ionizing radiation associated with radioactive elements. The only ones who think of microwave frequencies as being high frequencies are radio wavelength physicists and engineers.

The problem with microwaves isn't that they are radioactive. The problem is that the very feature that makes microwaves able to cook foods placed inside the oven makes microwaves able to heat things up outside the oven if the oven is not properly shielded.
Pythagorean
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Oct29-09, 03:41 PM
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Quote Quote by Si14 View Post
Thank you. but I didn't understand, what does it mean by 1st, 2nd and 3rd medium? Is the 3rd medium food? and the 2nd medium air? and 1st is the medium where microwave generated?
Am I correct?
I was referring to when you get your face close to an operating microwave. There's a glass wall between you and the microwaves, so we normally assume total internal reflection: that is, the microwaves are bouncing around inside the microwave, and staying inside there.

BUT, frustrated total internal reflection happens when you get your face close to the microwave. The waves will transmit through the 2nd medium (the air) to the third medium (your face) because the distance between your face and the microwave is on the order of microwaves (meters to millimeters). I don't know if enough power actually makes it through to be concerned about, but I don't NEED to put my face there, so I won't test it, personally.
waht
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Oct29-09, 03:42 PM
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Quote Quote by D H View Post
The only ones who think of microwave frequencies as being high frequencies are radio wavelength physicists and engineers.
Yes that's true. Microwaves are not ionizing - the standard designation does not reflect the whole electromagnetic spectrum.

Pythagorean
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Oct29-09, 03:45 PM
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Quote Quote by waht View Post
Yes that's true. Microwaves are not ionizing - the standard designation does not reflect the whole electromagnetic spectrum.

hey, what is voice frequency doing in there? Isn't voice frequency a pressure wave?
chroot
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Oct29-09, 04:03 PM
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Quote Quote by Pythagorean View Post
I was referring to when you get your face close to an operating microwave. There's a glass wall between you and the microwaves, so we normally assume total internal reflection: that is, the microwaves are bouncing around inside the microwave, and staying inside there.
I believe you are spreading misinformation. Your thoughts on FTIR are accurate, but you are applying the concept indiscriminately. The glass is wholly irrelevant to the propagation of the microwaves, or the safety of the people who use the oven.

The microwave door includes a fine mesh of metal, behind the glass. The holes in the mesh are large enough for you to be able to see your food (high-frequency visible photons pass right through the holes), but too small for the low-frequency microwave photons to escape. The microwaves have wavelengths on the order of 12 centimeters, and the holes are much, much smaller. The mesh is essentially a solid piece of metal, as far as the 12 cm radiation is concerned. The oven cavity is completed contained by this conductive metal, forming a Faraday cage. As you are aware, conductors block EM radiation.

You don't need to guess how much energy escapes microwaves -- it's easily measurable, and is certainly measured by the engineers who design it and qualify it.

Your microwave oven is not unsafe, even if you put your face near it. Relax.

- Warren
Si14
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Oct29-09, 04:34 PM
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D H and others:
Thank you for your time. Helpful answers.
Quote Quote by D H View Post
The only ones who think of microwave frequencies as being high frequencies are radio wavelength physicists and engineers.
.
This is applied to me. I am electrical eng. )

Quote Quote by D H View Post
The electromagnetic radiation in a microwave is of a much lower frequency than the electromagnetic radiation that comes out of the light bulbs in your house.
exactly!

Quote Quote by D H View Post
The problem with microwaves isn't that they are radioactive. The problem is that the very feature that makes microwaves able to cook foods placed inside the oven makes microwaves able to heat things up outside the oven if the oven is not properly shielded.
That's what I meant. and I think that they can make good shields for that. Since it looks simple, for shielding each frequency (at microwave ovens, I think they are around 2.5GHz), a good absorber needs to be fabricated.

The problem is with the high power at this frequency, I assume.

But my question is about the FOOD which is cooked with microwave oven.

Do you know what happens to them?
Si14
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Oct29-09, 04:47 PM
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Thank you chroot and Pythagorean:

Quote Quote by chroot View Post
The oven cavity is completed contained by this conductive metal, forming a Faraday cage. As you are aware, conductors block EM radiation.
So, can we have evanescence waves (as Pythagorean mentioned)inside a metallic cavity? I mean there's no loss inside the cavity and if we assume that the cavity is designed for the operating frequency of the power generator (like a resonating cage), there should be a standing wave. Right?
Pythagorean
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Oct29-09, 07:06 PM
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Quote Quote by chroot View Post
I believe you are spreading misinformation. Your thoughts on FTIR are accurate, but you are applying the concept indiscriminately. The glass is wholly irrelevant to the propagation of the microwaves, or the safety of the people who use the oven.

The microwave door includes a fine mesh of metal, behind the glass. The holes in the mesh are large enough for you to be able to see your food (high-frequency visible photons pass right through the holes), but too small for the low-frequency microwave photons to escape. The microwaves have wavelengths on the order of 12 centimeters, and the holes are much, much smaller. The mesh is essentially a solid piece of metal, as far as the 12 cm radiation is concerned. The oven cavity is completed contained by this conductive metal, forming a Faraday cage. As you are aware, conductors block EM radiation.

You don't need to guess how much energy escapes microwaves -- it's easily measurable, and is certainly measured by the engineers who design it and qualify it.

Your microwave oven is not unsafe, even if you put your face near it. Relax.

- Warren
So FTIR doesn't apply to conducting surfaces (remembering that they're not perfect conductors so there's some penetration depth)? It was my optics professor who brought up the concern, but he's a physicist, not an engineer.

You're right though, I've never seen a microwave without the mesh on the glass; I should have considered that.
Pythagorean
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Oct29-09, 07:23 PM
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also, I do have a microwave meter, and i DO pickup over 1mw/cm^2 (the needle tops out) into the front of the meter. But I haven't measured area of the front of the box. It's roughly 4x6 cm^2. This has been true for all three of the microwaves (~10 year old models) that I've measured it on.

I don't know if that's significant with regards to biology. The device I used was the TriField Meter: http://www.trifield.com/EMF_meter.htm

Also, I don't trust manufacturer claims, as I've been taught not to in my engineering courses (especially considering the economics of LEDs), so this:

You don't need to guess how much energy escapes microwaves -- it's easily measurable, and is certainly measured by the engineers who design it and qualify it.
isn't satisfying to me. But then, on the same token, I don't know how trustworthy my TriField meter is.
Moonbear
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Oct29-09, 07:24 PM
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Quote Quote by Si14 View Post
But my question is about the FOOD which is cooked with microwave oven.

Do you know what happens to them?
It gets cooked. It's fine to eat, if that's your question. Once the microwave oven is turned off, there is no more emission of the microwaves. It's not like a radioactive isotope that would contaminate something and linger.

The only potential issue is whether some foods are exposed to the microwaves long enough to kill bacteria with such a short cooking time.
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Oct29-09, 07:50 PM
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Quote Quote by Moonbear View Post
It gets cooked. It's fine to eat, if that's your question. Once the microwave oven is turned off, there is no more emission of the microwaves. It's not like a radioactive isotope that would contaminate something and linger.

The only potential issue is whether some foods are exposed to the microwaves long enough to kill bacteria with such a short cooking time.
Thank you. I somehow got the answer.
russ_watters
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Oct29-09, 08:08 PM
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Quote Quote by Pythagorean View Post
...isn't satisfying to me. But then, on the same token, I don't know how trustworthy my TriField meter is.
Though I'm not sure of the mechanism for enforcement, they are required to be tested to meet government standards on leakage:
All new microwave ovens produced for sale in the United States must meet the Food and Drug Administration/Center for Devices and Radiological Health (FDA/CDRH) performance requirements in Title 21, CFR, Part 1030.10. This requirement states that new ovens may not leak microwave radiation in excess of 1 mW cm–2 at 5 cm from the oven surface. It also states that ovens, once placed into service, may not leak microwave radiation in excess of 5 mW cm–2 at 5 cm from the oven surface. The "Procedure for Field Testing Microwave Ovens" (HEW Publication (FDA) 77-8037) is the standard method for verifying that these oven performance criteria are met.
http://www.hps.org/hpspublications/a...owaveoven.html


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