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Microwave Radiation?

  1. Mar 12, 2009 #1
    Can standing in front of a microwave actually cause you harm?
     
  2. jcsd
  3. Mar 12, 2009 #2

    mathman

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    Microwave ovens are designed so that no radiation is emitted. So unless the oven is defective you won't be harmed.
     
  4. Mar 12, 2009 #3

    jambaugh

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    Not from the microwave. Microwaves are radio waves essentially. It is called "radiation" because it radiates outward from the source. Sunlight is "solar radiation" for example as is the light coming from your lamps. Now you'll hear fantastic claims (usually backed by lawyers trying to sue cell phone companies) that the microwaves from cell phones may be dangerous but the claimed "statistically significant" levels of brain tumors in cell phone users is so close to those of non-users that a.) I wouldn't worry about it and b.) I suspect an error in the statistical reasoning. (If you do enough studies on a random variable you will get variations enough that one will show a "stastically significant" trend of whatever you choose as a premise. If you want to evaluate statistical significance for repeated studies you must update the level of significance to take this into account.)

    What is dangerous is specifically ionizing radiation which can come in the form of electromagnetic radiation or high-energy particle radiation. Ionizing electromagnetic radiation starts with ultraviolet on up through x-rays and gamma rays. Below these in frequency are the visible spectrum, then infrared and then below that microwaves and then lower frequency radio bands such as UHF,VHF, HF (shortwave & AM commercial broadcasts) on down to LF and VLF and ULF which covers the 60Hz e-m noise from your AC power lines and such.

    In the ionizing particle spectrum you have beta radiation (fast electrons) and alpha radiation (fast He nuclei). You can also have neutron radiation which is not so bad itself but tends to make whatever it hits radioactive. The three types alpha, beta, and gamma all come from radioactive isotopes hence their letter classification which was coined when radioactivity was investigated.

    All this having been said, if you are standing in front of a microwave, there is a "statistically significant" chance it may be because you are waiting for some junk food to heat up which itself may be harmful. ;-)
     
  5. Mar 12, 2009 #4
    I once saw a sign posted by a microwave oven in a hotel which stated(roughly):

    "If you wear a pacemaker, please stay at least 3-feet away during oven operation"

    That's what it said, I don't know if there is any scientific data to support the warning.
     
  6. Mar 12, 2009 #5

    Integral

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    Such warnings are of the "better safe then sorry" variety. The integrity of the RF screens cannot be guaranteed under conditions such as a hotel room where you have no way of knowing what the previous guests did to it.
     
  7. Mar 13, 2009 #6
    F.Y.I my understanding of what is heating things up in a microwave is the "dipole moment", from a magnetron tube. This as explained above is very different from X-rays, etc. X-rays are more of a high energy photon.

    The microwave ovens rapidly fluctuating magnetic field causes "polar" molecules to vibrate in this field. This is what causes their heat. Water is a very "polar" molecule and vibrates/heats well. Oils are usually not so "polar" and dont vibrate/heat as well. Fortunately most foods have a high water content.

    "polar" means polarized. One side/area of the molecule more "electronegetive" than another.

    Hopefully others will elaborate more on this. I hope it was helpful.
     
    Last edited: Mar 13, 2009
  8. Mar 13, 2009 #7

    mgb_phys

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    It's not the microwaves I would be concerned about but RF emmission from the microwave generator. Some older pacemakers had an external wire that can act as an antenne - especially if they have just been fitted it lets the doctors tune them to the patient heart before they are fixed permanently.

    At microwave frequencies (2.4Ghz) any leakage is going to cook you before it poses an electrical problem for a metal cased surgical embedded pacemaker.
     
  9. Mar 13, 2009 #8

    alxm

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    You're exposed to 2.4GHz radiation all the time from wi-fi and other sources, so obviously 'any' leakage is not going to cook you. And it wouldn't be the GHzes as much as the Watts that did.

    It's true it is not going to hurt a pacemaker, but because they're shielded against this. Old, non-shielded pacemakers were vulnerable to RF from many sources.
     
  10. Mar 13, 2009 #9

    f95toli

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    Note also that many pacemakers are sensitive to magnetic fields (including dc-fields), so any piece of equipment that contains a "strong" magnet of some sort (permanent- of electro-) should have a warning sign on it.
    Note that the "better-safe-than-sorry" applies here as well meaning the fields are still quite weak; where I work there are large ares where no one with a pacemaker is allowed to entet but the stray fields in those areas are e.g. not strong enough to de-magnetize credit cards etc (unless you get too close to a magnet that is).

    Hence, the warning sign at the hotel might simply have been there due to the magnet in the magnetron.
     
  11. Mar 13, 2009 #10
    Many yars ago, my brother was stationed at a Nike missile site and radar station on Sandy Hook, New Jersey, opposite New York City. Once in a while they pointed the radar dish at birds in trees 1/2 mile (his words) away to make them fly away. Microwave radiation is non-ionizing radiation, because unlike radioactivity or particle beams, there is no ionizing radiation that can break biological molecular bonds in tissue.

    Standing in front of a high power X-band radar antenna is very harmful. You can be cooked from the inside out. When low power microwaves are applied by a physician, it is called microwave diathermy treatment. It essentially shakes the molecules in your body and heats them up (hyperthemia). The recently developed military "Pain Ray" Directed Energy Weapon (microwave gun) is designed for crowd control, and can be harmful but non lethal. Household microwave ovens (about 1000 watts) that have the interlocks properly working when the oven door is opened are very safe, however. If you have a pacemaker, follow the directions provided by the manufacturer. Commercial microwave ovens are higher power and can be more dangerous.
     
    Last edited: Mar 13, 2009
  12. Mar 13, 2009 #11

    mgb_phys

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    My point was that to have enough watts to affect the pacemaker electrically you are already going to be cooked!
    Stand in front of a 20Kw s-band search radar and you could affect the pacemaker eventualyl but it will be the least of your worries.

    The concern is probably the lower frequency radio field form the microwave tube driver. Even an unsheilded pacemaker is quite well sheilded inside you.
     
  13. Jul 4, 2009 #12
    I am a new member. Would I be out of order introducing a question on microwave detection sensors into this thread?
     
  14. Jul 4, 2009 #13

    negitron

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    Minor nitpick: designing an oven so that NO leakage occurs is physically impossible. There are, however, standards set by the FDA which set the maximum permissible leakage to a field strength of 5 mW/cm^2 as measured 5 cm from any outer surface of the appliance. Most new ovens do better than this by nearly an order of magnitude. Old and especially misused/poorly maintained ovens can do significantly worse.
     
  15. Jul 4, 2009 #14
    My mother has had a pacemaker for 19 years and has never given up using a microwave. She can't have an MRI on account of the pacemaker though.

    Some years ago a summer intern worked with me. She had had a pacemaker since she was very young. We could pick up her pacemaker pulses with an oscilloscope from over three feet away. In fact it was difficult for her to use an oscilloscope without picking up the pulses.
     
  16. Jul 5, 2009 #15
    Interesting, tell me more about this oscilloscope.
     
  17. Jul 5, 2009 #16
    There is some leakage of microwave energy from the oven. Some ovens will even trigger an automobile speed radar detector held near the door (I've seen it happen even with a cup of water in the oven to absorb some of the energy--although admittedly this was many years ago). There is not really any definitive study showing that low-level microwave energy is harmful, or is not harmful. Low-level (where heating is negligible) microwaves certainly don't directly break covalent bonds. I've wondered, though, whether they can cause problems through other mechanisms: altering the already very short lifetimes of extremely low-energy ionic bonds (bonds made in local temporary cold spots), altering reaction rates through polarization (big biomolecules line up in strong fields, making them behave a little differently together), increasing electrolysis rates, and causing protein damage or misfolding or just misbehavior through resonance (some structures on a protein might happen to vibrate at the same frequency as the microwaves, allowing them to absorb energy over a time without losing it).
     
  18. Jul 5, 2009 #17
    So, would I be safe in saying that standing in front of a microwave causes you no harm, as long as the microwave is fully operational with no damage.

    Which leads me to ask the question, "What kind of damage could a microwave cause to a person, if the microwave was faulty in one way or another?"
     
  19. Jul 5, 2009 #18

    DaveC426913

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    Just start a new thread.
     
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