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How do fires start in ovens?

  1. Jan 10, 2005 #1

    T@P

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    an ordinary paper fire is 451 degrees farenheit ( :biggrin: ), and the standard oven temp is 350. how do fires start in ovens? also where does the energy come for the first spark which starts the flame?
     
  2. jcsd
  3. Jan 10, 2005 #2
    where did spark come from?? battery... for some oven, others? your power outlet...
    how do fires start in oven?? didn't you just answer your question.... SPARK.....
     
  4. Jan 10, 2005 #3
    oh, sorry, it seems like i misunderstand the first part of your question, you are asking why would paper get on fire in oven, right?
    oven does not only generate heat, it also generate RADIATION, the air in the oven is 300 degree doesn't mean EVERYTHING in the oven is @ 300degree , oven doesn't heat up the air directly, is the radiation heat stuff up..... the radiaion heat the turkey, also the plate, the inside of the oven, and these stuff transfer there energy to air.... so..... the stuff in oven is hotter than the air in oven.... understand??
     
  5. Jan 10, 2005 #4

    Chronos

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    Where you get that oven? Mine goes over 500 degrees. The key is ignition temperature. Fat will ignite at about 475 degrees F. Of course you won't find may recipes that call for cooking at that high a temperature. Oven fires do, however, occur at much lower temperatures. One mechanism is steam bubbles. A steam bubble gets trapped, pressurizes and explosively releases 'spitting' fat [which rises to the surface] onto the heating element. Overflow is another cause of oven fires - dish is too small to contain the heated liquid when it expands.
     
  6. Jan 10, 2005 #5
    how would overflow start a fire? i mean if everything in the oven is at 350 then where does the temp build? and not to sound like i didnt hear about the radiation... but isnt that more microwavish? standard (old) ovens just produce heat in some conventioinal way...
     
  7. Jan 10, 2005 #6

    NoTime

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    The heating coils turn red in an oven.
    This translates to a temperature.
    Don't feel like looking it up, but probably somewhere between 1000 and 2000 degrees.
    More than hot enough to set something, like splashing grease, on fire.
     
  8. Jan 10, 2005 #7

    russ_watters

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    Yeah - with a red-hot heating element or an open flame.
     
  9. Jan 11, 2005 #8

    Chronos

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    In fairness to janzizka, the set temperature of a conventional [gas or electrically heated] oven is merely an approximation of the average temperature in the cooking chamber. The heating element is, of course, much hotter than the non heating elements of the oven. It becomes more readily apparent when you take into consideration the inverse square law. Note: Convection ovens do a much nicer job of cooking most foods [just not T-bone steaks, I like mine charred on the outside and red in the middle]. The temperature gradient is far lower.
     
    Last edited: Jan 11, 2005
  10. Jan 11, 2005 #9

    DaveC426913

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    "...somewhere between 1000 and 2000 degrees..."

    I would be quite surprised if the temp of the coil in an oven reached that kind of temp. Don't forget, the coils on top of the stove and in your hair dryer glow red too. 1000-2000 degrees??
     
  11. Jan 11, 2005 #10

    T@P

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    but dave for something to "glow red", the substance that glows red must achieve some temperature, and im sure that a thick metal would have a harder gatting that glow then an incredibly thin wire as in a blow dryer. but thanks i get the idea about ovens
     
  12. Jan 11, 2005 #11
    The diffrence between the hair dryer and the oven is that it takes much more energy to get the oven up to the red hot area then the hair dryer. In short the Oven draws more current to obtain higher temps. That is all.
     
  13. Jan 11, 2005 #12

    russ_watters

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    THIS is the best I could do with a little google. A candle glows orange at 1900K - I'd think a red heating element is a little, but not much below that. A gas burner is significantly hotter.
    More energy because its has more mass and surface area: if the color is the same, the temperature is the same.
     
  14. Jan 11, 2005 #13

    Integral

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    Here is another color to temp scale

    This sort of thing is pretty crude, but clearly the orange glow of a hot oven element corresponds to about 1000C.

    An Optical pyrometer is a very precise "thermometer" which measures temperature by comparison to a heated element. This of course only works on objects hot enough to glow in the visible range.

    To get an exact temperature one needs to know the emissivity of the glowing object. Since emissivity is always less then 1, your actual temperature will be HIGHER then that which corresponds to the color.
     
  15. Jan 11, 2005 #14

    DaveC426913

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    "but dave for something to "glow red", the substance that glows red must achieve some temperature, and im sure that a thick metal would have a harder gatting that glow then an incredibly thin wire as in a blow dryer. but thanks i get the idea about ovens"


    Nono. All I'm saying is, I find it hard to believe that these devices would be built that could hit temperatures of 1000 - 2000 degrees. I mention the blow dryer because it comes within inches of your face.

    Surely that hot a temp would be too dangerous in the hands of amateurs.
     
  16. Jan 11, 2005 #15

    Integral

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    Regardless of what you think ought to be, the color does not lie.

    Consider the amount of energy which must be transfered to the rapidly moving air in a blow drier? Consider the temperature [itex]\Delta T [/itex] and the time [itex] \Delta t [/itex] clearly the element temperature must be quite high to get the air as hot as it does in such a short time.
     
    Last edited: Jan 11, 2005
  17. Jan 11, 2005 #16

    Janus

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    Don't confuse temperature with heat content. The amount of heat contained in a hair dryer element is a lot less than that in an oven element. These elements are also encased such that you can't get close enough to them for enough heat to be transfered to burn you.
     
  18. Jan 11, 2005 #17

    Chronos

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    For the record [temperatures in fahrenheit]

    1000 Dark Red
    1200 Blood Red
    1375 Low Cherry Red
    1425 Medium Cherry Red
    1500 Full Cherry Red
    1550 Bright Red
    1650 Salmon
    1725 Orange
    1825 Lemon
     
    Last edited: Jan 11, 2005
  19. Jan 11, 2005 #18

    brewnog

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    These aren't colours, they're food!
     
  20. Jan 11, 2005 #19

    T@P

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    wow that went right over my head. but your probably right so :)
     
  21. Jan 12, 2005 #20

    DaveC426913

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    So that puts an oven at about 1550?
     
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