Difference between flash point and ignition temperature

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Even if they both sound very similar, there is a clear difference between the flash point and the ignition temperature. You should be aware of this difference for chemistry lessons, but also for storing the relevant substances.

You should know the flash point of a liquid before storing it.
You should know the flash point of a liquid before storing it.

This is to be understood by the term "flash point"

  • If a liquid is given a flash point, it does not generally mean that a fire will start immediately at that temperature.
  • It is correct: At this temperature or higher, a gas mixture can form above the liquid, which can easily be ignited as soon as there is a corresponding ignition source. Single sparks can be sufficient for this.
  • This is especially important when you work with these liquids, which can also be the case in the hobby area. For example, it is useful for turpentine when you want to dilute oil paints.
  • The flash point here is 33 ° C. This means that from this temperature on, one match is enough to ignite the gas around and above the turpentine. The general recommendation for storage is: The ambient temperature should be at least 15 ° C below the ignition temperature.
  • Important: Ignition below this exact point is not possible.
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The term "ignition temperature" makes the difference between the two statements clear

  • Ignition temperature indicates what this information means: Above this temperature, a substance can ignite by itself, i.e. without an additional ignition source.
  • The ignition temperature is in the chemistry generally most often referred to as ignition temperature or, somewhat less often, as self-ignition temperature, which makes the difference between the two figures even clearer.
  • To stay with the example of turpentine: Here it needs at least 255 ° C so that it can ignite without an external source of ignition. But that doesn't mean that nothing can happen between 33 ° C and 255 ° C. If the gases spread through the room, a small short circuit can be enough to ignite the gas.

By the way: The temperature difference between the flash point and the ignition temperature can also be significantly lower or higher. That depends on the substance.

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