Why is fire so hot

A low concentration of oxygen will slow the burning right down. An example of dangerous fire behaviour that can occur in a situation where there is a low concentration of oxygen is called backdraught. This is when an enclosed fire has used up most of the oxygen and is just smouldering.

If there is a sudden influx of oxygen like someone opening a door or window , the fire will immediately explode into flame. Relative humidity: This reflects the amount of moisture in the air.

If relative humidity is low, it will contribute to the drying of fuels. If it is high, fuels will absorb moisture from the air, making ignition more difficult.

Wind: This is a major factor in determining fire spread. Wind affects the rate of oxygen supply to the burning fuel controlling combustion and it tilts the flame forward so that unburned fuel receives energy by radiation and convection at an increased speed.

Wind can also dry out the fuel. Rainfall: This also has an effect on wetting fuels, but absorption of moisture is dependent on fuel size. Fine fuels absorb moisture more quickly than coarse fuels. Lack of rain precipitation is the biggest factor affecting the drying process of fuels. Increased temperatures: These will dry out potential fuel so that there will be less preheating of fuels to reach ignition temperature. Its easily observed when heating a piece of metal:.

However, flame color is not a good indicator of temperature because heated metal ions emit colored light. In other words, impurities in a fuel can produce a colored flame without increasing its temperature. For example, borax turns flames green , while potassium chloride turns fire violet. The hottest part of a visible flame is blue, but science students are asked to use the top part of the flame for maximum heat.

Another reason to use the top of a flame is because its temperature is more consistent. More about Kevin and links to his professional work can be found at www. At the center of a very hot fire, you may see a dull orange glow or even curious dark space. This is known as blackbody radiation , and is characteristic of very high temperatures for example, it's a feature of stars.

Metals that can heat up even more progress through other colors of this type of radiation that is, toward the violet end of the visible spectrum. How to Get Colored Lighter Flames. How Do Infrared Thermometers Work? Simple Chemical Reactions in Fireworks. What Causes Atmospheric Heating?

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Share Flipboard Email. Anne Marie Helmenstine, Ph. Chemistry Expert. Helmenstine holds a Ph. She has taught science courses at the high school, college, and graduate levels. Facebook Facebook Twitter Twitter. Updated November 21, Fire is always hot, regardless of the fuel that is used. Although combustion requires activation energy ignition , the net heat released exceeds the energy required. Breaking the chemical bond between oxygen molecules absorbs energy, but forming the chemical bonds for the products carbon dioxide and water releases much more energy.