If a fire spreads by radiation what does it mean?

A fire spreads by transferring heat energy in three ways: Radiation, Convection, and Conduction.

Radiation refers to the emission of energy in rays or waves. Heat moves through space as energy waves. It is the type of heat one feels when sitting in front of a fireplace or around a campfire.

It travels in straight lines at the speed of light. This is the reason that when facing the fire, only the front is warmed. The backside is not warmed until the person turns around.

In this form of heat transfer, the heat does not travel through a material like conduction nor does it flow through air or liquid currents like convection. It simply travels in rays similar to sun rays, in straight lines away from the fire.

The heat from the rays can be absorbed by combustible materials which cause them to heat up and perhaps ignite.

The main principle of radiation is: the closer the material is to the fire the more radiated heat it will receive.

Certain materials such as concrete do not allow radiation to pass through them. Therefore materials like concrete are good construction materials to help prevent fires spreading through houses or to nearby buildings. Radiated heat from a burning building can in some circumstances give rise to fire in a nearby building.

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