Radiative heat increases according to surface area.

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NOTES

The amount of heat radiated by a body increases in proportion to the surface area of the body.

Take these 3 fires (we will assume they are approximately conical in shape):

• The first is 1m wide at the base and 1m high;
• The second is 2m wide at the base and 2m high;
• The third is 4m wide at the base and 4m high.

Q: How does the radiated heat compare?- Click animation

A: 1st produces 1 unit of heat, 2nd produces 8.4 units of heat, and 3rd produces 67 units of heat - this is due to the increasing surface area, as fires grow radiant heat becomes very important in driving fire spread, particularly to remote exposures.