Page 7 - LEARN NOT TO BURN MAGAZINE by STEM XII-Group 5

METHODS OF HEAT TRANSMISSION

AND FIRE SPREAD

Once a fire has started it can spread by four different methods:

D
irect burning

The simplest method of fire spread, where a flame front moves
along or through the burning material. For example, if the corner of a piece

of paper catches fire, the flame front will spread across the paper.
C

onvection
The principle that hot air rises and cold air sinks. Hot gases

generated by the fire rise straight up from the fire:Inside a building these
hot gases will hit the ceiling and then spread out to form a layer underneath

the ceiling. When these hot gases touch any combustible material (such as a
wooden curtain pole) they may heat that material up sufficiently so that it

bursts into flame.Outdoors these convection currents will contain burning
embers that are carried on the currents until the air cools and the embers

are dropped to the ground. This is a common way for forest fires to travel
and jump over obstacles (such as roads).

C
onduction

The principle that heat can be transmitted through solid materials.
Some metals, in particular, conduct heat very efficiently (e.g. copper). Any

pipes, wires, ducts or services running from room to room can act as
conduits for heat and spread the fire.

R
adiation

Heat energy can be radiated through air in the form of infrared
heat waves, which travel in straight lines (just like light) and can pass

through transparent surfaces (such as glass). Radiant heat generated by a
fire shines onto nearby surfaces and is absorbed. If the material heats up

sufficiently it can burst into flames.

5 Learn Not to Burn DECEMBER 2020