An important aspect of fire control is the need to prevent it from spreading from one room into another (particularly escape routes). Heat is transmitted and fire spreads by:
- Conduction
- Convection
- Radiation
- Direct Contact
CONDUCTION:
Conduction explains the change in warm within a strong material from warmer to chilly parts. Different materials perform warm at different rates:
Metals perform warm well, e.g. once warm gets to a metal architectural member it will be performed quickly along it; and stones and tangible will perform warm at a much low cost.
If a metal joist or line goes through a walls or floor it may become the road by which sufficient warm can pass to start fire in nearby rooms. In the same way a non-combustible walls or roof may become so hot that warm will be performed through it even though it does not get rid of itself.
CONVECTION:
Hot air rises in currents causing the build-up of hot gases under the ceiling. It also passes easily through small gaps. The air in a burning room can exceed 1000°C. Air at this temperature will quickly allow a fire to spread from one room to another, passing through gaps around ill-fitting doors or where cables /pipes pass through ceilings, etc. It is estimated that convection accounts for approximately 75% of the heat spread of the majority of fires.
RADIATION:
Heat can be radiated through the air causing heating of materials at a distance from the fire. One of the reasons why a fire develops so quickly in an enclosed space is that radiated heat causes other parts of the room to heat rapidly. Materials that are not in contact with flames will reach their flash point (i.e. the temperature at which they give off sufficient gas/ vapour to be ignited).
DIRECT CONTACT:
In their early stages most fires spread almost entirely by direct burning between a flame and a combustible material, which heats up and eventually ignites. As they get hotter the materials liberate flammable vapours and these also ignite. These materials then transfer heat to other materials by radiation, conduction and convection as well as by direct contact with the flame.
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