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How do Fires Spread?

Transmission of Heat

The transfer of heat from one point or object to another is a basic concept in the understanding of fire. Heat can be transferred from one body to another by three mechanisms – conduction, convection, and radiation.

Conduction

Conduction is the transfer of heat through a solid or fluid. When a piece of metal rod is heated at one end with a flame, the heat travels  throughout the rod.

Some materials, such as metal shutters and ducting, can absorb heat and transmit it to the next room, where it can set fire to combustible
items that are in contact with the heated material.

Convection

Convection is the transfer of heat energy by the movement of fluids (liquids or gases). If you hold your hand over a flame, you can feel the heat even though your hand is not in contact with the flame. The heat is transferred to your hand by convection

Fire spread by convection is the most dangerous and causes the largest number of injuries and deaths. When fires start in enclosed spaces such as buildings, the smoke rising from the fire gets trapped by the ceiling and then spreads in all directions to form an ever-deepening layer over the entire room space.

The smoke will pass through any holes or gaps in the walls, ceiling, and floor into other parts of the building. The heat from the fire gets trapped in the building and the temperature rises.

Radiation

Thermal radiation is the heat transfer by way of electromagnetic waves. If you hold your hand near the side of a small fire, you would also be ab le to feel head. The heat reaches your hand by radiation. Radiation does not require an intervening medium. All warm objects radiate heat. The best example if the sun.

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heat transfer

Radiation is the dominant heat transfer mechanism for most exposure fires (fires ignited in material that is remote from the fire origin). In large fires, it is possible for the radiated heat to ignite material some distance away.

Conclusion

For more information on fire chemistry and fire spread you can attend one of our fire extinguisher courses.

If you need training or advice on fire safety in your workplace give us a call on 1300 990 336 or email us at info@intrinsicsafety.com.au to start the conversation.

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