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Fire Spread

A fire can be confined in the area in which it started if it is attacked quickly and efficiently. If allowed to burn unchecked it can generate large amounts of heat which will travel away from the fire area igniting additional fires wherever fuel and oxygen are available. And both are in plentiful supply in vessels.

Heat is transferred in one of three ways:

Conduction

Where the heat is transferred through a solid body. For example on a stove heat is transferred through the saucepan to its contents. Metal is an excellent conductor of heat and a fire can be checked by skilfully using large amounts of water in the form of spray to retard the conduction. A water spray is more efficient than a solid jet as it will absorb the heat more quickly, also there is less water used, which results in less run-off into the bilges reducing a potential stability problem.

Convection

Which is the transfer of heat through the motion of heated matter, that is, through the motion of smoke, hot air, heated gases produced by the fire, and flying embers. When it is confined (as within a ship) the convected heat moves in predictable patterns. The fire produces lighter-than-air gases that rise toward he high parts of the vessel. This is replaced by cool air which in turn is heated and the hot air and gases rise from the fire and so doing cool and drop down to be re-heated again. This is the convection cycle. To break this cycle on a ship, where it is not possible to easily cut a hole in an upper deck and release the gases to atmosphere, is to confine the fire to one area by closing off all doors and hatchways, where not in use, to prevent the spread through the alleyways.

Vents are a common source of fire spread, both by convection and by any dust or grease catching alight. It is important that any vent closures or dampers are effective, tested regularly and that all crew members are familiar with their operation and location. Do not overlook them when doing fire drills.

Radiation

Where the heat is transferred through a space without the intervention of solid material. A example of radiation is an electric heater. Radiated heat extends the fire by heating combustible substances in its path causing them to produce vapour, and then igniting the vapour. Intense radiated heat makes a fire extremely difficult to approach and protective clothing must be worn.

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