FIRE FIGHTING AND SAFETY ON Ship - Part two

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ref: Introduction Marine Engineering

Detection

The use of fire detectors is increasing, particularly with the tendency to reduced manning and unmanned machinery spaces. A fire, if detected quickly, can be fought and brought under control with a minimum of
damage. The main function of a fire detector is therefore to detect a fire as quickly as possible; it must also be reliable and require a minimum of attention. An important requirement is that it is not set off by any of the
normal occurrences in the protected space, that is it must be appropriately sensitive to its surroundings. Three phenomena associated with fire are used to provide alarms: these are smoke, flames and heat, The smoke detector makes use of two ionisation chambers, one open to the atmosphere and one closed (Figure 13.1). The fine particles or aerosols given off by a fire alter the resistance in the open ionisation chamber, resulting in the operation of a cold cathode gas-filled valve. The alarm sounds on the operation of the valve to give warning of a fire. Smoke detectors are used in machinery spaces, accommodation areas and cargo holds.
Flames, as opposed to smoke, are often the main result of gas and liquid fires and flame detectors are used to protect against such hazards. Flames give off ultra-violet and infra-red radiation and detectors are available to respond to either.Flame detectors are used near to fuel handling equipment in the machinery spaces and also at boiler fronts.

Smoke Detector