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AUTOMATIC FIRE DETECTION SYSTEMS
Automatic fire detection systems consist of normal and emergency power supplies, a fire detection control unit, fire detectors and vibrating bells.
Fire Detection Control Unit
The fire detection control unit consists of drip-proof enclosed panel containing the fire alarm signaling, trouble-alarm and power-failure alarm devices. These devices must register both a visual and an audible signal. The visible signals are lights:
A red light indicates fire or smoke. A blue light indicates trouble in the system. A white light indicates that the power is on in the system.
Fire detectors sense (and initiate a signal in response to) heat, smoke, flame or some other indication of fire. Not all types of detectors are used aboard ship - some are not practicable, and some are not necessary.
Light and Bell Signals
When fire is detected, the alarm lights stay on, the bells keep ringing until a resetting device is operated manually. A shutoff device may be used to silence the bells. However shutting off the bells will not extinguish the alarm lights. The alarm lights can be shut off only with the manual resetting device. Like the modern fire alarm boxes on land, shipboard fire alarms are noninterfering; any number of alarms can be received simultaneously. An alarm that is being received on one circuit will not prevent an alarm from being received on another circuit.
SMOKE DETECTION SYSTEMS
A smoke detection system is a complete fire detection system. Aboard ship, smoke detection systems consist generally of a means for continuously exhausting air samples from the protected spaces; a means of testing the air for contamination by smoke of all colors and particle sizes, and a visual (or visual and audible) means for indicating the presence of smoke.
Types of Smoke Detectors
The smoke detector is the device that tests the air samples for smoke. The available types include photoelectric, ionization, smoke sampler, resistance bridge, and cloud chamber detectors. Of these, some lend themselves to shipboard use, while others are more suitable to large buildings on land.
MANUAL FIRE ALARM SYSTEMS
Manual fire alarm systems consist of normal and emergency power supplies, a fire control unit to receive the alarm and the necessary fire alarm boxes. The fire control unit is similar to the automatic fire detection control unit; it must contain means for receiving alarm signals and translating these signals into audible and visible alarms. It must also have provision for registering trouble signals. And, as with automatic systems, vibrating bells are required for engine room notification.
There must be at least one manual fire alarm box in each fire zone of the vessel. Framed charts or diagrams in the wheelhouse and fire control station, adjacent to the fire alarm receiving equipment, should indicate the locations of the fire zones in which the alarm boxes are installed.
Manual fire alarm boxes are usually located in main passageways, stairway enclosures, public spaces and similar areas. They should be readily available and easily seen in case of need. Manual alarm boxes must be placed so that any person evacuating a fire area will pass one on the way out.
All new alarm boxes must be clearly marked: IN CASE OF FIRE BREAK GLASS. Older alarm boxes not so marked must be identified with the same instruction printed on an adjacent bulkhead in 1.27-cm (1/2-in.) letters. Every alarm box must be numbered to agree with the number of the fire zone in which it is located. The box must be painted red, with the operating instructions printed in a contrasting color.
Newer boxes are equipped with an operating lever. When the lever is pulled, the glass is broken and the alarm box mechanism transmits the alarm. Older boxes may not have a lever; instead, they may have a small hammer, attached with a chain, to be used in breaking the glass. Once the glass is broken, the lever must be operated to sound the alarm.
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