Increasing Your Fire Alarm Literacy
FIRE PROTECTION
Part five in a series that examines a vital link in the fire protection system.
The signaling system is the part of a fire alarm system that alerts occupants when an alarm initiating device detects an emergency condition. Signaling devices are either visible or audible.
VISIBLE SIGNALING DEVICES
The most common visible fire alarm signaling device is a flashing red light. All too often fire service personnel improperly refer to visible devices as “strobes.” Strobes are actually one type of visible annunciator.
The visible device is selected according to the application. Flashing lights are used in factories and office buildings. Strobe lights often are used in occupancies that serve the disabled. Where flashing lights are used for attention-getting purposes such as advertisements, strobe lights must be used for emergency warning; otherwise, the flashing lights will compete with the fire alarm signaling lights and confuse occupants. The high-intensity, short-duration strobe works well to attract occupants’ attention in emergencies.
AUDIBLE SIGNALING DEVICES
Audible devices emit sounds to notify occupants of an emergency. The sound output of audible devices is measured in decibels (dB). There are more types of audible devices than there are visible devices. Following are examples of audible devices.
Bells. These are the most common audible devices and are available in different sizes. Most common occupancies—business, storage, and mercantile-use bells to notify occupants. The bell’s diameter is a good indication of its sound power output.
Horns/klaxons. Industrial locations usually use horns or klaxons. They work well in high ambient noise settings because of their unique raucous signal. The noise output level is loud enough that occupants can hear and identify the signal over ambient noise in a factory or other industrial location.
Chimes. These are used in occupancies to notify staff that an emergency exists without instilling panic in other occupants. Nursing homes and hospitals frequently use chimes.
SOUND LEVELS
The sound level required in one occupancy usually is not the same for other occupancies. You can determine whether the sound level is adequate by using a decibel meter—an electronic instrument that measures sound intensity.
Each assembly, business, storage, mercantile, and residential occupancy has a typical day-to-day noise level. This level is called the occupancy’s ambient noise level. Nationally accepted engineering standards suggest that fire alarm signals be approximately 15 dB louder than an occupancy’s ambient noise level.
Fire alarm installers or inspection personnel who are familiar with the operation of decibel meters measure the ambient noise level in a room by placing the decibel meter in an agreed-on location approximately five feet above the floor. They obtain a reading that includes inside mechanical noises as well as outside noises that filter in.
When the fire alarm system activates, signaling devices should increase the meter reading at least 15 dB. If the reading does not increase sufficiently, the inspection team and the designer may select another location in the room. If this location does not provide a sufficient signal level, the authority having jurisdiction usually requires additional signaling devices.
PROVISIONS FOR THE DISABLED
Recent legislation on the federal and state levels has focused on providing adequate annunciation to people with disabilities. However, much of the design criteria is vague. For instance, it is not yet technically clear what light intensities and durations will attract the attention of a person with a hearing disability.
It is easier to attract the attention of people with vision loss because of sound’s ability to more readily travel around corners and through opaque objects such as walls. Strobe lights have a unique but limited ability to warn people with hearing disabilities because of their high instantaneous intensity and short flash duration.
SUPERVISION OF SIGNALING DEVICES AND CIRCUITS
Alarm initiating devices require special circuits to ensure that signaling zone wiring does not unknow ingly fail before a fire incident requires the zone to perform. If the circuit fails before the fire incident, the detection devices are useless when a fire does occur.
Signaling circuits are similarly protected with trouble monitoring features. If a wire breaks or one side of the signaling circuit touches the ground, a trouble signal indicates on the fire alarm control panel. Wiring failure in any signaling circuit in a fire alarm system causes a yellow trouble light to appear and an audible signal to sound at the control panel.
EMERGENCY VOICE ALARMS
In occupancies such as large assemblies, movie theaters, and churches, it is common to alert the occupants using an emergency voice alarm or voice evacuation system. The speakers and audio amplifiers associated with this system differ from regular public address systems: They have special circuits that “watch over” the integrity of the speakers, speaker wires, and circuits inside the audio amplifier driving the speakers. Emergency power supplies the amplifiers and speakers so that instructions can be given to the occupants even when the building’s regular electrical service is disrupted.
Operator’s Console
Master Program Keyboard –
Information Printout
Firefighter’s Telephone (Master)
One-way Voice Communications Microphone
Pre-recorded Safety Announcement Tape
Automatic voice annunciation. Fire companies occasionally may encounter an alarm system with prerecorded evacuation alarm messages. On operation of an alarm initiating device, the fire alarm control panel electronically commands the tape to start playing. The taped message instructs the occupants of the building.
Manual voice annunciation. With manual voice annunciation, a responsible person located in a protected room notifies the occupants. An annunciation panel monitors all of the building’s fire alarm initiating devices. This protected room is constantly manned when the building is occupied.
During building familiarization tours, fire companies study building layouts and identify notification zones. The companies also note how the voice communication system works. The special room and equipment allow the incident commander to instruct occupants to move toward one exit or another or not to move at all. For example, the incident commander can identify by name or number operational stair towers for firefighters and evacuation stair towers for occupants. The system also is used to calm occupants who otherwise might tend to panic. Incident commanders can use manual voice communication systems to guide firefighters throughout the building and to inform them of incident progress.
SUPERVISION OF EMERGENCY VOICE ALARM SYSTEMS
Since emergency voice alarm and communications systems are true fire alarm signaling systems, they must include circuit failure monitoring for the wiring and other critical circuits. This feature is called trouble monitoring and operates on the same principle as the monitoring of initiating and signaling circuits.
An emergency voice alarm system audio amplifier differs from a regular public address audio amplifier in that some of its more critical parts are monitored for trouble. If critical amplifier parts fail while not being used, an audible and visible alarm activates in the control room.
