Indicating the Alarm

Each required exit must have a fire alarm not more than 1.5 meters (5 ft) from the entrance to the exit to help occupants locate the exit during an emergency. Water flow switches in sprinklers can be used to set off an alarm and can show up on a sprinkler alarm panel.

Audible signals have minimum sound levels for public and private spaces. Setting these levels is highly technical and requires acoustic analysis of the space, the occupancy, and the characteristics of various devices. Alarm bells must not be placed inside a hung ceiling.

Visible signals are required primarily for hearing-impaired people. These may be lighted signs that flash "FIRE" above alarm bells, or rotating beacons or strobe lights. Different manufacturers use a variety of names for visible fire alarms, including visible alarm signals, visible signal devices, visible signaling appliances, and visual notification appliances. Strobe lights are usually Xenon flashtubes flashing at an interval that minimizes problems for people with photosensitive epilepsy. Careful placement also helps avoid problems. Visible signals must be visible from any point in the space regardless of the viewer's orientation. The maximum distance between strobes is 30 meters (100 ft). Where visible alarms are required, they must be placed in more locations than audible alarms, as they require direct sight lines.

The Americans with Disabilities Act (ADA) requires accessible warning systems to be both audible and visual (Fig. 46-5), and sets requirements for the type and specific locations. Where required, alarms must be provided in each restroom, hallway, and lobby, and in other common use areas such as meeting rooms, break rooms, examination rooms, and classrooms. In occupancies with multiple sleeping units, a percentage of the units must be equipped with a visible alarm as well as an audible alarm.

Because fire truck ladders can't reach the upper floors of tall buildings and travel down stairs filled with many people is very difficult, voice alarm systems are required by almost all major cities for high-rise con o o

Figure 46-5 Audio and visual fire alarm signal.

struction. The voice alarm issues specific instructions to occupants of each part of the building about safe refuge areas and the progress of rescue efforts. Voice alarms are also very good in any large building where people may not be familiar with the building, evacuation procedures, or the alarm system. This includes hotels and convention centers, where visitors often ignore or misunderstand bells and horns.

High-rise office buildings require emergency voice alarm communication systems. The system should allow full control of transmission and building-wide distribution of all tones, alarm signals, and voice announcements on a selective or all-call basis. Alert tones, signals, and prerecorded messages on independent channels should be distributed to selected areas over a building-wide system of loudspeakers. A voice alarm system can use a standard public address system independent of the fire alarm system, or the voice alarm can be electronically supervised and an integral part of the fire alarm system. Messages may be prerecorded or live. The system must have adequate sound quality for clarity.

In schools, and especially in elementary schools, rapid orderly evacuation is most important. Fire gongs should not be similar to program gongs, and the system must be arranged to allow fire drills.

In factories, large storage facilities, and other hazardous occupancies, fire alarm systems are tied to an audio system. This intercom system directs occupants out of the building, and may also give the location of the emergency. Industrial facilities have manual stations at points of egress, and horns instead of bells or gongs because of the high noise level.

Figure 46-5 Audio and visual fire alarm signal.

Part i/v


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