Unlike the screams, beeps, and yelps of horn and buzzer alarm systems, today's voice evac systems now have their say.
This lesson deals with voice evacuation systems - commonly called voice evac systems. These are specially designed public address systems, typically used during fire situations, which the Life-Safety Code requires for certain types of installations.
Voice evac systems are usually part of high-end fire alarm systems, primarily in places of assembly. The system uses spoken messages to evacuate public facilities in an orderly fashion during emergencies. A typical alarm message would state, "Attention please: There has been a report of an emergency. Proceed calmly to the nearest exit, and leave the building immediately." We consider voice-based systems better alternatives to buzzers and horns, because a voice is typically less frightening (causing less panic), and can give specific instructions.
These systems are not difficult to install, but do cost more than a traditional alarm system.
Code requirements. NFPA 101 (National Fire Prevention Association, document 101) requires you to install voice evac systems in certain types of buildings. It defines assembly occupancy as including, but not limited to, "all buildings or portions of buildings used for gathering together 50 or more people for purposes as deliberation, worship, entertainment, eating, drinking, amusement, or awaiting transportation."
More specifically, voice evac applies only to Class A and Class B assembly facilities that house more than 300 people. NFPA 101, Sec. 8-3.4.1 states that all Class A and Class B assembly occupancies and art theaters with more than one audience-viewing room shall be equipped with an approved fire alarm system. Other requirements include:
• Occupant notification shall be by means of voice announcements, either prerecorded, or initiated by the person in the constantly attended location.
• The announcement shall be made via an approved voice communications or public address system, provided with an emergency power source above the ambient noise level of the assembly occupancy.
• The authority with jurisdiction determines if it's "impractical to have a constantly attended location" and allows installation of a manual pull station-type fire system.
• Emergency voice alarm/communication systems are a requirement in high-rise buildings more than seven stories.
System design. Evac systems are not especially difficult to design or install. Obviously, you must place the speakers and control stations correctly, and then get appropriate conductors to each location by the use of an appropriate wiring method.
Here are some additional system design guidelines you need to be aware of:
• Locate the voice evacuation control panel and monitor in a convenient location for fire department and law enforcement personnel. Generally, this location will be either next to the fire panel, near the lobby annunciators, or at the entrance to an assembly area.
• Determine if zoning of the system is required. In multi-story facilities, a zoned multi-channel voice evac system is preferred. For example, if a fire occurs on the third floor of a building, the system can direct third- and fourth-floor occupants to immediately exit via the nearest stairwell. Meanwhile, the fifth-, sixth- and seventh-floor occupants can receive a voice message informing them of an emergency on the third floor and ask them to standby. Once the stairwell crowding has eased, the voice evac system will inform those floors to exit.
• Measure or estimate the ambient noise level and determine speaker wattage and locations. Use manufacturer's tables and recommendations.
• Determine if a standard voice message is acceptable or if you'll need a special message, such as instructions in English and Spanish or unique instructions that apply to the location. In general, a female voice has a more calming influence than a male voice. Moreover, its higher frequency makes it more intelligible over the loudspeaker than a deeper male voice.
• Most voice evac systems are unique to the manufacturer. Check manufacturers' specifications before installing. You'll find most manufacturers are willing to advise you on the installation process.
• You should use a strong alert tone prior to the recorded voice message. The "whoop" signal sweeps across many frequencies, and you can hear it even at high ambient noise levels. It's important to get people's attention before the voice evac system gives instructions.
Speaker placement. The placement of speakers for voice evac systems is critical. The general rules for speaker placement include:
• Place speakers at pull station locations and in main corridors, similar to the placement of conventional horns.
• At a minimum, make sure all occupied locations are within 50 ft of a speaker.
• You can tap speakers at different levels for audibility. They generally range from .25W taps to 4W taps.
• Doors and walls will drop the sound level by about 10 dB depending on their construction.
• Every time you double the distance from your sound source, you'll lose 6 dB from your expected sound level.
• Having most of the system's speaker set at their lower tap settings provides better intelligibility and more uniform sound levels.
• Always locate a speaker in boiler rooms, with a minimum 2W tap setting.
• Set speaker wattage taps to provide 15 dBA above ambient sound levels. (A setting of 1W is most common.)
• Locate speakers outside bathrooms and bedroom areas, so the message is clearly audible within.
• Be sure speakers are in normally occupied areas to protect workers or personnel.
• As a general rule, provide 1W of speaker power for every 1500 sq ft in divided areas and 2000 sq ft in open areas.
• Place additional speakers in rooms such as cafeterias, and isolated areas such as a computer room.
Power adjustments. Voice evac systems use a constant AC voltage output to drive a series of speakers. A fire alarm horn circuit operating at 24VDC and 1A can drive 10 100mA horn/strobes in parallel. A speaker circuit operating at 25VAC and 1A (25W) can drive 25 speakers at 1W in parallel.
The two standard voltages used for voice evac speakers are 25VAC and 70.7VAC. You use the higher voltage (70.7V) for long distances. Obviously, different transformers and power supplies are a requirement for the higher voltage.
High- and low-noise areas will dictate the speaker layout. In quiet areas, you can set the speaker locations to reach ambient +l5 dB in all areas. However, you should set overall speaker volumes below 90 dB so they don't startle people. In high-ambient areas, you should place speakers closer together and reach settings of a maximum of 15 dB to 21 dB above ambient. If the settings are too loud, the message can become unintelligible.
To determine decibel levels, use a certified decibel meter and take readings throughout the building. Don't be confused by the field meter reading versus the UL rating on the speakers. UL uses a complex process to calculate sound levels. Consequently, the ratings for fire alarm speakers are lower than you would find with a meter on site. The UL rating is often much less than the on-site meter reading, sometimes by up to 13 dB.
Wall-mount speakers are generally more efficient at delivering sound power than ceiling speakers. Therefore, ceiling speakers output about 3 dB less sound. You can calculate standby battery requirements using the following formula.
Additional battery amp/hours = (standby hours that are required x modules x standby current) + (alarm time x modules x alarm current).
Calculating for the proper use of your facility's voice evac system will help to ensure that necessary information will reach the people on the premises during emergencies.
Sidebar: Facility Security Uses
As we've seen, the traditional use of voice evac systems (and the one the Life Safety Code requires) is for fire alarm notification. However, this course deals with security issues. So how can a voice evac system help you with security issues?
Voice evac systems become important when there is an intruder in the facility. In such cases, one of your first concerns is to get people out of harm's way. The voice evac system is ideal for this. It allows one of your people to pick up a microphone and tell everyone in the facility what is going on, and how to leave the facility. This not only lets everyone know to get out, but it also informs them of where the danger is - so they can avoid it.
For example, during the Columbine High School shooting, it might have been helpful to have the following message come over the public address system: "Attention please. Shots have been fired in the Library. Please leave the building immediately and avoid this area." The students would have immediately known where the threat was located, and probably would have been less intimidated to move through other areas of the building to escape the danger. As it was, most students and teachers remained in the building, not knowing where the shooters were. Had they known, many of them may have escaped without injury.
Another benefit to this system is you can use it during an attack to notify law enforcement personnel as to where the assailants are, what they are doing, and where innocent people are in the building. Information is hypercritical, and the voice evac system gives you a way to disseminate that information.