Safety first
Jul 20, 1996 12:00 PM,
Eli Solomon
The perfect emergency voice evacuation system meets code requirements without unnecessary frills.
“For where two or three are gathered in my name, there am I in the midst of them.” Matt. 1:.20.
When it comes to voice evacuation, the speaker of that phrase could have been a regulator. Many state and local codes now require certain places of public assembly, such as churches, theaters and restaurants, to comply with the National Fire Protection Association (NFPA) life safety code 101. This article explains what an emergency communication system should provide and how to extract the most benefit from an expenditure that as with insurance may buy some peace of mind but little else.
As with any product or service, you will be offered options. This article will help you to understand the requirements for emergency voice evacuation and paging systems and the questions you should ask before deciding on equipment. This information will help you choose a system that will meet the code requirements and your needs without unnecessary frills.
Why emergency communication systems are requiredEmergency communication is required to provide warning for hazards, such as gas leaks or chemical spills, and for emergencies, such as those caused by severe weather conditions. Although many systems use a paging system to provide warnings, they don’t meet code requirements if they do not use equipment controls and loudspeakers listed for emergency voice evacuation. Loudspeaker circuits must be supervised for open and overload conditions and must also meet survivability requirements. Because most installations also require a fire alarm system, it would make sense to provide an integrated system.
Fire alarm notification differs because the circuit for the notification appliances, horns, bells or loudspeakers must be supervised and must be listed by an approval agency such as UL. A basic fire alarm control panel (FACP) performs the function of detecting fires and activating horns, bells and strobes. In the event of a fire or other emergency, these notification devices cannot convey sufficient information or guidance to occupants.
An emergency voice communication and evacuation system can provide the necessary instructions during an emergency via supervised loudspeakers. Emergency communication should broadcast a prerecorded message when an alarm is initiated (an increasing number of codes mandate a prerecorded message) and provide a microphone for emergency paging.
Understand what you are buyingYou are buying a piece of equipment with its own set of buzz words. Some of these words you may not understand; other words have to be seen from a different perspective from that of an audio system installer. You should be aware of a few terms if you want to make equipment comparisons.
* Power rating: A system may be rated at 20 W, 30 W, 40 W or 50 W. This rating can be arrived at by a number of means. Beware when a manufacturer emphasizes emergency power. This is often the maximum amplifier output with a square wave input. The amplifier rating should be stated as 20 W or 50 W.* Power-limited: This is a relatively new requirement. It ensures that external wiring will not present a safety risk if it is overloaded or short-circuited. Ask whether the power-limited circuit meets the amended (1995) UL requirement.* Frequency response or bandwidth: Remember, you are purchasing an emergency voice communication system, not a hi-fi system. Intelligibility is not compromised if the amplifier can provide a relatively flat output from 800 Hz to 3,200 Hz. The probability is that most systems provide flat outputs to at least 5,000 Hz. You shouldn’t pay more for a system with a higher frequency response. Loudspeakers listed for use with emergency systems have very poor response at frequencies higher than about 2,800 Hz, so an amplifier with a flat response to 15,000 Hz is not necessary.* Meets NFPA codes: Check whether it really meets the latest NFPA code changes and in particular NFPA 72: section 3.12.4.3.4 and section 3-2.4.* Listed or approved equipment: It does not follow that if equipment is listed or approved, it will meet code. For example, loudspeaker circuit survivability requirements may be waived if there is only one zone. Because most systems have more than one zone, it is best to install equipment meeting the survivability requirements. This will protect you from finding out too late you do not meet code and therefore have a liability problem.Some equipment manufacturers overlook the fact that communications refer to both the alarm tone and voice communication. Even fire inspectors may be unaware of this code requirement or may not test for short-circuited loudspeaker outputs during speech transmission.* UL approved: UL standard 864 is revised and amended periodically. Make sure the system you buy meets the codes in force for 1996. You may be buying equipment that can be sold under a grandfather clause, provided it was labeled before the new standards came into effect. Manufacturers may have stocked quantities of older models while waiting for the revised equipment to be approved. Look out for the phrase “awaiting UL approval.” This ranks with the phrase, “the check is in the mail.”* Style Y or class A: This is mandated by some states and local codes. It is a form of wiring using a four-wire loop such that an open in any one wire will result in a trouble indication. In addition, all devices connected to both sides of the break must be capable of being powered during an alarm.
Types of systemsUntil a few years ago, the only integrated emergency evacuation systems available were for high-rise or large installations. Smaller systems were band-aided together by vendors using assorted units. This unavailability led to the practice of adding modules to existing fire alarm controls.
There are two basic types of systems. The first is an adjunct to a fire alarm control, which should be a self-contained emergency communication system that can be tripped by either a dry contact supervised at the evacuation control or a reverse-polarity provided by the fire control. The second is a combination fire alarm and evacuation system that combines the features of an emergency communication system with that of a fire alarm control.
System architectureSome of the more important features required of a well-designed evacuation system that meets code requirements (see Figure 3) are:* Loudspeakers should be listed by an accepted approval authority (UL, FM, CSFM, MEA) for use with evacuation systems.* Loudspeakers should be capacitively coupled to the audio bus to allow for supervision by the end-of-line resistor.* The audio bus should be supervised for open, overload and short-circuited condition to meet code.* Where the audio is distributed or split into one or more zones or areas, it must meet the survivability requirement as detailed in NFPA 72, subsection 3-2.4. This section of the code states: “The system shall be so designed and installed that attack by fire (a) in an evacuation zone causing loss of communications to this evacuation zone shall not result in loss of communications to any other evacuation zone; and (b) causing failure or fault on one or more wiring conductors of one communications path shall not result in loss of communications to any evacuation zone.* Where a prerecorded message unit is used, the system must have a standby tone generator that automatically takes over if the message unit does not function or if the output level is too low.* A standby power source must automatically transfer to battery during a brownout or power outage. The standby source must be able to support the maximum loudspeaker load for 15 minutes after 24 hours of standby. Some specifications may require up to 72 hours standby.* The system must indicate a trouble condition for equipment failure or a warning that a loudspeaker circuit is open or overloaded.* All trouble conditions should have diagnostic LEDs to identify the cause of the trouble.* The power supply should provide overvoltage protection so that, in the event of the pass-transistor failing, the output voltage is limited to a level that will not damage any dependent circuits.
SurvivabilityThis is an important part of any system you decide to use. The loudspeaker and strobe circuits must be separately protected so an overload or short on one circuit will not affect the operation of other circuits connected to the same amplifier and power supply.
Figure 1 shows a block diagram of a basic system with three circuits powered from one amplifier. Loudspeaker supervisory modules one, two and three distribute audio to various areas of an installation. If, for example, circuit one has a short-circuit or overload during an alarm, excessive current will be drawn by this circuit from the amplifier.
A fuse or PTC in each loudspeaker output will not protect that circuit because the average amount of current provided during speech is very low. (See Figure 2.) Amplitude variations during speech, small pauses between syllables and the longer pauses between words and sentences reduce the average current. A fuse or PTC depends on the heating effect caused by an overload current. An alarm tone is usually a square or sine-wave signal, which has enough energy to trip a fuse or PTC. However, the NFPA code specifies the system should survive during communication that includes voice communication.
The output of a typical system is designed to provide a loudspeaker line voltage of 25 V or 70 V. Because listed systems must work when the standby is down to 20.3 V, a transformer is used to step up the audio output voltage. The output of the transformer is split into a number of circuits, each of which has to be independently protected from overload. Bearing in mind that the output to the loudspeakers are taken from the secondary of the transformer, the system designer must provide a means to fuse the audio output of each subcircuit with negligible insertion loss. Some techniques can achieve this, but not all systems provide this critical feature.
The authority that has jurisdiction, such as the fire department inspector, is not always aware that the system should be tested for survivability during voice transmission. An installer can avoid certification and liability problems by making sure that the evacuation system chosen will meet this survivability requirement. The question to ask a vendor is: “If I connect more than one supervisory loudspeaker circuit to an amplifier and short-circuit the output of one circuit during voice transmission, will that circuit disconnect itself and allow the other circuits to function normally?”
If the answer is yes, and it is not in the literature provided by the vendor, get the answer in writing. Then test a loudspeaker circuit by shorting the output during speech transmission. Only the circuit that has been short-circuited should switch off; the other circuits connected to the amplifier should continue operating. Optional strobe supervisory circuits must also meet the survivability requirement.
Buying a systemYou should look for certain features when specifying or buying a system:* Simplicity: Simple is better. The equipment you install is to be used in emergency situations. Avoid systems with keypads. Keypads are used because they are compact, provide multiple functions and are less expensive than separate function switches, but they can be confusing. A firefighter should not have to figure out the operation of a keypad during an emergency. Firefighters like to see big, clearly marked switches for each function, with directions right on the faceplate. Operation should be intuitive. Where zone-select switches are used, an LED or other indication should inform the operator which zone has been activated. Every function, such as all call, trouble silence and reset, should have a separate switch and should be clearly marked.* Approvals: Codes generally require Underwriter, Factory Mutual, California State Fire Marshal, MEA or other approval agency certification. Determine which approval agencies your fire department will accept. Remember, a listed or approved system may not meet the latest code requirements because listing or approval may have been obtained before the implementation of the latest codes.* Adequate amplifier capacity: Make sure you have a system with sufficient headroom. If your loudspeaker load is close to the amplifier rating, you should specify a system with more power in the same cabinet. Just increasing the output of each loudspeaker by a few decibels can make excessive demands on your amplifier because every increase of 3 dBA requires twice the power.
Just as there are features you will want in a system, the following features are something you will probably want to avoid when selecting an evacuation system:*You might not want to select an evacuation system with an add-on evacuation system module without its own power supply, battery charger, brownout detection and battery transfer built into the evacuation system control. A system with an external transformer or one that piggybacks on your existing fire alarm control has hidden installation costs and may not meet code. It robs the fire control of power; during an alarm, it may load the system excessively, resulting in degradation of the emergency audio output. You will also be paying for a minimum system when you might be able to purchase a complete stand-alone system for less.* Be especially careful if the product has an outboard power-supply or transformer because it will have to be connected in conduit to the system and will have to be wired to a dedicated and separately fused primary AC power source. Simply using the nearest outlet will not meet code.
Be wary of a system that supervises the loudspeakers via the fire alarm bell circuit or zone-splitter circuits. You will be paying for an evacuation system that is little more than an amplifier, and a high probability exists that the loudspeaker protection circuit will not meet code for supervision or survivability.* Consider whether the system’s capability is too limited and will cause problems with later expansion. Although a 25 W amplifier may be adequate for now, adding a few loudspeakers later may cause a problem. Typically, you may be offered a system with a 20 W or 25 W audio capacity with expansion to 40 W. Stand-alone systems with 50 W expandable to 100 W or more that cost less than smaller capacity, unself-contained systems are available.* Be careful if the system has a message unit that does not have the capability of simple on-location recording. Some units require a computer or special accessory device to access memory; others have a built-in microphone and tape input that allow direct recording into memory. * Check the type of message unit you are offered. Some vendors require you to send your memory chip to them for recording; it could take more than week to get it back. Ask how much it would cost to alter a message. Some units cost more than $200 for new recordings and even more for a custom recording in a language other than English. You should not have to pay more than $25 to have a new message recorded. If you need emergency messages in another language, it would be nice if you could record the messages yourself directly into the unit or download them from a tape recorder. You will also have the advantage of recording in a regional accent.
Choosing the best adjunct system* Choose a completely stand-alone, self-contained system listed and approved for use as an adjunct to any fire alarm control. This system should have its own power supply, battery charger, tone generator, message maker (prerecorded or field recordable voice message and alarm tone unit), supervised microphone, control switches and supervisory circuits for loudspeakers and strobes. It should not have the power supply or transformer outside the control cabinet.* The message unit should have a built-in microphone and tape input for on-location recording or downloading.* Choose a system with an amplifier rated for at least 50 W. Because of the 10 dB above ambient requirement, a basic system should have a capacity of at least 50 W with expansion to 100 W. This capacity will provide most installations with enough headroom for future expansions as well as a safety margin. A 25 W system is often rated for that wattage at 1,000 Hz with a resistive load. * Loudspeakers are variable inductive loads with impedances that can present a load many times greater than 25 W at lower frequencies. What may be fine for a paging system handling only voice or music will not work for an emergency evacuation system that provides steady, pulsating or swept tones and puts maximum demand on the amplifier for long periods. You must design a system with enough headroom.* Choose a vendor that offers a complete range of controls and options. Avoid using control equipment from various vendors, which may lead to compatibility problems. Your vendor should offer you a range of equipment, including a minimum 50 W self-contained system; optional systems for more than 50 W, expandable to any size; style Y or class A loudspeaker and strobe; an emergency firefighter telephone system; a message unit; and a remote supervised paging unit.
Choosing a combination fire alarm and evacuation systemIf you need a fire and evacuation system control, specify a combination fire control and voice evacuation system in the same cabinet. This setup will save material and installation costs while ensuring compatibility. Such systems provide module options for functions such as sprinkler water flow, sprinkler valve supervision, smoke detectors, manual pull stations, heat detectors, loudspeaker supervision, strobe supervision and digital communication for notifying a central monitoring station. A modular system allows the user to expand the system as the need arises without having to pay for unnecessary equipment at the entry level. Choose a system that will allow you to provide ADA strobe power and strobe supervision from the same control.
Technical notesJudging by the questions asked us over the past few years, installers are most concerned about the type and location of loudspeakers, wiring and amplifier power. Here’s some guidelines for these topics.* Type of loudspeaker: Loudspeakers for emergency communication usually range in output from 1/4 W to 5 W with dB ratings stated for a distance of 10 feet (3 m). Within this range, loudspeakers are available with tappings of 1/4 W, 1/2 W, 1 W and 2 W ; 1 W, 2 W and 5 W; or 1/4 W to 5 W. Some can be selected to operate at either 25 V or 70 V. Other loudspeakers are rated at higher wattages.
Although 6 dBA above ambient may be adequate for most installations, it is advisable to budget for 10 dB above ambient to avoid expensive rewiring later and to provide amplifier headroom. Before you lay out a system, you will have to find out the worst case ambient at the farthest location at which the loudspeaker has to provide this output (10 dB above ambient). Thus, if the ambient at 20 feet (6 m) from a loudspeaker is 80 dB, the loudspeaker must provide 90 dBA at 20 feet. Assuming a loss of 6 dBA when the distance is doubled, a loudspeaker rated at 96 dBA at 10 feet will have to be used. This is derived by assuming a loss of 6 dB when the distance is doubled from the rated 10 feet to 20 feet. This may be less or more than you require, depending on the characteristics of the area. All installers are aware of the effect of furnishings and walls on sound transmission. (For more on this subject, see “What Happens to Sound in Architecture” in the January 1996 issue.) The right output level cannot really be determined without actually conducting a test with a portable amplifier and a loudspeaker that can be tapped at various levels. This test is time-consuming, but it might eventually save you from rewiring an installation if the system is found not to meet code. Test equipment is available that will allow you to provide different outputs as well as simulate line loss.* Loudspeaker location: This concern goes hand-in-hand with loudspeaker selection. The fewer loudspeakers you have tapped at a higher output, the lower the installation cost. However, a loudspeaker that is tapped at 5 W and provides 90 dB will be excessively loud up close. Another problem: intelligible coverage is not as good as it would be if more loudspeakers were used at lower tappings.
Here again, using portable test equipment will help you determine the optimum location for loudspeakers. The question that arises frequently is what to do about large, open, noisy manufacturing areas. Here you may have no alternative but to use 5 W, 10 W or 15 W loudspeakers arranged in clusters distributed throughout the facility. Again, using portable test equipment, you should be able to optimize the location and the loudspeaker tapping requirement.
* Wiring: Use the heaviest gauge possible to minimize line loss. This is especially important for 25 V systems. AWG#12 wire is about the lowest most system connectors will handle. If you have long runs, use the 70 V amplifier output, which will reduce line loss but will require that wires run in conduit. (Contact the author for a chart showing the output level vs. line length for different gauge wires and for 25 V and 70 V systems.)* Amplifier power: Irrespective of the amplifier rating, allow a minimum of 20% headroom. Because of manufacturing tolerance, a loudspeaker rated at 2 W, for example, may require more. You will also have to take into consideration that the wattage was probably determined at 1,000 Hz. Because loudspeakers are inductive devices, power consumption will be much greater at lower frequencies.
A major problem may result if loudspeaker outputs must be increased after installation. Doubling the wattage of a loudspeaker will only increase the sound level by 3 dBA. It would be sensible to select a system with enough power to start with. Selecting a system with a miserable 25 W amplifier may cause problems later.
Looking for valueAn emergency communication system is needed only for an emergency. It will be looked upon as a nonproductive expense that must be incurred because of code. It would be an advantage if the evacuation system control could serve more than one function, and this is entirely possible. Under NFPA 101 Life Safety Code handbook, 1994, Section 7-6.3.10, a voice communication system “shall be permitted to be used for other purposes, subject to the authority having jurisdiction, if the fire alarm takes precedence over all other signals.” This means loudspeakers used for the alarm system can also be used for paging or other purposes as long as the system has also been listed for paging.
Specifying the product you require and asking the right questions will help you identify the proper system for your application. You should be able to purchase an adequately powered, completely self-contained system for the same or lower cost than one that is just an amplifier with zone splitter modules.
The reliability of the system you install is heavily dependent on you. You should be familiar with code requirements and work with the fire department ahead of time to make sure that the installed system will be approved.
You are buying a life safety product, and your first consideration should be reliability. Choose a vendor with a proven product that has survived the real world in hostile environments. You should select equipment with a history of surviving installation in areas like Florida and Louisiana, where lightning can be a problem. This will give you some indication of whether the transient protection is adequate. Remember that a listed or approved product meets a minimum standard and is no guarantee of reliability in actual field conditions.
Finally, you should select a knowledgeable vendor that will give you support and will help you work around your problems. The best vendor is one who feels the stone in your shoe.
Installation applicationsThese application notes should serve only as a guide. Loudspeaker outputs vary because of design or manufacture. You should always do a preliminary test to make sure the sound levels meet code requirements before you install the loudspeakers.
Use an amplifier with more than adequate output and with the capability of expansion to allow for increased loudspeaker outputs.
Here’s how to calculate sound level at various distances for different (watt) tappings:* Doubling the distance decreases output by 6 dBA. For example, 87 dBA at 10 feet is reduced to 81 dBA at 20 feet and 75 dBA at 40 feet.* Doubling the wattage increases output by just 3 dBA. For example, 87 dBA at a 2 W tap will increase to 90 dBA when set to a 4 W tap and 93 dBA at 8 W.
Applications #2, 3 and 4 show some of the possible locations for 1 W loudspeakers in corridors with a 65 dBA ambient. If different sound levels are required, refer to application #1 for loudspeaker output levels. Application #1 also shows you how to prepare your own dB vs. distance chart for each type of loudspeaker.
Loudspeaker output vs. distance for different tappings
This table shows the level that can be expected at different distances for 2 W to 15 W loudspeakers. Outputs will vary depending on the manufacturer and loudspeaker design. This is only a guide. Refer to the actual loudspeaker parameters supplied by the loudspeaker manufacturer.
You can design your own table for lower wattages using the manufacturer’s loudspeaker data.
Rules to follow: Reduce by 6 dBA when the distance is doubled. Increase by 3 dBA if the loudspeaker wattage is doubled.
Choosing a system
To find out which type of system you are being offered, ask the following questions.* Does the system have its own power supply rather than an external transformer? The power supply should be integrated within the control.* Does the system have its own battery charger and battery?* Does the system have its own brownout and ground-fault circuit with diagnostics?* Does the brownout circuit have automatic transfer to battery?* Does the system have its own loudspeaker supervisory module per circuit?* Is each loudspeaker circuit independently protected against an overload or short circuit during speech transmission so only that circuit will be affected while other loudspeaker circuits continue to function normally?
