Fire Alarm Systems for Life Safety Code Users/media/Files/forms and premiums… · · 2013-06-11through output signals. The simplest form of system described in Exhibit ... usually

cept of Mass Notification Systems used for emer-gency communication and management.

Specific requirements and designs for various oc-cupancies are not discussed in this supplement. Theoccupancy chapters of the Life Safety Code should beconsulted for specific requirements. The additionalcommentary contained in other chapters of this hand-book provides a good explanation of the require-ments and the philosophy behind their intent. Thissupplement provides an introduction to the opera-tion of required devices and systems. Designers,owners, installers, and inspectors will find useful in-formation to assist them in choosing among optionsnot specifically addressed within the Code. For exam-ple, a choice might need to be made between usingphotoelectric or ionization smoke detectors, or infor-mation might be required on how to reduce the likeli-hood of false and nuisance alarms.

OVERVIEW OF FIRE ALARM SYSTEMS

Four principal types of fire alarm systems are re-quired or recommended by various chapters of theLife Safety Code:

INTRODUCTION

This supplement starts with an overview that de-scribes how NFPA codes and standards categorizethe various types of fire detection and alarm systems.A section on fire signatures reviews the sensible ordetectable physical and environmental changes thattake place during a fire. A review of fire detectiondevices emphasizes proper selection in order to meetfire safety goals and to reduce the likelihood of falseand nuisance alarms. Power sources permitted bythe Life Safety Code for household smoke alarms arediscussed in the context of their reliability. The discus-sion of circuit types and allowable wiring methods in-cludes references to other NFPA codes and standards.The signaling section describes the goals and methodsfor both occupant notification and off-premises sig-naling for staff and emergency forces notification. Areview of testing and maintenance needs for fire de-tection andsignaling systems provides thereader withan understanding of how to extend a system’s life,reduce nuisance alarms, and ensure system opera-tion during a fire emergency. A section new to the2006 edition of this supplement introduces the con-

1113

S U P P L E M E N T 2

Fire Alarm Systems for Life SafetyCode UsersRobert P. Schifiliti, P.E.

Editor’s Note: This supplement is an introduction to fire alarm systems. It explains thevarious types of systems addressed by the Life Safety Code and describes their componentsin detail. In this supplement the term fire alarm is intended to include detection systemsand systems that provide control functions, such as elevator recall, and alarm informationor notification to occupants and emergency forces.

Robert P. Schifiliti is the founder of R.P. Schifiliti Associates, Inc., and is chair of theTechnical Committee on Notification Appliances for Fire Alarms Systems. Mr. Schifilitiserves as one of several faculty for the NFPA Fire Alarm Workshop and is a licensed fireprotection engineer. He received the degree of master of science in fire protection engineeringfrom Worcester Polytechnic Institute.

1114 Supplement 2 • Fire Alarm Systems for Life Safety Code Users

1. Smoke alarms or household fire alarm equipment2. Manual fire alarm systems3. Automatic fire alarm systems4. Supervisory systems for extinguishing systems or

other fire or building systems

Each of these categories can be viewed as consistingof three components, as shown in Exhibit S2.1. Detec-tion and initiating devices are either manual or auto-matic, as shown in the illustration, and are referredto as input devices. Manual initiating devices, suchas manual fire alarm boxes, are operated by peopleand in turn signal the control system. Automatic de-tection devices sense a change in the environment orequipment that is monitored and signal the controlportion of the system. The control or processing sec-tion receives the incoming signals and initiates out-put signals. The control system can also supply powerto and supervise the system’s various componentsand circuits and provide output signals when a faultoccurs or maintenance is needed. The control or proc-essor interfaces with people and other systemsthrough output signals.

The simplest form of system described in ExhibitS2.1 is a self-contained smoke alarm. This alarm con-tains a smoke sensor and a control system, whichincludes a power source and a notification system,usually a horn, used for occupant notification. In

more complex systems, initiating devices and notifi-cation appliances are separate, self-contained unitsconnected to a control panel by electrical circuits orradio waves. In these component systems, power isusually provided to the input and output devicesthrough the control unit. However, it is also possiblefor power to be provided directly to those units thatrequire it. Each of these three principal components(input, control, and output) is discussed in more de-tail in later sections of this supplement.

The occupancy chapters of the Life Safety Codespecify fire alarm requirements where appropriate.Those sections that contain requirements includesubsections that provide the requirements for initia-tion and notification. Where initiation is addressed,the occupancy chapter refers to either a completesystem or a partial system. In addition, the systemwill be described as manual, automatic, or both.Chapter 9, Building Service and Fire ProtectionEquipment, defines complete, partial, manual, andautomatic systems. Where automatic detection is re-quired, most chapters of the Code specify either par-tial or complete smoke detection. If an automatic firedetection system is required, but the type of detectionis not specified, any automatic units that comply withNFPA 72�, National Fire Alarm Code�, are permittedto be used interchangeably. An occupancy chaptermight also require separate smoke detection withindwelling units in addition to any required partial orcomplete system for the public or tenantless sectionsof the building.

Household fire alarm equipment is intended foruse within dwelling units such as apartments, hotelrooms, dormitory rooms, and one- or two-familydwellings. These devices or systems are intended todetect smoke conditions and alert the occupants ofthe dwelling units. In occupancies such as hotels,apartment buildings, and dormitories, these devicesare not intended to be connected to the overall build-ing fire alarm system.

Within the dwelling unit, household fire alarmequipment might be self-contained smoke alarms, orit might be a small system with detectors, a controlpanel, and notification appliances such as bells,horns, or strobe lights. The building system can con-sist of manual and automatic initiating devices, extin-guishing system supervisory devices, and notificationappliances that are all connected to a control unit.Therefore, there are two categories of fire alarm: onethat is located within the family dwelling unit andone that is intended to protect the entire building.

In some cases, an occupancy chapter of the Codemight require a partial automatic detection systemthat covers all common spaces. In addition, house-

2006 Life Safety Code Handbook

Detection Manual

AutomaticAlarm

Supervisory

Control/ProcessingLogic

Human interfacePower

Supervision

Signaling Occupant notification

Off premisesEmergency forces

Other systems

Exhibit S2.1 Overview of components of fire alarm systems.

1115Fire Signatures

transferred by conduction, convection, and radiation.The second signature group is categorized by thephysical/chemical changes that take place. This groupis comprised of solids, liquids, and gases producedby the fire. The solid and liquid particles are groupedtogether and called smoke or aerosols.

Conduction occurs when, during the combustionprocess, some of the energy released is conductedthrough the fuel to further the combustion process.Any time the temperature of one part of a materialdiffers from another part, heat energy is conductedfrom the hotter portion to the cooler portion.

Convection occurs when heat is transferred byfluid motion. During combustion, hot fire gases rise,entraining fresh air, which then heats and also risesuntil the mixture either collects at the ceiling or coolsto approximately room temperature. The energy car-ried away by the hot gases is referred to as convectedenergy.

Electromagnetic radiation is the third mode ofenergy transfer that occurs during the combustionprocess. Thermal radiation is one form of electromag-netic radiation and is proportional to an object’s tem-perature. Light is another form of electromagneticradiation produced during the combustion process.Unlike conduction and convection, a solid, liquid, orgaseous material is not needed to transfer energyby radiation. Electromagnetic radiation can travelthrough a vacuum such as space. Radiation travels inall directions and in straight lines. Thermal radiationbehaves in the same way as visible light radiation; ifyou turn your back to it, you can’t ‘‘see’’ it. Therefore,when you stand in front of a fire, your face is warmedby thermal radiation, but your back is not heated.You might, however, see or feel the effects of reflectedradiation.

hold fire alarm equipment might be required indwelling units. For purposes of occupant notification,the building system would cover all occupiablespaces, including the dwelling units. The householdequipment is required to signal only within the dwell-ing unit. Some building fire alarm systems are capa-ble of having system-connected smoke detectors inthe dwelling units programmed to operate like smokealarms. In this configuration, they receive power, in-cluding backup power, from the building system andare monitored for faults and sensitivity. When theyalarm, these systems provide an alarm signal (audi-ble, visible, or both) only in the dwelling unit. Theycan also send a supervisory signal to an attendedlocation.

In other cases, a complete automatic detectionsystem might be required in addition to the require-ments for the dwelling unit. The building systemmust then provide detection within all spaces, includ-ing the dwelling units. This detection for the dwellingunits is not redundant. The intent is for the householdfire alarm equipment to provide an alarm of smokeconditions to the occupants of the dwelling unit. Theadditional detectors connected to the building systemwould be heat detectors, which would notify the otheroccupants before a fire in the dwelling unit became athreat to those outside the dwelling unit. This designconcept is described thoroughly in the commentaryof the occupancy chapters in which it is required.

NFPA 72, National Fire Alarm Code, deals with theapplication, installation, performance, and mainte-nance of fire alarm systems and their components.Like this handbook, the National Fire Alarm CodeHandbook contains the text of NFPA 72, along withexplanatory information. The National Fire Alarm CodeHandbook, by Lee Richardson and Wayne D. Moore,P.E., is a good source of background information onthe National Fire Alarm Code.

FIRE SIGNATURES

Fire signatures are changes in the normal environ-ment caused by a fire. Understanding fire signaturesis important because it affects the choice of fire detec-tor for a given area. The objective is to choose a firedetector that will respond to an expected fire signa-ture without responding to similar signatures thatmight normally present in the area. At the same time,the response time of the detector in reaction to therange of expected fires must meet the fire safety goalsand objectives of the system.

Fire signatures can be placed in two categories,as shown in Exhibit S2.2. The first group is catego-rized by the energy produced by the fire, which is

Life Safety Code Handbook 2006

Physical/chemical Gases Solid particles Liquid particles

Ceiling

Floor

Energy Conduction Convection Radiation

Exhibit S2.2 Fire signatures.


All fires produce smoke and gases in varyingquantities. Perfect combustion of most (hydrocarbonbased) fuels produces only carbon dioxide and water,in addition to the energy released. Other materialsare produced when combustion is not 100 percentefficient. These materials include gases such as car-bon monoxide, and liquids and solids such as tar,carbon soot, and more complex hydrocarbon parti-cles.

The solid and liquid particles, which together arecalled smoke, are produced in a wide range of sizes.Some are small and invisible to the human eye, andothers are large and obscure our vision. Some particlesizes are produced in larger quantities than others.The color of the smoke also varies. Many of thesefactors depend on the fuel and also on the efficiencyof the combustion process. For instance, well-ventilated, hot, efficient fires produce mostly small,invisible, grayish particles in large quantities. Com-pared to flaming fires, inefficient, smoldering com-bustion produces mainly a smaller number of largeblack particles.

INITIATING DEVICES

Manual Fire Alarm Boxes

Manual fire alarm boxes are either coded or non-coded. Noncoded manual fire alarm boxes are themost common in use on new systems. When a non-coded fire alarm box is operated, a switch closes.All noncoded devices produce the same single bit ofinformation — a switch closure. Therefore, if morethan one switch is on a circuit, the circuit does notknow which switch operated. The exception is ad-dressable, microprocessor-based systems that can‘‘talk’’ to and recognize each device.

Coded manual fire alarm boxes house a mechani-cal code wheel that turns when the alarm is operated.Through its teeth, the wheel taps out a coded signalon a circuit. These coded wheels are essentially auto-matic telegraph keys, and each box has a differentcode through which information is transmitted. Thiscode might be transferred to a bell circuit in orderto notify the occupants of a building which box hasbeen operated.

Today’s addressable systems act like the oldermanually coded systems. Because the control unitknows exactly which device has originated an alarm,it can generate unique alarm signals. The control unitcan also activate or actuate a unique set of outputfunctions, such as starting or stopping certain fansand closing some doors but not others.

Manual fire alarm boxes, coded or noncoded, can

be single action or double action. When operating asingle-action box, the hand is used to pull the station.When operating a double-action station, two actionsare required — either the door is opened and thestation is pulled, or the glass is broken and a buttonis pushed. Double-action manual fire alarm boxestend to reduce false alarms caused by accidental op-eration. They also reduce nuisance alarms to somedegree.

Pull station protectors are clear plastic covers thatare mounted over manual boxes to provide protectionfrom weather, dust, dirt, and mechanical damage.They also serve to convert a single-action station intoa double-action station. When these covers are placedover a double-action station, three actions are re-quired to initiate an alarm signal — the protectormust be lifted, the cover must be opened, and thebox must be pulled.

Some versions of pull station protectors are avail-able with an internal battery-operated buzzer. Thisfeature has been shown to greatly reduce nuisancealarms in schools, shopping centers, and other publicareas. When the cover is lifted, the local buzzersounds, which tends to scare away vandals beforethey can operate the station. In locations such asschools or other crowded public areas, someone islikely to see or catch a vandal before the station isoperated. However, when the cover is removed andthe local buzzer sounds, a person might think thebuilding’s fire alarm system has been initiated. Forthis reason, it is important that pull station protectorsbe labeled properly and that the usual occupants ofthe area be instructed in their use.

The Life Safety Code permits either single- or dou-ble-action manual fire alarm boxes. The use of pullstation protectors is neither required nor restricted.The choice for both is up the designer, the owner,and the authority having jurisdiction (AHJ).

Where an occupancy chapter of the Life SafetyCode requires manual fire alarm boxes, Chapter 9describes the quantity and location. NFPA 72 alsocontains requirements concerning the location andoperation of manual fire alarm boxes. Essentially,manual fire alarm boxes are located at each requiredexit in the natural path of egress.

In a corridor with exits at each end, a manual firealarm box is located at the door to each exit. The boxshould be located on the same side as the door handleso that someone exiting from the space will see iteasily. In most cases, it is best to locate the box withinthe corridor, not on the other side of the door, so thatthe pull station is located within the space it serves.If a manual box were located on the other side of thedoor — for instance, in the stair tower — an occupant


1117Initiating Devices

nonrestorable. Restorable detectors reset themselvesafter the fire signature is no longer present, providedthey are not severely exposed to a fire. For instance,some heat detectors absorb heat until they respond,and may then cool off until they return to their origi-nal state. Self-contained household smoke alarms au-tomatically reset after the smoke has cleared fromtheir chamber (a slight time delay is generally builtinto the detector to ensure a minimum ring time).Nonrestorable detectors are destroyed upon activa-tion and must be replaced after exposure to the firesignature for which they were designed.

There are advantages and disadvantages to bothrestorable and nonrestorable detectors. Nonrestor-able detectors generally provide a positive visual in-dication of operation, whereas a restorable detectormight not have any visual cue that it is or has beenin the alarm state. This is true of most heat detectorsbut not of smoke detectors, which have visual alarmindicators. Restorable heat detectors can also be pro-vided with visual indicators, although this featuregreatly increases the cost of an otherwise relativelyinexpensive detector. One key advantage to restor-able detectors is their ability to test the units withthe same signature for which they are designed torespond. Most addressable heat detectors are restor-able and include an indicator light on the unit.

Heat Detection

Three basic types of heat detectors are available com-mercially — fixed-temperature, rate-of-rise, and ratecompensation detectors. The Life Safety Code allowsany of these units to be used interchangeably wher-ever heat detection is required. Addressable, analog,thermistor type heat detectors may exhibit a combi-nation of conventional detector characteristics, de-pending on how they are programmed by themanufacturer.

Heat detectors respond to hot smoke and firegases — that is, to convected energy. Because it takestime for a heat detector to absorb heat and thereforeto respond, the air and fire gases surrounding a detec-tor might be much hotter than the detector element.This response delay is called thermal lag. Thermal lagcan be illustrated by imagining a fixed-temperatureheat detector, such as a 165�F (74�C) sprinkler, that isdropped into a pan of boiling water. Although thewater is 212�F (100�C), there is a time delay or thermallag before the sprinkler link melts. The smaller themass of the link or detector element, the shorter thethermal lag. Thermal lag is a measure of detectorsensitivity. The shorter the thermal lag, the greaterthe sensitivity of the unit.

from the fifth floor might pull the box on the secondfloor, possibly slowing discovery of the fire’s location.

In addition to locations at required exits, addi-tional manual fire alarm boxes are required to ensurethat there is less than a 200 ft (60 m) travel distanceto a station. It is good practice to provide manual firealarm boxes near the telephone operator’s area ofa hotel or hospital and near portable extinguishersplaced adjacent to hazardous operations in a factory.NFPA 72 requires the mounting height of boxes to bebetween 31⁄2 ft (1.1 m) and 41⁄2 ft (1.4 m), althoughsome locally adopted codes for the disabled mightlimit the height to no more than 4 ft (1.2 m).

Automatic Fire Detectors — General

NFPA 72 classifies automatic fire detectors as eitherspot-type, line-type, or air-sampling detectors. Spot-type detectors include conventional smoke and heatdetectors. A spot-type detector’s response to a givenfire varies with the radial distance from the detector.The farther a fire is from the detector, the slower theresponse time of that detector. To illustrate, if a circlewere drawn and the detector placed in the center, agiven fire anywhere along the perimeter of the circlewould result in the same response time. If the samefire were moved closer to the detector at the centerof the circle, the response time would decrease. Ifplaced farther away from the same fire, the samedetector would have a longer response time. Engi-neers may adjust detector spacing in order to changethe coverage radius and achieve shorter detectiontimes for expected fires. Conversely, the spacing, andhence the radius, may be increased where longerresponse times are tolerable.

Projected beam smoke detectors and heat-sensitive cable are examples of line-type detectors.The response time for a line-type detector is aboutthe same when a particular fire is burning anywheredirectly under the line, except close to the ends. Ifthat same fire were to move farther away to a positionperpendicular to the line-type detector, responsetime would increase. Similarly, response time for agiven fire would be about the same anywhere alonga line parallel to the line-type detector, except at theends.

Air-sampling detectors draw air samples fromthe protected area, through a tube or pipe, back to aremotely located detector. The tube or pipe mighthave several holes or sampling ports, or it might haveonly one. In any case, NFPA 72 treats the samplingport like a spot-type detector with respect to its loca-tion and spacing.

Spot- and line-type detectors can be restorable or



Thermal lag enables a detector with a fixed tem-perature of 200�F (93�C) to respond to a fire morequickly than would a sprinkler with a fixed tempera-ture of 165�F (74�C). It is detector sensitivity that de-termines the number of detectors needed for aparticular application.

There are several ways to measure detector sensi-tivity. The term response time index (RTI) is used tomeasure sprinkler sensitivity. The smaller the RTI,the more sensitive the unit. The RTI of a unit can beused in calculations to determine when that unit willrespond to a given fire scenario. For heat detectors,the current measurement of sensitivity is the Under-writers Laboratories listed spacing or Factory Mutualapproved spacing. The higher the spacing rating, themore sensitive the detector. For instance, a detectorwith a listed spacing of 50 ft (15 m) is more sensitivethan one with a listed spacing of 30 ft (9 m). The listedspacing of a detector is determined by fire testingand cannot be used directly as part of any engineeringcalculations. Testing laboratories may soon test andreport the RTI of heat detectors.

Where heat detectors are used, NFPA 72 requiresthat they be spaced on smooth ceilings less than 10ft (3 m) high, in accordance with their listed spacing.The installed spacing is equal to the listed or ap-proved spacing. For ceilings higher than 10 ft (3 m),NFPA 72 contains reduction factors to be applied tothe listed spacing. Therefore, as ceiling height in-creases, the installed spacing becomes less than thelisted spacing. Reduction factors for joisted, beamed,and sloped ceilings are also contained in NFPA 72.The beams or joists must be at least 4 in. (10.1 cm)deep before reductions are required for heat detec-tors. Each of these features (high ceilings, ceilingsthat are not smooth, and so on) affects detector re-sponse. The reduction and correction factors con-tained in NFPA 72 are intended to provide someadjustments for these features. NFPA 72 should bereferenced for a list of all the various correction fac-tors. Designers, installers, and inspectors often missspacing reductions; yet these reductions can have adramatic effect on detector response time during afire. NFPA offers a three-day seminar on fire detec-tion and alarm systems that covers these require-ments in detail.

Fixed-Temperature Detectors. Fixed-temperatureheat detectors respond when the temperature of theirelement reaches a preset level. To reduce the likeli-hood of false alarms, the temperature rating selectedfor an application should be at least 20�F (11�C) abovethe maximum expected ambient temperature. Thesedetectors are available in a wide range of temperature

ratings, the most common being 135�F to 140�F (57�Cto 60�C) and 190�F to 200�F (88�C to 93�C). Fixed-temperature detectors are available as spot-type andas line-type.

Fixed-temperature heat detectors use severalmethods of operation. The two most common meth-ods use a fusible or bi-metal element. Fusible ele-ments melt at a preset temperature and are spring-loaded to close or open a set of electrical contacts.Bi-metal units use two or more metals that expandat different rates, causing the element to changeshape and initiate operation of a set of electrical con-tacts. Line-type, fixed-temperature heat detectorsgenerally operate either when insulation melts,allowing two conductors to short circuit, or when heatcauses a decrease in electrical resistance and an in-crease in conductivity between two conductors.

NFPA 72 contains basic operational descriptionsof these and other detection principles. For a moredetailed discussion of the many different types ofheat detectors available, consult NFPA’s Fire ProtectionHandbook or Fire Alarm Signaling Systems.

Rate-of-Rise Detectors. Rate-of-rise heat detectorsrespond when their temperature or the temperatureof the air surrounding them rises faster than somepreset rate — regardless of their actual fixed tempera-ture. Units are available with various alarm rates, acommon one being 15�F/min (8�C/min). The speedwith which a detector responds depends on how hotthe fire gases are compared to the detector’s startingtemperature, and also on the detector’s sensitivity.Therefore, if a rate-of-rise detector is initially moni-toring a room temperature of 65�F (18�C), and a firecauses the temperature around the detector to risequickly, it will respond in a given time. If the detectoris in a freezer at �20�F (�29�C) and the temperaturerises at the same rate, the response time would beabout the same.

Depending on environmental conditions, detec-tor sensitivity, and the fire growth rate, rate-of-risedetectors can respond much faster than fixed-temperature units. In many real fire situations, how-ever — such as a slowly developing fire — a rate-of-rise detector may not respond. For this reason, testinglaboratories, codes, and standards require these de-tectors to be backed up with fixed-temperature ele-ments.

As with fixed-temperature detectors, rate-of-riseheat detectors are available in many different config-urations. The most common spot-type unit works ona pneumatic principle. As the detector is heated, airinside a chamber is heated and expands. The air es-capes through a vent hole when heated slowly. How-



rate compensation detectors respond more quicklyto most fires than do fixed-temperature detectors,without producing false alarms due to moderate tem-perature fluctuations as can occur with the use ofrate-of-rise units. Rate compensation units are alsosuitable where precise temperature actuation isneeded.

Smoke Detection

General. Four principal types of smoke detectionequipment are currently on the market:

1. Spot-type ionization detectors2. Spot-type, light-scattering, photoelectric detectors3. Line-type, projected beam, light obscuration de-

tectors4. Air-sampling detectors

The Life Safety Code allows each of these types to beused interchangeably wherever smoke detection isrequired.

By definition and by design, smoke detectors re-spond to the solid and liquid aerosols produced bya fire. Each type responds differently to differenttypes of smoke. Because smoke detectors also re-spond to aerosols from non-fire sources, an under-standing of their operating characteristics is helpfulin their correct selection and placement to reducethe chances of false and nuisance alarms. Therefore,selection of a smoke detector should be based on thetype of fire and fuel expected, as well as on environ-mental characteristics.

At some point, the smoke detector transmits analarm signal either by sounding an internal alarm orby signaling a control panel. With digital and analog/digital systems, the detector sends information onthe amount of smoke in the chamber back to thecontrol panel, where a decision is made to performsome function, such as sounding an alarm. Such unitsare often called ‘‘smart’’ or ‘‘intelligent’’ devices. Be-cause they send all information back to a controlpanel or processor and do not make alarm decisions,these units are often referred to as ‘‘sensors’’ ratherthan detectors. In the case of conventional detectors,a decision to alarm is made internally. The conven-tional detector then signals an alarm either by activat-ing an internal audible or visual device or by signalingthe control panel. Additional information on howconventional and digital smoke detectors signal acontrol panel is contained later in this supplement,in the subsection Wiring Methods.

Where required by an occupancy chapter of theLife Safety Code, household smoke detectors — oftencalled single- or multiple-station smoke alarms —

ever, when heated faster than its preset rate, the aircannot escape quickly enough, and pressure buildsup in the detector. As the pressure increases, a dia-phragm moves and activates a set of electrical con-tacts. Line-type rate-of-rise detectors are alsoavailable using this pneumatic principle. Other rate-of-rise detectors use bi-metal elements or electricalconductivity to detect rapid temperature changes.

When using rate-of-rise heat detectors, it is im-portant to ensure that they will not be subjected tochanges in ambient conditions that might cause falsealarms. For instance, rate-of-rise detectors should notbe located too close to air supply vents or directlyover heat sources such as ovens, radiators, or largesinks where hot steam might set them off. Heat detec-tors can be used in high-temperature areas, but cau-tion should be used in situations where thetemperature might cool rapidly then rise againquickly enough to set off the rate-of-rise units. In alarge boiler house, for example, the temperature atthe ceiling might be 100�F to 150�F (38�C to 66�C)under normal circumstances. As long as the fixed-temperature backup to the rate-of-rise detector is atleast 170�F (77�C), there should be no false actuation.However, if a large door is opened in the winter, thetemperature could drop quickly. When the door isclosed, the temperature at the ceiling could rise fastenough to set off the rate-of-rise portion of thedetector.

Rate Compensation Detectors. Rate compensationheat detectors are more complex in operation thaneither fixed-temperature or rate-of-rise devices. Inshort, they combine the principles of both in orderto compensate for thermal lag. When the air tempera-ture is rising at a rate of about 40�F/min (22�C/min)or less, the unit is designed to respond almost exactlyat the point when the air temperature reaches theunit’s rated fixed temperature. The detector elementdoes not lag while it absorbs the heat and rises tothat temperature. At faster rates of temperature rise,the unit responds more quickly than most fixed-temperature detectors, even though some thermallag does occur. In addition, with these very fast tem-perature rises, rate-of-rise detectors generally re-spond more quickly than either fixed-temperature orrate compensation detectors.

Because of the precision associated with their op-eration, rate compensation heat detectors are wellsuited for use in areas where thermal lag must beminimized to provide fast response when tempera-tures exceed a certain level. At the same time, theyare stable even in areas where temperatures fluctuatebut do not exceed the preset alarm level. Therefore,



must be located and installed in accordance withNFPA 72, 2002 edition, Chapter 11. Chapter 5 of NFPA72 governs the location and placement of requiredsmoke detectors for protected premises systems. Un-less otherwise noted, all requirements and recom-mendations for smoke detector spacing contained inChapter 5 apply equally to ionization or photoelec-tric spot-type smoke detectors, to projected beamdetectors, and to the sampling ports or heads of asampling-type system.

For general area coverage with smoke detectors,Chapter 5 of NFPA 72 requires that spacing be basedon manufacturer’s recommendations. Chapter 5 alsorecommends an installed spacing of 30 ft (9 m) be-tween detectors. This recommendation applies tosmooth, flat ceilings, and is also in agreement withthe recommendation of most manufacturers. There-fore, in many cases, the installed spacing is the manu-facturer’s recommended spacing, which is usually 30ft (9 m), center to center. There is no listed or ap-proved spacing of smoke detectors, as is provided forheat detectors. Also, there is no specific requirementfor changing detector spacing depending on the sen-sitivity of the unit.

Chapter 5 of NFPA 72 requires detector spacingto be reduced for ceilings with beams or solid joists.Where smoke detectors are used, the beams or joistsmust be at least 4 in. (10 cm) deep before reductionsare required. Spacing adjustment is also requiredwhen airflow in the space is greater than about 8minutes per air change. The adjustment require-ments for smoke detector spacing on beamed orjoisted ceilings, sloped ceilings, and in the presenceof high airflow are cumulative and very complex.NFPA 72 should be consulted and studied in detailto determine the ultimate installed spacing require-ment.

Unlike its provisions for heat detectors, Chapter5 does not contain specific spacing reductions forsmoke detectors where ceiling height exceeds 10 ft(3 m). Instead, it advises following the manufacturers’recommendations and using good engineering judg-ment. Other factors that must be considered are dis-cussed later, in the section Selection and Placement.

Spot-type smoke detector sensitivity is generallybased on the percentage of light obscuration per footrequired for the unit to signal an alarm. The alarmthreshold can also be expressed in optical densityper foot (or per meter), which can be converted toobscuration per foot.

The Life Safety Code does not require that detec-tors have any minimum or maximum sensitivity, onlythat they comply with the National Fire Alarm Code.These documents also do not contain any explicit

requirements regarding detector sensitivity. Chapter5 of NFPA 72 only requires that the detector be testedand listed for its intended use. It is the listing labora-tory, acceptable to the authority having jurisdiction,that determines the range of acceptable smoke detec-tor sensitivity for a given application.

The National Fire Alarm Code requires detectorsto be tested and listed. ANSI/UL 217, Standard forSingle and Multiple Station Smoke Detectors, and ANSI/UL 268, Standard for Smoke Detectors for Fire ProtectiveSignaling Systems, contain requirements for minimumand maximum detector sensitivity to gray smoke.

The range of possible sensitivities for spot-typedetectors is generally between 1.0 and 4.0 percent perfoot (0.3 m) of obscuration due to gray smoke. Thisrange provides the designer of a smoke detectionsystem some choice with regard to sensitivity. Theimportance of this is explained later in this supple-ment, under the heading Selection and Placement. Itis possible to obtain smoke detectors that are spe-cially listed with higher sensitivities for use in specialsituations.

Ionization Detectors. Exhibit S2.3 shows an ioniza-tion smoke detector. Ionization smoke detectors havetwo parallel electrically charged plates separated byan air gap. A small, low-strength radioactive sourcecauses the air between the plates to be ionized. Be-cause of the voltage between the plates, the positiveions travel to the negative plate and the negativeions travel to the positive plate. This creates a smallelectrical current. As smoke particles enter the detec-tor, they slow down the movement of the ionizedair between the plates. The corresponding change inelectrical current is measurable by the detector andis proportional to the number and size of the smokeparticles between the plates. In the case of ionization


Current withclear air

0

1

2

+ +

++––

––

A

+

–

P1 P2

Radioactivematerial

Currentwith smoke

0

1

2

++

++––

–+

– Smoke particles

–

B

Exhibit S2.3 Ionization smoke detector.


the light is absorbed and some is scattered, reducingthe total amount reaching the receiver. The color andshape of the smoke particles are not as important asfor spot-type photoelectric detectors. In the case ofprojected beam smoke detectors, it is the size andquantity of smoke particles in the path that have thegreatest effect on the detector’s signal.

Projected beam smoke detectors respond to thetotal amount of light obscuration in their paths. Whenthe percentage of light obscured reaches a giventhreshold, the unit sounds an alarm. Typically, theunits are available with adjustable sensitivities be-tween 20 and 70 percent total obscuration. If the lightbeam is suddenly and totally obscured, the unitshould not alarm but should give a trouble signalafter a short time period. In general, fires do notsuddenly and totally obscure a light beam. Similarly,a very gradual loss of light is also probably not indica-tive of a fire but is more likely an accumulation ofdust or a misalignment of the beam. This situationshould also produce a trouble signal, not an alarmsignal.

Very large, fast developing fires, such as a largespill of flammable liquid, can cause a rapid decreasein the signal received by a projected beam smokedetector. For this reason, the detector must have asetting that permits it to allow a fast blockage to causean alarm signal rather than a trouble or supervisorysignal. This setting should be used only where thereis a real possibility of these types of fires.

When smoke detection is the objective, projectedbeam smoke detectors can have a measurable perfor-mance advantage over spot-type smoke detectors.Projected beam smoke detection can actually be moresensitive to real fires, yet less prone to nuisancealarms.

Air-Sampling Detectors. Sampling-type smoke de-tection devices are designed to draw air samples fromthe protected space to a separate detection chamber.The sampling portion might consist of a combinationof air pumps, filters, and tubing, or piping fitted with

smoke detectors, the strongest signal is obtainedwhen there are a large number of small particles inthe chamber.

Photoelectric Detectors. Exhibit S2.4 shows a photo-electric smoke detector. Spot-type photoelectricsmoke detectors operate on the light-scattering prin-ciple. A small light source, usually an infrared LED,shines a beam into the detector chamber. A light-sensitive receiver is located so that it normally seesonly a very small amount of light from the sourcereflected from the detector chamber. When smokeenters the detector chamber, additional light is scat-tered within the chamber, some of which reachesthe photosensitive receiver and changes the detectorsignal. As with ionization detectors, the magnitudeof the signal is related to the number and size of thesmoke particles.

Many other factors also affect the signal from alight-scattering smoke detector. The color of thesmoke affects the amount of light that is scattered.Dark smoke, such as that from some plastics andhydrocarbon fuels, absorbs more light than it reflects.Light-colored particles reflect a lot of light, so smallerquantities can produce strong signals. Particle shapealso affects the amount of light reflected or refracted,as does the wavelength of the light source and theangle between the source and receiver. However, inthe case of a particular scattering-type photoelectricdetector design, the strongest signal is generally ob-tained when large, light-colored smoke particles arein the chamber.

Projected Beam Detectors. Projected beam smokedetectors, as illustrated in Exhibit S2.5, operate on thelight obscuration principle. These detectors consist ofa source that projects a light beam across a space toa receiver. As smoke enters the beam path, some of


Pulsed light

Light sensorLight source

Scattered light

Smoke

Exhibit S2.4 Photoelectric smoke detector.

•

•• •

•

•

•

••

•

• •

•

•

•

••

•

•

••••

•

•

••

•

•

•

•

•

•

Clear air

Smoke particles

Light beamLight source

Receiver

Exhibit S2.5 Projected beam smoke detector.


sampling heads or perforated to draw room air sam-ples. The detection device might be self-contained ormight be part of, or served by, a control panel.

Air-sampling detectors should not be confusedwith duct smoke detectors. Sampling-type detectorsuse positive ventilation methods to draw an air sam-ple. Duct smoke detectors are usually only spot-typephotoelectric or ionization detectors in special hous-ings. Duct smoke detectors might use a sampling tubethat penetrates the duct to allow natural pressuredifferences to draw air into the detector housing.

There are two principal types of air-samplingsmoke detection systems. One type uses a cloudchamber to detect very small particles in a sample ofair from the protected space. In a cloud chamber,humidity is added to the air sample, and the pressureis reduced to lower its temperature. This causes waterto condense on small particles present in the sample.The resulting cloud is measured by an LED lightsource and a phototransistor light receiver. Thesecloud chamber units are very sensitive to very small(submicron) particles.

The second principal type of air-sampling smokedetection system uses a very sensitive photoelectriclight-scattering detector. Unlike a spot-type, light-scattering smoke detector, this system uses a high-power strobe light or a laser beam rather than aninfrared LED. Where combined with a sensitive lightreceiver, the unit can detect submicron-sized parti-cles in very small concentrations. Other sampling-type smoke detectors might use other detection prin-ciples such as an ionization chamber.

Other Detection Principles

Radiant Energy Detectors. Radiant energy detectorsare often called flame detectors. However, thebroader name, radiant energy detectors, includesunits designed to sense smoldering and glowingember combustion.

The radiant energy emitted during combustionof a fuel falls predominantly into three categories,distinguished by the wavelength of the radiation:

1. Ultraviolet: wavelength smaller than visible radia-tion (smaller than about 0.35 microns)

2. Visible: wavelength larger than ultraviolet radia-tion but smaller than infrared radiation (betweenabout 0.35 microns and 0.75 microns)

3. Infrared: wavelength larger than visible radiation(more than about 0.75 microns)

The two most common wavelengths detected by radi-ant energy detectors are the ultraviolet and infraredbandwidths. Except in very special applications, visi-

ble light comes from so many normal sources that itcannot be used effectively as a fire signature.

The application of radiant energy sensing detec-tors is beyond the scope of this supplement. The se-lection and use of flame and spark detectors iscomplex and requires thorough knowledge of fuelbehavior, environmental conditions, and specific de-tector characteristics. Generally, these detectors areused in special applications such as in aircraft han-gars and areas where flammable and combustiblesolids, liquids, and gases are handled, used, or con-veyed. Subject to the approval of the authority havingjurisdiction, these detectors can be used as part ofan automatic fire detection system required by theLife Safety Code where specific detection, such assmoke, is not mentioned in the occupancy chapter.

Chapter 5 of NFPA 72 contains descriptions ofthese radiant energy detection principles. For moredetailed information on these detectors and their ap-plications, consult the Fire Protection Handbook, FireAlarm Signaling Systems, and the manufacturers’ liter-ature.

Other Fire Detectors. Chapter 5 of NFPA 72 recog-nizes that there are, or might someday be, detectorsother than those already discussed, that are suitablefor use as automatic fire detectors. The selection, ap-plication, and use of any detector are governed bytheir principle of operation, their testing and/or list-ing (if any), and their manufacturers’ recommenda-tions.

Any fire detector listed or approved for its specificintended purpose is permitted to be used where theLife Safety Code requires automatic fire detection butdoes not specify the type. The authority having juris-diction must approve the selection.

Monitoring Other Fire Protection Systems

Fire detection and alarm systems can be intercon-nected to receive signals from other fire preventionand protection systems. These systems might be re-quired by parts of the Life Safety Code and includethe following:

1. Sprinkler systems2. Fire pumps3. Other extinguishing systems (CO2, water spray,

dry chemical, wet chemical, foam)4. Heating, ventilating, and air-conditioning systems5. Smoke control systems

The signals received from these other systems or de-vices might be a fire alarm or a supervisory signalindicating the status of the system or device. Detailed



one another. Trouble and supervisory signals at theprotected premise are permitted to have the sameaudible signal, as long as they have separate anddistinct visual signals. Therefore, the old practice ofwiring a valve tamper switch to open the waterflowalarm circuit and cause a trouble signal is not accept-able. The valve tamper switch would break the circuitjust as a broken wire would. Both would result in atrouble condition at the control panel. Correct andincorrect methods for monitoring supervisory de-vices are addressed in the section on wiring later inthis supplement.

Selection and Placement

Within the context of the Life Safety Code, some degreeof decision making is necessary concerning the typeof detector to be used in a given situation. For in-stance, where the Code requires a supervised firealarm system with initiation by smoke detection, itdoes not specify what type of smoke detection is per-mitted to be used. The Code intends only that lifesafety fire detection goals for this particular occu-pancy be met by smoke detection designed, installed,maintained, and tested in accordance with NFPA 72.The same is true for a required household fire alarmsmoke detector in a dwelling unit. The opportunityto choose a smoke detection method allows designflexibility for performance and economy.

The majority of detectors used to meet the intentof this Code are spot-type ionization, spot-type photo-electric, or projected beam detectors. Air-samplingsmoke detectors are very sensitive and cost more thansystems using spot- and beam-type detectors. Theiruse is generally limited to clean, high-value areassuch as computer rooms and industrial clean roomsfor manufacturing semiconductors. They have alsofound use in telecommunications facilities and powerplant control rooms. Because of their cost and sensi-tivity, these detectors are not a common choice formeeting requirements of most chapters of the LifeSafety Code, despite the fact that they are allowed.Design considerations for these systems are complexand beyond the scope of this supplement.

The first step in selecting a smoke detector is toconsider the type of fire likely to occur in the area.Photoelectric or projected beam detectors would pro-vide a faster response if the fire is likely to smolderfor some time because of the large particles producedduring smoldering combustion. If the fire is mostlikely to be fast and hot with open flames, the largerquantity of small smoke particles will set off an ion-ization smoke detector more quickly than will eithera photoelectric or projected beam detector.

descriptions of these systems are not possible in thisbrief introduction to detection and alarm signaling.However, some information on sprinklers, the mostcommon of these systems, is warranted.

Where an occupancy chapter of the Life SafetyCode requires an automatic sprinkler system, the re-quirement indicates whether the system must be su-pervised. Requirements for automatic sprinklersystem supervision are located in 9.7.2. Under Extin-guishment Requirements, the occupancy chaptermight also state that the system is required to beconnected to the fire alarm system. Under Detection,Alarm, and Communications Systems of the sameoccupancy chapter, the subsection titled Initiation in-dicates whether alarm signals must be activated bythe sprinkler system.

Where a supervised automatic sprinkler systemis required, it must produce a distinct signal to indi-cate conditions that might impair the satisfactory op-eration of the sprinkler system. This requiresmonitoring of such features as the opening and clos-ing of control valves, fire pump operation, water tanklevel and temperature, and both high and low airpressure on dry-pipe sprinkler systems. Chapter 9also requires supervisory signals to terminate withinthe protected premises at a constantly attended loca-tion or in an approved remote receiving facility.

Chapter 9 of the Life Safety Code also requireswaterflow alarm signals from required supervisedsprinkler systems to be transmitted to an approvedauxiliary, remote station, proprietary station, or cen-tral station facility. These systems are introduced laterin this supplement in the section entitled Signaling.Where the occupancy chapter requires a sprinklersystem to be monitored by and to produce an alarmon the protected premises system, NFPA 72 containsrequirements for connection of the system.

NFPA 72 has specific definitions of alarm, trouble,and supervisory signals, at the local protected prem-ises. Alarm signals indicate an emergency requiringimmediate action. A supervisory signal indicates theneed to initiate a specific action regarding some typeof protective service or equipment, such as guard touror extinguishing systems. For example, a closed-valvesignal on a sprinkler system is a supervisory signalindicating the need to investigate the signal and takecorrective action (that is, open the valve) when appro-priate. A trouble signal indicates a fault or problemwith a protective signaling system. Trouble signalsoccur because of faults in the protective signalingsystem, and supervisory signals are signals initiatedin conjunction with other systems or services.

The three different signals must be distinct from



The expected color of smoke should also be con-sidered. Color is important to photoelectric light-scattering detectors but not to projected beam andionization detectors. If black smoke is expected, pro-jected beam or ionization detectors will give the fast-est response. If the smoke is expected to be mostlylarge black particles, the ionization detector falls fur-ther down the list of choices. The projected beamdetector would probably respond first, followed byeither photoelectric or ionization.

Ambient environmental conditions must also beconsidered when selecting a smoke detectionmethod. Smoke detectors cannot be used where thetemperature is above or below the manufacturer’sstated range. This range is usually 32�F to 120�F (0�C to49�C), although lower and higher temperature unitsmight be found.

Cooking odors are blamed for a large numberof nuisance alarms. The odors that are produced bycooking contain a large number of small invisibleparticles. A smoke detector’s response to cookingodors is not a false alarm; it is a response to a validfire signature. An ionization smoke detector wouldprobably trigger a nuisance alarm in response tocooking odors, whereas a photoelectric smoke detec-tor would probably not activate the alarm unless thefood was well burnt and producing visible smoke.Therefore, unless the detector can be located farenough from the kitchen to avoid odors, the betterchoice is a photoelectric detector.

Steam from showers and large sinks contains lotsof small water drops and has much the same effectas cooking odors in causing nuisance alarms fromionization smoke detectors. The heavier the steam,the more likely it is to also cause photoelectric smokedetectors to alarm. However, the highly reflective na-ture of small water droplets in steam may cause pho-toelectric detectors to alarm even at low levels.Detectors can often be located to avoid these sourcesof false fire signatures.

Insects can set off either type of spot-type smokedetector. They are not likely to cause an alarm froma projected beam smoke detector because of the smallamount of light they obscure. Detectors with goodbug screens stop most insects, but some still manageto get into the detector chamber. Ionization smokedetectors are less prone to nuisance alarms from in-sects than spot-type photoelectric smoke detectors.Another solution that has been reportedly successfulis to place an insecticide strip on or near the detector.The detector manufacturer should be consulted be-fore taking this action. Some insecticides might pro-duce enough fumes to set off ionization detectors orharm electronic components. An insecticide should

never be sprayed in or near a functioning detector.It would probably set off the alarm, as would anyaerosol spray, and it could harm the detector.

Cigarette smoke causes nuisance alarms fromionization and photoelectric smoke detectors. Whenthe smoke dissipates to a light cloud, the ionizationdetector is likely to alarm first. When the smoke isheavy and thick, either type will alarm. Often, detec-tors can be placed to avoid such conditions. For in-stance, in elevator lobbies, smoke detectors shouldnot be placed directly in front of the doors wherepeople stand and where drafts from the shaft mightbring dust into contact with the detector. In officeareas, smoke detectors should not be placed directlyover a smoker’s desk or too close to a break room orcafeteria room, where smokers might congregate orwhere cooking might take place. Incidental cigarettesmoke is not likely to set off projected beam smokedetectors. As a smoker passes near the beam, a cloudof smoke 3 ft to 10 ft (1 m to 3 m) wide might beproduced, but it would not be dense enough to alarmthe detector.

Detectors of the ionization or photoelectric typecan be purchased with different sensitivities. Detec-tor sensitivity is usually labeled on the detector andon its specification sheet. The sensitivity is typicallybetween 1 percent and 4 percent per foot (0.3 m)obscuration. This is the amount of light obscurationmeasured immediately outside the detector when italarms during tests with gray smoke. Comparing la-bels on a photoelectric and an ionization smoke de-tector usually indicates the ionization unit to be moresensitive. Typically, ionization smoke detectors havelabeled sensitivities on the order of 1 percent to 2percent per foot. Photoelectric detectors range from1 percent to 4 percent per foot. This does not meanthat ionization detectors are always more sensitivethan photoelectric detectors, only that they might bemore sensitive to fires that produce smoke similar tothe gray smoke used in the test. A true comparisonof detector sensitivity must include consideration ofthe type of smoke expected, as discussed in the previ-ous paragraphs and in the section on fire signatures.

Sensitivity comparison is made more difficult bythe fact that the light obscuration measurement usedby the listing laboratories to rate sensitivity is notcomparable to the factors that actually set off eitherspot detector type. For photoelectric detectors, it isthe light scattered, not the light obscured, that is im-portant. For ionization units, it is the quantity andsize of the particle. The amount of light obscuredacross a given distance is only partly related to thesefactors. The published numbers are useful only as arelative comparison between detectors of a given type



sources of activation such as tobacco smokers, sinks,and kitchenettes.

Many other factors should be considered whenselecting smoke detectors. For instance, in a roomwith moderate to high air movement, smoke from afire that would normally set off a spot-type detectormight be dissipated to form a thin haze. The fire mustgrow larger before there is enough smoke present toset off a spot-type detector. Use of either projected-beam or air-sampling detectors would overcome thisdelayed response. For more discussion of this andother factors affecting detector selection, consultNFPA 72, Chapter 5, as well as the National Fire AlarmCode Handbook, the Fire Protection Handbook, or FireAlarm Signaling Systems. A review of manufacturers’specification sheets and the standards used by testinglaboratories for listing or approval can also providesome insight on detector selection.

The Code contains other choices concerning de-tector selection. In some cases heat detectors mightbe required or smoke detection simply cannot beused due to normal ambient conditions. In some loca-tions, the authority having jurisdiction might requirethe area to be made suitable for smoke detectors. Inother cases, it might be judged that heat detectorscould be used and the life safety intent of the Codewould still be met. These situations demand that achoice be made between the various types of heatdetectors.

If the area has no friendly sources that producerapid temperature changes, rate compensation orcombination rate-of-rise/fixed-temperature heat de-tectors provide good results. If a fast-growing firewere to occur, these detectors would respond beforea fixed-temperature heat detector. If a fire were slowgrowing, they would respond in about the same timeas a fixed-temperature heat detector. Where rapidtemperature changes are expected during normalconditions, fixed-temperature detectors should bechosen.

Detectors installed as household fire alarmequipment must be installed in accordance withNFPA 72, Chapter 11. This category includes single-and multiple-station self-contained smoke alarmsand small systems installed to meet the requirementswithin the dwelling unit. (The distinction among sin-gle, multiple, and system detectors is explained inthe section on wiring in this supplement.) Applicationof the Life Safety Code, combined with Chapter 11 ofNFPA 72, usually results in the installation of smokedetectors on each level of a dwelling unit, outside ofthe bedrooms, and at the base of any stairs leadingto upper levels. In new construction, detectors wouldalso be placed in each bedroom.

as they react to a given type of smoke. A photoelectricdetector having an alarm threshold of 2 percent perfoot obscuration is more sensitive than one with athreshold of 3 percent per foot. Similarly, an ioniza-tion detector with an alarm threshold of 1 percentper foot is more sensitive than one with a thresholdof 2 percent per foot. However, one cannot say thata photoelectric detector with a 2 percent per footobscuration threshold is as sensitive as an ionizationdetector with a 2 percent per foot threshold. It mightbe equally sensitive to the same gray smoke used bythe testing laboratories to evaluate the units, but ina real fire, many factors — including smoke color andsize — could cause one detector to respond beforethe other.

By nature of their design, projected beam smokedetectors are a good choice for large, open spaces.The source and the receiver of commercially availableunits might be placed as far as 300 ft (91 m) apart,with 30 ft (9 m) or more between adjacent beams.Therefore, there might be considerably fewer unitsto install. The sensitivity of projected beam smokedetectors is stated in total percent obscuration re-quired to alarm the unit, not percent per foot, as isthe case with spot-type detectors. The sensitivity isusually adjustable, between about 20 percent and 70percent total obscuration, allowing adjustment fordifferent distances between the source and the re-ceiver.

Because projected beam detectors respond to theaccumulated smoke in their path, they are sensitiveto real fires while remaining insensitive to many envi-ronmental factors that would alarm a spot-type detec-tor. For instance, insects in the light path are not likelyto block 20 percent of the beam. Similarly, a cigarettesmoker might create a cloud of 1 percent to 2 percentper foot smoke, which would be 5 ft or 10 f (1.5 m or3 m) in diameter. If this cloud were under a spot-type smoke detector, it would probably alarm unlessa less sensitive unit were installed. However, the samecloud produces between 5 percent and 20 percenttotal obscuration of a beam projected through thecloud, which projected beam detectors can be set todisregard. Nevertheless, in a real fire scenario, a 20-to 30-ft (6- to 9-m) cloud of smoke — which is 1percent to 2 percent per foot on average — is likelyto be produced by the time a spot-type detector isactivated and goes into alarm. A beam projectedthrough this cloud would be obscured about 20 per-cent to 60 percent, which would set off a beam detec-tor that had been calibrated in that range. Theprojected beam detector could be set for 30 percenttotal obscuration to respond sooner than a spot-typedetector to a real fire, while still disregarding small



However, where the smoke detectors also containthe alarm sounder to alert occupants, additional unitsmight be needed to achieve audibility in all spacesof the dwelling unit. Additional detectors might alsobe warranted to provide longer escape times for someoccupants or to provide faster response when com-plex floor plans are involved and smoke must travela good distance to reach a required detector.

Where the Code requires an automatic fire alarmsystem initiated by smoke detection or heat detection,Chapter 5 of NFPA 72 governs the spacing and place-ment of the chosen detectors. The first step is to placedetectors as close as possible to known hazards andas far away as possible from nuisance alarm sources.Any remaining space is then covered with evenlyspaced detectors. This approach might result in a fewmore detectors than are required, but will providebetter fire detection and reduced chances of false andnuisance alarms. For example, in a hall of a collegedormitory, conditions might allow smoke detectorsto be spaced 35 ft (10.7 m) on center. However, if suchspacing results in a detector immediately outside ashower room, it might be best to use a different incre-ment of spacing, such as 28 ft (8.5 m), and to putdetectors no closer to the shower room door than 14ft (4.3 m).

The maximum spacing between detectors or themaximum distance from any point on the ceiling to adetector is determined by the many factors previouslydiscussed for each detector type. For heat detectors,the installer should begin with the listed or approvedspacing, then make corrections for ceiling height,beams, joists, and slopes. Where using smoke detec-tors, the installer should start with the manufacturer’srecommended spacing, usually 30 ft (9 m), and makeadjustments for ceiling height, beams, joists, slopes,and high airflow. It is important to note that the actualcorrection factors given in NFPA 72 for smoke detec-tors are different from the factors for heat detectors.NFPA 72 should be consulted for the exact correctionfactors to be used.

Once detector spacing has been determined, de-tectors must be located in accordance with other re-quirements of NFPA 72. Exhibit S2.6, reproduced fromthe annex of NFPA 72, shows that ceiling-mounteddetectors must be installed at least 4 in. (10 cm) fromwalls. If the detector is to be wall-mounted, it shouldbe installed at least 4 in. (10 cm), but no more than12 in. (30 cm), from the top of the wall. The 4 in. �4 in. (10 cm � 10 cm) space is called the dead airspace. Detectors in that space will respond moreslowly because smoke and heat from a small fire tendto circumvent the wall–ceiling intersection.

When all correction factors have been applied

to determine a required spacing for detectors, areacoverage begins by locating the first detectors at one-half that distance from a wall. Exhibit S2.7, repro-duced from NFPA 72, demonstrates this concept. Onepart of the exhibit illustrates how spot-type detectorswould be spaced, and the other half indicates howline-type detectors would be evenly located. In thediagram, S is the corrected, or installed, spacing.These examples assume that the corrected spacingresults in a square, such as 30 ft � 30 ft (9 m � 9 m) or25 ft � 25 ft (7.6 m � 7.6 m). In the case of installationbetween beams or joists, the corrected spacing wouldcreate a rectangle such as 15 ft � 30 ft (4.6 m � 9m), the shorter distance being measured perpendicu-lar to the joists or beams. Note in Exhibit S2.7 thatno point on the ceiling can be farther from a detectorthan 0.7 times the installed spacing. This maximumdistance applies to all points on a ceiling and is usefulin laying out systems in irregularly shaped spaces.This concept is discussed in detail in NFPA 72.

If a ceiling has solid beams or joists, it must bedecided whether the detector should be located onthe bottom of the beams or joists or in the ceilingpocket. In the case of beamed ceilings, the detectorcould be located on the bottom of the beams or onthe ceiling in the pocket, depending on the beamdepth, beam spacing, and ceiling height. The readershould refer to NFPA 72 for specific requirements.Note that bar joists and trusses might not significantlyimpede the movement of smoke and heat. Unless thetop cord of the bar joist or truss that is in direct contactwith the ceiling is more than 4 in. (10 cm) deep, the


Ceiling

Acceptable here

Never here

Sidewall

Top of detectoracceptable here

Note:Measurements shown are to theclosest edge of the detector

4 in.(100 mm)

4 in.(100 mm)

min.

12 in.(300 mm)

max.

Exhibit S2.6 Dead air space.


ment or people walking, might set it off. If dust hascaused a detector to become more sensitive, evensmall amounts of cigarette smoke or other aerosolscould set it off. Note that many analog, addressablesmoke detectors have drift compensation algorithmsto compensate for dirty chambers. Plaster and gyp-sum board dust are very difficult to clear from a detec-tor without disassembly, cleaning, and subsequentrecalibration by factory-trained service personnel.

Despite demands for a certificate of occupancy,early installation of detectors will only lead to futureproblems and must be resisted. NFPA 72 specificallystates that smoke detectors are not permitted to beinstalled prior to the completion and cleanup of allother trade work. If acceptable to the authority havingjurisdiction, however, the detectors might be installedwhile covered with bags or part of their original pack-aging. However, covering will render the smoke de-tectors unable to respond to smoke during a fire. Theremainder of the system will be operational. Never-theless, the life safety aspects of the system will havebeen compromised until the smoke detectors are un-covered.

In an open office area with a 20-ft (6-m) ceilingheight, spot-type detectors might be used. However,

ceiling is considered smooth. In that case, the detec-tors must be mounted on the ceiling. Required detec-tors are not permitted to be mounted on the bottomof bar joists or trusses.

Detectors must also be located for ease of testingand maintenance. A smoke detector located over theopen part of a stair tower probably cannot be reachedvery easily once scaffolding is removed. As a result,smoke detectors are often not tested or cleaned andmight fail in a fire or cause false or nuisance alarms.Detectors should be located over a landing or wherea ladder can be placed to reach them. There is noneed to place the detector in the middle of the space.The space is considered to be adequately covered aslong as all points on the ceiling are within the detec-tor’s protection radius (0.7 times the installed spac-ing). Thus, in most stair towers, wall mounting wouldbe sufficient to cover the space.

Construction dust is one of the largest causesof false and nuisance alarms from smoke detectors.When smoke detectors are installed before all con-struction work is complete, they collect dust in theirchambers. The dust can cause immediate alarms, orit can bring the detector close to alarming. As a result,the slightest physical disturbance, such as air move-


S S S

S

S

S

0.7S 0.7S

Line-type detector

SSS

0.7S

S — Space between detectors

Spot-Type DetectorsLine-Type Detectors

Heat Detectors—Spacing Layouts, Smooth Ceiling

0.7S 0.7S 0.7S

Heat Detectors

¹⁄₂ S¹⁄₂ S

¹⁄₂ S ¹⁄₂ S

¹⁄₂ S

¹⁄₂ S

¹⁄₂ S

¹⁄₂ S ¹⁄₂ S

Exhibit S2.7 Spot- and line-type detector spacing.


once the area is occupied, maneuvering a high ladderfor the purpose of testing would be nearly impossible.This illustrates an application where a projectedbeam smoke detector would be preferred. The senderand receiver could be located on opposite walls wherea ladder can be leaned to reach the units for cleaningand testing.

Many other factors affect the selection and place-ment of fire detectors. Temperature stratificationsmight prevent smoke from reaching the ceiling; air-flow might speed the response of properly locateddetectors and slow the response of poorly locateddetectors; the height and width of fire and smokedoors might require additional smoke detectors fordoor release; machinery vibrations or radio frequencyinterference might result in the relocation of detec-tors to avoid false alarms. Complete familiarity withNFPA 72 is the best source of information for installinga reliable system. The reference list following thissupplement contains other valuable references to as-sist designers, installers, inspectors, and owners inachieving reliable fire detection while minimizing thechance of false or nuisance alarms.

POWER SOURCES AND SYSTEM WIRINGMETHODS

Household Fire Alarm Equipment

Dwelling units are most often equipped with eithersingle-station or multiple-station smoke alarms. Insome cases, small systems designed as household firealarm equipment, with detectors, a control panel, andsome notification appliances, are used. Often, thecontrol panel also serves as part of a security system.

Single-station smoke alarms are stand-aloneunits that detect smoke and provide occupant notifi-cation. Multiple-station units are actually single-station detectors that can be interconnected so that,if one is activated, all units sound an alarm. Mostsingle- and multiple-station smoke alarms containonly an internal horn, although some contain flashinglights as well. Units are also available with internalrelays that can be used to control other functions,such as door release, a nurse call signaling system,activation of a bed shaker to alert a hearing-impairedperson, or operation of a light outside the dwellingunit.

For existing construction, the detectors may bepermitted to be powered by battery or by commerciallight and power (usually 120 V AC). Chapter 11 ofNFPA 72 requires detectors used in new constructionto have both primary AC power and secondary powerby a battery. Alternatively, a detector with a non-

removable, 10-year battery is permitted. In existinghouseholds, AC power is preferred. However, whereAC is not practical, NFPA 72 allows the use of a moni-tored battery as the power source. Within the LifeSafety Code, some occupancy chapters require ACpower, even in existing facilities, where NFPA 72would allow battery-operated units.

One reason AC-powered detectors are preferredis that the detector is less likely to be subject to tam-pering. Battery-powered (only) units are often disa-bled when the battery is ‘‘borrowed’’ for a toy or otherdevice or removed due to false or nuisance alarms.Also, when batteries die they are often not replacedfor some time, leaving part or all of the dwelling unitwithout smoke detection.

Some argue that battery power is superior be-cause, during a power outage, people resort to can-dles for light and to fireplaces, stoves, or portableheaters for heat, all of which increase the probabilityof fire. However, the increased chance of fire maynot offset the fact that, over time, loss of commercialpower is less likely and shorter in duration than lossof battery power. NFPA 72 reflects the belief that thechance of fire during a power outage is smaller thanthe chance of fire occurring when a detector is ren-dered useless because it has no battery.

Single-station smoke alarms are now availablewith AC power and integral battery backup. Theseunits are allowed, but not required, by both the LifeSafety Code and NFPA 72 for existing construction, butthey are required by both for new construction. Localcodes, ordinances, or authorities can require theiruse.

NFPA 72, Chapter 11, requires that a switch notcontrol AC power and that the circuit not have aground fault interrupter — except where a groundfault interrupter serves all electrical circuits in thedwelling. Direct wiring to a power circuit is pre-ferred. However, if a plug-in electrical cord is used,the standard requires some restraining method tomake certain the unit is not accidentally unplugged.NFPA 72 permits AC power to come from either adedicated circuit or an unswitched power or lightingcircuit. Some experts prefer that AC-powered detec-tors be connected to an often-used light circuit,such as one feeding kitchen or hallway lights. Then,if a fault occurs, such as a blown fuse or circuitbreaker, it is likely to receive immediate attention. Ifthe detectors were connected to their own dedicatedcircuit or to one infrequently used, loss of powermight go unnoticed until the units were tested. AC-powered units must also have a visual ‘‘power on’’indicator.


1129Power Sources and System Wiring Methods

NFPA 72 Protected Premises and SupervisingStation Systems

Power. Systems intended to meet the requirementsof NFPA 72 are required to have two power sources —primary power and secondary power. Primary powermust come from a reliable source and is usually takenfrom a commercial light and power source, althoughNFPA 72 allows other sources to provide primarypower such as engine-driven generators. Primarypower must come through a dedicated branch circuit.Access to the circuit disconnecting means must berestricted and clearly marked ‘‘FIRE ALARM CIR-CUIT.’’

Secondary power is intended to operate all func-tions of the system in the event that primary power islost. Most often, standby batteries provide secondarypower. Engine-driven generators are also permittedto be used. All systems must be provided with sec-ondary power capable of operating the system for 24hours under normal loading conditions. Prior to the2002 edition of NFPA 72, some systems required 24hours and others required 60 hours of supervisorypower. At the end of the normal supervisory period,each system must have 5 minutes of alarm poweravailable, or if it’s an emergency voice/alarm commu-nication system, 15 minutes of full load power.

NFPA 72 Circuit Classifications. In addition to powersupply circuits, three principal types of circuits areused in fire protective signaling systems:

1. Initiating device circuits (IDCs)2. Signaling line circuits (SLCs)3. Notification appliance circuits (NACs)

An initiating device circuit (IDC) connects manualand automatic devices to a control panel or system.The main characteristic of an initiating device circuitis that the signal received at the control panel doesnot identify the device that operated. These circuitsare also called initiating zones of the fire detectionpanel. Because the devices are not readily identifiedat the panel, the quantity of devices on a circuit andthe area served by the circuit should be limited tomake identification of the source a bit easier.

In addition, because the control panel cannot rec-ognize the individual devices on the circuit, alarmdevices cannot be mixed with supervisory devices —such as valve tamper switches — on the same circuit.Exhibit S2.8 shows one version of incorrect and cor-rect methods for monitoring waterflow and valvetamper switches where using initiating device cir-cuits.

A signaling line circuit (SLC) might connect ini-

Chapter 11 of NFPA 72 contains requirements forunits that use batteries for primary power. Basically,these units must be designed so the battery will lastfor at least one year of normal use, including weeklytesting. Also, they must provide an audible troublesignal when the battery is low, well before the unitfails to operate. The unit must be capable of soundinga trouble condition at least once a minute for sevendays and still have enough battery power to operatethe alarm sounder for 4 minutes. Because of this re-quirement, it is very important that only battery typesrecommended by the manufacturer be used. Addi-tionally, the smoke detectors must visually indicatewhen the battery has been removed.

Where multiple-station units are used, they mostoften are connected to the same power circuit andalso have a trip wire that interconnects them. Whenusing multiple-station detectors, the manufacturer’swiring diagrams and instructions should be followedclosely. There is a limit on how many units shouldbe interconnected. Some models allow only five orsix detectors to be interconnected, while others allowup to thirty in a chain. However, Chapter 11 doesnot allow more than twelve multiple-station smokealarms to be interconnected unless the intercon-nection is monitored for integrity. Detectors fromdifferent manufacturers cannot be interconnected.Different models from the same manufacturer mightnot be compatible for interconnection. Compatibilitybetween different models allows both ionization andphotoelectric detectors to be used on the same circuitwhere each is advantageous and also allows varioussensitivities to be used in different areas of the dwell-ing unit.

The Life Safety Code and Chapter 11 of NFPA 72both allow the use of component systems, rather thansingle- or multiple-station units, within a dwellingunit. The system must be listed or approved for useas household fire alarm equipment. NFPA 72 containsrequirements, including supervision of detector cir-cuits, for the performance of component systemsused within the dwelling unit. The use of wirelessradio as the signal transmission medium is permitted,provided each detector has its own transmitter andthe unit automatically sends a test signal at least onceevery 24 hours. The installation of hard wiring forcomponent systems is required to meet Article 760of NFPA 70, National Electrical Code.�

NFPA 72 allows the use of combination systems,provided the fire detection and alarm portion of thesystem takes precedence over all other functions.Alarm signals for fire and any other function, suchas burglary, must be distinctive.



tiating devices to a control panel or system, or mightinterconnect various pieces of control equipment. AnSLC is characterized by its ability to carry multiplesignals, often in two directions, and to identify thesource of the signal. For instance, multiplex systems,often called smart systems, communicate with initiat-ing and control devices. Each device or group of de-vices might have a unique address. The panel signalsto a specific address and asks for the status of that‘‘point.’’ The device responds by repeating its addressand its current status, such as ‘‘alarm’’ or ‘‘trouble.’’Therefore, the circuit is carrying multiple pieces ofinformation and there is two-way communication.

Where signaling line circuits are used, it is possi-ble to combine alarm and supervisory devices on thesame circuit or data pathway. Because each device orgroup of devices is recognized at the control equip-ment, different output signals can be programmedfor each.

The third type of circuit, the notification appli-ance circuit (NAC), serves appliances such as horns,bells, lights, and other notification appliances. NACsare often called signal circuits because they connectto devices intended to signal the occupants of a fireemergency. Even though occupant notification appli-ances generate a signal, care must be exercised notto confuse the circuit designations within the scopeof NFPA 72. There are requirements for signaling linecircuits that differ from those for notification appli-ance circuits.

Circuit Supervision. NFPA 72 requires all means forinterconnecting equipment and devices to be moni-tored for integrity. This is commonly referred to as

circuit supervision. The Code also contains require-ments for monitoring power supplies as well as thecircuits to detectors and notification appliances.Monitoring power sources is primarily a function ofthe control equipment. Compliance with NFPA 72 re-quirements is checked during testing and listing orapproval of the system. See NFPA 72 for performanceand installation requirements.

The performance of IDCs, SLCs, and NACs is afunction of the equipment and the installation of thecircuits. Tables in NFPA 72 describe the performanceof each type of circuit — including open circuits,ground faults, and short circuits — during variousfaults. Circuits are categorized by class and by style.IDCs, SLCs, and NACs are either Class A or Class B,depending on their ability to operate during a singleopen circuit or ground fault condition. Circuit styledesignations are based on their ability to operate dur-ing different combinations of faults, includinggrounds, opens, and short circuits. Neither the LifeSafety Code nor NFPA 72 specifies the class or style ofcircuits that must be used for a given application.Unless the authority having jurisdiction specifies acertain style, it is up to the designer to make a selec-tion.

Some systems use selective signaling systems foroccupant notification during a fire. These systemswould sound evacuation signals or relocation signalsonly to certain areas of a building, such as the firefloor, floor above, and floor below. These are oftenpart of a protected premises system, forming what iscalled a ‘‘combination system.’’ The circuits con-nected to speakers and lights are referred to as notifi-cation appliance circuits. Because these systems aremost often used in high-rise buildings or in areassubject to levels of hazard that are higher than nor-mal, NFPA 72 contains requirements for survivabilityof the notification functions when the circuits areattacked by fire. By requiring the system to survivean attack by fire in certain locations, the standardnarrows the choice of circuit styles and the methodsof installation. For more information on these re-quirements, consult NFPA 72, Chapter 6.

The discussion of circuits for controlling auxiliaryfunctions, such as door release, fan control, and eleva-tor recall, is beyond the scope of this supplement. Itis important to note, however, that the Life Safety Codeand NFPA 72 require these circuits to be supervisedto within 3 ft of the device being controlled. See Chap-ter 9 of the Life Safety Code and Chapter 6 of NFPA72 for more information on these circuits.

Device Compatibility. Initiating devices and notifi-cation appliances must be compatible with the con-


Tamper switchcauses troublethe same asa broken wireINCORRECT

Circuit initiatesalarm signaland functions

Waterflowswitch closeson alarm

Valve tamperswitch openson activation

Circuit initiatessupervisorysignal andfunctions CORRECT

Waterflowswitch

Valve tamperswitch closeson activation

End-of-line device

End-of-line device

End-of-linedevice

Exhibit S2.8 Incorrect and correct wiring of valve tamper switch.

1131Signaling

Alarm Signaling Systems, and the approval or testagency’s performance standards.

To check system compatibility, it is necessary toknow the specific model of control panel as well asthe model and quantity of the initiating device inquestion. Compatibility should be checked by con-sulting each manufacturer and the testing or approvalagency acceptable to the authority having jurisdic-tion.

Addressable initiating devices must be compati-ble with the control equipment. They must speak thesame language as control equipment and meet thenetwork response characteristics required by NFPA72. However, many devices, such as waterflowswitches and projected beam smoke detectors will beconventional, contact type devices interfaced to thecontrol unit through compatible monitor modules —also called signaling line circuit interfaces by NFPA72.

Wiring Methods. Article 760 of NFPA 70, NationalElectrical Code�, covers the installation of wiring forfire alarm systems operating at 600 V or less. Article760 allows two types of wiring methods — power-limited and non–power-limited. For a circuit to bedesignated as power-limited, it must meet certainvoltage and power limitations. These are checked bythe listing or approval agency. Where a circuit is des-ignated as power-limited, the requirements for thewiring type and installation are less restrictive thanif the circuit is non–power-limited.

In addition to defining power-limited andnon–power-limited circuits, Article 760 provides de-tailed requirements for wiring methods. Included arerequirements for wire gauges, insulation require-ments, minimum requirements for stranded wires,overcurrent protection, circuit identification, and wir-ing raceways. Also included are restrictions on com-bining the use of power-limited and non–power-limited circuits and other nonfire circuits in the sameraceway or enclosure.

The National Electrical Code should be consultedfor details on wiring requirements. Additional dis-cussion of Article 760 is contained in the NationalElectrical Code Handbook, which provides an explana-tion of the reasoning and intent behind specific codeparagraphs.

SIGNALING

The subject of this section is output signaling, as op-posed to the type of signaling that occurs betweendetectors and control equipment discussed in the sec-tion on wiring. The principal signaling functions of

trol equipment to which they are connected. Whereaddressable, multiplex-type equipment is used, thereis no doubt that the equipment must be compatibleand must be designed specifically to work together.With notification appliances and conventional initiat-ing devices, however, there is more flexibility inchoice.

In the case of notification appliances, compatibil-ity is primarily a function of voltage and power con-sumption. Therefore, designers, suppliers, andinstallers can match notification appliances from onesource with control equipment from another source.However, the increased use of strobe lights and therequirement that they flash in synchronization havemade it more difficult to mix and match strobes andpanel power supplies. Changes may take place in the2006 edition of NFPA 72 and in listing organizationstandards to create categories of strobe and powerlistings that will require more careful matching bythe designer and installer.

For initiating devices, compatibility depends onwhether the device requires operating power. Me-chanical devices such as manual fire alarm boxes,most heat detectors, and waterflow switches do notrequire power to operate. When they alarm, theyclose a set of contacts, as a light switch does, to signalthe control panel. There is no compatibility issue be-cause these devices can be mixed and matchedamong various manufacturers.

If a device does require operating power, as asmoke detector does, compatibility depends onwhether its source of operating power comes fromthe initiating device circuit (often called the detectionzone) or from a separate, external power circuit.Where power comes from a circuit other than theone used to signal the control panel, there is nocompatibility issue. As in the case of notificationappliances, compatibility is then only a function ofvoltage and power consumption from the externalpower circuit. When the detector alarms, it closesa set of contacts to signal the control panel via theinitiating device circuit in the same way a mechani-cal pull station does.

However, where a device such as a smoke detec-tor obtains its operating power from the same circuitit uses to signal an alarm, compatibility is very im-portant. These devices are often referred to as two-wire, zone-powered, or circuit-powered detectors.The electrical characteristics of the control panel andthe detectors, including supervisory currents andalarm currents, must be matched carefully to ensureproper operation. Detector compatibility is a verycomplex issue. For more information on this subject,consult manufacturers’ data sheets, NFPA 72, Fire



a system are off-premises signaling to emergencyforces and occupant notification.

Off-premises signaling may be transmitted to asupervising station that is part of a central stationsystem, an auxiliary system, a remote station system,or a proprietary signaling system in accordance withNFPA 72. Where off-premises signaling is required ordesirable, Chapter 8 of NFPA 72 should be consultedconcerning installation and performance require-ments for the system. That chapter contains require-ments for the transmitter at the protected premises,the transmission method, and the receiving system.The standards allow only certain signaling methodsthat have shown themselves to be reliable. NFPA 72does not recognize telephone tape dialers, for exam-ple. Similarly, digital communicators with only onephone line are not permitted, except in householdfire alarm systems.

Each occupancy chapter of the Life Safety Codeclearly states where occupant notification and/oremergency forces signaling is required. The chaptermight also require specific occupant notification sys-tems, such as emergency voice/alarm communicationsystems in high-rise hotels and dormitories. Each oc-cupancy chapter should be carefully reviewed to de-termine which initiating devices are required toactivate occupant notification signals and off-premises signaling. In most cases, all initiating de-vices operate as general alarm devices and activateall output functions. However, there are cases wheredetectors in specific areas of a building might not berequired to sound evacuation signals. For example,duct smoke detectors may be permitted, or even re-quired, to sound only a supervisory signal, not analarm signal.

Where occupant notification is required, it mustbe distinct and clearly audible in all occupiablespaces. Chapter 7 of NFPA 72 contains criteria for thedefinition of Audible. The recommended noise levelfrom an alarm system is at least 15 dBA above the24-hour average ambient level or at least 5 dBA aboveany peak background noise that lasts 1 minute ormore (dBA stands for decibels, A-weighted. This is away of measuring sound pressure levels and ad-justing for the way the human ear hears.) In areasused for sleeping, a minimum of 75 dBA is requiredby NFPA 72. This is an increase of 5 dB over previouseditions, which required a minimum of 70 dBA.

There has been some concern that audible firealarm signals may be insufficient to awaken somepeople, including young children. The 75-dBA re-quirement (and the previous 70 dBA requirement) isbased on actual testing of a variety of ages. Drugs or

alcohol did not impair the subjects. For some subjects,actual awakening at these levels was achieved in sec-onds, while others were not awakened for severalminutes. It is expected that these levels are sufficientto awaken a very high percentage of the general pop-ulation. However, if regular occurrence of drug oralcohol impairment, heavy sleepers, or persons notcapable of self preservation are anticipated, thenother signaling strategies may be warranted, beyondwhat the code requires.

The use of inexpensive meters (under $40) allowsbackground levels in existing areas to be checked andsystems to be installed appropriately. Ambient andfire alarm noise levels should be measured with allintervening doors closed and with common equip-ment such as air conditioners operating. For new con-struction, NFPA 72, Annex A, provides examples ofambient noise levels in a variety of occupancies.

Once background levels have been determined,design methods can be used to determine where au-dible notification appliances should be located. Onesuch procedure is presented and discussed in TheSFPE Handbook of Fire Protection Engineering. Calcula-tions are not needed for existing construction. Porta-ble appliances can be tried in a variety of locationsbefore final mounting.

In most new construction, due to minimum insu-lation requirements and privacy laws, it is not possi-ble to place alarm devices in common hallways andexpect them to meet audibility requirements in adja-cent spaces. Tests show that, in most cases, an audibledevice may be loud enough in only one or two imme-diately adjacent spaces. Therefore, a large numberof units would be required in the common halls ofoccupancies such as apartments or dormitories. Costestimates often indicate that it is less expensive toput smaller devices in each space, rather than to pro-vide the required number of larger devices in com-mon spaces.

NFPA 72 includes provisions allowing the use ofnarrow band noise analysis and signaling. By analyz-ing the frequency content of noise, it is often possibleto design more efficient fire alarm signaling systemscompared to those designed using dBA measure-ments. Often, the noise is concentrated in one ormore octave bands. By using a signal in a differentoctave band, the alarm can be heard even though adBA measurement might not ‘‘hear’’ the signal. Formore information, consult the National Fire AlarmCode Handbook or the 19th edition of NFPA’s Fire Pro-tection Handbook.

In addition to audible appliances, the Life SafetyCode might require visual appliances for occupant


1133Signaling

sage should contain several key elements. These in-clude:

• Tell them what has happened and where.• Tell them what they should do.• Tell them why they should do it.

It is not possible to measure the audibility of a voicesignal in the same way as tone signals. In addition,audibility is insufficient to ensure that the message isclear and understood. The intelligibility of the voicesignal is measured in a different way that includesaudibility, clarity, distortion, reverberation and sev-eral other important components. The National FireAlarm Code Handbook includes a supplement describ-ing voice intelligibility.

In a large space used for public meetings, conven-tions and trade shows, an EVAC system needs to bereliably intelligible, because it is intended to giveinformation to a general public not familiar with thespace. In large public spaces, occupants should nothave to move any great distance to find a place wherethey can understand the message.

In a high-rise apartment building, it may not benecessary for the EVAC system to be intelligible inall parts of the apartment, even though it must beaudible in all parts. It may be sufficient to provide aspeaker in a common space to produce an adequateaudible tone to awaken and alert the occupants.When the voice message follows, it may not be intelli-gible behind closed bedroom and bathroom doors.The occupants, in a familiar space, can move to alocation where a repeating message can be intelligi-bly heard. The same signaling plan may work foroffice complexes — a person may have to open theiroffice door to reliably understand the message.

While an EVAC system is the most commonmethod of communicating information to occupants,it is not the only method. Research has shown thattext and graphical messaging greatly enhance occu-pant movement during evacuation and relocation.The message delivery can be via large screens usedin sports arenas or by small LCD display or CRTinformation kiosks located throughout a property.

Other types of output signaling that a fire alarmsystem might be required to provide include the fol-lowing:

1. Fan and damper control2. Heating, ventilating, and air-conditioning systems3. Smoke control systems4. Elevator control systems5. Emergency lighting systems6. Process control systems

notification. Chapter 7 of NFPA 72 would then beconsulted for the proper selection and placement ofvisual appliances to meet specific needs.

The signal produced by notification appliancesmust also convey the following information: FIREEMERGENCY. This is where the requirement for dis-tinct signals is applied. For instance, in a school, bellsshould not be used on a fire alarm system if bells arealso used to signal class changes and recess. Similarly,in buildings equipped with earthquake warning sys-tems, the fire signal needs to be distinct from anearthquake signal and recognizable by the occupants.NFPA 72 permits more than one signal to be used ina building, such as chimes in patient care areas of ahospital and horns elsewhere. However, both mustbe distinct and not used for any other purpose.

NFPA 72 has a requirement for a standard audibleevacuation signal. The signal, referred to as a tempo-ral coded three signal, can be produced on a varietyof appliances such as bells, horns, speakers, andchimes. A coded three signal is recognized interna-tionally as a distress signal. Thus, it would be thepattern of the signal, not the particular sound thatwould convey the information that there is a fireemergency.

Improvements and cost reductions in emergencyvoice alarm communication (EVAC) systems havemade it economical to provide prerecorded and man-ual voice announcement systems in many applica-tions. Most codes, including the Life Safety Code,require the use of voice signaling only in high-risebuildings, in large assembly occupancies, and in diffi-cult to evacuate situations. Nevertheless, these sys-tems can be used effectively in a variety ofapplications. Because the NAC circuits are connectedto speakers driven by amplifiers, it is easier than itis with conventional direct current devices and lessrestrictive to add additional appliances when audi-bility is an issue. Also, speakers generally haveadjustable power taps, permitting minor adjustmentin audibility that is not possible with most conven-tional sounders. Finally, it is well known that aproperly implemented voice announcement will re-sult in faster and more complete evacuation ofoccupants.

Fire alarm systems that only use audible tonesand/or flashing strobe lights impart only one bit ofinformation: FIRE ALARM. It has long been recog-nized that environments having complex egress situ-ations or high hazard potentials require occupantnotification systems that provide more than one bitof information. To reduce the response time of theoccupants and to effect the desired behavior, the mes-



SYSTEM INSPECTION, TESTING, ANDMAINTENANCE

Surveys and general field experience demonstratethe importance of continued testing and maintenanceof fire detection and signaling systems. Inspectionsare used to find changes in the building or environ-ment that might affect a system. Testing identifiesproblems before they impair a system’s ability to per-form during an emergency. Maintenance reducesfalse and nuisance alarms and keeps systems in ser-vice.

The Life Safety Code requires all fire detection andsignaling equipment to be maintained and tested inaccordance with the appropriate signaling standard.In the case of household fire alarm equipment, Chap-ter 11 of NFPA 72 is the governing standard. For othersystems, Chapter 10 of NFPA 72 contains require-ments for acceptance and periodic tests, visual in-spections, and maintenance. Chapter 10 containsthree important tables. The first lists the requiredfrequency for visual inspections. The second tablelists the methods for testing specific components, de-vices, and appliances. The third table lists the re-quired frequency for actual testing of the specificcomponents, devices, and appliances.

Whenever a system or device is to be tested, it isimportant to notify those who might hear or receivea signal from the system. Usually this means severaldays of advance notice to authorities and regular oc-cupants of the area. In addition, when systems will betested or worked on, the authority having jurisdictionmust be notified, even for periodic tests that theymight not witness. Other trades or specialists mightrequire notice to participate in the tests. For instance,testing of smoke detectors used for elevator recallmight require elevator technicians to be present, orHVAC mechanics or electricians may be required toreset air-moving equipment or dampers after the sys-tem has been tested. In addition, posting notices atentrances to the premises to alert people as they ar-rive is usually advisable. Notices should includephone numbers or brief procedures for reportingemergencies while the system is being tested or ser-viced.

The fire protection industry thinks of fire alarmtesting as a positive thing, designed to uncover faultsand increase reliability. However, a large segment ofthe public thinks of fire alarm testing negatively, asa nuisance and an interruption of their lives and work.Often, the public’s perception of testing is no differ-ent from that of false or nuisance alarms. This leadsto the Cry Wolf Syndrome. If long, drawn out testingof alarm systems several times each year ensures an

operable system but causes occupants to delay egressor even stay when the desired action is for them toleave, the actual increase in safety must be ques-tioned.

When testing occupant notification systems, it isimportant to keep to a posted schedule and minimizethe time of testing to prevent occupants from becom-ing desensitized to the signaling. This requires havingsufficient personnel and equipment to do a thoroughand fast test. Test programs should be designed tobe thorough, but to minimize their impact on unin-volved occupants. The tester should consider recruit-ing key occupants to assist in qualitative examinationof the notification system. Also, combining the audi-ble and visible appliance testing with a fire drill forall occupants minimizes the effect of Cry Wolf Syn-drome. The tester should also try to minimize thefrequency and duration of the tests. For example, testonly at 10:00 A.M. and again at 2:00 P.M. and for only30 to 60 seconds.

Household Fire Alarm Equipment

The requirements for testing and maintenance ofhousehold fire alarm equipment are kept simple sothat in most cases the homeowner can do the work.NFPA 72 requires that battery-operated units get newbatteries in accordance with the manufacturers’ rec-ommendations. In most cases, manufacturers recom-mend replacement of batteries at least once a year.Recent educational and awareness programs havepromoted battery changing at the same time thatclocks are changed from daylight savings time to stan-dard time in the fall of each year. Scheduled batteryreplacement, rather than waiting for the signal thatindicates the need for replacement, tends to increaseconfidence that the detector will work when needed.Facilities with large numbers of battery-operated de-tectors save time and labor by replacing all batteriesat the same time, whether or not it is indicated.

NFPA 72 requires monthly testing of householdfire alarm equipment. Where small systems with de-tectors and control panels are used in lieu of single-or multiple-station smoke alarms, NFPA 72 requiresthe owner to have the system tested by qualified tech-nicians at least every 3 years.

All tests, inspections, and maintenance recom-mended by the manufacturer must be performed inaccordance with its instructions. This emphasizes theimportance of providing the owner, member of thehousehold, or occupant with the manufacturer’s in-struction booklet(s). Without the proper documenta-tion, the individuals performing the test may not beaware of their responsibilities or the correct methods


1135System Inspection, Testing, and Maintenance

after installation and wiring tests have been com-pleted. A final version is to be issued and distributedafter all operational acceptance tests have been com-pleted. A sample copy of a certificate of completionis included in NFPA 72.

Following final acceptance of the system, the in-staller or supplier must provide the owner with anowner’s manual or manufacturer’s installation in-struction, as well as final ‘‘as-built’’ drawings. Duringacceptance or reacceptance testing, the certificate ofcompletion and as-built drawings must be verified foraccuracy and completeness. If necessary, correctionsshould be made to the master documents, and anyold copies should be replaced or updated.

Installation testing includes checking the entiresystem for stray voltages, ground faults, short circuits,and open circuits. Ground fault testing includes test-ing all conductors not intentionally connected toground.

The loop resistance of initiating and notificationappliance circuits must be measured and recorded.The measured value should be checked against themaximum allowable loop resistance indicated by themanufacturer of the control equipment. Signalingline circuits should also be tested in accordance withthe manufacturer’s recommendations. This usuallyincludes measurement of circuit capacitance as wellas resistance.

System testing is done after all installation testshave been performed. After replacing any equipmentremoved during testing of the circuits, the controlunit and all devices should be verified as being inthe normal supervisory mode. Each circuit should bechecked for proper supervision and integrity. Thisincludes testing open circuit trouble indication aswell as ground fault and short circuit fault indicatorswhere provided. Where the style of circuit allowsalarm receipt during specific faults, correct operationshould be checked by testing devices electrically be-fore and after the location of the test fault. It is usefulduring the testing to use a copy of the wiring styletables from NFPA 72 as a checklist.

Every initiating device and indicating appliancemust be checked for correct alarm operation. Thisverifies correct operation of the device, the circuit,and the control equipment. For systems that responddifferently and result in different outputs dependingon the device or devices in alarm, a programmingmatrix should be prepared and checked. The matrix,or system description, should explain what occurswhen each particular device or group of devices isoperated. For instance, an alarm from any first floordetector might cause bells to ring, doors to release,and a connection to the fire department to be acti-

for testing and maintenance. NFPA 72 requires theinstaller or supplier to provide this and other infor-mation to the owner. In addition to the instructions,the owner must receive information on how to estab-lish an evacuation plan and information on detectorparts that require regular replacement, such as bat-teries. The owner must also receive written informa-tion on where to obtain repair and replacementservice. It is important that users of household firealarm equipment understand that the code-requiredminimum may give them only seconds to react andget out. In situations where a person might be im-paired due to alcohol or drugs, or where elderly per-sons, young children or mobility-impaired personsneed evacuation assistance, the warning given bycode-required minimum coverage may be insuffi-cient.

Each smoke detector for use in any applicationdetailed in NFPA 72, Chapter 11 is required to havean integral test method. An aerosol, such as cannedsmoke, should be used to verify that the smoke detec-tor is not blocked by excessive dust accumulation orby intentional blocking of the screen or ports. It isoften impossible to tell by visual inspection alone ifa detector has been blocked.

Cleaning of smoke detectors is necessary to pre-vent false and nuisance alarms and to ensure detectoroperation during a fire. NFPA 72 leaves the methodsand frequency of cleaning up to each manufacturer.Most manufacturers recommend cleaning once ortwice a year by vacuuming around the outside of thedetector. Some detectors are now available that canbe washed in a soap and water solution. Most manu-facturers do not recommend disassembly of detectorsfor cleaning except by qualified technicians. If thedetector is cleaned and properly maintained fromthe time it is new, the need for factory cleaning andcalibration is almost eliminated.

Acceptance Testing

NFPA 72 requires 100 percent testing of the entiresystem upon completion of any installation or alter-ation. The test must include all devices and equip-ment and must test the system in all modes, includingalarm, trouble, and supervisory. Satisfactory testsmust be made in the presence of the authority havingjurisdiction or a designated representative. NFPA 72recognizes reacceptance tests on parts of systems af-fected by alterations or repairs.

A preliminary certificate of completion is re-quired to be issued to the owner and, if requested,to the authority having jurisdiction prior to the finalacceptance test. The preliminary certificate is issued



vated. On the other hand, only certain smoke detec-tors might activate a smoke management system. Theuse of a table or matrix describing these optionsspeeds testing and future work on the system. ExhibitS2.9 shows a partial system operation matrix.

Power supplies must also be tested during accep-tance and reacceptance tests, including testing theswitchover from primary to secondary power by dis-connecting the primary supply. While the system ispowered by the secondary supply, the standby cur-rent should be measured in accordance with the man-ufacturer’s recommendations. The required standbycapacity can then be calculated and compared to thestandby power that was provided. While on second-ary power, the system should be tested for full alarmperformance for at least 5 minutes. This test shouldbe repeated with the system on primary power andwith any secondary supply disconnected. Supervi-sion of power supplies should also be tested.

Smoke detectors must be tested in accordancewith Chapter 10 of NFPA 72. During an acceptancetest, it is not necessary to measure the detector’s sen-sitivity. A pass/fail or go/no go test using smoke oranother unmeasured aerosol is acceptable. All smokedetectors, including duct and air-sampling types,must be checked to ensure that smoke is entering thedetector’s chamber. In all cases, the manufacturer’sdirections should be followed.

NFPA 72 requires acceptance testing records tobe retained for 2 years. All equipment should betested in accordance with the requirements of NFPA72 and the manufacturers’ recommendations.

Periodic Testing

In addition to provisions for acceptance testing, NFPA72 contains requirements for periodic tests and main-tenance. Essentially, NFPA 72 requires all testing tobe performed by qualified persons who understandthe equipment. Ultimately, the owner of the systemis responsible for ensuring that all required tests aredone on time. Owners are permitted to rely on awritten maintenance agreement with others, ratherthan use their own specialists. Delegation of respon-sibility for testing and maintenance must be in writ-ing.

The required frequency for testing a device var-ies. Chapter 10 of NFPA 72 contains the required fre-quencies for all devices.

NFPA 72 requires the sensitivity of all smoke de-tectors to be checked within 1 year of the acceptancetest, and every other year thereafter. During the yearswhen sensitivity tests are not required, a pass/failtest using smoke or another unmeasured aerosol isstill required. The intent of the sensitivity test is toensure that the detector is within its listed andmarked sensitivity range. Detectors that are more


System OutputsOccupant Notification & Information

Floor QtyDevice/Input A B C D E F G H I J K L M N O P Q R S T U272829303132333435363738394041424344454647

1886465

122390961466701

smoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detectionsmoke/heat detection

smoke/heat detectionsmoke/heat detection

Conn. Elev. Pent.S Level

6th Connector7th Connector

Penthouse 1 NPenthouse 1 S

M Level5th

6th7th8th9th

10th11th12th

4th3rd2nd1stG

Bsmt

Paging zones

Bsm

t spe

aker

s an

d st

robe

s

G fl

oor

spea

kers

an

d st

robe

s

1st f

loor

spe

aker

s an

d st

robe

s

2nd

floor

spe

aker

s an

d st

robe

s

3nd

floor

spe

aker

s an

d st

robe

s

4th

floor

spe

aker

s an

d st

robe

s

5th

floor

spe

aker

s an

d st

robe

s

6th

floor

spe

aker

s an

d st

robe

s

7th

floor

spe

aker

s an

d st

robe

s

8th

floor

spe

aker

s an

d st

robe

s

9th

floor

spe

aker

s an

d st

robe

s

10th

floo

r sp

eake

rs

and

stro

bes

11th

floo

r sp

eake

rs

and

stro

bes

12th

floo

r sp

eake

rs

and

stro

bes

Pen

thou

se 1

N

spea

kers

and

str

obes

Pen

thou

se 1

S

spea

kers

and

str

obes

6th

Con

nect

or fl

oor

spea

kers

and

str

obes

Con

nect

or e

lev.

pen

t.sp

eake

rs a

nd s

trob

es

7th

Con

nect

or fl

oor

spea

kers

and

str

obes

M fl

oor

spea

kers

an

d st

robe

s

S fl

oor

spea

kers

an

d st

robe

s

Evacuation zone for simultaneous M leveland 6th floor connector smoke detection.

Evacuation zone for ground floorsmoke detection

Exhibit S2.9 Partial system input/output matrix.

1137Conclusion

provide alerting but no additional information, andare intended to be used only for fire warning, leavingthe recipient to take actions they deem appropriate orfor which they have been trained or ‘‘programmed.’’However, the title and definition of mass notificationsystems are meant to encompass greater possibilitiesfor communication, information dissemination, andpersonnel management.

Depending on the situational needs, an MNS maybe a simple alarm system, or it may be a highly securecommand and control system suitable for use in avariety of situations including biological, poisonousgas, and nuclear terror threats; bombings; anti-personnel attacks; etc. Also, the system may be one-way or two-way. That is, it may be used only to giveinformation to the target audience or area, or it maybe designed to also receive and transmit informationto a command center in the form of real-time sensordata or text, voice, or video communications from thescene.

Though not directly required by any current LifeSafety Code requirements, mass notification systemsmay be used in many types of occupancies. It is ex-pected that the inclusion of them as a category ofsystem in NFPA 72 will result in their more wide-spread use in the future.

CONCLUSION

Fire alarm systems range from very simple units tolarge complex systems. This supplement has onlybriefly introduced the reader to the many require-ments and good practices associated with their de-sign, installation, testing, and use.

One of the most common failures associated withfire detection and alarm systems is the failure to pro-vide fire protection. A fire detection and alarm systemis not a fire protection system unless it does some-thing to affect the fire, the property, or the people.For example, a complete fire detection system withsmoke detectors and heat detectors in every roomand space does little good if the system sounds a localalarm in the middle of the night when the building isnot occupied and does not automatically communi-cate to the fire department, or if it does summon thefire department but the fire is too large for the arriv-ing fire fighters to safely attack. Perhaps this systemis protecting an historic library in a community witha part-paid fire company whose nearest apparatus is5 miles distant — uphill. These examples illustrate afailure to engineer. The Life Safety Code and the Na-tional Fire Alarm Code address common occupancyand hazard conditions. Many requirements for firedetection and alarm are ‘‘pre-engineered’’ solutions

than 0.25 percent per foot obscuration out of rangemust be recalibrated or replaced.

The most common methods for testing detectorsensitivity use either control panels that can checkdetector sensitivity remotely or meters that plug intothe detector for testing. In some cases, the meters arecommon volt–amp meters, and in other cases they arefactory-supplied devices. Test instruments are alsoavailable that generate measured smoke clouds,which can be used to test any brand of detector. Usingunmeasured aerosols such as cigarette smoke orcanned smoke does not measure sensitivity. The useof such unmeasured aerosols might prove that a de-tector is operational, but the sensitivity might be solow that the amount of smoke required to cause analarm is enough to have already caused harm or adelay in that detector’s response to a real fire. Con-versely, a detector might alarm when tested with ciga-rette smoke but be so sensitive that it would alsonuisance alarm due to small amounts of friendlysmoke.

In terms of smoke detector cleaning, NFPA 72simply states that the frequency of service should bebased on the ambient conditions. If the area is veryclean, 1 to 2 years between cleanings might be possi-ble. In very dusty or dirty areas, or areas with highairflow, cleaning might be required every 3 to 6months. In most residential, business, and institu-tional occupancies, yearly cleaning is usually suffi-cient. A sensitivity test must be performed on anydetector that has been washed or disassembled forany reason, including cleaning.

Once a year, air duct smoke detectors must bechecked to verify that they are properly sampling theair stream. The manufacturer’s recommendations fortesting should be followed. Testing may involve mea-suring the pressure difference between the air sam-pling and air return tubes.

MASS NOTIFICATION SYSTEMS

The Mass Notification System (MNS) is a new cate-gory of communication and emergency managementsystem addressed by NFPA 72. An MNS is used toprovide information and instructions to people in abuilding, area, site, or other space using intelligiblevoice communications and possibly visible signals,text, graphics, tactile, or other communications meth-ods.

In a broad context, an MNS is a communicationand emergency management tool. In its simplestform, it may be used to manually alert or notify someor all occupants of a space that an emergency exists.Many fire alarm systems fit this description — they



for the expected conditions. However, where perfor-mance-based solutions are used, or in situationswhere owners have goals that go beyond simple codecompliance, the designer may need to provide morethan what the code requires.

The Life Safety Code and the National Fire AlarmCode contain a wealth of information for persons in-volved with any phase of a fire alarm system’s life. Bydrawing on the expertise of hundreds of professionalsand specialists, users of these NFPA documents bene-fit from years of combined experience, which no sin-gle person or company could hope to attain.

REFERENCES

For additional information concerning the design, in-stallation, testing, maintenance, and use of fire alarmsystems, consult these references

Bukowski, R.W., and Moore, W.D., eds., Fire AlarmSignaling Systems, 3rd edition, National Fire Pro-tection Association, Quincy, MA, 2003.Cote, A.E., ed., Fire Protection Handbook, 19th edi-tion, National Fire Protection Association,Quincy, MA, 2002.DNenno, P.J., ed., The SFPE Handbook of Fire Protec-tion Engineering, 3rd edition, Society of Fire Pro-tection Engineers, National Fire ProtectionAssociation, Quincy, MA, 2001.Training Manual on Fire Alarm Systems, NationalElectrical Manufacturers Association, 2101 LStreet, Washington, D.C., 1997.Guide for Proper Use of System Smoke Detectors,National Electrical Manufacturers Association,2101 L Street, Washington, D.C., 1997.Guide for Proper Use of Smoke Detectors in DuctApplications, National Electrical ManufacturersAssociation, 2101 L Street, Washington, D.C.,1997.NFPA 72�, National Fire Alarm Code�, 2002 edition,

National Fire Protection Association, Quincy,MA.NFPA 90A, Standard for the Installation of Air-Con-ditioning and Ventilating Systems, 2002 edition, Na-tional Fire Protection Association, Quincy, MA.Richardson, L.F., and Moore, W.D., National FireAlarm Code� Handbook, 2002 edition, National FireProtection Association, Quincy, MA.NFPA 70, National Electrical Code�, 2005 edition,National Fire Protection Association, Quincy,MA.National Electrical Code� Handbook, 2005 edition,National Fire Protection Association, Quincy,MA.ANSI/UL 217, Standard for Single and Multiple Sta-tion Smoke Alarms, Underwriters LaboratoriesInc., Northbrook, IL, 1997.ANSI/UL 268, Standard for Smoke Detectors for FireAlarm Signaling Systems, Underwriters Labora-tories Inc., Northbrook, IL, 1996.

In addition to the preceding publications listed andstate and local authorities, the following organiza-tions are sources for information on fire detectionand signaling systems:

Automatic Fire Alarm Association, P.O. Box951807, Lake Mary, FL 32795-1807.http://www.afaa.orgFM Global, 1301 Atwood Avenue, P.O. Box 7500,Johnston, RI 02919. http://www.fmglobal.comNational Fire Protection Association, 1 Bat-terymarch Park, Quincy, MA 02169-7471.http://www.nfpa.orgNational Institute for Certification in EngineeringTechnologies, 1420 King Street, Alexandria, VA22314–2794. http://www.nicet.orgUnderwriters Laboratories Inc., 333 PfingstenRoad, Northbrook, IL 60062–2096.http://www.ul.com


Documents

Fire Alarm Systems for Life Safety Code Users/media/Files/forms and premiums… · · 2013-06-11through output signals. The simplest form of system described in Exhibit ... usually