Fire protection engineering Summer 2001

8/17/2019 Fire protection engineering Summer 2001

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FIRE PROTECTIONFIRE PROTECTION

PERFORM A NCE M ETRICS

FOR FIRE DETECTION

PSYCHOLOGICAL

VARIA BLES THAT M AY

AFFECT FIRE ALARM

DESIGN

UNDERW RITERS

LABORATORIES

CONTRIBUTIONS FOR

FIRE A LARM SYSTEM S

42

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PROVIDING PRACTICE-ORIENTED INFORMATION TO FPEs AND ALLIED PROFESSIONALS

S U M M E R 2 00 1I ss u e N o . 1 1

A L S O :

INTEGRATING FIRE

ALARM SYSTEM S W ITH

BUILDING AUTOM ATION

A ND CONTROL SYSTEM S

5

Intel l igentFire DetectionIntel l igentFire Detectionpage 15

21


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Fire Protection Engineering

3 VIEW PO IN TAn Added Level of SafetyBra d Keyes, Safety Manager, Rockfor d Health System

5 INTEG RATING FIRE ALARM SYSTEM S W ITH BU ILDINGAUTOM ATIO N AN D C O NTRO L SYSTEM SThe pop ularity of BACnet system s are grow ing around the w orld and are w ellsuited for integrating fire alarm system s w ith building autom ation system s.Steven T. Bu shby

21 PERFO RM ANC E M ETRICS FOR FIRE DETECTIO NM ore progress is needed tow ard credible m etrics for accurately predicting theperform ance of heat and sm oke detectors.John M. Cholin , P.E., an d Chri s Mar ri on, P.E.

33 UN DERW RITERS LABO RATO RIES C O N TRIBUTIO NS FO R FIREALARM SYSTEM SThis article describes the certification activity perform ed by U nderw ritersLaboratories that contributes to the predictable operation of a fire alarm system .John L. Par ssinen, P.E., Paul E. Patty, P.E., and Lar ry Shudak, P.E.

42 PSYCH O LO G IC AL VARIABLES TH AT M AY AFFECT FIREALARM DESIG NThere are a num ber of behavioral and psychological principles that, w henidentified, enable fire protection engineers to m ore effectively design, specify,and install fire alarm system s.Dr. John . L. Bryan

50 CAR EERS/CLASSIFIEDS

52 SFPE R ESO U RC ES

56 FR O M TH E TEC H N IC A L D IR EC TO RA Responsibility to O urselvesMorgan J. Hur ley, P.E.

Cover: Bill Frymir e/Master fil e For m ore inform ation about the Society of Fire Protection Engineering or Fire Protection Engin eeri ng m agazine, try us at w w w .sfpe.org.

Invitation to Submit Articles: For inform ation on article subm ission to Fire Protection Engin eeri ng , go to http://w w w .sfpe.org/publications/invitation.htm l.

contents S U M M E R 2 0 0 115COVER STORY IN TELLIG EN T FIR E ALAR M SYSTEM SU nw anted fire alarm s can seriously underm ine the effectiveness of installedalarm system s, pressing the need for m ore intelligent alarm system s.Jeffr ey S. Tubbs, P.E.

Subscription and address change correspondence should be sent to: Fire Protection Engineering,Penton M edia, Inc., 1300 East 9th Street, Cleveland, O H 44114 U SA. Tel: 216.931.9566. Fax: 216.696.7668.E-m ail: jpulizzi@ penton.com .

Copyright © 2001, Society of Fire Protection Engineers. All rights reserved.

FIRE PROTECTIONFIRE PROTECTION

Fire Protection Engineering ( ISSN 1524-900X) is

published quarterly by the Society of Fire Protection

Engineer s (SFPE) . The miss ion of Fire Protection

Engineering is to advance the practice of f ire protection

engineer ing and to r a ise i ts v is ib il i ty by provid ing

information to f ir e pro tec t ion engineer s and a l l ied

profess iona ls . The opin ions an d pos i t ions s ta ted a re

the a u thor s ’ an d do n ot necessa r i ly r ef lect those of SFPE.

Edit ori al Advisory Board

Car l F. Ba ldassa r ra , P .E. , Schirm er Engin eer ing Corpora t ion

Don Bath ur s t , P .E.

Ru ssell P. Flemin g, P.E., Nationa l Fire Sprinkler Association

Douglas P . For sman , F ir escope Mid-Am er ica

Morgan J. Hurley, P.E., Society of Fire Protection Engineers

Willia m E . Koffel, P.E., Koffel Associa tes

Jane I . Lataille, P.E.

Margaret Law, M.B.E., Arup Fire

Rona ld K. Menge l , Honeywell , Inc .

Warren G. Stocker, Jr ., Safeway, In c.

Be th Tubbs , P.E. , In te rna tion a l Conference of Build ingOfficials

Regional Editor s

U.S. H EARTLANDJohn W. McCormick, P.E., Code Consultants, Inc.

U.S. M ID -ATLANTICRober t F. Gagnon , P.E. , Gagnon Engineer ing , In c .

U.S. NEW ENGLANDTho m as L. Caisse, P.E., C.S.P., Robert M. Cu rrey &Associates, In c.

U.S. SOUTHEASTJe f fr ey Har r ing ton , P.E. , The Har r ing ton Group, In c .

U.S. WES T COASTMarsha Savin, Gage-Babcock & Associates, Inc.

ASI APeter Bressington, P.Eng., Arup Fire

AUSTRALIARichard Custer , Arup Fire

CANADAJ. Kenne th Rich ardson , P .Eng. , Ken Rich ardson Fir eTechn ologies, In c .

NEW ZEALANDCarol Caldwell, P.E., Caldwell Consulting

UN IT E D KIN G D O MDr . Louise Jackman , Loss Prevention Counc il

Publ i shing Advisory Board

Bruce Larcomb, P.E., BOCA International

Doug las J. Rollm an , Gage-Babcock & Associates, Inc.

George E. Toth, Rolf Jensen & Associates

Personnel

P U BL IS H E RKathleen H. Almand, P.E., Executive Director, SFPE

TECHNICAL ED I T O RMorgan J. Hurley, P.E., Technical Director, SFPE

AD V E RT IS IN G / SALESTer ry Tanker , Penton Media , Inc .

M ANAGING ED I T O RJoe Pulizz i , Cus tom Media Group, Penton Media , Inc .

ART D IRE CT O RPat Lang , Cus tom Media Group, Penton Media , Inc .

COVER D E S IG NDave Bosak , Cus tom Media Group,Penton Media , Inc .


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By Br ad K eyes

Rockford M em orial H ospital islocated in Rockford, Illinois, andserves northern Illinois and

southern W isconsin w ith a 50,000 m 2

(500,000 ft2), 490-bed facility. Likem any hospitals, the cam pus has beenbuilt increm entally over a num ber ofyears w ith the earliest portion con-structed in 1951. Along w ith m ajorbuilding additions, num erous internalrem odelings have taken place to m eetthe changing needs of healthcare. Each

change and addition w as designed andbuilt to m eet the requirem ents ofbuildings and life safety codes in forceat the tim e. O ver the years the codeshave evolved, and as a result, RockfordM em orial has tried to keep currentw ith these changing requirem ents.

In July of 1993, a H ealth CareFinancing A dm inistration (H CFA) surveyfound num erous deficiencies w ith vari-ous aspects of the building’s life safetyfeatures. At the tim e, the fire detectionsystem included a com bination of firealarm panels, w hich w ere located in

three different areas of the hospital.W hile the hospital had a w orking

m anual fire alarm system , the level ofsm oke detection w as not consistent.O ne w ing had detection in room s,w hile another had detection only in thehallw ays; other areas had no detectionat all. After the H CFA survey, a FireSafety Evaluation Survey (FSES) w asconducted to evaluate the existing firesafety features. As a result, it w as decid-ed to install a new autom atic fire detec-tion system to gain additional points onthe FSES for sm oke detection in corri-

dors and habitable spaces in the entirefacility. Along w ith the addition of anew fire alarm system , it w as alsodecided to com plete the installation ofthe w ater-based sprinkler system for the

entire facility. This w ould provide addi-tional points on the FSES and grant thehospital exceptions to certain coderequirem ents.

These tw o m ajor projects begansim ultaneously in D ecem ber of 1993

and had to be com pleted by M arch1995. This did not allow m uch tim e todesign, im plem ent, and com m issioneach phase of the project. After consid-ering several options, the hospitalchose a fire alarm system w hich incor-porated the latest generation of equip-m ent available on the m arket.For construction purposes, the build-

ing w as divided into w orkable sections,by nursing units or departm ent.Cooperation betw een staff and contrac-tors w as extraordinary. As each unitw as com pleted, the system s w ere acti-

vated and placed into operation. Thiscreated challenges in keeping recordsand docum ents current, as w ork pro-gressed rapidly. At tim es, there w ere sixdifferent crew s installing sprinklers andthree different crew s installing the firealarm system .In February 1999, the H CFA visited

Rockford M em orial for another valida-tion survey. The survey revealed incon-sistencies w ith testing and recordkeep-ing procedures. For exam ple, the firealarm service contractor w as inconsis-tent w ith testing frequencies, providing

qualified technicians, and responding tothe needs of the hospital. Since the fire

alarm system is an integral part of thelife safety features, the FacilitiesM anagem ent departm ent decided totake control of all testing and serviceon the fire alarm system . Techniciansw ere trained by the fire alarm m anufac-turer, and all testing and service arenow conducted by Rockford M em orial’sow n staff. This has proven to be am ajor im provem ent as the hospital canbetter control all activity on the firealarm system .

Recent im provem ents to the firealarm system include the addition of anetw orking com puter allow ing expand-ed com m unication betw een the fourpanels and rem ote operation term inals.

This is a significant enhancem ent astechnological im provem ents m ade inthe hospital put increasing dem ands onthe fire alarm system . A rem ote m onitorw as installed in the hospital’s Securitydispatch office w hich displays the loca-

tion of every alarm initiated w ith analphanum eric description. Alarm infor-m ation is quickly transm itted to thehospital’s fire response team via tw o-w ay radios. O ther im provem ents includeexpander circuit cards to allow over500 additional initiating devices to m eetthe needs of recent building additions.N ot everything concerning the instal-

lation w ent as w ell as the hospitalw ould have liked. W ith a fire detectionproject this large, som e problem s andm istakes did occur. The m ost em bar-rassing one w as the day the fire alarm

m anufacturer brought a contingent offacility m anagers from other hospitalsto see the ongoing installation of thenew fire alarm system . U nbeknow nst toRockford M em orial’s facility m anager,w ho w as greeting the contingent at thefront entrance, an installer accidentallyw ired line voltage into the initiating cir-cuit on one panel and blew out all thefirm w are and control circuit boards. Bythe tim e the proud facility m anagerbrought the visitors to the fire panelroom , he found all the internal boardsand pow er supplies from one panel

scattered across the floor w ith w orkersfrantically trying to rectify the situation.O ne key issue the hospital w ould

change is the decision to install the fire

alarm w iring using plenum -rated tw ist-ed pair cable, instead of installing thew ire in conduit. W hile this decisionsaved tim e and m oney at the point ofinstallation, it has been the source ofm any ground fault troubles, due in partto the num erous tradesm en w orkingabove the ceilings and inadvertentlydam aging the cable.All things considered, the Rockford

M em orial Facilities M anagem ent depart-m ent is pleased w ith their new firealarm system . They have a system thatis user-friendly, and they m aintainexcellent as-built docum ents and draw -ings. W ith their ow n staff conducting

testing and repairs, they feel they havecom plete control over the system .

Brad Keyes is with the Rockford Health

System.

S U M M E R 2001 Fire Protection Engineering

An Added Level of Safety

view point


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By Steven T. Bush by

INTRODUCTION

Integrating fire alarm system s w ith buildingautom ation system s can result in m anyeconom ic and operational benefits. Such

integration requires com m unication standardsand careful design practices. BACnet is aninternationally recognized com m unicationprotocol standard specifically designed forintegrating building autom ation and control

system s. Thousands of BACnet system s canbe found around the w orld, and its populari-ty is grow ing. N ew ly proposed additions toBACnet m ake it very w ell suited for integrat-ing fire alarm system s w ith building autom a-tion system s.


IN TEG R ATIN G

Fire Alarm Systems with

Building Automation andControl Systems


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6 Fire Protection Engineering N U M B E R 11

M aintaining the integrity of fire alarmsystem s w hen they are integrated w ithother building system s requires m orethan just com m unication standards.Best design practices, appropriate test-ing procedures, and m odernized build-ing are also needed.

The technology of building autom a-tion and control system s has advancedrapidly over the past fifteen years.Today’s technology provides buildingow ners and designers w ith a richassortm ent of options and flexibility.Pow erful personal com puter w orksta-

tions and intelligent distributed con-trollers that process com plex algorithm squickly and efficiently characterizestate-of-the-art building autom ation andcontrol system s. These advances havetaken place across a variety of buildingservices including heating, ventilating,and air conditioning (H VA C) controlsystem s, lighting control system s, accesscontrol system s, and fire alarm system s.

In spite of these advances, buildingow ners have been frustrated by theinability to bid projects com petitivelyand to integrate innovative products

m ade by different m anufacturers in w aysthat best suit the unique needs of theirfacility. The m ain obstacle has beenincom patible proprietary com m unicationprotocols. The adoption of BACnet1 asthe standard com m unication protocol forintegrating building control products haschanged the industry and opened thedoor to new innovation in building con-trol technology and true integration ofpreviously isolated building system s.

In the U nited States, the N ationalElectrical M anufacturer’s Association(N EM A) Signaling, Protection, andCom m unication Section (3SB) hasendorsed the use of BACnet as the pre-ferred w ay to integrate fire alarm sys-tem s w ith other building control sys-tem s. The N ational Fire ProtectionAssociation (N FPA) is in the process ofrevising N FPA 722 to address designissues related to integrating fire alarmsystem s w ith other building system s.First-generation BACnet fire alarm sys-tem products are already available in

the m arketplace in the U nited Statesand in Europe. These are clear indica-tions of interest in integrating fire alarmsystem s w ith other building system sand in using the BACnet protocol as am eans to accom plish that goal.

A BACNET OVERVIEW

BACnet is a standard com m unicationprotocol developed by the Am ericanSociety of H eating Refrigerating, andAir-Conditioning Engineers (ASH RAE).It has been adopted as a prestandard

by the European Com m unity3,4 and hasbeen proposed as an ISO standard.

Today there are over 70 com paniesw ith registered BACnet vendor identi-fiers. These com panies are located inN orth Am erica, Europe, Asia, andAustralia. Com m ercial BACnet productofferings range from gatew ays thatconnect proprietary system s to com -plete product lines that use BACnet asthe prim ary or sole m eans of com m u-

nication. There are thousands ofinstalled system s ranging in com plexityfrom a single gatew ay to very largeoffice buildings w ith top-to-bottomnative B ACnet system s, to cam pus orcity- w ide system s linking m ultiplebuildings. BACnet products includeH VAC controls, lighting controls,access controls, and fire detectionsystem s.Fundam entally, BACnet, like any

com m unication protocol, is a set ofrules that provide a w ay to exchangeinform ation. BACnet w as designed and

optim ized specifically to m eet theneeds of building autom ation and con-trol applications, and to convey thedata needed by these applicationsincluding, but not lim ited to, hardw arebinary input and output values; hard-w are analog input and output values;softw are binary and analog values;schedule inform ation; alarm and eventinform ation; files; and control logic.BACnet does not define the internalconfiguration, data structures, or controllogic of the controllers.BACnet is designed to be scalable

from very sm all, low -cost devices tovery large com plex system s that m ayinvolve thousands of devices and m ulti-

ple buildings located anyw here in thew orld. It achieves this by com bining anobject-oriented representation of theinform ation to be exchanged, flexiblechoices for local area netw ork (LAN )technology, an ability to interconnectlocal area netw orks, and an ability touse Internet protocols (IP) to link build-

Figure 1. BACnet Protocol Architecture

BACnet Application Layer

BACnet Network Layer

BACnet LayersEquilaventOSI Layers

Application

Network

Data Link

Physical

ISO 8802-2 (IEEE 802.2) Type 1

ISO 8802-3(IEEE 802.3) ARCNET

MS/TP

EIA - 485

PTP

EIA - 232

LonTalk


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ings over w ide area netw orks. Thestructure of the B ACnet protocol and itsrelationship to the O pen System sInterconnection (O SI) –Basic ReferenceM odel5 is show n in Figure 1.

BACnet represents the inform ationand functionality of any device bydefining collections of related inform a-tion called “objects,”each of w hich hasa set of properties that further charac-terize it. For exam ple, an analog inputis represented by a BACnet AnalogInput object that has a set of propertiesthat include its present value, sensortype, location, alarm lim its, and others.Som e properties are required and oth-ers are optional. A device is represent-ed by an appropriate collection of net-w ork-visible objects. O nce the inform a-

tion and functionality of a device arerepresented on the netw ork in term s ofstandard objects and properties, m es-

sages can be defined to access andm anipulate this inform ation in a stan-dard w ay. This com bination of standardobjects and standard m essages toaccess and m anipulate their propertiesm akes up the BACnet application layer.O nce the inform ation to be

exchanged and m essage structures are

defined, it is necessary to provide aw ay to transfer the inform ation fromone place to another. BACnet providesa choice of five LAN technologies tom eet this need. Several choices are pro-

vided because different building controlapplications m ust m eet different costand perform ance constraints. A singlenetw ork technology cannot m eet theneeds of all applications. A LA N isdefined by a com bination of the datalink and physical layers of the O SIm odel. The LA N options available inBACnet are show n in Figure 1.The first option is ISO 8802-3, better

know n as “Ethernet.”It is the fastestoption and is typically used to connectw orkstations and high-end fielddevices. The second option is ARCN ET,

w hich com es in m odestly high speedsor in slow er, low er-cost versions.BACnet defines the M S/TP (m aster-

slave/token-passing) netw ork designedto run over tw isted-pair w iring.Echelon’s proprietary LonTalk* netw orkcan also be used. The Ethernet, ARC-N ET, and LonTalk options all support avariety of physical m edia. BACnet alsodefines a dial-up or “point-to-point”protocol called PTP for use over phone

lines or hardw ired EIA-232 connections.A key point is that BACnet m essages

are the sam e no m atter w hich LAN isused. This m akes it possible to easilycom bine LAN technologies into a single

system . The purpose of the netw orklayer is to provide a w ay to m ake suchinterconnections. It is com m on in largesystem s to com bine high-speed (andhigh-cost) netw orks w ith low er-speed(and low er-cost) netw orks in a singlesystem . Such a system is show n inFigure 2. Figure 2 also illustrates thatBACnet has w ide area netw orkingcapability that is im plem ented using IP.In principle, BACnet m essages can

be transported by any netw ork technol-ogy. This m eans that technologies thathave not even been invented yet can

be used in the future to convey B ACnetm essages, and they can be integratedinto today’s system s in the sam e w ay

that m ultiple existing netw ork technolo-gies can be com bined today. This lackof dependence on today’s technology isa very im portant feature of BACnet.The object-oriented structure also

provides a w ay to add new applicationfunctionality to BACnet by definingnew objects and/or new application

Internet

Unitary Controllers

Low-Speed LANs High-Speed LANs

Field Panel

Field Panel

Field Panel

Field Panel

Field Panel

Field Panel

Workstation Workstation

Router

Router

EthernetEthernet

Unitary Controllers

Low-Speed LANs

Figure 2. A Hierarchical Building Control System Structure


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services. This is being done to addfunctionality needed for fire alarm sys-tem s. Tw o new BACnet objects, LifeSafety Point and Life Safety Zone, have

been developed. The Life Safety Pointobject represents the features of anindividual detection or enunciationdevice. The Life Safety Zone object rep-resents the status of a collection or“zone”of life safety devices. W henthese objects detect an alarm , the alarm

status latches until a reset com m and isexecuted. A new application servicehas also been developed that providesa w ay to reset latched alarm s and tosilence annunciating devices. All theseadditions w ere developed w ith assis-tance from the fire alarm industry andhave been approved by the BACnetcom m ittee. They are currently undergo-ing a public review process and are

expected to be approved as part of theBACnet standard.6

M ore detailed inform ation aboutBACnet concepts and structure m ay be

found elsew here.7 There is also tutorialinform ation and an extensive bibliogra-phy available on a W eb page m ain-tained by the BACnet com m ittee(w w w .BACnet.org).

W HY INTEGRATE FIRE ALARM

SYSTEMS W ITH O THER BUILDING

SYSTEMS?

There are m any reasons for integrat-ing fire alarm system s w ith other build-ing autom ation and control system s.Exam ples include sm oke control, single-

seat access to building inform ation, easi-er m aintenance, sharing sensor data,obtaining inform ation about the location

of people during an em ergency, andproviding infrastructure for new tech-nology to im prove perform ance andsafety.Fire detection system s have been

integrated w ith door locks and w ithH VA C fan and dam per controls forsm oke m anagem ent for several years,

but these system s have relied on relayscontrolled by the fire alarm system tooverride the norm al controls. This kindof integration has prim arily involvedconstant-volum e H VA C system s andrequired only on/off control of fansand dam pers to be m oved to fullyopen or fully closed positions.

M any m odern H VAC system s are farm ore com plex. Variable air volum e sys-

tem s are used to reduce energy con-sum ption. These system s require sophis-ticated control algorithm s to operateeither a continuously variable-speed fanor inlet guide vanes to control the staticpressure in the supply air duct. Variable-air volum e boxes control the airflowfrom the supply duct into individualroom s by m odulating dam pers. Thecontrol algorithm s for these system s arecom plicated and require interlocks andsafeties to prevent overstressing duct-

w ork in the event that dam pers do notopen w hen fans are turned on. Sm okem anagem ent is m uch m ore com plicatedw ith these system s and outside of thecapability of m ost fire alarm system s.

W hat is needed is a w ay for the firealarm system to com m and the H VACcontrol system to enter a sm oke controlm ode and let the H VA C controllersm anage the equipm ent.N ew sensors are being developed

that can recognize various contam inantsin the air that can represent a fire signa-ture or a hazardous contam inant that

poses a life safety threat. In an integrat-ed system , these sensors could be usedby the H VA C control system to controlventilation rates w ith no adverse im pacton their life safety functions. M ultipleuses for the sam e inform ation w illm ake it m ore cost-effective to im ple-

m ent new sensor technology.In som e buildings, access control sys-

tem s m onitor the location of buildingoccupants. Providing access to thisinform ation to the life safety system scould be very helpful in an em ergency.Em ergency response personnel w ould

know w here to look for occupants w honeed to be evacuated. They could alsoreduce the risk to them selves by avoid-ing dangerous areas w here no peopleare present.Research is now underw ay at the

N ational Institute of Standards andTechnology (N IST) to develop a newgeneration of sm art fire alarm panelsthat can m ake use of sensor data from

an integrated system to calculate heat

release rates in a fire. U sing this infor-m ation, a fire m odel in the panel canpredict how the fire w ill grow andspread. Em ergency response personnelcan use these predictions to plan a strat-egy for fighting the fire. It could even

be transm itted by the building system sto fire stations or fire trucks so that

planning can begin before em ergencypersonnel reach the site. This could sig-nificantly im prove response tim e, savinglives and reducing property loss.For all of these reasons and probably

others, integrating fire alarm system sw ith other building system s m akes a lotof sense. The technology is already beingdriven in that direction by m arket forces.

OTHER INTEGRATION ISSUES

Several im portant integration issues

m ust be addressed if these potential

benefits are to be realized. The prim aryconcerns are ensuring the integrity offire alarm system s in em ergencies andisolating them from interference causedby failures of other building system s,m eeting code and U nderw ritersLaboratory (UL) listing requirem ents,and regulating and tracking hum anresponses to alarm s and troubleconditions.M aintaining the integrity of the fire

alarm system and protecting it fromfailures in other building system s areprim arily a m atter of system design

practice. Today this is being handled byusing a gatew ay to isolate the fire alarmsystem from outside interference. Allcom ponents of the fire alarm systemreside on one side of the gatew ay andcom m unicate using proprietary proto-cols in the sam e w ay that they didbefore BACnet. The BACnet gatew ayprovides a w ay for other building sys-tem s to get inform ation from the firealarm system but protects it from inter-ference from outside. This provides thenecessary protection, but it also lim itsthe integration possibilities.

An alternative approach is to developbest design practices for constructingnetw orks of integrated system s. Byappropriate selection of netw ork tech-

nology and appropriate use of routersand bridges to filter traffic, interferenceproblem s and concerns about guaran-teed access to netw ork bandw idth inan em ergency can be effectively elim i-nated. Business netw ork system s com -m only use these techniques today, and


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there is no reason w hy they cannot beapplied to building autom ation system s.H aving fire alarm system s tested by

U L and listed for their intended purpose

is an expensive and tim e-consum ingpractice. It is unrealistic to expect m an-ufacturers of other building autom ation

devices to absorb this expense w hentheir products are not directly involvedin detecting or responding to a fire justbecause they can com m unicate w ith

listed fire-detection devices. The testingand listing procedures need to beupdated to recognize this reality. Bycom bining good design practices w ith

tests that ensure the integrity of the firealarm system under conditions that canoccur if the design practices are fol-

low ed, safety concerns can be satisfiedw ithout sacrificing the benefits of inte-gration. In som e locations, buildingcodes m ay need to be m odified so that

they are based on perform ance criteriainstead of prescriptive requirem ents.In fire alarm system s, it is very im por-

tant to ensure that only authorized per-

sonnel can silence alarm s, reset alarm s,and perform other operations that sig-nificantly affect the perform ance or sta-

tus of the system . Traditionally this hasbeen accom plished by having dedicatedfire system w orkstations that providethe operator w ith capabilities that areassigned w hen the operator logs in. Inan integrated system , there m ay bem any w orkstations w ith the ability tosend m essages to fire alarm systemcom ponents. Fire alarm panels need tobe protected from accidental or inten-tional disruption from other devices orw orkstations in the building. BACnetprovides m echanism s for authenticating

m essages but they are not w idely

im plem ented. This is another designissue that needs to be addressed.

INTERNATIONAL STANDARDS

AC TIVITIES

As stated before, BACnet has beenadopted as a standard in the U nitedStates and as a prestandard in theEuropean Com m unity. The Internation-al O rganization for Standardization(ISO ) Technical Com m ittee 205 is delib-erating the adoption of BACnet as aw orld standard. This is being done as

part of the activities of W orking G roup3, Building C ontrol System D esign. Theparticipants in this activity include rep-resentatives from the U nited States,Europe, Japan, and A ustralia. BACnet isnow at the “com m ittee draft”(CD ) stageand is expected to advance to the “draftinternational standard”(DIS) stage soon.The ISO activities are being coordinatedw ith the ongoing m aintenance ofBACnet in the U nited States. The inten-tion is to incorporate into the U .S. stan-dard any additional features needed toobtain international acceptance of the

protocol. It is also expected that anyadditions that com e from the continu-ous m aintenance process in the U .S.

w ill be incorporated into the ISO stan-dard. An effort is being m ade to coordi-nate BACnet testing and certificationprogram s in Europe and the U .S. Thereis a strong international consensus thatit is in everyone’s interest to be able tofreely m arket BACnet products any-w here in the w orld. A com m on stan-


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dard and reciprocal certification recogni-tion are critical if this is to happen.There are a variety of im portant rea-

sons for integrating fire alarm system s

w ith building autom ation system s.These include sm oke control, single-seat access to building inform ation, eas-

ier m aintenance, sharing sensor data,obtaining inform ation about the loca-tion of people during an em ergency,and providing infrastructure for newtechnology to im prove perform anceand safety. A standard com m unicationprotocol is a critical infrastructure com -ponent to m ake this integration possi-ble. BACnet is such a protocol, and it isgaining popularity around the w orld.M ore than just com m unication stan-

dards need attention. System s m ust bedesigned and m aintained in w ays that

w ill assure the integrity of the fire

alarm system even w hen other com po-nents of the building autom ation sys-tem fail. It is also necessary to designthe system so that bandw idth is avail-able to the fire alarm system w hen anem ergency arises. Best practice designguidelines can m eet these needs. U Ltesting and listing procedures need tobe updated to address open integratedsystem s. In som e cases, building codesm ay need to be revised to perfor-m ance-based approaches.M arket forces are already pulling the

industry in the direction of integrated

system s. As new technology is devel-oped that adds capabilities because of

the integration, the pressure to integratesystem s w ill grow . The end result w illbe buildings that are easier to operateand are safer for the occupants.

Steven Bu shby is wi th the Nationa l

In stitu te of Standar ds and Technology.

* Certai n tr ade names and company products

are menti oned in the text i n order to specify ade-

qua tely the equi pment u sed. In n o case does

such identifi cation imply recommendation or

endorsement, nor does it imply that the products ar e necessar il y the best for the purpose.

REFERENCES

1 ASHRAE 135. BACnet –A D ata Com m unica

tion Protocol for Building Autom ation and

Control Netw orks. Am erican Society of

H eating Refrigerating, and Air-Conditioning

Engineers, Atlanta, G eorgia.

2 N FPA 72.National Fire Alarm Code .

N ational Fire Protection Association,

Q uincy, M assachusetts, 1999.

3 EN V 1805-1: European C om m ittee for

Standardization.

4 EN V 13321: European Com m ittee for

Standardization.

5 ISO 7498, Inform ation Processing System s

–O pen System s Interconnection –BasicReference M odel, International

O rganization for Standardization, 1984.

6 Addendum c to ASHRAE 135 , First Public

Review D raft, 2000. Am erican Society of

H eating, Refrigerating, and Air-

Conditioning Engineers, Atlanta, G eorgia.

7 B ushby, S. T., “BACnet, a standard

com m unication infrastructure for intelli-

gent buildings,”Autom ation in C on-

struction 6 (1997). Elsevier, pp. 529-540.

For an onli ne version of this arti cle, go

to www.sfpe.org.


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Intel l igentFir e Alar mSystems

Intel l igentFir e Alar mSystems

By Jef fr ey S. Tubbs, P.E.

INTRODUCTION

The fire protection com m unity faces grow ing needs forreliable fire-detection system s that give the earliestpossible w arning of fire. These needs draw attention

to p roblem s associated w ith false or unw anted fire alarm s.U nw anted fire alarm s can seriously underm ine the effective-ness of installed alarm system s, interrupt business, and, atw orst, m ay cause occupants to ignore the fire alarm systemduring an actual fire.

H istorically, fire alarm m anufacturers have addressed

unw anted alarm s through tw o approaches:• D ecreasing detector sensitivity. M aintenance personnelare able to set individual detectors to be less sensitiveafter the devices are installed to alleviate false alarm s.

Typically, detector sensitivity is only decreased; the sensi-tivity is rarely increased to im prove detection capability.

• U sing alarm verification. Alarm verification essentiallyintroduces a detection delay tim e. W hen the detectorreports an alarm condition, the fire alarm system w aitsfor a specified program m ed delay tim e (typically, a 30-second delay) to confirm that the detector continues toreport an alarm condition. If the detector is in alarm afterthe delay tim e, the alarm sequence is actuated.


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Although decreasing detector sensi-tivity and using alarm verification canreduce the potential for unw antedalarm s, occupant notification m ay alsobe delayedIntelligent fire alarm system s have

been developed to address unw antedalarm s w hile m aintaining the desiredlevel of detector sensitivity. Althoughthe capabilities of intelligent system svary betw een m anufacturers, intelligentsystem s can provide a num ber of bene-fits, including faster occupant notifica-

tion, increased detector sensitivity, anddecreased potential for unw antedalarm s. Also, intelligent system s canprovide users w ith notification of need-ed detector m aintenance.

INTELLIGENT VS. CONVENTIONAL

DEVICES

Artificial intelligence has becom e abuzzw ord in m any fields involvingtechnical products. Intelligent system shave been used in virtually every tech-nical field involving a w ide range ofindustries, from system s designed forthe space shuttle to m any com puter

gam es. The term “artificial intelligence”is typically associated w ith system s thathave the ability to reason or learn.A num ber of new fire alarm products

have becom e available, m any of w hich

are labeled as com ponents of intelligentfire alarm system s. W hile intelligent firealarm system s are not as advanced andsophisticated as w hat is typicallythought of as artificial intelligence, theydo incorporate som e of the sim plelogic techniques incorporated in suchsystem s.Intelligent fire alarm system s w ere

initially another nam e for addressablesystem s. Addressable system s provide a

unique address for each detectiondevice, providing a increased level ofinform ation to the user. Today’s intelli-

gent system s do m ore.Currently, intelligent fire alarm sys-

tem s incorporate detectors that usedecision-m aking algorithm s to deter-m ine alarm conditions. Som e em ploym ultisensor approaches, w hile othersuse m ultidetector approaches or profilecom parisons. In m ost cases, m easure-m ents, such as sm oke concentrationand tem perature, are received by oneor m ore sensors. This inform ation is

then analyzed by specific algorithm s todeterm ine if these m easurem ents indi-cate that a fire condition m ay be pre-sent.Som e intelligent detection devices

m ake all the alarm decisions, w hile oth-

ers report conditions to the alarm sys-tem control equipm ent w hich m akesthe alarm decision. Conversely, conven-tional fire alarm detectors use setthresholds in a single sensor to deter-m ine alarm conditions. Thus, conven-tional devices are rigidly designed to

signal alarm conditions only after a spe-cific level has been reached.

INTELLIGENT DEVICES

Fire alarm devices labeled as intelli-gent are usually thought of as analog-

type detectors.1

Analog-type detectorsprovide continuous, real-tim e m easure-m ents of air properties w ithin a detec-tion cham ber w hich is, in turn, affectedby the surrounding air. These detectorscan have set thresholds such as con-ventional detectors to initiate an alarmsequence based upon these m easure-m ents. In addition, m any intelligent

detectors use algorithm s to process lev-els low er than those threshold valuesset to indicate an alarm . These aredefined here as prealarm signals. Pre-alarm signals can be com pared w ith a

num ber of analog signals from otherdetectors and sensors w ithin the space,com pared w ith previous signalsreceived from the affected detector orcom pared w ith predeterm ined fire pro-files obtained through fire tests. Thesetechniques allow an increase in detec-tor sensitivity, w hile decreasing thepotential for false alarm potential.To be listed or approved, intelligent

detectors m ust m eet the criteria for

conventional detectors. As such, w henan intelligent detector reaches thealarm threshold specified for conven-

tional detectors, it m ust initiate analarm signal.A discussion of som e of the decision-

m aking algorithm s used in intelligentfire alarm system s follow s.

AU TO M ATIC SEN SITIVITY

COMPENSATION

D ust, dirt, hum idity, age, and otherenvironm ental factors affect sm oke

detector sensitivity. These factors shiftthe base reading of detectors closer toor further from an alarm threshold,depending upon the type of contam ina-tion and type of sensor. As this basereading is shifted, higher or low er con-

centrations of sm oke are required forconventional detectors to reach the pre-set alarm threshold. This m akes sm okedetectors m ore susceptible to unw antedalarm s or delayed activation over tim e.M any analog detectors are designed

w ith autom atic sensitivity com pensa-

tion. W hile detectors incorporatingautom atic sensitivity com pensation, or“drift”com pensation, m ay or m ay notbe classified as intelligent detectors perthe definition suggested w ithin N EM ATraining M anual on Fire A larmSystem s,1 “drift”com pensation is includ-

ed w ithin som e intelligent detectionand is discussed here to provide back-ground.Since the detectors have a continu-

ous range of sensitivities, the alarmthreshold can be shifted higher orlow er, based on the analog prealarmsignal. If the sensitivity increases as thedetector becom es dirty, the alarm

threshold is shifted upw ard w ithin thedetector’s range of sensitivity, com pen-sating for the increased analog read-ings. W hen, over tim e, the analog sig-nal is shifted close to the upper sensi-

tivity lim it, the detector provides am aintenance signal, notifying the userof service requirem ents before unw ant-ed alarm s occur. This allow s the detec-tor to com pensate for contam inationand environm ental factors w hile allow -ing for optim um detector sensitivity.

PRES ET S ENS ITIVITY

ADJUSTMENT

D etectors w ith preset sensitivityadjustm ents operate sim ilar to thosew ith autom atic sensitivity com pensa-

tion. This design adjusts the sensitivityaccording to preset conditions. Som espaces m ay routinely require anincrease or decrease in detector sensi-tivity. For instance, a highly protectedspace m ay require a higher level ofprotection during off-hours or a nightclub m ay require a decrease in detectorsensitivity during norm al business hoursto com pensate for occupant sm oking.This allow s optim um sensitivities to be


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used for each predictably changingbackground condition w ithin a givenspace.

PROFILE CO M PARISO N

Fires tend to have unique sm oke andheat profiles based upon specific fuelsburning. For instance, fires in plasticm aterials tend to produce m ore sm okethan fires in flam m able liquids. Som efire alarm m anufacturers have devel-oped proprietary databases w ith detailscharacterizing products of com bustion

for a large range of fuels. These data-bases include m easurem ents of tim e-dependent properties, such as photo-electric detector readings, ionizationdetector readings, and tem peraturereadings. D ata have been grouped

according to fuel packages and specifictraits have been determ ined for eachtype of fuel package.Although individual fire alarm m anu-

facturers use different m ethods, analogm easurem ents from individual detectorsare com pared w ith predeterm ined val-ues obtained in fire tests. This allow sdetectors to filter out conditions thatare not typically associated w ith fires.

The com parison algorithm is based onthe predeterm ined values obtainedfrom testing. Therefore, large spikes inproperties such as obscuration noticed

w hen insects enter sm oke cham bers orlarge spikes in ionization values due toradio frequency interference can berecognized and ignored.Since alarm verification allow s detec-

tors to use a tim e delay to confirmalarm conditions, the detector can usethe alarm verification delay tim e to ana-lyze the prealarm signal. If the pre-alarm value is consistent w ith condi-tions typically associated w ith fire con-ditions, the alarm is verified, and analarm is reported im m ediately. Since

unw anted alarm conditions are filtered

out, detector sensitivities can be signifi-cantly low ered, allow ing early detectionof fires.Various m anufacturers use different

m ethods w ith this approach. Som egroup the test results from variousenvironm ents such as offices, w are-houses, or hospitals, w hile others usea single-representative approach tocom pare recorded readings to actualreadings.

MULTISENSOR COMPARISON

D etectors using m ultisensor com par-isons operate sim ilar to single-sensorcom parison detectors described earlier.H ow ever, several m ethods of detection

are used. Com binations of ionization,photoelectric, and heat detectors areincorporated into a single detectiondevice. This device can then com pareinform ation from several differentsources. This approach m ay enhancethe ability to filter out unw anted condi-tions and allow s for increased sensitivi-ties. For instance, a quick rise in obscu-ration, w ithout any associated rise intem perature, can be filtered out.

Another benefit m ay be that thesedetectors use algorithm s to process theanalog values from all of the sensors.

The conditions for reporting an alarmcan then be based upon a com binationof inputs from each sensing elem ent,w hich further increases reliability byenhancing stability, sensitivity, or both.

MULTIDETECTOR COMPARISON

As sm oke flow s across a ceiling, ittends to affect m ore than a singledetector. M ultidetector com parisonsm ake use of this trend. Affected detec-tors analyze adjacent detector prealarm

conditions. Alarm s are initiated w hen

the prealarm conditions of adjacentdetectors indicate a sim ilar rise in theassociated value. Sim ilar to the detec-tors that com pare profiles, these detec-tors can com pare m ultiple locations andelim inate local spikes caused by aninsect or radio frequency interference.This allow s decreased alarm thresholds,faster detection tim es, and greater sys-tem stability.

OTHER FEATURES

Pow erful system processors allow

additional features, such as:• Autom atic A ddressing: detectorsautom atically determ ine an inde-pendent address and integrate itinto the system .

• Setting of Prealarm s: one or m oreprealarm s can be set.

• D etector M em ory: detectors canstore a variety of inform ationincluding the rate of environm entalcom pensation, last m aintenance

date, and analog signal for lastalarm .

• Intelligent N otification: notification

devices can be given discreteaddresses to allow a single circuitto cover m ultiple independentnotification zones. This also allow sindividual notification device test-ing.

Intelligent fire alarm system s can pro-vide additional inform ation to the con-trol equipm ent and ultim ately to theuser. Each building layout and environ-m ent is unique, and application ofthese system s should be carefully eval-uated to provide the best approach.Since analog detectors can com pareconditions w ith know n values and pro-vide increased inform ation, this tech-

nology provides m any enhancem ents totoday’s system s.Intelligent detectors w ill likely

becom e the typical or standard detectorfor m any applications. This w ill be due,in part, to the cost of these detectorsbecom ing com parable to that of typical

detectors. Currently, several intelligentdevices are only slightly m ore costlythan that of standard devices. As thecost of intelligent technology decreases,m ore and m ore of these devices w ill beused in fire alarm system s.Finally, it is im portant to note that all

detectors, w hether com bination and/orintelligent, require m aintenance to beeffective. Even w ith all of the new tech-

nology, m aintenance program s fordetectors and fire alarm system s shouldbe view ed as one of the m ost im por-tant aspects of fire alarm system s.

Jeffr ey Tubbs was formerly wi th Rolf

Jensen & Associates.

REFERENCES

1 Train in g Manu al On Fir e Alar m Systems ,

N ational Electrical M anufacturers

Association, W ashington, D C, 1992.

For an onli ne version of this arti cle, go

to www.sfpe.org.


13/33


By Joh n M . Choli n, P.E., and

Chr is Ma r r ion, P.E.

O VERVIEW

The concept of a sm oke detectoris over 75 years old. In E.M eili’s book “M y Life W ith

Cerberus,”1 M eili states that H .G einacher reported in the B ulletin ofthe Sw iss Association of ElectricalEngineering in 1922 of experim ents heperform ed using an ionization cham -ber and how they could be applied toanalyzing sm oke concentrations. Thenext docum ented indication of a sim i-

lar-type device w as from French patentapplications dated 1937/1938 byM alsallez and Breitm an1 describing afire detector based on using ionization

cham bers.

O ver 25 years ago, Custer andBright published their sem inal publica-tion,Fir e Detection : State of the Art .2 Inthis docum ent, they conclude:“Several ar eas of the detection pic-

tu re, however, need impr ovement i n

order to provide data wh ich wi ll allow

effective engineeri ng judgements to be made i n selectin g the appropriate

detector for specif ic applica tion s...

Chan ges need to be made in the test-

in g and approval procedu res to pro-

vide engin eeri ng data for a pproved

detectors. Da ta should be provided

whi ch accur ately descri be the per for-

man ce of approved u ni ts over a wi de

range of smoke sources, ai r veloci ti es,

rates of heat evoluti on, an d i nstalla-

tion configur ation s. These data can

permi t better engin eeri ng of detecti on

systems wi th r espect to the expected fi r e

exposur e and response time cri teria . By lim iti ng approval testin g to a na rr ow

ran ge of fir e signa tur es, ambient con-

ditions and in stallation configuration,

or testin g again st a standar d device

such a s an automa tic sprin kler head,

many detectors whi ch have desir able

char acteristics for specifi c appli cati ons

may be exclud ed fr om the mar ketplace

whi le others whi ch may have undesir -

able properti es, such as insensiti vity to

certa in fi r e signatu res, may be accept-

ed. This can r esult in detector fai lur es

due to lack of engin eeri ng data con- cer n in g the capabi li ti es of a li sted or

approved un it.”

O ver 20 years ago, H eskestad andD elachatsios stated in their landm arkresearch:“There is a n eed to ti e the spaci ng of

detectors, heat as well as smoke, to

realistic fir e situ ation s, recognizi ng

effects of fir e-grow th ra te, ceil in g

height, combustible materi al (i n the

case of smoke detectors), an d ceil in g

configur ati on. The spacing should be

such that a thr eshold f ir e size, Q d (kW,Btu /s), is not exceeded at detec-

tion.” 3

As seen, it has been alm ost 80 yearssince the initial developm ent of sm okedetectors and at least 20 years sincetw o significant publications in the fireprotection industry identified the needfor developing perform ance m etricsfor detectors. Yet given all this tim e,

Performance

Metrics

for FireDetection


14/33


and the identified need, the fire pro-tection industry has m ade virtually noprogress tow ard a credible m etric foraccurately predicting the perform anceof either heat or sm oke detectors.The engineering com m unity has

accepted the concept of perform ance-

based fire engineering design for thebuilt environm ent. The SFPE Engineeri ng Gui de to Per form ance-

Based Fir e Protection Ana lysis and

Design of Bu ild in gs outlines the fram e-w ork and the design m ethodology forperform ance-based design. The Life Safety Code ,® N FPA 101-2000, and theICC Per form ance Code adopt the per-form ance-based design m ethod as rep-resenting an acceptable m eans to pro-vide equivalent life safety throughalternative designs. N ow that the con-cept of perform ance-based design for

the fire protective system s has beenaccepted, how can its prom ise be ful-filled? H ow can a perform ance-baseddesign or analysis be conducted effec-tively w hen the response of heat orsm oke detectors to even the sim plestof fire scenarios cannot be predictedw ith any reasonable degree of engi-neering precision or confidence? Sincem any fire safety aspects (including

occupant notification, notification ofthe responding fire service, activationof special suppression system s, initia-tion of sm oke m anagem ent system s,

release of door holders and otherdevices to com plete the com partm enta-tion, etc.) rely on determ ining w hensm oke or heat detectors w ill respond,an accurate assessm ent of detector per-form ance is necessary. Yet fire detec-tion system s are relied upon for all ofthese critical fire safety functions w ithno credible m eans of accurately pre-dicting w hen, if ever, these functionsw ill be initiated.It is interesting to note that the least

com m only used type of fire detection

has perform ance m etrics and, hence,

the best design tools. A N ationallyRecognized Testing Laboratory (N RTL)listing radiant energy-sensing detectorsin the U .S. has a long-standing, estab-lished practice of providing a perfor-m ance m etric for flam e detectors. Thisperform ance m etric has perm itted per-form ance-based design in confor-m ance w ith N FPA 72, the National Fire Alar m Code,4 and its predecessordocum ent N FPA 72E-1990 Standar d on

In iti ati ng Devices .5 Indeed, perfor-m ance-based design has been therequired m ethod of designing flam eand spark/em ber detection system ssince 1990. U nfortunately, over 10years after perform ance-based designutilizing detector perform ance m etrics

w as first incorporated into N FPA 72,the designer still has no such m ethodand m etric for heat detectors andsm oke detectors, the m ost com m onlyused types of detection.

HEAT DETECTOR PERFORMANCE

METRICS

The fundam ental prem ise underlyingperform ance-based design is that, ifthe inform ation regarding the com part-m ent, am bient conditions, detectionsystem characteristics, and hazards are

adequately defined, engineering toolscan be used to predict how a fire candevelop once ignited. These sam eengineering tools can be used to pre-dict conditions in the com partm ent offire origin at a location relative to thefire plum e and som e specified tim esubsequent to ignition. This w ouldthen enable one to predict the intensi-ty of the fire signature at a hypotheti-

cal detector location as a function ofthe fire size and grow th rate, androom configuration. O stensibly, thisperm its the engineer to predict detec-

tor response.This concept w as the basis for

Appendi x C – Engineeri ng Gui de for

Automati c Fir e Detection Spacing toN FPA 72E-1984,Standar d on Automati c Fir e Detectors .5 This appen-dix utilized the correlations developedby H eskestad and D elachatsios3 to pro-duce a set of tables that specified heatdetector spacing as a function ofdesign fire size, fire grow th rate, detec-tor location relative to the fire, ceiling

height, and detector response param e-ters including operating tem perature

and therm al response. The therm alresponse of a heat detector w as esti-m ated by using a correlation to thetest m ethodology for determ iningResponse Tim e Index (RTI) for sprin-klers. This correlation is outlined inSection B-3-2.5.1 of N FPA 72-1999, theNationa l Fir e Alarm Code .4

U nfortunately, as Schifiliti and Pucci6

have pointed out, this correlationintroduces an error of unquantified

m agnitude due to the different ceilingjet velocities encountered at fire sizesnorm ally associated w ith heat detectorresponse versus the fire size requiredfor sprinkler response. H eat transferbetw een a fluid and a heat sink is afunction of fluid flow velocity.7

Consequently, w hen a sim ple coeffi-cient of heat transfer is to be deter-m ined for any heat transfer device,sprinkler, or heat detector, it m ust bem easured at flow velocities close tothose for w hich the device is beingdesigned. The test m ethodology fordeterm ining RTI utilizes a flow velocity

of 1.5 m ./sec. (5.0 ft./sec.), consider-ably larger than the ceiling jet velocityone w ould expect to observe at a heatdetector location during a fire thatw ould norm ally be anticipated as thedesign basis for a heat detection sys-

tem . The m agnitude of the error intro-duced by using the test m ethodologyfor RTI has not been quantified andm ay be large enough to invalidate adesign. W ithout conducting furtherresearch, how ever, it is difficult to tell.Since heat detectors are not, as part

of their listing exam ination, subjected tothe test to determ ine R TI, a correlationtable w as included into the Append ix C – Engin eeri ng Gui de for Automa tic Fir e

Detection Spacin g to N FPA 72E-1984,Standar d on Au tomati c Fir e Detectors .5

H ow ever, this correlation is of lim ited

precision as the exact sam e heat detec-tor m ay obtain a different “listed spac-ing”from the various NRTLs due to theslightly different test conditions thatm ay be found at each N RTL. Listedspacing is a lum ped param eter com -prised of num erous independent vari-ables, m any of w hich are determ inedby the test and not the detector undertest. Consequently, a correlationbetw een listed spacing and RTI is tenu-ous at best. Thus, RTI m ay be of quite

lim ited use in the context of being ableto accurately predict the response of

heat detectors.Listed spacing w as originally intend-

ed as a m eans of com paring onedetector to another and not as a designtool. Since listed spacing is a lum pedparam eter that encom passes detectorcharacteristics, fire characteristics, testroom characteristics, and test condi-tions into a single value, the designerhas no m ethod of separating out theeffect of any one param eter from the


15/33


lum ped param eter for design purposes.Consequently, the lum ped param eterof listed spacing is of very lim ited use-fulness in the context of perform ance-

based design. It does not appear thatany published study exists that sup-ports the notion that heat detectorsinstalled pursuant to their listed spac-ing actually provide the expected per-form ance in term s of fire size at alarminitiation. This therefore leaves theengineer w ithout the proper tools toaccurately predict w hen the detectorw ill respond to a given fire scenariow ith a high degree of certainty.To confidently and accurately design

a heat-detection system in a perfor-m ance-based design environm ent, thedesigner m ust know the operatingtem perature (Tr) and the Therm al

Response Coefficient (TRC) of the

detector. W ithout both of these m et-rics, the designer is forced to estim ateresponse by using a correlationbetw een the listed spacing of thedetector and RTI. Since there areunknow n inaccuracies in the listedspacing to RTI correlation, the design-er m ust perform their design calcula-tions using a range of RTI values andanalyze the sensitivity of the design toinaccuracies in the correlation. Theresult is a design of questionable cred-ibility and hence large safety factors.Such a design rarely lives up to the

full potential of perform ance-baseddesign as an engineering concept.

A SO LUTION

In view of the need for a heatdetector perform ance m etric, theTechnical Com m ittee on InitiatingD evices for the National Fire Alarm Code (N FAC) adopted language in the1999 edition m andating the determ ina-tion and publication of the Therm alResponse Coefficient, a perform ancem etric analogous to R TI, for a heat

detector as part of its listing. Thisrequirem ent w as established w ith aneffective date of June 2002 to providesufficient tim e for the developm ent of

the test m ethodology and the determ i-nation of the TRC for currently listeddetectors. W ith a properly developedm ethod for determ ining TRC, thedesign of fire detection system s usingheat detectors could be based on theprincipals of fire dynam ics rather than

listed spacing, yielding designs w hoseperform ance could be predicted m oreaccurately. The strategy w as to p ublisha TRC that had the sam e form as RTI.

This w ould enable the fire protectionengineer to use existing perform anceprediction correlations and fire m odels,originally developed for sprinklers, topredict the perform ance of detectionsystem s using heat detectors.U nfortunately, as of this w riting,

despite the fact that tw o research pro-posals w ere presented to the m anufac-turers of heat detectors and U L overtw o years ago, there has yet to beagreem ent on how to fund theresearch to develop the test m ethodol-ogy. In addition, recent proposals toN FPA 72 have been m ade to retractthis requirem ent from the code.Consequently, the engineering com m u-

nity is still left w ith no validated per-form ance m etric for heat detectors.

SMOKE DETECTOR

PERFORMANCE METRICS

As if the situation w ith heat detec-tors is not sufficiently challenging, thesituation does not get better w hen itcom es to perform ance m etrics forsm oke detectors. O ptical density orobscuration is usually used as a m ea-sure of sm oke concentration. Thism easure w as apparently adopted due

to the presum ed objective for sm okedetection: to provide occupant notifi-

cation w hile there w as still sufficientvisibility to allow escape of the occu-pants prior to the onset of untenableconditions. U nfortunately, the opticalproperties of sm oke vary substantiallyw ith variations in a num ber of param e-ters including fuel, fire ventilation,sm oke tem perature, and sm oke age. Am ore detailed analysis of sm oke alsoleads to other m easurable param eterssuch as particle size distribution, m assconcentration, particle num ber concen-

tration, and sm oke color that deter-m ine the gross, m acroscopic opticalproperties of sm oke. The dynam ics ofsm oke production, aging, and m ove-

m ent have been and continue to be anarea of ongoing research.8

In the U .S., the sensitivity of sm okedetectors is stipulated as the percentper foot obscuration at w hich thedetector renders an alarm in the U L268 Sm oke Box.9 This is also a lum ped

param eter. The test for determ iningthis value relies on a carefully con-trolled air flow , tem perature, relativehum idity, fuel (a cotton lam p w ick

obtained from a specific source), andtest box. Consequently, the sensitivitystipulated on the detector that isderived from the U L 268 Sm oke Box isonly valid in the sm oke box. N oresearch has been found that substan-tiates the use of the m arked sensitivityon the sm oke detector as an engineer-ing basis for the design of a sm okedetection system ; unless, of course, thedesign objective is to detect a sm older-ing lam p w ick located inside a U L 268Sm oke Box. Yet designers routinelyuse the sensitivity m arked on thedetector in conjunction w ith a firem odel to leap to the conclusion that asm oke-detection system w ill respond

at a given sm oke obscuration level.The closest thing to a perform ancem etric for sm oke detectors available todesigners using U .S. products is theperform ance im plied by the full-scaleroom fire tests that are conducted aspart of the listing evaluation by U L.U L conducts three room fire tests w iththe detector under test located 5.3 m(17.5 ft) from the fire plum e center-line,im plying a spacing of 7.6 m (25 ft.).These fires are sum m arized in Table 1.The m axim um obscuration levels

tabulated in Table 1 represent the m in-

im um acceptance criteria for sm okedetectors that are m arked w ith the 1%

to 4% obscuration sensitivity found onthe detector label. N ote that for thepaper fire in an actual room test, theobscuration level can be up to 37tim es that w hich is listed on the detec-tor before it is required to alarm . Thesm oke used in the sm oke box is alight gray in color, ideally suited fordetectors that rely on reflected light fordetection, w hereas the sm oke pro-duced by the test fires is far from opti-m al. N evertheless, the disparity in the

criteria for the room fire tests and them arked “sensitivity”gives rise to con-cern that there m ight be significantdelays in sm oke detector responseunder real fire conditions.

The size of the test fires is notexplicitly stipulated in the U L test stan-dard. Consequently, if a designer w ereinclined to use this test data as a basisfor a perform ance prediction, theym ust infer the fire size from the


16/33


descriptions in the standard and thenscale up to their design fire. W hilepossible, this process has the potentialfor producing errors in accurately pre-dicting response.Also, there is no “listed spacing”for

a sm oke detector resulting from theU L listing evaluation. Instead, the m an-ufacturer is left to “recom m end”a

spacing for its detector. In spite of thefact that the im plied spacing derivedfrom the U L Full-Scale Room Fire Testis 7.6 m (25 ft), m ost m anufacturers

and N FPA 72 recom m end a spacing of9.1 m (30 ft), w ith no reference todesign goals/objectives or the designfire for w hich this spacing is deem edappropriate.Finally, w hile U L at one tim e includ-

ed a Black Sm oke Test in U L Standard

268 to determ ine the differentialbetw een the response of a detector toblack sm oke com pared to its responseto the light gray sm oke produced bythe cotton lam p w icking, there is nocurrent evaluation for the im pact ofsm oke color on the response of thesm oke detector listed by U L Since m ostspot-type photoelectric sm oke detectors

operate on a reflected light principal,sm oke color can have a profoundeffect on the ultim ate response of thedetector to real-life fires. Table 2 illus-

trates the variation in response to grayand black sm oke.This difference in response is the

artifact of a num ber of variables,including sm oke concentration m ea-surem ents and reflectance propertiesof sm oke. The sm oke concentration is

derived from the attenuation of a pro-jected light beam w hile, for instance,spot-type photoelectric sm oke detectorresponse is derived from the intensity

of reflected light. O ptically absorbentsm okes produce high attenuations butpoor reflectance, w hile light graysm oke is deem ed to be equallyabsorbent and reflectant. This diver-gence betw een the sm oke m easure-m ent and sm oke detection m ethodscontributes to inconsistency of the testresults. H ow ever, the sm oke yield ofthe fires in question also contributes tothe divergence in the test results. Thisfact is inescapable: the sam e detectorscan respond at different obscurationlevels to different fuels, different com -bustion m odes, and different types ofsm oke.Exam ples of this w ide variation in

response w ere show n by H eskestadand D elachatsios3 in full-scale teststhey perform ed alm ost 25 years ago.Som e of their results are sum m arizedin Table 3.N ote the large variations of optical

density at response that can vary by afactor as large as 200. These variationsare due not only to the variations inthe detector technology but also thevariation in sm oke concentration andcolor. This underscores the im portanceof having a m eans to accurately pre-dict sm oke detector response that can

be correlated to the detector as w ell asthe characteristics of the sm oke, if

sm oke detectors are to be relied uponfor critical fire safety functions.The above should not be construed

as a criticism of U L or its test standard,U L 268. U L 268 w as designed to pro-vide a uniform test of product allow inga purchaser to be assured that theproduct w as generally acceptable for aspecific purpose. It has never been theintent of U L 268 to provide a perfor-m ance m etric for use in the design ofsystem s. H ow ever, as the needs of soci-

ety change, the testing standards uponw hich that society relies m ust alsochange. If society’s need for fire-safebuilt environm ents are to be addressed

through perform ance-based design,then the testing standards m ust evolveto serve that em erging need.H aving no credible perform ance

prediction m ethodology from eitherU L or the m anufacturers, one is tem pt-ed to look to fire plum e and ceiling jet

Test Fuel Max. %/m (%/ft)Obs.

Max. ResponseTime

Smoke Color Variance (Max/Min)Acceptable Response Range

A Paper 78 (37) 4 minutes

B Wood 46 (17) 4 minutes

C Toluene/Heptane

Material Ionization

102 Dur m-1(ft-1)

Scattering

RelativeSmoke Color

37 (13) 4 minutes

WoodCotton

Polyurethane

PVC

1.6 (0.5)0.16 (0.05)

16 (5.0)

33 (10.0)

4.9 (1.5) 0.26 (0.8)

16 (5.0)

33 (10.0)

LightLight

Dark

Dark

Variation 200:1 12.5:1

1.6 %/m (0.5 %/ft) to 12.5 %/m (4.0 %/ft)

1.6 %/m (0.5 %/ft) to 29.2 %/m (10.0 %/ft)

Grey Smoke

Black Smoke

7.8

18.25

Material Ionization

Temperature Rise C ( F)

Scattering

Wood

Cotton

Polyurethane

PVC

14 (25)

1.7 (3)

7.2 (13)

7.2 (13)

42 (75)

28 (50)

7.2 (13)

7.2 (13)

Average 7.5 (14) 21 (38)

Table 1. Summary of the UL Full-Scale Room Fire Tests in UL 268

Table 3. Values for Optical Density at Response (for flaming fires only)6

Table 2. UL 268 Smoke Detector Test Acceptance Criteria forDifferent Colored Smoke9

Table 4. Temperature Rise for Detector Response6


17/33


w hich the illusion of a correlation w asem braced underscores the urgency ofthe need for a perform ance-predictivetool for sm oke detectors. Sadly, thepracticing engineer has very lim ited per-form ance estim ation m ethods at theirdisposal w hen designing fire-detectionsystem s utilizing sm oke detection.

A SO LUTION

To confidently and m ore accurately

design system s using sm oke detectors,the designer needs tw o m etrics. Thefirst is the inherent sensitivity of the

detector. There is som e disagreem entregarding the actual form of this m et-ric. Som e propose a m etric basedupon the optical characteristic of thesm oke, w hile others propose the useof m ass per unit volum e of air andcorrelations to correct for the opticalcharacteristics.

Figure 2. Response of

ionization smoke

detector plotted for a)

mass concentration

versus b) number

concentration for mono-

disperse DOP aerosol.11

0 20 40 60 80 100 120 140 160 180 200

Mass concentration (mg/m3)

D e t e c t o r o u t p u t - B a c k

g r o u n d ( v o l t s )

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

D e t e c t o r o u t p u t - B a c k

g r o u n d ( v o l t s )

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5 10 15 20 25

Number concentration (103/cm3)

20% DOP 65 m

20% DOP 0.53 m

6.3% DOP 0.5 m

2.1% DOP 0.22 m

0.67% DOP 0.15 m

0.3% DOP 0.14 m

55% DOP 0.90 m

100% DOP 1.05 m

Line indicates changein particle size

Figure 1. Response of

photoelectric smoke

detector plotted for a)

mass concentration

versus b) number

concentration for mono-

disperse DOP aerosol.11

D e t e c t o r o u t p u t - B a c k g r o u n d ( v o l t s )

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.00 20 40 60 80 100 120 140 160 180 200

Mass concentration (mg/m3)

D e t e c t o r o u t p u t - B a c k g r o u n d ( v o l t s )

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

0 5 10 15

Number concentration (105/cm3)

8.3% DOP0.5 m

20% DOP0.75 m

100% DOP1.2 m

2.1% DOP

0.26 m

20%

DOP0.75 m

8.3%DOP0.50 m

2.1% DOP0.20 m

0.67% DOP0.17 m

0.10% DOP0.79 m

0.013% DOP0.043 m

dynam ics for a m ethod. H eskestad andD elachatsios offered the notion that,for a given fire and detector, the tem -perature rise at the detector andsm oke concentration could be deem edto be a constant.3 In fairness to theseresearchers, it should be noted thatthey contem plated the developm ent ofa series of tem perature rise versusresponse correlations over a range offuels for each sm oke detector as partof its listing evaluation. To illustrate

their hypothesis, they selected a tem -perature rise correlation of 13°C(20°F). U nfortunately, readers of this

research incorrectly concluded thatsuch a correlation actually existed,assum ed one num ber as representativefor all detectors and all fuels, and thenbegan using it as the basis for design.The truth is that no such correlationexists. Schifiliti and Pucci6 have show nthat there is not a basis for using a

13°C (20°F) tem perature correlation asthe basis for an actual design. Table 4show s the tem perature rise at alarmfor the range of fires used byH eskestad and D elachatsios. Clearly,this data does not support the notionof a single correlation for all fires.Furtherm ore, even if there w as a reli-

able correlation betw een tem peraturerise and sm oke concentration, the tem -perature rise w ould be a different valuefor each pairing of fuel and detector.

D espite the fact that the “13°C tem pera-ture correlation”does not exist, m anydesigns have been based upon the

assum ption that it does. Engineers stillcling to the idea because it gave theman ability to predict sm oke detector acti-vation based upon the plum e and ceil-ing jet produced by the fire. Clearly, thisis w hat the design com m unity needs inorder to execute a perform ance-baseddesign. Indeed, the enthusiasm w ith


18/33


In 1980, M ulholland w rote,11

“The two most importan t aerosol properties aff ectin g the

per formance of these detectors ar e the concen tra ti on of the

smoke aerosol and the part icle siz e.”

This statem ent w as taken from his w ork w ith the N ationalBureau of Standards –again alm ost 20 years ago. H is state-m ent is based on the relationships observed for these charac-

teristics, as indicated in part in the Figures 1 and 2.From the figures, it is clear that M ulholland’s research

dem onstrated a significant correlation betw een detectorresponse, m ass concentration, and num ber concentration.Clearly, additional research is necessary to p rovide sufficientdata to develop a basis for a design correlation. N evertheless,M ulholland’s findings look quite prom ising. It certainly justi-fies the notion that, given a few years and a concertedresearch effort, reasonable test m ethods could be developedthat w ould provide a perform ance m etric that can be used topredict response to a given design fire under a range of envi-

ronm ental conditions.Research is needed to determ ine the m ost effective form of

the sm oke detector perform ance m etrics as w ell as the m eans

of determ ining their num erical values for real sm oke detectors.For exam ple, is it m ore practical to quantify detector sensitivityas a function of optical density, or is it m ore practical to char-

acterize it as a function of aerosol m ass per unit volum e andcorrelate for optical properties? W ithout research, the potential

efficacy of these tw o approaches rem ains unresolved.Currently, the concept of tw o m etrics, one quantifying detec-tor sensitivity to the sm oke aerosol and a second quantifyingthe sm oke entry tim e delay, still seem s to m ake the m ostsense. U ltim ately, the objective is to have one or m ore perfor-

m ance m etrics that can be used in the context of currentlyavailable fire m odeling tools to predict sm oke detectorresponse w ithin a range of situational conditions.A proposal requiring the publication of sm oke detector

perform ance m etrics in the form of a Sensitivity Factor and aSm oke Entry Factor has been subm itted to the TechnicalCom m ittee on Initiating D evices for the 2002 edition ofN FPA 72, the National Fire Alarm Code . This proposal hasbeen offered to create the necessary sense of im m ediacy togalvanize the m anufacturing com m unity into funding theresearch. O stensibly, a code requirem ent w ould produce

the necessary econom ic incentive for action. H ow ever, thereality is that this proposal w ill not survive w ithout the sup-port of the engineering com m unity.

John Cholin is with JM Cholin Consultan ts, In c. Chris

Marri on is with Arup Fire.

REFERENCES

1 M eili, E.,My Li fe wi th Cerberus – Successes an d Setbacks , printed

Zurichseee D ruckerei Stafa, 1990.

2 Custer, R. L. P. & Bright, R. G ., “Fire D etection: The State of the

Art,”N BS Technical N ote 839, N ational Bureau of Standards, June

1974.

3 H eskestad, G . & D elachatsios, M .A., “Environm ents of Fire

D etectors, Phase I: Effect of Fire Size, Ceiling H eight and M aterial,”

N BS-G CR-77-95, N ational Bureau of Standards, W ashington, D C,

July 1977.

4 N FPA 72-1999,National Fire Alarm Code , N ational Fire Protection

Association, Q uincy, M A, 1999.

5 N FPA 72E-1984,Stand ard on Au tomatic Fir e Detectors , N ational

Fire Protection Association, Q uincy, M A, 1984.

6 Schifiliti, R. P. & Pucci, W .E.,”Fire D etection M odeling: State of the

Art,”Fire detection Institute, Bloom field, CT, 1996.

7 W hite, F. M .,Heat Tran sfer , Addison W esley Publishing C om pany,

Inc., 1984.

8 M ulholland, G . “Sm oke Production and Properties,”The SFPE

Han dbook of Fir e Protection Engin eeri ng , 2nd Ed., N ational Fire

Protection A ssociation, Q uincy, M A, 1995.

9 U L/AN SI 268,Smoke Detectors for Fir e Protective Sign ali ng ,U nderw riters Laboratories, N orthbrook, IL, 1996.

10 H eskestad, G . & D elichatsios, M . A. “Environm ents of Fire

D etectors, Phase 1: Effect of Fire Size, Ceiling H eight and

M aterial,”M easurem ents vol. I (NBS-G CR-77-86), Analysis vol. II

(N BS-G CR-77-95). N ational Technical Inform ation Service (NTIS),

Springfield, VA 22151.

11 M ulholland, G . & Liu, Response of Sm oke D etectors to

M onodisperse A erosols,Jour na l of Research of the Nati ona l

Bureau of Standar ds , Volum e 85, N o. 3, M ay-June 1980.

For an on li ne version of th is arti cle, go to www.sfpe.org.

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FIRE

ALARMSYSTEMS

By Joh n L. Par ssinen, P.E.,

Pau l E. Pat ty, P.E, an d

Lar r y Shu dak , P.E.

Factors that assure that fire alarm system sfunction effectively include: (1) initialdevice design, (2) third-party certification,

(3) analysis of the protected area, (4) testing, and(5) m aintenance of the system . This article

describes the certification activity perform ed byU nderw riters Laboratories (U L) that contributes tothe predictable operation of a fire alarm system .U L’s certification includes review of installationinstructions, product construction analysis, perfor-m ance tests for com pliance w ith requirem ents inStan da rd s for Safety , follow -up surveillance toconfirm that products w hen shipped m atch theproducts tested during the initial product investi-gation, and certification of the installed fire alarm

system .


Underw r i t ers

LaboratoriesContributions for


20/33


STANDARD TYPE OF EQUIPM ENT UL LISTINGOR SERVICE CATEGORY

UL 268 – Smoke Detectors for Fire-Protective Smoke Detectors UROX

Signaling Systems Smoke Detectors for Releasing Service SYSW

Smoke Detector Accessories URRQ

Smoke Detectors for Special Application URXG

UL 268A – Smoke Detectors for Duct Application Duct-Type Smoke Detectors UROX

UL 38 – Manual Signaling Boxes for Use with Noncoded Boxes UNIU

Fire-Protective Signaling Systems Coded Boxes UMUV

UL 228 – Door Closures-Holders, With or Releasing Devices for Door Holders GTIS

Without Integral Smoke Detectors

UL 346 – Waterflow Indicators for Fire-Protective Extinguishing System Attachments USQT

Signaling Systems

UL 521 – Heat Detectors for Protective Heat Detectors UQGS

Signaling Systems Heat Detectors for Release SZGU

Device Service

Heat Detectors for Special UTHV

Application

UL 464 – Audible Signal Devices Audible Appliances ULSZ

UL 1971 – Signaling Devices for the Hearing-Impaired Visual Signal Appliances for UUKC

the Hearing-Impaired

UL 1638 – Visual Signaling Appliances – Visual Signaling Appliances UVAV

Private Mode Emergency and General Utility Signaling

UL 1480 – Speakers for Fire-Protective Speakers UUMW

Signaling Systems

UL 864 – Control Units for Fire-Protective Control Units UOJ Z

Signaling Systems Control Unit Accessories UOXX

Releasing Device Control Units SYZV

Control Units and Accessories, Marine UXWK

Releasing Device Equipment SZNT

Releasing Device Accessories SYSWEmergency Communication and UOQY

Relocation Equipment

UL 1711 – Amplifiers for Fire-Protective Amplifiers UUMW

Signaling Systems

UL 1481 – Power Supplies for Fire-Protective Signaling Power Supplies UTRZ

Systems

Table 1. UL Standards Relating to Fire Alarm Equipment


21/33


INSTALLATION INSTRUCTIONS

The initial activity of UL’s investiga-tion of devices intended for use in firealarm system s is the review of them anufacturer’s installation instructions.

These instructions, w hich cover boththe intended application of the productand how the product is to be used tom eet that application, are prim arilyreview ed for consistency w ith theNational Fir e Alarm Code , N FPA 72. U Ladditionally review s the instructions forop erational claim s and uses the docu-m ent as the basis for electrically load-ing and interconnecting the productduring the evaluation. Because of the

significance of the docum ent in relatingU L’s testing to the actual use of theproduct, the draw ing num ber and revi-

sion level of the installation instruc-tions/w iring diagram are required to beincluded in the product m arking forreference by both the installer andinspection authority.

PRODUCT C ONSTRUCTION

The second com ponent is an analy-sis of the product’s construction. Thisinvolves a review to confirm the prod-uct is constructed so that it w ill bepractical and sufficiently durable for its

intended installation and use.

G enerally, all electrical parts of a prod-uct shall be enclosed to provide pro-tection of internal com ponents andprevent contact w ith uninsulated liveparts. Enclosures m ust have thestrength and rigidity necessary to resistthe abuses to w hich the product islikely to be subjected during intendeduse w ithout increasing the risk of fire,electrical shock, and/or injury to per-sons. All current carrying parts m ust besufficiently rated for the application,and the product m ust provide m ain-tained spacings betw een uninsulated

live parts and the enclosure or deadm etal parts, and betw een uninsulated

live parts of opposite polarity.

PERFORM ANC E TESTS

The third com ponent is perform anceevaluation that is based on the Standardfor Safety for the specific product. Thestandards in Table 1 are used in theevaluation of fire alarm equipm ent.

The perform ance tests in the applic-able U L Standard are used to helpdeterm ine the reliable perform ance ofthe product. The evaluation generallyincludes a series of tests as follow s:1. Environm ental tests to test for

false alarm s (variable tem peratureand hum idity for control, detec-

tion, and notification equipm ent;corrosion for both detection andnotification products; and acceler-ated aging, stability, and velocitysensitivity for detection units);

2. M echanical abuse tests to evaluatethe stability of the m echanicalassem bly and circuit connections(jarring for all equipm ent; vibra-tion for both detection and notifi-cation products; and drop/im pactfor portable equipm ent); and

3. Various electrical tests (endurance,variable input voltage, transients,abnorm al, and com ponent tem -perature for all equipm ent; and

static discharge for detectionproducts).

As part of the aforem entioned tests,the acceptable operation of the productis verified before and, depending uponthe conditioning, either during orim m ediately after each test. Thisinvolves exam ining control equipm entfor m inim um required operation, evalu-ating am plifiers for acceptable harm on-

ic distortion and frequency responselevels, verification of stable sensitivityfor detection products, and m aintainingrated audible and visual outputs, asapplicable, for notification appliances.Additionally, the above tests are con-

ducted to determ ine that no false

alarm s occur and to confirm the condi-tioning does not have an adverse affecton the threshold response for sm okedetectors w hen adjusted to m axim umsensitivity settings. This procedure alsoestablishes the upper sensitivity lim it ofthe production w indow . D uring the

sm oldering sm oke test, no alarm m ayoccur before 0.5 percent per footobscuration.Sm oke detection initiating devices

are subjected to w ood, paper, gas, andplastic fire tests as w ell as a sm olderingsm oke test w hile calibrated to theirleast fav

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