System Sensor Smoke Alarm A05 1003 002 User Manual

A P P L I C A T I O N S  
G U I D E  
System  
Smoke Detectors  
 
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The purpose of this guide is installers should find the contents both educational and  
to provide information con- informative.  
Introduction  
cerning the proper application of smoke detectors used in  
conjunction with fire alarm systems. It outlines basic prin- Though this information is based upon industry expertise  
ciples that should be considered in the application of early and many years of experience, it is intended to be used  
warning fire and smoke detection devices. Operating char- only as a technical guide. The requirements of applicable  
acteristics of detectors and environmental factors, which codes and standards, as well as directives of the Authorities  
may aid, delay or prevent their operation, are presented.  
Having Jurisdiction (AHJ’s) should be followed. In partic-  
ular, the most current version of NFPA 72 for installation  
Fire protection engineers, mechanical and electrical engi- and testing of systems is a key element in the effectiveness  
neers, fire service personnel, fire alarm designers and of smoke detection systems.  
Section 1  
ICBO’s Uniform Building Code is generally used through-  
out the West and Southwest regions of the United States.  
NFPA Codes and  
Standards  
NFPA publishes standards for  
the proper application, instal-  
Standards That  
Apply  
Southern Building Code Congress International (SBCCI)  
900 Montclair Road, Birmingham, Alabama 35213-1206  
SBCCI’s Standard Building Code is generally used in the  
South and Southeast regions of the United States.  
lation, and maintenance of automatic smoke detectors. The  
principal codes and standards that should be reviewed  
before specifying or installing automatic smoke detectors  
are listed below:  
International Code Council, Inc. (International Building  
Code/International Fire Code)  
5360 Workman Mill Road, Whittier, California 90601-  
2298  
The organizations listed above have formed an umbrella  
organization known as the International Code Council  
(ICC), for the purpose of combining the codes produced by  
the above three organizations into a single set of model  
building and fire codes. ICC’s International Building Code  
and International Fire Code were first published in 2000  
and have been adopted by some states.  
National Fire Protection Association (NFPA)  
Batterymarch Park, Quincy, Massachusetts 02269-9101  
NFPA publishes codes and standards concerning all phas-  
es of fire protection. Among those which directly concern  
automatic smoke detectors are:  
NFPA 70: National Electrical Code  
NFPA 72: National Fire Alarm Code  
NFPA 72 covers minimum performance, location, mount-  
ing, testing, and maintenance requirements of automatic  
fire detectors.  
Testing Laboratories  
Testing laboratories test smoke detectors, control panels  
and other components of fire alarm systems to verify con-  
formance with NFPA requirements and their own stan-  
dards. Equipment that passes their tests are identified by a  
label and/or listing.  
NFPA 90A: Standard for the Installation of Air  
Conditioning and Ventilating Systems  
NFPA 92A: Smoke Control Systems in Malls, Atria, and  
Large Areas  
NFPA 90A and 92A provide information for the use of  
smoke detectors in ducts of HVAC systems and smoke con-  
trol systems.  
Underwriters Laboratories, Inc. (UL)  
333 Pfingsten Road, Northbrook, Illinois 60062  
1655 Scott Boulevard, Santa Clara, California 95050  
1285 Walt Whitman Road, Melville, New York 11747  
12 Laboratory Drive, P.O. Box 13995, Research Triangle  
Park, North Carolina  
NFPA 101: Life Safety Code  
NFPA 101 specifies the requirements for smoke detection in  
both new and existing buildings depending on the type of  
occupancy.  
UL publishes an annual directory listing fire protection  
equipment which bear the UL label. Its standards which  
apply to smoke detectors are:  
Building and Fire Codes  
There are three independent regional organizations which  
write model building and fire codes which become law  
when adopted by local and state governments. These codes  
specify smoke detector requirements based on building  
type and occupancy. The organizations are:  
UL 217: Single and Multiple Station Smoke Detectors  
UL 268: Smoke Detectors for Fire Protection Signaling  
Systems  
UL 268A: Smoke Detectors for Duct Applications  
UL 864: Standard for Control Units for Fire Protective  
Signaling Systems  
Building Officials and Code Administrators (BOCA)  
4051 West Flossmoor Road, Country Club Hills, Illinois  
60478-5795  
BOCAs National Building Code is generally used through-  
out the northeast and midwest regions of the United States.  
Factory Mutual Research (FM)  
1151 Boston-Providence Turnpike, P.O. Box 9102,  
Norwood, Massachusetts 02062  
International Conference of Building Officials (ICBO)  
5360 Workman Mill Road, Whittier, California 90601-  
2298  
FM publishes an annual report listing fire protection equip-  
ment which bears its label.  
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Industry Publications  
Manufacturer’s Publications  
NEMA Guide for Proper Use of Smoke Detectors in Duct  
Applications  
The manufacturer of the smoke detectors being used  
should be contacted for any published information on their  
products.  
NEMA Training Manual on Fire Alarm Systems  
NEMA Guide to Code Requirements for Fire Protective  
Signaling and Detection Systems  
NEMA Guide for proper Use of System Smoke Detectors  
Section 2  
There are two basic types of Electronic circuitry monitors both chambers and compares  
smoke detectors in use today; their outputs. If the humidity or the atmospheric pressure  
ionization and photoelectric. changes, both chambers’ outputs are affected equally and  
The sensing chambers of these cancel each other. When combustion particles enter the  
How Smoke  
Detectors Work  
detectors use different principles of operation to sense the sensing chamber, its current decreases while the current of  
visible or invisible particles of combustion given off in the reference chamber remains unchanged. The resulting  
developing fires.  
current imbalance is detected by the electronic circuitry.  
(See Figure 5.) There are a number of conditions that can  
affect dual-chamber ionization sensors; dust, excessive  
humidity (condensation), significant air currents, and tiny  
insects can be misread as particles of combustion by the  
electronic circuitry monitoring the sensors.  
Ionization Smoke Detector Operation  
A typical ionization chamber consists of two electrically  
charged plates and  
a
radioactive source (typically  
Americium 241) for ionizing the air between the plates.  
(See Figure 1.) The radioactive source emits particles that  
collide with the air molecules and dislodge their electrons.  
As molecules lose electrons, they become positively  
charged ions. As other molecules gain electrons, they  
become negatively charged ions. Equal numbers of positive  
and negative ions are created. The positively charged ions  
are attracted to the negatively charged electrical plate,  
while the negatively charged ions are attracted to the pos-  
itively charged plate. (See Figure 2.) This creates a small  
ionization current that can be measured by electronic cir-  
cuitry connected to the plates (“normal” condition in the  
detector).  
Figure 2: Ion Distribution  
Figure 1: Particle Radiation Pattern  
Particles of combustion are much larger than the ionized  
air molecules. As particles of combustion enter an ioniza-  
tion chamber, ionized air molecules collide and combine  
with them. (See Figure 3.) Some particles become posi-  
tively charged and some become negatively charged. As  
these relatively large particles continue to combine with  
many other ions, they become recombination centers, and  
the total number of ionized particles in the chamber is  
reduced. This reduction in the ionized particles results in a  
decrease in the chamber current that is sensed by elec-  
tronic circuitry monitoring the chamber. When the current  
is reduced by a predetermined amount, a threshold is  
crossed and “alarm” condition is established.  
Figure 3: Ion and Particles of Combustion Distribution  
Changes in humidity and atmospheric pressure affect the  
chamber current and create an effect similar to the effect of  
particles of combustion entering the sensing chamber. To  
compensate for the possible effects of humidity and pressure  
changes, the dual ionization chamber was developed and  
has become commonplace in the smoke detector market.  
Sensing Chamber  
(Current Decreasing)  
Sensing Chamber  
Source  
A dual-chamber detector utilizes two ionization chambers;  
one is a sensing chamber that is open to the outside air.  
(See Figure 4). The sensing chamber is affected by partic-  
ulate matter, humidity, and atmospheric pressure. The  
other is a reference chamber that is partially closed to out-  
side air and affected only by humidity and atmospheric  
pressure, because its tiny openings block the entry of larg-  
er particulate matter including particles of combustion.  
Reference  
Chamber  
(Current Stable)  
Reference Chamber  
(Current Stable)  
Figure 5: Dual Chamber with  
Particles of Combustion  
Figure 4: Dual Chamber  
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Photoelectric Light Obscuration Smoke Detector  
Photoelectric Smoke Detector Operation  
Another type of photoelectric detector, the light obscura-  
tion detector, employs a light source and a photosensitive  
receiving device, such as a photodiode (see Figure 8).  
When smoke particles partially block the light beam  
(Figure 9), the reduction in light reaching the photosensi-  
tive device alters its output. The change in output is sensed  
by the detector’s circuitry, and when the threshold is  
crossed, an alarm is initiated. Obscuration type detectors  
are usually of the projected beam type where the light  
source spans the area to be protected.  
Smoke produced by a fire affects the intensity of a light  
beam passing through air. The smoke can block or obscure  
the beam. It can also cause the light to scatter due to reflec-  
tion off the smoke particles. Photoelectric smoke detectors  
are designed to sense smoke by utilizing these effects of  
smoke on light.  
Photoelectric Light Scattering Smoke Detector  
Most photoelectric smoke detectors are of the spot type and  
operate on the light scattering principle. A light-emitting  
diode (LED) is beamed into an area not normally “seen” by  
a photosensitive element, generally a photodiode. (See  
Figure 6.) When smoke particles enter the light path, light  
strikes the particles (Figure 7) and is reflected onto the pho-  
tosensitive device causing the detector to respond.  
Light Source  
Light Sensitive Device  
Light Source  
Light Sensitive Device  
Light Sensitive Device  
Figure 6: Light Scattering Detector  
Figure 7: Light Scattering Detector with Smoke  
Light Source  
Light Sensitive Device  
Light Source  
Figure 8: Light Obscuration Detector  
Figure 9: Light Obscuration Detector with Smoke  
Smoke Detector Design Considerations  
Considerations in Selecting Detectors  
Smoke detectors are based on simple concepts, but certain The characteristics of an ionization detector make it more  
design considerations need to be observed. They should suitable for detection of fast flaming fires that are charac-  
produce an alarm signal when smoke is detected, but terized by combustion particles in the 0.01 to 0.4 micron  
should minimize the impact of an unwanted signal which size range. Photoelectric smoke detectors are better suited  
can arise from a variety of causes. In an ionization detec- to detect slow smoldering fires that are characterized by  
tor, dust and dirt can accumulate on the radioactive source particulates in the 0.4 to 10.0 micron size range. Each type  
and cause it to become more sensitive. In a photoelectric of detector can detect both types of fires, but their respec-  
detector, light from the light source may be reflected off the tive response times will vary, depending on the type of fire.  
walls of the sensing chamber and be seen by the photo-  
sensitive device when no smoke is present. The entrance of Because the protected buildings normally contain a variety  
insects, dirt, drywall dust, and other forms of contamina- of combustibles, it is often very difficult to predict what  
tion into the sensing chamber can also reflect light from size particulate matter will be produced by a developing  
the light source onto the photosensitive device.  
fire. The fact that different ignition sources can have dif-  
ferent effects on a given combustible further complicates  
Electrical transients and some kinds of radiated energy can the selection. A lighted cigarette, for example, will usually  
affect the circuitry of both ionization and photoelectric produce a slow smoldering fire if it is dropped on a sofa or  
smoke detectors and be interpreted by the electronic cir- bed. However, if the cigarette happens to fall upon a news-  
cuitry to be smoke, resulting in nuisance alarms.  
paper on top of a sofa or bed, the resulting fire may be  
characterized more by flames than by smoldering smoke.  
The allowable sensitivity ranges for both types of detectors  
are established by Underwriters Laboratories, Inc. and all The innumerable combustion profiles possible with vari-  
are verified by their performance in fire tests. Regardless of ous fire loads and possible ignition sources make it difficult  
their principle of operation all smoke detectors are required to select the type of detector best suited for a particular  
to respond to the same test fires.  
application.  
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For more information, see NFPA 72-1999, paragraphs A-2- save more in the future. Nevertheless, smoke detectors do  
3.6.1.2, A-2-3.6.1.1, A-2-3.6.1.2(a), and A-2-3.6.1.2(b).  
have limitations. They may not provide early warning of a  
fire developing on another level of a building. A first floor  
NFPA 72 requirements also dictate that alarm notification detector, for example, may not detect a second floor fire.  
appliances (including smoke detectors with built-in For this reason, detectors should be located on every level  
sounders) produce the 3-pulse temporal pattern fire alarm of a building. In addition, detectors may not sense a fire  
evacuation signal described in ANSI S3.41. (Audible developing on the other side of a closed door. In areas  
Emergency Evacuation Signals)  
where doors are usually closed, detectors should be locat-  
ed on both sides of the door.  
Situations Where Other Types of Detectors May Be Used  
In certain circumstances where standard smoke detectors  
are unsuitable, special-purpose detectors, such as flame  
detectors, heat detectors, and other detection devices may  
be used.  
As already indicated, detectors have sensing limitations.  
Ionization detectors are better at detecting fast, flaming  
fires than slow, smoldering fires. Photoelectric smoke  
detectors sense smoldering fires better than flaming fires.  
Because fires develop in different ways and are often  
unpredictable in their growth, neither type of detector is  
always best. A given detector may not always provide sig-  
nificant advance warning of fires when fire protection prac-  
tices are inadequate, nor when caused by violent explo-  
sions, escaping gas, improper storage of flammable liquids  
such as cleaning solvents, etc.  
The application of these special types of detectors should  
be based on an engineering survey and used in accordance  
with the manufacturer’s installation instructions provided.  
Smoke Detectors Have Limitations  
Smoke detectors offer the earliest possible warning of fire.  
They have saved thousands of lives in the past and will  
Section 3  
Wiring Supervision  
Class B Circuits  
Typical System  
Layout  
The initiating circuits that con- Class B circuits differentiate between short circuits across  
nect smoke detectors to a con- the loop (alarm) and opens on the loop (trouble).  
trol panel should be super- Supervision of this circuit is accomplished by passing a low  
vised so that a fault (trouble) condition that could interfere current through the installation wiring and an end-of-line  
with the proper operation of the circuit will be detected resistor. Increases or decreases in this supervisory current  
and annunciated.  
are monitored by the fire alarm control panel and will  
cause alarm or trouble conditions, respectively, to be indi-  
Smoke detectors are generally categorized as either 2-wire cated. A single open in a Class B circuit disables all devices  
or 4-wire detectors. Two-wire detectors derive their power electrically beyond the open.  
directly from the same fire alarm control panel alarm initi-  
ating device circuit over which they report an alarm.  
Because of their dependency on the initiating circuit, 2-wire  
END OF LINE  
RESISTOR  
detectors must be tested and listed for compatibility with  
the control panel to be used, to ensure proper operation.  
Four-wire detectors are powered from a separate pair of  
wires, and, like the 2-wire detector, apply an electrical  
short across the associated alarm initiating device circuit to  
transmit an alarm (Figure 10). Because they do not derive  
power from the alarm initiating device circuit, electrical  
compatibility is predicated upon the operating parameters  
TYPICAL  
INITIATING  
DEVICES  
of the power supply to which the detectors are connected  
and not the initiating circuit. Supervision of the power to  
4-wire detectors is mandated through the use of an end-of-  
line power supervision relay. When power is on, the relay  
contacts of the end-of-line relay are closed and connected  
in series with the end-of-line resistor beyond the last initi-  
ating device. Loss of power at any point in the power sup-  
ply circuit will cause the relay to de-energize and a trouble  
condition to occur on the initiating circuit.  
INITIATING DEVICE  
CIRCUIT  
ZONE 1  
TROUBLE  
ALARM  
NOTE*: Refer to the fire alarm control panel manufacturer’s  
operating manual to determine the ability of a specific initi-  
ating circuit to react in a “Class B” or “Class Afashion.  
FIRE ALARM CONTROL UNIT  
PRIMARY  
POWER  
SUPPLY  
*NFPA 72 now classifies initiating device circuits by “Style” and “Class”. Style B  
is an example of a Class B circuit; Style D is an example of a Class A circuit.  
Figure 10: Two-Wire Detector Circuit  
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Class A Circuits  
Class A circuits also differentiate between short circuits  
across the loop and opens on the loop. Supervision is  
accomplished by monitoring the level of current passing  
through the installation wiring and the end-of-line resistor,  
which in a Class A circuit is an integral part of the fire  
alarm control panel. Class A wiring must return to and be  
terminated in the control panel. This technique requires a  
minimum of four conductors to be terminated at the panel,  
and further requires that the fire alarm control panel is  
designed to monitor Class A circuits. The additional cir-  
cuitry necessary for Class A supervision enables the con-  
trol panel to “condition” the initiating circuit to monitor  
the initiating circuit from both ends when in a trouble  
mode due to an open fault on the loop. This “conditioning”  
ensures that all devices are capable of responding and  
reporting an alarm despite a single open or non-simultane-  
ous single ground fault on a circuit conductor.  
TYPICAL  
INITIATING  
DEVICES  
INITIATING DEVICE  
CIRCUIT  
INITIATING DEVICE  
CIRCUIT RETURN  
ZONE 1  
TROUBLE  
ALARM  
The compatibility considerations of smoke detectors that  
were detailed in Class B circuits apply with Class A as well  
(Figure 11).  
FIRE ALARM CONTROL UNIT  
PRIMARY  
POWER  
SUPPLY  
Figure 11: 2-Wire Detectors – Style D (Class A) Circuit  
Wireless Circuits  
Fire Safety Functions  
Wireless detectors and their internal transmitters derive Often smoke detectors are utilized to control ancillary  
their operating power from their internal battery or batter- equipment. Most detectors used in releasing service have  
ies and are listed by Underwriters Laboratories, Inc. in auxiliary relay contacts which are directly connected to the  
accordance with requirements of NFPA 72. Supervision of system or device to be controlled. Care should be taken to  
the internal battery power source is incorporated within ensure that detectors utilized in such a manner are  
the smoke detector circuitry. If the battery power source approved for releasing service. A few of the typical appli-  
depletes to the threshold specified by Underwriters cations are as follows:  
Laboratories, the smoke detector will sound a local alert  
and initiate a trouble signal once each hour for a minimum  
of seven days or until the battery or batteries are replaced.  
To control the flow of smoke in air handling and air  
conditioning systems.  
To release doors to contain smoke in a fire situation.  
To release locks to allow exit in a fire situation.  
To capture and recall elevators in a fire situation.  
To activate a suppression system.  
The wireless initiating devices are supervised for tamper  
and/or removal by initiating a distinct trouble signal. Each  
wireless device also initiates a test transmission every hour  
to verify the reliability of the communication circuit. Any Spacing and placement requirements for detectors used in  
device failing to communicate is identified on the control releasing service may be different from detectors used in  
panel no less than every four hours.  
conventional open area applications. It is recommended  
that 4-wire detectors be used in these situations because  
depending on the control panel and detectors used, more  
than one detector relay on a circuit may not receive enough  
power from the 2-wire circuit to operate during alarm.  
General Zoning Guidelines  
The faster the source of an alarm can be pinpointed, the  
faster action can be taken. Although formal rules for zon-  
ing are not given in fire protection codes, except for wire-  
less devices where each smoke detector must be individu- Smoke Detector Installation  
ally identified, it is always sensible to zone any system that Wiring Installation Guidelines  
contains more than  
a
small number of detectors. All fire alarm system installation wiring should be installed  
Experienced detector installers and system designers rec- in compliance with Article 760 of NFPA 70, the National  
ommend the following:  
Electrical Code (NEC), the manufacturer’s instructions and  
the requirements of the authority having jurisdiction.  
• Establish at least one zone on every protected floor.  
• Zone natural subdivisions of a large building, such as  
separate wings on a single floor.  
Typical Wiring Techniques  
• Minimize the number of detectors in each zone. Fewer The primary rule of installation wiring is:  
detectors on a zone will speed up locating the fire and  
simplify troubleshooting.  
“Follow the Manufacturer’s Instructions”  
This rule cannot be overemphasized. The requirement for  
• Install duct detectors in different zones than open-area electrical supervision of the installation wires and their  
detectors for troubleshooting and locating purposes.  
connections to initiating devices makes fire alarm system  
installation wiring very different than general wiring.  
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A manufacturer’s installation wiring drawing routes wires  
and shows connections in a certain manner to accommo-  
date supervision requirements. Any variance from the  
manufacturer’s drawings might cause a portion of a circuit  
to be unsupervised and, if an open or short circuit fault  
occurred, it could prevent the circuit from being able to  
perform its intended function without giving the required  
trouble indication.  
Smoke Detector “A”  
The rules of supervision are not very complex. However,  
unless an installer is experienced in fire alarm system instal-  
lations, he or she would not likely be familiar with them.  
Smoke detector manufacturer’s installation drawings will  
show how their detectors are to be connected into a system.  
However, a manufacturer’s drawings may not show how  
devices located on the same floor, but served by a different  
riser (vertical wiring run), should be connected. The dia-  
grams on the following page should be considered as typi-  
cal initiating device circuits utilizing smoke detectors. They  
are offered to illustrate proper and improper installation  
wiring and termination techniques. Since there are always  
exceptions to typical installation drawings, experienced  
installers use the primary rule of installation wiring: Follow  
the manufacturer’s instructions, and meet the local codes.  
Smoke Detector  
Smoke Detector  
Figure 12: Incorrect Wiring Method  
Smoke Detector  
Figure 12 illustrates improper wiring of smoke detector A”.  
This wiring method is referred to as “T-tapping.” This com-  
mon installation error is often made in riser wiring as well  
as single floor wiring. The smoke detector may operate  
properly under alarm conditions. If it becomes disconnect-  
ed from the installation wiring loop beyond the “T-tap”,  
however, the detector would not function, and no “trou-  
ble” condition would occur.  
NOTE: “T-tapping” may be permitted with some  
“intelligent” fire alarm systems. Refer to manufacturer’s  
recommendations.  
Smoke Detector  
Smoke Detector  
Figure 13: Correct Wiring Method  
Figure 13 illustrates the correct installation wiring method  
for smoke detectors. None of the connections can be bro-  
ken without opening the circuit, causing loss of supervi-  
sion, and the fire alarm control panel to indicate trouble.  
Smoke detectors should be connected to supervised instal-  
lation wiring in a manner that ensures electrical supervision  
of the device. Removal of a detector from its associated ini-  
tiating circuit should cause the loop to open, resulting in a  
trouble condition. The required termination at the smoke  
detector may involve either screw terminals or wire pigtails.  
Regardless of the method utilized, removal of the smoke  
detector or a single installation wire must open the initiat-  
ing circuit and result in a trouble signal at the control panel.  
Figure 14: Proper Termination  
Screw termination of either side of the initiating circuit may  
require only one or two screws. Figure 14 is an example of  
proper termination when one screw terminal is used. Note  
that the installation conductor has been cut before termina-  
tion. This assures full supervision of the smoke detector.  
Figure 15 details common connection errors. In both exam-  
ples, removal of the smoke detector wire does not open the  
initiating circuit. The fire alarm control panel will not rec-  
ognize a trouble condition, and the detector that has been  
deliberately or inadvertently disconnected will be disabled.  
Figure 15: Improper Termination  
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Figure 16 is an example of properly connected  
smoke detectors provided with pigtails. This  
method of termination supervises all wiring to  
the point at which it connects to the detector.  
may require more power than the initiating device cir-  
cuit can supply. This could result in the inability of the  
relay to control auxiliary equipment to which it is con-  
nected.  
Wire Nut  
• When using wireless detectors, follow the manufactur-  
er’s installation instructions to assure proper radio  
communication between the smoke detector and the  
control panel.  
• Observe polarity when required.  
• Protect detectors against contamination during con-  
struction or renovation.  
Smoke  
Detector  
Figure 17 shows an incorrect pigtail connec-  
tion. This is a form of “T-tapping” discussed  
earlier. Note that the conductor between the  
wire nut (or splice) and the detector is unsu-  
pervised, and could be cut or disconnected  
without resulting in a trouble signal.  
Figure 16: Pigtail Connections –  
Correct Wiring Method  
• Carefully follow the manufacturer’s installation  
instructions.  
Wireless Systems  
Wireless smoke detectors do not require any  
field wiring as the power for the initiating  
devices is contained and incorporated within  
the device. Removal of a wireless smoke detec-  
tor initiates a distinct tamper or trouble signal.  
Follow the instructions in the manufacturer’s  
installation manual for wireless systems.  
Wire Nut  
Don’t:  
• “T-tap” smoke detectors or circuit conductors, except  
when specifically permitted by the manufacturer as  
part of an intelligent/addressable system.  
• Loop uncut installation conductors around screw ter-  
minations.  
• Exceed the maximum resistance permitted for the ini-  
tiating device system.  
• Exceed the number of 2-wire detectors allowed on a 2-  
wire initiating circuit (specified by UL).  
Installation Do’s and Don’ts  
Do:  
Smoke  
Detector  
Verify that 2-wire smoke detectors to be  
used have been tested and UL listed for  
compatibility with the equipment to  
which they are connected. If necessary,  
contact the manufacturer for this informa-  
tion.  
• Locate any end-of-line devices electrically  
at the end of the circuit, beyond all initi-  
ating devices (not at the control unit,  
except in a Class A installation).  
• Use caution when utilizing 2-wire detec-  
tors with integral relays, because they  
Wiring and System Checkout  
As required for all installation wiring of fire alarm systems,  
check the detector loop wiring for grounds, short circuits,  
and open faults before the system is placed into operation.  
Each detector should be tested in accordance with the  
manufacturer’s instructions.  
Figure 17: Pigtail Connections –  
Incorrect Wiring Method  
When using wireless detectors, verify the radio signal trans-  
mission strength in accordance with the installation manual.  
Section 4  
After all detectors have been Some codes or ordinances have minimum objectives such  
installed, test the complete as capturing elevators or preventing circulation of smoke  
system to ensure that no through the HVAC systems instead of early detection of fire.  
wiring faults exist, and that all  
parts of the system operate as A user should weigh the costs against the benefits of  
intended. A complete system installing a complete fire detection system when any detec-  
Proper Detector  
Applications,  
Placement and  
Spacing*  
checkout consists of testing each detector at its installed tion system is being installed. The location, quantity and  
location and following the panel manufacturer’s instruc- zoning of detectors should be determined by what objec-  
tions for system checkout. Also, refer to NFPA 72 for addi- tives are desired rather than the minimum requirements of  
tional information.  
any local codes or ordinances.  
Total coverage”, as defined in NFPA 72, is the definition  
of a complete fire detection system. In some of the speci-  
fied areas of coverage, such as attics, closets, under open  
loading docks or platforms, a heat detector may be more  
appropriate than a smoke detector. Careful consideration  
should be given to the detector manufacturer’s instructions  
and the following recommendations in this guide.  
Where to Place Detectors  
Detector placement is critical to early warning functions.  
To provide effective early warning of a developing fire sit-  
uation, smoke detectors should be installed in all areas of  
the protected premises. Total coverage as defined by NFPA  
72 should include all rooms, halls, storage areas, base-  
ments, attics, lofts, and spaces above suspended ceilings  
including plenum areas utilized as part of the HVAC sys-  
tem. In addition, this should include all closets, elevator  
shafts, enclosed stairways, dumbwaiter shafts, chutes and  
other subdivisions and accessible spaces.  
In general, when only one detector is required in a room or  
space, the detector should be placed as close to the center  
of the ceiling as possible. Central location of the detector is  
best for sensing fires in any part of the room. If a center  
location is not possible, it may be placed no closer than 4  
inches from the wall, or if listed for wall mounting, it may  
Fire detection systems installed to meet local codes or ordi-  
nances may not be adequate for early warning of fire.  
*The guidelines in this section of the guide are adapted from Standards published by the National Fire Protection Association, Quincy,  
Massachusetts, USA. These standards include NFPA 72, National Fire Alarm Code; NFPA 70, “National Electrical Code”, Article 760; and NFPA  
90A, “Installation of Air Conditioning and Ventilating Systems”.  
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be mounted on the wall. Wall-mounted detectors should be  
located not less than 4 inches nor more than 12 inches  
from the ceiling to the top of the detector, and at least 4  
inches (10 cm) from any corner wall junction. (See Figure  
18.)  
4 in. (10 cm)  
Ceiling  
When air supply and/or air return ducts are present in a  
room or space, the detector(s) should not be placed in the  
path of the air flow supply or return duct (NFPA 72, 1999  
Edition).  
Smoke tests are helpful in determining proper placement.  
Special attention should be given to smoke travel directions  
and velocity, since either can affect detector performance.  
Never Here  
Acceptable Here  
Placement of detectors near air conditioning or incoming  
air vents can also cause excessive accumulation of dust  
and dirt on the detectors. This dirt can cause detectors to  
malfunction and cause unwanted alarms. Detectors should  
not be located closer than 3 feet from an air supply diffuser  
or an air return vent.  
Top of Detector Acceptable Here  
Spot type detectors, in properly engineered systems, may  
also be placed in return air ducts, or in approved duct  
detector housings designed for this application. Although  
duct detectors are not a substitute for open area detectors,  
they can provide an effective method of initiating building  
control functions to prevent smoke from being transported  
from the fire area to other parts of a building. (See Duct  
Smoke Detector Applications Guide.)  
Note: Measurements shown are to the  
closest edge of the detector.  
Side Wall  
Figure 18: Wall Mounted Detector – Placement  
Extreme Cold or Hot Environments  
Where Not To Place Detectors  
Avoid very cold or very hot environments, or unheat-  
ed buildings or rooms where the temperature can fall  
below or exceed the operating temperature range of  
the detector. At temperatures above or below the oper-  
ating range of the detector*, its internal components  
may not function properly.  
See Table A-2-3.6.1.2A in NFPA 72-1999.  
One of the major causes of unwanted alarms is improper  
placement of detectors. The best way to avoid unwanted  
alarms is not to install detectors in environments that can  
cause them to malfunction, or to install detectors specially  
designed for those environments. Examples follow:  
Excessively Dusty or Dirty Areas  
*Manufacturers’ specifications should list acceptable  
temperatures in these ranges.  
Areas with Combustion Particles  
In excessively dusty or dirty areas consider using the  
Filtrexsmoke detector. This detector incorporates a  
microprocessor-controlled air intake fan and filter that  
allows the unit to be installed in areas where ordinary  
detectors cannot be used. Filtrex is an intelligent  
smoke detector that removes airborne particles before  
they reach the sensing chamber. It is ideal for textile  
mills, dusty manufacturing facilities, paper mills, and  
recycling centers. For more information see System  
Sensor’s FiltrexApplications Guide.  
Avoid areas where particles of combustion are nor-  
mally present, such as in kitchens or other areas with  
ovens and burners; in garages, where particles of com-  
bustion are present in vehicle exhausts. When a detec-  
tor must be located in or adjacent to such an area, a  
heat detector may be appropriate.  
Manufacturing Areas  
Avoid manufacturing areas, battery rooms, or other  
areas where substantial quantities of vapors, gases, or  
fumes may be present. Strong vapors can make detec-  
tors overly sensitive or less sensitive than normal. In  
very large concentrations, gases heavier than air, such  
as carbon dioxide, may make detectors more sensitive,  
while gases lighter than air, such as helium, may make  
them less sensitive. Aerosol particles may collect on  
detector chamber surfaces and cause nuisance alarms.  
Fluorescent Light Fixtures  
Outdoors  
Avoid using detectors outdoors, in open storage sheds,  
or other open structures affected by dust, air currents,  
or excessive humidity and temperature extremes.  
Wet or Excessively Humid Areas  
Avoid damp, wet or excessively humid areas, or next  
to bathrooms with showers.  
Elevator Lobbies  
Avoid placement near fluorescent light fixtures.  
Electrical noise generated by fluorescent light fixtures  
may cause unwanted alarms. Install detectors at least  
1 foot (0.3 m) away from such light fixtures.  
Do not place over ashtrays or where people will smoke  
while waiting for the elevator.  
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to use system detectors and manual fire alarm stations in  
the hallways and common areas of the complex and resi-  
dential single station type smoke detectors and heat detec-  
tors in the individual apartments. The system detectors,  
manual stations and heat detectors would be connected to  
a control panel, sound a general alarm and automatically  
notify the proper authorities that a fire condition exists.  
The residential smoke detectors located in the apartments  
would be interconnected only within the individual living  
quarters of each apartment. These residential units would  
sound an alarm only in the apartment where a fire started.  
Special Application Detectors  
The guidelines in this document generally apply to stan-  
dard open-area smoke detectors. System Sensor has a num-  
ber of advanced technology detectors that are optimized  
for specific environments and should be considered.  
PinnacleLaser technology smoke detector is designed for  
use in areas that require extremely early warning of fire. It  
is designed to detect the earliest particles of combustion  
making it ideal for clean rooms, computer rooms or  
telecommunication centers — any area where any damage  
is too much. As Pinnacle is ultra-sensitive to smoke — as  
much as 100 times more sensitive than standard detectors  
— care and judgement of application is needed to prevent  
unwanted alarms. See System Sensor’s Pinnacle™  
Applications Guide.  
Detector Spacing  
General Spacing Guidelines  
Some fire protection codes specify detector spacing on a  
given center-to-center distance between detectors under  
ideal conditions. These distances are based on rooms with  
smooth ceilings with no physical obstructions between the  
contents being protected and the detectors. Moreover, they  
are also based on a maximum ceiling height, and on the  
assumption that the value and the combustible nature of  
the contents of the room to be protected do not warrant  
greater protection or closer spacing.  
For environments classified as hazardous, System Sensor  
offers Intrinsically Safe Detectors designed to provide  
detection for high-risk areas such as oil production facili-  
ties, refineries and chemical plants. These units operate on  
low energy levels and are used with a safety barrier. See  
our Guide for Proper Use of Intrinsically Safe Fire  
Protection Devices.  
If we assume a typical center distance spacing guideline is  
30 feet (90 meters), how do we determine whether a given  
room or space can be protected by a single detector? Figure  
19 shows four detectors spaced horizontally and vertically  
30 feet (9 meters) apart. Detectors B and D, however, are  
more than 30 feet apart. Clearly, in this example detector  
spacing can exceed the given 30 foot spacing and still com-  
ply with the code if any source of combustion is within  
21.2 feet (6.4 meters) of the horizontal projection of a  
detector, and if no more than 900 square feet (82.8 square  
meters) are being protected by one detector.  
Standards for Smoke Detectors  
Underwriters Laboratories (UL) has three standards for  
smoke detectors: one for duct detectors, UL 268A; one for  
single and multiple station smoke alarms, UL 217; and one  
for systems type detectors, UL 268. Detectors should only  
be used for the applications for which they are specifically  
listed.  
The 2000 NFPA 101 Life Safety Code notes in Section  
9.6.2.10.4 that single station smoke alarms shall sound an  
alarm only within an individual living unit, suite of rooms,  
or similar area and shall not actuate the building fire alarm  
system unless otherwise permitted by the authority having  
jurisdiction. Section 9.6.1.5 states, All systems and com-  
ponents shall be approved for the purpose for which  
installed.”  
To determine what coverage patterns are permissible with-  
in the 30 foot spacing, start by tracing a circle with a radius  
of 21.2 feet. Keeping in mind the fact that most rooms and  
areas to be protected are rectangular or square in shape, any  
square or rectangle that fits within the circumference of the  
circle may be protected by one detector. (See Figure 20.)  
In addition to possible code noncompliance, the following  
deficiencies would exist in a series of residential smoke  
detectors, connected in a system mode:  
A
B
• Since the system is not supervised, vandals or others  
could disconnect a detector or the entire system, leav-  
ing a building without protection. The residents would  
be unaware of this serious life threatening condition.  
• Residential smoke alarms do not latch in alarm. In  
other words, the smoke alarm self-resets. One smoke  
alarm in alarm will sound all the smoke alarms con-  
nected together. It would be difficult to identify or  
locate a specific smoke alarm that initially put the sys-  
tem into alarm after the alarm condition was cleared.  
30 ft. (9.1 m)  
6.4 m)  
21.2 ft. (  
F
System detectors latch in alarm. They do not reset until  
power is momentarily disconnected. This makes it conven-  
ient to identify the location of a detector that caused the  
control panel to alarm. In addition, system detectors are  
specifically designed to connect to a panel. Two-wire detec-  
tors require a UL compatibility review to verify that the  
detector and panel operate together. A typical life safety  
fire protection system for an apartment complex would be  
D
C
Figure 19: Typical Detector Spacing  
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In other words, if a diagonal through the center of the room  
is no greater than the diameter of the circle, or 42.4 feet  
(12.8 meters), one detector can be used under ideal condi-  
tions. Figure 21 shows how a length of hallway can be pro-  
tected by only two detectors under ideal conditions.  
Rectangles  
A 10 ft. × 41 ft. = 410 sq. ft.  
B 15 ft. × 39 ft. = 585 sq. ft.  
C 20 ft. × 37 ft. = 740 sq. ft.  
D 25 ft. × 34 ft. = 850 sq. ft.  
E 30 ft. × 30 ft. = 900 sq. ft.  
Special Spacing Problems  
The ideal conditions upon which code guidelines are based  
do not exist in the majority of buildings. Detector installers  
usually have to deal with a variety of problems, such as  
uneven ceilings or ceilings crossed by beams and joists;  
storage racks and partitions that obstruct the path of smoke  
toward detectors; air stratification due to uninsulated roofs,  
peaked or sloped ceilings, or localized heating or cooling  
from heating, ventilating, and air conditioning systems;  
and extensive variability in the value and combustion char-  
acteristics of building contents. The following are suggest-  
ed techniques for dealing with some of the special detector  
spacing problems:  
Figure 20: Detector Coverage Patterns  
10 ft.  
• Solid joist and beam construction. Per NFPA 72-1996,  
solid joists are to be considered equivalent to beams  
for smoke detector spacing guidelines. For ceiling  
heights of 12 ft. (3.66 m) or lower and beam depths of  
1 ft. (0.3 m) or less, smooth ceiling spacing running in  
the direction parallel to the run of the beams is to be  
used, and 1/2 the smooth ceiling spacing is to be used  
in the direction perpendicular to the run of the beams.  
Spot-type detectors may be located either on the ceil-  
ing or on the bottom of the beams. For beam depths  
exceeding 1 ft. (0.3 m) or for ceiling heights exceeding  
12 ft. (3.66 m), detectors are to be located on the ceil-  
ing in every beam pocket. If the beamed ceiling is also  
sloped, use the spacing determined for flat beamed  
ceilings. Use the average height over the slope as the  
ceiling height in such cases. Note that, by definition in  
NFPA 72, ceilings are to be considered smooth unless  
the beams or joists are more than 4 in. (0.1 m) in  
depth.  
20.5 ft.  
41 ft.  
82 ft.  
20.5 ft.  
Figure 21: Detector Placement in Hallways  
lating, or air conditioning (HVAC) system creates arti-  
ficial hot or cold air layers in a room, the layers may  
affect the flow of smoke to the detectors.  
• Uninsulated Roofs. Uninsulated roofs present special  
placement problems. Air movement toward ceiling  
detectors is not impeded when the outside tempera-  
ture is cool, but stratification can occur when outside  
temperature is warm or hot, or when the roof is heat-  
ed by the sun on bright, sunny days. Although true  
thermal barriers are not present in many installations,  
smoke tests should be run in factories or warehouses  
with metal roofs on warm sunny days to determine  
whether such a thermal barrier exists.  
• High storage racks. Multi-level storage racks present  
special problems for early fire detection. Developing  
fires, especially smoldering fires, on the lower levels of  
the racks may not be sensed rapidly by ceiling mount-  
ed detectors. Upward convection of smoke can be  
slowed or blocked by goods stored on the upper levels  
of the racks. Multi-level fire detection is required.  
Detectors should be installed on the ceiling above each  
aisle and on intermediate levels of the racks adjacent  
to alternate pallet sections, shown in NFPA 72-1999,  
A-2-3.6.5. A consultant’s judgement may be required  
for specific installations.  
• Partitions. Partitions and many types of large, tall  
equipment standing on the floor can block the flow of  
smoke toward detectors. Any partition or similar  
obstruction that is less than 18 inches (45 cm) from  
the ceiling should be treated as a side wall dividing the  
area protected.  
• Peaked or Sloped Ceilings. Peaked or sloped ceilings  
can foster air stratification. Codes may specify spacing  
detectors by using horizontal spacing from the peak of  
the roof or ceiling. For instance, if the specified dis-  
tance from the peak is 3 feet (1 m), the dis-  
tance is measured on the base of the  
right triangle formed by a vertical line  
dropped from the peak of the roof,  
with the roof incline as the  
Detector may be placed  
anywhere in shaded area.  
hypotenuse. Additional detec-  
tors are installed on the  
3 ft.  
3 ft.  
selected spacing, using  
the horizontal distance,  
not the distance  
along the incline of  
the ceiling. (See  
Figure 22.)  
• Air Stratification. Air stratification in a room may keep  
air containing smoke from reaching ceiling-mounted  
detectors. Three conditions are known to accentuate  
air stratification: when a layer of hot air exists under a  
poorly insulated roof heated by the sun, cooler air will  
stratify the hot air layer at the ceiling; when a layer of  
cold air exists under a poorly insulated roof cooled  
from the outside by cold air, the heated air is cooled as  
it reaches the cold air layer; or when a heating, venti-  
S/2  
S
S
S/2  
S = Detector Spacing  
Figure 22: Detector Spacing Layout – Sloped Ceilings (peaked type)  
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• Alternate Detector Mounting. Mounting alternate  
detectors up to 3 feet (1 m) below the ceiling can  
increase detection of small or smoldering fires when  
the possibility of air stratification exists. Figure 23  
illustrates such an installation. Specific designs for  
such an alternate detection should be based upon an  
engineering survey.  
• Heating, Ventilating and Air Conditioning (HVAC)  
effects on air flow and air stratification should be  
determined and considered when planning detector  
placement. In rooms where forced-air ventilation is  
present, detectors should not be located where air  
from supply diffusers could dilute smoke before it  
reaches the detector. This may require additional  
detectors, because placing detectors only near return  
air openings may leave the balance of the area with  
inadequate protection, especially when the Heating,  
Ventilating and Air Conditioning (HVAC) system is not  
operating.  
• Detectors placed in an above-ceiling air handling space  
should not be used as a substitute for open area pro-  
tection, because smoke may not be drawn into the air  
handling space when the ventilating system is shut  
down. The detector will be less responsive to a fire  
condition in the room below than a detector located on  
the ceiling of the room below due to dilution and fil-  
tering of the air in the air handling space before the  
smoke reaches a detector. (See the discussion of detec-  
tor placement in Section 4: Where To Place Detectors).  
• Burn characteristics and the value of assets being pro-  
tected influence the spacing of detectors and the  
amount of protection provided in a specific room or  
area. Refer to NFPA 72-1999, Section 2-3.6 for more  
detailed information on spacing of detectors under  
special applications. Likewise, if the contents are espe-  
cially valuable, for example, sophisticated and expen-  
sive machinery or irreplaceable records, detectors  
should be placed closer together.  
Detectors in Air Handling and Air Conditioning  
Systems  
See NEMA Guide for Proper Use of Smoke Detectors in  
Duct Applications and NFPA 72, National Fire Alarm Code  
for more specific information.  
Detectors in Above-Ceiling Plenum Areas  
Including Plenums Utilized as Part of the HVAC  
System  
Detectors should be placed in plenum areas (above ceiling  
air handling space) in addition to the open area detectors  
installed in the open areas below and duct detectors  
installed in the ducts. Plenum detectors are required to be  
listed or tested and approved for the air velocities within  
the environment in which they are to be installed.  
Detectors placed in plenums MAY NOT be used as a sub-  
stitute for open area protection, because smoke may not be  
drawn into the plenum when the ventilating system is shut  
down. When the system is operating, the detector may be  
less responsive to a fire condition in the room below than  
will a detector located on the ceiling of the room below.  
This may be due to blockage, dilution, and filtering of the  
air prior to its arrival at the detector location in the plenum  
area.  
Since the air circulating through the plenums is usually at  
higher velocities than would be prevalent in the room  
below, detector spacing should be reduced.  
Also, the dilution of the smoke in plenum spaces is an  
important consideration when utilizing smoke detectors  
rated for higher velocities. Therefore, plenum detectors  
should be utilized to detect fire in the plenum but should  
never be utilized as a substitute for duct detectors and  
open area detectors.  
Maintenance requirements of detectors exposed to unusu-  
al velocities (above 300 fpm) are generally increased due to  
the excessive dirt buildup and contamination present in  
these environments.  
A
A
3 ft. Minimum  
Smoke Detectors at Ceiling  
Smoke Detectors below Ceiling  
Figure 23: High Ceiling Area  
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Smoke detectors are designed  
to be as maintenance free as  
possible. However, dust, dirt,  
and other foreign matter can  
accumulate inside a detector’s  
sensing elements and change  
its sensitivity. They can  
Section 5  
If a detector’s sensitivity is within specifications, nothing  
further needs to be done to the detector. If the detector’s  
sensitivity is outside specifications, clean the detector and  
retest. If that does not place the sensitivity within the unit  
specified range then follow the manufacturer’s recom-  
mended procedure.  
Testing,  
Maintenance  
and Service of  
Detectors  
become either more sensitive, which may cause unwanted  
alarms, or less sensitive, which could reduce the amount of  
warning time given in case of a fire. Both are undesirable.  
Therefore, detectors should be tested periodically and  
maintained at regular intervals. Follow closely the manu-  
facturer’s specific recommended practices for maintenance  
and testing. Also refer to Appendix B of NFPA 90A and  
NFPA 72, Chapter 7.  
Restore zone or system at the completion of testing.  
Notify the proper authorities that testing has been com-  
pleted and the system is again operational.  
Refer to paragraph 7-4.1 of NFPA 72 for additional infor-  
mation.  
To assure that each smoke detector is within its listed and  
marked sensitivity range it should be tested using either:  
• A calibrated test method, or  
• The manufacturer’s calibrated sensitivity test instru-  
ment, or  
• Listed control equipment arranged for the purpose, or  
• Other calibrated sensitivity test method acceptable to  
the authority having jurisdiction.  
Caution  
Smoke detectors are sophisticated electronic devices that  
need periodic testing and maintenance. To maintain the  
integrity of any fire alarm system, it is important to have a  
qualified person periodically test the system.  
Typical Inspection, Test and Maintenance  
Practices  
Detectors should be given a visual inspection at installation  
and at least twice a year thereafter. This ensures that each  
detector remains in good physical condition and that there  
are no changes that would affect detector performance,  
such as building modifications, occupancy hazards, and  
environmental effects.  
Detectors found to have a sensitivity of 0.25 percent/ft.  
obscuration or more outside the listed and marked sensi-  
tivity range should be cleaned and recalibrated or replaced.  
Exception: Detectors listed as field adjustable may be  
either adjusted within the listed and marked sensitivity  
range, cleaned and recalibrated, or replaced.  
Restore the zone or system at the completion of testing.  
Notify the proper authorities that the smoke detector is  
undergoing maintenance, and therefore the system will  
temporarily be out of service. NOTE: Disable the zone or  
system undergoing maintenance to prevent unwanted  
alarms and possible dispatch of the fire department.  
Notify all the persons contacted at the beginning of the test  
that testing has been completed and the system is again  
operational.  
Some individuals rely on an aerosol chemical spray to test  
the sensitivity of a detector. This can give unsatisfactory  
results since an aerosol chemical spray does not accurate-  
ly test detector sensitivity. NFPA 72-1999, Chapter 7,  
Section 7-3.2.1 notes that, “The detector sensitivity shall  
not be tested or measured using any device that adminis-  
ters an unmeasured concentration of smoke or other  
aerosol into the detector.” The duration of spray, distance  
between the detector and the aerosol container, angle of  
discharge, and different environmental conditions can pro-  
duce random results. In addition, many aerosols leave an  
oily residue. Over a period of time, this oily residue can  
attract dust or dirt, which can make a detector more sensi-  
tive and result in nuisance alarms.  
Use a high power vacuum cleaner and remove dust from  
the detector by placing the nozzle as close as possible to  
the openings in the outside housing. A nozzle with a brush  
attachment will assist in dust removal. Some detector’s  
sensing chambers can be removed for more thorough  
cleaning; refer to the manufacturer’s recommended proce-  
dure for details.  
Test each detector’s sensitivity per the manufacturer’s rec-  
ommended procedure within one year after installation  
and every alternate year thereafter.  
Test each detector functionally in place annually, as  
detailed in NFPA 72 1999 (Chapter 7).  
Be sure to follow the manufacturer’s recommendation on  
test gas, aerosol or smoke.  
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Section 6  
Make sure that all the detectors in the zone or pinpointed  
device(s) that show an alarm are checked before deciding  
that it is a false alarm. If a fire does exist, more than one  
detector may be in the alarm state, although no signs of fire  
may be evident in the vicinity of the first activated detec-  
tor. The fire could be overlooked.  
What to Do About  
Unwanted Alarms  
Troubleshooting  
Techniques  
No detection system is imper-  
vious to unwanted alarms.  
Statistically, as the system size and the total number of  
detectors increases, the total number of nuisance alarms  
per year tends to increase. Historical experience in a given  
installation or data on similar sized buildings with similar  
utilization patterns can provide a basis for a rough indica-  
tion of how many nuisance alarms are probable during a  
12 month span; however, no two installations are identical.  
Maintain an Alarm Log  
The next step for all alarms should be entry of a report into  
an Alarm Log. A typical Alarm Log is shown in Appendix  
2 (page 19). Such a log serves immediate and long-term  
purposes.  
In small- to moderate-sized detection systems protecting  
relatively combustion-free environments, like office build-  
ings, more than one or two unwanted alarms per year  
would be unusual. In more adverse environments, such as  
laboratory or manufacturing facilities where combustion  
processes are present, more frequent alarms can be antici-  
pated. In very adverse environments, one alarm per month  
might not be considered excessive.  
The Alarm Log indicates which individuals responded to  
the alarm and whether or not they took appropriate action.  
Periodic review of the cumulative Alarm Log can help those  
responsible for the detection system discern patterns in the  
reported alarms. Generally, several months (or even years)  
of data may be necessary before patterns begin to emerge.  
In a worst case example, a pattern of repeated alarms or  
small fires in a particular area may indicate a serious defi-  
ciency in safety practices that should be promptly correct-  
ed. In less obvious cases, patterns are indicated by repeat-  
ed alarms in the same or adjacent zones with similar prob-  
able causes, or repeated alarms in the same zone that  
occur at about the same time of day, or time of year.  
After the first few months, which serve as a shakedown  
period, it should be possible to arrive at some reasonable  
expectation for probable unwanted alarms from the sys-  
tem. After that, any unexpected change in frequency or dis-  
tribution indicates a problem that should be investigated.  
The best way to monitor alarm frequency and distribution  
is to maintain an alarm log.  
Effects of Location or Environment  
Reasons for Unwanted Alarms  
Check for the effects of location and environment. Review  
the information in this guide Where To Place Detectors and  
Where NOT to Place Detectors to determine whether the  
detector’s location or its environment is potentially causing  
the unwanted alarms. Also, refer to the installation manu-  
al for further information.  
Unwanted alarms can result from a wide variety of causes,  
including:  
• Improper locations are environments where they will  
not operate properly because of temperature extremes;  
excessive dust, dirt, or humidity, excessive air flow  
rates, or the normal presence of combustion particles  
in the air streams surrounding the detectors.  
• Improper installation can occur when detectors and  
their wiring are not protected from interference from  
induced currents and noise in adjacent wiring systems,  
radio-frequency transmissions, and other types of elec-  
tromagnetic effects.  
• Inadequate maintenance can result in the accumula-  
tion of dust and dirt on the detector’s sensing cham-  
bers over a period of time.  
• Seasonal effects such as the reactivation of a building  
heating system after an extended summer shutdown  
can cause alarms.  
One often overlooked source of problems is the placement  
of detectors where air streams carry smoke or chemical  
fumes from some areas of an installation past detectors in  
other areas unrelated to the source of the contaminants.  
Diagnosing problems of this kind requires that air move-  
ments into the problem area, especially near the ceiling, be  
carefully checked and their sources be determined.  
Experienced heating, ventilating, and air conditioning  
(HVAC) engineers or contractors usually have the training  
and specialized equipment (flow meters, etc.) to conduct  
such a study. In very difficult cases, a full-scale smoke test  
may be required to solve the problem.  
• Building maintenance issues, such as accidental trig-  
gering of a detector’s magnetic test switch, or the  
introduction of plaster dust from drywall repairs into a  
detector’s sensing chamber can cause unwanted  
alarms.  
Conversely, strong air streams near air inlet or supply  
ducts, etc. can also prevent a detector from signaling an  
alarm when a fire is present by blowing smoke away from  
the detector heads.  
• Induced current effects from lightning storms can  
cause alarms.  
• Infestation from insects small enough to enter the  
detector’s sensing chamber.  
Vandalism or mischievous acts — detectors set off as a  
prank have been found to be a problem in dormitories.  
Inspect Detector for Dirt and Review Maintenance  
If the Alarm Log indicated that after several months or a  
year with a fairly stable alarm rate, there is a gradual  
increase in the frequency of unwanted alarms, this is usu-  
ally an indication that the detectors in the system should  
be cleaned.  
If an alarm occurs and a fire does not exist, the alarm  
should be silenced, the problem unit located, and the  
alarm system controls reset so that the effectiveness of the  
detection system is restored.  
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NFPA standards require and smoke detector manufacturers or other dust-producing operations in the vicinity of the  
recommend that all detectors be visually inspected twice detector heads to prevent false alarms due to the dust get-  
a year.  
ting into the detector sensing chambers. In new construc-  
tion applications drywall dust contamination affects all  
Clean the detectors at least once a year, or more frequent- types of smoke detectors. To help overcome this problem, it  
ly if environmental conditions warrant it. See the section is strongly recommended that installation of detector heads  
on Detector Testing and Maintenance in this guide for more be delayed until after drywall installation is completed or to  
details.  
protect detector heads from dust contamination.  
In cases where the probable cause of a number of alarms  
appears to be dust or dirt on the detectors, detector main- If alarms occur whenever the heating system is turned on  
tenance schedules should be reviewed to determine the after an extended shutdown, due to the accumulated dust  
dates when the detectors were last cleaned and tested. If burning off as the system components heat, the detector  
the detectors are due or overdue for maintenance, schedul- system can be turned off for a short period while the heat-  
ing and performing the recommended cleaning and testing ing system is activated and checked out, or the start-up of  
should eliminate the problem.  
the heating system can be scheduled for an evening, week-  
end or other off-hours period to minimize the effects of  
If the problem resulted from a temporary overall increase alarms on regular daytime activities.  
in airborne dust due to nearby construction, scheduling a  
one-time special cleaning for all the detectors in the system Not all unwanted alarms are caused by dirt, interference or  
should alleviate the problem. If the problem is confined to other effects on the detectors. If the control panel shows an  
one or two zones and is the result of higher dust levels in alarm but no detectors in the zone are indicating an alarm  
a particular area, scheduling the detectors in those areas condition, the possibility of interference or a failure of a  
for more frequent maintenance and cleaning may prevent control panel component should also be investigated.  
the development of similar alarm problems in the future.  
Responsibilities of Detector Owners and  
Installers  
Effects of Other Systems on Alarm System  
In checking for the effects of other systems on the alarm  
system wiring the Alarm Log may be very valuable in help-  
ing to pinpoint relationships among apparently causeless  
alarms. One important fact that can be obtained from an  
Alarm Log is the beginning date for a rash of apparently  
causeless alarms that may or may not be grouped around  
one particular zone. The sudden onset of such a group of  
alarms may result when an addition or change in the alarm  
system or in another electrical or electromechanical system  
in the building affects the detectors or the alarm system  
circuitry.  
The owners of smoke detector-equipped fire alarm systems  
are responsible for maintaining the integrity of the detec-  
tion system. This can be accomplished by:  
• Maintaining an Alarm Log and training appropriate  
personnel to properly maintain the system as  
described above in the section titled What To Do When  
Unwanted Alarms Occur.  
• Maintaining a Detector Maintenance Log that records  
inspection, testing and cleaning data for each detector  
in the system. (Refer to Section 6 of this manual –  
Testing, Maintenance and Service of Detectors for  
information on recommended testing and maintenance  
intervals and procedures, and a sample Detector  
Maintenance Log page.)  
• Maintaining a complete file of information on the  
alarm system in a readily accessible location. This file  
should include specifications and installation instruc-  
tions for the detectors, control panel, and auxiliary  
devices, wiring diagrams and wire location informa-  
tion, and the manufacturer’s recommendations for iso-  
lating the detection system wiring from other electrical  
wiring to prevent interference and unwanted alarms.  
• Making certain that maintenance personnel or con-  
tractors working on the building’s electrical systems  
are given copies of the alarm system wiring layout and  
locations so that potential interference from other  
wiring systems can be prevented by proper insulation  
and spacing during installation.  
Systems that can affect the alarm system include: other  
security systems; walkie-talkie; mobile telephones; heat-  
ing, ventilating, and air conditioning controls; elevator call  
systems; remote control equipment (door closers, etc.);  
and even the installation of microwave antenna. If the  
alarm pattern supports the possibility of some kind of  
interference with a fairly definite initiation date, all equip-  
ment changes made in the building immediately prior to or  
concurrent with the beginning of the development of the  
alarm pattern should be reviewed. In addition, the wiring  
layouts of the alarm system and any recent building or sys-  
tem modifications should be compared to make sure that  
the spacing and/or shielding required to protect the alarm  
system wiring from other potentially interfering electrical  
systems was maintained.  
Miscellaneous Causes of Unwanted Alarms  
Isolated alarm causes such as a maintenance person acci-  
dentally triggering an alarm by touching a detector with a  
magnetic screwdriver can be ignored, except to periodical-  
ly remind maintenance personnel to be careful when work-  
ing around detectors.  
• Keeping accurate records of installation and modifica-  
tions to all other building electromechanical systems  
that could cause interference with the alarm system,  
including updating schematics, wiring layouts, and  
wiring location information whenever changes are  
made, so that problems can be promptly found and  
eliminated.  
Steps should also be taken to protect detectors from dust  
whenever maintenance requires sawing, sanding, drilling,  
• Making a record of everything done during investiga-  
tion of a series of alarms, indicating a problem exists.  
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If assistance must be sought from the installer or man-  
ufacturer, there will be an indication of the tests that  
have already been done by the owner’s personnel.  
• Helping the owner set up appropriate Detector  
Maintenance and Alarm Logs for the system.  
• Providing initial instruction and training to the  
owner’s personnel or outside organization which will  
be monitoring and maintaining the system.  
• Providing troubleshooting assistance if nuisance alarm  
problems cannot be solved satisfactorily by the  
owner’s personnel or outside organization.  
These services can be provided by qualified outside  
organizations.  
The installers of smoke detector equipped alarm systems  
are responsible for providing the owners with the neces-  
sary information and training so that their personnel can  
maintain the integrity of the alarm system. These respon-  
sibilities should include:  
• Providing copies of the specifications and installation  
instructions for the detectors, control panel, and auxil-  
iary devices; wiring diagrams and wire location infor-  
mation; and the manufacturer’s recommendations for  
isolating the detection system wiring from other elec-  
trical wiring to prevent interference and unwanted  
alarms.  
Where to Get Help if the Source of Unwanted  
Alarms Can’t be Found  
In the event a series of unexplained unwanted alarms  
and/or a review of the Alarm Log indicates that a problem  
situation exists, the owner should conduct the initial inves-  
tigation to find a solution. If the owner’s personnel are  
unable to determine the cause for the alarms, the installer  
or representative of the manufacturer should be contacted  
to help pinpoint the problem.  
Verifying that the alarm system installation meets all  
applicable code requirements.  
• Completely testing a newly installed, expanded, or  
modified alarm system to ensure that all components  
are working properly.  
• Providing troubleshooting assistance to the owners for  
a specified break-in period after installation in case  
problems develop.  
Manufacturers can be contacted by phone for additional  
suggestions. If factory assistance is needed, a factory engi-  
neer may be able to explain the source of the problem with  
data from your Alarm Log, complete description of your  
alarm system including detector model numbers, make and  
model number of the control panel and other components,  
and a complete summary of all aspects of the problem that  
have already been checked.  
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Appendix 1  
Addressable System Smoke End of Line Relay  
Detector Device used to supervise power (for four-wire smoke  
System smoke detectors, detectors) and installed after the last device on the loop.  
Glossary of Terms  
which, in addition to providing alarm and trouble indica-  
tions to a control unit, are capable of communicating a  
unique identification (address).  
False Alarms  
An unwanted alarm caused by non-smoke contaminants  
such as dust or insects.  
Air Sampling-type Detector  
Fire  
A sampling-type detector consists of piping or tubing distri-  
bution from the detector unit to the area(s) to be protected.  
An air pump draws air from the protected area back to the  
detector through the air sampling ports and piping or tub-  
ing. At the detector, the air is analyzed for fire particulate.  
A chemical reaction between oxygen and a combustible  
material where rapid oxidation results in the release of  
heat, light, flame and/or smoke.  
Flame Detector  
A device that detects the infrared, ultraviolet, or visible  
radiation produced by a fire.  
Alarm (Signal) Notification Appliance  
An electromechanical appliance that converts energy into  
audible or visible signal for perception as an alarm signal.  
Four-wire Smoke Detector  
A smoke detector which initiates an alarm condition on  
two separate wires (initiating loop) apart from the two  
power leads.  
Alarm Signal  
A signal indicating an emergency requiring immediate  
action, such as an alarm for fire from a manual box, a  
waterflow alarm, or an alarm from an automatic fire alarm  
system, or other emergency signal.  
Heat Detector  
A device that detects abnormally high temperature or rate-  
of-temperature rise.  
Alarm Verification Feature  
Initiating Circuit  
A feature of automatic fire detection and alarm systems to  
reduce unwanted alarms, wherein automatic fire detectors  
must report alarm conditions for a minimum period of time  
or confirm alarm conditions within a given time period,  
after being reset, to be accepted as a valid alarm initiation  
signal.  
A circuit which transmits an alarm signal initiated manu-  
ally or automatically, such as a fire alarm box, smoke, heat,  
or flame sensing device, sprinkler waterflow alarm switch  
or similar device or equipment to a control panel or any  
similar device or equipment which, when activated, caus-  
es an alarm to be indicated or retransmitted. An Initiating  
Device Circuit (Loop) is a circuit to which automatic or  
manual signal initiating devices are connected where the  
signal received does not identify the individual device  
Annunciation  
A visible and/or audible indication of system status.  
Automatic Fire Alarm System  
A system of controls, initiating devices and alarm signals in operated.  
which all or some of the initiating circuits are activated by  
Initiating Device  
Any manually operated or automatically operated equip-  
ment which, when activated, initiates an alarm through an  
automatic devices such as smoke detectors.  
Class A Circuit (Loop)  
An arrangement of supervised initiating device, signaling alarm signaling device.  
line, or indicating appliance circuits that prevents a single  
Intelligent (Analog, Smart) System Smoke Detector  
open or ground on the installation wiring of these circuits  
from causing loss of the system’s intended function.  
A system smoke detector capable of communicating infor-  
mation about smoke conditions at its location to a control  
unit. This type of detector typically communicates a  
Class B Circuit (Loop)  
An arrangement of supervised initiating device, signaling unique identification (address) along with an analog (data)  
line, or indicating appliance circuits, which does not pre- signal, which indicates the level of smoke at its location.  
vent a single open or ground on the installation wiring of  
these circuits from causing loss of the system’s intended  
An ionization smoke detector has a small amount of  
function.  
Ionization Smoke Detector  
radioactive material that ionizes the air in the sensing  
Combination Smoke Detector  
chamber, thus rendering it conductive and permitting a  
A smoke detector that combines two or more smoke or fire current to flow between two charged electrodes. This gives  
sensing technologies.  
the sensing chamber an effective electrical conductance.  
When particles of combustion enter the ionization area,  
they decrease the conductance of the air by attaching  
themselves to the ions, causing a reduction in mobility.  
When the conductance is less than a predetermined level,  
the detector responds in a fire alarm condition.  
Detector Coverage  
The recommended maximum distance between adjacent  
detectors or the area that a detector is designated to protect.  
Drift Compensation  
The capability of a detector to automatically adjust its  
alarm sensitivity to compensate for any changes over time  
in the factory settings for smoke and/or fire detection. In  
analog systems, this may be done by the panel.  
Light Scattering  
The action of light being reflected and/or refracted by  
smoke particles for detection by a photoelectric smoke  
detector. The action of light being refracted or reflected.  
End of Line  
Listed  
A device such as a resistor or diode placed at the end of a  
Class B wire loop to maintain supervision.  
Equipment or materials included in a list published by an  
organization (e.g., Underwriters Laboratories) acceptable  
to the “authority having jurisdiction” and concerned with  
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product evaluation, that maintains periodic inspection of Smoothing Algorithms  
listed equipment or materials and whose listing states A method of “smoothing out” a detector’s interpretation of  
either that the equipment or material meets appropriate sudden, short-duration increases in obscuration within the  
standards or has been tested and found suitable for use in sensing chamber, intended to reduce the occurrence of nui-  
a specified manner.  
sance alarms.  
Note: The means for identifying listed equipment may vary  
for each organization concerned with product evaluation,  
some of which do not recognize equipment as listed unless  
it is also labeled.  
Spot (Point) Detector  
A device whose detecting element is concentrated at a par-  
ticular location. Typical examples are bimetallic detectors,  
fusible alloy detectors, certain pneumatic rate-of-rise detec-  
tors, most smoke detectors and thermoelectric detectors.  
Maintenance Condition  
Method of providing annunciation of a smoke detector that  
it is out of its listed sensitivity range.  
Stratification  
An effect that occurs when air containing smoke particles  
or gaseous combustion products is heated by smoldering  
or burning material and, becoming less dense than the sur-  
rounding cooler air, rises until it reaches a level at which  
there is no longer a difference in temperature between it  
and the surrounding air. Stratification can also be caused  
by forced ventilation.  
National Fire Protection Association (NFPA)  
An organization that administers the development and  
publishing of codes, standards, and other materials con-  
cerning all phases of fire safety.  
Nuisance Alarm  
An unwanted alarm caused by smoke from cooking or cig-  
arettes.  
Trouble Supervision  
The ability of a fire alarm control unit (FACU) to detect a  
fault condition in the installation wiring, which would pre-  
vent normal operation of the fire alarm system.  
Obscuration  
A reduction in the atmospheric transparency caused by  
smoke usually expressed in percent per foot.  
Thermal Lag  
Particles of Combustion  
When a fixed temperature device operates, the temperature  
of the surrounding air will always be higher than the oper-  
ating temperature of the device itself. This difference  
between the operating temperature of the device and the  
actual air temperature is commonly spoken of as thermal  
lag, and is proportional to the rate at which the tempera-  
ture is rising.  
Substances (products that either remain at the site of burn-  
ing such as ash, or scatter as volatile products) resulting  
from the chemical process of a fire.  
Photoelectric Smoke Detector  
In a photoelectric light scattering smoke detector, a light  
source and a photosensitive sensor are so arranged that the  
rays from the light source do not normally fall on the pho-  
tosensitive sensor. When smoke particles enter the light  
path, some of the light is scattered by reflection and refrac-  
tion onto the sensor, causing the detector to respond.  
Two-wire Compatibility  
Per NFPA 72, 1999 edition: All fire detection devices that  
receive their power from the initiating device circuit or use  
a signaling line circuit of a fire alarm control unit shall be  
listed for use with the control unit.”  
Projected Beam Smoke Detector  
In a projected beam detector the amount of light transmit-  
ted between a light source and a photosensitive sensor is  
monitored. When smoke particles are introduced into the  
light path, some of the light is scattered and some  
absorbed, thereby reducing the light reaching the receiver,  
causing the detector to respond.  
Two-wire Smoke Detector  
A smoke detector which initiates an alarm condition on the  
same two wires that also supply power to the detector.  
Unwanted Alarm  
Any false alarm or nuisance alarm.  
Wireless Smoke Detector  
Rate-of-rise Heat Detector  
A smoke detector which contains an internal battery or  
batteries that supply power to both the smoke detector and  
integral radio frequency transmitter. The internal power  
source is supervised and degradation of the power source  
is communicated to the control panel. On stimuli, the  
detector transmits a radio signal to a repeater or Fire Alarm  
Control Unit (FACU) that in turn generates a signal or sta-  
tus condition.  
A device which will respond when the temperature rises at  
a rate exceeding a predetermined amount, usually 15° per  
minute.  
Remote Maintenance Condition  
NFPA 72 listed method of providing annunciation at the  
control unit that the smoke detector is outside of its listed  
sensitivity.  
Smoke Detector  
A device that detects the visible or invisible particles of  
combustion.  
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Appendix 2  
Fire Alarm Log  
Customer Name:  
Installation Date:  
Installing Contractor:  
Inspection and Test Date:  
Inspection and Test Performed By:  
Check one  
Fire  
Location  
Action Taken By  
Name and Date  
Date  
Time  
Recorded By  
Trouble  
(Bldg, Zone, Det #)  
Probable Cause  
Action Taken  
19  
 
©2002 System Sensor. The company reserves the right to change specifications at any time.  
A05-1003-002  
 

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