System Smoke Detectors: Applications Guide
System Smoke Detectors: Applications Guide
System Smoke Detectors: Applications Guide
System
Smoke Detectors
A P P L I C A T I O N S G U I D E : S Y S T E M S M O K E D E T E C T O R S
System
Smoke Detectors
Contents
Foreword................................................................................................................2 Wireless Systems..................................................................................................9
NFPA Codes and Standards...............................................................................3 Proper Detector Applications, Placement, and Spacing*............................9
Ionization Smoke Detector Operation.................................................................4 Detectors in Above-Ceiling Plenum Areas Including Those Utilized
as Part of the HVAC System..............................................................................13
How Smoke Detectors Work.............................................................................4
Testing, Maintenance, and Service of Detectors.........................................13
Photoelectric Smoke Detector Operation...........................................................5
Typical Inspection, Test, and Maintenance Practices......................................13
Photoelectric Light Scattering Smoke Detector.................................................5
Troubleshooting Techniques .........................................................................14
Photoelectric Light Obscuration Smoke Detector..............................................5
What to Do About Unwanted Alarms................................................................14
Smoke Detector Design Considerations............................................................5
Reasons for Unwanted Alarms..........................................................................14
Considerations in Selecting Detectors................................................................5
Maintain an Alarm Log.......................................................................................14
Smoke Detector Limitations.................................................................................6
Effects of Location or Environment....................................................................14
Typical System Layout.......................................................................................6
Inspect Detector for Dirt, Review Maintenance...............................................15
Wiring Supervision................................................................................................6
Effects of Other Systems on Alarm System......................................................15
Class B Circuits.....................................................................................................6
Miscellaneous Causes of Unwanted Alarms...................................................15
Class A Circuits.....................................................................................................6
Responsibilities of Detector Owners and Installers.........................................15
Wireless Circuits....................................................................................................7
Where to Get Help if the Source of Unwanted Alarms Cannot be Found.....16
General Zoning Guidelines..................................................................................7
Glossary of Terms.............................................................................................17
Fire Safety Functions............................................................................................7
Fire Alarm Log ..................................................................................................19
Smoke Detector Installation.................................................................................7
Foreword
The use of early warning fire and smoke detection systems results in significant reduction in fire deaths. The sooner a fire is detected, the better the out-
come for saving lives. This document provides guidance for the proper operation of fire detection systems for those who apply, install, and maintain them.
Correct installation and maintenance of smoke detectors prevents unwanted nuisance alarms. Occupants can become desensitized when repeated
nuisance alarms occur. In worst case scenarios, technicians could disconnect alarms from the system to avoid the unnecessary disruption. Either situ-
ation negates a detector’s potential life saving benefit, making the proper operation of an early warning fire and smoke detection system indispensable.
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S Y S T E M S E N S O R
The purpose of this guide is to provide information concerning the proper International Code Council, Inc. (International Building Code/
application of smoke detectors used in conjunction with fire alarm sys- International Fire Code)
tems. The guide outlines basic principles that should be considered in the BOCA, ICBO, and SBCCI formed an umbrella organization known as the
application of early warning fire and smoke detection devices. It presents International Code Council (ICC), to combine their codes into a single set
operating characteristics of detectors and environmental factors, which of model building and fire codes. The ICC International Building Code and
may aid, delay, or prevent their operation. International Fire Code were first published in 2000 and were adopted by
some states.
This document presents information for fire protection, mechanical, and
electrical engineers; fire service personnel, fire alarm designers; and install- 5360 Workman Mill Road
ers. A key element in the effectiveness of smoke detection systems is the Whittier, CA 90601-2298
latest version of NFPA 72 for installation and testing of systems. Installation
must comply with all code requirements and directions from Authorities Testing Laboratories
Having Jurisdiction (AHJs). AHJ directives always take precedence over
other codes and exercise final authority over installations and maintenance Testing laboratories test smoke detectors, control panels, and other compo-
procedures. nents of fire alarm systems to verify conformance with NFPA requirements
and their own standards. Equipment that passes their tests is identified by
NFPA Codes and Standards a label and/or listing.
NFPA 101: Life Safety Code NEMA Guide for Proper Use of Smoke Detectors in Duct Applications
NFPA 101 specifies the requirements for smoke detection in both new and NEMA Training Manual on Fire Alarm Systems
existing buildings depending on the type of occupancy. NEMA Guide for Proper Use of System Smoke Detectors
Manufacturer’s Publications
Two basic types of smoke detectors are used today: ionization and photo-
electric. The sensing chambers of these detectors use different principles
of operation to sense the visible or invisible particles of combustion given
off in developing fires.
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A P P L I C A T I O N S G U I D E : S Y S T E M S M O K E D E T E C T O R S
Particles of combustion are much larger than the ionized air molecules.
As particles of combustion enter an ionization chamber, ionized air mol-
ecules collide and combine with them. (See Figure 3.) Some particles
become positively 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 par-
ticles in the chamber is reduced.
Section 2
How Smoke Detectors Work
This reduction in the ionized particles results in a decrease in the cham-
ber current that is sensed by electronic circuitry monitoring the chamber.
When the current is reduced by a predetermined amount, a threshold is Figure 3: Ion and Particles of Combustion Distribution
crossed and an “alarm” condition is established.
Sensing Chamber
Changes in humidity and atmospheric pressure affect the chamber current
and create an effect similar to the effect of particles of combustion entering Source
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.
Reference Chamber
A dual-chamber detector utilizes two ionization chambers; one is a sens- (Current Stable)
ing chamber, which is open to the outside air. (See Figure 4). The sensing
chamber is affected by particulate matter, humidity, and atmospheric pres- Figure 4: Dual Chamber
sure. The other is a reference chamber, which is partially closed to outside
air and is affected only by humidity and atmospheric pressure, because its
Sensing Chamber
tiny openings block the entry of larger particulate matter including particles
(Current Decreasing)
of combustion. Electronic circuitry monitors both chambers and compares
their outputs. If the humidity or the atmospheric pressure changes, the out-
puts of both chambers are affected equally and cancel each other. When
combustion particles enter the sensing chamber, its current decreases
while the current of the reference chamber remains unchanged. The result- Reference
ing current imbalance is detected by the electronic circuitry. (See Figure Chamber
5.) There are a number of conditions that can affect dual-chamber ioniza- (Current Stable)
tion sensors such as dust, excessive humidity (condensation), significant
air currents, and tiny insects. All of these can be misread as particles of
combustion by the electronic circuitry monitoring the sensors. Figure 5: Dual Chamber with Particles of Combustion
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S Y S T E M S E N S O R
Most photoelectric smoke detectors are of the spot type and operate on Figure 9: Light Obscuration Detector with Smoke
the light scattering principle. A light-emitting diode (LED) is beamed into
an area not normally “seen” by a photosensitive element, generally a pho- Smoke Detector Design Considerations
todiode. (See Figure 6.) When smoke particles enter the light path, light
strikes the particles (Figure 7) and is reflected onto the photosensitive Although smoke detectors are based on simple concepts, certain design
device causing the detector to respond. considerations need to be observed. They should produce an alarm signal
when smoke is detected, but should minimize the impact of an unwanted
Photoelectric Light Obscuration Smoke Detector signal which can arise from a variety of causes. In an ionization detec-
tor, dust and dirt can accumulate on the radioactive source and cause it
Another type of photoelectric detector, the light obscuration detector, to become more sensitive. In a photoelectric detector, light from the light
employs a light source and a photosensitive receiving device, such as a source may be reflected off the walls of the sensing chamber and be seen
photodiode (see Figure 8). When smoke particles partially block the light by the photosensitive device when no smoke is present. Insects, dirt, dry-
beam (Figure 9), the reduction in light reaching the photosensitive device wall dust, and other forms of contamination can accumulate in the sensing
alters its output. The change in output is sensed by the detector’s circuitry, chamber and reflect light from the light source onto the photosensitive
and when the threshold is crossed, an alarm is initiated. Obscuration type device.
detectors are usually of the projected beam type where the light source
spans the area to be protected. Electrical transients and some kinds of radiated energy can affect the
circuitry of both ionization and photoelectric smoke detectors and be inter-
preted by the electronic circuitry to be smoke, resulting in nuisance alarms.
The allowable sensitivity ranges for both types of detectors are established
by Underwriters Laboratories, Inc. (UL). Detector performance is verified
in fire tests. All smoke detectors are required to respond to the same test
fires regardless of their principle of operation.
Light Source Light Sensitive Device
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A P P L I C A T I O N S G U I D E : S Y S T E M S M O K E D E T E C T O R S
NFPA 72 requirements also dictate that alarm notification appliances Class B Circuits
(including smoke detectors with built-in sounders) produce the 3-pulse tem-
poral pattern fire alarm evacuation signal described in American National Class B circuits differentiate between short circuits across the loop (alarm)
Standards Institute (ANSI) S3.41 Audible Emergency Evacuation Signals. and open faults on the loop (trouble). Supervision of this circuit is accom-
plished by passing a low current through the installation wiring and an
Situations for Other Types of Detectors end-of-line resistor. The fire alarm control panel monitors the increases or
In certain circumstances where standard smoke detectors are unsuitable, decreases in the supervisory current and sends an alarm or trouble con-
special-purpose detectors, such as flame detectors, heat detectors, and dition, respectively. A single open in a Class B circuit disables all devices
other detection devices may be used. electrically beyond the open.
END OF LINE
The application of these special types of detectors should be based on RESISTOR
an engineering survey and used in accordance with the manufacturer’s
installation instructions.
Smoke detectors offer the earliest possible warning of fire. They have saved
thousands of lives. Special application rules can compensate for the limita-
tions of smoke detectors. Smoke detectors may not provide early warning
of a fire developing on another level of a building. Detectors should be
located on every level of a building. Detectors may not sense a fire devel- TYPICAL
oping on the other side of a closed door. In areas where doors are usually INITIATING
DEVICES
closed, detectors should be located on both sides of the door.
TYPICAL • to control the flow of smoke in air handling and air conditioning systems,
INITIATING
DEVICES
• to release doors to contain smoke in a fire situation,
Figure 11: 2-Wire Detectors – Style D (Class A) Circuit Wiring Installation Guidelines
All fire alarm system installation wiring should be installed in compliance
Wireless Circuits with Article 760 of NFPA 70, the National Electrical Code (NEC), the manu-
facturer’s instructions, and the requirements of the AHJ.
Wireless detectors and their internal transmitters use one or more inter-
nal batteries as the source for their operating power and are UL listed. Typical Wiring Techniques
Supervision of the internal battery power source is incorporated within the The primary rule of installation wiring is to Follow the Manufacturer’s
smoke detector circuitry. If the battery power source depletes to the thresh- Instructions. This rule cannot be overemphasized. The requirement for
old specified by UL, the smoke detector will sound a local alert and initiate electrical supervision of the installation wires and their connections to ini-
a trouble signal once per hour for a minimum of seven days or until the bat- tiating devices makes fire alarm system installation wiring very different
tery or batteries are replaced. than general wiring.
The wireless initiating devices are supervised for tamper and/or removal A manufacturer’s installation wiring drawing routes wires and shows connec-
by initiating a distinct trouble signal. Each wireless device also initiates tions in a certain manner to accommodate supervision requirements. Any
a test transmission every hour to verify the communication circuit. Any variance from the manufacturer’s drawings might cause a portion of a
device failing to communicate is identified on the control panel no less circuit to be unsupervised and, if an open or short circuit fault occurred,
than every four hours. it could prevent the circuit from being able to perform its intended function
without giving the required trouble indication.
General Zoning Guidelines
The rules of supervision are not very complex. However, unless installers
The faster the source of an alarm can be pinpointed, the faster action can are experienced in fire alarm system installations, they probably would not
be taken. Although formal rules for zoning are not given in fire protection be familiar with them.
codes, an exception is the rule for wireless devices stating that each smoke
detector must be individually identified. It is always advisable to zone any Smoke detector manufacturers’ installation drawings will show how their
system that contains more than a small number of detectors. In addition to detectors should connect into a system. However, manufacturers’ draw-
the zoning requirements of NFPA 72-2010, Section 10.16.6, experienced ings may not show how devices located on the same floor, but served by a
detector installers and system designers recommend the following: different riser (vertical wiring run), should be connected. The diagrams on
this and the following page should be considered typical initiating device
• Establish at least one zone on every protected floor. circuits utilizing smoke detectors. They are offered to illustrate examples of
proper and improper installation wiring and termination techniques. Since
• Zone natural subdivisions of a large building, such as separate wings there are always exceptions to typical installation drawings, experienced
on a single floor. installers use the primary rule of installation wiring: follow the manufactur-
er’s instructions, and meet the local codes.
• Minimize the number of detectors in each zone. Fewer detectors on a
zone will speed up locating the fire and simplify troubleshooting. Figure 12 illustrates improper wiring of smoke detector A. This wiring
method is referred to as T-tapping. This common installation error is often
• Install duct detectors in different zones than open-area detectors for made in riser wiring, as well as single floor wiring. The smoke detector may
troubleshooting and locating purposes. operate properly under alarm conditions. If it becomes disconnected from
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A P P L I C A T I O N S G U I D E : S Y S T E M S M O K E D E T E C T O R S
the installation wiring loop beyond the T-tap, however, the detector would Figure 13: Correct wiring method for smoke detectors monitored by a conventional
not function, and a “no trouble” condition would occur. fire alarm panel
NOTE: T-tapping is allowed with most intelligent fire alarm systems. Refer
to manufacturer’s recommendations.
Figure 13 illustrates the correct installation wiring method for smoke detec-
tors. None of the connections can be broken without opening the circuit,
causing loss of supervision, and triggering the fire alarm control panel to
indicate trouble.
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 termination. This assures full supervision of the smoke detector.
Smoke
Detector
Figure 12: Incorrect wiring method for a conventional fire panel Figure 16: Pigtail Connections – Correct Wiring Method
Smoke Detector Figure 17 shows an incorrect pigtail connection. This is a form of T-tapping
discussed earlier. Note that the conductor between the wire nut (or splice)
and the detector is unsupervised, and could be cut or disconnected with-
out resulting in a trouble signal.
Wire Nut
Smoke
Smoke Detector Smoke Detector Detector
• Do verify that 2-wire or addressable smoke detectors have been tested Because detector placement is critical to early warning functions, smoke
and UL listed for compatibility with the equipment to which they are detectors should be installed in all areas of the protected premises. Total
connected. If necessary, contact the manufacturer for this information. coverage as defined by NFPA 72 should include all rooms, halls, stor-
age areas, basements, attics, lofts, and spaces above suspended ceilings
• Do locate any end-of-line devices electrically at the end of the circuit, including plenum areas utilized as part of the HVAC system. In addition,
beyond all initiating devices (not at the control unit, except in a Class coverage should include all closets, elevator shafts, enclosed stairways,
A installation). On Class A loops, the end-of-line device is built into the dumbwaiter shafts, chutes, and other subdivisions and accessible spaces.
panel circuit. An end-of-line device must not be used.
Installed fire detection systems that meet local codes or ordinances may
• Do use caution when utilizing 2-wire detectors with integral relays, not be adequate for early warning of fire. Some codes or ordinances have
because they may require more power than the initiating device circuit minimum objectives such as capturing elevators or preventing circula-
can supply. This could result in the inability of the relay to control auxil- tion of smoke through the HVAC systems instead of early detection of fire.
iary equipment to which it is connected.
A user should weigh the costs against the benefits of installing a com-
• Do follow the manufacturer’s installation instructions to assure proper plete fire detection system when any detection system is being installed.
communication between the smoke detector and the control panel when The location, quantity, and zoning of detectors should be determined by
using wireless detectors. Testing following a fire alarm system instal- desired objectives that meet the minimum requirements of all local codes
lation or the addition to an existing system shall confirm the intended or ordinances.
sequence of operation under the most stringent conditions.
Total coverage, as defined in NFPA 72, is the complete fire detection sys-
• Do observe polarity when required. tem. In some of the specified areas of coverage (e.g., attics, closets, and
areas beneath open loading docks or platforms) a heat detector may be
• Do protect detectors against contamination during construction or more appropriate than a smoke detector. Careful consideration should be
renovation. given to the detector manufacturer’s instructions and the following recom-
mendations in this guide.
• Do follow the manufacturer’s installation instructions carefully.
*The guidelines in this section of the guide are adapted from Standards pub-
Don’t: lished by the National Fire Protection Association, Quincy, Massachusetts,
USA. These standards include NFPA 72, National Fire Alarm Code and
• Don’t T-tap smoke detectors or circuit conductors, except when specifi- Signaling Code; NFPA 70, National Electrical Code, Article 760; and NFPA
cally permitted by the manufacturer as part of an intelligent/addressable 90A, Installation of Air Conditioning and Ventilating Systems.
system.
In general, when only one detector is required in a room or space, the
• Don’t loop uncut installation conductors around screw terminations. 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
• Don’t exceed the maximum resistance permitted for the initiating device room. If a center location is not possible, the detector may be wall mounted
system. within 12 inches from the ceiling if the detector is listed for wall mounting.
(See Figure 18.) (NFPA 72-2010, Figure A.17.7.3.2.1.)
• Don’t exceed the allowable number of detectors specified by the equip-
ment manufacturer on any system. Note: Longer than allowed initiating When air supply and/or air return ducts are present in a room or space,
device circuits or Signaling Line Circuit loops may cause a malfunction the detector(s) should not be placed in the path of the air flow supply or
of the detectors/or the system even though the prescribed number of return (NFPA 72-2010).
detectors has not been exceeded.
Smoke tests are helpful in determining proper placement. Special atten-
Wiring and System Checkout tion should be given to smoke travel directions and velocity, since either
can affect detector performance.
Check the detector loop wiring for grounds, short circuits, and open faults
before the system is placed into operation as required for all installation Placement of detectors near air conditioning or incoming air vents can
wiring of fire alarm systems. Each detector should be tested in accordance cause excessive accumulation of dust and dirt on the detectors. This dirt
with the manufacturer’s instructions. 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
When using wireless detectors, verify the radio signal transmission strength air return vent.
in accordance with the installation manual.
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A P P L I C A T I O N S G U I D E : S Y S T E M S M O K E D E T E C T O R S
Spot type detectors in properly engineered systems may also be placed in • Elevator Lobbies
return air ducts, or in approved duct detector housings designed for this
application. Although duct detectors are not a substitute for open area –– Do not place above ashtrays in elevator lobbies.
detectors, they can provide an effective method of initiating building con-
trol functions to prevent smoke from being transported from the fire area to • Extreme Temperatures
other parts of a building. (See Duct Smoke Detector Applications Guide.)
–– A
void very cold or very hot environments, or unheated buildings or
Ceiling rooms where temperatures can fall below or exceed the operating
temperature range of the detector. At temperatures above or below
the operating range* of the detector, its internal components may
not function properly.
–– A
void areas where particles of combustion are normally present,
Acceptable Here such as in kitchens or other areas with ovens and burners; or in
garages, where particles of combustion are present from vehicle
exhausts. When a detector must be located in or adjacent to such
an area, a heat detector may be appropriate.
Top of Detector Acceptable Here
• Manufacturing Areas
12 in. (30 cm)
Maximum
–– A
void manufacturing areas, battery rooms, or other areas where
substantial quantities of vapors, gases, or fumes may be present.
Strong vapors can make detectors overly sensitive or less sensitive
than normal. In very large concentrations, gases heavier than air,
Note: Measurements shown are to the such as carbon dioxide, may make detectors more sensitive, while
closest edge of the detector. gases lighter than air, such as helium, may make them less sensi-
tive. Aerosol particles may collect on detector chamber surfaces and
cause nuisance alarms.
Side Wall
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S Y S T E M S E N S O R
Multi-Criteria detection contains multiple sensors that separately respond Detector Spacing
to physical stimulus such as heat, smoke, or fire gases. An alarm signal
is determined through advanced algorithms based on input from these General Spacing Guidelines
sensors. System Sensor offers several types of multi-criteria detection Some fire protection codes specify detector spacing on a given center-to-
including and Acclimate detector which combines photo and heat signals center distance between detectors under ideal conditions. These distances
and an Advanced Multi-Criteria detector which combines four signals : are based on rooms with smooth ceilings having no physical obstructions
photo, thermal, carbon monoxide and infrared. The combination of sen- between the contents being protected and the detectors. Moreover, they
sors offers better immunity to nuisance alarms in challenging environments are based on a maximum ceiling height, and on the assumption that the
with faster response times to real fires. value and the combustible nature of the contents of the room to be pro-
tected do not warrant greater protection or closer spacing.
Combination Carbon Monoxide and Smoke detectors are also available.
Combining two functions into one device improves installation time and cost If we assume a typical center distance spacing guideline is 30 ft (9.1 m),
as well as offering a more aesthetically pleasing final product. This device how do we determine whether a given room or space can be protected
type provides separate signals for each event. In this device the CO sen- by a single detector? Figure 19 shows four detectors spaced horizontally
sor may or may not be used for determining the presence of smoke/fire and vertically 30 ft (9.1 m) apart. Detectors B and D, however, are more
depending upon the type of device. For additional information regarding than 30 ft apart. Clearly, in this example detector spacing can exceed the
Carbon Monoxide detection see the System Sensor System-Connected given 30-ft spacing and still comply with the code if any source of combus-
Carbon Monoxide Detectors Application Guide. tion is within 21 ft (6.4 m) of the horizontal projection of a detector, and if no
more than a 900 sq ft (82.8 sq m) area is being protected by one detector.
Standards for Smoke Detectors
To determine which coverage patterns are permissible within the 30-ft spac-
UL has standards for three types of smoke detectors: duct detectors, UL ing, start by tracing a circle with a radius of 21 feet. Any square or rectangle
268A; single and multiple station smoke alarms, UL 217; and systems that fits within the circumference of the circle may be protected by one
type detectors, UL 268. Detectors should be used as specified for the detector. (See Figure 20.)
listed applications.
In other words, if a diagonal through the center of the room is no greater
Section 9.6.2.9.4 of the 2006 NFPA 101 Life Safety Code states that single than the diameter of the circle, or 42.4 feet (12.8 meters), one detector can
station smoke alarms shall sound an alarm only within an individual living be used under ideal conditions. Figure 21 shows how a length of hallway
unit, suite of rooms, or similar area, and shall not actuate the building fire can be protected by only two detectors under ideal conditions.
alarm system unless otherwise permitted by the authority having jurisdiction.
A B
In addition to possible code noncompliance, the following deficiencies
would exist in a series of residential smoke detectors, connected in a sys- 30 ft. (9.1 m)
tem mode:
)
m
.4
(6
• Since the system is not supervised, vandals or others could disconnect
ft.
30 ft. (9.1 m)
.2
21
a detector or the entire system, leaving a building without protection.
The residents would be unaware of this serious life threatening condition. F
System detectors latch in alarm. They do not reset until power is momen-
tarily disconnected. This makes it convenient to identify the location of a Figure 19: Typical Detector Spacing
detector that caused the control panel to alarm. In addition, system detec-
tors are specifically designed to connect to a panel. Two-wire detectors Special Spacing Problems
and addressable smoke detectors require a UL compatibility review to Code guidelines are based on ideal conditions that do not exist in the
verify that the detector and panel operate together. A typical life safety majority of buildings. Detector installers usually have to deal with a variety
fire protection system for an apartment complex would use system detec- of problems, such as uneven ceilings or ceilings crossed by beams and
tors and manual fire alarm stations in the hallways and common areas of joists; storage racks and partitions that obstruct the path of smoke toward
the complex and residential single station type smoke detectors and heat detectors; air stratification due to uninsulated roofs, peaked or sloped
detectors in the individual apartments. The system detectors, manual sta- ceilings, or localized heating or cooling from heating, ventilating, and air
tions and heat detectors would be connected to a control panel, sound conditioning systems; and extensive variability in the value and combustion
a general alarm and automatically notify the proper authorities that a fire characteristics of building contents. The following are suggested tech-
condition exists. Residential smoke detectors located in the apartments niques for dealing with some of the special detector spacing problems:
would be interconnected only within the individual living quarters of each
apartment. These residential units would sound an alarm only in the apart- • Solid joist and beam construction. Per NFPA 72-2010, solid joists
ment where a fire started. are to be considered equivalent to beams for smoke detector spac-
ing 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 half of the
smooth ceiling spacing is to be used in the direction perpendicular to
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A P P L I C A T I O N S G U I D E : S Y S T E M S M O K E D E T E C T O R S
the run of the beams. Spot-type detectors may be located either on the • Peaked or Sloped Ceilings. Peaked or sloped ceilings can foster air
ceiling or on the bottom of the beams. For beam depths exceeding 1 ft stratification. Codes may specify spacing detectors by using horizontal
(0.3 m) or for ceiling heights exceeding 12 ft (3.66 m), detectors are to spacing from the peak of the roof or ceiling. For instance, if the speci-
be located on the ceiling in every beam pocket. If the beamed ceiling is fied distance from the peak is 3 ft (1 m), the distance is measured on the
also sloped, use the spacing determined for flat beamed ceilings. Use base of the right triangle formed by a vertical line dropped from the peak
the average height over the slope as the ceiling height in such cases. of the roof, with the roof incline as the hypotenuse. Additional detectors
Note that, by definition in NFPA 72, ceilings are to be considered smooth are installed on the selected spacing, using the horizontal distance, not
unless the beams or joists are more than 4 in (0.1 m) in depth. the distance along the incline of the ceiling. (See Figure 22.)
• Two factors influence the spacing of detectors and the amount of pro-
tection required in a specific room or area: the fire’s burn characteristics
Figure 20: Detector Coverage Patterns and the value of the protected assets. Refer to NFPA 72-2010 17.7.6 for
more detailed information on spacing of detectors under special appli-
21 ft. 21 ft.
cations. Likewise, if the contents are especially valuable, for example,
21 ft. 21 ft. 10 ft.
sophisticated and expensive machinery or irreplaceable records, detec-
tors should be placed closer together.
20.5 ft. 41 ft. 20.5 ft.
82 ft.
Section 5
Testing, Maintenance, and Service of Detectors
Smoke detectors are designed to be as maintenance free as possible; how-
ever, dust, dirt, and other foreign matter can accumulate inside a detector’s
sensing elements and change its sensitivity. They can become either more
sensitive, which may cause unwanted alarms, or less sensitive, which could
A A
reduce the amount of warning time given in case of a fire. Both are unde-
sirable; therefore, detectors should be tested periodically and maintained
at regular intervals. Always follow the manufacturer’s specific recom-
mended practices for maintenance and testing. Also refer to Annex B of
NFPA 90A and NFPA 72-2010 Chapter 14.
Caution
3 ft. Minimum Smoke detectors are sophisticated electronic devices that need periodic
testing and maintenance. To maintain the integrity of any fire alarm sys-
Smoke Detectors at Ceiling tem, it is important to have a qualified person periodically test the system.
Smoke Detectors below Ceiling
Typical Inspection, Test, and Maintenance Practices
Figure 23: High Ceiling Area
Detectors should be given a visual inspection at installation and at least
Detectors in Air Handling and Air Conditioning Systems twice a year thereafter. This ensures that each detector remains in good
physical condition and that there are no changes that would affect detec-
See the System Sensor Duct Application Smoke Detectors Guide and NFPA tor performance, such as building modifications, occupancy hazards, and
72, National Fire Alarm Code for more specific information. environmental effects.
Detectors in Above-Ceiling Plenum Areas Including Those Notify the proper authorities that the smoke detector is undergoing mainte-
Utilized as Part of the HVAC System nance, and therefore the system will temporarily be out of service. NOTE:
Disable the zone or system undergoing maintenance to prevent unwanted
Detectors should be placed in plenum areas above the ceiling, in the open alarms and possible dispatch of the fire department.
areas below, and in the ducts. Plenum detectors are required to be listed or
tested and approved for the air velocities within the environment in which Use a high powered vacuum cleaner and remove dust from the detector
they are to be installed. Duct detectors should be installed in the ducts. 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. The
Detectors placed in plenums MAY NOT be used as a substitute for open sensing chamber on some detectors can be removed for more thorough
area protection, because smoke may not be drawn into the plenum when cleaning. Refer to the manufacturer’s recommended procedure for details.
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 Test each detector’s sensitivity per the manufacturer’s recommended pro-
a detector located on the ceiling of the room below. This may be caused cedure within one year after installation and every alternate year thereafter.
by blockage, dilution, and air filtering prior to its arrival at the detector loca-
tion in the plenum area. Test each detector functionally in place annually, as detailed in NFPA
72-2007 (Chapter 14).
Since the air circulating through the plenums is usually at higher veloci-
ties than would be prevalent in the room below, detector spacing should If a detector’s sensitivity is within specifications, nothing further needs to
be reduced. 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
Also, the dilution of the smoke in plenum spaces is an important consider- the unit specified range, then follow the manufacturer’s recommended
ation when utilizing smoke detectors rated for higher velocities. Therefore, procedure.
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. Restore zone or system at the completion of testing.
Maintenance requirements of detectors exposed to unusual velocities are Notify the proper authorities that testing has been completed and the sys-
generally increased due to the excessive dirt buildup and contamination tem is again operational.
present in these environments.
Refer to NFPA 72-2010, Section 14.4.1 for additional information.
Test each smoke detector to verify that it is within its listed and marked sen-
sitivity range using either:
• Other calibrated sensitivity test methods acceptable to the authority • Improper installation: detectors and their wiring are subject to inter-
having jurisdiction. ference from induced currents and noise in adjacent wiring systems,
radio-frequency transmissions, and other types of electromagnetic
Detectors with a sensitivity of 0.25 percent/ft obscuration or more outside effects;
the listed and marked sensitivity range should be cleaned and recalibrated
or replaced. • Inadequate maintenance: gradual dust and dirt accumulation on the
Exception: Detectors listed as field adjustable may be either adjusted detector’s sensing chambers;
within the listed and marked sensitivity range, cleaned and recalibrated,
or replaced. • Seasonal effects: for example, the reactivation of a building heating sys-
tem after an extended summer shutdown can cause alarms;
Restore the zone or system at the completion of testing.
• Building maintenance issues: for example, accidental triggering of a
Notify all the persons contacted at the beginning of the test that testing has detector’s magnetic test switch, or the introduction of plaster dust from
been completed and the system is again operational. drywall repairs into a detector’s sensing chamber;
Some individuals rely on an aerosol chemical spray (canned smoke) to test • Induced current effects from lightning storms;
the sensitivity of a detector. This can give unsatisfactory results since an
aerosol chemical spray does not accurately test detector sensitivity. NFPA • Infestation from insects small enough to enter the detector’s sensing
72-2010, Chapter 14.4.5.3.7 states, “The detector sensitivity shall not be chamber;
tested or measured using any device that administers an unmeasured con-
centration of smoke or other aerosol into the detector.” • Vandalism or mischievous acts: for example, dormitory pranks.
Canned smoke should only be used to verify smoke entry. The duration of If an alarm occurs and a fire does not exist, the alarm should be silenced
spray, distance between the detector and the aerosol container, angle of by an authorized service technician following procedures recommended
discharge, and different environmental conditions can produce random by the NFPA. The problem unit must be located and the alarm system con-
results. In addition, many aerosols leave an oily residue. Over a period of trols reset, so that the effectiveness of the detection system is restored.
time, this oily residue can attract dust or dirt, which can make a detector
more sensitive and result in nuisance alarms. Be sure to follow the manu- Be sure to check all the detectors in the zone or addressable device(s)
facturer’s recommendation on test gas or canned aerosol testers. 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
Section 6 in the vicinity of the first activated detector. The fire could be overlooked.
Troubleshooting Techniques
Maintain an Alarm Log
What to Do About Unwanted Alarms
The next step for all alarms should be a written report in an Alarm Log. A
No detection system is impervious to unwanted alarms. Statistically, as the typical Alarm Log is shown on page 19 of this guide. Such a log serves
system size and the total number of detectors increase, the total number immediate and long-term purposes.
of nuisance alarms per year tends to increase. Historical experience in a
given installation or data on similar sized buildings with similar utilization The Alarm Log indicates which individuals responded to the alarm and
patterns can provide a basis for a rough indication of how many nuisance whether or not they took appropriate action.
alarms are probable during a 12-month span; however, no two installa-
tions are identical. Periodic review of the cumulative Alarm Log can help those responsible
for the detection system discern patterns in the reported alarms. Generally,
In small- to moderate-sized detection systems protecting relatively combus- several months (or even years) of data may be necessary before patterns
tion-free environments, like office buildings, more than one or two unwanted begin to emerge.
alarms per year would be unusual. In more adverse environments, such
as laboratory or manufacturing facilities where combustion processes are In a worst case example, a pattern of repeated alarms or small fires in a
present, more frequent alarms can be anticipated. In very adverse environ- particular area may indicate a serious deficiency in safety practices that
ments, one alarm per month might not be considered excessive. should be promptly corrected. In less obvious cases, patterns are indicated
by repeated alarms in the same or adjacent zones with similar probable
After the first few months, which serve as a shakedown period, it should be causes, or repeated alarms in the same zone that occur at about the same
possible to arrive at some reasonable expectation for probable unwanted time of day, or time of year.
alarms from the system. After that, any unexpected change in frequency
or distribution indicates a problem that should be investigated. The best Effects of Location or Environment
way to monitor alarm frequency and distribution is to maintain an alarm log.
Check for the effects of location and environment. Review the information in
Reasons for Unwanted Alarms this guide on Where To Place Detectors and Where NOT to Place Detectors,
to determine whether the detector’s location or its environment is poten-
Unwanted alarms can result from a wide variety of causes, including: tially causing the unwanted alarms. Also, refer to the installation manual
for further information.
• Improper environments: detectors will not operate properly because
of temperature extremes; excessive dust, dirt, or humidity; excessive One often overlooked source of problems is the placement of detectors
air flow rates; or the normal presence of combustion particles in the air where air streams carry smoke or chemical fumes from some areas of an
streams surrounding the detectors; installation past detectors in other areas unrelated to the source of the con-
taminants. Diagnosing these problems requires that air movements into the
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S Y S T E M S E N S O R
problem area, especially near the ceiling, be carefully checked to deter- Miscellaneous Causes of Unwanted Alarms
mine their sources. Experienced HVAC engineers or contractors usually
have the training and specialized equipment (flow meters, etc.) to con- Isolated alarm causes such as a maintenance person accidentally trigger-
duct such a study. In very difficult cases, a full-scale smoke test may be ing an alarm by touching a detector with a magnetic screwdriver can be
required to solve the problem. ignored, except to periodically remind maintenance personnel to be care-
ful when working around detectors.
Conversely, strong air streams near air inlet or supply ducts can also pre-
vent a detector from signaling an alarm when a fire is present by blowing Steps also should be taken to protect detectors from dust whenever
smoke away from the detector heads. maintenance requires sawing, sanding, drilling, or other dust-producing
operations in the vicinity of the detector heads, to prevent false alarms
Inspect Detector for Dirt, Review Maintenance due to the dust getting into the detector sensing chambers. In new con-
struction applications drywall dust contamination affects all types of smoke
If the Alarm Log indicates a fairly stable alarm rate for several months or detectors. To help overcome this problem, it is strongly recommended
a year, and then there is a gradual increase in the frequency of unwanted that installation of detector heads be delayed until all trades have com-
alarms, this is usually an indication that the detectors in the system should pleted work and job site clean up has occurred in accordance with NFPA
be cleaned. requirements.
NFPA standards require that all detectors be visually inspected twice a year. If alarms occur whenever the heating system is turned on after an extended
Smoke detector manufacturers also recommend this schedule. shutdown, due to the accumulated dust burning off as the system compo-
nents heat, the detector system can be turned off for a short period. If the
Clean the detectors at least once a year, or more frequently if environmental system is being shut down for inspection, the work must be performed by a
conditions warrant it. See the section on Detector Testing and Maintenance qualified technician following procedures prescribed by the NFPA. Another
in this guide for more details. option would be scheduling the start-up of the heating system for an eve-
ning, weekend, or other off-hours period to minimize the effects of alarms
In cases where the probable cause of a number of alarms appears to be on regular daytime activities.
dust or dirt on the detectors, detector maintenance schedules should be
reviewed to determine the dates when the detectors were last cleaned and Not all unwanted alarms are caused by dirt, interference or other effects on
tested. If the detectors are due or overdue for maintenance, scheduling the detectors. If the control panel shows an alarm but no detectors in the
and performing the recommended cleaning and testing should eliminate zone are indicating an alarm condition, the possibility of interference or a
the problem. failure of a control panel component should be investigated.
If the problem resulted from a temporary overall increase in airborne dust Responsibilities of Detector Owners and Installers
due to nearby construction, scheduling a one-time special cleaning for all
the detectors in the system should alleviate the problem. If the problem The owners of smoke detector-equipped fire alarm systems are respon-
is confined to one or two zones and is the result of higher dust levels in a sible for maintaining the integrity of the detection system. This can be
particular area, scheduling the detectors in those areas for more frequent accomplished by:
maintenance and cleaning may prevent the development of similar alarm
problems in the future. • Maintaining an Alarm Log and training appropriate personnel to prop-
erly maintain the system as described above in the section titled, What
Effects of Other Systems on Alarm System To Do When Unwanted Alarms Occur.
In checking for the effects of other systems on the alarm system wiring, the • Maintaining a Detector Maintenance Log that records inspection, test-
Alarm Log may be very valuable in helping to pinpoint relationships among ing and cleaning data for each detector in the system. (Refer to Section
apparently causeless alarms. One important fact that can be obtained 6 of this manual, Testing, Maintenance, and Service of Detectors for
from an Alarm Log is the beginning date for a rash of apparently cause- information on recommended testing and maintenance intervals and
less alarms that may or may not be grouped around one particular zone. procedures, and a sample Detector Maintenance Log page.)
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 • Maintaining a complete file of information on the alarm system in a
system in the building affects the detectors or the alarm system circuitry. readily accessible location. This file should include specifications and
installation instructions for the detectors, control panel, and auxiliary
Systems that can affect the alarm system include: other security systems; devices, wiring diagrams, wire location information, and the manufac-
walkie-talkies; mobile telephones; HVAC controls; elevator call systems; turer’s recommendations for isolating the detection system wiring from
remote control equipment (door closers, etc.); and even the installation other electrical wiring to prevent interference and unwanted alarms.
of microwave antenna. If the alarm pattern supports the possibility of
some kind of interference with a fairly definite initiation date, all equipment • Making certain that maintenance personnel or contractors working on
changes made in the building immediately prior to or concurrent with the the building’s electrical systems are given copies of the alarm system
beginning of the development of the alarm pattern should be reviewed. In wiring layout and locations so that potential interference from other wir-
addition, the wiring layouts of the alarm system and any recent building ing systems can be prevented by proper insulation and spacing during
or system modifications should be compared to make sure that the spac- installation.
ing and/or shielding required to protect the alarm system wiring from other
potentially interfering electrical systems was maintained. • Keeping accurate records of installation and modifications to all other
building electromechanical systems that could cause interference with
the alarm system so that problems can be promptly found and elimi-
nated. Consider keeping records of schematic update schedules, wiring
layouts, and wiring location information.
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A P P L I C A T I O N S G U I D E : S Y S T E M S M O K E D E T E C T O R S
• Verifying that the alarm system installation meets all applicable code
requirements.
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S Y S T E M S E N S O R
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A P P L I C A T I O N S G U I D E : S Y S T E M S M O K E D E T E C T O R S
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S Y S T E M S E N S O R
Appendix 2
Fire Alarm Log
Customer Name:
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A P P L I C A T I O N S G U I D E : S Y S T E M S M O K E D E T E C T O R S
©2016 System Sensor. The company reserves the right to change specifications at any time. SPAG9102 • 4/16