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Page IMSA Journal2Continued on page 43
The ABCs of Fire Alarm Systems - Section IBy Anthony J. Shalna
2009Principal IMSA Representative to the Automatic Fire Alarm
Association
President: Southeastern Signalmen of MassachusettsApprovals
Manager: Gamewell-FCI by Honeywell
A fire alarm system is used primarily to evacuate the prem-ises
in the event of occurrence of a fire condition and then secondarily
to report the fire to the proper authorities.
A fire alarm system differs somewhat from a security system. The
security system only recognizes two states or conditions: normal or
alarm, and cannot differentiate between a line break and the
opening of an alarm switch. The fire alarm system recognizes four
different states or conditions: normal, alarm, trouble and
supervisory.
Simplistically speaking, a basic system consists of a fire alarm
control panel (FACP) to which are connected initiating (input)
devices, notification (output) appliances, a source of operating
power, and a source of standby power in the event the operating
power should fail.
The function of a fire alarm control panel is basically
three-fold:
) Accept an alarm or supervisory input from an initiating
device.
2) Provide an alarm output to the notification appliance(s).
) Monitor the integrity of the panel itself and also the wir-ing
to the above devices.
MINIMUM BASIC SYSTEMFire alarm systems have changed dramatically
over the past few years, primarily due to the ad-vent of the low
priced micropro-cessor. Basically there are two different
approaches used for the fire alarm control panel, conven-tional and
addressable.
We are concerning ourselves in this installment with the
con-ventional (hard-wired) system as opposed to an addressable
system, which will be covered in a following installment.
The minimum basic components of a conventional system are:
) A locked fire alarm control panel listed for the purpose by a
Nationally Recognized Testing Laboratory, (NRTL) as recognized by
OSHA. The standard governing fire alarm control panels is ANSI/UL
Standard 8, current-ly entering its ninth edition. OSHA currently
recognizes Underwriters Laboratories, Factory Mutual Approvals and
ETL-Semko as certified to test equipment per this standard.
2) A primary operating power sup-ply (20 VAC).
) A secondary or standby power supply. This is most often a
rechargeable storage battery, although genera-tors are permitted
subject to certain conditions.
) At least one initiating device circuit to which is wired at
least one manual station, automatic heat or smoke detec-tors,
waterflow switch activated by a sprinkler system, etc. These
devices are located in one area, or zone, so an alarm condition in
this zone can direct fire fighting personnel to the source of the
alarm. Typically, a zone usually consists of a floor of a small
building, or wing of a larger building, etc. with area limitations
defined in the National Fire Alarm Code (NFPA 72).
) At least one (output) notification appliance circuit to which
is wired at least one horn, bell, and strobe, if required.
The basic minimum system is shown in Figure .
The secondary power supply (usually a battery) automati-cally
furnishes operating power to the system in the event of failure of
the main 20 VAC supply or if the main supply voltage falls below 8%
of normal (Brown-out condition). The battery must be of the
rechargeable type, since dry cells are not permitted.
Figure 1
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May/June 2009 Page
Continued from page 42
A gel- cell battery is a rechargeable battery.) The battery must
operate the system for a specified period of time in a standby or
quiescent condition, and have sufficient reserve at the end of the
standby period to operate the panel in an alarm condition for a
period of five () minutes. Batteries are required by the National
Fire Alarm Code in all fire alarm systems not having multiple
standby generators. The control panel must also be capable of
recharging the battery within a specified period after a
discharge.
BASIC SYSTEM OPERATIONInitiating devices employed in a
su-pervised, conventional system usually have normally open, dry
contacts which close on alarm. (Dry contacts are contacts that have
no voltage ap-plied to them.) Exceptions to this are 2-wire smoke
detectors, which receive their operating power from the
(supervisory) current flowing through the circuit, and alter the
characteristics of the circuit when they go into alarm. These will
be covered in a separate article.
The act of operating a manual station or actuation of an
automatic detector closes the contacts of the device and applies
power to the alarm circuitry, causing the panel to go into alarm,
light one or more red LEDs on the panel, and energize the
notification appliance(s). This appears to resemble the classic
operation of a doorbell system, but the BIG difference here is that
the fire alarm control has the ability to monitor its own
integrity, commonly referred to as supervision.
SUPERVISIONA supervised system (sometimes referred to as a
closed circuit system) will create a trouble signal in the event of
a break in the field wiring, disconnection or removal of an
initiating device or notification appliance, failure of main
operating power, discon-nection of the standby battery, or
off-normal position of a panel switch. A trouble condition will
light one or more yellow LEDs on the panel and cause an audible
signal, (usually a piezoelectric device) to sound. The audible
signal can be silenced by operating the Trouble Silence switch on
the panel. Since the panel is locked, the trouble sounder can only
be silenced by authorized personnel who have access to the key.
In a conventional system, supervision is made possible by use of
an End of Line (EOL) device, usually a resistor, although other
components may be used, depending on the designer.
TROUBLE CIRCUITRYMany years ago, manufacturers used relays to
achieve supervision. Two relay coils, alarm and supervisory, were
connected in series with the initiating device circuit. The
supervisory relay was rated at a lower voltage and was continually
energized by the reduced current flowing through the circuit via
the EOL device. The alarm relay was rated at the operating voltage
and would only energize when the current was increased by an
initiating device that short-circuited the EOL device. If the
circuit is opened by a break in the wiring, or unauthorized removal
of a detector or station, or if the winding of either relay opened,
the trouble relay contacts would fall out, applying voltage to the
trouble LED and sounder. These
The ABCs of Fire Alarm Systems - Section I . . . relays were
eventually replaced by solid state compo-nents, mostly
microprocessors, that monitor the circuit supervisory current.
In Figure 2, we see an initiating circuit of a Fire Alarm
Control Panel (FACP). Current flows out of the FACP and through the
circuit, in and out of one contact of the initiating devices,
through the end of line resistor (EOL), through the second contact
of each initiating device and back to the FACP. (We will discuss
the in and out wiring to the contacts later.)
Continued on page 44
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Page IMSA JournalContinued on page 45
In the event of a break in the outside wiring, unauthorized
removal of a detector or sta-tion, failure of the main power
supply, or re-moval of the EOL device, the microprocessor will
sense the change in circuit current and create a trouble condition,
energizing the yellow System Trouble LED, a yellow Zone Trouble LED
dedicated to that circuit, and an audible sounder inside the panel,
signify-ing a trouble condition. The sounder may be silenced by
operating a Trouble Silence switch, but the yellow LED(s) will
remain lit. Once the trouble condition is rectified and the circuit
in question is restored to normal, the audible signal will sound
again, or ring back. The trouble silencing switch is then restored
to the normal position, silencing the sounder and extinguishing the
Trouble LED(s).
ALARM PROCESSINGIn the event of an alarm, the contacts in the
initiating device close, shunting out the EOL, raising the circuit
voltage to full operating voltage, and energizing the alarm
circuitry. The alarm circuitry will then ap-ply operating power to
the notification appliance circuit, sounding horns, flashing
strobes, and performing other functions.
This type of circuit is referred to as a Class B, Style B
circuit. The National Fire Code, NFPA Standard 72, makes references
to both Classes and Styles for circuits. The Class A or B
designa-tion has been traditionally used for discussion purposes,
while the Style designations refer to a wider variety of cir-cuits
having subtle differences which are beyond the scope of this
article. (The 200 Edition of the National Fire Alarm Code will
apparently do away with style classifications and adopt new
definitions of Classes.)
CLASS B, STYLE B INITIATING CIRCUITThus, a Class B (or Style B)
circuit is a two-wire circuit with external EOL. Any device
electrically located beyond a break in the field wiring will be
disabled. Any devices located electrically before the break will
still be able to turn in an alarm. A Class B system is economical,
since it only uses two wires, but has several drawbacks, such as
surviv-ability, or inability to operate if a device beyond the
break goes into alarm. Also, the EOL is often installed in the last
initiating device, the location of which is often unknown if a less
than competent installer doesnt document the location at the FACP.
Therefore, we see the need to develop a better circuit. The Class
A, Style D circuit is an answer.
CLASS A, STYLE D INITIATING CIRCUITA Class A (or Style D)
initiating circuit uses four wires, and has the EOL device located
on the FACP terminal board or at least, inside the cabinet. Figure
shows a typical Class A circuit. The circuit operates in the same
fashion as a Class B circuit, but the wiring returns to the FACP
after the last initiating device. In the event of a wiring break,
etc., the
Continued from page 43The ABCs of Fire Alarm Systems - Section I
. . .
trouble circuitry operates and connects line A to line D, and
line B to line C, thus effectively shunting out a single break
anywhere in the circuit. Alarm operation otherwise is exactly the
same as in the Class B circuit. A Class A circuit therefore, has
the ability to turn in an alarm in spite of a single break in the
circuit. This gives the circuit a greater degree of sur-vivability
than the Class B circuit, eliminates the problem of lost EOL
devices, and makes trouble shooting easier. The main disadvantage
is that it requires twice the amount of wires and the codes require
that the return pair be run in separate raceways or conduit from
the outgoing pair to ensure survivability. One typical trouble
situation is often caused by a different trade unknowingly cutting
through a conduit. There are numerous horror stories regarding
this.
CLASS B, STYLE Y NOTIFICATION APPLIANCE CIRCUITNotification
appliances, such as bells, horns, strobes or combination
horn/strobes are likewise installed in Class B or Class A
configurations. However, the supervision of these appliances is
made possible by use of blocking diodes wired internally in each
device. As you probably already know, a diode only conducts DC
voltage in one direction. If the polarity of the supply voltage is
reversed, the diode will become an open circuit, and no conduction
occurs. See Figure .
Every notification appliance is equipped with a blocking diode.
Thus the appliance is supervised up to the point of connection to
the circuit. The internal coils, etc. are NOT
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supervised. Supervisory voltage is applied to the notification
appliance circuit, which conducts the current to each appliance
where it is blocked by the diode, travels through the EOL device,
and back to each appliance and hence to the FACP. In the event of a
break or removal of an appliance, the circuit will open and a
trouble condition will occur, just as in an initiating circuit.
During alarm, the polarity of the voltage is reversed by panel
circuitry, and the blocking diodes conduct the current to the
interior components of the appliance.
SUPERVISORY CIRCUITSupervisory circuits are basically used to
detect off normal condi-tions in the sprinkler system, if one
exists in the building. A super-visory circuit is basically an
initiating type of circuit, Class A or B, to which are connected
supervisory or tamper sprinkler system switches. These switches
transfer if a gate valve has been operated to shut off a sprinkler
system, if sprinkler pressure is dropping due to a leak, if the
water level in a rooftop tank is too low, too high, or if a freeze
up is imminent, etc., or in general, indicate a problem or
tampering with the sprinkler system. In this case, the supervi-
Continued from page 44The ABCs of Fire Alarm Systems - Section I
. . . sory switch process the signal in the same manner as an
alarm, but the panel circuitry is programmed not to energize the
notification appliances or transmit an alarm signal off premises.
Instead, the circuit lights its associated LED and the trouble
sounder may sound, as the sharing of the audible trouble signal by
both trouble and supervisory circuits is permitted. Some-times a
single notification appliance may be energized, such as a flashing
yellow light, etc.
Thus, we see the operation of a simple, basic system. A larger
system would have additional initiating cir-cuits, notification
appliance circuits, circuits that make off premise notification
(fire department) by various means, and control circuits to capture
elevators, shut down air circulating equipment, and perform various
required auxiliary functions.
Our next installment will cover the devices that place a
conventional fire alarm system into alarm.
It seems like we just finished cleaning the desert sand off our
clubs, and here we are already thinking about next years Outing.
The Florida Section is already hard at work planning what we hope
will be a great golf outing at one of the premier golf courses in
Central Florida.
The National Course at Champions Gate was designed by Greg
Norman and offers a great mix of American style bunkers to
challenging tee shots for every skill level. As you drive towards a
couple of the greens there's enough sand and water to make you
think your over on Daytona Beach.
The Outing is going to be held on Saturday the 22nd at 8:00 AM.
The price is $55.00 per person. This will include your round, cart
and a catered lunch after in the Club House. Registrations can be
downloaded from the IMSA web site or contact the Golf Committee for
more information and pricing on club rentals.
We hope all of you can join us for one of the more unique events
of the conference.
Sincerely, The Officers of the Florida Section
Golf Committee:John Lemonias 727-464-8887
[email protected] Dyar 727-464-8909
JDAYAR@CO,PINELLAS.FL.USTyson Evatz 727-464-8982
[email protected]
2009 Golf Outing
August 228 a.m.
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Page IMSA Journal36
The ABCs of Fire Alarm Systems - Section IIBy Anthony J. Shalna
2009Principal IMSA Representative to the Automatic Fire Alarm
Association
President: Southeastern Signalmen of MassachusettsApprovals
Manager: Gamewell-FCI by Honeywell
In our first installment, we discussed basic fire alarm con-trol
panels that contain one or more initiating circuits and
notification appliance circuits. We will go into greater detail
about addressable panels in future installments, but now want to
discuss some of the devices that place the initiating circuits in
alarm.
INITIATING DEVICES
Initiating devices commonly used to activate the initiating
circuit of a fire alarm control panel are: heat detectors, smoke
detectors, water flow switches and manual (pull) stations.
In this installment, we will concern ourselves with heat
detec-tors, which, like sprinkler heads are basically intended for
property protection rather than for life safety.
Heat detectors fall into two basic styles of protection: Line,
and Spot detection. Line detection protects areas over an elongated
path. Spot detection protects an area resembling the area lit by a
spotlight.
LINE DETECTION
Line heat detection is less common, but is invaluable for
protecting certain hazards. One of the most common line detectors
in use today consists of a twisted pair of wires insulated with a
thermal coating that has a specific melting point. If excess heat
is applied to the cable, the insulation melts, the wires short
circuit together, and the control panel goes into alarm. The system
is restored by cutting out the damaged section of cable and
splicing in a new section. Figure 1 shows a typical line detection
device.
Other types of line detection make use of eutectic salts or
similar insulation that is non-conductive until it reaches a
specified tem-perature and then conducts current from one
conduc-tor to the other. U n l e s s m a j o r damage occurs, the
insulat ion again becomes non-conductive when the temperature
drops, thus making this type of detection essentially
self-restoring. Some older systems use copper tubing installed
throughout the area, filled with air or gas under pressure.
Diaphragm arrangements then respond to increases in pressure caused
by heat, and close contacts, creating an alarm.
Line detection is best suited to servicing conveyor belts,
escalators, raceways, wire troughs, tunnels, grain elevators,
silos, etc. Weatherproof versions of line detection cable are
also available. This line can be stapled under piers or wharfs,
allowing out-door weatherproof protection where no other sensors
would function properly.
SPOT DETECTION
Spot detectors cover a finite area that varies according to the
rated sensitivity of the detector and the distance (height) of the
detector from the floor.
The most commonly used types of spot heat detectors are: Fixed
Temperature, Rate of Rise, and Rate Anticipation detectors.
Electronic (thermistor/microprocessor) detectors have been
introduced fairly recently and may be used only with com-patible
control panels, usually addressable panels. With the exception of
the electronic versions, heat detectors are mechanical in nature,
and contain contacts that close when the detector is in alarm,
making them compatible with any conventional control panel.
FIXED TEMPERATURE DETECTORS
The fixed temperature detector goes into alarm ideally when the
ambient temperature reaches a certain setpoint. The most commonly
used fixed temperature detectors operate on two different
principles: fusible alloy and bimetallic strip.
FUSIBLE ALLOY FIXED TEMPERATURE DETECTORS
The fusible alloy unit uses an alloy physically resembling
sol-der, but with a much lower melting point. The most common
temperature melting points are in the vicinity of 135o F and
190-200o F, depending on the manufacturer. The alloy holds a spring
type mechanism in place. This mechanism holds a spring in an
extended position keeping a set of contacts open. When the alloy
reaches its melting point, the spring is released, allowing the
contacts to close, placing the detector in alarm. The detector is
usually non-resettable, and either the detector or fusible unit
must be replaced after actuation. Figure 2 shows a popular fixed
temperature detector with replaceable element.
Figure 1
Figure 2
Continued on page 38
BIMETALLIC STRIP FIXED TEMPERATURE DETECTORS
The bimetallic strip unit contains a strip of metal, plated on
each side with a different metal, each of which has a different
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Page IMSA Journal38
Continued from page 36The ABCs of Fire Alarm Systems - Section
II . . .
Figure 3A
Figure 3B
Figure 4 shows a typical rate compensation heat detector
Continued on page 39
coefficient of expansion. This means that, when heat is
ap-plied, the metals expand at different rates, causing the strip
to bend, or warp. When the strip bends enough, it touches a
contact, completing the circuit. Bimetallic strip detectors are
mostly used in household applications, since their listed area of
coverage is usually insufficient to meet Code require-ments for
larger buildings. Advantages and disadvantages of the various types
of heat detectors will be summarized at the end of the article.
RATE OF RISE HEAT DETECTORS
Another type of widely used heat detector is the Rate of Rise
detector. This detector contains a chamber with a calibrated vent
hole and diaphragm at the top. An actuator strip is located above
the diaphragm, just below a set of contacts. When the air outside
the detector rises in temperature, the air inside the chamber
likewise gets warmer, and as we all know, it expands. If the air
expands gradually, it escapes through the calibrated vent. If the
air heats rapidly and expands too fast to be vented, pressure is
exerted on the diaphragm, causing it to bulge, pushing the contacts
closed and placing the detector in alarm. The rate of temperature
rise required to place a detector in alarm is 15o F in one minute,
or equivalent, such as five de-grees in 20 seconds. Therefore, this
detector does not depend upon high temperatures to go into alarm,
but senses a rapid rise in temperature. The rate of rise detector
is self-restoring, since the diaphragm returns to normal as the
ambient air cools. The ROR detector often has a fixed temperature
feature as a back-up in the event high temperatures are reached,
while the temperature rises too slowly to activate the rate of rise
feature. This detector is referred to as a combination Fixed
Temperature and Rate of Rise detector. Figures 3A and 3B show
typical rate-of-rise/fixed temperature detectors. Figure 3A shows a
high profile detector while Figure 3B shows a low profile version
developed for use in finished interiors. Both operate
identically.
RATE ANTICIPATION DETECTORS
The fixed temperature detector depends upon heat absorp-tion to
activate it, and in some instances, a rapidly increasing
temperature could conceivably reach a hundred or more degrees
higher than the setpoint of the detector before the
fusible alloy could absorb enough heat to melt it. This is
referred to as thermal lag. The rate anticipation detector was
designed to eliminate ther-mal lag. The rate anticipation detector
is cylindrical (cigar shaped), sealed, and contains a pair of bowed
struts each containing a contact. In normal operation, the struts
are bowed away from each other, separating the contacts. The
cylindrical case is made from a special alloy with a coefficient of
expansion that allows it to expand rapidly. When the am-bient
temperature rises, the detector case expands, (actually stretching
or elongating) until the internal struts are likewise stretched,
causing their contacts to close, placing the detector in alarm.
This detector has very little thermal lag, and will go into alarm
as soon as the ambient temperature reaches the setpoint of the
detector regardless of the rate of rise. Since this detector is
sealed, it is a simple matter to weatherproof or make it explosion
proof. See Figure 4.
ELECTRONIC HEAT DETECTORS
The electronic detector depends upon thermistors or similar
components that change value when exposed to heat. This detector
requires operating voltage in order to measure the change in value,
and must also be listed by a Nationally Recognized Testing
Laboratory (NRTL) as being compatible with the particular control
panel initiating circuit, since it does not contain dry contacts,
but alters the characteristics of the circuit, placing it into
alarm. This will be discussed in greater detail in a future
installment.
APPLICATIONS
The rate of rise detector (ROR) responds to rapid increases in
temperature. Therefore, these detectors can be used in any normal
ambient and are rated for greater spacing than the fixed
temperature detectors. They are especially suited for cooler
ambients where they can detect a developing fire long before a
fixed temperature unit can actuate. These de-tectors commonly
incorporate a fixed temperature element for reliability and are
referred to as combination FT/ROR detectors.
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July/August 2009 Page 39
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Continued from page 38
The ABCs of Fire Alarm Systems - Section II . . .
The fixed temperature detector (FT) alarms when the ambient
temperature reaches a certain setpoint, commonly 135 or 200o F, and
ignores any fluctuations or sudden increases in temperature.
Therefore, the fixed temperature detector is best suited for
applications where rapid fluctuations in temperature can be
encountered, such as attics, boiler rooms, kitchens, bathrooms and
loading platforms with forced hot air heaters. The 200o F version
should al-ways be employed in attics, boiler rooms, garages or
kitchens. The most common fixed temperature detectors are usually
destroyed upon activation and must be replaced after the alarm.
The rate anticipation detector outperforms the fixed temperature
detector since it will alarm faster than the FT detector in the
event of a rapid temperature increase up to the setpoint. It is
costlier than the FT de-tector, but is also self-restoring, so
doesnt require replacement after actuation. This is a great
advantage in installations where staging or scaffolding would be
required to replace the detector.
ROR and FT detectors are available in weatherproof and explosion
proof ver-sions, but require fairly costly housings for these
versions. The rate anticipation detector, being sealed, lends
itself to weatherproof or explosion proof applica-tions at a
moderate cost.
The rated spacings of these detectors vary. The ROR detector
mounted on low ceilings can be spaced up to 50 feet on centers,
depending on its listing, while the fusible element FT detector is
typically rated at only 15 feet on centers. The bimetallic strip is
rated for even less. Electronic/thermistor detectors may be rated
for greater spacings. For spacing information, refer to NFPA
Standard 72, National Fire Alarm Code. This publica-tion contains
all types of information regarding installation, layout and spacing
of detectors on all types of ceilings and elevations. Most state
codes are now based on this standard.
Now that we have a basic understand-ing of the devices that
place a fire alarm control panel into alarm, our next install-ment
will concern itself with addressable (microprocessor based) fire
alarm control panels.
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Page IMSA Journal28
Addressable Fire Alarm SystemsUntil now we have been concerned
with conventional fire alarm systems. These systems require
specialized wiring practices using in and out connections to
devices in order to maintain supervision of the devices. T tapping
is an-other practice also not permitted in conventional systems.
These will be covered in detail in a later installment.
Addressable systems are a different matter. No specialized
methods of wiring are required. These systems are controlled by
microprocessors and their operation relies on communi-cation
between the microprocessor in the central processing (control)
unit, and connect-ed devices which have their own microprocessors.
Ad-dressable systems feature an LCD or similar visual display that
may give loca-tion and specific informa-tion about the connected
devices, depending on how it is programmed. Some systems show
detailed in-formation via an alpha-nu-meric display while other
smaller, economy type sys-tems might display only a code number
assigned to the device. These systems have been nicknamed smart or
intelligent systems.
Addressable systems are obviously much more complex than
conventional systems, but they have an infinitely greater
flexibility. Oddly enough, even though they may be exceed-ingly
complex, describing them is a relatively simple matter. The
initiating devices and notification appliances are either connected
to or incorporate a transponder that has a specific address
assigned to it. These transponders are connected to a circuit of
the central processing unit which interrogates each transponder in
sequence. When interrogated, a device may respond that it is
normal, or if an initiating device, that it is in an alarm
condition. If a device is inoperative, disconnected, damaged, etc.,
it will not respond. The central processor then creates a trouble
condition and a device missing message will be displayed. Present
standards require a maximum of five () seconds for a CPU to report
an alarm from a device. The speed of interrogation has increased
dramatically in recent years with the development of better and
faster microprocessors. Now there exists a signaling protocol for
certain models of smoke sensors where the CPU interrogates a large
cluster of sensors instead of individually. This cluster will
instantly report an alarm condition when interrogated and then
indi-cate the address of the specific device in alarm. This saves a
significant amount of time that would be otherwise required to
interrogate each device individually.
The ABCs of Fire Alarm Systems Part IIIBy Anthony J. Shalna
2009Principal IMSA Representative to the Automatic Fire Alarm
Association
President: Southeastern Signalmen of MassachusettsApprovals
Manager: Gamewell-FCI by Honeywell
The addressable system operates over a circuit known as a
Signaling Line Circuit (SLC). Depending on the manufacturer and
design, the circuit can be wired in various methods in regard to
fail-safe operation. These methods are presently referred to as
Styles, but I understand that the 200 Edition of NFPA 72, National
Fire Alarm Code, will revert to an older Class designation. At any
rate, I recom-mend consulting the charts of the current edition of
NFPA 72 for further information.
The SLC does not resemble conventional initiating circuits since
it is a data gathering circuit, while conventional devices, having
normally open alarm contacts, place a short circuit across their
initiating device circuit. A short on an SLC will cause a trouble
condition instead of alarm.
Connected to this SLC are addressable smoke or heat sensors,
monitor modules, output modules and/or data gathering panels.
Dif-ferent manufacturers all
have their own various designations for these modules, but
generically, they are usually referred to as transponders and in
common conversation as modules.
The sensors and modules all may be intermingled on the SLC
regardless of their (input or control) function. (See illustration)
As stated above, they have their own unique address that is
assigned when the system is programmed. This address is assigned to
the transponder at installation via a DIP or rotary switch. Again,
the variety of modules, sensors and data gathering panels is
limited only by the manufacturers imagination and technical
expertise. Addressable smoke or heat detectors are usually referred
to as sensors to distinguish them from conventional detectors.
These sensors may either contain an integral address switch, or in
older or economical systems, they may simply be conventional
detectors installed in an addressable base. Conventional detectors
installed in an ad-dressable base would constitute an Addressable
System. Smoke sensors containing microprocessors now report their
status to the CPU. While a conventional detector has only two
conditions: Alarm or Normal, the newest sensors can notify the CPU
that they smell smoke, or are approaching an alarm condition, or
signal that they are dirty and require cleaning, etc. Their
sensitivity can be varied by the control panel and new features are
being announced continually.
Systems employing these sensors are known as Analog Continued on
page 30
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Page IMSA Journal0
The ABCs of Fire Alarm Systems Part III . . . Continued from
page 28Addressable since their condition is dis-played in an analog
fashion rather than a digital normal or alarm condition.
Many people erroneously use the term Analog Addressable to
describe all devices connected to an SLC, but technically this term
does not apply to devices such as manual pull stations or
electronic addressable heat detec-tors that have been employed in
these systems until now. Even though heat sensors may be
addressable and signal an alarm via the SLC, they can only report
the two states, alarm or normal. Now appearing on the horizon are
heat sensors that can indicate their chang-ing condition in the
same manner as a smoke sensor, such as reporting an increase in
ambient heat, so nothing is etched in concrete regarding the
ability and features of these sensors.
Monitor modules have their own as-signed addresses and commonly
fea-ture a conventional initiating circuit complete with an end of
line resistor. Conventional dry contact initiating devices are
connected to this circuit. These may be electromechanical heat
detectors, manual pull stations, water-flow switches, etc. When any
of these devices go into alarm, the monitor mod-ule provides a
collective address for the devices on its circuit. Newer modules
are now available featuring multiple initiating circuits and
provide different addresses for each of these circuits.
Some modules are small enough to fit inside a device housing or
backbox. These modules are usually intended for connection to a
single initiating device. An example of this would be a module
installed inside a pull station, providing an address for the
station. Some manufacturers preassemble the monitor modules into
pull stations, etc. while others prefer to sell the module only,
and allow the installer to connect the modules in the field.
Other monitor modules have an initiat-ing 2-wire circuit that
may be extended considerably, and can accommodate a specified
number of conventional 2-wire compatible conventional smoke
detectors in addition to a number of dry contact initiating
devices. This module provides one address for each circuit, and is
useful in large areas, such as auditoriums, atriums or gymnasi-
ums where only a collective address is needed to guide
fire-fighting forces to the source of the fire.
Data gathering panels have been used since the earliest days of
addressable systems. These panels resemble a small conventional
fire alarm control panel and contain a number of conventional
initiating circuits, battery standby, etc. These panels in effect
provide a subsystem with its own address, but I wouldnt be
surprised if some of the latest ones provide multiple addresses,
one for each initiating circuit.
Output or control modules may also be installed anywhere on the
SLC. These modules likewise have their own unique address and may
be pro-grammed to perform a function in the event of an alarm or
trouble on any individual or combination of monitor modules or
sensors. These control modules may contain dry contacts that
transfer on command, but again, new configurations are arriving on
the mar-ket on a daily basis. Some will accept an audio input and
provide supervised loudspeaker appliance circuits, while others
will supervise and operate notifi-cation appliance circuits. Still
others can be used to energize releasing solenoids or provide smoke
damper operation in smoke control systems.
System programming also varies with the manufacturer. In the
earlier days some small system manufacturers used burn-in chips, or
PROMS for the programming. Larger systems are programmed via
software. In these sys-tems, the programming is often done in the
office on a computer and then down-loaded to the control panel in
the field via lap-top computer. Some software programs are user
friendly while others are not, and usually require specialized
training. The easiest ones to use contain drop-down menus and the
programmer need only to literally fill in the blanks in order to
complete the program.
When the system is programmed, a description of the device can
also be included (in systems with alphanu-meric display) such as
ionization sensor, main lobby, right wing. Thus, when the device
goes into alarm, this message will display on the readout, giving
firefighters explicit information as to the location of the
fire.
OPERATION SUMMARYThe microprocessor in the main control
interrogates or polls the transponders in sequence, with only
nanoseconds being required for each device or cluster of sensors.
When a transponder is polled, it responds that it is either in a
normal state or in alarm. In Analog Address-able Systems, a
transponder installed in a smoke sensor will also indicate the
condition of the sensor, such as dirty, approaching alarm
condition, etc. If the transponder is disconnected for any reason
(malfunction or break in the wir-ing) the panel will show a system
trouble and show a device missing message (or code) on the display,
which will give a specific location of the device. Other fault
messages can be for an SLC break, circuit shorted, etc. Some
systems may indicate a circuit break by displaying a list of
missing addresses located beyond the break or short.
One disadvantage of the addressable system is that polling or
interrogation consumes a fraction of a second per device polled. If
a substantial number of devices are installed in an individual
signaling line circuit, a considerable amount of time could elapse
until an alarm is processed. Present control panel standards
require a maximum of seconds for a panel to process an alarm after
it is received from an initiat-ing device. The development of
sensors that will operate in a cluster mode has made this an easier
matter. However, it is common to use a larger number of SLCs with
fewer devices installed on them rather than have one huge SLC with
numerous devices.
The addressable system is also pro-grammed to make specific
responses depending on the device activated. Thus the system can
process an alarm from a sensor with complete alarm re-sponse
including notification of the fire department and operation of
elevator capture devices, operation of smoke dampers, etc. It may
also process a su-pervisory signal from a tamper switch with
sounding of dedicated appliances only, or indicate that a control
module has been activated and has performed its required
function.
Now that we have described the basic operation of both
conventional and ad-dressable fire alarm controls, our next
installment will concern itself with smoke detection.
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THE ABC'S OF FIRE ALARM SYSTEMS - IV (2009)
Anthony J. Shalna
SMOKE DETECTION
Unlike heat detectors or sprinkler heads that rely on detection
of excessive heat for their operation, the basic purpose of smoke
detectors is to save lives. The secondary purpose is to save
property, especially in conditions where there is considerable
smoke build-up and the smoke could do as much or more damage than
fire before sufficient heat is generated to actuate sprinkler heads
or heat detectors.
With the advent of microprocessor-based smoke detectors, the
science of smoke detection has expanded with no end in sight.
Information published today will definitely be surpassed in the
near future, limited only by the ingenuity of the manufacturers and
cutting edge microprocessor technology.
RUDIMENTARY SMOKE DETECTION
The smoke with which we originally were concerned for many years
had as its signature, both the visible and invisible particles
emanating from combustion. The particles given off nearest to the
flame are hot and invisible. As the distance from the flame
increases, the particles cool and combine, or agglomerate, so they
become visible to the naked eye. Thus they possess less "thermal
lift" than the hotter particles. Thermal lift causes smoke to rise.
Additional signatures that were beyond the state of the art until
recently, were thermal output, carbon monoxide components, infrared
radiation and carbon dioxide components.
CONVENTIONAL SMOKE DETECTION TECHNIQUES
Conventional smoke detection falls into two basic techniques at
present, ionization and photoelectric. Conventional smoke detectors
at present make use of these techniques. However, the expanding use
of microprocessors is rapidly changing this picture and Im sure it
will change drastically in the future. Conventional smoke detectors
latch-in at alarm and require resetting by interrupting the power
source momentarily.
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IONIZATION PRINCIPLE
As stated above, one of the basic signatures of smoke is the
generation of particles of combustion. The conventional ionization
detector is concerned with these. This detector contains a
radioactive source, usually a minute amount of Americium 241, which
bombards the air between two plates, or electrodes in a detection
chamber, ionizing the air in the chamber, making it conductive.
Since this ionized air is conductive, if a voltage is applied to
the plates, a current will flow between them. When particles of
combustion enter the chamber, they adhere to the ionized air
molecules, neutralizing them so they are no longer conductive, and,
simplistically speaking, interrupt or decrease the current flow in
the sensing chamber. Detector circuitry senses the decrease in
current and puts the detector into an alarm condition. Note the use
of fail-safe technology, which is the keystone of fire alarm
systems. Ionization detectors respond best to the invisible
particles of combustion. In simplistic terms, ionization detectors
smell smoke, rather than see it.
PHOTOELECTRIC PRINCIPLE
The conventional photoelectric detector uses an entirely
different detection approach. This detector contains a smoke
chamber that houses a light source, usually an infrared LED, which
emits a light beam. The chamber also contains a photocell that is
placed at an angle to the light source so it cannot normally see
the light.
If you go outside at night and shine a flashlight into the air,
the flashlight beam will be invisible unless there is smoke, fog,
mist or dust in the air. If any of these factors are present, the
light beam becomes visible to the eye because these conditions
scatter the light so it can be seen. This is also the case with the
photoelectric detector. Introduction of visible smoke (usually
3%/ft. obscuration of gray smoke) in the chamber scatters enough
light so the photocell can see it and register an alarm. Most
photoelectric detectors use verification techniques of some sort.
The most common technique is to flash the LED at a fixed rate. If
the photocell sees light, the flash rate usually increases. If a
predetermined number of accelerated flashes still reveal scattered
light, the detector goes into alarm. Some detectors may reset
themselves between verification flashes while
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others may not. The verification (flash) rate varies widely
between manufacturers and models.
Recent advances in microprocessors have resulted in one
manufacturer developing a detector that is normally set to very low
sensitivity to minimize unwanted alarms. Upon detection of traces
of other signatures, such as carbon monoxide, etc. it automatically
increases its sensitivity to a high level placing it in a high
state of readiness in the event of alarm conditions.
In simplistic terms, photoelectric detectors see smoke rather
than smell it.
DETECTION STYLES As in the case of heat detection, smoke
detection styles in common use today are "Spot" detection and
"Line" detection. With "Spot" detection, a detector is placed so
that it protects an area or "spot", while the "line" detector
protects an elongated path. Other methods of smoke detection, such
as air sampling and video smoke detection are in use. However since
the above-mentioned techniques comprise the vast majority of smoke
detector installations today, we will presently concern ourselves
only with these.
SPOT DETECTION Spot detectors typically cover an area up to 900
square feet, (30 foot centers) based on smooth ceilings 15 feet
high, and with minimal air movement. This spacing is based on the
smoke detector manufacturers recommendation. Extensive engineering
studies are presently being conducted to determine the validity of
this spacing and results of the studies may alter these
spacings.
LINE DETECTION Line detection smoke detectors at present consist
of projected beam smoke detectors. These detectors rely on a
slightly different approach from spot detectors inasmuch as the
beam detector depends on a gradual obscuration of the light beam
with a sudden obscuration causing a trouble condition. These
detectors will be covered in greater detail in a future
article.
TEST REQUIREMENTS All photoelectric and ionization detectors
used with fire alarm control panels meet requirements of ANSI/UL
Standard 268.
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Smoke detectors intended for residential use are tested to a
different standard, ANSI/UL217, and differ in operation slightly.
While system detectors usually latch or lock in when alarmed,
requiring reset at the control panel, residential detectors usually
self-restore. These detectors usually contain an audible alarm
signal, and so are better described as smoke alarms.
ADVANTAGES AND DISADVANTAGES Ionization detectors, because they
detect small or invisible particles of combustion that by nature,
are hot, respond more readily to fast, flaming fires or fires in
their incipiency. One of the weaknesses of this type of detector is
that over-heated metal cookware, exhaust from internal combustion
engines (gasoline or diesel powered), aerosols from sprays, even
strong fumes, such as from ammonia, all produce particles similar
to products of combustion, causing unnecessary alarms. There are
legendary tales 25 or 30 years ago, of alarms caused when
ionization detectors were originally installed in racing stables.
When a horse urinated, it caused the ionization detectors to go
into alarm! These weaknesses caused no end of serious problems also
around the same time when ionization detectors were widely used in
household applications. Cooking odors caused numerous unwanted
alarms causing occupants to disconnect these detectors or remove
the batteries and then forgetting to place them back in service.
Inevitably, in many instances, when actual fires later broke out
fatalities resulted due to detectors being disabled. Different
manufacturers have been able to overcome some of these difficulties
to various extents but the problem remains, overall, a generic one.
Additional problems also encountered in past years which have been
overcome to an extent, resulted from high air velocity and also
from burning polyvinyl chloride (PVC) which gives off large amounts
of dense, cold smoke but contains few invisible (hot)
particles.
Photoelectric detectors, because of their ability to detect
scattered light, react to visible (gray) smoke, and are quite
immune to problems caused by invisible particles resident in their
environment. However, they are also affected by anything that
scatters light in the same manner as visible smoke, such as steam,
fog or dust. In addition, miniscule insects in some areas have had
a tendency to set up housekeeping in the smoke chamber despite use
of insect screens. These insects may grow rapidly, often in a
period of hours. Their physical presence, cobwebs, etc. scatter
light and can be a source of unwanted alarms. Photoelectric
detectors also have difficulties with black smoke, since black
smoke obviously doesn't scatter light.
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CONFIGURATIONS Conventional smoke detectors are also sub-divided
into two configurations, 2-wire and 4-wire. Both configurations
have their advantages and disadvantages. The 4-wire detector
requires an extra pair of conductors which furnish operating power
to the detector. These are in addition to the initiating circuit
wiring. The detector may operate on either the ionization or
photoelectric principle, and contain a relay that energizes upon
alarm. The dry contacts of this relay connect to the system
initiating circuit in the same manner as a pull station. Since the
power to the detector is unsupervised, an end-of-line (EOL) relay
is connected to the last detector on the voltage supply circuit.
(This may not necessarily coincide with the initiating circuit
wiring, so care must be exercised here.) If the voltage supply
wires are tapped off another supply circuit, an end-of-line relay
must be connected to the end of each branch. This EOL relay
contains contacts which are normally closed while the relay is
energized and open when the relay de-energizes (due to power
failure). The contacts of this relay are connected in series with
the end of line device on the initiating circuit so a power
failure, breaking of the power circuit, or removal of a smoke
detector will cause an initiating circuit trouble signal. The
2-wire detector also connects to the system initiating circuit but
uses the initiating circuit supervisory current as its source of
operating power. In alarm, the detector draws enough current to
cause the circuit to go into alarm. It cant place a short across
the circuit since this would leave no current to light the alarm
LED in the detector and absence of current would cause the detector
to reset itself, then again energize into alarm, and reset itself,
causing it to act like a vibrator or buzzer. Because the detector
draws current from the initiating circuit, usually in the range of
microamperes, it also stands to reason that there is a limitation
as to the quantity of detectors that can be supported by a circuit.
If the detector impedance is too low, the total impedance of a
large number of detectors could draw enough current to put the
circuit in alarm. Another possibility is that the impedance could
also be low enough that a break in the circuit could go undetected,
as the impedance would fool the circuit into thinking that an EOL
resistor was still connected to it. The situation becomes more
complex when one realizes that the amount of current the detector
draws in alarm may not be enough to place the initiating circuit in
into alarm, since both detector and initiating circuit possess
their own peculiar response curves. This presents us with the
problem of compatibility.
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COMPATIBILITY Since 4-wire smoke detectors require a separate
source of current, until lately any NRTL Listed four-wire smoke
detectors may be used with any NRTL Listed control panel with
similar operating voltage if the failure of the operating power is
supervised. Lately however, the NRTL Standards are in the process
of being changed since a situation was uncovered not long ago,
where a control panel by one manufacturer, in worst case
conditions, didnt provide sufficient voltage to power a 4-wire
smoke detector. Care should be taken, also, that the particular
model of detector does not require current filtering or regulation
which the panel may not be able to provide.
2-wire detectors, because of considerations listed above present
an entirely different problem. NRTL requirements state basically
that two-wire detectors cannot be connected to control panels
unless they are Listed as compatible with that model of panel.
Compatibility testing is performed or confirmed by the NRTL, and
compatibility identifiers must be displayed both on the detector
and initiating circuit module in the panel. The suitability of
two-wire smoke detectors for use with any control panel is
determined very simply. The manufacturer lists all compatible
detectors either in the Installation/Operating Manual or in an
official Compatibility Document, with the admonition to use only
the detectors listed in the document. If the detector is not listed
in these publications, it is not compatible.
Another means of establishing compatibility is by the back door
compatibility method. A smoke detector manufacturer purchases a
number of different control panels, tests his detectors with these
panels and has the test results confirmed by an NRTL. The smoke
detector manufacturer then will also publish a compatibility
document. The writer feels that the safest course to take in this
instance is to use only detectors specified by the control panel
manufacturer. In the event of a major disaster, the question of
liability will eventually be established by the courts. The panel
manufacturer will disclaim all responsibility if the detectors
installed are not those specified in his manual. This will lead to
any other parties having to bear a much greater burden of
proof.
2-WIRE ELECTRONIC HEAT DETECTORS Electromechanical heat
detectors have been previously covered in this series, but we
avoided discussing thermistor and
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microprocessor type heat detectors until now. Electronic heat
detectors operate on the ability of an electronic component, the
thermistor, often in conjunction with a microprocessor chip, to
change resistance when exposed to heat. The resistance change is
measured in a bridge type circuit in the detector, which places the
detector into alarm when a specific temperature is reached. This
detector operates in the same manner in the control panel
initiating circuit as the 2-wire smoke detector. Therefore, these
units must also meet compatibility requirements.
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ADVANTAGES AND DISADVANTAGES
Four-wire detectors have the disadvantage of requiring an extra
pair of voltage supply wires and installation of an end-of-line
relay at the end of each voltage branch. The detectors and the EOL
relays also consume current, and this has to be taken into
consideration when calculating the size of the standby batteries.
However, compatibility with the control panel is not presently a
problem, although this may change as noted above. Since dry
contacts are employed, there is virtually no limitation to the
number of detectors that can be connected to an initiating circuit.
In addition, the detector alarm relay can contain auxiliary
contacts which will reliably perform any intended auxiliary
function, regardless of how many detectors on the same circuit are
in alarm condition. The four-wire detector is preferred for use in
duct detectors since these detectors are often used for a number of
smoke control functions in addition to just turning in a single
alarm. Two-wire detectors draw miniscule amounts of current and
dont require end-of-line relays, so they have minimal effect on the
size of standby batteries. Installation costs are lower since only
two wires are required, and they lend themselves to retrofit
(replacing heat detectors) using existing wiring. However, NRTL
compatibility requirements come into play now, and because of the
loading on the initiating circuit in an alarm condition, their
ability to perform auxiliary functions is severely limited. Also,
because of this loading, there is a definite limitation regarding
the quantities of detectors which can be installed on a single
initiating circuit, and in many cases, the number is reduced
further when Class A, Style D circuits are involved. Some models
contain auxiliary relay contacts or have them in their bases, but
these contacts may not transfer if other devices on the initiating
circuit are in an alarm condition, especially dry contact devices.
Therefore, two-wire detectors are recommended mainly for putting an
initiating circuit into an alarm condition, and not to perform
auxiliary functions.
VERIFICATION CIRCUITRY (CONTROL PANEL) Verification circuitry in
a fire alarm initiating circuit introduces a delay period into the
smoke detector operation that could diminish unwanted alarms caused
by transient conditions. ANSI/UL Standard 864, which covers Fire
Alarm Control Panels, contains the regulations governing use of
verification circuits. Per this standard, initiating circuit
verification can only be used with smoke detectors that have a
verification (flash rate) time of less than 10 seconds.
Verification can be used with
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either 2-wire or 4-wire smoke detectors, although the use of
verification with 4-wire detectors is unknown, since verification
cannot be used with open contact devices. Many control panels with
verification circuitry can differentiate between two-wire smoke
detectors and open contact devices. With open contact devices, the
verification sequence is usually automatically by-passed. Per
ANSI/UL 864, a verification circuit has a sequence that operates
like this: When one detector goes into alarm, the cycle begins with
a 20 second pre-alarm window. The panel shows a trouble condition
during this period, with the trouble light usually flashing. This
window is followed by a 4 second automatic reset time (the trouble
light usually stays lit constantly at this time), followed by a 100
second alarm verification window (flashing trouble light). The
alarm verification window holds the circuit in the pre-alarm state,
waiting for the first alarm to repeat itself. If a subsequent alarm
comes in during this period from the pre-alarmed detector (or any
other detector in the circuit), a system alarm will occur. If an
alarm is not received within the 100 second period, the panel
returns to normal condition. Its my opinion that the expanding
application of microprocessors will eventually increase detector
reliability to the extent that the verification requirement will no
longer be necessary.
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DUCT DETECTORS Duct detectors are used primarily to prevent the
spread of smoke in a ventilation system by shutting down the HVAC
system in case of fire. They should not be used as a substitute for
area detectors because smoke may not enter the ducts if the HVAC
system is shut down. Duct detection techniques usually involve
either ionization or photoelectric spot detectors mounted in a
housing fastened to a wall of the duct. Perforated or slotted tubes
extend from the duct housing through the wall of the duct and
extend across the duct. These tubes, commonly referred to as
"sampling tubes", allow air flow from the duct to be channeled into
the detector housing and detector. Duct detectors are used in
systems with airflow greater than 2,000 cubic feet per minute
capacity and are usually rated for air velocities of roughly 500
FPM to 3,500 FPM, although recent advances in technology may alter
this. Spot detectors also have a velocity rating that can range up
to 3,500 FPM depending on the model, etc. In the event of physical
difficulties (duct too small) in mounting a duct detector, or if
the air flow in a duct is too low for sampling tubes, a spot
detector may be mounted inside the duct as long as it has a listed
air velocity rating compatible with the air velocity in the duct,
has a remote alarm indicator, and it can be readily tested in place
or remotely. Care should be taken in determining the air velocity
rating of a detector, as different manufacturers use different
terminology. For example, a detector rated at 300 FPM might be
capable of turning in an alarm at that velocity, while another
manufacturer might rate a detector at 2,000 FPM meaning that the
detector will be stable (will not false alarm) at that velocity.
The detector might not be able to turn in an alarm at that
velocity, however as the smoke may not linger long enough to create
an alarm. A spot detector mounted in a duct is also subjected to
contamination and therefore the maintenance intervals should be
reduced.
APPLICATIONS The comments given in the advantages and
disadvantages paragraph above give guidance in regard to
applications. As in the case of suppression systems, the detectors
should be chosen in regard to the fire load, or what type of fire
would be expected to occur in the area being protected. If a
smoldering fire could be reasonably expected to occur, such as in
the case of dormitory or hotel occupancies, a photoelectric
detector might be the best choice. If a fast flaming (or arson)
fire could be expected, an ionization detector would provide the
quickest response. In the case of computer rooms, a mix of both
types is often used.
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LIMITATIONS "Spot" type smoke detectors are limited by Standard
to indoor operation between 32oF and 120oF, and maximum relative
humidity of 90%. Areas of installation should be relatively clean.
Detectors in an ambient outside these parameters may or may not
function properly as high ambient temperatures may cause detectors
to "go to sleep" or conversely, cause the unit to go into alarm.
Any environments outside the prescribed parameters are referred to
as "hostile" environments.
TESTING According to Standard, smoke detectors should be tested
in accordance with manufacturers' instructions. Some of these
manufacturers are very insistent that testing be performed
according to their instructions, and in many cases, prohibit use of
other methods or application of foreign substances, going so far as
to invalidate warranties and disclaim all responsibility and
liability if instructions are not followed explicitly.
ADDRESSABLE AND ANALOG ADDRESSABLE SMOKE DETECTION. Addressable
or analog addressable Smoke detectors are commonly referred to as
smoke sensors since they are microprocessor based and used only
with intelligent or analog addressable fire alarm controls. Recent
advances in detection technology make this a major topic in itself
that will be reviewed in a future article.
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January/February 2010 Page 7
The ABCs of Fire Alarm Systems - Part V Putting It All
Together
By Anthony J. Shalna 2009 Principal IMSA Representative to the
Automatic Fire Alarm AssociationPresident: Southeastern Signalmen
of Massachusetts
Approvals Manager: Gamewell-FCI by Honeywell
In previous articles we discussed the fire alarm control panel,
devices that place it into alarm and the most com-mon devices that
are turned on by the panel. The main feature that distin-guishes a
fire alarm control panel from burglar alarm or switching panels is
that the fire alarm panel is supervised, which means that it has
the ability to monitor its own integrity.
Unlike the burglar alarm panel, which has only two conditions,
normal and alarm, the fire alarm control has a number of conditions
or states. These are: normal, alarm, trouble, and (fairly recently)
supervisory. The normal and alarm states are obvious.
The supervisory state monitors sprin-kler devices so the panel
can indicate that a waterflow device, such as gate valve, is in an
off-normal condition. It is desirable to know that someone turned
off the water supply to a sprinkler sys-tem (or forgot to turn it
back on after service), but there is no need to create an alarm
condition. Other supervisory devices can monitor water tanks for
freezing, low or high water levels, etc. The supervisory condition
results in a signal that differs from both alarm and trouble
conditions, although the supervisory condition may share the
trouble sounder.
The last state or condition is the trouble condition. This
condition is character-ized by a yellow light on the panel
accompanied by the sounding of an au-dible device, such as a buzzer
or piezo-electric sounder, which may be silenced or acknowledged
temporarily. Upon correction of the trouble condition, the sounder
will re-energize, indicating that the panel is back to normal.
Re-turning the silencing switch to normal or pressing the
acknowledgment button will silence the sounder and return the panel
to a quiescent condition. This is known as ring back, a phrase that
was common in the past, but not used very frequently nowadays.
Trouble signals are caused by numer-ous things. Some of these
are a break
in the field wiring, AC power failure, battery disconnection or
failure, ground faults, open fuses, removal of plug-in detectors,
disarrangement of panel switches, etc.
We have seen how supervised circuits of conventional fire alarm
panels oper-ate with the aid of end of line devices that maintain a
current flow through the supervised circuit. Addressable systems
operate in a different man-ner and will be the subject of a future
article. The current flow through the supervised field circuit must
be maintained through the field wiring. This is why conventional
fire alarm systems must be wired in a prescribed manner.
Terminations to a detector or appliance must be made by cutting
the field wires at their respective terminals. In other words, one
wire must bring current into a terminal of the detec-tor or
appliance, and a second wire must exit from the same terminal and
connect to the next device. See Figure 1. If a field wire is not
cut, but looped around a screw, there will be no interruption of
the su-pervisory current should the head of the screw shear off.
The device will be disconnected from the circuit but there will be
no trouble indication. The panel will never know that the device is
disconnected. If the field wire is cut and both ends connected to
two separate terminals, the shearing of a screw head or loss of a
wire crimp lug will cause the ends to separate and a trouble
condition will immedi-ately result.
One termination method is to have two screw terminals on the
same
metal terminal plate with the plate providing continuity between
the screws. See the illustration at the bot-tom of Figure 1. Thus
the in wire will connect to one screw and the out wire to the
second. Pressure plate terminals are also widely used. Two wire
ends are stripped and inserted under a pressure plate. A screw
holds the plate down and maintains continuity between the wires.
See Figure 2 for a description of the proper and improper
terminations with this type of terminal.
Another method of termination is with four () pigtail
connections, two for the in wiring and two for the out wiring. See
additional illustrations in Figure 2 for both improper and proper
methods of connecting the pigtails. An X shows the unsupervised
wire which, if cut, will remain undetected.
Continued on page 48
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Page IMSA Journal8
The ABCs of Fire Alarm Systems Part V . . . Continued from page
47Wiring to initiating devices in a conventional system or
notification appliances in addressable or conventional sys-tems
must be made in an in and out fashion. Branching or T-tapping is
not permitted in these circuits. Again, the reason for this is that
the current must flow in and out of each device and finally through
the end of line device so supervi-sion is maintained. Therefore,
removal of a device from the circuit or a break in the wiring will
interrupt the supervisory current and create a trouble condition.
If a T-tap is used, a break in the T-tap branch will go undetected,
since the supervisory current will not be interrupted. Figure 2
also shows both proper and improper methods of connection. An X
indicates a break that will go undetected.
Note that T-tapping is permitted in an addressable system, since
the microprocessor polls all addressable devices and will promptly
detect a missing device.
A third method of wiring is commonly used with plug-in style
two-wire conventional smoke detectors. One wire goes in and out of
one base terminal, usually a pressure plate type of terminal. The
other wire connects to a second terminal in the base and exits from
a third. The detector has a built-in jumper that maintains contact
between the second and third terminals, so if the detector is
unplugged, it will cause a break in the wiring resulting in a
trouble signal.
The type of wire used for field wiring should conform to the
codes in effect in the area. These codes are almost always based on
Article 70 of the National Electrical Code, NFPA 70, but some
states make additional requirements. One state not only specifies
the acceptable types of wire, but also speci-fies the insulation
color, with DC power, initiating circuit wiring, initiating circuit
return (Class A) wiring, notification appliance circuits, etc. all
having different insulation color requirements! The prudent thing
to do is to consult with the Authority Having Jurisdiction, such as
wiring inspector, fire marshal, etc.
Until recently, solid or bunch-tinned stranded wire, 18 gauge
minimum, UL Listed for fire alarm use, were the only types of wire
acceptable for fire alarm. The reasoning behind this requirement
was that solid or bunch-tinned stranded wire would be most likely
to break cleanly, giving an instant trouble indication. If a
stranded cable were to be damaged, leaving only one strand intact,
the one strand would conduct supervisory current and maintain
normal operation. During alarm, a notification appliance circuit
could draw enough current to burn out the single strand, with a
resultant failure at the most critical time. Now the NEC contains
exceptions allowing stranded wire under certain circumstances. In
addition, communication cable is also allowed in certain
instances.
Power limited and non-power limited wiring also comes into
account. There is no hard and fast simple rule about what types of
circuits are power limited. The only way an installer can make this
determination is that power limited and non-power limited
designations are printed by the manufacturer on the control panel
door label or on the ter-minals themselves. A typical label might
state: All circuits are power limited with the exception of the AC
input, battery
and city box connection.
Again, consult the local Authority Having Jurisdiction about the
wire hierarchy chart in the NEC, if your State Code is based on the
NEC.
Improper Termination Proper Termination
Figure 1
Figure 2
Fire Alarm Control Panel
Fire Alarm Control Panel
End of Line Device
End of Line Device
Smoke DetectorSmoke Detector
Smoke DetectorSmoke Detector
Pigtail ConnectionsCorrect Wiring Method Pigtail
ConnectionsIncorrect Wiring Method
Correct Wiring Method
Incorrect Wiring Method
-
Page IMSA Journal2
The ABCs of Fire Alarm Systems - Part VIBy Anthony J. Shalna
2009 Principal IMSA Representative to the Automatic Fire Alarm
Association
President: Southeastern Signalmen of MassachusettsApprovals
Manager: Gamewell-FCI by Honeywell
NOTIFICATION APPLIANCESSo far, we have covered the basic
operation of control panels and the initiating devices that place
the pan-els in an alarm condition. We are now going to review the
notification appli-ances that are energized or turned on by the
control panel.
The term notification appliance cir-cuits has undergone somewhat
of an evolution in the past few years. These were designated for
many years as signal circuits, alarm circuits, and also indicating
circuits. Revi-sions to NFPA Standards a few years ago adopted the
term notification appliances and notification appliance circuits
(NACs) to avoid confusion and misunderstanding and also to
differentiate them from the commu-nication circuits used by
addressable fire alarm systems.
Notification appliances are divided into two very basic
categories, au-dible and visual. Obviously, the audible appliances
make loud noises and the visual appliances flash bright lights.
Recently, tactile devices have been developed for the hearing
im-paired, but are used at the present only in very specialized
applications and only as a secondary or ancillary unsupervised
device. One example of this would be a bed shaker which is used to
awaken the hearing impaired.
AUDIBLE APPLIANCESInstalled audible notification ap-pliances
should differ from other audible devices in use in the area. For
example, if a school uses bells to signal the start of classes,
bells should not be used as notification appliances in that
building.
The most widely used audible appli-ance is the horn. Horns
presently on the market employ both electro-mechanical and
electronic designs.
Electromechanical horns have been used for many years and are
con-structed using a set of breaker points and diaphragm. These
horns are capable of providing a surprisingly loud sound output,
but have the dis-advantage of the mechanical breaker points
oxidizing, corroding, or going out of adjustment. In addition, the
loud output requires a substantial amount of current to do the job.
Other disadvantages are that only one tone is available, the
breaker points create spikes which can be transmitted back to the
control panel, and elec-tromagnetic interference (EMI) can be
radiated from the area where the horn is sounding. Manufacturers
have designed their horns to minimize these problems, but EMI in
the past has been known to cause unwanted alarms from smoke
detectors located immediately in front of the horn.
One of the newest developments in this area is the electron-
mechanical horn which uses the old familiar dia-phragm, but has an
electronic circuit in place of the breaker points, much in the same
manner as electronic ignition replaced the old automobile breaker
points. This type of horn has the advantage of generating
substan-tial sound output without the inher-ent disadvantages of
breaker points.
Electromechanical disadvantages led to the development of solid
state horns, which mostly operate on a piezo-electric principle.
These horns offer good sound output combined and have a much lower
current draw. They also offer a variety of tones, with siren,
steady or warbling tones being commonly available, often by merely
selecting the proper jumper position inside the enclosure. The
disadvantages of electronic horns presently on the market are their
loudness and the fact that many electronic horns are not suitable
for weatherproof use. The loudness of these horns is measured at a
higher frequency than the electro-mechanical horns. While the
decibel measurements are comparable, in actual applications the
electronic horns sometime are not as audible to the average human
ear, or especially to people with deteriorating hearing. Recent
research indicates that a lower frequency tone, in the vicinity of
20 Hz is heard much more readily by people with deteriorating
hearing. Sound output, of course, is dependent upon building
construction, layout, furnishings, etc.
The latest fire alarm requirements require a temporal pattern
which requires the notification appliances to sound three rounds of
three blows each, with specified intervals between blows and rounds
of code. Temporal patterns are usually programmed at the factory by
the panel manufacturer and the installer need not be not be
concerned with the proper time du-ration of the blows and rounds.
The most the installing technician need be concerned with is
selecting the proper jumper or programming the panel to provide
this sound pattern.
Bells have historically been associated with fire alarms and are
still in use
Continued on page 53
Horn Strobe
-
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The ABCs of Fire Alarm Systems Part V . . . Continued from page
52today, although their use is rapidly decreasing due to the
Temporal Pat-tern requirements. Bells presently in use usually
range from to 10 inches in diameter.
Most bells encountered today are made in vibrating, motor-driven
or single stroke variations with vibrating or motor driven bells in
the majority. The single stroke bell is suited only for march time
or coded applications (including tem-poral pattern) as it emits a
louder, cleaner sound than a vibrating bell. The disadvantage is
that it draws considerably more current than the vibrating or
motor-driven bells and cannot operate on uninterrupted or non-coded
current, as the bell would give one blow and then hang up.
Vibrating bells draw moderate amounts of current, while motor bells
usually draw less cur-rent. A disadvantage of the motor driven bell
in the past was the ten-dency of the motor to stick or bind because
it sat idle for long periods. To be sure, present manufacturers
again have overcome many of the shortcomings, but these problems
are inherent in the principle of op-eration. Vibrating bells do not
lend themselves readily to Temporal Pattern signaling.
Chimes operate in the same man-ner as bells, and are usually
con-structed similarly to bells, using the same mechanism, only
with a chime kit mounted in place of the gong shell. Chimes do not
have adequate sound output for use as general evacuation
appliances, but are mostly used in hospitals, etc. as prealarm or
presignal devices to alert available personnel that an emergency
exists and a general evacuation may be imminent.
The last audible appliance is the loudspeaker. Obviously, these
are intended for voice evacuation systems, and must be listed by a
Nationally Recognized Testing Lab-oratory (NRTL) for fire alarm
use. Speakers are installed in supervised circuits and the great
majority are used in high-rise buildings where
selective evacuation is necessary due to the difficulty of
evacuating a building completely in an emergency. The results of
the 9-11 disaster indicate that this prac-tice is far from being
resolved and much effort is now being dedicated to mass
notification measures. Emergency voice evacuation and mass
notification systems will be discussed in a future article.
Continued on page 54Speaker Strobe
-
Page IMSA Journal
The ABCs of Fire Alarm Systems Part V . . . Continued from page
53VISUAL APPLIANCESVisual appliances employed in the past included
flashing incandescent lights and various types of strobe lights.
With the advent of the Ameri-cans With Disabilities Act, (ADA),
only high intensity strobes are ca-pable of producing the light
intensi-ties required. The ADA guidelines (ADAAG) have been updated
in the recent past, are quite complex, and have been the subject of
many lectures and much discussion. There was great confusion in the
early days of the ADA, since the ADA is a federal law, enforceable
basically in court, and local code enforcement officials had no
authority to either approve or interpret the ADA. In fact, these
requirements have been the subject of entire publications and are
beyond the scope of this article. Many state codes have been
harmonized in ac-cordance with ADAAG guidelines, so now meeting
these codes also satisfies the ADA, but not all codes have been
updated in this fashion. Anyone planning to become involved with
the layout of fire alarm systems is well advised to consult one or
more of these publications.
And now to return to strobe lights. These have a high intensity
out-put, with some providing a light intensity as high as 110
candela. Light intensity levels are defined as CANDELA (effective
candlepower) which is the measuring criteria per ANSI/UL Standards
1638 and 1971, and is defined as the average light output generated
during one flash cycle. This should not be confused with peak
candlepower which is im-mensely greater. Before strobes were
standardized, some manufacturers used peak candlepower figures in
their literature which led to some confusion.
Other strobes in common use are rated as 1/7 candela, as they
emit a 15 candela flash when viewed from the side, but exhibit 7
candela when viewed directly.
Both the fire alarm designer and in-staller should be aware of
one prob-lem with strobes. A strobe flash rate
greater than 1 Hertz per second could induce epileptic seizures
in persons afflicted with this disorder. There-fore, the ADA
mandates a flash rate between 1 and Hertz/second. If two or more
strobes are observable from a single location, synchronization of
the strobes is necessary to meet this requirement. Microprocessor
based panels currently on the market are designed to meet this.
The other important thing to remem-ber when using strobes is
that the high intensity light output is directly related to current
consumption. In many cases, the quantity of strobes required for an
installation may ex-ceed the capacity of a smaller control panel
which might have a limited number of notification appliance
circuits. Many of these circuits are commonly rated at 1.7 amp.
maxi-mum per circuit with a total panel limitation being somewhat
less, such as a maximum of amperes for both circuits combined. It
doesnt take many strobes at .2 amperes each to exceed the capacity
of such a circuit. In these instances, a larger panel or NAC
extender panel will be required. These supply additional
notification appliance circuits and correspond-ingly larger power
supplies. Strobe lights depend on the charging and discharging of a
capacitor to flash their xenon flash tube. If the current to the
strobe is interrupted or pulsed, it could interfere with the proper
operation of the strobe. Micropro-cessor-based controls and
extender panels are designed with provision for synchronization of
strobes and temporal patterns for the horns.
Strobes are most often mounted on horn and speaker covers so
both the audible and strobe comprise a single unit. This makes for
simpler wiring and combines both into a compact package. Strobes
are also available in stand alone configurations and ceil-ing
mount, although ceiling mount units do not at present completely
meet ADA requirements, as the light intensity requirements are
based on the strobes being observed directly, something difficult
to do with an overhead device. Strobes are also
available on plates which accommo-date bells or chimes, so they
can also be installed in one package.
Some jurisdictions require (errone-ously) that only the audible
appli-ances can be silenced after an alarm with the strobes
continuing to flash until the panel is reset. This practice has
been criticized recently, as flash-ing strobes indicate an
evacuation signal to the hearing impaired.
COMPATIBILITYUntil fairly recently, compatibility was not an
issue as far as notifica-tion appliances were concerned. The
devices merely had to have the same nominal operating voltage as
the noti-fication appliance circuit. The advent of microprocessor
panels has resulted in some control panels operating at somewhat
higher voltage levels, resulting in instances, depending on the
supply line voltage to the panel, where the operating voltage was
outside the range of some notification appliance. This, in addition
to flash synchronization requirements makes it necessary for
strobes and horns to be tested for compatibility with indi-vidual
control panels. If there is any question about device
compatibility, the panel installation manual or man-ufacturers
compatibility document will list the compatible devices.
The only exception to this compat-ibility requirement is for
loudspeak-ers. There are no existing require-ments at present. The
main thing to remember, however, in the case of strobe/speaker
combinations, the strobe is still subject to compatibility
requirements.
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Page IMSA Journal2Continued on page 26
The ABCs of Fire Alarm Systems - Part VII Advanced Smoke
Detection
By Anthony J. Shalna 2009 Principal IMSA Representative to the
Automatic Fire Alarm AssociationPresident: Southeastern Signalmen
of Massachusetts
Approvals Manager: Gamewell-FCI by Honeywell
Line detection techniques use a projected beam of light that
covers an elon-gated path. Therefore, all line type smoke detectors
are of the photoelectric projected beam design. The typical
projected beam detector consists of a light source (transmitter), a
light beam receiver and a re-ceiver control which may or may not be
combined in the same housing with the receiver. The latest beam
detectors now in-corporate both transmitter and receiver in the
same housing, with a mirror or reflector placed at the far end of
the path to be covered. The majority of units on the market are of
the four-wire configura-tion. That is, the receiver control
requires power from the control panel or power supply, usually
contains both alarm and trouble dry contacts and is wired to an
initiating circuit in the same manner as a four-wire spot detector
except that an end-of-line relay may not be required, since the
receiver/control contains its own trouble contacts.
The light source projects a beam across a protected area. The
light beam is typically infrared, and in some cases is modulated,
to eliminate the possibil-ity of extraneous infrared radiation
interfering with the operation. If a smoke build-up causes a
gradual obscuration of the beam over a period of several sec-onds,
the receiver control causes the alarm contacts to transfer. An
abrupt in-terruption of the beam will cause a trouble
indication.
Thus the receiver can also perform the function of an
end-of-line relay so a trans-mitter power failure will be
immediately detected as an abrupt interruption.
At present, the projected beam detector protects ar-eas of up to
19,80 square feet (which is approximate-ly the coverage of 21 spot
type detectors) as opposed to the 900 square foot area typically
protected by spot detectors. Even though the width of the beam
might seem relatively narrow es-pecially at extreme ranges,
(typically up to 100 meters), the standard recognizes the tendency
of smoke to billow or mushroom as it rises, hence the large area of
protection. Thus the detec-tor is primarily concerned with
visibility of the beam over a long path, rather than with the
amount of smoke entering a spot de-tector smoke chamber.
Sensitivity of line detec-tors is expressed in terms of
percentage obscuration. One such detector will go into alarm upon a
0 to 90% obscuration of the beam for a period of or more seconds.
In comparison to spot detector sensitivities of 2-% per foot, this
does not sound sensitive at all. However, remember this obscuration
applies over an elongated path which could be over 00 feet long.
Therefore when expressed in terms of obscuration per foot, the
detector has a sen-sitivity which the standard lists as 0.2 to 2.%
per foot depending on the length of the protected area. Because the
projected beam detector works on an obscuration
basis and not on light scat-ter, the detector is color blind and
responds read-ily to black smoke.
Since line detectors must project a light beam, it stands to
reason that current consumption will be higher than that of a spot
detector. Attempts to alleviate this situation have met with mixed
success. One such method is to flash both the transmitter and
receiver simultaneously and thus drastically reduce current
consumption much in the same manner as spot detec-tors. Advanced
technology using microprocessors have largely overcome this
prob-lem, so both two-wire and intelligent addressable
configurations are now becoming common.
EnvironmentSince projected beam detec-tors are not dependent on
smoke chambers, most of the spot detector limita-tions do not
apply. Depend-ing on the manufacturer, ambient temperatures can
range from -22oF to 11oF, and some units are listed as waterproof,
so the trans-mitters and receivers may be hosed down to remove
contaminants. Most units are unaffected by presence of low levels
of contami-nants in the surrounding atmosphere.
Virtually all projected beam detectors contain AGC (Au-tomatic
Gain Control) cir-cuitry of one sort or another which makes
compensat-ing sensitivity adjustments in the event of build-up of
contaminants on the lenses. One such unit is capable
of making a number of periodic adjustments and then will cause
an intermit-tent trouble signal after the final adjustment. Various
manufacturers have shown different preferences in regard to the
length of the adjustment period, which may range from minutes up to
8 hours.