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August 10, 2003

                             ET NEWS
Issue No. 111           8-10-2003

- News
- ET Journal
- NICET Test Dates
- AFAA Class Schedule
- Comments & Acknowledgements


AFAA names new executive director

LAKE MARY, Fla. - Thomas Hammerberg, former vice president,
education for the Automatic Fire Alarm Association, has been
named president/executive director of the association, following
the death of the group's executive director, Larry Neibauer, in
late June.

Hammerberg, who has been with the association since 1994,
represents the AFAA on NFPA 72, National Fire Alarm Code,
Technical Committee of Inspection, Testing and Maintenance and
serves as the editor for that chapter in the 2003 National Fire
Alarm Code Handbook. He also sits on the executive board of
National Fire Protection Association's Building Fire Safety
Systems Section and is AFAA's representative to the International
Code Council Industry Advisory Committee.

Certified by NICET Level IV in fire alarm systems and a certified
fire protection specialist by the NFPA, Hammerberg is also
president of Hammerberg & Associates Inc.



I'll see you in Knoxville, TN this week

Have fun!



NICET Fire Alarm Systems Level IV

38007 is a Level IV Special work element.

Understand the theory of operation of smoke detectors of the
ionization, projected beam, aspiration, photoelectric, and cloud
chamber operating principle of operation. Know the proper and
improper applications of smoke detectors, the way each type of
smoke detector responds to a fire, and the methods used by
testing labs to determine the suitability of a smoke detector for
listing. (NFPA 72, UL-268, Fire Protection Handbook)



Fire Protection Handbook

"Understand the theory of operation of smoke detectors of the
ionization, projected beam, aspiration, photoelectric, and cloud
chamber operating principle of operation. Know the proper and
improper applications of smoke detectors, the way each type of
smoke detector responds to a fire, and the methods used by
testing labs to determine the suitability of a smoke detector for

Glossary of terms

An ionization smoke detector uses a small amount of radioactive
material to ionize the air in the sensing chamber, thus rendering
it conductive and permitting a current flow through the air
between two charged electrodes. This gives the sensing chamber an
effective electrical conductance. When smoke particles enter the
ionization area, they decrease the conductance of the air by
attaching themselves to the ions, causing a reduction in ion
mobility. When the conductance is below a predetermined level,
the detector responds.

Smoke detectors utilizing the photoelectric light-scattering
principle are usually of the spot-type. They contain a light
source and a photosensitive device so arranged that light rays do
not normally fall onto the photosensitive device. When smoke
particles enter the light path, light strikes the particles and
is scattered onto the photosensitive device, causing the detector
to respond. The photosensitive device used in light-scattering
detectors usually is a photodiode or phototransistor.

Smoke detectors utilizing the photoelectric light-obscuration
principle consist of a light source, which is projected onto a
photosensitive device. Smoke particles between the light source
and the photosensitive device reduce the light reaching the
device, causing the detector to respond. Most light-obscuration
smoke detectors are the beam type and are used to protect large
open areas. They are installed with the light source at one end
of the area to be protected and the photosensitive device at the

Cloud chamber smoke detection is accomplished by drawing an air
sample from the protected area into a high humidity chamber and
lowering the chamber pressure to create an environment in which
the resultant moisture in the air condenses on any smoke
particles present, forming a cloud. The cloud density is measured
by photoelectric principle. The density signal is processed and
used to convey an alarm condition when it meets preset criteria.
Cloud chamber smoke detectors are usually of the air-sampling

In addition to the cloud chamber smoke detection devices; there
are other smoke detection devices that actively and continuously
sample the air from a protected space. The air-sampling system
consists of sampling pipes spaced uniformly over the ceiling,
together with two supplemental pipes arranged to sample the
return air exiting from the monitored space. Each one of the
ceiling pipe drops is capped and has a small sampling hole
drilled in the cap to draw in a sample of air from that location.
There are also sampling holes drilled in the sections of the
supplemental pipes that extend across the return-air grilles.

This network of piping is connected to the detector/control unit
where there is a fan, or aspirator, that creates a flow of air in
the piping network. This airflow creates a pressure differential
between the area being sampled and the detector/control unit.

The sampled air is drawn through a filter to the detector
assembly. Inside the detector is a very intense light source that
irradiates the sampled air. If there are smoke particles in the
sampled air, the device, which can sense smoke particles in
extremely low concentrations, will activate the first of three
levels of alarm conditions.

These systems are typically used in applications where dollar
densities are very high, such as in electronic data-processing
areas and museums, or where equipment survival is paramount to
continuity of operations, such as in the communications industry.

By Les Shew, P.E. 
In certain high-value or critical areas susceptible to damage
from smoke, the detection of a potential fire in advance of
damage to equipment is vitally important. For example, many of
today's sophisticated telecommunications, computer and business
systems can be regarded as vital to particular operations. In
fact, even a minor interruption in service, or loss of data,
could seriously impact operational continuity. Through the use of
early fire detection technology available today, the performance
of fire detection features provided for these areas can be
greatly enhanced. The fire alarm system design engineer for
systems can apply the appropriate combination of such technology
to meet established performance goals, as part of an effective
protection scheme for the area.

Once system performance goals have been established, one of the
first considerations in developing an appropriate overall fire
protection scheme is selecting the type of smoke detection to be
provided. Developments in air sampling and laser detector
technology has resulted in systems that can detect extremely
small amounts of combustion particles provided by incipient
fires. These detectors can be more sensitive than conventional
smoke detectors depending upon the fire and physical
characteristics. We will present a brief review of the current
state-of-the-art technology in what has become known as "very
early smoke detection."

Detector Sensitivity
The sensitivity of a smoke detector describes the quantity of
smoke required within the detector to sense the presence of
smoke. The sensitivity of smoke detectors is measured by the
percent obscuration of a light source by smoke per unit length.
Increased sensitivity over the level of detection normally
provided by conventional smoked detectors is the key advantage of
"very early smoke detection" devices in detecting fires in their
incipient stages for unique applicators. 

Given the same conditions, a smoke detector with a sensitivity of
one percent per foot obscuration will operate before the same
detector with a sensitivity of four percent per foot obscuration.
Typical conventional smoke detectors can detect smoke in the
range of 0.4 to four percent per foot obscuration, whereas very
early smoke detectors detect smoke at levels as low as 0.003
percent per foot obscuration. Obscuration is somewhat related to
the size of smoke particles generated during combustion. However,
detectors available today actually can discriminate between smoke
particle sizes.

Air Sampling Smoke Detection
Smoke movement, especially cooler smoke produced during the
incipient stages of a fire, can be affected by the area's HVAC
system, which can cool or transport the smoke away from the
detector. For example, typical environments in certain protected
areas may be maintained at 70 to 75 degrees F and 45 to 50
percent humidity. High air change rates also can adversely affect
detector operation due to dilution effects. In summary, three
factors affect the responses time of a smoke detector: the path
available for smoke to travel from a source to the detector, the
extent of smoke dilution during its travel and the sensitivity of
the detector.

Spot-type detectors are "passive" devices, whereas air sampling-
type detectors are "active" devices. Conventional spot-type
detectors typically are installed on the ceiling or perhaps in an
underfloor space and must "wait" for a sufficient amount of smoke
to actually reach the detector before it activates. Air sampling
detectors use a network of piping or tubing to transport samples
of air in the protected zone to the detector. This protection
zone can be a room, an underfloor space or even the interior of
equipment cabinet enclosures. The sampling pipe is a commercially
available smooth bore pipe or tubing with airtight connections.

Typical materials used include PVC, CPVC, EMT or copper. The pipe
network can be concealed in the ceiling space with sampling
points consisting of short "capillary tubes" arranged to
penetrate the ceiling. The air-sampling network continually draws
air samples through the pipe network from the protected zone by
means of an integral aspirator. The aspirator includes air pumps
or fans to draw air continuously through the piping network to
the detector unit.

Once the air in the sampling tube reaches the detector unit, a
variety of technologies are used for detection varying by
manufacturer. One method is known as a cloud chamber, which
enables the detector to identify extremely small particles by
causing them to appear physically larger through a process
involving water condensation on the otherwise invisible
particles. This method allows for detection of an incipient stage
fire. A signal, which may be undetected by conventional spot-type
detectors in some scenarios. In this operation, water vapor
condenses in the chamber to form visible droplets, when solid
particles are present to serve as nuclei for condensation.

In very early smoke detection applications, optically invisible,
pre-combustion products act as the nuclei for water condensation.
The particles then grow to an optically measurable size and form
a visible cloud that subsequently can be seen by a photo-
detector. The density of the cloud is directly related to the
population of sub micron particles in the air sample which, in
turn, relates to the pre-combustion or combustion condition. The
cloud chamber method is very sensitive yet is not susceptible to
false alarms because dust or other particles contribute no more
to cloud density than the smallest combustion particle. The dust
particles entering the chamber are always much larger in size and
much smaller in number than products of combustion. The dust
particles are not able to develop a cloud dense enough to
generate a significant reading, therefore, they are not
susceptible to false alarms in the cloud chamber sampling system.

Another method of detection used by air sampling detectors is the
light scattering principle. The air is drawn through the sampling
tubes and into a specially constructed detector unit where it is
exposed to a broad-spectrum xenon light source. Light, scattered
by smoke particles, passes through a series of optical components
to an extremely sensitive solid-state light receiver. The
receiver converts the light energy into an electronic signal,
representing the level of smoke in the air sample. The receiver
sends this signal to the microprocessor where it is translated
and presented on a bar graph display representing alarm level

Typically, the alarm levels are determined by a microprocessor in
the control unit. This type of sampling detector uses a washable
filter to trap dust particles (20 microns or larger), while
allowing the smoke particles to pass through. These detectors
have been used successfully in many applications and are still in
service today. However, for newer installations, the xenon method
of light scattering is being replaced with the newer laser

The laser light source technology used in air sampling detectors
utilizes a laser beam inside the detector chamber. The detector
head is a sealed unit containing a laser particle counter. The
laser is focused through the center of the detection chamber to
a very small width of approximately 100 microns. A spherical lens
is located near this beam, focused onto the receiver electronics.
As air is drawn through the detector, the particles pass through
the laser beam and reflect light onto the receiver, which
generates pulses from the particles.

The signal processor determines the number and sizes of the
particles. Only small particles in the 0.2 micron to 10 micron
range are then used to generate the apparent smoke level. As with
the other sampling detection methods, the dust particles usually
are larger (10 microns) in size. Typically, the larger particles
are screened by system software to prevent random large particles
from generating an alarm condition. This particle size
discrimination inhibits false alarm conditions by allowing the
device to only react to those particles in the predetermined size
ranges. Detectors also are available to provide both the light
scattering and particle counting techniques, using the same laser
light source.

Most air sampling detection systems utilize a separate control
panel, which contains the system display status, the air
aspirator or fan, the power supply and, most important, the
detector itself. These control panels usually are installed in
close proximity to the protected area. Depending on the size of
the space being protected, the control units can be configured
for single or multiple zones of detector coverage ranging from
5,000 square feet to 80,000 square feet. Systems now can be
installed in a networked configuration with multiple detector
units on a single wiring loop to address the needs of larger
facilities and/or multiple protection areas.

One manufacturer provides a control panel containing both the air
sampling detection features as well as integrated suppression
releasing and alarm functions. Air sampling detection control
units have auxiliary alarm and trouble contacts to facilitate
monitoring by the building's main fire alarm control panel.

Intelligent Spot-Type Very Early Smoke Detection
These detectors have a similar appearance to standard spot-type
photoelectric or ionization detectors and utilize laser
technology for their detection methodology. The major differences
are in the internal components of the detector and the software
providing continual particle discrimination inside the detector's
sensing chamber. This detector uses an extremely bright laser
diode, combined with special lens and mirror optics to achieve a
signal-to-noise ratio that is much higher than traditional
photoelectric detectors. In addition, the tightly focused light
beam, combined with sophisticated software at the control panel,
allows the system to differentiate between dust and smoke
particles, Consequently, the detector can be set to a very high
sensitivity level, yet can reject signals caused by dust or other

The system architecture of conventional smoke detection systems
and intelligent spot-type very early smoke detection is very
similar, consisting of the detectors connected by initiating
device circuits to the control panel. The control panel provides
the power and annunciates the location and type of device that is
in alarm or trouble condition. The control panel typically is
located within the protected area, perhaps in proximity to the
main exit or at a central command center. The very early spot-
type detectors are addressable, allowing the exact location of a
specific detector in an alarm or trouble condition to be
annunciated at the control panel. The same control panel can
activate evacuation signals, release fire suppression systems and
shut down HVAC or power systems.

A critical factor in the detection of a potential fire event in
a high-value or high-risk area is the time between the release of
products of combustion and detection. Most events in data
processing or telecommunications facilities start as shorts, arcs
or overheat conditions in equipment or power cables. If fire
growth increases to the flaming stage, significant damage can
occur. Today's availability of very early smoke detection
technology can greatly enhance protection schemes for high-value
or critical areas, susceptible to damage from smoke in the early
stages of a fire. It also can provide early waning to facility
personnel prior to the need for manual or automatic intervention
to extinguish the fire.

Prior to the selection of a detection methodology, the design
engineer must assess the hazards and potential losses within the
space to develop an integrated systems protection scheme. This
scheme may include a combination of very early smoke detection,
gaseous agent suppression, power and equipment controls, data
backup, trained personnel response and automatic sprinkler
protection. Development of specific design goals for each
application can provide the most complete fire protection
strategy for the facility.

A photoelectric light-obscuration smoke-sensing fire detector
operates on the light extinction principle, which analyzes the
rate at which light extinction occurs therefore minimizing
nuisance alarms.

A cloud chamber smoke detector depends upon the particles of
combustion acting as condensate nuclei.

NFPA 72, Appendix B "Engineering Guide for Automatic Fire
Detector Spacing" presents data related to:
 o Size of fire to be detected
 o Rate of growth of fire to be detected
 o Ceiling height
 o Ambient temperature
 o Response characteristics of the detector

Smoke detectors installed in air duct systems are not considered
to be substitutes for open-area detection. This is because of
dilution of smoke-laden air by clean air from other parts of the
building and because the smoke may not be drawn into the HVAC
system when the system is shut down.



OR1 PCC Sylvania, Portland;
Test 11/15/03. Postmark deadline 9/27/03.
Test ??/??/04. Postmark deadline 12/1/03.

OR2 Clackamas Community College, Oregon City;
Test 9/27/03. Postmark deadline 8/9/03.
Test 11/15/03. Postmark deadline 9/27/03.

These dates are from the NICET web site. For a complete list of
all test centers and test dates, visit:


August 18-19, 2003 Tulsa, OK - Conducted by OK AFAA
Automatic Fire Detection and Fire Alarm Systems Seminar

August 21-22, 2003 Oklahoma City, OK - Conducted by OK AFAA
Automatic Fire Detection and Fire Alarm Systems Seminar

September 9-11, 2003 Batavia, NY - Sponsored by NYBFA
Intermediate Fire Alarm Seminar

September 15-18, 2003 Oakland, CA - Sponsored by CAFAA
Plan Review Seminar
Intermediate Fire Alarm Seminar

September 22-25, 2003 Lafayette, LA - Sponsored by LA AFAA
Intermediate Fire Alarm Seminar

September 16-18, 2003 Philadelphia, PA - Co-sponsored by PA AFAA
Intermediate Fire Alarm Seminar

October 8-9, 2003 Wichita, KS - Sponsored by KS AFAA
Plans Review Seminar.
Fire Alarm System Testing and Inspections Seminar.
More information will be available soon.

October 15-17, 2003 Boston, MA - Sponsored by New England AFAA
Intermediate Fire Alarm Seminar
More information will be available soon.

October 21-23, 2003 Anchorage, AK
Advanced Fire Alarm Seminar

November 3-6, 2003 Anaheim, CA - Sponsored by CAFAA
Plan Review Seminar
Advanced Fire Alarm Seminar
More information will be available soon.

November 4-7, 2003 Boston, MA - Sponsored by New England AFAA
Advanced Fire Alarm Seminar
More information will be available soon.

November 21, 2003 Reno, NV
Plan Review Seminar
More information will be available soon.

December 2-4, 2003 Phoenix, AZ - Co-sponsored by AZ AFAA
Advanced Fire Alarm Seminar
More information will be available soon.

December 9-11, 2003 San Antonio, TX - Co-sponsored by TX AFAA
Advanced Fire Alarm Seminar
More information will be available soon.


Engineering Technician info:

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This reprinted material is not the complete and official position of the NFPA on the referenced subject, which is represented only by the standard in its entirety.