Distributed Intelligence
Where there’s fire,
there isn’t always smoke
Microprocessor-based intelligence has knocked the perennial bugs out of today’s
life safety systems. But can any fire alarm be truly fail-safe under all conditions?
www.GESecurity.com
T he airport terminal was a hive
of activity when the fire alarm
evacuation signal sounded. Thousands
emergency response personnel arrived
on the scene that the fire was discovered.
By then, the terminal had already filled
from mundane processing tasks; and
decentralise the system’s core processing
functions. With the lightning speed we
of anxious travellers were herded to with smoke. have come to expect of the technological
the exits as staff and security personnel This scenario, though hypothetical, age, this approach is quickly becoming
tried their best to reassure the crowds illustrates just how fragile the integrity an industry standard.
that they had reached their destinations of a fire alarm system can be and just In itself, distributed intelligence is
and their connecting flights, despite the how serious the outcome can get. False nothing new. The Internet, for example,
fact that the terminal would have to be alarms and the unpredictable nature of was originally conceived of, decades
emptied. Tempers flared. Flights were fires make a dangerous combination. But ago, as a means of providing a kind of
missed. And a good deal of money was advances in technology have cleared the
lost. way for new products and approaches
No one was injured in the fire, and that would make it virtually impossible
only minimal property damage resulted. for an airport’s fire alarm system to fail.
But the costs were both real – and
avoidable. Self-monitoring detec-
The fire started in a maintenance tors improve reliability
room on the departures level. However,
because the initial flames were fed by
cleaning fluid, they produced no smoke
I n recent years, designers and
manufacturers of fire alarm systems
have ventured beyond conventional
and so the detector just outside the technologies into the realm of distributed
room failed to respond until the fire had intelligence. Like most revolutionary
spread into the walls. Even then, airport ideas, distributed intelligence rests on a Intelligent detectors make alarm
staff, harassed by a series of false alarms deceptively simple premise: spread the decisions that free up computing
power at the control panel. The result
in the weeks leading up to the incident, computing power of a life safety system is faster response and an end to
were slow to react. It wasn’t until among its devices; free the control panel nuisance alarms
Febru ary 2009 44 www.indiasafe.com
life safety system that would support The driving force behind this ago, and of addressable devices a few
military communications in the event of development has been the need for years before that, manufacturers were
war. On a micro-scale, modern fire alarm a design that is more reliable and able to assign sliding alarm thresholds
systems provide much the same fail-safe less susceptible to nuisance alarms. to devices.
backup that enables them to continue to This has been accomplished through This enabled the device to monitor
provide basic life safety functions, even modifications to the way information its own sensitivity and ‘understand’ its
if the control panel or network node is is processed, rather than to the way it environment. If dust or humidity levels
knocked out of action. is gathered: even though tremendous increase the chance of a false alarm,
What is new is the capacity of gains in detector reliability have been the device itself is able to compensate
today’s intelligent life safety devices made over the past few years, the basic automatically by raising its own alarm
to do much more than simply send principles of detection have remained threshold. There is no danger, however,
information to the control panel. The virtually unchanged. Ion, photo, and that the threshold will be pushed so far
result is something that is both subtle heat sensors – the mainstays of any as to compromise the device’s ability to
and complex. Intelligent systems fire alarm system – still have their own detect fire: before that point is reached,
monitor their surroundings and adjust specific applications for which they are the device sends out a message that it is
themselves to compensate for naturally best suited. time for cleaning.
occurring environmental conditions. In Onboard microprocessors have
other words, they know the difference Trade-offs characterise also provided a means of addressing
between smoke and something that may past approaches another concern: the perennial problem
look like smoke.
B ecause
unpredictable
of
of fire, manufacturers have
the
nature
of choosing the best type of detector for
a particular application. With the advent
of multisensor detectors, photo, ion and
found it necessary to modify heat sensors have been incorporated into
detectors so that they perform a single unit.
reasonably well under a whole Independently, these different types
range of conditions. of sensors can come up with conflicting
For example, a photoelec- conclusions concerning the same envi-
tric detector must also be able ronmental conditions. But when they are
to respond to a smouldering- combined in a single smart detector they
type fire. The result is a device can be monitored over time, thus reduc-
that operates reasonably well, ing the chance of the device reacting to
but not optimally. the wrong set of circumstances.
The trade-off has come And that is where the sophistication
at a price, and false alarms of the system comes into play. True
have become the nature of multisensor detectors compare values
the beast. The problem stems received from the onboard independent
from the fact that detectors sensors to a pre-set algorithm. The
that are sensitive to smoke are device’s microprocessor can then
also sensitive to dust; those determine whether there is an actual
sensitive to heat can also be danger, or whether one of the sensors is
affected by humidity. reacting to a non-threatening environ-
Intelligent systems have mental condition such as dust or
furnished the means of humidity. This data filtering process
The whole is greater than the sum of its parts: overcoming this problem. means the detector will only initiate an
multisensor detectors overcome With the introduction of the alarm when conditions exactly match
the inherent shortcomings of
single-element designs analogue detector a few years the characteristics of a fire.
Febru ary 2009 45 www.indiasafe.com
PRINCIPLES OF DETECTION
Like a pyramid, multisensor detection rises from three them with a positive charge. The free electrons then
cornerstones of sensor technology: attach themselves to other air molecules giving them a
negative charge.
Photoelectric
The movement of the charged ions towards their
Photoelectric detectors react to medium and large
respective plates is what creates the small current flow.
particles – from 0.05 to 10,000 microns – the type
Smoke particles entering the chamber of an ionisation
of smoke typical of a slow, smouldering fire. These
smoke detector interfere with and reduce this current
detectors operate by projecting a light source into a
flow by attaching to ions, thereby increasing their mass
sensing chamber. A light receiver is positioned at some
and slowing them down so they have trouble reaching
angle relative to the light source. If smoke is present in
the plate.
the chamber, light is reflected and refracted by smoke
onto the receiver to produce a signal. The first such In the early days of ionisation smoke detector technology,
devices used miniature energy-hogging incandescent the strength of the radioactive isotope used was great
light bulbs that had to be replaced frequently. Advances enough to be of some concern. But technical advances
since then have provided a much more efficient light in the field have brought solid-state devices that allow
source. the use of negligible amounts of isotope today.
Ionisation Thermal
Ionisation detectors react to a range of much smaller Heat detectors also play an important role in fire
particles – from 0.001 to 2 microns – which are detection. In a case where there may be more flame
characteristic of gases and fast flaming fires. These than smoke, as in an alcohol fire, it is the heat detector
detectors work by means of an electrical current instead that provides the best protection. Heat detectors use
of light. Inside the detector, two plates are separated by neither ionisation nor photoelectric detection principles,
an air gap. To create the current, a voltage is applied but instead employ various techniques from solid-state
to the plates and a small radioactive isotope emits to bi-metal contacts to indicate the presence of heat
high-energy alpha particles into the air gap. The alpha when the temperature has exceeded a specific value
particles knock electrons off the air molecules leaving or rate-of-rise.
Refinements simplify how far the technology has brought the In short, they are demanding that system
installation and industry, and where it will eventually sophistication be amply tampered with
maintenance lead. As the technology becomes more ease of use.
W hile all of this marks a great leap
in terms of the dependability
of fire alarm systems, such complex
sophisticated, so too, must its application.
Installing and maintaining these systems
requires a higher level of skill than ever
And manufacturers are listening.
New software streamlines system setup
and verification, mimicking the familiar
refinements raise serious questions about before. Windows interface. Control panels
The life safety industry is already are becoming easier to operate. Touch
addressing this issue. Now that the screens offering graphical displays of
technology is established, there is less building plans are rapidly replacing
experimentation with radically new rows of buttons and switches.
processes. Instead, developers have
begun to turn their attention to refining Opportunities to merge
what they know works, and customers with other building
themselves are exhibiting more savvy systems
when it comes to assessing new
equipment. Today’s customers are less
likely to be dazzled by the technology
W ithout a doubt, the future of life
safety is inextricably entwined
with the technology that drives it.
True multisensor detection combines element
readings over time, based on an algorithm that and more inclined to question its place if Approaches are constantly being
precisely profiles environmental conditions it makes the system unduly complicated. reworked and reinvented. Some believe
Febru ary 2009 46 www.indiasafe.com
that eventually all building systems will
merge into one almost organic circulatory
system that consolidates HVAC, security,
life safety and communications.
But wherever the industry goes, one
thing is certain: people and property are
a lot better protected today than they
were just a short time ago.
GE Security, a wholly owned
indirect subsidiary of the
General Electric Company,
is a leading global supplier
of security and life safety
technologies, with a
broad product portfolio
covering explosives
and narcotics detection,
intrusion and access
control, video surveillance,
key management, and fire
detection. GE Security’s
products are used to protect
people and property across
a wide range of industries
including aviation, law
enforcement, banking,
education, healthcare, mass
transit, residential and retail
Had an intelligent system suppor-
ting multisensor detectors been insta-
lled in the airport terminal described
earlier, the building probably would
not have had to be evacuated. The
detector would have caught the situation
before the fire spread. And because
the system would have virtually
eliminated false alarms, airport staff
would have been more attentive and
quicker to react. The fire would have
been put out with all but a few building
occupants even being aware that there
was a problem at all.
Article and images courtesy
of GE Security, Asia Product
Marketing, Fire Detection.
F