Smoke Alarms: The Science Behind Detection
Smoke Alarms: The Science Behind Detection
Joe Hirschmugl, Global Media Relations Manager, Underwriters Laboratories, +1-847-664-1508
moke alarms have been saving lives for decades, but today the technology behind them is
making headlines thanks to changes in the
modern home environment and recent scientific research.
In 2007, Underwriters Laboratories (UL) and the Fire
Protection Research Foundation (FPRF) completed the
Smoke Characterization Project, releasing extensive
quantitative data and analysis that expanded on previous technical studies conducted by the National Institute of Standards and Technology (NIST), United
States Fire Administration (USFA) and National Fire
Protection Association (NFPA). Project results provided further insight into modern fire scenarios. The
data offered unprecedented detail about the smoke
produced in home fires and how it is unique to each
occurrence, depending on variable factors such as
how the fire ignites, home furnishings, air movement
and room size.
The groundbreaking project also generated discussion
about the different types of smoke alarms available,
which detect smoke differently depending on the origin of the fire.
Ionization smoke alarms, the most commonly found
smoke alarms in North American homes because they
often are more economical, are best suited for alerting home occupants of fires originating from a flaming
source – such as a lit candle igniting a towel carelessly
left next to its open flame.
Photoelectric smoke alarms are most effective at
sounding when fires originate from a smoldering
source – such as a lit cigarette falling into a couch
Dual-technology alarms combine the science of ionization and photoelectric sensors into a single unit.
The availability of different technologies could cause
consumers to stand in store aisles, overwhelmed by
the many smoke alarm choices, wondering which
alarm is right for them.
“The simplest answer is that smoke alarms of any kind
serve as effective, life-saving tools by providing necessary warnings in home fire situations,” says John
Drengenberg, UL’s Consumer Affairs Manager. “But
we’ve found, in part because of changing home environments, people can optimize the effectiveness of
smoke alarms by having both ionization and photoelectric smoke alarm technology in their home.”
SMOKE ALARM PACKAGING—Be sure to look for the UL
Mark on all smoke alarms and follow manufacturer's
directions when installing a smoke alarm.
Photos courtesy of Underwriters Laboratories (UL)
While consumers can install a dual-technology alarm
to incorporate both technologies, that isn’t the only
answer. If ionization alarms are present, consumers
can install photoelectric alarms to complement the
already present ionization technology.
Drengenberg says that simply having both technologies
present in a home is the best choice because every
home fire is unique and unpredictable.
“One can’t know in advance how a particular household fire will start – if that were possible, the fire
could be prevented entirely,” he says. “In addition,
the unpredictability of fires is based on a number of
factors that vary with each fire – from ignition source
to furnishings fueling the fire to air movement within
a room, and the geometry and orientation of the
rooms within the structure.”
The recommendation to have both smoke alarm technologies in the home is supported by the Consumer
Product Safety Commission (CPSC), International Association of Fire Chiefs (IAFC), and National Association
of State Fire Marshals (NASFM), as well as NFPA and
Along with UL and its affiliate Underwriters Laboratories Canada (ULC), these organizations also recommend installing smoke alarms on every level of the
home, outside sleeping areas, and inside bedrooms.
Residents should replace batteries annually and test
the smoke alarms monthly. In Canada, such recommendations are contained in CAN/ULC-S552
(Maintenance and Testing of Smoke Alarms) and CAN/
ULC-S553 (Installation of Smoke Alarms).
Another technology option for consumers to consider
for optimal detection in existing structures is interconnected smoke alarms. The National Fire Alarm
Code (NFPA 72) and the National Building Code of
Canada require the interconnection of smoke alarms
for newly constructed homes. These alarms can be
connected to each other by hard wire or wireless
technology. If one alarm is triggered, all interconnected alarms in your home will sound, possibly alerting you to a fire earlier.
Beyond today’s technology
Smoke alarm technology continues to evolve. Thanks
to the collaborative research efforts of the fire safety
community, government agencies and public safety
advocates, industry experts know more about smoke
and fire behavior in residential fires than ever before.
UL is continually using that knowledge in pursuit of
measurable advancements in smoke alarm performance through its nationally accredited standards development processes in Canada and the United States.
“When talking about smoke alarm requirements, consensus is the operative word. UL and ULC don’t develop or update standards arbitrarily or in a vacuum,”
says Drengenberg. “Our scientists and engineers collaborate with foremost experts in the field through
the UL Standards Technical Panel (STP) and the ULC
Technical Committee.”
In fact, UL has more than 300 STPs and ULC has 17
Technical Committees, each focusing on a different
area of expertise, ensuring that efforts are clearly
focused on a highly specialized area, such as smoke
The North American standards relating to smoke
alarms are UL 217 (Single and Multiple Station Smoke
Alarms) and CAN/ULC-S531 (Smoke-Alarms). These
standards are under constant review by the respective standards groups that draw on the expertise of
UL/ULC representatives and a balanced panel of industry representatives, including regulators, trade
associations, advisory groups, consumer groups, manufacturers, and other testing, certification and standards organizations.
UL 217 and CAN/ULC-S531 have been updated many
times since modern smoke alarms were introduced
and the standards will continue to advance in response to evolving hazards, scientific studies and advancements in technology. The UL STP for smoke
alarms currently has seven task groups that include
some of the nation’s foremost fire science experts.
Included in the work of these groups is an evaluation
of recent smoke research findings and recent technological improvements in smoke alarm development.
Their proposed revisions to the smoke alarm standards
are expected to include new procedures and test requirements that better reflect the modern home environment, pursuant to optimizing escape times in
home fires. Their proposals may also include more
aggressive alarm threshold limits to potentially improve response to non-specific fires while avoiding
nuisance alarms – alarms that sound in response to
burning toast, for example.
The ULC Technical Committee is represented in the
work of this STP and vice versa. Information is shared
between the two committees and the ultimate intention is to develop a bi-national (Canada and the
United States) standard on smoke alarms.
“As an independent organization that has been developing standards, testing and certifying products for
more than 110 years, UL and ULC are proud to be active partners in improving fire and life safety,” says
Drengenberg. “It is our hope that continued collaboration between government and safety organizations
will only make smoke alarms even more effective than
they have been over the last 30 years.”
Reprinted with Permission from UL, Inc.
Additional info from UL
Types of Smoke Alarms
Smoke Alarm Tips
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