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Here are some facts and common questions frequently
asked about Smoke detectors
and the answers to those questions. |
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How often and how
should I clean my smoke detector? |
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How often should I
change the battery in my smoke detector? |
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What if my smoke
detector "chirps"? |
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How effective are
smoke detectors? |
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When do I need to
replace my smoke detector? |
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How many smoke
detectors should I have? |
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Are there places
where I should NOT put a smoke detector? |
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Is there more than
one type of smoke detector, and how do they differ? |
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Is one type better
than the other? |
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My smoke alarm goes
off when I cook. How can I stop this? |
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How can I test my smoke detector? |
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Smoke Detector Facts: |
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Over 93 percent of
homes in the U. S. now have at least one smoke detector.
As the number of smoke detectors in homes increased over
the years, the residential fire death rate has dropped
nearly 50 percent. This success story is tempered by the
fact that the number of inoperable smoke detectors is
growing. Experts warn that the trend to fewer fire
deaths will reverse if we do not solve the problem of
inoperable smoke detectors. They estimate that one in
three homes have an inoperable smoke detector. Some fire
departments have found units in one half of homes to be
disabled.
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How often and how should I clean my smoke detector?
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You should clean your
smoke detector every six months with the bristle
attachment on you vacuum.
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How often should I change the battery in my smoke
detector? |
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You should change the
battery twice a year; "Change your battery when you
change your clocks" is the recommended interval.
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What if my smoke detector "chirps"? |
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People often mistake
the low-battery signal for a nuisance alarm. When the
battery is getting low, smoke detectors are designed to
"chirp" every minute or so while the battery still has
enough power to warn you that it is about to stop
working.
The "chirp" is
distinctive because it is a single, very short sound
that occurs every minute or so. If your smoke alarm does
this intermittently, first replace the battery to see if
that solves the problem. If not, then the unit needs
replacement due to old age or needs cleaning.
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How effective are smoke detectors? |
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Residential fire
deaths have decreased steadily as the number of homes
with smoke detectors increased. Reports from the
National Fire Protection Association show that people
have nearly a 50 percent better chance of surviving a
fire if their home has the recommended number of smoke
detectors.
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When
do I need to replace my smoke detector? |
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Smoke detectors that
are 10 years old are near the end of their service life
and should be replaced. Some people think that their
smoke detector sits idle until smoke is present. But it
is working every minute, constantly monitoring the air
24 hours a day. For example, an ionization smoke
detector goes through 3.5 million monitoring cycles in
10 years. In a photoelectric smoke detector, a light
operates 24 hours a day to check for smoke particles in
the air.
Just like any
electrical appliance, the components of smoke detectors
wear out over time. When a smoke alarm reaches 10 years
of use, the potential of failing to detect a fire
increases substantially. Replacing them after 10 years
reduces the likelihood of failure.
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Are there places where I should NOT put a smoke
detector? |
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Smoke detectors are
not designed to work in extreme heat or cold, or in
areas where smoke and dust are common. Thus, they are
not recommended for unheated attics or similar spaces.
The manufacturers instructions will include the
temperature range that the unit is designed for. Smoke
detectors should not be used in garages for two reasons.
First, garages are usually not heated or cooled, and
thus are sometimes above or below the temperature range
that the unit was designed for. Second, the smoke from
engine exhaust fumes will cause nuisance alarms and clog
the smoke detector.
Another area of concern is the kitchen. A smoke
detector that is installed too close to cooking
appliances may result in nuisance alarms. NFPA 72
addresses this problem by requiring that when a smoke
detector is installed within 20 feet of cooking, it
should either be photoelectric or have a silencing
button.
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How many smoke detectors should I have? |
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All but the smallest
home or apartment needs more than one. The exact number
depends on two things, the number of levels in the home
and the number of bedrooms. The following
recommendations are based on a standard published by the
National Fire Protection Association (NFPA 72), which
contains a chapter on household fire alarms. For new
homes, the standard requires a smoke detector in each
bedroom, one outside the bedroom area that is close
enough to be heard through closed doors, and a minimum
of one on each level of the home. The objective of
having a smoke detector outside the bedroom area is to
alert sleeping occupants of a fire that starts outside
of the bedrooms. For this reason, if the bedrooms in a
home are located in different areas, then each area
should have its own smoke detector. If a home is large,
it is better to use more than one on each level. The
closer the smoke alarm is to the fire source the faster
it will work, so extra units give you more safety.
The requirements for existing homes are not as
stringent. The State of Illinois Statute requires that
ALL existing homes, a smoke detector outside the bedroom
area and one on each level of the home. However, it also
recommends that homeowners install additional smoke
alarms, and we recommend that existing homes be equipped
with at least the same number of smoke detectors that
are required in new homes. It makes sense to install a
smoke detector in each bedroom. A good number of fires
start in bedrooms, and the closer the smoke detector is
to the fire, the faster it will alert you.
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Is
there more than one type of smoke detector, and how do
they differ? |
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There are two types
of smoke detectors designed for homes. One type is
called an ionization detector because it uses "ions", or
electrically charged particles, to detect smoke in the
air. Smoke particles entering the sensing chamber change
the electrical balance of the air. The greater the
amount of smoke, the higher the electrical imbalance.
The horn will sound when the electrical imbalance
reaches a preset level.
The other type of detector is called photoelectric
because its sensing chamber uses a beam of light and a
light sensor. The sensing chamber is designed so that
the light beam does not strike the sensor, but smoke
particles entering the chamber deflect the light onto
the sensor. The greater the amount of smoke entering the
chamber, the more light will be deflected onto the
sensor. The alarm sounds when the amount of light
hitting the sensor reaches a preset
level.
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Is one type better than the other? |
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Both types can meet
the test standards of Underwriters Laboratories, but
each has its own advantages. The ionization detector
responds faster to small smoke particles, while the
photoelectric responds faster to large smoke particles.
Flaming fires produce more small smoke particles and
smoldering fires produce more large particles.
Fire researchers have learned that a fire that
generates a lot of small smoke particles will cause an
ionization smoke detector to sound sooner than a
photoelectric. The time delay between the two is
relatively small, but these types of fires will make the
room untenable to life more quickly, so time is of the
essence. On the other hand, a fire with a lot of large
smoke particles will cause a photoelectric smoke
detector to sound sooner than an ionization. In this
case the time delay between the two can be relatively
long, but these types of fires take longer to make the
room untenable to life. If you want the advantages of
both, you can install one of each everywhere that a
smoke alarm is required or recommended, or you can buy
"combination" units that have both sensors.
Because the ionization type detector is sensitive to
small smoke particles, it will respond more quickly to
cooking. If you experience this problem, you have
several options: |
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Move
the unit farther away from the cooking area. The cooking
gases will be more diluted in the air when they reach
the smoke detector. If you choose this option, be aware
of how air is flowing through the space. You don't want
to move it away only to find out that the air current is
carrying the cooking gases right to the new location. |
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Install a
photoelectric smoke detector. You lose some warning time
in a fire that generates smaller smoke particles, but
you gain by removing the one nuisance that results in a
lot of smoke detectors being disabled. |
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Install a
combination ionization/photoelectric detector. When the
two sensors are combined in one unit, the ionization
sensor is set at a slightly less sensitive level. Thus
the unit is less prone to nuisance alarms and you have a
unit with greater sensitivity to both fast-flaming and
slow smoldering fires. |
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Install an ionization
smoke detector that has a hush button. This allows you
to silence the unit for 15 minutes while you remove the
source of the nuisance alarm (e.g., burnt toast) and
clear the air. This is not as convenient as options 2 or
3, but it will work as long as you can reach the button
and don't get aggravated enough to remove the battery.
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My smoke alarm goes off when I
cook. How can I stop this? |
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Ionization-type
smoke detectors are more sensitive to cooking smoke and
gases than the photoelectric type. Although you cannot
see any smoke, the combustion from the flame is causing
"products of combustion" to be released. When these
particles are under one micron in size, they cannot be
seen with the naked eye; when they are larger than one
micron, these "products of combustion" become visible
smoke. Although the small particles are too small to be
seen, they will change the electrical balance in the
ionization-sensing chamber, thus making the smoke
detector operate. There are several options for handling
this problem. One way is to replace the ionization alarm
with one that has a "silence button" that quiets it for
a few minutes.
Another option is to
move the alarm farther away from the cooking area,
giving the particles a chance to dissipate; The fewer
particles per volume of air, the less likely they are to
cause the imbalance in the sensing chamber. If the smoke
detector is ceiling-mounted, moving it to a wall can
also reduce nuisance alarms. However, this will also
make it a little slower to respond to a real fire. If
you do this, make sure to follow the manufacturers
instructions for the correct height. If you misplaced
your instructions, stop in at a hardware store and
review the instructions in one of the smoke detector
boxes.
Another option is to
replace the ionization-type detector with a
photoelectric alarm. This alarm is less sensitive to the
smaller (sub-micron) smoke particles and thus is less
affected by cooking smoke. You can also select a
combination ionization/photoelectric detector (both
sensors in one unit). It will be less sensitive to
cooking and will respond faster to smoldering fires than
ionization units. The reason that it is less sensitive
to cooking is because the manufacturer can make the
ionization sensor less sensitive when a photoelectric
sensor is also present.
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How can I test my smoke detector? |
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Every smoke detector
comes with a test button. We recommend that people test
their alarms regularly, at least once a month.
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