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Fire Safety - Smoke Detector
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Updated On: Jan 04, 2010 (14:58:00)
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 Home fires are a serious threat to your family's safety. Every year in the
United States, approximately 5,000 people are killed and more than 40,000 are injured
by residential fires. In addition, more than $8 billion worth of property damage is
done by home fires. Many fire victims die of inhalation of smoke and toxic
gases, not because of burns. Most deaths and injuries occur in fires that happen at
night while the victims are asleep. Sleepers must be warned before it is too late.
When properly installed and maintained, the home smoke detector is one of the
best and least expensive ways to provide early warning when a fire begins.
Before the concentration of smoke reaches a dangerous level, or before the fire
becomes too intense, the alarm will sound. Smoke detectors save lives, prevent
injuries and minimize property damage. The risk of dying from fire is twice as high
in homes that do not have functioning detectors.
How Do They Work?
Smoke detectors work by sensing the rising smoke from a fire and sounding a piercing
alarm. There are two types of smoke detectors on the market today: Ionization Chamber
detectors use a radioactive source to produce electrically charged molecules (ions) in the
air. This sets up an electric current within the detector chamber. When smoke enters the
chamber, it attaches itself to the ions and reduces the flow of electric current, thus setting
off an alarm. Photoelectric detectors sound when the smoke is dense enough to deflect a
beam of light.
Smoke detectors also differ by power source. The batteries in battery-powered smoke
detectors last approximately one year. When the battery begins to lose power and needs
to be replaced, the detector will begin to emit "beeps" every minute or so. Some will keep
this up for a week or longer.
Smoke detectors that operate on household electric current operate as long as there is
current in the circuit to which they are connected. They are, therefore, vulnerable to power
failure. Plug-in units must be located near an electric outlet where they will not be
unplugged or turned off by a wall switch. They should not get their power from a distant
plug using an extension cord.
Always use the hold-in clips to prevent accidental plug removal from the outlet.
Heat detectors are also available, sometimes as part of a smoke detector and sometimes as
separate products. These use a special metal that melts or distorts when heat enters the air
surrounding it. When built into smoke detectors, these set off the smoke detector's main
alarm.
Alone, they may sound their own alarm or a central alarm, if part of a system. Heat
detectors add protection, but by themselves are not effective early-warning devices. They
must be very close to a fire to be set off. Therefore, they are useful in places where smoke
detectors can be fooled, such as a kitchen. They are also useful in areas of the home where
smoke detectors cannot function because it is too hot or cold. Remember, smoke, not heat,
is the leading cause of death in home fires.
What Kind of Smoke Detector Should I Buy?
Each type of detector, if properly installed and maintained, is effective. Since photoelectric
detectors react more quickly to smoldering fires and ionization units will respond faster to
flaming fires, you may wish to buy at least one unit of each or a combination detector.
However, because most home fires produce a mixture of smoke types with detectable
amounts of large particle and small particle smoke early in the fire growth, either an
ionization or a photoelectric detector will meet most needs.
Several new features are available in smoke detectors today. These include detectors that
have an escape light, are portable, or transmit their alarm to a central console by radio
signal as part of a unified emergency alert system. These can be used with burglar and
other warning or detection devices. Electric current detectors with a rechargeable battery
for power outages are also available.
How Many Do I Need?
There should be at least one smoke detector on every floor of the house. Tests conducted
by the National Bureau of Standards have shown that two detectors, on different levels of a
two-story home, are twice as likely to provide enough time for escape as one detector.
Although the upstairs detector senses smoke wherever it originates, the downstairs unit will
react sooner to a fire that could block escape routes on the first floor.
Having two detectors also allows you to select both an ionization type and a photoelectric
model, giving you the best capabilities of both. In addition, it lets you select one battery-
powered and one plug-in or wired-in model. Neither a battery failure nor a power outage will
leave your family unprotected. Finally, two smoke detectors are far less likely to be
inoperative at the same time as is possible with a lone detector.
Why Have A Smoke Detector?
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