Smoke Detectors For Your Home

By The Old House Web

Home fires are a serious threat to your family's safety. Every year inthe United States, approximately 5,000 people are killed and morethan 40,000 are injured by residential fires.

In addition, more than$8 billion worth of property damage is done by home fires. Many firevictims die of inhalation of smoke and toxic gases, not because ofburns. Most deaths and injuries occur in fires that happen at nightwhile the victims are asleep. Sleepers must be warned before it istoo late.

When properly installed and maintained, the home smokedetector is one of the best and least expensive ways to provide earlywarning when a fire begins. Before the concentration of smoke reachesa dangerous level, or before the fire becomes too intense, the alarmwill sound. Smoke detectors save lives, prevent injuries and minimizeproperty damage. The risk of dying from fire is twice as high inhomes that do not have functioning detectors.

How Do They Work?

Smoke detectors work by sensing the rising smoke from a fire andsounding a piercing alarm. There are two types of smoke detectors onthe market today: Ionization Chamber detectors use a radioactivesource to produce electrically charged molecules (ions) in the air.This sets up an electric current within the detector chamber. Whensmoke enters the chamber, it attaches itself to the ions and reducesthe flow of electric current, thus setting off an alarm.Photoelectric detectors sound when the smoke is dense enough todeflect a beam of light.

Smoke detectors also differ by power source.The batteries in battery-powered smoke detectors last approximatelyone year. When the battery begins to lose power and needs to bereplaced, the detector will begin to emit "beeps" every minute or so.Some will keep this up for a week or longer.

Smoke detectors thatoperate on household electric current operate as long as there iscurrent in the circuit to which they are connected. They are,therefore, vulnerable to power failure. Plug-in units must be locatednear an electric outlet where they will not be unplugged or turnedoff by a wall switch. They should not get their power from a distantplug using an extension cord. Always use the hold-in clips to preventaccidental plug removal from the outlet.

Heat detectors are alsoavailable, sometimes as part of a smoke detector and sometimes asseparate products. These use a special metal that melts or distortswhen heat enters the air surrounding it. When built into smokedetectors, these set off the smoke detector's main alarm. Alone, theymay sound their own alarm or a central alarm, if part of a system.Heat detectors add protection, but by themselves are not effectiveearly-warning devices. They must be very close to a fire to be setoff. Therefore, they are useful in places where smoke detectors canbe fooled, such as a kitchen. They are also useful in areas of thehome where smoke detectors cannot function because it is too hot orcold. Remember, smoke, not heat, is the leading cause of death inhome fires.

What Kind of Smoke Detector Should I Buy?

Each type of detector, if properly installed and maintained, iseffective. Since photoelectric detectors react more quickly tosmoldering fires and ionization units will respond faster to flamingfires, you may wish to buy at least one unit of each or a combinationdetector. However, because most home fires produce a mixture of smoketypes with detectable amounts of large particle and small particlesmoke early in the fire growth, either an ionization or aphotoelectric detector will meet most needs.

Several new features areavailable in smoke detectors today. These include detectors that havean escape light, are portable, or transmit their alarm to a centralconsole by radio signal as part of a unified emergency alert system.These can be used with burglar and other warning or detectiondevices. Electric current detectors with a rechargeable battery forpower outages are also available.

How Many Do I Need?

There should be at least one smoke detector on every floor of thehouse. Tests conducted by the National Bureau of Standards have shownthat two detectors, on different levels of a two-story home, aretwice 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 blockescape routes on the first floor.

Having two detectors also allowsyou to select both an ionization type and a photoelectric model,giving you the best capabilities of both. In addition, it lets youselect one battery-powered and one plug-in or wired-in model. Neithera battery failure nor a power outage will leave your familyunprotected. Finally, two smoke detectors are far less likely to beinoperative at the same time as is possible with a lone detector.


U.S. Consumer Product Safety Commission, What You Should Know AboutSmoke Detectors (January 1985).

Acknowledgments to Michelle L. Wallingford for her contributions tothis publication.

Reviewed by Mr. Randall Reeder and Dr. Jim Papritan, Department ofAgricultural Engineering, and Dr. Judy Wessel, Department of FamilyResource Management . Funded in whole or in part from Grant NumberU05/CCU506070-03, "Cooperative Agreement Program for AgriculturalHealth Promotion Systems," National Institute for Occupational Safetyand Health.

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