Friday, February 02, 2007
Types of smoke detectors, fire alarms: Pros and Cons
By Ann Robinson and Annie Vernon
Fire is the third leading cause of accidental death in the United States, and four out of five people who die in a fire die in a home. Fortunately, we have access to devices designed to give early warnings of a fire and other hazards. Whether remodeling or not, you should know what devices are available and make sure your home has the best protection for your family.
Smoke detectors are the most common form of residential fire protection. One type is an ionization smoke detector. A sensor ionizes the air between two electrodes, and when smoke particles disrupt the electrical conductivity of the air between the electrodes, an alarm sounds. This type of device works well detecting small particles from open, flaming fires. However, it is also prone to false alarms caused by steam or cooking vapors.
Another kind of smoke detector is photoelectric. This directs a light into a chamber aimed past a light sensor. When smoke particles enter the chamber, they deflect the light beam onto the sensor which in turn sounds the alarm. This device is most effective with a smoldering fire that emits larger particles. This type is also better at eliminating false alarms.
A third type of smoke detector is usually used in commercial applications. This shoots an infrared beam across a space that trips an alarm if smoke disrupts the beam. In homes, this type of detector may be appropriate for large open spaces, since the other kinds of detectors depend on the smoke accumulating around the actual sensor.
Another type of fire detection is a heat detector. An alarm sounds when a preset temperature is exceeded. These should not be used in place of smoke detectors, but they can be used where smoke detectors are ineffective, such as crawl spaces or attics.
Carbon monoxide is another concern in homes. This deadly gas cannot be smelled or seen as smoke can. Carbon monoxide detectors are installed near (but not over) combustion appliances such as a gas water heater or forced-air furnace. They should be placed within 18 inches of the floor because the gas is heavier than air and settles in a room.
The 2006 International Residential Code requires smoke alarms in each sleeping room, in each area outside sleeping rooms (i.e., halls), and one on each additional story of the home. Carbon monoxide detectors are required in every area with a combustion appliance.
Smoke alarms should be mounted away from corners since smoke will spread last to these areas. They should not be installed on walls or ceilings with little or no insulation, because these cold areas will also be slow to experience the spread of smoke or fire.
Smoke detectors and carbon-monoxide alarms are available as individual, battery-operated units. However, code for new construction or remodeling requires that the alarms be hard-wired together so if one alarm sounds, they all sound. There is an exception for remodeling that says that if you are not already removing plaster or dry wall, you do not have to remove it to connect smoke alarms. But if another path is available to make this connection, such as a crawl space or an attic, then the connection is required.
It is critical that you choose the proper kinds of warning devices and see that they are installed correctly and maintained properly so your family has every chance of escaping safely should a problem arise in your home. As always, we welcome your home architect design questions at firstname.lastname@example.org.