Smoke Alarms


Smoke Detectors: Early Detection is the Key to Survival

Statistical data

While smoke detectors have been around since the 1930’s, the first affordable battery-operated units were not introduced into the residential consumer market until 1965. Today, according to the National Fire Protection Association (NFPA), nearly 96% of American homes have at least one smoke detector. But the more important – and troubling – number, is that no smoke detectors were present, or none operated, in two out of five house fires from 2005-2009. Almost two-thirds of home fire deaths resulted from fires in homes with no smoke detectors or no working smoke detectors.

The key qualifier in that last statement is “working”. As data from the NFPA confirms; most people die in fires where a detector is present, but not in working order. Of those homes with a smoke detector installed,  25% have a detector that either has no power source (battery or electrical), a damaged sensing mechanism, or the detector is outside of its service life.

Types of Smoke Detectors

There are two primary types of smoke detectors on the market today, and they each have a unique way of sensing smoke and alerting occupants.

  • Ionization Smoke Detectors are smoke detectors that contain a small quantity of radioactive isotope material, that create ionization of air in the presence of smoke, triggering the alarm to sound. Ionization smoke detectors are designed to alert the occupants during the early phases of a flaming fire, where the smoke particles are relatively small.
  • Photoelectric Smoke Detectors are smoke detectors that use a lens-beamed light source (either incandescent or LED) and a detection diode (sensor). In the absence of smoke, the light passes in front of the sensor in a straight line. When smoke enters the optical chamber across the path of the light beam, some light is scattered by the smoke particles, directing it at the sensor, triggering the alarm to sound. Photoelectric smoke detectors are designed to alert the occupants during the early phases of a smoldering fire, where the smoke particles are relatively larger than those of a flaming fire.

In general, ionization detectors can be expected to give earlier warning than photoelectric detectors during a fire that is burning in the flaming mode of combustion. Flaming fires can be expected to create conditions that are too smoky for easy escape, as well as incapacitating levels of carbon monoxide and heat within a few minutes in a residential structure.

 Smoke detectors are made that have a combination of both types of sensing mechanisms in one unit. A reputable, laboratory certified combination detector costs about $40.00, and is available at most hardware and home improvement stores.

 Frequently Asked Questions

  • How Many Should I Have, and Where Should They be Placed?

It’s recommended that a smoke detector should be placed on every level, with at least one – especially if it’s the only one – near the sleeping area, preferably the hallway near the master bedroom. This provides protection when you are the most vulnerable; when you’re asleep. Early detection is tantamount to survival.

Smoke has a tendency to rise and accumulate at the ceiling level before banking down. As a general rule, smoke detectors should be placed on ceilings at least twelve inches from the wall, or high on walls at least twelve inches from the ceiling. Each manufacturer has their own recommendations in the instructions as to where the detector should be placed, and you should follow their guidelines.

 Avoid placing smoke detectors in areas where false “nuisance” alarms can be prevalent, such as near ovens or stoves. Smoke detectors should be placed at least ten feet away from a cooking appliance.

  • How Often Should I Replace the Battery, and When Should the Detector Be Replaced?

The battery should be changed annually. This is also true if the detector is hard-wired directly into the home’s electrical circuit. Pick a date that is easy to remember, such as with the spring or fall time change. Detectors should be replaced ten years from the date of manufacture, or as otherwise specified in the manufacturer warranty information or installation instructions.

Perform a function check on the detector every so often by pressing and holding the test button. If the alarm does not activate; it’s time for a replacement, or a new battery.

  • What is the Difference Between a Low-Battery Alarm and an Alarm Activation Due to Smoke?

Smoke detectors have a built-in battery power sensor that will emit an intermittent “chirp” when the battery is low. This chirp will occur every few minutes. An activation of the detector due to the presence of smoke will result in a consistent, frequent, loud audible alarm.

  • How Should I Clean my Smoke Detector?

The instructions included with your detector will have routine maintenance guidelines. If you’ve lost the instruction booklet, you can often find it on the manufacturer’s website. Vacuuming monthly, with a residential vacuum wand attachment, is generally the only required cleaning. Avoid spraying cleaning chemicals on the detector, as this can damage or destroy the sensing mechanisms. Never paint or otherwise alter the detector.

If you have any questions regarding carbon monoxide or smoke detectors, or to schedule a courtesy fire safety inspection of your home, please contact Independence Township Fire Department at (248)625-1924.