Fire detection in your home
Fire can spread very quickly in your home. Here’s a video link that gives you some idea of how quickly a small flame grows to engulf the whole house http://www.youtube.com/watch?v=QqMVm72FMRk&feature=related. As you can see in the video, fires grow from small to large in a very short period of time. As this news video shows, smoke is the usual killer in home fires http://www.youtube.com/watch?v=SnAaeTDRxek. How an ionization detector works can be found here http://www.youtube.com/watch?v=QjJnxUwcfoQ&feature=related. I couldn’t find a decent video on photoelectric smoke detectors, so I’ll just explain how they work. Inside the smoke detector is a chamber with ventilation to the air in the room. A light inside the detector is pointed away from a photoelectric eye, and cannot detect the light unless smoke particles or something similar reflects the light onto it. It would be similar to shining a flashlight into the sky on a clear and moonless night; nothing would reflect the flashlight’s light back into your eyes. If you were to do the same on a foggy evening, you would see the light because the fog would reflect the light to your eyes.
Local, or monitored?
Smoke or fire alarm detectors can be local only, or monitored. Local only means that they just make noise- beeping, buzzing or a recorded voice. Monitored detectors are connected to an alarm system that is monitored by a central station, where an operator can dispatch the fire department for you. While local detectors are less expensive, they are designed to protect life only. A monitored system can save your life just as well, but it may also save your property by alerting firefighters while the fire may still be small. Since I and my employer sell fire alarm systems, I’m going to be honest about my bias towards monitored systems: If you can afford to have one properly installed and monitored, do it. If the fire traps you by blocking your means of escape, wouldn’t you prefer to have someone else call the fire department? Smoke detectors can be connected to most burglar alarm or automation systems, will work if you lose electrical power, and will even notify the central station if they have technical problems.
Photoelectric detectors will give false trips when exposed to dust or steam, as well as intentional fires- fireplaces, car exhaust, or dubious culinary activity. As the video above demonstrated, photoelectric detectors are not optimal for detecting open flame fires. To offer greater detection, fixed heat detectors have been added to photoelectric detectors, such as this product: http://www.homecontrols.com/GE-Security-Photoelectric-SmokeHeat-Detector-wCleanMe-2-Wire-GE521BXT. Heat detectors detect the heat of a fire, which will be far more extreme than will be found in normal conditions inside your home. Coupled with the photoelectric smoke detector, they should detect both open flame and smoldering fires. In extreme environments, such as an attic, smoke detectors are likely to be fouled with dust and difficult to access to maintain. In some instances, even the extreme temperatures required to trip a heat detector will exist in the attic. In these cases, rather than using a heat detector set to trip at a fixed temperature, a heat detector that detects a “rate of rise” in temperature should be used. These detectors usually have a very high fixed temperature threshold so that they will detect a fire, but are far less sensitive to ambient temperatures that may be extreme. These detectors look for a rapid rise in temperature such as an open flame fire would create, with the fixed temperature trip acting as a failsafe. Consult local codes and a qualified designer for installations.
Make some noise!
Fire alarm annunciation should be customized to the occupant. Those who are hard of hearing should have strobes in addition to horns or sirens. Where strobes are to be used, they must be synchronized if two strobes can be simultaneously observed to avoid epileptic seizures. A strobe light mounted on the exterior of the home or flashing lights will help guide emergency responders to your home quickly.
Test your system regularly using the manufacturer’s instructions, or hire someone who is licensed and competent to test them for you. Monitored detectors should notify you if there is a problem with wiring, batteries or dust accumulating in the detectors. Local detectors typically have a push button to test them. Monitored detectors will sometimes have provisions for testing with a magnet, or spray cans of “smoke” can be purchased for testing purposes. Avoid using too much spray smoke because it will lead to the detector prematurely failing due to dust sticking to the inside of the detector.