There is no doubt that today's modern smoke alarms with their advanced technology save countless lives each year. In fact, many municipalities require them in residences and offices as part of standard building codes. This article will take a look at a pair of the most common detectors available as well as some ideas to keep them in working order so they can continue to save lives.
Two Primary Types of Smoke Alarms
There are two primary types of smoke alarms available for home use today: ionization and photoelectric. Ionization smoke alarms generally are more responsive to flaming fires. Inside an ionization smoke detector, there is a negative and positive electrode connected to a battery to form a circuit (see #1 in image below). Additionally, there is a substance within the detector called Americium-241 which converts air molecules into negative and positive ions (see #2). Since opposites attract, the negative ions gravitate and align toward the positive electrode, while the positive ions do the same toward the negative electrode. This movement by the ions creates the circuit or path of electricity. Once smoke enters the detector, the ions bond to the incoming smoke which breaks the circuit, setting off the alarm (see #3).
Ionization:
Photoelectric smoke alarms are generally more responsive to fires that begin with a long period of smoldering, or a smoldering fire. Within a photoelectric smoke alarm, there is an LED light (see #1 in image below) that sends a beam of light in a straight line across the internal chamber of the alarm. In a separate area of the chamber, there is a photosensor that detects light. During a smoldering fire, once smoke enters the chamber, it interrupts the LED light beam (see #2) which scatters it in many directions. Invariably, the scattered light will hit the sensor, setting off the detector (see #3).
Photoelectric:
Along with these two primary types of smoke detectors, there are combination (or dual-sensor) alarms available that include both technologies in the same detector.
Smoke Alarm Installation
For maximum benefit and safety, the National Fire Protection Association (NFPA) recommends that a smoke alarm should be installed in each bedroom within your house, outside each sleeping area and on every floor of your home, including the basement. In the basement, it should be installed on the ceiling at the bottom of the stairs leading to the next floor. On floors without bedrooms, alarms should be installed in dens, living rooms or family rooms, or near the stairs leading up to the next floor. Since smoke rises, all alarms should be installed near the top of the wall, with the top of it no more than 12" from the ceiling. Larger homes may need additional smoke alarms for maximum safety.
Keep smoke alarms at least 10' from stoves, cooktops, and other cooking appliances to avoid a false alarm while cooking. And they shouldn't be installed near doors, ducts, windows, or anywhere a draft could interfere with the operation of the smoke detector. If the alarm is installed on a pitched ceiling like an A-frame, place it within 3' of the peak, but not any closer than 4" from the peak. Keeping it within that 4" to 3' range will provide maximum operating efficiency. Finally, don't paint a smoke alarm to try and match a wall color or blend into the interior of a room. This could seriously compromise the functionality of it and keep it from working properly.
If possible, interconnect all smoke alarms together via either hard-wiring or wireless capabilities. This ensures maximum protection since when one alarm sounds, they all sound. Just be sure when interconnecting alarms that they're all from the same manufacturer; otherwise you may have compatibility issues and they may not sound. Once installed, be sure everyone in the house understands the sound of the alarm, what it means, and to react properly to it.
Maintaining and Replacing Smoke Alarms
On average, you should be testing your smoke alarms monthly by depressing the test button to ensure they're working properly. And twice a year at Daylight Savings Time in the spring and fall, change out the 9-volt battery for a fresh one each time you change your clocks. It's easy to remember and could be a lifesaver. If at any time the alarm beeps or chirps, it's an indication the battery should be replaced immediately. When changing one battery in one alarm, it's a good idea to be sure to change all other alarm batteries to be safe.
For 10-year lithium-powered smoke alarms, you won’t need to replace the battery every 6 months. Instead, after 10 years, change out the entire smoke alarm for a new one. 10 years is generally the life expectancy of any smoke alarm; so whether it's powered by a 9-volt alkaline battery or a lithium one, you should replace any smoke alarm after 10 years. Even though it may look perfectly fine, and you get it to beep when you press the test button, all that does is confirm the electronics, battery, and alert system are functioning. It doesn’t mean that the smoke sensor is working. So, be safe and replace. Regardless of whether or not your alarms are hard-wired into your home's electrical system, follow the same procedures to replace the battery and the unit itself as if they were standalone alarms.
Keeping all smoke alarms in working order is not only a smart way to protect your house and everyone in it, but it could also be a lifesaver. Don't ever compromise when it comes to maintaining them regularly. It's the smart thing to do!
Product Compliance and Suitability
The product statements contained in this guide are intended for general informational purposes only. Such product statements do not constitute a product recommendation or representation as to the appropriateness, accuracy, completeness, correctness or currentness of the information provided. Information provided in this guide does not replace the use by you of any manufacturer instructions, technical product manual, or other professional resource or adviser available to you. Always read, understand and follow all manufacturer instructions.