Smoke alarms are one of the most important parts of keeping your home and family members safe from a preventable disaster. In a 2014 report, the National Fire Prevention Association (NFPA) said three of every five home-fire deaths resulted from fires in homes with no smoke alarms or with none that worked. But, many people are not sure about the types of smoke alarms that exist, how often the batteries should be replaced, and how often you should purchase and install new detectors. Today we will address all of these issues.
First, it is important to understand the two major types of detectors that exist: ionization and photoelectric. Ionization smoke detectors contain a very small amount of americium-241 within an ionization chamber. They create an electric current between two metal plates, which sound an alarm when disrupted by smoke entering the chamber. These are best for detecting fast moving fires; however, these are extremely prone to being tripped by mistake if they are installed in a kitchen or bathroom setting from either mild smoke from cooking or from steam from the shower. The second type of detector which is ideal for the two previous settings is a photoelectric detector. Photoelectric smoke detectors contain a light source in a light-sensitive electric sensor, which are positioned at 90-degree angles to one another. Normally, light from the light source shoots straight across and misses the sensor. When smoke enters the chamber, it scatters the light, which then hits the sensor and triggers the alarm. These are ideal for detecting a fire early on when it is smoldering. The final type of detector is a hybrid detector that combines both of the previously mentioned types.
As far as batteries are concerned, they should be replaced every 6 months. A good way to remember when your detector needs to have its batteries replaced is to change them when you change your clocks for daylight savings. As far as the detectors themselves are concerned, dust and other contaminants will collect over time, degrading the integrity of the detectors system, so every 10 years, or when the system continues to chirp even after a battery replacement, consider replacing the detector. Newer units contain a non-replaceable battery that is said to last 10 years, forcing the owner to replace when the detector is no longer effective.
One issue that is also debated is battery powered or hardwired. One huge benefit of a hardwired unit is the ability to interconnect units so they all go off when one goes off. There are newer battery only units that can be interconnected wirelessly, but these are less common and more expensive. Hardwired alarms are more likely to have operated in an actual fire over battery only ones. See the following links at the end for more information.
The final question is, which one is better? Because they function in different ways, and the costs associated with each can be vastly different, it’s really up to you as a consumer to make the best choice for your budget. The International Association of Fire Fighters (IAFF) - the largest firefighters union in the U.S. and Canada - recommends: photoelectric smoke detectors. During their 2008 conference, the IAFF adopted an official position recommending only photoelectric smoke alarms and stated that dual sensor alarms are no longer acceptable. However, NFPA recommends a mix of different units or combination units (9/15), as the technology is getting better. We recommend a mix of units, with photoelectric type units being used in kitchen areas and ionization or more ideally, combination ionization/photoelectric units being installed in the general living and bedroom areas. It is important to note that the testing standards vary based on type of unit and combination units should meet BOTH the standards for photoelectric and ionization types. The technology used in ionization smoke detectors leads to a delayed warning in smoldering fires, which can lead to greater loss of life. Ionization detectors are also weaker in high airflow environments, so the delay may be even longer. Photoelectric smoke alarms are more effective at warning of smoke from smoldering fires and are less susceptible to nuisance alarms.