The House Detective: by Barry Stone, Certified Home Inspector
Dear Barry: I installed new smoke alarms in my home about a year ago. Now that I’m selling the property, the buyer’s home inspector says these are not the best kind of smoke alarms. He recommends replacing them with the “photoelectric” kind. As long as the smoke alarms work when tested, what difference does it make if they’re one kind or another? Ben
Dear Ben: The purpose of a smoke alarm is to detect minute particles in the air and to make a loud noise when particles are present. There are currently three kinds of detectors on the market: ionization detectors, photoelectric detectors, and combinations of both.
When smoke alarms came into common use in the 1970’s, the only kind available was the ionization type. Ionization smoke detectors contain a small amount of a radioactive substance known as americium-241. This material creates a small electrical current between two metal plates. When smoke particles pass between these plates, the current is interrupted, and the alarm is activated. The problem with ionization detectors is that they respond best when there is a flaming fire but are slow to respond when there is smoke from a smoldering fire.
Photoelectric smoke detectors were developed in more recent years and have a different means for sensing the presence of particles in the air. In a photoelectric detector, there is a light source and a light-sensitive electric sensor. The light, however, is not directed toward the sensor. When smoke particles are present, the light strikes these particles and is reflected against the sensor, and this activates the alarm. The advantage with this type of smoke alarm is that it senses fires that are in their early stages of smoldering, before they burst into flames. This can make a life-saving time difference in many fire situations.
For maximum fire protection, dual alarms are available. These contain ionization and photoelectric sensors in a single unit. Unfortunately, there are no industry standards for the sensitivity of sensors in dual sensor alarms. Because of this, the ionization sensors in some dual alarms are not reliable. However, as long as the photoelectric sensor is functional, the alarm meets national standards established by Underwriters Laboratories.
Photoelectric smoke alarms are recommended by the International Association of Fire Fighters (IAFF) because they are the most reliable and give the most advanced warnings when a fire begins to occur. The IAFF regards ionization alarms and dual alarms as unacceptable. This is why your buyer’s home inspector recommended that you upgrade to photoelectric smoke alarms.
Upgrading your smoke alarms may not be a legal requirement in your local area or in your purchase contract, but it is still advisable. It is also recommended that you get combination alarms: the kind that detect carbon monoxide (CO) as well as smoke because CO alarms can save lives and are now required near bedroom entrances and in other interior locations. If you do replace the current smoke alarms with combo alarms, find the ones that have a voice recording, indicating whether smoke or CO has been detected.