News & Info
Smoke Detectors - Part 1
October 8, 2017
At Duke-Allen Inspections we find many homeowners and homebuyers are confused about the requirements for smoke alarms (detectors). According to the Minnesota Building Code, at least one smoke alarm and one carbon monoxide alarm are required in all single-family dwellings regardless of age. Additional alarms may be required depending on the city, whether any remodeling has taken place, and in newer homes. However, without regard to what the Code may or may not say, the intent is really simple…do occupants in the home have adequate warning in the event of fire carbon monoxide? For those of you who have used Duke-Allen Inspections to perform home inspection on your new property, or those of you who have seen our home inspection videos or other articles, you will know we stress safety.
Single family home, two-family home, townhouses (MRC buildings) fall under the Minnesota Residential Code (MRC) and there are three basic types of smoke detector installations.
· Single-station: One smoke alarm powered by a home electrical system and/or battery that sounds an alarm from the device when smoke is detected.
· Multiple-station: Two or more single station smoke alarms powered by a home electrical system and batteries that are interconnected and sound an alarm from all devices when smoke is detected in anyone of the devices
· Multiple-station wireless: Two or more single station smoke alarms powered by a home electrical system or batteries that are interconnected wirelessly and when a device detects smoke all devices sound an alarm via a wireless network created by the devices.
There are also different types of smoke detectors, each having a particular application dependent upon the environment and need. Most companies who sell detection equipment offer two main types of smoke detectors: ionization and photoelectric. It’s important to understand the distinction between the two technologies. Ionization detectors usually respond best to what the industry terms “fast-flame” fires. Photoelectric alarms are better at detecting slow fires that smolder. The third type of smoke detector includes both an ionization and photoelectric sensors. There are no industry-standard sensitivity levels for dual sensors, and to pass inspection they just only must meet requirements for photoelectric or ionization, not both. For those reasons, we recommend placing a combination of ionization and photoelectric smoke alarms in your home to provide the best coverage.
Ionization smoke detectors
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. Ionization smoke alarms are designed to quickly detect the small amounts of smoke produced by fast flaming fires, such as cooking fires or fires fueled by paper or flammable liquids.
This type of smoke detector, which is commonly used in kitchens, is prone to nuisance tripping. For example, we’ve all experienced the loud annoying chirping when we leave a cake in the oven too long, spill something on the burner, or add oil to an extremely hot pan. When this happens, people often resort to trying to disable the alarms, leaving that area unprotected.
Photoelectric smoke detectors
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. Photoelectric detectors are best for slow burning and smoldering fires.
Studies have shown that while ionization detectors activate 30 to 90 seconds faster to fast-flame fires than photoelectric smoke detectors, they respond to smoldering fires anywhere from 15 to 50 minutes slower than their counterparts. Smoke inhalation, rather than contact with actual flames, is the cause of the majority of home fire fatalities. Smoldering fires produce more smoke, so it’s a good idea to have a photoelectric detector to catch those fires quickly.
Often when performing a home inspection, we find that homeowners and home buyers are often unaware that detectors need to be maintained and replaced periodically. Smoke detectors are required by the Minnesota fire code to be replaced when they exceed 10 years from the date of manufacture. We usually recommend during an inspection that if the unit is about 7 years old they should be thinking of a replacement. The date is usually located on the back of the alarm. If there is no date, the smoke alarm is probably over 10 years old.
Duke-Allen Inspections may recommend new smoke detector installation when the smoke alarm fails an operability test, they are located in adverse conditions with much dust and smoke, and they clearly show their age. Replacement does not prevent an upgrade by replacing battery powered alarms with electrically powered alarms paired with a battery backup. Often during home inspections we find smoke detectors that were hardwired at one time, but for whatever reason they were simply replaced with battery-operated detectors. If the smoke detector was originally hardwired, then replacements must also be hardwired.
Every year, millions of fires occur worldwide and most of these happen in homes. The injuries and fatalities caused by these fires, could have been minimized had many of these homes properly installed and maintained their smoke detectors. The difference between life and death can often be just a few minutes, which is what smoke detectors are designed for. Most fatalities occur not because of the flames, but because of smoke inhalation. Smoke from fire is dangerous because it contains carbon monoxide and hydrogen cyanide, a deadly poison that can kill quickly. Even in an enclosed area, smoke from a small fire can be enough to eliminate all visibility which can make escape impossible. A few minutes of exposure to smoke is enough to be fatal, therefore, early warning of a fire is essential and good reason proper installations and the right type of smoke detectors are that important as the first line of defense.
In the second part of this article I will discuss proper locations of smoke detectors, and some of the mysteries surrounding smoke detectors, such as “why do they go off in the middle of the night for no apparent reason?”.
Duke-Allen Inspections prides itself on adhering to three simple principles in all home inspections we perform, these principles being "Quality, Integrity, and Service". In fact, it is our motto!