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Smoke Detectors

Most home owners only think about their smoke detectors when the TV weathermen suggests that they should change their batteries when the clocks change twice a year. Did you know that smoke detectors only have a useful design life of approx. 10 years? Most people assume that if it beeps when you hit the ‘test’ button, the smoke detector will reliably alarm if there was a fire. This assumption can have deadly consequences.

You’d also be surprised at the number of homes that I inspect that have no (zero!) smoke detectors installed. I seem to run across this situation at least a few times per month. Just as many homes seem to have smoke detectors that do not 'beep' when tested (indicating no power or a dead battery).

The smoke detector’s test button only confirms that the smoke detector has power, not that the unit will necessarily 'go off' if there was a fire. You would need a source of smoke, for example, to fully test that function. The test button simply confirms that there is 120 Volt household power (if a hardwired unit) or that the battery is still good (if battery powered). A 20 year old smoke detector may have power (from the home and/or battery) but may not reliably 'go off' if there was an actual fire. Why risk your family’s safety for a $10 device that's well beyond its design life?

Many smoke detector manufacturers started stamping the manufacture dates on smoke detectors in the late 1990s and early 2000s. Prior to that, most units, I have found, don’t have their manufacture dates listed. When did you last check your smoke detectors’ manufacturer dates? If you’re like most people, probably never. I often ask this to my clients during their home inspection and nearly 100% of the time, I get a ‘deer in the headlight’ look back to me and a ‘I didn’t know I need to’ response. If your smoke detectors have no dates stamped on their back, it is probably safe to say that they are more than 10 years old and are in need of replacement now.

There are two types of smoke detectors: ionization and photoelectric. They each have a different purpose and way of detecting smoke or fire. The ionization type of smoke detector is installed in the vast majority of homes in the USA.

The ionization type tends to be best for what is called ‘fast flame’ fires which is a less common type of house fire. This type of smoke detector tends to have more frequent nuisance alarms which may cause the home’s occupants to disable this type of smoke alarm, by removing the batteries. Now you have no alarm. Ionization smoke detectors tend to nuisance trip from burnt toast or taking a steamy shower. When a house fire occurs, the fire department or the fire marshall are often called in to investigate the cause. Studies have been released stating that many fire fatalities could have been prevented if the home had photoelectric smoke detectors. Similarly, some studies also indicate that some of these fatalities were linked to ionization smoke detectors not going off early enough to alert the home’s occupants to wake up and get out.

The photoelectric type tends to be better at detecting smoldering smokey fires. Most home fires tend to be the smoldering type and, according to statistics, approximately 2/3 of house fires happen when everyone is asleep. A smoldering fire is the type that most often starts small and takes time, possibly hours, to build, such as a cigarette setting a mattress on fire. A smoldering fire often has slow moving, but large dense particles which are often best detected by the photoelectric type of smoke detector.

There’s been a lot of talk lately within home inspection and code circles about the potential issues with various smoke detector types. Some states and cities have started changing their codes or ordinances to now require photoelectric smoke detectors in homes and other buildings. To the best of my knowledge, none of the local municipalities in the Lancaster, Harrisburg, York, or Lebanon areas have done this yet.

Smoke detectors are required to meet Underwriters Laboratory’s (UL) 217 standard (also called UL 217). This standard sets the minimal criteria that must be met for testing smoke detectors. Tests have been done by various groups to examine the two smoke detector types and see how well and how quickly they each respond to various common fire scenarios. Some of the results have been quite shocking. In many of the most common house fire-type tests, the photoelectric smoke detectors went off 15-50 minutes BEFORE the ionization smoke detectors went off. In some tests, the ionization smoke detectors never went off at all. If you look on the back of your smoke detectors, you can often tell if you have ionization or photoelectric units. Some units will actually say "ionization" or "photoelectric" or may simply have an “i” or “p” either in the model number or stamped somewhere on the back of the unit.

Combination type photoelectric and ionization smoke detectors do exist, however based upon testing, these units tended to work less reliably than photoelectric.

Modern building codes (for new construction) require smoke detectors in all bedrooms, the areas (such as hallways) outside the bedrooms, and on all levels of the home (including the basement) and some also require attics. These must be hardwired and interconnected meaning they are powered by the home’s 120 Volt AC power supply and if one unit goes off, they all go off. They also must have a battery backup installed. The current building code in PA (2009 International Residential Code) does not say, however, whether these required smoke detectors have to be the photoelectric or ionization type. Some local townships, cities, and boroughs (such as Manheim Township, Columbia Borough, and Lancaster City) have specific smoke detector ordinance requirements that do not depend on the home’s age. These local ordinances closely follow the current IRC code regarding required locations for smoke detectors within a home. To find the requirements for your area, contact your local township/city/borough code official. It is a good idea that if you’re a Realtor and will be listing or selling homes across a wide range of Lancaster County municipalities that you know what each township, borough, or city requires in terms of smoke detectors (and any other local requirements).

As you know, home inspectors don’t inspect to the building codes, but we use the IRC as a general reference for common building, electrical, and plumbing standards. Based upon the testing data that’s been done, I believe that a future code revision (the IRC is updated every 3 years) may actually spell out a photoelectric requirement at some point since this type tends to be more reliable at earlier detection of the most common types of fires. In the meantime, it is best to have photoelectric smoke detectors installed in your home that meet the location requirements stated above (in all bedrooms, in the hallway(s) outside the bedrooms, and on each level).

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About the Author

Matthew Steger, WIN Home Inspection
2133 Andrew Avenue
Elizabethtown, PA 17022

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