Those white smoke alarms hanging from your ceiling may all look alike, but there are significant differences in the two kinds of sensor technology.  The older and more common type uses an ionization sensor.  More than 90% of smoke alarms installed in the US are ionization type (keep this in mind as you keep reading).  The newer and less common type uses a photoelectric sensor.

What is the difference?

Ionization smoke alarms are less expensive and are better at sensing the small smoke particles associated with flaming fires.  Photoelectric smoke alarms are slightly more expensive and are better at sensing the large smoke particles associated with smoldering fires.   This is why many organizations have recommended installing smoke alarms with dual sensors. This is typically where the discussion ends.

However it is not quite that simple. Photoelectric smoke alarms are significantly better at sensing smoldering fires and will sound 20 to 30 minutes faster.  A smoldering fire will also deplete the available oxygen and emit carbon monoxide making it difficult for occupants to escape.  Ionization alarms are slightly better at detecting flaming fires but our prone to false alarms from cooking and many people will disable this type to reduce the annoying false alarms – leaving them with no protection at all.  Another consideration is that the smoke chambers for the different technologies used different designs and combining both technologies in one smoke chamber will compromise the effectiveness of both.  This is why many cities, such as Albany, CA, have banned smoke alarms that use ionization technology.

How do you know what kind of smoke alarm is in your house?

Many brands will have a small “i” or ”p” on the face, to indicate the technology used, but many don’t. The label on the back will sometimes have the information clearly identified, but it is important to note that ionization type labels will always have a radiation warning, because ionization sensors use a very small amount of radiation to detect the smoke particles.

Smoke alarms have a lifespan?  

Most manufacturers recommend replacing smoke alarms once they are 10 years old.  So the chances are 90% that you have an ionization alarm and unless you’ve done some remodeling in the last 10 years, your smoke alarms have probably “expired.”  I think it is time to see what kind of smoke alarms you have hanging from the ceiling.  This five-minute task could save a life.

JMC Inspections: Service, Experience, Professionalism since 1994
“Good decisions are made with good information”


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