IONIZATION VS PHOTOELECTRIC
The
two most commonly recognized smoke detection technologies are ionization
smoke detection and photoelectric smoke detection.
Ionization
smoke alarms are
generally more responsive to flaming fires.
How they work: Ionization-type smoke alarms have a small amount of radioactive material between two electrically charged plates, which ionizes the air and causes current to flow between the plates. When smoke enters the chamber, it disrupts the flow of ions, thus reducing the flow of current and activating the alarm.
How they work: Ionization-type smoke alarms have a small amount of radioactive material between two electrically charged plates, which ionizes the air and causes current to flow between the plates. When smoke enters the chamber, it disrupts the flow of ions, thus reducing the flow of current and activating the alarm.
Photoelectric
smoke alarms are generally more responsive to fires that begin
with a long period of smoldering (called “smoldering fires”).
How they work: Photoelectric-type alarms aim a light source into a sensing chamber at an angle away from the sensor. Smoke enters the chamber, reflecting light onto the light sensor; triggering the alarm.
How they work: Photoelectric-type alarms aim a light source into a sensing chamber at an angle away from the sensor. Smoke enters the chamber, reflecting light onto the light sensor; triggering the alarm.
For each type of
smoke alarm, the advantage it provides may be critical to life safety in some
fire situations. Home fatal fires, day or night, include a large number of
smoldering fires and a large number of flaming fires. You can not predict the
type of fire you may have in your home or when it will occur. Any smoke alarm
technology, to be acceptable, must perform acceptably for both types of fires
in order to provide early warning of fire at all times of the day or night and
whether you are asleep or awake.
The best evidence has
always indicated that either type of smoke alarm will provide sufficient time
for escape for most people for most fires of either smoldering or flaming type.
However, research is ongoing, and standards are living documents. If at any
time, research points to a different conclusion, then that will lead to
proposals for changes in the NFPA standard or the closely related Underwriters
Laboratories standard for testing and approving smoke alarms. Both
organizations currently have task groups looking at smoke alarm
performance in the current home environment.
