<<<  25 of 39  >>>

1. 1. Response-Time Comparisons of Ionization
      and Photoelectric/Heat Detectors
      
      1. Introduction
      
      

   2. •“Despite the recent introduction of new technologies, the vast majority of smoke detectors sold
      and in service today are based on either the photoelectric or the ionization principle. In the twenty-five years since
      smoke detectors began to attain widespread acceptance as essential life/safety fire protection devices [1], it has
      become generally accepted that “ionization smoke detection is more responsive to invisible particles
      (smaller than 1 micron in size) produced by most flaming fires” [2].
      
      

   3. •It is also generally accepted that photoelectric detection is “more responsive to visible particles (larger
      than 1 micron in size) produced by most smoldering fires”, “somewhat less responsive to smaller particles
      typical of most flaming fires”, and “less responsive to black smoke than lighter colored smoke” [2]. However, the
      relative merits of the two detector types continue to be a subject of discussion [3].”8

1 of 4 . . .

(c) Copyright July 09

1. 1. •“Consistent with the results of the earlier investigation comparing ionization smoke detectors to photoelectric
      detectors, the results reported here show that in UL 268 Smoldering Smoke tests, photoelectric detection occurred
      many minutes earlier than ionization detection. The results also show that in UL 268 Flammable Liquid Fire tests
      and TF-5 type liquid heptane fire tests, photoelectric and ionization detection occurred at about the same time.”

Slides: 25, 26, 27 and 28:
These slides will show you not all testing demonstrates that the ionization is fast during a flaming fire.  In a conference sponsored by NIST in 2001, a UL test was presented.

The results again show the photoelectric’s were much faster to respond in a smoldering fire, depending on the placement of the detector to the fire, by as much as almost 19 minutes when they were set at the sensitively levels sold to home owners.

Note:

     The Photoelectric in this test also was faster by literally a few seconds than the ionization in the flaming tests as well.

     Remember that sensitively levels can be manipulated by manufacturers.  When the sensitivity levels were set the same, to the most sensitive levels, the Photoelectric was 11 seconds faster than the ionization in the flaming tests but was 30 minutes faster in the smoldering tests.