- Author
-
Oldweiler, A. J.
- Title
- Investigation of the Smoke Detector L-Number in the UL Smoke Box.
- Coporate
- Worcester Polytechnic Inst., MA
- Report
-
Thesis
May 1995
151 p.
- Keywords
-
smoke detectors
|
smoke detection
|
time lag
|
ionization detectors
|
optical density
|
velocity
|
smoke measurement
- Identifiers
- experimental apparatus and fuel; characterization of the test chamber
- Abstract
- It has been recognized that there is a delay from the time that the smoke outside a smoke detector reaches a given level and the time that level is reached in the sensor. The L-number was suggested by Heskestad to quantify this delay. The L-number is thought to be a function strictly of the physical detector, and independent of the smoke and flow conditions. The objective of this research was to determine if the L-number is independent of fuel type, rate of rise, and velocity. The L-number was determined for an ionization spot smoke detector using Heskestad's model. The smoke level outside the detector was measured with a measuring ionization chamber (MIC) and compared to the output of the ionization smoke detector which senses smoke by the same principle, the ionization chamber. The L-number for the same smoke detector was also determined with reduced entry restrictions. A modified version of the smoke box used in the sensitivity tests in the UL smoke detector approval standards. A gray smoke was generated with smoldering wood blocks, and a black smoke was generated with flaming kerosene. The rate of rise of the smoke level was varied by using different amounts of fuel. The velocity of the smoke was controlled by the test apparatus fan. Although a single L-number could be determined using all the test data, significant changes from this "average" L-number were found when the effects of velocity were examined independently. The L-number was found to vary inversely with velocity. There also appears to be some effect of the smoke source on the L-number. However, both black and gray smokes exhibited the same influences from the velocity. Finally, a reduction of the entry restrictions produced a lower L-number.