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5.3
Sensitivity Ranges
Smoke detector manufacturers are required by UL to specify the nominal sensitivity range of their production
detectors. The ranges vary widely among manufacturers and between types of detectors. Typically, nominal
sensitivity for a photoelectric type is about 3.0 ± 0.5 %/ft and for an ionization type is about 1.5 ± 0.5 %/ft.
If a nominal sensitivity is given without a range, then according to NFPA 72: 7-3.2.1 (1996), a detector will
pass if it alarms between 0.5 and 4.0 %/ft. obscuration (See UL 268 Standards, 31.1, January 4, 1999 ed.).
All the detectors of a given model may not necessarily fall within the extreme values provided by the
manufacturer. Consult the manufacturer, if necessary.
Because of the built-in uncertainty of ± 0.4 %/ft in relating field test results from the Gemini 501-B to that of
the UL smoke chamber, detectors with results ± 0.4 %/ft beyond the given range may be considered
acceptable. As an extreme example, results as high as 2.4 %/ft may be considered acceptable if the listed
sensitivity is 1.5 ± 0.5%/ft
5.4
Test Procedures (For duct detectors, please refer to APPENDIX G.)
Start the test with the nominal sensitivity value given by the manufacturer. Depending on the test result, you
can stop or do additional test using either the upper or lower limit of the sensitivity range. For example, if the
specified sensitivity is 1.5 ± 0.5 %/ft, your first test would be 1.5 %/ft and your second could be 1.0 %/ft (1.5 -
0.5), 2.0 %/ft (1.5+ 0.5) or no test, depending on the result from the first test. The third test if needed, could
be 0.6 (1.5 - 0.5 - 0.4) or 2.4 (1.5+0.5+0.4) %/ft.
Start testing after the initial warm-up period and total emulsification of the liquid in the reservoir. The
pressure and dilution air LEDs should stay at green.
Place the shroud over the test detector. Adjust the flow meter reading to the desired level shown by the
appropriate scale. Reset or note the timer as you begin. If the detector alarms within 30 to 40 seconds, hold
the shroud in place while you reduce the concentration to zero. Immediately turn the compressor switch off.
Wait an additional 5-10 seconds before removing the shroud and shutting off the blower.
If the detector does not alarm in less than 30 to 50 seconds, increase the concentration to the next higher
value with the shroud still in place. Wait 30 to 50 more seconds for it to alarm.
If the test detector alarms and you want to continue the test at a lower setting, you must reset the alarm.
Before testing at a lower value, allow at least 20 seconds to flush out the old smoke with the shroud in place
and compressor off.
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