Analysis of the Effects of Temperature and Velocity on the Response Time Index of Heat Detectors

Abstract

Recent revisions to NFPA 72, the National Fire Alarm Code, have specified the response time index (RTI) as the sensitivity listing for heat detectors. Originally derived as a sprinkler sensitivity rating, there has been little work performed to validate the use of the RTI rating for heat detectors. RTI values are determined by plunging the devices into a hot wind tunnel at 200 C (392 F) and 1.5 m/s (4.9 ft/s). These test conditions are unrealistically severe for the majority of expected ceiling jet profiles. While the RTI correlation is purported to be independent of temperature and velocity, data from previous studies indicates otherwise. This study examined the effects of low temperature and low velocity plunge test conditions on the constancy of the RTI for several common heat detectors. The RTI correlation was found to be inconsistent across temperature and velocity test conditions.