Performance of Home Smoke Alarms - National Institute of ...

Figures 108 through 114 show smoke obscuration near the ceiling (20 mm below the ceiling)and near face height (900 mm from ceiling or 1.5 m from floor) at several locations throughoutthe home. Like the gas temperatures, peak values are highest near the fire (an optical density ofnearly 5.0 m -1 near the ceiling in the main bedroom) and peak values less than 2.0 m -1 furtherremoved from the fire. In the main bedroom, the smoke meter near the ceiling shows an initialpeak beginning about 50 s not evident in other locations. Examination of the video for this testshows little reason for this initial peak so it may indicate a malfunction in the instrument.Values at the 1.5 m level are naturally lower, typically below 1.0 m -1 . In the closed bedroom, anincrease in obscuration is noticeable, but still near ambient levels throughout the test.Figure 115 shows carbon monoxide concentration 900 mm below ceiling level (1.5 m from thefloor) at several locations throughout the home. Peak values range from a high of 0.099 %volume fraction near the fire down to 0.043 % volume fraction remote from the fire – bothshortly after initiation of suppression. Just prior to suppression, these values are 0.049 % volumefraction and 0.017 % volume fraction, respectively. Similarly, values from carbon dioxide(figure 116) range from 2.3 % volume fraction near the fire down to 0.74 % volume fractionremote from the fire overall and 2.0 % volume fraction down to 0.25 % volume fraction prior tosuppression. Oxygen concentration (figure 117) lowers quickly in the main bedroom fire roomto a low of about 19 % volume fraction. By the end of the test, concentrations at allmeasurement points are similar at just under 20 % volume fraction.A total of 43 fire alarms were monitored in each test. Figures 118 to 121 show the measuredoutput for the alarms at one measurement location (just outside the main bedroom). Many of thesmoke alarms (figure 118) respond within about 40 s after ignition. In this test, all but one of thealarms responded to the fire. One alarm, Ion-4 (see figure 10 for details of the alarmidentification codes), showed little response by the end of the test. The carbon monoxide alarms(figure 119) begin to respond within about 50 s, with significant output after 100 s. One of thealarms, CO-1, was inadvertently disconnected during this test. The heat alarm at 127 s(figure 120) and tell-tale sprinkler at 147 s (figure 121) respond within 20 s of one another. Oneof the photoelectric alarms shows little response until late in the test.5.3 Calculation of Alarm TimesFor each of the analog alarms, voltage readings were converted to engineering units typical forthe alarm – obscuration for smoke alarms (from table 1) and concentration for carbon monoxidealarms (from a linear calibration with reference gases). Calibrations of each individual alarm wasdetermined in the FE/DE (see section 2) and are shown in table 13. Typical alarm points for eachtype of alarm were used to determine a time of alarm for each alarm at each measurementlocation:104