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

of approximately 1.1x10 6 particles/cm 3 . Initially, the ionization chambers follow the numberconcentration trend, but from 800 s on they continue to climb while the number concentrationstarts to level off. This observation, along with the steady rise in the mass concentrationsuggests that the mean particle size was increasing during the test.Time to Alarm Threshold (s)A180016001400120010008006004002000PE lowPE midPE highION lowION midION highA B C D E F GAlarm LocationMass Concentration (mg/m 3 )C50403020100MassNumber0 400 800 1200 1600Time (s)2 10 61.5 10 61 10 65 10 50Number Concentration (particles/cm 3 )Air Temperature ( o C)B35302520temperaturerelative humidity0 400 800 1200 1600Time (s)504540353025Relative Humidity (%)Ion Chamber (volts)D54.84.64.44.24Chamber 1Chamber 2Number0 400 800 1200 1600Time (s)2 10 61.5 10 61 10 65 10 50Number Concentration (particles/cm 3 )Figure 179. Smoldering cotton wicks -eight sets of four wicks were ignited with a 12 s delayusing the staged wick ignition device, located on the living room floor at the chair burn location.Fan was on. Ignition sequence started at t=30 sThe following generalizations characterize the smoldering cotton scenarios:• Ionization alarm thresholds were reached earlier and at more locations than photoelectricalarm thresholds.• The mass and number concentration by the end of the test were nearly the same for bothcases.198