2. Background
Historically, smoke detectors are tested by UL and given a rating based on the smoke box test. The smoke box test is
conducted at a fixed high velocity, while full-scale tests and real fire situations generally have much lower velocities at
the time of detector activation. As a result, full-scale testing has demonstrated that detector alarms operate at a smoke
concentration significantly higher than the value determined in the smoke box test. Therefore, smoke box ratings
cannot properly be used to determine when the detector will activate in a real world fire situation, because at lower
velocities the detector will not alarm when the threshol