Variability and Error Rates in Fire Alarm Audibility Measurements and Calculations

Audibility of fire alarm systems at mandated levels is critical to ensure a warning is heard by building occupants. To accomplish this, designers and installers utilize on-scene measurements as well as design calculations to ensure that the audibility of the fire alarm system is as designed as required. Despite this, there is a dearth of information on the error and variability rates associated with these experiments and calculations. To fill in this gap, a three-room and connected corridor test setup was utilized and multiple repeat audibility tests were conducted across 12 configurations of different receiving rooms and door positions. Calculations were then conducted utilizing two oft-used and referenced methods. Ultimately, the experimental measurements had a coefficient of variation of 3.0% to 10.9% depending on the configuration. The calculation methods had differences from the experimental average of − 6.8% to 8.0% combined. It is shown that designers and installers should consider making multiple measurements to capture the experimental variability or at least assume it is 10% and if the measurement errors are randomized, could be as high as 20% or more. Meanwhile, a 10% factor of safety should be considered with the calculation methods to ensure the design implementation exceeds the intended audibility. Some additional observations from the experiments and calculations are also discussed including that the tests and calculations provide justification for the code requirements that a notification appliance be present in each bedroom or room that may have a door closed and, if it is a smoke alarm, that it be interconnected to other alarms to ensure audibility.