Low Frequency Alarm Signal Effectiveness

For decades the requirements for alarm signaling have required a sound pressure level of 85 dBA at a distance of 10 feet for single and multiple station smoke alarms. Research into waking effectiveness for sleeping occupants has shown an increase in performance for low frequency harmonic tones, especially for at-risk groups including the hard of hearing, children, and those affected by drugs and alcohol. Producing an equivalent 85 dBA alarm tone at this frequency requires up to four times the raw signal power compared to traditional alarms. This study, conducted for the Fire Protection Research Foundation, compared 40 years of code requirements and sleeping studies to determine if a reduction in the required sound pressure level can be justified for low frequency tones that would still provide better waking effectiveness compared to traditional alarm signals. The results are discussed and assessed to justify potential changes to codes and standards.