Section 5-10. Requirements for acoustic signals

Acoustic signals must:
  1. a.
    have a sound level that is considerably higher than the background noise level and be audible without being unnecessary loud or painful;
  2. b.
    be easily recognisable, especially with regard to the duration of the sound pulses and the frequency between them or between groups of sound pulses, and be distinct from other acoustic signals and ambient background noise.
If a device can emit an acoustic signal at variable and constant frequencies, the variable frequency should be used to indicate a higher level of danger or a more urgent need for the requested/imposed intervention or action than indicated by the constant frequency.
Acoustic signals for evacuation must be continuous.