Emergency Alert and Evacuation Tones and sounds are standardised in:
ISO 7731 specifies the temporal pattern and frequency range for the tones but requires consideration of the installed environment to ensure that the signal is clearly audible and can be unambiguously discriminated from the ambient noise.
ISO 8201 selects a unique three-pulse, "on/off" temporal sound pattern and the required sound pressure level in the signal reception areas. The ISO signals are quite different from the existing Australian signals, which are slower, continuous ramped tones. For the audible evacuation signal to be recognisable, it is not necessary to specify the signal's spectral content. The spectral content should be selected to satisfy the specific site requirements.