Temporal T3 Evacuation Tones

International Standard ISO 8201:2017 covers the requirements for an audible signal that is used alone and as a general evacuation signal for a building. ISO 8201:2017 defines the acoustic parameters of the audible emergency evacuation signal are defined being the temporal pattern and the required sound pressure level at all places within the intended reception area of the signal.

Russ Porteous
CEO, Firewize
07 Jun, 2021

According to the introduction of ISO 8201, there has been growing interest in in the development of an international audible signal which, when heard would unequivocally mean "evacuate the building immediately"

In searching for an appropriate audible signal, it was considered that levels of background noise and frequency patterns are so variable, particularly in the industry, that no signalling device would be able to “penetrate” all background noises and frequency patterns.

A temporal evacuation pattern typically consists of three audible pulses (T3) with a 0.5 second ON phase and a 0.5 second OFF phase.  The three pulses are then repeated after a 1.5 second delay OFF, and should repeat indefinitely in this sequence or for a minimum of 180 seconds. In certain environments where the ambient (A-weighted) sound pressure level exceeds 110dB, additional visual and/or tactile signals shall also be provided to complement the audible warning signals within the building.

T3 Temporal Warning Tone Waveform

An additional advantage of using a standardised temporal pattern as the distinguishing characteristic of an audible emergency evacuation signal is that the temporal pattern can be applied to visual and tactile signals to aid those who have impaired hearing.

Australia adopted the Temporal "T3" tone from 2003 and makes the tones described in Australian Standard AS2220 redundant in for new buildings.