4.2.6.3-9 Signal Level

The signal intensity should be such that users can reliably discern the signal above the ambient control room noise.

Additional Information:
The intensity of an audio signal should be such that users are alerted aurally to an alarm occurrence under the most adverse anticipated background noise conditions. A signal level 10 dB(A) above average ambient noise is generally considered adequate. It has also been recommended that sound intensity should be limited to a maximum of 95 dB(A), but that signal levels of 115 dB(A) may be used if considered absolutely necessary to achieve required attention-getting reliability for alarms indicating extreme danger. The tendency for designers to err on the side of conservatism results in many audio signals being more intense than is necessary to ensure reliable detection (see Guideline 4.2.6.3-10, Design of Audio Signals).