1.3.11-10 Confusable Signals

Audio warning signals that might be confused with routine signals or with other sounds in the operating environment should not be used.

Additional Information:
Auditory signals intended to alert the user to a malfunction or failure must be different from routine signals such as bells, buzzers, and normal operating noises. Examples of such signals include trains of impulses that resemble electrical interference, or signals similar to noise generated by air conditioning or other equipment. The frequency of a warning tone should be different from that of the electric power employed in the system, to preclude the possibility that a minor equipment failure may generate a spurious signal.