When visual signals are insufficient, acoustic signals provide critical alerts through pure tones, specific frequencies, or spoken messages. These are categorized by urgency and should be designed to be distinguishable from ambient factory noise. IEC 60073:2002
(flashing) are used to attract urgent attention. IEC 60073 specifies two flashing speeds: Normal (High Priority): 84–168 flashes per minute. Slow (Low Priority): 24–48 flashes per minute. 2. Acoustic Coding iec 60073 pdf
Color is the most effective means of attracting attention, but it must be used strictly according to the defined meanings: Safety Meaning Condition of Process/Equipment Emergency or Fault (e.g., E-Stop activated) Yellow Abnormal condition or transition state Green Normal condition; "Go" or circuit healthy Blue Requires specific operator action White No specific safety meaning; often used for auxiliary states IEC 60073 specifies two flashing speeds: Normal (High