Sound Signals, Verbal Communications and Hand Signals
Coded sound signals, often referred to as acoustic signals, are safety signs. Where used these must:
- have a sound level considerably higher that that of the ambient noise without being excessive or painful;
- be easily recognisable and clearly distinct from any other acoustic signal and ambient noises.
If the device can emit both variable and constant frequencies, the variable frequency should be used to indicate a higher level of danger or more urgent need for action than is indicated by the constant frequency. Similarly, if the device can vary the intervals between sound emissions, the shorter intervals should indicate greater urgency than the longer intervals.
Where an acoustic signal is used to order evacuation (whether at constant or variable frequency, or with a continuous or intermittent noise), the signal should continue throughout the evacuation.
A safety sign in the form of a verbal message must in a language understood by the people involved so that it is pronounced and understood correctly and can be reacted to accordingly.
A live or recorded voice may be used. Messages must be as short, simple and clear as possible.
Sometimes the verbal message should be repeated in several languages, such as important safety messages on ferries or aircraft.
For direction of hazardous operations, the regulations include a table of words and meanings.
Safety signs in the form of hand signals must be precise, simple, expansive, easy to make and understand, and clearly distinct from other gestures.
The regulations include a table that defines the meanings of arm and hand movements and positions which are described and illustrated.
The operator must be able to recognise the signalman without difficulty, such as by distinctive clothing worn (eg. bright sleeves or armbands) or exlusive accessories used (eg. bats).