Visual danger signals (such as information signs, safety colours, luminous and verbal as well as manual signals) or acoustic danger signals (i.e. alarms) have to meet the following requirements:
- The message must be clearly understandable, and any possible confusion must be eliminated.
- An optimum effect is to be achieved through the type, sequence, scope, number, location, functions and design of such signals.
- Visibility and audibility must not be impaired (i.e. ambient noise affecting acoustic signals).
- It must also be possible for workers with impaired hearing or vision (also resulting from personal protective equipment) to perceive these signals. See also Emergency Signals.