The Health and Safety (Safety Signs and Signals) Regulations 1996

5.    Interchanging and combining signs

The effectiveness of a sign must not be adversely affected by:

5.1. the presence of another emission source of the same type which interferes with visibility or audibility; therefore, in particular,

5.1.1. the placing of too many signs too close together should be avoided;

5.1.2. two illuminated signs which are likely to be confused are not to be used at the same time;

5.1.3. an illuminated sign is not to be used in the proximity of another similar illuminated source;

5.1.4. two acoustic signals are not to be used at the same time;

5.1.5. an acoustic signal is not to be used if there is too much ambient noise;

5.2. poor design, insufficient number, incorrect positioning, poor state of repair or incorrect functioning of the signs or signalling devices.