Designing An Emergency Lighting System: Part 3
For your emergency lighting system to conform to fire and safety regulations you need to ensure that exit signs are the correct format and size and that they are illuminated correctly.
BS 5266 Part 7 states ‘Signs which are provided at all exits intended to be used in an emergency and along escape routes shall be illuminated to indicate unambiguously the route of escape to a point of safety.’.
The below guidelines summarise some of the factors you need to take into account. As always, if you are unsure about any of the points or you need clarification on any matters, be sure to consult a qualified emergency lighting system designer or your local Fire Authority.
Sign Formats Should Not Be Mixed
Over the years there have been a few styles of emergency exit sign produced and sanctioned for use in emergency exit systems. It is important that throughout your building you are consistent in your use of exit signs to help avoid confusion.
Old buildings may have exit signs that are no longer acceptable for use. If there is ever any doubt as to which emergency exit sign format you should use, consult your local Fire Authority.
Viewing Distances
Exit signs should be easily visible to all users. For internally illuminated signs, those in use with a backlit box, the maximum viewing distance is 200 x the height of the exit sign panel e.g. if the panel height is 20cm the maximum viewing distance will be 40 metres.
For externally illuminated exit signs, those with a light source above them, the maximum viewing distance is 100 x the height of the panel. In this case for a 20cm tall exit sign the maximum viewing distance is 20 metres.
Exit Sign Illumination
Emergency signs must conform to many regulations. These include the colour of the sign, which must be in line with ISO 3864. This states that exit signs and first aid signs should be white with green as a contrast colour.
The luminance ratio of emergency signs is also strict. The luminance ratio of the white to the green colour must be somewhere between 5:1 and 15:1. Any 10mm2 patch of the sign must be illuminated to at least 2cd/m2 and the ratio of either colour’s maximum to minimum luminance should be less than 10:1.
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