Escape routes must be marked right up to safe areas, particularly exits leading outside, which applies for general power supply conditions as well as failure thereof. They must be clearly identifiable in any situation and be made visible using emergency lighting in cases of power failure.
EU directive 92/58/EEC on minimum provisions for safety and health in work places specifies the formats for signs to be used in safety signage e.g. for escape route designation and for designating first aid stations.
The signs themselves are standardised in detail by ISO 3864, and in Germany additionally by DIN 4844-2 as well as the trade association regulations BGV A8 (formerly VBG 125) (see figure). Safety signs, both illuminated and backlit (escape sign luminaires) must exhibit 50% of the required luminance within 5 seconds, and 100% within 60 seconds. Colours are specified in ISO 3864. For escape route signage, the safety colour green applies. Green areas of the sign must feature a luminance of at least 2 cd/m2 at any point and a uniformity Lmin/Lmax of 1:10. Where smoke can develop, said luminance must be at least 10 cd/m2. Possible development of smoke must be identified using a previous hazard analysis. The average luminance of white surfaces must be 5 to 15 times the (average) luminance of the green surface.
Backlit signs lead to a doubled recognition range compared to illuminated signs of the same size. The recognition range d is derived from the height of the entire sign p and a constant s:
d = s · p
s = 200 for backlit signs
s = 100 for illuminated signs