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Author: Philip Payne Admin | Date: 6th Oct 2021

BS5499-4, Clause 4.6c makes it very clear that “mounting height greater than 2.5m may be used, e.g. in large open spaces or for operational reasons, but such signs should be both conspicuous and identifiable and therefore large signs might be necessary”.

To assist evacuees with the prediction of the location of successive signs, the following principles should be applied:-

  1. Sign mounting heights are measured to the base of the sign.
  2. All signs should be mounted so that they are readily visible.
  3. Signs above doors or open spaces should be mounted between 2m and 2.5m from floor level, measured to the base of the sign and be sited as close to the centre line of the escape route as practicable;
    NOTE 1 This mounting height is intended to ensure that signs can be readily seen, e.g. over the heads of people.
  4. Signs sited on walls should be mounted between 1.7m and 2m, from floor level measured to the base of the sign;
    NOTE 2 This mounting height is intended to ensure the signs are within the immediate field of vision.
  5. Mounting heights greater than 2.5m may be used, e.g. in large open spaces or for operational reasons, but such signs should be both conspicuous and identifiable and therefore larger signs might be necessary*;
  6. Signs should be sited at the same height throughout the escape route, so far as reasonably practicable.

BS EN 1838:2013 makes it very clear that “you should avoid mounting signs more than 20 degrees above the horizontal view”

It would be good practice to reduce the viewing distance according to BS5499-4 Annex C

Using our previous technical blog about “Legend Viewing Distances” for signs mounted less than 2.5m

Example for 3m mounting height using an average eye level of 1.5m.

Firstly we need calculate the sign level above eye level, this is:

Onto the radius of viewing distance reduced for a 4m mounting height this is calculated by:

Therefore the viewing distance normal to the sign for a 4m mounting height would be:

The typical viewing distance for the sign mounted >2.5m calculated at 26m compared to the >2.5m viewing distance of 25.8m you will see a loss of 0.2m distance.

Something to consider……Viewing distances should then be reduced if the sign is to be viewed predominantly from the left or right of its centre.

For example, if you (the observer) are viewing from 30 degrees to the left or right of centre, the effective viewing distance is reduced by the cosine of the angle

To improve conspicuousness of the exit sign for mounting heights above 2.5m we would suggest using our larger 300 range.

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