What colour is a safe sign?

There are 5 main types of safety signs in common use in the UK. Each sign type has a specific 'safety colour' associated with that type of safety message & a special graphic shape. The 5 types of safety sign described by BS5499 part 1 (Specification for geometric shapes, colours and layout) are:

• Prohibition signs which have a main safety colour of red, with a contrast colour of white and a crossed through circle in red with a graphical symbol colour of black.
• Mandatory action signs have a main safety colour of blue, with a contrast colour of white and a circle in blue with a graphical symbol colour of white.
• Hazard (warning) signs have a main safety colour of yellow, with a contrast colour of black and a yellow equilateral triangle with radiused corners and black border with a graphical symbol colour of black.
• Safe Condition, Escape Route and Safety Equipment signs have a main safety colour of green, with a contrast colour of white and a green rectangle or square with a graphical symbol colour of white.
• Fire Equipment signs have a main safety colour of red, with a contrast colour of white and a red rectangle or square with a graphical symbol colour of white.

For each of these named safety colours – there are colorimetric properties specified in BS 5378-2. This means that to meet BS5499, not only do safety signs have to use the right colours for the right application (type of safety message) but the actual colour used has to be measured by the manufacturer and must meet the properties specified with the given tolerance limits. These colorimetric and photometric properties are also specified in ISO 3864-1984 – but the tolerance limits particularly for blue are wider in the British Standard.

Each colour is specified using a CIE chromaticity diagram (CEI 45-15-2001) on this colour space an area is defined within which the measured colour must lie.

The safety colour of each type of safety sign can be measured with a spectrophotometers such as the i1 from X-rite. This particular device won't give the CIE xyZ co-ordinate directly – but if measured using L*a*b values, these can be translated using a number of colour space translation engines.

The boundary of each area is defined by the x & y co-ordinates of 4 points. When plotted on the same chart the actual measured colour of the safety sign colour must lie within this boundary to meet the specification.

All this may seem overly complicated for a simple safety sign – but the idea is uniformity – and from this universal understanding. The standards were originally drawn up during the formative years of the European Economic Union – when workers from different counties were more likely to be migrating to a country whose language was not their own. Through the use of specific colours and symbols for specific safety messages, across the whole of Europe – common understanding and increased safety for workers has been achieved.

1) CIE (Commission Internationale de l’Eclairage) Vocabulary Publication No. 17, 1970, “International lighting vocabulary”.