I am led to believe that writing on Fire Exit Signs should start with an upper case letter an the remainder to be lower case to conform with BS5499 and disability legislation, other examples show all the letters in upper case, which is correct?

Fire exit signs supplementary text did adhere to BS5499-1 and the first letters should be in capitals and the remainder should be lower case. This is because people with dyslexia and other reading problems may struggle to understand signs where the lettering is all capitals. BS 5499 part 1 2002 has now been withdrawn and replaced by BS ISO 3864-1:2011 but the new standard doesn’t deal with the style of text to be used so I would use the guidance provided by BS 5499 part 1 although it has been withdrawn.