Good luck with that one Rob - even the DDA Code of Practice does not specifically recommend the use of tactile braille fire safety signs - I quote - apologies for the small print !
"Visual impairments
5.31 For people with visual impairments, the range of auxiliary aids
or services which it might be reasonable to provide to ensure
that services are accessible might include one or more of
the following:
• readers;
• documents in large or clear print, Moon or Braille;
• information on computer diskette;
• information on audiotape;
• telephone services to supplement other information;
• spoken announcements or verbal communication;
• accessible Websites;
• assistance with guiding;
• audiodescription services;
• large print or tactile maps/plans and three-dimensional
models;
• touch facilities."
Such wisdom from a 101 page document that doesn't mention the word 'egress' or 'means of escape' once.