This report provides guidance in the specification of Safe Rooms designed as a response to the threat to people from Chemical, Biological or Radiological (CBR) incidents. It does not provide guidance in respect of protection from energetic missiles or explosives. The document is to be considered as a route map for those interested in developing their own Safe Room, not detailed design advice. It provides sufficient detail such that an interested party (e.g. a school, office or factory) can understand the key design parameters that they will need to specify to a detailed design specialist. It also provides a stepwise process (to be undertaken with the help of expert parties e.g. security experts, architects etc) to the development of a detailed specification that can be handed-on to other expert parties to develop the detailed solution. Its use will thus ensure that the user is an "intelligent customer" who procures what is needed rather than what is simply available or offered.