Like all Approved Documents, following the guidance contained in ADB will result in a compliant solution, it is however not the only solution available for many building designs.
Building Regulation Approved Document B can be applied to more common building solutions, but can prove unacceptable for larger, more complex buildings. By taking a more holistic view to fire safety, BS 9999 allows compensatory measures to offset, e.g. travel distances and/ or total escape door width.
In a worked example for a supermarket, by following ADB, maximum travel distances of 18 m for egress in a single direction and 45 m for escape in two directions, and a minimum aggregated exit width (after discounting the largest exit) of 7500 mm would need to be applied. Following the basic approach suggested in BS 9999, the maximum travel distances could be increased to 20 m and 50 m, with the aggregated exit width reduced to 6150 mm. By introducing variations such as automatic fire detection and increased ceiling height, to the basic calculations, the maximum travel distance could be increased to 25 m and 62.5 m and exit width reduced to 4613 mm. One word of warning however, although satisfying the Regulations for Part B, you may fall foul of other parts, e.g. Approved Document M.
BS 9999 has in part superseded BS 5588, the only parts of which are still current are those that relate to residential properties. BS 9999 has to be applied in its entirety, you cannot dip into it for piecemeal solutions.
Although some fire safety knowledge is required, BS 9999 could be a useful tool for many designers.