BS 5839-6
The code of practice for fire detection and fire alarm systems in domestic premises. It sets out grades A to F, which describe the type of system, and categories LD1, LD2 and LD3, which describe the level of protection. Grade D systems use mains powered detectors with a back-up supply: D1 has a tamper proof back-up (such as a sealed long life cell) and D2 has a user replaceable back-up. Grade F systems are battery only: F1 tamper proof, F2 user replaceable. LD1 covers the whole dwelling, LD2 covers escape routes and higher risk rooms, and LD3 covers escape routes only.