The Grade System - is the system of engineering, not the level of protection.
Grade F - one or more battery powered smoke and heat alarms.
Grade E - a system of interlinked mains powered smoke and heat alarms with NO battery back up.
Grade D - a system of interlinked mains powered smoke and heat alarms with battery back up.
Grade C - a system consisting of smoke detectors and sounders (which may be smoke alarms) connected to a common power supply, comprising of mains power and a stand by supply with central control equipment
Grade B - fire detection and alarm system comprising of fire detectors (other than smoke alarms), fire alarm sounders and control and indicating equipment to either BS EN 54-2 and power supply to BS EN 54-4, or to Annex C of BS 5839 pt6.
Grade A - fire detection incorporating control and indicating equipment to either BS EN 54-2 and power supply to BS EN 54-4 installsd to BS 5839 : Pt 1 with some minor execeptions.
Grade D is required for new, owner occupied buildings of up to three storeys, two storey rented properties, and existing owner occupied buildings of up to two storeys. Very large storeys may require a Grade B alarm system.
Levels Of Protection
LD1 - a system installed throughout the dwelling, incorporating detectors in all circulation spaces that form part of the escape routes from the dwelling and in all rooms and areas in which fires may start, other than toilets, bath and shower rooms.
LD2 - a system incorporating detectors in all circulation spaces that form part of the escape routes from the dwelling, and in all rooms or areas that present a high risk of fire.
LD3 - a system incorporating detectors in all circulation spaces that form part of the escape routes from the dwelling.
