← Engineer Tools / Reference Table
BS 5839‑6 Category Table
Grades and LD categories for domestic fire detection, current to the BS 5839‑6:2019+A1:2020 revision.
Grades
System type & power source.
| Grade | Type |
|---|---|
| A | Full BS EN 54 system — control and indicating equipment, detectors and sounders on mains power with standby power per BS EN 54‑4. The highest specification, used for larger or communal systems. |
| C | Detectors and sounders on a common power supply (mains plus standby) with a central control unit, but without a BS EN 54 control panel. |
| D1 | Mains‑powered detectors, each with a tamper‑proof, non‑replaceable standby battery (typically a sealed 10‑year lithium cell). |
| D2 | Mains‑powered detectors, each with a user‑replaceable standby battery. |
| F1 | Battery‑only detectors with a tamper‑proof primary battery. |
| F2 | Battery‑only detectors with a user‑replaceable primary battery. |
Grades B and E were removed in the 2019+A1:2020 revision; Grade D and Grade F were each split into two (D1/D2 and F1/F2) to distinguish tamper‑proof from user‑replaceable batteries. Older references to a single "Grade D" or "Grade F" predate this split.
Categories
Coverage extent.
| Category | Coverage |
|---|---|
| LD1 | Detectors in all circulation spaces on the escape route, plus every habitable room and high‑risk area — the highest level of domestic protection. |
| LD2 | Circulation spaces on the escape route, plus specific high‑risk rooms such as the kitchen and principal living room. |
| LD3 | Circulation spaces on the escape route only — the minimum level of protection. |
| PD | A separate property‑protection category, layered alongside an LD category where property protection is wanted in addition to life safety. |
For a new‑build dwelling, Approved Document B states Grade D2, Category LD3 as the minimum considered adequate, though BS 5839‑6:2019 itself recommends the higher D1/LD2 combination as good practice. For rented and HMO properties, requirements are set by the local authority's licensing conditions rather than a single fixed figure — a common minimum specified is Grade D1/LD2, with larger or higher‑risk HMOs (three or more storeys, or five or more occupants) often requiring Grade A with LD1. Always check the specific licence schedule for the property.
Specifying detection for a rental or HMO?
Tell us about the site and what you need — we'll get back to you with a straight answer.