The short answer
BS 5839-1 sorts commercial fire alarm systems into three groups. Category M is manual only (call points, no automatic detection). Categories L1 to L5 protect life, from L1 (detection throughout the building) down to L4 (escape routes only), with L5 for a bespoke design. Categories P1 and P2 protect property rather than people. The fire risk assessment for the premises sets the category.
The categories at a glance
Manual call points and sounders, no automatic detection. Relies on people discovering the fire and raising the alarm.
Automatic detection throughout all areas of the building. The highest level of life protection, typical in care homes and hospitals.
Everything in L3, plus detection in rooms the risk assessment identifies as high risk, such as kitchens, plant rooms or sleeping areas.
Detection on escape routes and in the rooms that open onto them, so people are warned before a fire blocks their way out.
Detection within the escape routes themselves: corridors, circulation areas and stairways.
Detection placed to meet a specific fire engineering objective that the other categories do not cover.
Automatic detection throughout, designed to call the fire service as early as possible and limit damage. Often an insurer requirement.
Detection only in parts of the building with a high fire risk or high-value contents.
How do I know which category my building needs?
The fire risk assessment decides it. The responsible person must have a suitable and sufficient assessment under the Regulatory Reform (Fire Safety) Order 2005, and it should state the category the building needs and why. The designer then specifies the system to that category under BS 5839-1.
If your assessment does not state a category, or the building has changed since the system went in (an extension, a change of use, new sleeping accommodation), the system may no longer match the risk. That is one of the most common gaps we find on a first survey.
Can a building have more than one category?
Yes. Categories are often combined, for example L2/P2, where life protection covers escape routes and high-risk rooms while property protection is added to a server room or stock area. The design certificate should record exactly what was installed where.
What about flats and HMOs?
Houses in multiple occupation and blocks of flats often fall under BS 5839-6, the code for domestic premises. It uses grades (how the system is built, from a panel-based Grade A system to mains-powered alarms with battery backup, Grades D1 and D2) and categories LD1 to LD3 (how much of the dwelling is covered). The communal areas of larger HMOs and blocks may need a BS 5839-1 system. Your local housing authority and the fire risk assessment will say which applies. See our HMO landlord guide.
Does the category change how often it is serviced?
No. Every category is serviced by a competent person at intervals of no more than six months under BS 5839-1, with quarterly visits common for larger or higher-risk premises. Larger categories simply mean more devices to test on each visit. See fire alarm servicing.
Common questions
What is the difference between L1 and L2?
L1 puts automatic detection in every area of the building. L2 covers escape routes and the rooms that open onto them, plus only the rooms the fire risk assessment identifies as high risk.
What fire alarm category does a care home need?
Almost always L1, because residents sleep on the premises and may need help to evacuate, so the earliest possible warning matters. The fire risk assessment confirms it.
What category is most common in offices?
It depends on the fire risk assessment, but many offices use L3 or L2, with manual call points throughout. Some small, simple premises use Category M.
Is a P1 system a legal requirement?
Not usually. Property protection categories are normally required by an insurer rather than by fire safety law, often as a condition of cover.