P1 and P2 Fire Alarm Systems Explained

P1 and P2 are the two property-protection categories of fire alarm system in BS 5839. They aim to detect a fire early enough to limit damage to the building and its contents — often driven by insurance requirements.

P1 — detection throughout

A P1 system provides automatic detection throughout the building, including areas of low fire risk. The goal is the earliest possible detection anywhere, minimising property loss. It is the most comprehensive property category.

P2 — detection in defined areas

A P2 system provides automatic detection only in specified areas — typically those of higher fire risk or where a fire could cause disproportionate damage. It is more economical than P1 and used where the risk assessment (and often the insurer) accepts targeted coverage.

P versus L

Remember that P categories protect property, while L categories protect life. Many buildings need a system that satisfies both aims, and the design is set accordingly. See fire alarm categories for the full classification.

In practice

The choice between P1 and P2 comes from the fire risk assessment and any insurer requirement. Whichever is installed, it must be tested and maintained to BS 5839 to remain effective.