Passive Fire Protection vs Active Fire Protection — A Specifier's Guide

It is a common misconception — sometimes encountered even at design stage — that a building with a comprehensive sprinkler system has reduced need for fire-rated doors and curtains, or vice versa. In reality, passive and active fire protection are not competing strategies where investment in one offsets the need for the other. They are two distinct, complementary layers of defence, and UK building regulations, guided by Approved Document B and BS 9999, require both, addressing different failure modes.

Two Systems, One Objective

The shared objective of both systems is the same: protect occupants and limit damage by controlling a fire. But they pursue this objective through entirely different mechanisms. Active fire protection systems detect a fire and respond to it — they require power, water pressure, mechanical actuation, and in most cases, a functioning detection and control system. Passive fire protection systems are physically built into the structure and fabric of the building — they do not detect or respond to anything; they simply exist as barriers that contain fire and smoke by their construction and material properties.

What Active Systems Do

Sprinklers, smoke detection, fire alarm panels, smoke extraction fans and pressurisation systems are all active systems. Their strength is speed and suppression — a sprinkler head can begin discharging water onto a fire within seconds of activation, often controlling or extinguishing a fire before it grows large enough to threaten the building's structure. Their vulnerability is dependency: they require electrical power (or backup power), correctly maintained mechanical components, and — in the case of sprinklers — an adequate, pressurised water supply. A fire that starts during a power outage, or in a system that has not been maintained, may not receive an active response at all.

What Passive Systems Do

Fire doors, fire curtains, fire-rated walls and floors, and fire stopping at service penetrations are passive systems. A 120-minute rated fire door does not need power, does not need to detect anything, and does not need maintenance beyond ensuring its self-closing mechanism and seals remain functional — it provides its rated performance simply by being correctly installed and closed. This is why BÖLDT's automatic fire curtains are engineered with gravity fail-safe deployment: even within a 'passive' product category, the deployment mechanism is designed to function with no dependency on power or battery backup, closing the gap between passive and active failure modes.

Why Codes Require Both

Approved Document B's requirements for fire doors and fire curtains exist precisely because active systems can fail or be delayed, and because even a successfully suppressed fire generates smoke and heat that compartmentation needs to contain while occupants evacuate and fire services respond. A sprinkler system controlling a fire in one room does not prevent smoke from that room spreading through an open door into a corridor — that is the job of the fire door. Specifiers should treat the passive fire protection package — doors, curtains, and the compartment lines they complete — as a primary life-safety system in its own right, not a secondary measure to be value-engineered once the active systems budget is set.