Fire Alarm Interface with Stairwell Pressurisation
In many taller buildings the protected stair is kept usable in a fire by pushing air into it — stairwell pressurisation, a smoke-control measure that holds smoke back so people can escape. The fire alarm is what wakes that system up: on detecting fire, it triggers pressurisation through a defined interface. It is a clean division of labour that goes wrong quietly when the interface is assumed rather than proven. This guide covers what the fire alarm's part is and what to check.
The central point is that the fire alarm detects and triggers pressurisation via an agreed cause and effect, while the pressurisation design itself is a specialist smoke-control matter.
Who this is for
This is for competent fire alarm engineers dealing with interfaces to stairwell pressurisation. The experience level assumed is competent engineer. Use it for the principles; what the interface should do comes from the smoke-control and fire strategy, implemented through the fire alarm within BS 5839-1, with actuation following BS 7273-4 where relevant. The pressurisation system's performance is verified by the relevant smoke-control specialists.
What the interface does
Stairwell pressurisation raises the air pressure in a protected stair to help keep smoke out and the escape route usable. On a fire signal, the fire alarm typically activates the pressurisation through a defined interface and the system cause and effect: detection starts the agreed response. The fire alarm's role is to detect and to trigger that action reliably. The pressurisation design itself — how it achieves and holds the right conditions — is a specialist smoke-control matter, coordinated with BS 5839-1 and BS 7273-4 where actuation applies. The interface is the handshake between two systems that must work together for the stair to stay protected.
Whose job is what
Keeping the responsibilities clear avoids most confusion. The pressurisation system's design — how much air, under which conditions, and how it performs — is a specialist smoke-control matter, not the fire alarm engineer's remit. The fire alarm's responsibility is to detect fire and activate the agreed cause and effect that starts pressurisation. So the fire alarm implements a trigger defined by the smoke-control and fire strategy; it does not design or size the pressurisation. Its part follows BS 5839-1, with actuation following BS 7273-4 where relevant. When something about the interface seems wrong, the first question is often whether the fire alarm's trigger is correct, and the second is whether the pressurisation itself performs — two different specialisms.
Where the interface fails
Interfaces spanning two systems are where problems hide. From field experience, the recurring failures are an interface commissioned at the panel but never proven end to end, pressurisation that does not actually start or perform as the cause and effect intends, and changes to either system that leave the interface out of date. Because it crosses the fire alarm and the smoke-control installation, it can fall into the gap between trades, each assuming the other owns it. The interface must be proven against the documented cause and effect, following BS 5839-1 and BS 7273-4 where actuation applies, with the smoke-control performance verified by the relevant specialists rather than presumed.
Proving the interface on service
On maintenance, the fire alarm's part of the interface deserves deliberate testing, not a panel-only tick. Confirm the interface operates per the documented cause and effect — that detection triggers pressurisation as intended — that changes to either system have been reflected, and that the interface is proven end to end. From field experience, untested interfaces and changes never carried through to the cause and effect are the common findings. Record the results, and flag anything where the fire alarm's trigger cannot be fully proven, or where the pressurisation performance is in doubt, for specialist review. The fire alarm engineer proves the trigger; the specialist proves the airflow.
Common points to check
Recurring issues include interfaces proven only at the panel, pressurisation not starting or performing as intended, and changes not reflected in the cause and effect. Confirming the fire alarm's trigger works end to end against the documented cause and effect is the essential check.
When not to rely on this alone
When not to use this article: do not use it to design or verify the pressurisation system's performance. That is a specialist smoke-control matter; the fire alarm implements the agreed cause and effect, applied by competent professionals.
Relevant standards
The fire alarm's part in the interface sits within BS 5839-1, a code of practice, with actuation following BS 7273-4, serving the smoke-control and fire strategy. The legal duty for fire precautions in most non-domestic premises sits under the Regulatory Reform (Fire Safety) Order 2005. Separate the legal duty from the recommended methods, and always work to current editions.
Professional disclaimer
This is an educational and workflow resource for competent engineers and does not replace the current British Standards, the smoke-control design, the fire strategy, or competent judgement. Verify the interface against the documented cause and effect, with pressurisation performance verified by specialists.
Related documentation
Use this with the current BS 5839-1 and BS 7273-4, the smoke-control design, the fire strategy and the system cause and effect. Record interface tests end to end, and re-prove the trigger after any change to either system.