Most people responsible for a building know they need a fire alarm. Fewer know that their building may also legally require an AOV system, a PAVA system, or both, and the distinction between a fire alarm and an evacuation system catches people out more often than you would expect. This post explains what each system does, when regulation requires them, and how they work together with fire detection.
What is the difference between fire detection and evacuation systems?
Fire detection tells you there is a fire. AOV and PAVA manage how people get out safely. A fire detection and alarm system does exactly what the name says: it detects fire and raises an alarm. What it does not do, on its own, is manage the conditions people evacuate through, or tell them clearly what to do. Modern building regulation increasingly treats AOV and PAVA as essential components of a complete life safety strategy rather than optional extras.
What is an AOV system?
AOV stands for automatic opening vents: a smoke control system that opens vents automatically when fire is detected. Smoke, not flame, is the primary killer in building fires. Vents at the head of stairwells, in smoke shafts or in corridors open to release smoke and heat, keeping escape routes passable for the people using them and for firefighters coming the other way.
AOV systems are a common requirement in residential buildings above certain heights, in buildings with single-stair escape routes, and wherever a smoke control strategy forms part of the building’s fire engineering design. In many cases they are a Building Regulations requirement rather than a recommendation, and like fire detection they must be maintained and tested to remain compliant. An AOV that has seized shut through years of neglect is a life safety failure waiting to be discovered at the worst possible moment.
What is a PAVA system?
PAVA stands for public address and voice alarm: a system that delivers clear, intelligible, zone-specific spoken messages during an emergency. Research going back decades, including work by the Fire Research Station, has consistently shown that people respond faster and more decisively to spoken instructions than to alarm tones. A bell or sounder tells you something is happening. A voice message tells you what to do about it.
In a phased evacuation, standard in taller and more complex buildings, PAVA allows different messages in different zones: evacuation instructions on the fire floor, alert-and-standby messages elsewhere. This is not achievable with conventional sounders, which is precisely why PAVA is specified for buildings where phased or staged evacuation forms part of the fire strategy.
PAVA is also increasingly relevant beyond fire. Under Martyn’s Law, qualifying premises will need procedures for invacuation and lockdown as well as evacuation, scenarios where the right instruction is emphatically not “evacuate the building”, and communication with people on the premises is itself one of the Act’s four named procedure areas. A conventional alarm tone cannot distinguish between “get out” and “stay in and shelter”. The Act mandates no particular system; it requires communication procedures that work in practice, and many organisations may conclude that voice messaging is how theirs will.
When do you need them?
It depends on your building: its height, layout, use, occupancy and evacuation strategy, which is why this is a design question rather than a checklist question. As a rough guide: residential buildings over 11 metres frequently require smoke control provision including AOV; buildings using phased evacuation typically require voice alarm; and buildings within Martyn’s Law scope should be actively assessing their emergency communication capability now.
The most common gap we encounter is not buildings missing these systems entirely. It is buildings where the systems exist but have fallen out of maintenance, or where the building has changed use or layout since the systems were designed, leaving the original smoke control or evacuation strategy quietly obsolete.
How do these systems integrate with fire detection?
Through cause and effect programming: the logic linking detection zones to vent operation and voice messaging, which is where the real engineering lives. AOV and PAVA do not operate in isolation. They are triggered by, and coordinated with, the fire detection system. BS 5839-1:2025 now formally requires that end users receive a Cause and Effect document explaining exactly how these interactions work, a change that reflects how critical this integration layer is.
It also raises the evidence question every life safety topic ends at: if an inspector asked tomorrow whether your AOVs opened on last month’s test, and what has been done to the vent in stairwell two since installation, could you show them? For Smartec clients, every AOV actuator, amplifier and speaker circuit we maintain sits in the Client Portal with its full test and defect history in a tamper-proof Digital Logbook, with Photo-Verified Defect Reporting. The systems get people out. The Portal proves they will.
Smartec designs, installs and maintains AOV and PAVA systems as part of an integrated life safety approach, alongside fire detection, disabled refuge and evacuation systems. If you are unsure whether your building’s smoke control or evacuation communication provision matches its current use and regulatory position, a review costs far less than discovering the gap during an incident or enforcement visit. Our team is happy to talk it through.