Smoke Control and Automatic Opening Vents (AOVs)
Smoke, not flame, is what most often stops people escaping and stops firefighters getting in. Smoke control systems exist to manage that, and automatic opening vents are one of the most common ways they do it. Fire alarm engineers meet smoke control mainly at the interface — where detection tells the vents to operate — so understanding the overview helps you commission and service that interface correctly. This guide gives that overview.
Smoke control design itself is a specialist field; what follows is orientation, not a design guide.
Who this is for
This is for competent fire alarm engineers who interface with, commission or service smoke control and AOV systems. The experience level assumed is competent engineer. Use it for the overview; smoke control design and performance come from specialist designers, the fire strategy and the relevant standards.
What smoke control does
A smoke control system manages smoke to keep escape routes and firefighting access usable for longer. Depending on the strategy, that might mean venting smoke out of a stairwell, corridor or lobby, or maintaining conditions that keep smoke away from where people need to move. Automatic opening vents — powered vents that open on detection of fire — are a common component, letting smoke escape from the protected route. The specific approach is set by the building's fire strategy and Building Regulations guidance in Approved Document B.
AOVs and the detection interface
AOVs and smoke control are frequently actuated by the fire detection and alarm system, so that the right vents operate when the relevant detectors trigger. That actuation follows the cause and effect and the requirements of BS 7273-4, the code of practice for operating fire protection measures. In this arrangement the fire alarm system provides the trigger and the smoke control system performs the venting. As with any interface, the two systems must be correctly connected and tested together.
Who designs it
Smoke control is a specialist design discipline. The system is designed by competent smoke control designers as part of the fire strategy, sometimes supported by engineering calculations or smoke modelling. Fire alarm engineers usually work at the interface rather than designing the smoke control, so the important thing is to understand how detection is meant to drive the system and to verify that it does.
Servicing the interface
When servicing the interface, the key checks are that the correct detection actuates the correct vents per the cause and effect, that the vents actually operate and reach the intended position, and that fault and power-loss conditions behave as designed. Because this work often crosses into mechanical equipment maintained by others, coordinate and record what you find. Any change to the cause and effect means the interfaces must be re-tested. Common issues include vents that no longer reach full travel and cause-and-effect changes that were never reflected in interface testing.
When not to rely on this alone
When not to use this article: do not use it to design a smoke control system, size vents, or determine performance. Those come from specialist smoke control design, the fire strategy and the relevant standards. Fire alarm engineers should work strictly to the cause and effect and BS 7273-4 at the interface.
Relevant standards
Actuation of smoke control from the fire alarm system is addressed by BS 7273-4, a code of practice. Building Regulations statutory guidance in Approved Document B covers smoke control within the wider fire strategy, and 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 when advising a client, and always work to current editions and the specialist design.
Professional disclaimer
This is an educational and workflow resource for competent engineers and does not replace specialist smoke control design, the current British Standards, the fire strategy, or competent judgement. Verify all interface and actuation arrangements against current documentation.
Related documentation
Use this with the smoke control design and specialist documentation, the current BS 7273-4, and the system cause and effect. Record all interface tests and coordinate with the parties maintaining the smoke control equipment.