Phoenix Journal · Fire Safety
The fans that keep a kitchen comfortable and the systems that clear smoke in a fire are not the same thing, but they share the same ductwork, and how they interact decides whether smoke stays contained or spreads.
Two very different jobs run through the same ceiling void. Comfort ventilation moves heat, steam and stale air out of a busy kitchen so people can work; smoke control moves the products of a fire out of escape routes so people can leave. They are often confused, because both push air through ducts, but they are designed, regulated and maintained for opposite moments: one for every ordinary shift, the other for the one emergency you hope never comes.
Everyday mechanical ventilation is sized for the heat load of the cooking line and the fresh air the room needs. A smoke control system, by contrast, exists to keep a stairway or corridor tenable long enough for evacuation and for the fire service to work. In UK buildings the two are governed by different guidance: Approved Document B under the Building Regulations sets the statutory expectation, while BS 9991 for residential buildings and BS 9999 for non-residential ones give the design codes, and BS 7346-8 covers the planning, installation and maintenance of smoke control systems themselves. Treating one as if it does the other's job is a common and dangerous mistake.
Where the systems meet
The point where ventilation and smoke control genuinely interact is the ductwork that penetrates a fire compartment. A duct that runs through a fire-rated wall or floor punches a hole in a barrier the building relies on to contain fire and smoke. The control that restores that barrier is a damper. A fire damper is a passive device: under normal airflow its blades sit open, and when heat reaches it a thermal element, commonly a fusible link rated to melt at about 72 degrees Celsius, releases spring-loaded blades that snap shut and seal the opening. A smoke control damper is an active device that closes, or in some designs opens, on a signal from a smoke detector, because smoke travels ahead of heat and a fusible link would react too late.
That distinction matters because the two failure modes are different. Fire dampers maintain compartmentation where ducts cross boundaries; they conform to BS EN 15650 and are tested to BS EN 1366-2. Smoke control dampers form part of an engineered smoke ventilation system and are tested to BS EN 1366-10, keeping a smoke path open where it is wanted and closed where it is not. Combination fire and smoke dampers do both. Approved Document B expects dampers wherever ducts breach a compartment, and a poorly maintained damper that seizes open quietly undoes the fire strategy of the whole building.
None of this works if the hardware is unreachable or fouled. Dampers seize, blades jam and access panels get plastered over, which is why BS 9999 expects fire dampers to be tested at least annually and smoke control systems to be inspected and maintained under BS 7346-8, typically on a set service interval with batteries replaced on schedule. A damper you cannot reach is a damper you cannot prove works, and on the day it matters, unproven is the same as failed.
The special case in a kitchen
The grease-laden extract duct is the exception. Fire dampers are generally avoided in the grease extract itself, because grease would foul the mechanism and stop it closing, so compartmentation is instead maintained by fire-rated ductwork or a fire-rated enclosure, and the fire load is controlled by keeping the duct clean. That makes the extract a live illustration of how fire spreads through building voids and ductwork: a greasy run is a ready-made flue that carries flame past every barrier the building put in its way. Cleaning, not damping, is what holds the line here.
The takeaway for operators
The practical lesson is that your everyday extract fan is not a smoke control system, and a smoke control system is not there to clear steam. Each needs its own design, its own testing regime and its own records, and where they share ductwork the dampers and fire-rated construction are what keep the two safely separated. This is the same principle behind the link between ventilation and fire compartmentation: ventilation openings are deliberate weaknesses in the fire barriers, and they are only safe while the controls that close them are maintained and the ducts that pass through them are clean.
Questions
No. A kitchen extract fan is comfort and hygiene ventilation, designed to remove heat, steam and grease-laden air during normal cooking. A smoke control system is a separate, life-safety installation designed to keep escape routes tenable during a fire. They may share ductwork, but they are designed, tested and maintained differently and cannot substitute for one another.
Because grease would clog the damper mechanism and stop it closing when needed. In grease-laden extract, compartmentation is usually maintained instead by fire-rated ductwork or an enclosure, and the fire risk is managed by cleaning the duct to remove the grease that would otherwise fuel and spread a fire.
UK guidance points to fire dampers being tested at least annually under BS 9999, and smoke control systems being inspected and maintained under BS 7346-8, often on a twice-yearly basis with batteries replaced on a set schedule. The exact regime should follow the system design and the manufacturer's recommendations.
Phoenix Duct Clean · by the numbers
Grease-laden extract is a fire path that smoke control cannot fix. Phoenix cleans the whole system to TR19 Grease and documents it, UK-wide, overnight.