Designing Stairwell Pressurization Systems to Keep Escape Routes Smoke-Free

Why Stairwells Need Protection from Smoke

In a building fire, smoke rather than flame is usually the greatest threat to life. Enclosed stairwells are the main escape route in multi-storey buildings and the access path firefighters rely on, so they must stay tenable for the whole evacuation. Fire-rated walls and self-closing doors help, but every time a door opens, smoke from the fire floor can be drawn into the stair core. Stairwell pressurization solves this by supplying outside air into the stair so that its pressure is slightly higher than that of the adjoining corridors. Air then flows out of the stair through door gaps and open doors, pushing smoke back instead of letting it in.

Key Design Parameters

The design starts from the requirements of the Saudi Building Code and civil defense, which govern when pressurization is needed and the performance it must achieve. The MEP team then balances two opposing limits. The pressure difference must be high enough to resist smoke, yet low enough that occupants, including children and older people, can still open the stair doors against it. Getting this balance right depends on several inputs:

• Air leakage through door gaps, walls, and shafts, estimated for the actual construction rather than idealized figures.
• The number of doors expected to be open at the same time during evacuation, which sets the airflow needed to keep a protective velocity at open doors.
• Supply fan capacity, the location of the fresh-air intake away from smoke exhaust points, and the use of single or multiple injection points in tall stairs.
• Barometric relief dampers or variable-speed fans that release excess pressure when doors close, keeping door opening forces within acceptable limits.

Tall buildings add another challenge: the stack effect caused by temperature differences between inside and outside can distort the pressure profile along the stair height. Distributing supply air at several levels, or controlling fans from pressure sensors, helps keep conditions even from the lowest to the highest floor.

Integration, Testing and Maintenance

A pressurization system only works if it starts at the right moment and runs on a reliable supply. It is therefore interfaced with the fire alarm system so that fans start automatically on alarm, and it is fed from fire-rated circuits connected to emergency power. Ductwork serving the stair should be protected or routed through fire-rated shafts, and fire dampers must not close on the supply path by mistake. Coordination with the architectural team matters as well, since door hardware, door undercuts, and shaft sizes all affect performance. Before handover, commissioning should measure the pressure difference with doors closed, air velocity through open doors, and the force required to open each stair door, with results documented for the civil defense inspection. After occupancy, periodic tests of fans, dampers, sensors, and alarm links keep the system ready, so that stairwells remain clear, breathable escape routes whenever they are needed.