Escape Routes and Fire Stairs: The Design Logic

An escape route is a path along which occupants can reach a safe external area continuously and under protection. The words "continuously" and "under protection" summarise the entire design.

Three parts

1. Access to escape. From the room to the corridor and on to the stair door. This is where the fire risk is highest.
2. Protected escape. The stair enclosure or protected corridor. This part must stay clear of smoke and heat.
3. Escape exit. From the stair discharge to the external area. Obstruction, locked doors and parked vehicles are the usual problems here.

Core principles

• Two-way escape. Occupants must be able to turn the other way when one direction is blocked by fire. Single-exit arrangements are accepted only for limited areas and occupant numbers.
• Travel distance. The walking distance from the most remote point to an exit is limited; the occupancy class and the presence of sprinklers affect that limit.
• Exit capacity. Door and stair widths are calculated from the number of people using them. The calculation covers the whole chain, not a single door — the narrowest point sets the capacity.
• Door swing and hardware. In crowded spaces doors open in the direction of escape, with panic hardware and no key needed in the escape direction.
• Dead ends. The length of blind sections where occupants cannot choose between two directions is limited.

Protected stairs and pressurisation

Keeping the stair enclosure clear of smoke is achieved in one of two ways: natural ventilation or pressurisation. A pressurisation design must satisfy two conflicting requirements at once:

• With doors closed, enough pressure difference to keep smoke out of the enclosure.
• With doors opening, no more than the force limit an occupant can overcome.

Both are only achieved together with pressure relief and correct fan control. At commissioning both the pressure difference and the door opening force are measured — checking only one is a common omission.

Emergency lighting and signage

The escape route must stay visible when power fails. Points to watch:

1. Lighting is concentrated at changes of direction, stair heads, level changes and exit doors.
2. Signage must form an unbroken chain; the next sign should be visible from every point.
3. A mounting height below the smoke layer is preferred; a sign mounted high disappears in smoke.
4. Battery duration and periodic functional testing are recorded.

The eight most common breaches on site

• Stair landings used for storage.
• Fire doors wedged open.
• Exit doors locked for security reasons.
• Vehicles parked in front of the escape exit.
• Corridor width narrowed with cupboards and boards.
• Signage removed during refurbishment and never refitted.
• Emergency luminaires with batteries past their life.
• Services pipework or cable tray routed through the stair enclosure.

What those eight have in common is that they are operational, not design, failures. Fire safety management is therefore the complement to the design, not an alternative to it.

Frequently Asked Questions

Why must an escape route be continuous and protected?

Occupants must be able to travel from where they are to the external area without being exposed to fire or smoke at any point. If one link in the chain is unprotected, the whole route fails.

How is exit capacity calculated?

Door and stair widths follow the number of people using them, and the calculation covers the whole chain. The narrowest point sets the capacity.

Which two measurements are taken on a pressurisation system?

The pressure difference with doors closed, and the door opening force with a door opening. Checking only one is a common omission.

Do sprinklers change travel distance?

Some distance and area limits may be assessed differently in a sprinklered building, but core principles such as two-way escape and protected stairs remain.

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