The Two Evacuation Strategies

When a fire alarm sounds in a residential building, should all residents evacuate immediately, or should most residents stay where they are while the fire service deals with the fire in the compartment of origin? This question — the choice between simultaneous evacuation and stay put (also called progressive horizontal evacuation in some contexts) — is one of the most fundamental decisions in the fire strategy for a residential building.

What Is Stay Put?

Stay put — formally known as "defend in place" — is the traditional evacuation strategy for blocks of flats in the UK. The principle is that if a fire starts in one flat, the fire-resistant compartmentation between flats means that residents in other flats are safer remaining in their own flats than evacuating down shared stairwells that may become smoke-logged.

Under a stay put strategy, only the residents of the flat where the fire starts evacuate. Other residents stay in their flats, keep doors closed and wait for the fire service. The strategy relies absolutely on the integrity of fire compartmentation — particularly flat front doors and the construction between flats.

What Is Simultaneous Evacuation?

Simultaneous evacuation means all occupants evacuate the building at the same time when the fire alarm sounds. This is the traditional strategy for offices, hotels, schools and most commercial buildings, and is increasingly being applied to residential buildings where stay put is not considered appropriate.

Why Does This Matter After Grenfell?

The Grenfell Tower fire raised fundamental questions about the stay put strategy. The fire spread to the external cladding and progressed rapidly up the building, overtaking the compartmentation that stay put relies on. Following the Grenfell Inquiry, building owners and fire engineers have had to reconsider whether stay put remains appropriate for higher-risk residential buildings — particularly those with any cladding or external wall concerns.

How Is the Decision Made?

The evacuation strategy for a building is determined by the fire strategy. The fire engineer assesses the building's compartmentation, the means of escape, the building's height and occupancy, the reliability of the fire alarm system, and any factors that affect the appropriateness of stay put — including external wall construction and any known compartmentation weaknesses.

For new higher-risk residential buildings, Approved Document B and BS 9991 now require more detailed consideration of evacuation strategy, and the Building Safety Regulator expects a clear and justified evacuation strategy in the Gateway 2 fire strategy submission.