A UK evacuation case study using Pathfinder questions the suitability of fire safety guidance

Stewart Brown BSc (Hons) Dip Stat FIFireE
University of South Wales, UK

Content

UK Guidance for staircases

Sizing staircases

Flow rate and capacity to hold people taken into account when sizing staircases

Stair1

Time to safety

When the last person enters the staircase people are safe

door1

The starting point

Bldg1

Guidance

ADB

BS9999

Guidance

ADB says maximum of
350 people

BS 9999 says maximum of
427 people

The observed evacuation drill

Times

One staircase discounted

fire1

Model

Model2

Times for each floor to evacuate

Table1

Safe?

Building not considered safe
Remedial works were undertaken

Remaining Question

If the building had been code compliant
what would the evacuation times have been?

Pathfinder

Model1
Evacuation reproduced in Pathfinder

Model adjustments

Model2
Priorities and speeds adjusted to closely match observed evacuation times.

Typical run

Evacuation times

Population reduced to
be code compliant
(BS 9999)

Table2

Is there a problem?

There appears to be a problem as people are unlikely
to survive on a fire floor for over 6 minutes.

And yet we have no history of deaths in office buildings

BS 9999

This is new code
It is less onerous than ADB
It has not stood the test of time as ADB has

ADB compliant building

Table 3
Population reduced to ADB max. and model run again

Methodology

Summary

Pathfinder modeling shows that the assumed 2 and a half minutes is unachievable when populations at maximum, under current assumptions

But there is no history of fire deaths

New guidance (BS 9999) produces worse results than traditional approach (ADB)

But ADB results were not great

Maybe we are too pessimistic about the performance of staircases

As use of BS 9999 continues to grow time may reveal the answer