How a 1990 fire in New York’s Empire State Building changed smoke control design specifications in the UK in 2015!
I was on detachment from London Fire Brigade to the FDNY in 1990 studying high-rise firefighting when a fire in the Empire State Building in Manhattan broke out on the 51st floor of the 102-storey building. I didn’t attend the fire but the lessons I took from this fire were passed onto me by those who did and they appeared in my first book in 1992. In particular, the issues surrounding how pressure differentials can have such a negative impact on firefighter safety stayed with me. The lessons also included how FDNY firefighters were deployed into the stairs to search for occupants under the direct command of the Search and Rescue Battalion Chief as well as how ‘smoke proofing the stairs’ is achieved in evacuation stairs (Fire Towers). However, at this fire one of the determining factors was how FDNY firefighters were forced to redeploy an attack hose-line from an alternative stairwell where two 65mm hose-lines were being forced back having initially and incorrectly attacked from the Fire Tower stairs. This caused high heat from a wind driven fire to head towards the lower pressure created by the smoke shaft located at the rear of the firefighting advance. One of the reasons for placing a lobbied smoke shaft in the Fire Tower (evacuation stair) was to keep these stairs clear of smoke. The negative pressure behind firefighters causes heat, smoke and fire to head in that direction if the lobby door is held open by hose.
The alternative corridor deployment, some 30 minutes later, from another fire attack stair (no smoke shaft) enabled firefighters to make headway on the fire and complete extinguishment.
In the early 2000s we began seeing the removal of stairs from UK residential buildings that led to extended dead-end corridors protected predominantly by mechanical extract smoke control systems. However, these systems were commonly located in the corridors, adjacent to stair doors, and the potential for recreating the same effect as the Empire State fire was apparent. This led to Kent Fire and Rescue Service leading a national campaign from 2011 to change the locations of smoke shafts in corridors and site them away from stairs. The Smoke Control Association, in their revision of the 2015 design guidance for residential flats, proposed a maximum of 30 metres in any dead end corridor protected by a Mechanical Smoke Ventilation System (MSVS) and practical application of smoke shaft location places the shaft (or vent opening) at the end of the corridor, or within 7.5 metres of.
This amendment in smoke shaft design has dramatically increased firefighter safety in extended corridor situations. However, more still needs to be done. The location of natural or mechanical smoke shafts in stairwells used for firefighting, even where lobbied, can create negative pressure differentials in what is a fire attack stair. If the rising main outlets are within the stair or lobby itself this ‘suction’ of smoke, heat and fire may still occur and this in itself can lead to exterior windows failing and acting as additional air for fire development. We need to consider how an evacuation stair and a fire attack stair can combine to the benefit of both residents who are leaving the building and firefighters who are advancing on the fire. In single stair buildings it may be necessary to site rising main outlets off the stair and into the accommodation corridor/lobby to ensure untenable amounts of smoke and heat does not find its way into the stairwell.
Equally, in two (multiple) stair residential buildings, the fire service should be provided with voice communication systems to every flat or apartment so that they can direct and control any necessary evacuation to the safest evacuation stair. The current public consultation for fire service-controlled alarms (DPC BS 8629 Evacuation systems for use by the Fire Service in flats and maisonettes) does not go far enough and is recommending a simple alarm button with sounders to assist the reversal of a stay-put strategy. This could send occupants heading straight into smoke laden stairways and untenable environments.