When a building is deemed to be tall or high rise, it represents some unique challenges for all fire-safety stakeholders involved in its design, construction, occupation and firefighting. Policy makers must grapple with risk at all stages of the development. One of the current questions that is causing much debate is the adoption of a mandatory requirement for a minimum of two staircases in high-rise buildings. Hitherto, the UK has allowed development of high-rise residential buildings (unlimited height) with a single staircase. Many other countries take a different view and require a second stair as a minimum.
Often the perceived risk of fire in high-rise buildings is dictated by reactive fire data from real fires, fire tests and modelling. Most fires do not result in death or serious injury, and these fires dominate the available fire statistics. This reality led to a common position in the UK during the recent past of ‘high rise does not mean high risk’. Since the Grenfell Tower disaster in 2017, this position has been reversed and is evident in the new characterisation of high-rise buildings (over 18m) as Higher Risk Buildings (HRBs).
The Council for Tall Buildings and the Urban Habitat (CTBUH) have recorded the growth and proliferation of high-rise buildings around the world in the last 50 years. Despite tragic events such as the New York’s Twin Towers catastrophe, the rate of building and increasing height and complexity of tall buildings has not reduced. Many cities around the world have entire areas with high-rise buildings, housing many thousands of residents. If this trend continues, there will be many new high-rise buildings in the coming decades. It is also likely that they will be built in novel ways with new materials to exacting sustainability standards.
In making risk-based policy decisions, we must seek and identify relevant data sets and research. For many of the considerations listed in this article and to make an ‘evidence based’ policy decision, there is very little existing relevant data. Catastrophic high-rise fires are low probability/high consequence events that do not normally get considered in standard symmetrical risk management approaches, i.e. probability and consequence are proportionate and equal. We therefore need to consider a non-linear risk management approach. To quote Prof. Jose Torero at the Grenfell enquiry: ‘Foreseeable risk must always be multiplied by the enormity of consequence; especially so when the chance of the event happening was actually increasing – as it was with cladding fires.’
During the design conception of a tall building development, those with responsibility for the performance of the building need to decide what level of fire safety they want to ‘build in’. Most fire codes and standards represent the lowest adequate level of safety permissible. This delivers a functional requirement of life safety. In other words, no one should die in the building when fire occurs. These functional requirements are based on several assumptions:
- The building is designed, constructed and commissioned correctly.
- Occupants can escape if they choose to do so.
- The building is well managed, and all systems are working correctly in line with the fire strategy.
- Any fires that do occur conform to foreseeable ‘common’ scenarios and heat release rates.
- Arson, terrorism and deliberate fire raising are not considered.
- The building is occupied and used as designed in the fire strategy, i.e. capacity.
- There will be a fire service response within agreed timeframes, with adequate resources.
- Sufficient firefighting water is available at required pressures and flowrates.
Going beyond the levels of fire safety detailed in the codes and standards is not common, especially in high-rise residential towers used for social housing. Risk cost benefit assessments are also used in the fitting and retrofitting of sprinkler systems. Adoption of sprinklers in HRBs has also been mandated in the UK since the Grenfell Tower Fire. However, only 18.9% of high-rise social housing blocks in the UK have been fitted with sprinklers to date (Inside Housing Magazine research). In a tight financial budgetary environment, it may be very difficult to justify going beyond what is widely accepted as adequate, or proportionate.
Resilience has been defined as ‘the capability of an organisation to anticipate, and respond and adapt to, incremental change and sudden disruptions in order to survive and prosper’ (British Standards). Resilience within building design is vital to cope with change, non-compliance and uncommon events such as arson, firefighter strikes, adverse weather etc. A core aspect of resilience is redundancy. Redundancy is the term given to additional resources within a design that exceed the statutory adequate minimum. If the accepted response to a fire in a high-rise building is termed plan A, we need to consider what measures are available to migrate to a plan B, C, D etc.
For example, if on arrival at the scene of a high-rise residential fire, the officer in charge determines that the building is not performing as designed (smoke issuing from windows on several levels) then she may well need to change tactics and allocate resources accordingly. Having the flexibility to change the plan due to prevailing circumstances is a highly resilient attribute and should be part of a discussion at concept stage. As well as increasing the building’s resilience to fire, it will have the commercial benefit of improving the insurability of the building for its designed life.
High-rise building fire-safety factors for a second staircase:
1. Residents with a disability
Within the UK, 1 in 5 people have some degree of disability or vulnerability. Vulnerability can include:
1.1 Persons under the age of 18
1.2 Elderly persons whose mobility may be reduced due to age
1.3 Persons with a permanent, or temporary, physical or sensory impairment which, in interaction with the building features may hinder their full and effective evacuation
1.4 Persons who have difficulty with social interaction and communication, or responding to fire alarms, evacuation alerts and/or first responders’ instructions.
1.5 Persons misusing alcohol, drugs or prescription medicines.
1.6 Persons with mental health problems, learning disabilities or suicidal intent.
In high-rise residential buildings there is only the plan A of ‘stay put’ or ‘remain in place’ for most people with vulnerability. If during a fire, the decision is made to evacuate a disabled person from a high-rise residential block, it is not a straightforward option. Fires in high-rise residential buildings take a disproportionate toll on vulnerable residents. More than one stair would provide options and flexibility for their escape if required.
2. Ignoring stay put evacuation strategy
In designing a high-rise building around a stay put strategy, the available single staircase is never intended to service the full occupant capacity of the building in a simultaneous evacuation combined with fire service operations. Since Grenfell Tower there is evidence from London Fire Brigade statistics that show that many occupants are self-electing to evacuate before the arrival of the Firefighters. If this trend continues, then additional stair capacity will be needed.
3. Non-availability of lifts/elevators
Many high-rise buildings rely on lifts/elevators to make the building functional and ‘liveable’. Accurate data on lift/elevator performance in high-rise residential buildings within the UK is not easy to find. A recent study in Hong Kong detailed monthly maintenance calls for ‘out of service’ lifts as high as 50 per month for a residential building. The firefighter switch on the lift/elevator at Grenfell Tower was inoperable due to being clogged with builders’ debris. A second staircase would provide redundancy for non-availability of life safety systems such as firefighter lifts.
4. Hoarding and occupant reckless behaviour
The behaviour and lifestyles of occupants within high-rise buildings can significantly impact on the level of fire safety in a building. One issue that is becoming more understood is that of hoarding. Hoarding is when occupants store and retain huge quantities of furniture, clothes, papers, books and other items way beyond the designed capacity of the room or apartment. It has been estimated that 2–5% of the UK population (London Fire Brigade) has hoarding tendencies. Hoarding is a fire-safety issue in any building, but if it takes place on the lower floors of a high-rise building, it can change the design parameters of the fire strategy. Hoarding can have the following effects:
- Increases likelihood and severity of fire
- Hinders escape of resident in event of fire
- Hinders access/egress of firefighters in event of fire
- Risk to neighbouring properties
- High fuel loading/ extended burning duration
- Water absorption/structural damage
A second stair will provide resilience and redundancy to mitigate reckless occupant behaviour.
5. Hazard zone
There have been several significant fires in high-rise buildings that have caused large elements of the facade system to fail and fall off. Depending on wind velocity and direction, the falling debris can spread over a large area and represents a hazard to anyone within the zone. The falling debris may also be alight and start subsequent fires. A second stair and alternative escape route would help if confronted with this scenario.
6. Cramming
In Melbourne, Australia in 2014, a fire occurred in a high-rise building called the Lacrosse Tower. In a report after the fire, the Melbourne Fire Service highlighted that the number of occupants for the building far exceeded their expectations. High-rise buildings are designed for a set occupancy, normally based on floor-space factors or accepted norms for residential accommodation.
A worrying trend is the over-occupation of residential flats and apartments. Known as ‘cramming’ it is particularly prevalent is urban areas with housing shortages, high rents and communities with large numbers of deprived residents. Again, it is difficult to find accurate data on this sensitive subject; however, anecdotally from several serving fire officers across the UK, it is widespread and growing. Put simply, it is where there are far more people in a building than the fire strategy was designed for. In a fire evacuation this could mean far more people trying to escape down a single staircase. Clearly this is a fire-safety management issue. If we acknowledge that it is occurring then redundancy with additional staircase provision will provide additional capacity and help mitigate the cramming issue.
7. High-rise firefighting standard operating procedures
Having studied many of the standard operating procedures (SOPs) for high-rise firefighting from around the world, it is clear that the most common approach is for two staircases. One for firefighting and one for evacuation. Formation of a firefighting bridgehead two floors below a fire in a high-rise building, fire hose management, breathing apparatus control, etc. whilst residents are trying to evacuate down the same stairs is challenging to the point of non-viability. Two staircases should be a minimum in high-rise buildings for firefighting operations.
8. Build quality
As stated earlier, in order for the fire strategy to be valid within an existing high-rise building, the construction must be completed to a high standard. Sadly this does not appear to have happened at Grenfell Tower. In recent years since Grenfell, the author of this article has seen multiple examples of poor workmanship in high-rise buildings. This reality must be taken into account when conducting fire-risk assessments. Refurbishments and alterations post completion can also have a detrimental effect on the fire-safety performance. This reality gap is depicted in the graph below.
Summary
As we look forward to building many more tall buildings, we must invest in suitable research to answer some of the questions raised in the article. A minimum requirement of two staircases in high-rise buildings provides resilience and redundancy. These issues will be discussed and debated at the 8th International Tall Building High Rise Fire Safety Conference to be held between 15 and 17 April 2024 alongside FDIC in the US.
Full details and lots more information can be found at www.tallbuildingfiresafety.com
About the Author
Russ Timpson CEng BEng(hons) FIFireE MBCI is a former firefighter and Global Fire Strategy Lead for BAA Airports. He is also a chartered fire engineer and fellow of the IFE. Russ organises the Tall Building Fire Safety Network focused on higher risk buildings: www.tallbuildingfiresafety.com
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