16 April 2017
As buildings become larger, taller and more complex, fire protection must be improved to mitigate the devastating impact of fire on life safety and business resilience. Russ Timpson explains
THE COSTS of business interruption and consequential damage from fires are rising as the modern built environment becomes increasingly complex. Recent fires in tall buildings have highlighted the need both for those who design and build tall buildings and those who manage them to fully understand how such buildings behave in a fire and how fire safety can be managed within them.
Any fire in a tall building can have a catastrophic impact but several recent fires in the United Arab Emirates (UAE) have drawn attention to the phenomenon of ‘full-height’ fires. This is when fire propagates on the external façade of the building and results in the entire vertical surface of the structure becoming involved.
The latest blaze, in Ajman on 29 March 2016, was the third within a year in the UAE. It is reported to have affected at least two residential towers, with the blaze spreading from one building to an adjacent block. Earlier incidents ‒ at The Address Downtown on New Year’s Eve 2015, the Torch in February 2015 and the Tamweel tower in 2012 ‒ involved rapid external fire spread due to the use of non-fire-rated cladding materials on building façades and resulted in the full evacuation of each building involved.
But the problem is not confined to the UAE. Another serious example of this type of fire occurred in Baku, Azerbaijan, in May 2015, where 16 people died. Similar blazes have occurred in France, Australia, China and Russia.
While there is more and more guidance to help businesses improve their resilience in the event of such fires, it is often overlooked during the early design and construction phases of a new building project. Capital expenditure, rather than lifetime costs, is usually the main driver. This often leads to materials and fire-protection systems being specified solely on the basis of cost, without any consideration of the impact of these choices on the buildings once they are occupied.
The business-continuity level of performance means that the building’s fire specification will provide statutory compliance (everyone gets out), building preservation (the building is viable post-fire) and ensure that the business function of the building will not be fatally impaired, i.e. post-fire clean-up and return to work will be quick and straightforward.
The highest level of performance is ‘full flexibility of use’. This means that the building can adapt to significant changes of use without the need for major alterations to fire design and strategy. It can also be deemed to have ‘fully protected status’, as some insurers call it.
The distinction between compliance and resilience is important; the first implies cost and little commercial value, while the second is increasingly seen as a vital aspect of modern business in a changing world.
A useful model for persuading project managers during design and construction to invest in additional fire measures other than those required for building-control approval is the fire safety corridor. This aims to steer focus away from capital expenditure of the project (CAPEX) and towards the lifetime operational costs of the building (OPEX).
CAPEX will obviously reflect the design and build costs, and pressure will be exerted on fire engineers to reduce these by minimising fire resistance of materials, reducing the number of staircases and avoiding the need for sprinklers and other fixed systems. In contrast, OPEX should take into consideration factors such as maintenance costs, flexibility of use of the building, insurance premiums and resilience of the building. Given the increase in mixed-occupancy developments, incorporating offices, residential accommodation, retail, leisure and storage facilities, careful specification of fire safety equipment will help in terms of the flexibility required.
The conceptual model of a fire safety corridor is a design journey that starts with the need to satisfy statutory compliance. This also implies that statutory compliance is the lowest level of building fire-risk performance. As the line in figure one denotes, this leaves lots of gaps for fire risk to incubate over a period. Moving further down the corridor we reach a level of building performance whereby protection in the event of foreseeable fires, including arson, is provided. Such protection may include sprinklers or other fixed systems.
Managing fire safety
With more and taller buildings planned and higher building density likely, a greater understanding of fire safety management in such buildings is also necessary. The tall-building fire incidents described above have served to highlight the importance of ensuring that fire safety in such buildings is managed by someone who not only fully understands the building and recognises the need to develop a detailed fire-safety strategy and building-continuity plan but will also ensure that plans are practised.
Full-height fires have the potential to cause smoke and fire incursion on multiple floors in a short period of time, with the possibility of ‘overrunning’ any sprinkler protection that may be provided. They can also quickly turn a progressive evacuation strategy within a tall building into a simultaneous evacuation in staircases that do not have the design capacity.
The Tall Building Fire Safety Network (TBFSN) was founded in 2009 to promote fire-safety best practice among those who design, construct and manage tall buildings, as well as those who may have to fight fires in them. The Network highlights several key characteristics of such buildings:
- Extended vertical travel distances for occupants;
- Enhanced gravitational effects on fixed systems, such as wet risers;
- Amplified effects of wind loading;
- Vertical movement of internal airflow (stack effect);
- Problematic access for firefighters;
- Legacy design issues (curtain walls); and
- Mixed occupancy without common purpose towards ‘whole-building’ fire safety.
Fire engineers and fire safety managers will need to factor these issues into any tall-building fire strategy, as the highly concentrated nature of tall buildings means that the potential losses are very high if multiple fires or system failures occur.
The TBFSN defines the five key aspects of tall-building fire-safety management as: prevention, detection and alarm, escape strategy, fire containment and firefighting.
Prevention is key to reducing the risk of fire. Fire-safety management systems based on regular fire risk assessments are essential in preventing fires from starting. Adequate staff training is also vital here. The TBFSN has defined five main fire-ignition hazards in tall buildings, and recommends ways to minimise the risk of fire occurring:
- Catering – The risk can be reduced through adequate fire-safety training and kitchen extract and ductwork management. Catering fire-suppression systems and thermostats can also be installed to prevent fires from spreading, should they occur;
- Electrical equipment – Thorough testing and cable management are key, as are strict management policies for portable electrical equipment and the introduction of ‘run to fail’ equipment;
- Contractors – Good housekeeping and hot-work/permit-to-work systems will help prevent fires from starting during construction and refurbishment work;
- Arson prevention audits and checks and good security can reduce the risk of deliberate fire-setting; and
- Good housekeeping should ensure that fire-loading is kept to a minimum. Policies should be in place to manage compressed gases, highly flammable liquids, temporary heating and air conditioning, and smoking
Understanding the purpose, design and specification of detection and alarm systems is essential to fire safety management in tall buildings, since these systems not only raise the alarm but also impact on the evacuation strategy. It is essential to know the types of system installed and to understand how they interact with other building systems. Some may use a two-stage alarm, which provides time for fire investigation, and may interact with the public-address systems. It is essential to keep false alarms to a minimum, as these can result in complacency.
The type of escape strategy must also be defined, as many tall buildings have a phased evacuation system in place, where occupants of only fire-affected floors will leave. Other buildings may require a simultaneous evacuation, or a combination of the two. The strategy should take into account typical human behaviour. It may also cover the use of lifts and include policies for the mobility-impaired. Evacuation marshals can play a vital role and must be adequately trained.
Understanding the systems in place for fire containment is also important. Passive protection and steel protection will be built into the building structure to contain the fire in the compartment of origin and maintain the building’s structural stability. Active suppression systems, such as sprinklers, are designed to contain and extinguish the blaze. These systems must be adequately maintained throughout the life of the building. Wherever fire walls are breached by services, such as pipes and cables, it is vital they are reinstated to their original specification using correctly installed fire-stopping systems.
Planning for firefighting intervention is the final part of any fire safety-management strategy in a tall building. The plan should consider firefighting operations and capabilities, taking into account the impact of wind-driven fires and fire dynamics in tall buildings.
The Tall Building Fire Safety Network offers regular courses and conferences on Tall Building Fire Safety Management in locations around the world and has a full schedule of events planned for 2017.
Russ Timpson is the organiser of the Tall Buildings Safety Network and CEO of Horizonscan