What is the passage of time teaching us about different and complex buildings? We asked Bill Jones to give us his thoughts
OVER THE decades, a large stock of buildings of various designs and materials have developed that are used in a multitude of different ways. There is no easy definition of ‘different and complex’ as, at a basic level, the modern industrial unit could be described as completely different from a factory of the late 1800s – and numerous examples of these still exist.
For this article therefore, all larger buildings can be considered, but it is likely that the focus will be on those constructed from the late 1950s to today, including those still just an idea on paper. Over this period designers, technology and the construction industry have evolved to allow taller buildings to be erected, basements to go deeper, podiums and atria to be used, and the size of floor footprints to increase. Also, the materials have altered to improve the sustainability, thermal efficiency and environmental credentials of the completed buildings for their lifetime use.
All this has happened using legislation – the Building Regulations – which solely consider life safety within the completed building. A variant of these regulations, an engineered solution, exists to achieve the intent of the regulations without strictly following them.
An alternative aim is that of property insurers, whose ambition is to achieve an enhanced set of standards that provide more resilience for the structure and the business operating from it in the event of a fire. These property protection requirements are included within Approved Document B of the Building Regulations, but they are considerably more complex to fulfil when other factors are taken into account.
Changes in contents
One of the major changes that affects every building in the time frame being considered is the ‘fuel’ that is now available to support a fire.
The contents of buildings have seen a transition from timber and metal based furniture, natural fibre based floor coverings and generally carbon based materials to those using plastics and man made fibres. The outcome in broad terms is a fiercer, faster developing fire that produces toxic smoke and gases, presenting increased hazards to the occupants and attending firefighters, and resulting in greater damage to the fabric of the building.
In addition, more consideration is given to the environment. This is partly driven by the Building Research Establishment Environmental Assessment Method (BREEAM), launched in 1990, which provides a sustainability assessment and certification scheme for the built environment. One of the outcomes has been the increased use of insulation materials incorporated into the walls, floors and roofs of buildings.
The insulation materials used for thermal and acoustic solutions range from non combustible to highly combustible. For example, mineral wool is at the non combustible end and expanded polystyrene (EPS) at the other end, with all the other materials, including the regularly seen polyisocyanurate (PIR) and polyurethane (PUR), somewhere in between.
Generally in an open fire situation, everything will be a fuel to a greater or lesser degree, unless it is inherently mineral wool based. The Building Regulations define the standards required of
the materials in place around and enclosing the insulation materials, so that they are not exposed until sufficient time has elapsed to allow escape or rescue from the building. There are numerous British Standards and European test standards to confirm the required criteria for these materials.
There are some PIR or PUR panels which achieve the Loss Prevention Certification Board (LPCB) standards (or similarly recognised international standards) and which also can be considered not to add to the early stages of a developing fire.
If you are involved in the food production industry, it’s likely you that you will be familiar with foamed plastic insulated panels. In the 1970s and 1980s extensive use was made of composite panels using EPS as the insulation for cold stores and cool rooms. Although this material is thermally efficient, it quickly and easily supports combustion and, after numerous severe fires, the influence of insurers and the fire and rescue services led to the panels being replaced with less combustible, alternative panels.
Trend for taller
Taller buildings for residential and commercial use, including offices, mixed use and hotels, are becoming more the trend, especially within inner city areas, due to a shortage or the cost of land to build on. The financial district of the City of London is an ideal example but compared to some other countries, the UK is lagging behind in the number of such properties built. High rise buildings in use in London include prestigious designs such as the Shard, the Leadenhall Building (the Cheesegrater), 20 Fenchurch (the Walkie Talkie) and 30 St Mary Axe (the Gherkin) which are unique and more individual than the traditional skyscraper shape. In the pipeline there are also numerous others at various stages of design.
These taller complex buildings do and will provide more challenges for the fire and rescue services (FRSs) and all authorities in achieving their aim of life safety. The heights firefighters are capable of reaching from outside the building are at most ten storeys and are more likely to be lower than this if vehicle access close to the building is restricted.
The Building Regulations and alternative engineered solutions reflect this risk with measures such as live sprinkler systems, dry or wet risers, automatic fire detection, smoke extraction and compartmentation. The combination designed into any building is aimed to provide protection for the occupants until they escape from the building or are rescued by the FRSs. Where everybody is evacuated or there is nobody in a building that is on fire, such as a warehouse or offices, the FRSs are most likely to adopt a defensive firefighting approach of extinguishing the fire from an external safe location and to
protect surrounding properties. As a result, the extent of the damage to the property is likely to be significantly greater and the interruption to the business trading from the premises to be longer.
Basements and atria
In the last few years, more projects have involved the use of a podium slab over a basement level or several levels. In the completed building, the basements are often used for plant and car parking. On top of the podium slab, there could be several multi storey apartment blocks, offices or hotels where all the building cores extend to the basement car park to allow easy access. Once again, the Building Regulations and engineered solutions are there for the necessary life safety standards.
However, there are some recent examples in Europe of fires in car parks that have resulted in the loss of numerous vehicles and increased building damage, which underline the fire load from plastic and fuel within the modern car and the difficulties of extinguishing a fire in that environment. Design and risk management in car parks needs to be looking ahead to the risks of charging and storing electric and hybrid vehicles, which bring another change to the environment. Once again, there is the obvious disconnect between the need for life safety and the standards that are required to maintain property and business resilience. Is there a danger that the Buildings Regulations won’t keep up with technological advances?
Atria are used as a design feature, especially in prestige buildings and also large shopping centres. In the shopping centres these are generally malls and not extending through more than three floors, but in the retail units they could extend through many more floors and in apartments or offices through numerous floors.
Generally, they contain very little to support a fire in the event of one starting and the Building Regulations cover the topic. The key to control in these areas is maintaining them as sterile areas, as any increase in fuel will, in the event of fire, introduce more smoke into an open plan area, where the original design expectation was that there would be minimal amounts.
So far we have looked at the aspects of the building structure and measures in place for its safe use to protect lives, but there is a further major factor to be considered – the behaviour of the human being undertaking the work. All those undertaking fire risk assessments, insurance surveys of property and so forth regularly see the designs of the buildings to protect life compromised in some manner.
Some of the simpler examples, because they can easily be seen, will include repairs or damage not being addressed properly. These might include missing or damaged fire stopping in service risers or through compartment walls, damage to the intumescent strip in fire doors or doors not closing correctly, and sprinkler heads painted over.
More complex examples, because they rely on technical knowledge, include the storage heights and storage arrangements when sprinklers are installed, the servicing and maintenance of critical plant such as smoke extraction systems or sprinklers, and compromising the joined up fire compartmentation strategy.
The age of the building can be an influencing factor as general wear and tear occurs, or the reason for the designed-in measures for life safety (eg the compartment walls) being forgotten. Furthermore, the use of single cores containing the stairs, lifts and service risers may increase the hazards to occupants, especially during or after remedial works when maintaining safety measures or undertaking repairs is not taking place.
Over time, buildings are adapted in layout or use, and when this occurs, the original safety measures could be compromised by poor workmanship or economic decisions that may come into play. Recent examples include the proposal to locate prefabricated pod style offices in an atrium as it was cheap, but this increased the fire load in the sterile area, as well as the installation of ‘market’ style stalls in the general mall area of shopping centres, especially in the Christmas period, as an easy option to increase revenue earned, but increasing the fire load in an area not designed for this purpose.
All of the previous information relates to completed and occupied buildings that have life safety protections – in complex buildings, these will probably include combinations of automatic fire detection, sprinkler systems, compartments, fire stopping and smoke extraction. However, throughout the construction phase of such buildings, none of these permanent life safety features are likely to be in place and operating. However, the structure will be at its finished height, where firefighters can encounter difficulties and the insulation materials are likely to be exposed and so available to fuel a fire.
What can we do?
Changes are generally made to legislation following catastrophic incidents involving the loss of life, such as at Grenfell Tower. Any changes to legislation, such as the Building Regulations, are often applied to new builds and not retrospectively due to the economic penalty that would be placed on existing property owners to make good their buildings.
Altering human behaviour and culture is a long term project to ensure that the life safety design standards of a building are maintained throughout the building’s lifetime. In multi occupancy buildings this becomes a greater challenge. It is likely that a combination of education, training, setting high standards and penalties is going to be required.
The conclusion to be drawn is that, to achieve the basic life safety standard, the Building Regulations have to undergo regular review to attempt to stay ahead of technology, rapidly changing construction methods, materials and the likely use of a building. Strengthening the standards should lead to improved community resilience to protect lives and livelihoods, and ensure that businesses survive and continue to contribute to a community’s prosperity.
To complement the regulation, the methods for testing materials have to be fit for purpose to allow the understanding of how a fire will start and spread in a realistic, larger size test sample. Unfortunately, the laboratory style testing favoured in the past may not represent the actual circumstances of use and therefore needs to be reconsidered. In addition, the opportunity could be taken to use less combustible material in the design and construction, making it easier to deliver safer and more resilient outcomes.
Bill Jones is property risk engineer at Aviva. For more information, view page 5