Heritage buildings and contemporary fire safety codes traditionally do not sit well together. But as Nathan Hewitt, a fire engineer at Arup Fire, says, holistic fire engineering solutions are giving a breath of fresh air to some older properties.
The methods, tools and fire engineering principles available in the restoration of heritage buildings can reduce construction costs and ensure an acceptable level of safety which is also in keeping with their historical nature.
It is clear that the guidance set out in Approved Document B, which is geared towards new build developments, is difficult to apply to existing buildings – especially if those buildings are of historical importance or listed status. It has been a challenge for approving authorities, architects and engineers alike to provide acceptable fire safety solutions for these types of properties. But as fire engineering develops this becomes easier to achieve, ensuring that more and more disused buildings of historical importance are being brought back to life, or are being put to better use.
One of the main obstacles is the increased cost of renovation, as a result of inflexible traditional building materials and set geometries. This can place significant restraints on architecture and function and often makes a development unfeasible. The use of fire engineering allows significant flexibility in the layout of the building, which can turn an unfeasible development into a profitable scheme. Fire engineering, as part of a holistic approach to modern day restoration of heritage buildings, is allowing properties to be developed in a way that is sensitive to the original construction.
Upstairs downstairs
One major difficulty with existing buildings is relocation of staircases. If a historic building is to be converted into public use, which may subsequently have high numbers of people inside, building regulations in the UK require that they can safely escape in a fire. If the building is extremely old or unusual, it is doubtful that it would have a distribution of staircases that resembles a modern day development. If the building does not meet the standard guidance, the first approach would be to demonstrate an acceptable means of escape provision using hand calculations. Many methods are available, including those described in CIBSE Guide E or the SFPE Handbook of Fire Protection Engineering. However, geometries and changes in levels can become extremely complex in historic properties, so the services of a computational evacuation modelling programme may be required.
Arup Fire uses the computational model STEPS for analysis of complex evacuation. The main benefits of this model are to assess evacuation times and to identify bottlenecks which could cause delays in the evacuation. Local changes to geometry can then be applied to the building to address these blockages. These changes, which would not be identified without the use of STEPS, can be subtle and minimal but can result in a major reduction in evacuation times. In addition, computational evacuation modelling is very useful to demonstrate to the approving authorities how an evacuation would be carried out, and where occupants would need to go.
An example of justifying extended travel distances in a historic building is at the Portland Art Museum in the United States. The North Wing extension will incorporate the new Center for Modern and Contemporary Art, historic ballrooms, offices and library, and is intended to renew this landmark as a cultural and civic resource for the City of Portland. In order to overcome a number of smoke management system design challenges, Arup developed a performance-based analysis using Fire Dynamics Simulator (FDS), in conjunction with STEPS computer egress modelling.
Signposts
It could be argued that if the escape routes are so complex that a computational model is needed to analyse them, people may struggle to find ways out of a building. This can be a valid concern in complex, unusual historic buildings, so increased importance should be placed on careful positioning of fire exit signage, as well as on staff management of an evacuation. It may also be important to provide active fire safety protection systems to assist in the evacuation, including fire detection and alarms, and smoke control.
Fire detection and alarm is a vital addition to any densely occupied building, especially if the means of escape is extended or complex. In this way, occupants begin their escape as soon as possible, so maximising the time available for escape. In addition, the use of an addressable system ensures that the management of the building are provided with information on the location, size and spread of any fire. A fire detection and alarm system will also ensure that the fire service is alerted as early as possible. This provides additional occupant safety as well as improved property protection. After all, it would be a shame to renovate a derelict property that has stood empty for 50 years, only to lose it through fire due to the fire loads and ignition sources introduced into the premises. At the Buxton Opera House, for example, aspirating smoke detection was concealed behind ornate coving to provide early detection of smoke, so allowing people sufficient time to escape and affording an additional level of property protection.
Smoke control can also play a role in the protection of occupants during their escape. A modern day fire engineer has a multitude of options available to control the spread of smoke to evacuation routes, including pressurisation, smoke extract, depressurisation and automatic smoke curtains. All of these can have a role to play in a holistic fire engineered solution.
A highly valuable tool for assessing the spread of smoke through complex geometries is Computational Fluid Dynamics (CFD). Arup Fire uses the large eddy simulation software called Fire Dynamics Simulator to carry out complex smoke modelling. This software has been used many times to demonstrate that a fire engineered solution is as good as – or better than – a code compliant solution. FDS was used in conjunction with STEPS to model the onset of untenable conditions at the Portland Art Museum.
This brings us on to the use of sprinklers. Few people can question the increase in property protection offered by sprinklers, and many would also claim an increase in life safety. There are many innovative solutions to concealing or disguising sprinkler heads in historically sensitive or aesthetic areas of buildings, such as in a delicate ceiling rose at Banff Hall in Aberdeenshire. This project involved the refurbishment of a 300 year old listed property, and a sprinkler system was needed to improve property protection and protect some valuable works of art. Careful installation of concealed sprinkler heads on the ornate ceiling cornices minimised the visual impact of the system. The sprinkler system also allowed flexibility in other aspects of the fire safety design, ensuring that the internal layout of the building remained as originally designed.
Older structures
Another challenge involved in the restoration of older buildings is that of traditional building methods and materials. Lath and plaster walls may not achieve the level of fire resistance required in modern design guides, nor might a structure consisting of wrought or cast iron. But what if it is not in keeping with the historic nature of the building to replace these with modern day construction methods and materials? Cutting-edge fire engineering methods are now available, which use advanced structural fire analysis to demonstrate whether these older building materials can still achieve acceptable levels of fire resistance when exposed to real fires.
The structure at the Langham Hotel in London, for example, consisted of cast iron, wrought iron and early steelwork, which preceded any fire testing requirements. One option was to clad all the columns to guarantee that the fire resistance requirements were met. This would have resulted in the loss of the columns’ ornate finishes. An alternative approach was adopted using structural fire engineering techniques to assess the ability of the columns to support the structure at elevated temperatures. It was demonstrated that the columns would maintain structural integrity without additional fire protection.
Performance based fire engineering is a developing discipline, and is great news for the conservation of buildings of historical importance. A building will only be economically successful if the needs of the users are met, which can be very difficult, if not impossible if a code compliant approach to fire safety is adopted. The use of fire engineering allows otherwise redundant, dilapidated but beautiful buildings a second chance and gives them the potential of being around for many more years.
Nathan Hewitt is fire engineer at Arup Fire
