Fire engineering: different methods
Special cases for fire safety
20 February 2019
It isn’t always possible to follow the guidelines on fire safety, and when it comes to unusual buildings bespoke fire engineering can be necessary
It is not realistic to expect standard fire safety guidance to give adequate coverage to all aspects of fire safety in every building type. Even very specific guidance such as the Technical Standards for Places of Entertainment 2015 (revised 2018) is not wholly applicable to the fire strategy developed by the Fire Surgery for the untreated timber, candle-lit Sam Wanamaker Playhouse at Shakespeare’s Globe.
In such circumstances, fire engineering is used to demonstrate compliance with the Building Regulations for fire safety, without being restricted to generic guidance documents. It represents the application of knowledge in fire science, human behaviour, technology and the performance of materials and systems to develop alternative solutions. BS 7974 offers a recognised, structured approach to use fire safety principles as the basis for a unique strategy. Regular qualitative design reviews are then undertaken with key stakeholders on all aspects of this, providing a clear audit trail.
What makes a building unusual could be its special contents, such as Sir Isaac Newton’s manuscripts at Clare College, Cambridge; it can be the age, such as the scheduled ancient monuments at Winchester Cathedral; or it can relate to structures other than buildings, such as the restored Cutty Sark.
Typically, it is where there is potential for higher fire growth – such as more combustible materials or the presence of ignition sources – and the occupants are unfamiliar with the layout, for example in museums, galleries, castles, ships, domes, piers, stadia, theatres or nightclubs.
The first stage of an unusual building fire strategy is to determine clear project objectives. Compliance with legislation is a given, for the purposes of life safety. Most unusual buildings will have far wider requirements, though, extending to the implications of contents and property protection, brand or image, business continuity and even competitor advantages, as if a fire takes out a building or business, it may allow a local competitor to benefit.
Clearly identifying the objective in a fire engineering brief is important. For example, the Sam Wanamaker playhouse was designed as though it had been built in 1666, so balancing modern fire safety requirements with Restoration architecture became part of the objective.
The second stage of the strategy is to identify all key stakeholders. Obvious among these are approvers, insurers and designers, who are usually consulted at an early point. All stakeholders should be identified, however, including licensing, users, facilities managers and possible tenants. Understanding their requirements and getting early input can ensure a more robust fire strategy and a smoother route through approvals.
The third stage is to establish how the building is to be used. Event scenarios should consider all possible uses of the building, as clients always want flexibility. Thus, considering what creative functions the events team may lease the spaces for will inform a sustainable fire strategy.
At one popular public assembly building, for instance, almost any space is useable in some way, so keeping routes fire-sterile – that is, allowing no combustible materials – may not be possible. Knowing this early allows decisions to be made on the design of escape routes and on the choice of active and passive systems; respectively, automatic fire suppression and detection, and fire-resisting walls and floors, for instance.
The fourth stage is to undertake a fire hazard assessment. The risk of fire should be established in all relevant locations, and these scenarios should be agreed with the stakeholders so mitigating measures can be considered. The possibility of a single accidental fire in areas where there is fire loading and ignition sources should be considered, with suitable sensitivity studies to test the robustness of design principles.
For example, fire size is not usually a key factor in smoke modelling, and growth rate and soot yield are much more important than smoke layer height and visibility. This will then determine what active and passive measures are needed, such as higher extraction rates over a stage area or even the addition of a fire curtain. Different scenarios will have different effects on means of escape, firefighting and the structure, which should also be considered.
The fifth stage is to understand the operational fire safety management resource. The success of any fire strategy lies with the operational fire safety management, because fire safety is a balance between the technical systems in a building and the way it is used and managed. It is not possible to rely solely on the former, so the management must play an active part.
It is important that the number, roles, training and responsibilities of all staff in the building, including employees, contractors and tenants, are established. How much reliance, if any, may be placed on the management to undertake more bespoke measures can then be determined.
The key to the fire strategy’s success at the playhouse is managing the safe use of the candles, and a strategy was developed covering how these are stored, moved, installed, ignited, trimmed, extinguished, removed and discarded. The Globe employs a permanent technician to supervise this.
In the past, a fire engineer would only be appointed to develop a fire strategy that would achieve approvals, going just part of the way through the Royal Institute of British Architects’ design stages. We have always encouraged our clients to use our services through to stage 5, construction, to monitor the building fire strategy and ensure our intentions are realised. We always encourage contractors to update our fire strategies to as-built conditions, using trackers through the construction stage. We even perform the first fire risk assessment. This is called complete fire engineering.
One good example of an unusual project is the Victorian pleasure pier at Worthing, which projects about 300m into the English Channel and has several architecturally important buildings on it, including the grade II listed Southern Pavilion.
The success of any fire strategy lies with the operational fire safety management, because fire safety is a balance between the technical systems in a building and the way it is used and managed
Piers have a long history of destructive fires, and Worthing’s is no exception: in 1933 it survived a significant blaze, which was recently brought sharply back into focus following a near-miss incident with smoking materials in 2015.
After this, pier owners Adur & Worthing Councils commissioned a full review of fire safety arrangements to improve both life safety and property protection. Adopting a qualitative design review approach akin to that in BS 7974 and fully engaging those who own, manage and work on the pier, this assessed passive and active fire protection measures along with operational procedures.
Figure 1: A full review of fire safety arrangements on Worthing Pier was commissioned in the light of an incident with smoking materials in 2015
Unsurprisingly, very little UK fire safety guidance exists for pleasure piers specifically, and therefore references were drawn from international guidance, for example NFPA 307, and from known work completed on other piers around the country.
By methodically and holistically considering each of the buildings on the pier and its substructure, a full fire strategy was developed, with this then forming the foundation for completing fire risk assessments. Key features included:
- an Available Safe Egress Time/Required Safe Egress Time (ASET/RSET) assessment, considering the evacuation of up to 1,000 people from the pier, with the worst case involving a fire where people would have to travel up to 350m back to the land to an ultimate place of safety;
- a review of the pier-wide automatic fire detection and alarm systems, with opportunities identified to enhance coverage and use a voice alarm, including external sounders on the deck;
- a review of an historic sprinkler system installed in the pavilion theatre, with opportunities to identified to modernise this and extend protection to other buildings, providing significant life safety and property protection benefits;
- consideration of the cast-iron supporting structure of the pier, timber decking, and overall unique environment and usage of the pier;
- review of firefighting access and the existing horizontal fire main infrastructure with the local fire and rescue service;
- identifying opportunities to improve passive fire protection measures in the buildings on the pier, cognisant of sensitivities about their historic and heritage value;
- examining the cause of the most recent fire and introducing additional control measures to reduce the risk of a repeat incident, such as designated smoking areas and an imperforate zone on top of the timber decking around the main buildings to prevent accumulation of debris;
- improving cooperation and coordination between all relevant stakeholders in relation to fire safety.
Ultimately, the fire risk on this iconic seafront attraction will be significantly reduced as a result of the review.
Andrew Nicholson is founder and director of the Fire Surgery