Fire engineered solutions need to embrace a building's use and management as well as its physical characteristics. Nick Troth and Andy Passingham examine this process using an innovative theatre design as a working example.

Arup Fire develop fire strategies for many complex and challenging projects. Our fire engineered solutions frequently depart from conventional code guidance to facilitate the architectural vision and functionality of the building. Without fire engineering, many of our most iconic buildings would not function effectively, or key elements of the design would be compromised.

In many buildings, fire incident management forms an integral part of the fire strategy. It is therefore essential that the building operator fully understands the fire strategy, and that the fire engineer understands how the end user or client will manage the building.

Developing a fire strategy
Today’s buildings are complex creations. As fire engineers, we work closely with a fully integrated team to ensure that our fire strategy meets the functional and aspirational needs of the building, as well as providing a safe environment for its occupants. The fire strategy for the building touches on many elements of the building design process. We consider the spatial planning of the building when examining the means of escape and the need to divide the building into separate fire compartments. The structure and fabric of the building must withstand the impact of fire to a reasonable period to assist egress and the actions of firefighters. The systems that we introduce into the buildings must be appropriate to the level of hazard in the building, the overall aim being to reduce the risk and impact in the event of a fire.

The fire engineer’s job is essentially to use fire safety measures as a ‘kit of parts’ to develop a tailored package that address the specific levels of hazard in a building. We use prescriptive guidance as the basis of this process. Documents such as Approved Document B and BS9999 provide accepted methods for meeting the Building Regulations requirements for the various aspects of fire safety in buildings. It is important to understand, however, that these documents cannot address the measures required for all buildings, and are often based on lessons learnt from historical fires that may not be relevant to the particular design. The often quoted example is the 2½ minute exit flow time which the means of escape provision in Approved Document B is based on. This comes from a fire in the Empire Palace Theatre in Edinburgh in 1911, where the orchestra played the National Anthem to help keep the occupants calm during an evacuation. This took 2½ minutes and still forms the basis of egress design today. While the code guidance will usually give a good benchmark level of life safety, there is clear scope to examine the behaviour of fire, smoke, building occupants and the response of the building to these to produce a more effective and efficient fire safety solution.

Whether the final fire safety solution is based on the code guidance or not, it is essential that it is not developed in isolation. The fire engineer must work closely with the other building design disciplines and the client to ensure that the fire strategy is as simple, robust and practical as possible.

The impact on building management
During the design and construction phase of a project, the emphasis is typically on the fabric of the building – , after all this is what drives the project finances and is the focus of the design. The design is also, of course, reflecting the needs of the end user, and this applies equally to the development of the fire strategy. There is no point developing a fire strategy that relies on a great deal of clever analysis and fire modelling, if the building does not retain its usability, or imposes unmanageable restrictions on the end users.

The fire engineer must understand how the client is intending to operate their building, including in the event of a fire emergency and the need to potentially evacuate the building. It is the responsibility of the building operator (defined as the Responsible Person under the Regulatory Reform (Fire Safety) Order of 2005) to ensure the safe evacuation of the building occupants, and hence the fire strategy must reflect the management capabilities of the client. This is particularly the case for public buildings where the occupants are more likely to be unfamiliar with the building layout, and a higher degree of management will be required. In larger buildings the fire strategy may also adopt a phased evacuation approach, whereby only the fire affected part of the building will be evacuated initially, and other areas placed on alert to evacuate if necessary. These types of buildings always require a high level of management, with perhaps the ultimate example of this being a large hospital.In this situation, evacuating bed ridden patients incurs its own risk to the life safety of the patient, so a highly managed form of evacuation – known as progressive horizontal evacuation – is adopted, moving patients horizontally through a series of fire resisting compartment walls, away from a fire location.

These processes of staff guided evacuation procedures in buildings are applicable, in varying degrees, to all types of buildings, particularly when the issue of evacuation of disabled occupants is considered. A good fire strategy will encompass these issues into the building design, without the need for additional fire safety measures or overly complex management procedures. It is vital that the fire strategy that the client inherits from the design team works with their intended levels of staffing and training.

Case study – Curve Theatre, Leicester

The stage can be open to the foyer as well as the auditorium

In recent years, Arup Fire have steadily become more and more involved with the full process of handing the building over to the client, and helping them to understand and operate the building. For a building such as the Curve Theatre in Leicester, we were involved for over seven years, from the earliest stage of design, right through the Building Regulations approval process, and then extending our appointment to work directly for the client, helping them to develop their fire management strategy. To facilitate this we created fire risk assessment templates, and helped them carry out the first risk assessment for the building.

The Curve is the first performing arts centre to be designed in the UK by New York based architect Rafael Vinoly. From the outset it was clear that this would be a challenging project, for one key reason: a theatre has not been designed this way before.

Conventional theatre design is to fully enclose the stage and auditorium, with the means of escape from the auditorium either direct to protected exit routes, or through the entrance foyer. This traditional approach greatly simplifies the egress design, as the two principle egress routes (front and rear of auditorium) are typically separated by fire rated construction, providing alternative escape routes.

 

Layout of the Curve Theatre

However, the design intent for Curve was to give the theatre transparency and to enable this, the stage can be open to the foyer and the two halls and stage form islands, surrounded by the foyer. Rehearsal rooms and seminar spaces are located on top of the halls, with the egress stairs from these spaces and the halls discharging directly into the foyer. The ground floor plan shows the layout.

To allow the escape route through the foyer, a fully fire engineered approach was adopted; this utilised scenario based populations and carefully defined fire scenarios. We worked closely with the client to fully understand the workings of the theatre and areas of simultaneous occupation. Fire and smoke growth analysis was carried out to demonstrate that egress would occur in tenable conditions.

Since completing the fire strategy for the project, we have been involved through to the completion and opening of the building. We have helped train the theatre staff to carry out their fire risk assessments and have written the management strategy for the building, holding workshops with the client to develop this document. With a fully fire engineered building it is essential that the client sufficiently understands the fire strategy, and the scenarios that it is based on. As the egress is based on analysis rather than a code approach, we also produced an additional graphic report to allow the client to understand the population capacity of each of the key spaces in the building, and how these relate to the overall building capacity. This document will be used to plan special events in the building and ensure that the various event spaces are used to their full potential. It effectively illustrates the fire safety design constraints for the end user.

Disabled evacuation
The typical approach to refuge design is to provide a single wheelchair sized space in each protected escape stair enclosure. However, in a large public building this may be insufficient to cater for the potential numbers who would have to rely on these provisions. This is an even more important aspect of the Curve theatre, which is associated with disabled performance groups, so there can be a significant number of disabled occupants in the building at any one time.

At the Curve, we were able to use the natural geometry of the building to assist in the provision of disabled evacuation refuges, or temporary waiting areas. The auditoria can act as a refuge area in the event of a fire in the foyer, and vice versa. This provides a better, more flexible approach to the issue of disabled egress than the typical approach of a single refuge at each level within each protected stair, which would not have been sufficient for the end users in this building.

A similar approach was used for fire strategy for the new Mary Rose Museum in Portsmouth. Here we used scenario based egress to enable museum galleries to act as refuges. This has several advantages: the galleries will be staffed by the attendants who will be trained in evacuation methods: this allows the refuges to be in relatively open spaces, where visibility is good, rather than tucked away in a stair lobby; we would also consider this to be a more inclusive design approach, as the refuge is the space used by all the building occupants, rather than a separately defined space. From a design perspective, this approach has also allowed the stairs from the galleries to be open , as opposed to traditional enclosed stairs. In this case the protection to the escape routes is provided by the gallery itself, rather than the conventional enclosure being provided around the stair.

To summarise, the projects and approaches discussed above illustrate why the safety strategy, and the fire engineer producing it, needs to look beyond the traditional role of producing technical reports that are aimed solely at gaining Building Regulations approval for each project. The fire safety engineer has to fully understand the client’s needs and anticipated operational procedures for the building. Designing-in overly complex procedures at an early stage in the design process can severely impact on the end user's ability to operate and manage the building efficiently. Furthermore it is also important that the client and building end user are fully aware of the fire strategy applicable to their building. By considering these at an early stage of the project with the end user and client, we can incorporate these needs into the design, producing safer buildings that are more easily managed, integrating appropriate fire safety procedures rather than adding them at a later stage.

Nick Troth is associate director at Arup Fire