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March 3, 2010

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Fire safety in complex buildings

Designing safer buildings requires the fire-safety engineer to gain a full understanding of the user’s needs and intentions in running the building, as Andy Passingham explains.

Today’s buildings are complex creations. fire engineers, as a result, need to work as part of a fully integrated team to ensure that any fire strategy meets the functional and aspirational needs of the building, as well as providing a safe environment for its occupants.

In many buildings, fire-incident management is an integral part of the fire strategy. It is therefore essential that the building operator has a full understanding of the fire strategy, and that the fire engineer fully comprehends how their client intends to manage the building.

The fire strategy for the building touches on many elements, including the spatial planning of the structure 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 fire to a reasonable degree, to assist egress and the actions of fire-fighters. The systems introduced into the buildings must also be appropriate to the level of hazard in the building.

The fire engineer’s job is essentially to use fire-safety measures as a ‘kit of parts’ to develop a tailored package that addresses the specific levels of hazard in a building. Ideally, this process should be based on prescriptive guidance, and Approved Document B and BS9999 provide accepted methods for meeting the requirements of the Building Regulations for the various aspects of fire safety in buildings.

However, it is important to understand that these documents cannot address 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 two-and-a half minute evacuation time, on which the means of escape provision in Approved Document B is based.

The origin of this goes back to 1911, when the orchestra at the Empire Palace Theatre in Glasgow played the National Anthem to help keep the occupants calm during an evacuation from a fire. The process took two-and-a-half minutes and still forms the basis of egress design today.

The Approved Document B guidance usually states a conservative benchmark of life safety in relation to the overall design, so, by following the code, you can be reasonably confident that the design is considered safe. Nevertheless, there is clear scope for a more scientific examination of the behaviour of other elements, such as fire, smoke, building occupants, etc, to produce a more effective and efficient fire-safety solution.

However, 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.

Impact of a fire strategy on building management

During the design and construction phase of a project, the emphasis is typically on the fabric of the building. But the fire engineer must understand how the client intends to operate their building, especially in reaction to a fire emergency and the potential need to evacuate the building.

It is the responsibility of the building operator — defined as the Responsible Person under the Regulatory Reform (Fire Safety) Order 2005 — to ensure the safe evacuation of the building occupants.

Consequently, the fire strategy must reflect the management capabilities of the client and their intended levels of staffing and training. This is particularly important for public buildings, where the building occupants are more likely to be unfamiliar with the building layout, and a higher degree of management will be required.

Larger buildings may also use a phased evacuation approach, whereby only the fire-affected part of the building will be evacuate initially, and other areas placed on alert to evacuate if necessary.

These types of buildings always require a high level of management, none more so than in the case of a large hospital, where evacuating bed-ridden patients incurs its own risk to the life safety of the patient. In this example, a highly managed form of evacuation known as progressive horizontal evacuation is often adopted, involving the moving of patients horizontally through a series of compartments, away from a fire location.

To varying degrees, these processes of staff-guided evacuation procedures are applicable to all types of buildings, particularly in relation to the issue of evacuation of disabled occupants. A well thought-out fire strategy will encompass these issues into the building design, without the need for additional fire-safety measures, or overly complex management procedures.

Egress in action

The Curve theatre in Leicester is the first performing arts centre to be designed in the UK by New York-based architect, Rafael Vinoly, and, from the outset, it was clear that this would be a challenging project.

Conventional theatre design involves the full enclosure of 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 principal egress routes — at the front and rear of the auditorium — are typically separated by fire-rated construction materials, providing alternative escape routes.

However, the design aim of the Curve was to give the theatre a feel of transparency by allowing the stage to be open to the foyer, while the two halls and stage form islands, surrounded by the foyer. Rehearsal rooms and seminar spaces are located above the halls, with the egress stairs from these spaces and the halls leading directly into the foyer.

To allow the escape route through the foyer, a fully fire-engineered approach was adopted, based on scenario-based populations and carefully  defined fire scenarios. The fire engineer worked closely with the client to fully understand how the theatre operated, and analysis was carried out to demonstrate that effective egress would occur under real-life conditions.

 

Since the fire strategy for the project was completed, the theatre staff have been trained to carry out fire risk assessments and, following a series of workshops between the client and the fire engineer, a management strategy for the building was created.

As the egress strategy is based on analysis rather than a code or guidance, an additional graphic report was produced to give the client an understanding of 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.

The Curve has associations with disabled performance groups, so it expects to have a significant number of disabled occupants in the building. 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, so the designers must be aware of the likely number of disabled users in a building.

 

The engineering solution for the Curve used the building’s natural geometry to assist in the provision of refuges. Consequently, the auditoria can act as refuges in the event of a fire in the foyer, and vice versa, providing a more flexible approach to the issue of disabled egress than the typical approach of a single refuge within each protected stair, which would not have been sufficient for this building.

 

In the case of the new Mary Rose Museum in Portsmouth, scenario-based egress was used to enable museum galleries to act as refuges. One ofthe advantages of this approach is that the galleries will be staffed by attendants trained in evacuation methods. This allows the refuges to  be situated in relatively open spaces, where visibility is good, rather than tucked away in a stair lobby. This design approach is also considered to be more inclusive, as the refuge is the space used by all the building occupants, rather than a separately defined area.

 

From a design perspective, this method has also allowed the stairs from the galleries to be open, as the protection for the escape routes isprovided by the gallery itself, rather than the conventional enclosure around the stair.

 

Summary

The projects and approaches discussed above demonstrate how fire engineers need to look beyond their traditional role of gaining approval under the Building Regulations for each project. They need to fully understand the client’s needs and their anticipated operational procedures. By considering these issues at an early stage of the project, they can be incorporated into the design, resulting in safer buildings that are more easily managed.

Andrew Passingham is an associate director at Arup Fire

Fire Safety in 2023 eBook

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