The British Museum Queen Elizabeth II Great Court Project Fire Engineering: enabling effective design for heritage buildings

Facilities

ISSN: 0263-2772

Article publication date: 1 October 2001

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Citation

(2001), "The British Museum Queen Elizabeth II Great Court Project Fire Engineering: enabling effective design for heritage buildings", Facilities, Vol. 19 No. 10. https://doi.org/10.1108/f.2001.06919jaf.001

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Emerald Group Publishing Limited

Copyright © 2001, MCB UP Limited


The British Museum Queen Elizabeth II Great Court Project Fire Engineering: enabling effective design for heritage buildings

The British Museum Queen Elizabeth II Great Court Project Fire Engineering: enabling effective design for heritage buildingsKeywords: Fire safety, Building design, Structural engineering, Internal environment

Introduction

The fire strategy for the Queen Elizabeth II Great Court at The British Museum provides a high standard of safety and property protection, with minimum intervention to the existing, Grade 1 listed, historic structure. Buro Happold FEDRA achieved an optimal strategy by careful coordination with the client and design team; enabling the project to efficiently satisfy all client, legislative, architectural and engineering objectives. Effective collaboration with Lawrence Webster Forrest (LWF) ensured the seamless integration of the Great Court fire strategy with that for the surrounding existing museum spaces.

This article describes the project and the specialist fire engineering techniques that were developed and applied in order to design the fire strategy; a strategy to enable, not constrain.

Project description

The British Museum's Georgian buildings were designed in 1823 by Robert Smirke, and originally comprised four wings containing galleries set around a large rectangular courtyard. Subsequently the courtyard became filled with extension buildings, including the world-famous round Reading Room, housing the British Library, and adjoining book-stacks (1854-1857). The stone-clad museum quadrangle and iron-framed Reading Room are Grade 1 listed buildings.

The Reading Room, designed by Robert Smirke's brother Sydney, is 42.7m in diameter. An iron frame of 20 ribs are clad externally with a 19m high brick drum, pierced by large high-level arched windows and capped by a copper-clad dome. Hemispherical dome rises to a central lantern 12.2m in diameter, 32.3m above the floor.

The historic Reading Room is now the centrepiece of the largest covered courtyard in Europe. The 6,700m2 (92 x 73m) courtyard, a little bigger than a football pitch, is enclosed by a spectacular glass-and-steel roof. The Reading Room has become a hub at the centre of the museum complex. providing new modern galleries, education resources and visitor facilities, including shops and a restaurant. The project realises the opportunity to rediscover the inner courtyard of The British Museum and capitalise on the Grade 1 listed facades that overlook it. The new development has a total public floor area of approximately 10,000m2, compared with approximately 25,000m2 in the existing museum.

Having worked with the Sir Norman Foster and Partners architectural team on the winning competition entry, Buro Happold was appointed by The British Museum as the structural engineer, building services engineer, fire engineer and planning supervisor for the development.

Principles of the fire strategy

The fire strategy provides an appropriate level of safety and property protection, with minimum intervention to the existing, Grade I listed structure. The guiding principle was to maximise the measures in the new construction, with the objective of minimising reliance on the existing, listed, buildings.

Fundamental fire engineering and risk management systems were applied, complemented by appropriate use of sophisticated analysis and assessment techniques:

  • HAZOP: structured hazard identification, risk assessment, and information gathering methodology was used to develop fire scenarios and to inform the design and decision-making process.

  • Computational fluid dynamics, wind-tunnel testing, and evacuation modelling: sophisticated analyses and assessments were used to demonstrate and develop the design.

  • Means of escape: a combination with phased, staged, and progressive horizontal evacuation was developed to make most effective use of the escape routes from the Great Court and enable the existing routes to serve the design population; thereby avoiding the need to create new escape routes with consequent impact on the existing listed structure. The means of escape strategy also dovetailed with the means of escape strategy for disabled people.

  • Means of escape for disabled people: This comprises a combination of structural provisions (ramps, lifts, stairs) and management procedures for assisted escape. The strategy allows for a flexible response to different situations, without undue reliance on management procedures.

  • Exploiting the performance of the structure: taking advantage of the inherent performance of the structure to minimise the need for fire protection

HAZOP

A structured fire hazard identification study was undertaken using HAZOP (HAZard and OPerability) methodology. HAZOP is an advanced hazard identification technique used in the nuclear, transport, and oil and gas industries as a basis for the development of safety cases. HAZOP was used to gain information about the Great Court and its operation, and identify potential fire scenarios which were then used in the development of the fire strategy and management procedures. The principal benefits of the HAZOP are that it is systematic, comprehensive, and auditable.

To undertake the HAZOP study, the Great Court was divided into representative nodes, including:

  • galleries;

  • storage;

  • voids (to explore the potential for movement of smoke in hidden voids within the existing construction of the museum);

  • storage;

  • conference facilities.

Guidewords were applied to every node; typically:

  • occupancy (numbers, staff, public, contractors);

  • fire load;

  • activities;

  • electrical;

  • smoker's materials;

  • accidental activation of fire systems (to explore the risk of inadvertent operation of systems, such as sprinklers);

  • management communications.

A HAZOP team was assembled, comprising members of the museum staff and the design team; people who were familiar with the proposed operation and design of the Great Court. The team was involved in developing the nodes and the guidewords. FEDRA chaired the HAZOP, leading and controlling discussion prompted by application of each guideword to every node.

For every fire scenario identified by the HAZOP, the team estimated a "likelihood of occurrence" rating (on a scale of 1-5), together with a "consequence" rating (also on a scale of 1-5). Two types of consequences were defined – life safety and property protection/business loss. The property/business risks identified by the fire safety HAZOP were also fed into the Cost Risk Register. A symmetrical risk-ranking table was devised to prioritise risks (see Table I).

Risk management

Risks identified in the HAZOP study were addressed in the design of the fire strategy.

Risks can be managed in three fundamental ways:

  1. 1.

    Risk removal:

  2. 2.
    • eliminate the risk by removal of the hazard.

  3. 3.

    Risk retention/acceptance:

  4. 4.
    • Retain the risk at its current level.

  5. 5.

    Risk reduction – reduce the risk by introduction of safeguards:

  6. 6.
    • engineering control;

    • management control.

The fire strategy was developed on "ALARP" principles; risks were removed wherever feasible, and the remainder reduced As Low As Reasonably Practicable (ALARP).

Coordination of environmental design and smoke control strategy

Wind tunnel tests carried out by Bristol University estabished expected wind pressures at ventilation openings in the museum (doors and roof vents) due to the range of wind conditions throughout the year. These data were then used in a Computational Fluid Dynamics model to predict air-flows within the Great Court for the different external conditions. One primary objective of the design was to ensure an upwards air movement, which has two principal benefits:

  • Environmental: hot, vitiated air is removed from the comfortable occupied zones and exhausted at high-level.

  • Fire: cool smoke is carried upwards by these environmental flows, away from the concourse escape routes.

Furthermore, the environmental strategy is designed to provide comfortable conditions without the need to open the existing sash windows in the quadrangle building for throughflow. This coordination enabled the sash windows to be fixed shut; the alternative, where the windows would need to be modified to allow them to close automatically in the event of a fire, was costly and impracticable.

Continuing advances by Buro Happold in Computational Wind Engineering, have since developed a "virtual wind tunnel". In many cases, expensive and time-consuming wind tunnel tests can now be replaced by computer modelling, which also has the benefit of providing a "picture-like" visualisation of the results.

Means of escape strategy

The objective of any means of escape strategy is to ensure that the escape routes are safe for the period required for escape; escape is a function of available time rather than allowable distance. The fundamental "time-based" approach for the Great Court applied concepts that were later developed within BS 9999: Part 1 Means of Escape, drafted by Buro Happold for the British Standards Institute.

Realistic assessments of population within the Great Court were made by post-processing of the LWF survey data. In particular, it was noted that appropriate design floor space factors for galleries within The British Museum were 2.2m2/person, rather than the 5.0m2/person prescribed by Approved Document B. Thus the rote application of standard guidance would have resulted in lower design population for means of escape than appropriate; another example where the fire-engineered approach results in increased safety over traditional methods.

The means of escape strategy combined phased, staged and progressive horizontal evacuation to make maximum use of the available routes from the Great Court through the existing museum. This strategy avoided the need to create new routes.

Phased/staged evacuation has four major benefits over total evacuation:

  1. 1.

    The existing escape routes are used more effectively, since priority is given to those in the fire zone.

  2. 2.

    Improved management of the evacuation, due to a smaller number of people being evacuated (at any one time) than if the entire museum were evacuated simultaneously.

  3. 3.

    Improved evacuation from the standby zone, as the disabled/low mobility visitors will have had the opportunity to evacuate or transfer to a refuge area.

  4. 4.

    Reduced disruption to operations of The British Museum. The standby signal can be cancelled in the event of a false alarm. It is important to minimise disruption, as it is recognised that the effect of disruption caused by a false alarm is to reduce the response to future alarms, with a subsequent decrease in safety.

Progressive horizontal evacuation enables immediate evacuation from the fire zone, with extended, managed evacuation available from the secondary zone.

The means of escape strategy was developed using Building EXODUS, an evacuation modelling code being developed by Buro Happold in partnersnip with tne University ot Greenwich.

Means of escape for disabled persons

Buro Happold Access Consultants were involved in developing an innovative strategy for means of escape for disabled persons; to ensure a standard of escape consistent with the standard of access. The principles of the strategy included:

  • Assessment of likely distribution of disabled persons within the Great Court: Demographic data supplied from the representative national institutes based on national survey data was used to determine the percentage of the population with different types of disabilities. These data were combined with the design floor space factors to determine the likely numbers of persons with disability in all types of accommodation within the Great Court.

  • The evacuation requirements for the different types of disability were determined, taking account of latest knowledge and experience.

The strategy comprised a combination of structural provisions (e.g. lifts, refuge areas, ramps) and management procedures (e.g. communications and assisted escape). The strategy was designed to enable a flexible response to different situations without undue reliance on management procedures.

The types of evacuation in order of priority are:

  1. 1.

    Lateral evacuation (progressive horizontal evacuation): level escape to another fire compartment, a place of relative safety.

  2. 2.

    Evacuation by evacuation lift.

  3. 3.

    Evacuation by stairs:

  • Carry down: evacuation chairs can also be used in carry down. This is where the disabled person transfers onto a chair that is a hybrid between a deck-chair and a sledge, and is slid down the stairs by a person trained to use the evacuation chair.

  • Carry up: carry-up is difficult and requires three or four persons for a wheelchair, and is thus staff-intensive. Carry-up is only used in limited applications.

Refuges are sited adjacent to evacuation stairs or lifts. The strategy for the Great Court was to create large open refuges in preference to the traditional isolated refuge in stair enclosures. To apply this concept, rooms adjacent to stairs, together with the connecting circulation spaces, were upgraded to fire-resisting standard. Communication with the designated refuge points completes the strategy.

Exploiting the performance of the structure

All structure has an inherent performance in fire, and it is well known that unprotected structures perform better than would traditionally be expected. The standard approach is to ignore this inherent performance when determining the requirements for fire protection. The objective of the Great Court fire strategy was to take maximum account of the performance; enabling cost-effective and space-efficient solutions. The presence of sprinklers in risk areas reduces the heat transmitted to the structure to significantly less than that assumed by the standard BS 476: Part 20 fire curve; this serves to further increase the performance of the structure.

VULCAN, a finite-element structural fire analysis code being developed by Buro Happold, in collaboration with the University of Sheffield, allows greatest advantage to be taken of the inherent performance.

This performance can be exploited for elements of structure, compartmentation and fire-resistant enclosures. Frequently, the best solution is obtained by combining the performance of a number of elements, to create a "system". An example of this is the "Round Reading Room Wall System", which is designed to perform two primary functions:

  1. 1.

    Compartmentation between the Round Reading Room and the concourse.

  2. 2.

    Compartmentation between the general concourse upper and lower levels; the void between the inner wall and the cladding contains the basement smoke extract ducts, rising from the compartments below the concourse.

The Round Reading Room Wall System comprises an inner wall of existing brickwork and new blockwork, the void containing the smoke extract ducts, all surrounded by stone cladding. The system was developed as follows:

  • The inner wall provides the compartmentation between the Round Reading Room and the concourse.

  • Smoke extract ducts to provide integrity, not insulation. The inner wall and cladding (the cladding does not have smoke integrity) provide the insulation performance.

The benefits were that the smoke extract duct was not required to be insulating, maximum advantage was taken of the full compartmentation performance of the existing inner wall, and the cladding solely needed to achieve an insulation performance.

Conclusions

Buro Happold FEDRA applied fundamental engineering principles to enable a design for the Queen Elizabeth II Great Court that would not have been possible using traditional methods, and to produce best-value; enabling a safe building while minimising impact on design, architecture, and cost.

A key element of the success of the strategy has been the collaboration with The British Museum and the design team, with LWF, and with Camden Building Control. In particular, Gerry Jordan and Graham Lelliott, of Camden, demonstrated the knowledge, understanding, and appreciation of fire engineering principles and objectives; contributing to effective development of the fire strategy and an efficient approvals process.

Nigel Hiorns, Technical Manager, Buro Happold FEDRA: www.burohappold.com

Buro Happold is a multi-disciplinary international practice of consulting engineers, established in 1976, offering civil and structural engineering, mechanical and electrical engineering, quantity surveying, building services and environmental engineering, infrastructure and traffic engineering, geotechnical engineering, façade engineering, fire engineering, Computational fluid dynamics analysis, access consultancy, project management, urban design and a range of specialist CAD services.

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