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Above: The new City of Manchester Stadium (42k). Fire Engineering allows natural aspects of stadia design to be
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Modern stadia are often landmark, icon projects, carrying with them civic pride. It can be difficult to fulfil these aspirations in a cost effective manner within traditional, prescriptive fire safety guidance. Fire Engineering aims to maintain standards of safety whilst at the same time facilitating innovation in design and limiting cost implications. The success of Fire Engineering is largely due to the ability of the discipline to free designers and reduce costs, whilst maintaining high standards of safety. With reference to the new Manchester Stadium, this article discusses how Fire Engineering can be applied in arenas and stadia. Most countries around the world have fire regulations that can be
applied to stadia. Typically, these codes are prescriptive (or rely on
prescriptive guidance) and have developed over time as a result of
research programmes initiated after fire-related disasters. Such
prescriptive codes are typical of the "The designer must do
X." format. |
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This approach should yield designs that provide an adequate level of safety (although this is not always the case). However, the prescriptive approach can hamper innovation in design as such codes are always based on generic assumptions. The central tenet of such codes is the sorting of buildings into a small number of categories. Each category is then assumed to have similar occupant characteristics and fire hazards. This categorisation may, for example, result in the fire hazard in a 100,000-seater stadium complex being assumed to be identical to a village hall. Clearly, there are many differences between such buildings. However, the categorisation of buildings means that prescriptive fire codes must assume the worst and treat all buildings of the same generic type as identical with respect to fire safety. In the case of buildings with a lower fire hazard than that assumed in the prescriptive code, unnecessary additional costs and design restrictions may arise. Fire Engineering is the alternative approach to prescriptive codes. Instead of specifying design restrictions for a building that a prescriptive code might set (e.g. "Door A must be at location X and be W metres wide"), a Fire Engineering led approach makes use of functional objectives of the type; "The escape routes from the building must be such that all occupants potentially at risk can be evacuated before injury or undue anxiety occurs." This approach can be readily extended to business related issues as well as the life safety concerns addressed by fire codes (e.g. "If a fire occurs, the building should be operational again within X hours"). Functional objectives for a Fire Engineering approach may be set by the client (e.g. loss prevention criteria) or by Statutory Authorities. In this case, the functional objectives may be either enshrined in law (such as those set out in the UK Building Regulations) or require that the Fire Engineer demonstrate that the proposed design is at least as safe as the 'standard' approach (such as the risk equivalency approach set out in the US NFPA Life Safety Codes). As functional objectives are not specific design requirements, they do not dictate the building form or function. Also, they are not based on the assumed characteristics of a generic building type. Instead, the Fire Engineer can tailor the fire precautions to the needs of a particular project, assessing the fire risks and taking into account the inherent safety factors in the design. In a Fire Engineering study, a risk assessment exercise will be undertaken to determine what aspects of the building design or operation could raise fire safety issues. Analytical techniques can then be applied to assess the hazards and what precautions (if any) are necessary to maintain a safe building or limit loss in the event of fire. Analytical techniques include:
Typical precautions that can be incorporated into the design may be:
If considered in isolation, these provisions may add capital costs to a project. However, when used as a part of a holistic Fire Engineered strategy, they can generate cost savings. Quantitative risk assessment techniques can take this further by allowing different strategies to be compared from a risk perspective to ascertain which designs offer the best value for money. Fire Engineering allows natural aspects of stadia design to be exploited to enhance fire safety, forming a synergy between fire safety design and day-to-day operation. This is important as a fire is a rare event and if fire precautions are in conflict with normal operations, the fire precautions may become ineffective. A classic example of this is the jamming open of fire doors to ease access. The fire engineering solution to this is to hold the doors open with a detente which can be released by the fire alarm. Many common aspects of stadia design also have fire safety benefits. The generally non-combustible nature of many modern designs (in particular the use of concrete pre-formed terracing) is such that rapid fire spread through the building is unlikely. If fire spread can be prevented, it is then possible to evacuate the building in a phased manner, starting with the stand, which is initially at risk and then followed by other occupants, if required. This approach has been adopted at the new Manchester Stadium for the Commonwealth Games in 2002. The intention is that no credible fire scenario would result in a total building evacuation. Instead, the nature stadium construction has been exploited and areas of fire risk are separated such that, in many scenarios, occupants of the stands would not be evacuated. Stadium management who will be able to liase with fire officers and the police will control this 'phased' evacuation. This will ensure that unnecessary interruptions to events and potential security problems are avoided without compromising safety. Many fire precautions, such as smoke control on arena concourses are common. However, when developing a Fire Safety Strategy for the concourse areas of an arena, a Fire Engineer should not start by considering how the smoke control system will be designed (even though standard guidance or fire codes may prescribe this). Instead, one should start by asking whether or not smoke control is actually required. This can be assessed by determining:
A good example of this lateral approach to fire precautions arose on the Manchester Stadium where special consideration was given to the separation of the concessions from the concourses. This was necessary as the concession areas represent one of the most significant fire hazards in the building but are also located on the concourses such that a fire in a concession could impact on the escape routes from the stands.
Direct smoke extraction from the concessions was difficult, as it required large dedicated smoke extractor fans and fire rated ductwork. This would have placed a significant demand on plant space in the building, potentially reducing commercial opportunities and introducing additional capital costs to the project. Also, the standard solution calls for the provision of sprinklers. This was considered undesirable because of the cost and design complications that the introduction of a sprinkler system would have caused. Faced with the important functional objective of protecting the escape routes whilst aiming to meet the needs of the design team, Arup Fire set about finding an alternative solution. The concept that was developed was the 'Sweeper' system (see diagram below).
In the Manchester Stadium, each concession is to be provided with a pair of fire rated shutters, arranged in parallel. In the event of a fire, both shutters descend (the outer shutter stopping just above floor level) and a small volume of air is extracted from the space between the shutters. The inner shutter stops most of the smoke escaping from the unit. However, roller shutters can leak substantial quantities of smoke. Any smoke that escapes through the inner shutter is 'swept' away from the inter-shutter space. The primary advantage of the double shutter arrangement is that smoke is first cooled by passing through the inner shutter and then cooled further by the flow of air in between the shutters. As a result of this, it was possible to demonstrate that smoke temperatures would be below 100øC. This allowed non-fire rated ductwork and fans to be used. The airflow required by the system is substantially less than would be used for traditional smoke extractor systems. In the case of the Manchester Stadium, this would allow the fans provided for the toilet extractor system to be used for the 'Sweeper' system. Using these fans would have the added benefit of ensuring a high level of system reliability, as the toilet fans are required to run constantly for stadium operations. The system is intended to prevent smoke from entering the concourses. In the event that the fans fail, the double shutter arrangement in isolation provides a significant level of protection and is independent of the extract system. The approval of the design, by the regulatory authorities, was achieved by working in collaboration with representatives from Manchester City Council Building Control throughout the project. Having protected the concourses to a high level using the 'Sweeper' system, the egress from the stands could be considered from a Fire Engineering perspective. Detailed evacuation studies were carried out to model how occupants would respond to a fire alarm signal (see diagram below).
This gave confidence that the proposed numbers of seats, seatways, gangways and vomitories would be acceptable. Additional studies demonstrated how effective spiral ramps could be as the primary means of access and egress to/from the higher levels of the stands. By adopting a Fire Engineered approach on the Manchester Stadium, it has been possible to demonstrate to the Statutory Authorities that the building will be safe, rather than assuming that the building would be safe. At the same time, costs have been reduced (both capital and lifetime costs) and design aspirations have been realised. Fire Engineering can also be used on steel framed stadia and stands. Expensive intumescents, fire resistant boarding or cementitous sprays are often applied to steel members to bring their fire resistance up to the levels demanded by standard fire resistance tests. However, the conditions simulated by standard fire resistance tests are severe and only consider the reaction of individual elements in isolation. In practice, steel framed structures act in a composite manner and share loads around the frame if some members are weakened. Also, 'realistic' fire conditions are often less onerous than the standard test. In particular, steelwork in external applications is subjected to a much lower fire severity than the standard test would assume. By applying Fire Engineering techniques, a reduction in the level of applied fire resistance or the total removal of additional protection can often be achieved. Using similar techniques the need or otherwise for fire resistant glass can be considered for areas such as hospitality suites and entrance arcades. Fire Engineering has much to offer the design of stadia and arenas.
Alternative prescriptive codes are available. However, as stadia designs
become more adventurous and greater commercial opportunities are sought
out, Arup Fire offers a cost effective, design enabling solution to the
problems of fire safety in these large public buildings. Simon Lay is a Senior Fire Engineer with Arup Fire based in Leeds and can be contacted by email: simon.lay@arup.com
Objectives of Fire Engineering:
The key advantages that Arup Fire offers stadia designers and operators are:
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ire Engineering is one of the fastest growing of the 'specialist
engineering' skills that have become prevalent in modern building
design. With one year to go before the City of Manchester Stadium
becomes the focus for the 2002 Commonwealth Games and home from 2003 for
Manchester City Football Club, Arup Fire discusses how Fire Engineering
can be applied to stadia and arenas.
The standard solution to the problem of concession fires is to
suppress the fire using sprinklers and either extract smoke from the
unit directly, or, allow smoke to enter the concourse area and extract
it at high level. In the case of the Manchester Stadium, the
architectural concept was to maintain a clean soffit on the concourses,
without visible services or ventilation ducts (see right). This ruled out the use of
concourse smoke extraction.
