A view on Fire Safety in the Green Guide
An article by guest contributor Andrew Foolkes - Tenos
Since the Fifth Edition of the Guide to Safety at Sports Grounds was published in 2008, there have been many changes in the approach to design and management of sports grounds. Technological advances have also taken place in fire safety engineering methods that can be used in the design of sports facilities, including dynamic crowd modelling and structural fire modelling. Consequently, there are areas in the current edition of the Green Guide which may benefit from consideration in the re-drafting.
As an example, the limitation of the maximum travel distance from spectator seating would benefit from consideration. Currently travel distance is limited by the guidance to a maximum of 30 metres, but it is not clear in the guide whether the reason for this is from an evacuation; general safety (crowd control) or in-performance comfort perspective.
This distinction is particularly pertinent when considering the fire safety design. An extended travel distance will be of limited consequence, given it will be the number and width of the vomitories, rather than a limited travel distance, which throttles the flow rate to the concourse and will govern the time to evacuate the seating areas.
A commentary on this distinction would also be useful to assist with the design of the maximum number of seats in a row. The philosophy behind the current maximum recommended limit of 28 seats is not clear. It is important to understand these reasons, given BS 13200, (which also remains mute on the reasons for the limits) permits up to a maximum of 40 seats in a row.
Given the Green Guide is now used internationally, it would also be logical for any subsequent edition of the guide to consider and provide appropriate commentary on the interaction between the Guide and other local fire safety design codes.
Similarly, explanation of the relationship between the Green Guide and current UK fire safety design guidance would be welcomed, in particular, BS 9999: 2008. Whilst BS 9999 may be a suitable design guide for hospitality areas, it must be used with caution given it addresses very different risk profiles and proposes very different emergency exit arrangements to the Green Guide. Meshing the BS9999 and Green Guide risk based recommendations, particularly where egress systems are shared between spectator viewing and hospitality accommodation, does throw up potential conflicts.
Given these issues, dynamic evacuation modelling programs are now widely used to inform the design of shared evacuation routes, but these models are numerous and varied, e.g. Legion, Pathfinder, Exodus or Pedestrian Dynamics to name a few. The models have their differences and care has to be taken by the user when defining the ‘agent’ (person) parameters and routing options. For example, the choice of path of least effort and the affinity of the ‘agent’ (person) to switch exits may significantly alter the analysis results. An explanation of the relationship between crowd modelling and the published calculation methodology in the Green Guide would also be useful; can dynamic modelling be used in lieu of static calculation, do the fundamental principles of that guidance still apply (e.g. no narrowing of exit route from the vomitory onwards)?
Currently, there is no published standard by which dynamic evacuation models (or their application in fire engineering design) may be validated and assessed. Each model therefore embodies only its own developer’s validation and verification efforts and assumptions regarding human behaviour.
Consequently, it may be beneficial to reference a minimum level of information to be provided as part of any design using evacuation models. For example, stadia assumptions for crowd behaviour and possible benchmark scenarios to validate the model. Stadium concourses have developed into areas where retail offerings can be directed at a target audience. Therefore, alleviating congestion around vomitories to improve circulation during the interval of an event will bring obvious revenue benefits. However, providing vomitories wider than those needed to meet the Emergency Evacuation Time (EET), can have a subsequent effect on the design of the stairs leading off the concourse since Green Guide guidance states that there must not be narrowing of an exit route.
In reality, even where stairs narrow the escape route adequate means of escape may still be achieved as an appropriately low risk concourse will provide holding capacity in a place of relative safety for occupants. Permitting narrowing of the exit route, but recognising a need for retaining a minimum width, would provide the flexibility needed by designers to optimise the Stadium design.
Whilst optimisation of the stadium design is important, clearly, any fire safety design needs to be proportionate to the level of risk to occupants. Interestingly, the current version of the Green Guide does not differentiate between the protection afforded between a lower and upper concourse. Occupants of the latter, unlike the former, do not have an alternative evacuation route off the terrace i.e. on to the playing surface. A more risk based approach to upper level concourse design could, for example, consider suppression systems for concessions on upper concourses, or, perhaps sub-division of the concourse and lateral movement across the terrace.
Extending the principle of using additional fire safety measures to create viable escape routes through areas other than General Admission concourses could safely increase design freedom. As an example, escape from spectator seating through associated hospitality lounges would, under the current guide be considered as a high risk strategy. However, with the inclusion of additional fire safety measures such as automatic fire suppression, enhanced compartmentation or smoke control this may permit the risk profile to be considered as normal.
Whilst the Fifth Edition of the Guide to Sports Grounds has remained ‘as is’ since 2008 the design of sports grounds has had to change in response to significant changes in the commercial aspirations for these environments. There is an opportunity for the 6th Edition of the Green Guide to provide regulators and designers with a clear and coordinated document that reflects these changes and allows innovation and design flexibility in the delivery of compliant safe stadia in the coming years.