In several cases, the management of risks associated with temporary demountable structures at major public events has been found to be inadequate. Paul Thomas explains what has been going wrong, and how procedures can be improved.
In recent years there has been an increase in the use of large video screens, vast stages, and complex seating/dancing arrangements to cater for huge numbers of people at big outdoor and indoor events.
The supporting structures to these various items are becoming more sophisticated in order to cope with the increasingly complex imposed loadings from lighting, sound, etc. Combined with these issues is the element of erection and dismantling time, which can be extremely demanding.
These matters have given rise to a situation whereby the industry needs to control increasing risks to workers and members of the public. The HSE has recently investigated a number of major incidents involving temporary demountable structures, including: a Children In Need concert at Colwyn Bay; a Christian festival at Lincoln Grandstand; and World Cup football broadcasts at Millennium Point, Birmingham.
These incidents could have resulted in multiple fatalities to workers and members of the public. So what have these investigations revealed about what has been going wrong, and how can the risks be adequately controlled?
Universal issues
Various contributory causes were found to be common to these incidents.
Usage:
The London 2012 Olympics will see increasing demand for these high-profile public events, and the consequent use of temporary demountable structures. The pressure on the industry to compete, not only financially but also in terms of time and programmes, will place even more emphasis on the need for industry to apply effective risk-control measures.
As the size of the public audience grows, so does the need for improved performance of these structures. This becomes a considerable design challenge – for example, during the Wimbledon tennis championships, the All England Lawn Tennis and Croquet Club installed a temporary large video screen located at ‘Henman Hill’/’Murray Mound’. As the crowds grow larger, the screen will inevitably increase in size.
Design:
The supporting structures were designed to accommodate sophisticated lighting, sound, and dynamic human performances over large spans using extremely lightweight modular sections. The design, erection and dismantling sequence of these structures requires specialist input, which can only be satisfactorily obtained in the UK from a few engineering sources.
Planning:
Large numbers of technical personnel from multiple organisations were present during the erection, use and dismantling of structures. The control of risk to these staff, and ensuring good communication at all times were major challenges.
The large public audiences at these events resulted in pre-planned focus of risks in certain areas of the process, rather than in the overall process.
Installation:
Commercial pressures – it is apparent that some contractors are appointed on the basis of lowest cost, without sufficient regard to competence and resource.
Pressure on contractors for “the show to go on!”
Contracts and competency
There are usually a large number of competent technical people involved in the planning, erection and dismantling of temporary demountable structures. Structural designers, event planners, supervisors, and riggers from various organisations all take part during the process of providing an event structure. Lack of coordination of the design process, and ineffective implementation of design information on site often lie at the heart of problems encountered with these incidents.
Problems tend to start with the form of contract between the various parties involved, i.e. there is frequently no formal contract. This is a small elite industry, with players who are well known to each other. Most of the people I have encountered in my investigations have been very competent technically but possess a “no problem” attitude. A lack of formal contracts has resulted in a dilution of responsibilities through the procurement chain, which has inevitably culminated in misunderstandings during the planning audits, on-site inspection checks, and installation process.
Allied with this approach has been the lack of effective competency checks on contractors. Again, in some instances, this procedure was found to have been too relaxed and lacking any form of effective audit. Basic competency checks by clients and contractors were often not undertaken. This has resulted in contractors undertaking roles on site that they were unable to fulfil, and making poor judgements through inexperience. Contractors’ workforces were very skilled at their particular operations but were often found to be working beyond their competence.
Lack of design control
Another major issue has been the lack of a ‘controlling designer’. Throughout the procurement process there is a need for a competent person to take overall charge of the structural design. This role of ‘controlling designer’, which is a recommendation contained in existing industry guidance,1 also involves undertaking an independent design review, and providing an effective on-site information package on structural performance.
A typical structure starts with a concept design by the client or supplier, which will then be developed by a designer commissioned by the contractor. A support system is designed to accommodate the client’s requirements for lighting, sound and advertising. Finally, an installer usually designs the temporary foundation details of the structure.
This multiple-designer approach has led to significant problems, resulting in incomplete and/or incompatible designs. If no overall designer is responsible for the complete design package, who ensures the overall structure and procedures are robust?
The modular units used to build the structure are designed by the manufacturer to resist forces imposed by vertical loadings hung on to the structure. When bolted together for an outdoor event these units are formed into a structure, which also attracts significant horizontal wind forces, particularly when advertising banners are attached to it. Investigations have revealed that not only are these structures struggling to accommodate foreseeable winds with regard to overall stability but the individual units are being exposed to excessive stresses – beyond the manufacturers’ recommendations – at the welded joints.
Gaps in checking procedures
The installation contractor for the event usually commissions a structural engineer to develop the design concept into a final design package, which should include calculations, erection drawings, and a performance specification for the user on site. It is essential for the safe performance of these structures that the final design package is completed and reviewed before building work begins on site.
Investigations have revealed that this procedure has not been followed and, as a result, unsafe structures have been erected. In some cases these structures have failed in foreseeable environmental conditions. In these situations the public and operators on site have been exposed to risks of injury and fatality.
In theory, the final design-review process starts with the local authority, often the licensing authority, which has a duty to ensure the safety of the public at community events under the Licensing Act 2003. As part of this process the local authority should ensure that an independent design check of the final design information is undertaken.
Again, this essential auditing procedure is not always undertaken, and this has resulted in incomplete designs being adopted by the user on site. In some cases, such as the incident that occurred at Millennium Point, Birmingham, this has lead to catastrophic structural failures.
Wind-management plans
HSE investigations have also revealed that these design procedures themselves may need review. The main industry design guidance for temporary demountable structures2 suggests two options for the structural design regarding wind forces. Option (a) is to design for the maximum likely wind force to be experienced. Option (b) is to design for the maximum operational wind gust speed. The latter option requires an effective operational wind plan to be developed by the designer for the on-site user as part of the final design package. The wind plan includes an on-site monitoring and implementation sequence for the user in the situation of rising wind speeds.
The wind-management plan should provide a clear sequence of operations for the user during rising wind conditions, and clear instructions as to how to monitor, measure and interpret these wind speeds on site. Investigations have shown that either wind plans have been non-existent or unclear, leading to confusion as to when to evacuate the site.
In cases where rising wind speeds were a factor, the HSE has found evidence that contractors were put under pressure to continue with events. Often those left on site were not competent to undertake such responsibility, or the responsible person had not been clearly identified. This has generated confusion, which in turn has often led to delays in stopping installation, or user participation.
There was found to be a general lack of procedural control through the supply chain from client to contractor, despite these issues being covered in specific industry guidance.2, 3 Had this guidance been followed these problems could have been avoided, so there needs to be a greater awareness within this sector of the industry as to the negative consequences of failing to follow such best practice.
The way forward
The HSE has been working closely with the Standing Committee on Structural Safety (SCoSS) to find a way to help the industry prevent future incidents involving temporary demountable structures.
To alert the industry to these concerns, the SCoSS has produced a topic paper SC/08/0081, in which a questionnaire to aid good procurement is contained. Examples of the questions designers and others should ask themselves include:
Do those who assemble individual modular screen units into overall assemblies provide critical design data to allow those using them to check that they are suited to the specific circumstances of use?
For typical events, are responsibilities clear contractually, and statutorily, in respect of the safe use of screens? and
Do management plans outline practical measures to be taken in the event of high winds?
The committee also convened an afternoon workshop in April this year, attended by the HSE, designers, local authorities, and industry representatives. During this workshop, the attendees aired their views on the findings of these investigations, and discussions led to the forming of several recommendations and outcomes. These included:
Key organisations had messages to take back to their members;
An emphasis on basic management needs, communication, competence, coordination, and cooperation;
SCoSS promised to contact CEOs at local authorities regarding their obligations.
A subsequent letter from the committee to those involved in the workshop referred participants to a technical investigation report into the Millennium Point incident (see panel), and asked them to bring the workshop’s recommendations to the attention of those involved in such events.
Finally, the HSE and SCOSS are currently trying to find ways to engage with local authorities, which are key to the success of this process. Local authorities work in very different ways and there is a need to embed these issues into their procurement and authorisation processes.
Of course, other risks, such as fire safety, crowd safety, work at height, working with electricity, manual handling, etc are also a concern with such events, but did not contribute to these specific incidents. Readers should refer to the HSE’s event safety guide,3 which provides guidance on the control of these risks.
Summary
It has been pure good fortune that multiple fatalities have not resulted from the incidents described above. The risks associated with the erection and dismantling of temporary demountable structures are well known in the industry, and relevant control measures have been formulated into official written guidance. The various parties concerned with the procurement, authorisation, design, and installation of these structures need to ensure their members employ planning and on-site working practices in accordance with this guidance, to avoid recurrence of further incidents in the future.
References
1 SCoSS (2008): Risk issues associated with large TV/video screens at public events, SC/08/008 www.scoss.org.uk/publications.asp
2 The Institution of Structural Engineers (2006): Temporary Demountable Structures, Third edition
3 HSE (1999): The event safety guide, HSG195, Second editionh
The Safety Conversation with SHP (previously the Safety and Health Podcast) aims to bring you the latest news, insights and legislation updates in the form of interviews, discussions and panel debates from leading figures within the profession.
Find us on Apple Podcasts, Spotify and Google Podcasts, subscribe and join the conversation today!
