CROSS Safety Report
Licensing of temporary structures
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Temporary structures, such as stages, marquees, lighting towers, video screens and the like are erected at a huge number of events in the UK each year.
A reporter who inspects many such structures raises concerns that the systems in place for ensuring their stability are not working.
Key Learning Outcomes
For event organisers and construction professionals:
Be aware that the design and installation of temporary structures should be given the same degree of attention as primary structures to ensure they are safe
It is good practice to carry out independent design checks on temporary structures. A Chartered Engineer having adequate skill and experience can carry out these checks.
Carrying out independent erection checks by a person who is competent to do so, can ensure that the temporary structure is built in accordance with the design
For civil and structural design engineers:
Careful consideration needs to be given to temporary structures to ensure they have adequate lateral stability to resist wind loads
Helpful guidance is provided in the Standing Committee on Structural Safety (SCOSS) Alert on Temporary Stage Structures
Information on all aspects of temporary structures can be found in the Institution of Structural Engineers publication Temporary demountable structures
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Temporary structures, such as stages, marquees, lighting towers, video screens and the like are erected at a huge number of events in the UK each year. I have, says a reporter, inspected many such structures and have concerns that the systems in place for ensuring their stability are not working. Because of the number of people in close proximity, they continue, the failure of such a structure could have very serious consequences.
The reporter works for a local authority and there are a large number of outdoor events held each year in his area which require a public entertainment licence. In granting the licence, the local authority has a duty to consider the structural stability of any temporary structure. In the reporter’s authority, the licensing department consult with building control and request that they deal with this aspect.
There are however no controls under building control legislation to deal with such structures, so any enforcement must be through licensing laws. Failures of such structures can occur for a number of reasons, such as; design faults, erection faults, component failure and management failings. The Institution of Structural Engineers publication ‘Temporary demountable structures’ is an excellent guide for all those involved with these structures. Below are problems found by the reporter.
It is important that the design of such structures is undertaken by competent engineers. However, there is still the risk of errors in the design, and in recent times, continues the reporter, they have received structural calculations where moments have been calculated incorrectly and inadequate factors of safety used.
In the opinion of the reporter, this is the most common type of problem. Structures are often erected without any or little reference to the design calculations, and frequently the ballast provided is far less than required by the design. In addition, the fixing of the ballast to the structure is often inadequate, especially when intermediate Bulk Containers (IBC) filled with water are used.
They have also witnessed columns supporting a large balcony supported only on ply decking with no support directly beneath, and even base plates to a footbridge on steeply sloping ground wedged with dead branches. It was intended that 5,000 people would use the bridge.
Structures are often erected without any or little reference to the design calculations, and frequently the ballast provided is far less than required by the design
Components may fail for a number of reasons and it is important to ensure that damaged components are not re-used.
Rather than designing for maximum likely wind speeds as would be required for permanent structures, many temporary structures are wind managed. This requires an effective wind policy to be in place to monitor wind speed and take appropriate action when the wind reaches certain pre-determined speeds. Failure to abide by this wind policy could have disastrous consequences, and the reporter frequently comes across situations where there is no such policy in place.
There are a number of organisations that they have dealt with, says the reporter, which have excellent systems in place to ensure that design calculations have been checked, that erection is in accordance with the design and that the management policy is robust. However, from his experiences, he has real concerns that in general terms the industry is not able to self-regulate itself at present, and therefore, if we are to reduce so far as practicable the risks, it is important that there is sufficient external checking of such structures and adequate supervision on site.
Having regard to the faults that he has identified, the reporter believes that the standard of checking by local authorities is extremely variable, or possibly even non-existent in some cases. Frequently erectors state ‘this is how we always do it’ when clearly this is not in accordance with the design. The question has to be asked why structures are not being erected in accordance with the design.
Communication of design information
It is believed by the reporter that the main reason for this is that, very often, important design information is hidden in the structural calculations and is not readily interpreted by people without experience in structural design. By producing a simple summary sheet to their calculations which clearly identifies important aspects of the design, such as the ballast and bracing requirements and maximum wind speed, designers could assist both the erectors and checking authority. They believe this would significantly assist in ensuring that structures are erected in accordance with the design. This is a recommendation of the IStructE guide (TDS3) but is clearly not being followed in the majority of cases.
Checking of temporary structures
Certainly, local authorities need to consider whether they are carrying out sufficient checks and perhaps guidance should be produced for licensing authorities in this respect. It could of course be argued that there have not been too many serious incidents in recent years in this country involving such structures. However, when things go wrong, it does seem that it is often as a result of concurrent circumstances, such as erection and management failings together with adverse weather conditions, and perhaps we have just been fortunate. Based on his experience, the reporter believes that unless systems are improved a serious incident will occur, and at that time questions will be asked about the checking process.
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The reporter is to be complimented on bringing to the forefront an issue which is serious and timely. The design and construction of temporary stages has been developed within the industry to include some very large and complex structures. Many of these are perfectly satisfactory but there have been catastrophic failures in recent years.
- Millennium Point Birmingham June 2006; collapse of large video screen – see SCOSS Topic Paper: Risk issues associated with large TV/video screens at public events
- Bearded Theory Music Festival Derbyshire May 2009 failure of saddlespan tent– see SCOSS Alert: Temporary event structures: ‘saddle span’ type tents
- Madonna Concert Marseilles July 2009 – stage roof collapse during construction with 2 fatalities and 8 injured
- Big Valley Jamboree Alberta August 2009 – stage roof failure with 1 fatality and 75 injured
- Guns N’ Roses Concert Brazil March 2010 – stage roof failure with several injured
- Bluesfest Concert Toronto July 2011 – main stage collapse with 3 injured
- Sugarland Concert Indiana August 2011 – main stage roof collapse with 6 fatalities and 44 injured (Figure 1)
- Flaming Lips Concert Oklahoma August 2011 – large video screen collapse
- Pukkelpop Music Festival Belgium August 2011 – main stage collapse with 5 fatalities and 140 injured
- Jovanotti Concert Trieste December 2011 – ground support stage structure collapsed during construction with 1 fatality and 12 injured.
These failures should provide a serious warning to local authorities and others involved. Guidance on temporary structures is contained in Temporary demountable structures, Guidance on procurement, design and use, Third edition, published by the Institution of Structural Engineers, 2007 (TDS3). The SCOSS Alert: Temporary Stage Structures, published in January 2012 draws the attention of site owners, promoters, contractors and their designers, local authority licensing officers and building control officers and insurers to potential risks.
In some cases, wind forces have been cited in press reports as contributing to some of the above collapses, but as stated in TDS3 there must be monitoring of wind speed and a plan of action if there are design restrictions on safe wind loads. The issue of a licence for a temporary structure should not be any less effective than the process of gaining approval under Building Regulations. Licensing mechanisms should preclude the possibility of workers and the public being at risk from the collapse of temporary structures but are the regulations tight enough and are they being applied with sufficient rigour?
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