As there is at present a marked on-going increase in different types of tent structures – right up to three storeys high – SP together with Brandskyddslaget has applied for and received funding from the Swedish Fire Research Board (BRANDFORSK). The name of the project is fire protection requirements for temporary tents and tent-like building structures.
It can also be mentioned in this context that MSB intends to publish an updated version of its Advice on temporary tents, with associated handbook. The research project will also provide material for this work.
The main focus of the work of the project is on requirements applicable to materials for tent fabrics, although the supporting structure and escape facilities will also be considered. At present, these areas are regarded as not covered by specific regulations.
Examples of tent structures
In addition to circus tents and similar types of applications, which have previously been the main focus of fire protection requirements, there are now many newer application areas:
• A two storey structure was erected at the Solvalla racecourse against the side of one of the existing buildings. The structure consisted of an unprotected steel framework, with weather protection provided by tent fabric. The upper floor carried a bar, providing a good view of the winners’ enclosure.
• A tent structure, intended for serving meals, will be constructed on the Stockholm Opera House roof terrace.
• Every year, Sergels Torg in Stockholm is the site of a tented Christmas market, with considerable quantities of flammable material.
• Uppsala is planning to construct a tent like canopy linking to the Uppsala Concert and Congress Hall, partly in order to be able to utilise the backstage features of the hall.
• Conventional buildings under construction are often covered by ‘tea cosies’, in order to enable work to be carried out in the dry.
• In some cases, when renovating buildings, those in which residents remain while the work is being carried out may be protected by weather protection up to four storeys high.
Permanent stores structures, providing covered working areas protected by single layer fabrics, are common.
Construction of tent structures
Depending on the intended purpose, the fabric of a tent can vary in thickness, density and type of material. The material may be either cotton or, more commonly, PVC coated polyester membranes. They can be supported by internal or external structures, which may be either frameworks or an arrangement of poles etc. Load carrying structures for second and third storeys consist of uninsulated ‘steel scaffolding’. Load carrying lines may be synthetic, aluminium or steel.
In some cases, walls may be of plywood, which may also be used as the floor material in two- and three-storey structures. In order to improve thermal insulation, the fabrics may sometimes consist of two layers, with or without an intermediate insulating layer. In this project, as far as the surface properties are concerned, only single layer structures will be considered. However, future regulations should also consider these insulated types.
• If a tent structure is permanent, i.e. is not moved for about 4-5 weeks, it is covered by the requirements of Section 19 of the Building Regulations. This section specifies that the minimum requirement for single layer fabrics is nowadays Class E in accordance with EN 13501 1. Previously, such fabrics would have been classified in accordance with the requirements of SIS 65 00 82. It is not clear whether the new requirement represents a tightening up or a relaxation of the regulations, and so this will be investigated in the project.
• If the tent is used as a permanent meeting place, it is covered instead by B s1, d0, for roofs and walls.
• Permanent tents used for industrial purposes must meet the requirements of Activity Class 1, Vk1 of Section 19 of the Building Regulations. Note that all the rules in the Building Regulations and the National Board of Housing, Building and Planning’s EuroCode regulations (EKS) must be complied with in the above two cases in respect of evacuation, division into fire cells, cladding layer, load carrying capacity and the risk of spread of fire to other buildings.
• Another type of tent structure is that of weather protection for new building construction or renovation. If occupants remain in the building, then the requirements of Section 19 of the Regulations apply. One of the effects of this is that the presence of the fabric must not interfere with any requirements for emergency evacuation through windows.
• When buildings of different types are enclosed or incorporated in other buildings, the arrangement of the workplace, as governed by the Work Environment Authority’s Provisions and General Recommendations (AFS), must be considered in order to ensure that the building workers have satisfactory emergency evacuation arrangements. This means that consideration must also be given to the fact that such covering may make smoke evacuation difficult in the event of fire. In this case, too, it is not certain as to what requirements apply to the fabric.
Temporary tent structures
Temporary tent structures – those that are not left up for more than about four weeks – are covered by completely different regulations from those applicable to permanent tent structures.
• The Swedish Work Environment Authority’s Provisions and General Recommendations for Building Works apply for weather protected buildings, regardless of whether the protection is regarded as temporary or permanent. It is not certain as to which requirements apply to fabrics.
The Act Concerning Protection Against Accidents (LSO)
• Permission to erect and use temporary public tent structures is covered by the requirements of the Public Order Act (1993:1617, as revised in SFS 2010:1625). Requirements for fire protection are covered by § 12, which specifies that tents may be used for public events only if they provide adequate fire resistance and adequate stability. This means that fire protection is expressed in a somewhat general manner, leaving the way open to different interpretations.
• Tents intended for occupation by more than 150 persons must be inspected and approved.
• If tents are to be inspected, they must also meet the requirements of the Ordinance Concerning Tents for Public Use (1993:1633, as modified up to and including SFS 2011:808). The approval certificate must indicate the permitted number of persons. This states that, in addition to compliance with the requirements of the Public Order Act, more detailed regulations concerning inspection of such tents can be found in SRVFS 1995:1, issued by MSB.
• SRVFS 1995:1 states that:
– The tent must be capable of being safely evacuated.
– Load bearing parts shall comply with the National Board of Housing, Building and Planning’s BFS 1995:18 in respect of own weight, load-carrying capacity/snow loading and wind loading. However, BFS has been withdrawn, and replaced by EKS. Note that the effect of fire is not included as a load. This is a serious shortcoming with respect to multi storey structures, which could mean that a fire at ground level could result in collapse of higher levels before they could be evacuated.
• SRVFS 1995:1 is being revised, and a very early consultation document has been sent to the National Police Board, the National Board of Housing, Building and Planning and SWEDAC. The document has the title ‘General Guidelines for Tents Intended for Public Use’. The draft document is based on requirements expressed in SS-EN 13782:2005 ‘Temporary facilities – Tents – Safety’, and considers only single layer fabrics.
Summarising, a review of the regulations shows that there is considerable uncertainty as to how multi storey tents (in particular) and weather protection arrangements should be constructed in terms of fire protection and fire safety. One of the reasons for initiating this BRANDFORSK project has been to tackle these shortcomings, although the main focus of the work is on the fabrics’ surface layer.
Permanent buildings can be designed either in accordance with simplified methods or analytically. If, for example, the designer departs from the rule of thumb of 1.2 m unobstructed door opening widths, he must be able to show by calculations that the interior can nevertheless be evacuated safely.
There is no reason that fire protection should be poorer in a complex temporary structure than in a permanent structure. It is therefore appropriate, when designing a temporary tent like structure, to follow the rules in the Buildings Regulations. Specific problem areas, for which answers cannot be directly found in the Building Regulations, are:
• How should double layers of tent fabric be considered?
• How can evacuation be arranged from upper storeys? According to Section 19 of the Building Regulations, a staircase in a separate fire cell must start there.
• Can unprotected plywood really be accepted as a floor supporting structure in upper storeys? What requirements must the supporting members meet? Can EKS be applied?
• How can a tent structure be built onto an existing building so that fire cannot spread between them?
• How can, for example, occupants’ safety in respect of evacuation arrangements be guaranteed when the use of escape ladders is prevented by weather protection covering?
Parts of these questions will be considered, and solutions found, in the BRANDFORSK project.
AFS – Swedish Work Environment Authority’s Provisions and General Recommendations for Building Works
BBR – National Board of Housing, Building and Planning’s Building Regulations
BFS – National Board of Housing, Building and Planning’s Regulations
EKS – National Board of Housing, Building and Planning’s Regulations Concerning EuroCodes
EN – European Standard
LSO – The Act Concerning Protection Against Accidents
MSB – Swedish Civil Contingencies Agency
PBF – The Planning and Building Regulation
PBL – The Planning and Building Act
SFS – Swedish Code of Statutes
SIS – Swedish Standards
SRVFS – Swedish Rescue Services Agency Code of Statutes
SS-EN – European standard accepted as a Swedish Standard
Vk – Activity class in the National Board of Housing, Building and Planning’s Building Regulations (BBR)
Written by Staffan Bengtson