Steel Fire Performance – an introduction

This page outlines the general requirements for steel fire performance for cladding panels, and describes how those requirements may be met when using Steadmans twin skin and composite panels.

Note

This page contains only general information about steel fire performance and the treatment of roofing and cladding panels: when determining the requirements for specific building projects designers should obtain guidance from suitably qualified persons. Steadmans Technical Department is also able to offer information and test results for individual products.

Testing

British Standards

The test methods for steel fire performance set out in British Standards establish test methods and results categories: the required performance levels are set out in Building Regulations or other documents. Whilst British Standards are currently being harmonised with European Standards there is at present no means of directly transposing the requirements of one system into those of the other, regulations therefore often quote performance measures from British and European standards.

Growth of fire

BS 476-7: 1971 or 1987 – Surface Spread of Flame Test.
This test measures the rate of spread of a flame front across a material surface, but does not consider emission of toxic smoke and gas.
Class 1 is the highest classification, with the slowest rate of spread, Class 4 is the highest.

BS 476-6: 1981 or 1989 – Fire Propagation Test.
This test assesses the heat potential for a material or system.
Results are reported as an index of performance I

The values obtained in the two tests can be used to classify materials as Class 0, Class 1 and Class 3.

Fire resistance

BS 476-22: Methods for the determination of the fire resistance of non-loadbearing elements of construction.
This test measures the steel fire performance of a sample construction in terms of its insulation value and integrity.
Results are reported as minutes of insulation and integrity provided.

Commercial standards

Standards for commercial purposes – commonly insurance requirements are determined by industry bodies such as the Loss Prevention Certification Board (LPCB now part of BRE) and Factory Mutual.

LPS 1181-1: 2005. Requirements and tests for built-up cladding and sandwich panel systems for use as the external envelope of buildings.

This test measures the reaction to fire of a sample construction and also takes account of the results of testing to LPS 1208-2.1.

LPS 1208-2.1: LPCB Fire Resistance Requirements for Elements of Construction Used to Provide Compartmentation.

This standard sets out fire resistance requirements for elements including built-up and composite wall and roof panels, mainly by reference the British Standards for fire resistance.

Products which satisfy the reaction to fire requirements of LPS 1181-1 only are graded EXT-B. Those which also satisfy the requirements for fire resistance are graded EXT-A. For life safety, EXT-A products should achieve 30 mins and 15 mins.

Steadmans Systems

AS35 Panels

When tested to BS 476:7 1987 AS35 panels achieve Class 1 surface spread of flame (Euro Class B), equivalent to Class 0 surface spread of flame as described in Approved Document B.

When tested to BS 476:3 1975 AS35 panels achieve an FAA/SAA rating.

AS35 panels have been tested by LPCB to LPS 1181:2003. Standard AS35 panels achieve grade EXT-B; AS35 wall panels achieve grade EXT-A15. Further details of test results are available from Steadmans.

Twin skin systems

When tested to BS 476-7:1997 AS20/1000 and AS30/1000 profiles achieve Class 1 surface spread of flame (Euroclass B), equivalent to Class 0 surface spread of flame and when tested to BS 476-3:2004 the profiles achieve an FAA/SAA rating all AS series weather sheets achieve an AA rating against external spread of flame and may be used on any location on the roof.

The AS Fire Resistant Wall System, which includes two 80 mm layers of Rockwool Firesafe insulation, achieves 125 minutes integrity and 35 minutes insulation when tested to BS 476-22:1987 (Warrington Fire Safety test report 150032 Issue 2). Full specification details of the Fire Resistant Wall System are available from Steadmans Technical Department.

General Requirements

The statutory steel fire performance requirements for buildings are set out in Building Regulations: Part B in England and Wales, Section 2 in Scotland and Part E in Northern Ireland.

The intention of Building Regulations is to preserve life during a fire, not to promote the continued usability of the building following a fire, consequently the regulations set out to:

  • Facilitate escape from buildings
  • Ensure safe access for the fire brigade
  • Prevent the spread of fire to neighbouring properties

The main performance requirements which Building Regulations make for roofing and cladding panels are:

  • Internal linings should resist the spread of flame across their surfaces and should not contribute unduly to the development of a fire (Regulation B2), so slowing the development of a fire and maximising the occupants opportunities for escape.
  • The building must retain its structural integrity for a reasonable period, again to ensure the occupants have sufficient opportunity to escape and minimise the risk to firefighters who may be engaged on search or rescue operations (Regulation B3). Although roofing and cladding panels are not structural, wall linings may form part of the fire protection to the building structure. Also, wall and roof constructions may also need to incorporate cavity barriers to reduce the potential for unseen smoke and flame spread.
  • The construction of roofs and external walls must restrict the risk of spread of flame over their surfaces and the risk of ignition from an external source. Walls must also have a low rate of heat release, to prevent ignition of neighbouring buildings (Regulation B4).
  • Additional provisions designed to minimise the effect of a fire upon a building may be required by the building owners or occupiers, or by their insurers. Those requirements will commonly include active fire protection measures, such as fire detectors, fire doors and sprinkler systems, but will also include requirements for passive fire protection, but with more stringent requirements.

Requirements of Regulations

Building Regulations – Surface Spread of Flame

Class 0 materials may be used without restriction within a building. AS twin skin panels and AS35 composite panels may therefore be used to form roof and wall linings without any additional treatment.

External spread of flame

Whilst the performance of roof coverings can be determined by testing to BS 476-3:2004 or BS EN 13501-5:2005 certain common roof coverings have standard classifications under the regulations. Single or twin skin profiled steel roof panels with or without insulation, and composite roof panels with polyurethane insulation are classified as AA and can be used without restriction. Steadmans AS twin skin panels and AS35 composite panels may therefore be used at any area of a roof: they may also be used as the external surfaces of walls without restriction.

Fire Resistance

The required fire resistance for a wall depends on the building type, the wall height, the distance to the nearest building and the arrangement of openings. Generally, the requirements in Scotland are more onerous that those in England and Wales or Northern Ireland.

In England, Wales and Northern Ireland a standard AS twin skin system may be used on walls more than 1m from a boundary: see Approved Document B sections 12 and 13 (England & Wales) and Technical Booklet E (N. Ireland) for details of fire resistance and boundary conditions.

Walls within 1m of a boundary should be constructed with the AS Fire Resistant Wall System.

In Scotland the AS Fire Resistant Wall system should be used for all walls which require a fire resistance period. See Scottish Building Standards Technical Handbook Section 2 for details of boundary conditions and fire resistance requirements.

LPC Design Guide for the Fire Protection of Buildings

The LPC Design Guide requires both the external wall and the roof on each side of a compartment wall is fire resisting. To meet the risk based assessment concept of the Design Guide there are three levels of fire resistance depending on the outcome of the risk assessment.

Grade Integrity (Minutes) Insulation (Minutes) Typical Application
EXT-A60 60 60* 4b Retail warehouse and superstore
6b Industrial and 7a storage
EXT-A30 30 30* 4a Shop and Commercial and 6a Industrial
EXT-A15 30 15 Fully sprinklered buildings

* Systems that achieve an insulation time within 90% of this figure can be deemed to satisfy the requirements for this grade.

Additional Considerations

The in-situ fire performance of any roof or wall cladding will be dependant on the whole construction, including the supporting steelwork and fixings, and not only the cladding sheets or panels.

The fire performance of thermoplastic rooflights will not match that of the rest of the roof construction, consequently there are restrictions on their type and location. Not as good as the rest of the roof they sit in: they are classified according to their material, and are subject to restrictions as to where they can be used.