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Fire Safety

INTRODUCTION

Steel framed glazed windows, screens and door assemblies can be designed and installed to protect life and property in the event of fire. Combining the transparency of glass with fire safety is a challenge to the window industry that demands high standards of construction, independently tested and assessed by recognised competent authorities.

Some of the steel framing solutions developed for members by the SWA and examined by Warrington Fire Research to meet such standards are illustrated in this Fact Sheet, which summarises key features of construction, indicates a variety of appropriate glass types, and gives pointers to their scope of application. They use solid hot rolled steel profiles from the F, W20 and W40 ranges to provide fire resistant glazed windows, doors and screens which will maintain their integrity in a typical fire for 30 or 60 minutes.

The complete assessments C118328 and C118420 produced by Warrington Fire Research, plus test reports referenced therein, which support the summarised information in this Fact Sheet, are available to specifiers of named projects on a confidential basis from member companies. When detailing specific projects it is strongly recommended that specifiers and contractors consult individual specialist manufacturers and study the full test reports and assessments with them.

Some member companies also offer complementary systems which use hollow cold formed steel profiles to assure integrity, together if necessary with radiant heat insulation, for equivalent or longer periods of up to 120 minutes. Information including test reports on these proprietary cold formed precision steel tube systems (CFS in the tables below) can be obtained directly from them.

FIRE SAFETY CRITERIA

Glazing systems are tested in accordance with BS476: Part 22: 1987 "Methods for determination of the fire resistance of non-loadbearing elements of construction" and assessed with respect to their ability to satisfy the performance criteria referred to in paragraph 7.6.1: integrity and insulation.

The integrity criterion is satisfied when for the required duration a test specimen neither collapses nor develops cracks or apertures through which can pass flame or hot gases.

The insulation criterion is satisfied when for the required duration the mean temperature of the unexposed surface of a test specimen rises by no more than 140°C, or the temperature at any one point on the unexposed surface rises by no more than 180°C.

A summary of product range suitability
Criteria Duration Product Range fixed
lights
screen
assemblies
doors &
windows
double
glass
Integrity only Half-hour F(SMW)
W20
W40
CFS
yes
yes
yes
yes
yes
yes
yes
yes
no
no
no
yes
no
no
yes
yes
Integrity only One hour F(SMW)
W20
W20 modified
W40
CFS
yes
yes
yes
yes
yes
no
no
yes
no
yes
no
no
yes
no
yes
no
no
no
yes
yes
Integrity and Insulation


Integrity and Insulation
One hour
Half-hour


One hour
One hour
CFS



CFS
yes



yes
yes



yes
yes



no
yes



yes

FIXED SCREEN ASSEMBLIES: 30 minutes fire resistant integrity

The classic lines of the Standard Metal Window (SMW) manufactured from F range profiles since the 1920s, and of the heavy duty purpose made window constructed with W20 profiles in production since the 1960s, are still available today -positively rustproofed by hot dip galvanizing, factory painted, and upgraded for insulating glass units. For improved thermal insulation while retaining the traditional slender appearance, the W40 range has recently been introduced. The lines of all three can be matched in fire resistant glazing required to maintain its integrity for 30 minutes.

Composition

The framing is made of special hot rolled steel sections from the F, W20 or W40 ranges.

Manufacture

Corner joints are mitre cut and welded, after holes for fixing and glazing have been pierced in the bars. Tee glazing bars are tenon riveted and/or welded into the frames, and may have a maximum span of 1.0m. Composite windows can be assembled by connecting windows with mullions and transoms, up to a maximum height of 3.0m and a maximum mullion spacing of 1.5m.

Finish

Frames are first positively rustproofed by hot dip galvanizing to BS EN ISO 1461, then finished with a stoved polyester colour coating to BS 6497. Glazing beads of galvanised steel are likewise finished with a stoved polyester coating which can be of a matching or contrasting colour.

Fixing

Countersunk steel screws N°12 diameter in plastic fixing plugs at no more than 150mm from corners and 450mm centres (250mm for 60 minutes integrity) secure the frame to a structural surround, either directly through the frame or via 25mm wide by 2mm thick steel fixing lugs. The surround, of brick, block, concrete, masonry, steelwork or other material, must have stability and integrity in fire greater than that of the glazed screen.

Glazing:

resisting glass, positioned on non-combustible setting blocks, eg mineral fibreboard, is retained by cold formed 0.6mm steel channel bead snapped over steel mushroom headed studs screwed into the frame rebate at no more than 75mm from corners and 300mm centres. This bead sandwiches the glass between ceramic or mineral fibre tape, to be capped by a silicone sealant. Suitable glass includes 6mm wired Pyroshield and Pyroshield Safety, 6mm borosilicate Pyran, 5mm ceramic Firelite, and 6mm modified toughened Pyrocet, Pyroswiss or Tempaflam.

The modified toughened glasses must be bonded to the glazing rebates with Autostic adhesive, reinforced in the case of Pyroswiss with stainless steel mesh.

Where thermal insulation in external façades is required in addition to fire resistance, the W40 range can accommodate special 20mm thick insulating glass units made up of 6mm toughened glass, a steel spacer and 6mm Pyroshield, Pyran or Vetroflam fire resisting glass. Glass size limitations see below

FIXED LIGHTS: 60 minutes fire resistant integrity

The same F range, W20 and W40 constructions can maintain integrity for 60 minutes as single pane fixed frames, glazed with a restricted range of glass types, subject to glass size limitations , provided their perimeter is secured with more closely positioned fixings at no more than 250mm centres.

GLAZED SCREEN AND DOOR ASSEMBLY: 60 minutes fire resistant integrity

Where full height glazed screens and doors are required to maintain their integrity in fire for at least one hour, a modified W20 construction is available, developed jointly for the benefit of all Association members.

Authority:

A fixed screen prototype 3.0m x 2.6m divided into 6 panes, glazed with Pilkington "Pyroshield" polished wired glass, has been tested to BS 476: Part 22: 1987 and maintained its integrity for 77 minutes. A further test, discontinued after 75 minutes, has confirmed the performance of an enhanced version, incorporating a single leaf door 2133mm high by 1000mm wide, and Pilkington "Pyrostop" fire insulating laminated glass, which was assessed by Warrington Fire Research as satisfying the integrity requirement for one hour, and insulation for 14 minutes.

Application:

This system is suitable wherever a specifier wishes to combine one hour fire safety with maximum daylight and vision. Its weather and corrosion resistant properties make it suitable for external fenestration as well as internal screens, particularly to complement other adjacent hot rolled steel windows and doors which do not have to be fire rated.

Composition:

The framing is made of special hot rolled steel sections from the W20 range, combined with 2.5mm thick steel angle glass clamps concealed by extruded aluminium clip on beading.

Manufacture

Corner joints are mitre cut and welded, after holes for fixing and glazing have been pierced in the bars. Door leaves have glazing frames screwed into them and 200mm high double skin galvanised pressed steel panels filled with mineral fibre insulation inserted at head, sill and lock rail. Glass clamp angles of 2.5mm thick galvanized sheet steel are cut to length, perforated and pressed into shape. Composite screens can be assembled by connecting fixed lights and doorsets with mullions and transoms, up to a maximum height of 2.6m and a maximum mullion spacing of 1.5m.

Finish:

Frames are first positively rustproofed by hot dip galvanizing to BS EN ISO 1461, then finished with a stoved polyester colour coating to BS 6497. Glass clamp cover beads of extruded aluminium are likewise finished with a stoved polyester coating which can be of a matching or contrasting colour.

Fittings

Door leaves are hung on galvanised steel butt hinges and fitted with a CERTIFIRE approved surface mounted overhead door closer and interlinked multi-point exit device including all steel components and reinforced bolt guides.

Fixing

Countersunk steel screws N°12 diameter in plastic fixing plugs at no more than 150mm from corners and 450mm centres secure the frame to a structural surround, either directly through the frame or via 25mm wide by 2mm thick steel fixing lugs. Couplings are bolted together with 6mm diameter steel machine screws and nuts at similar centres. All joints in external fenestration are made watertight with acrylic or silicone sealant. The surround, of brick, block, concrete, masonry, steelwork or other material, must have stability and integrity in fire greater than that of the glazed screen.

Glazing:

Fire resisting glass, positioned on hardwood or non-combustible fibreboard setting blocks, is retained by steel glass clamps screwed into the frame rebate at no more than 75mm from corners and 300mm centres. This bead sandwiches the glass between ceramic or mineral fibre tape, to be capped by a silicone sealant. Suitable glass includes 6mm wired Pyroshield and Pyroshield Safety, 6mm borosilicate Pyran, 5mm ceramic Firelite, 6mm modified toughened Pyrocet, Pyroswiss or Tempaflam, and laminated intumescent interlayered glass such as 13mm Pyrodur, 14mm Pyrobel or 15mm Pyrostop.

The modified toughened glasses require a reduced edge cover of 11mm +/- 1mm and must be bonded to the glazing rebates with Autostic adhesive, reinforced in the case of Pyroswiss with stainless steel mesh.

GLASS SIZE LIMITATIONS

Based on test experience, glass pane sizes are subject to the following limitations:

  • maximum pane area is 1.53m 2 ,
  • maximum pane height is 1696mm when the width does not exceed 900mm,
  • maximum pane width is 1450mm when the height does not exceed 1053mm,
  • at the most favourable aspect ratio of 1 : 1 the maximum height and width is 1237mm,
  • no limitation is imposed on the aspect ratio providing the area is not exceeded.

FIRE RESISTANT GLASS TYPE SUITABILITY

The Steel Window Association represents the great majority of UK steel window manufacturers, ranging in size from the smallest of craft-based companies that specialise in replacement and repair work, particularly on windows for Heritage buildings, through to large, multi-site companies that manufacture and install windows in literally every type of building. There is not a single steel window project of any description, anywhere in the UK, that one of the SWA members cannot handle.

All windows produced by SWA members in hot rolled steel sections to BS.6510 are protected by the hot dip galvanizing process in accordance with BS.729. Cold formed steel section windows are also available and all steel section windows can be supplied with a decorative finish available in a range of colours. This process, in which polyester powder is electrostatically applied then heat fused under factory controlled conditions to BS.6497, gives a high quality, attractive and durable finish with a life expectancy of at least 20 years.

The Steel Window Association supports its member companies with a wide ranging service relating to product development, market research and promotion and the SWA helps ensure that each member operates to the highest industry standards. Every contract undertaken has the personal attention of senior management and SWA member companies operate established and flexible services in window design, manufacture, installation and repair and refurbishment.

Every effort has been made to ensure that the information in this fact sheet is correct at the time of going to print. However, the technical information and services referred to in it are subject to revision from time to time and may be added to or withdrawn. © Steel Window Association 2012


The Steel Window Association represents the great majority of UK steel window manufacturers, ranging in size from the smallest of craft-based companies that specialise in replacement and repair work, particularly on windows for Heritage buildings, through to large, multi-site companies that manufacture and install windows in literally every type of building. There is not a single steel window project of any description, anywhere in the UK, that one of the SWA members cannot handle.

All windows produced by SWA members in hot rolled steel sections to BS.6510 are protected by the hot dip galvanizing process in accordance with BS.729. Cold formed steel section windows are also available and all steel section windows can be supplied with a decorative finish available in a range of colours. This process, in which polyester powder is electrostatically applied then heat fused under factory controlled conditions to BS.6497, gives a high quality, attractive and durable finish with a life expectancy of at least 20 years.

The Steel Window Association supports its member companies with a wide ranging service relating to product development, market research and promotion and the SWA helps ensure that each member operates to the highest industry standards. Every contract undertaken has the personal attention of senior management and SWA member companies operate established and flexible services in window design, manufacture, installation and repair and refurbishment.

Every effort has been made to ensure that the information in this fact sheet is correct at the time of going to print. However, the technical information and services referred to in it are subject to revision from time to time and may be added to or withdrawn. © Steel Window Association 2012