How new fire regime could affect your building

Andy Kay of Hilti points out that curtain walling and compartmentation are specific areas of concern.

A number of new fire regulatory initiatives will be introduced this autumn, which will effectively shift responsibility and liability for ensuring fire safety to specifiers and installers.

Andy Kay of Hilti points out that curtain walling and compartmentation are specific areas of concern.

The February 2005 fire in Madrid's Torre Windsor Tower spread to 30 of the 32 floors, leading to the eventual collapse of large parts of the structure.

The initial findings pointed to a failure in the compartmentation strategy of the building combined with insufficient fire protection to the steel structure and curtain wall glazing.

Compartmentation is designed to limit the spread of a fire but the failure of the design occurred between the curtain wall and the edge of the floor slab, a critical joint for good compartmentation.

Without an adequate fire stop material in the Torre Tower, flame and smoke spreading upwards through the building and downwards from the spread of burning droplets.

Curtain wall systems and compartmentation.

Despite the publication in 1998 of the 'Going Up in Flames' Report by Dr Louise Jackman, the issue of fire resisting curtain wall constructions has not yet been adequately addressed.

Due to the perceived additional costs involved, the market has barely moved, with probably less than 1% of curtain wall facades having fire resistant glazing.

Cost realities.

In reality, the installed cost differential is not high.

According to Mike Wood of Pilkington, fire resistant glazing should form part of a fire risk strategy in a building.

It can and should be used to provide compartmentation at critical points in the building layout, so the costs should be regarded within that context.

So, for example, internal, re-entrant corners and external escape stairs would be perfect situations for fire-resistant glazing in the facade.

Glazing adjacent to flat roofs and external escape ways would also be candidates, as would important key connections between different areas of the building.

Slab edges and compartmentation.

In 2001, independent assessment of the fire stop products used in the UK market for the slab edge application found that, despite the large number of products that could achieve the necessary fire rating, the movement capabilities, smoke resistance and acoustic properties did not necessarily meet the critical performance required.

A curtain wall is subject to fluctuating wind loads as well as occupational live loads.

This means that any fire stop products have to be able to demonstrate their ability to compress and recover over a series of cycles without a gap opening up.

They are also required to accommodate sheer movement.

In a fire scenario the deformation of the curtain wall will often lead to fire stop products simply falling out of the gap.

Standards and movement.

Until the publication of BS8414 in 2002, there was no requirement to test the products used to fill the slab edge gap in a full curtain wall fire application.

The 2 leading products currently in the UK market have only been tested to BS476 in a static joint test between masonry products, not replicating a curtain wall.

In contrast, the construction fire prevention industry in North America has moved away from rigid boards friction fitted into the gap in favour of a sprayed coating that can meet all of the requirements highlighted by the 2001 assessment.

A typical leading product by the world's leading fire stop company Hilti is their CP 672 Speed Spray is applied over a compressed low density mineral wool as a sprayed mastic.

It provides fire resistance and insulation, a smoke and air seal, good acoustic performance and most importantly, proven movement capabilities fully assessed on various gap widths against a variety of curtain wall constructions.

In independent accredited fire testing, the test sample was cycled 500 times at 30 cpm in accordance with the ASTM regulations.

This test substantiates that the Hilti product can accommodate up to 15% movement of the curtain wall construction in both a non-fire and fire environment.

Time and motion studies conducted by a number of UK curtain wall installers have also shown the system to be up to 4 times faster to install.

Despite the product being relatively new to the UK market, Hilti has already seen it used on Canary Wharf and by Dane Architectural on the Unity Project in Liverpool, a mixed residential, office and commercial development consisting of 2 tower blocks, 16 and 27 storeys high.

It will also be installed on the Manchester Royal Infirmary in a Scheldebouw curtain wall system, Western Harbour, Edinburgh, a Systems Aluminium project as well as a number of Norking Aluminium contracts.

The Hilti Firestop Academy will be holding a one day event for architects and building specifiers at Wembley on 10th January 2007.

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