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Liverpool trailblazers

Structures - Last year's blaze in Madrid's Torre Windsor drove home the importance of fire protection in tall buildings.Mark Hansford reports from a highrise which has got the message.

Almost a year after the Al-Quaeda bombings of commuter trains in March 2004, Madrid feared the worst last February when a massive blaze broke out in the 32 storey Torre Windsor (NCE 17 February 2005). Fortunately no-one was killed in the fire that spread to all but two of the tower's floors, caused a partial collapse and left the structure facing total demolition.

The cause of the massive blaze was not terrorism, however. It is believed to have been the result of something much more avoidable - the absence of fire stops between floor slabs and the building's curtain walling, allowing flames to spread between floors.

Vertical fire spread via cladding failure and radiant heat ignition of floors above the original source of fire has also been a feature of blazes in the UK, notably the 1991 Basingstoke office block fire (NCE 25 April 1991).

As a result British Standard BS8414 now demands that tall buildings have fire stops - typically mineral wool pads fitted between floor slabs and curtain walling. However, there are concerns that such systems would not perform adequately in a real fire, as the standard to which they are tested assumes that the external cladding system retains its shape in a fire. Madrid proved that this assumption cannot be relied on, with photographic evidence showing the cladding bulging outwards, allowing fire stops to fall from their place.

Fortunately there is a solution, and it is now being put to the test on the £60M Unity Sentinel project in Liverpool.

The development comprises a 27-storey residential and a 16storey office building, the latter being the first Grade A office to be built in Liverpool. The building complex is intended to form a striking landmark on the city's waterfront, which has just been awarded World Heritage Status.

Kingspan off-site façades are being used on the project, with 1,500 frame assemblies up to 5.2m wide by 3.2m high being manufactured in North Yorkshire.

The frames incorporate Kingspan K15 phenolic insulation and a carrier bracket system that retains the outer aluminium rainscreen. Aluminium windows are integrated into the facade system units.

Fire protection consists of a specially developed spray-applied latex system that expands to accommodate 15% joint width movement in a fire. The system offers two hours fi re protection to curtain wall assemblies.

Developer and supplier is Hilti Firestop Systems.

'It's amazingly simple, ' comments façade design and build subcontractor Dane Architectural's contract manager William Morrison. 'It takes minutes to pack and spray and you can use semi-skilled labour as you are not relying on a good fit of wire wool.' Wire wool is still installed with the Hilti system, but only to support the 4mm deep joint spray during its seven day curing period.

'If there is a negative then it is the drying time, because you have to keep water from it. But if it does need repair, you just spray it again, ' says Morrison.

The major benefit of the system is speed of installation, he claims. The facade frame assemblies are transported directly to site and then craned into place on the concrete framed building and connected with locator brackets to the main structure. This method allows rapid closure of the building, accelerating internal fit-out.

'We started on site in April last year and are programmed to be out this June. That's very rapid for the entire external façade.

Fire stopping could have had a major effect on the programme.

But with this system it's not even on the critical path. You get a floor done in a day.' Because it is quicker to install there is also a cost saving, compensating for the added cost of the spray product.

'The raw material is more expensive, but when you combine that with the reduction in labour it works out only marginally more expensive, ' notes Morrison. He estimates the cost of fire stopping to be £50,000 out of a façade contract worth £9.5M on a job worth £60M overall. 'The cost is minuscule compared to the entire cost.' The ease of installation also means you get a better job done, he adds. 'Traditionally it has been a job that nobody has liked doing because all your time is spent on your knees. It was the least cared about bit of the job, yet is potentially the most important. It was a thankless task and you were never reassured that it had been done 100%. Here you can go away with 110% confidence, because you can see it, ' Morrison says, referring to the visible red bond left by the spray.

This is the first UK use for Kingspan off-site cladding and for the Hilti fire stop system, but it will not be the last - Dane's next job is to install the façade for Manchester University's new maths and physics building. And despite the construction industry's penchant for the tried and tested, there has been considerable interest from other potential clients. 'Fire in flats is a major concern, ' says Morrison.

In Liverpool, wall panels are being installed on the 18th floor of the building, with completion on schedule really in the hands of the weather. Services installation and fit out are due for completion in the autumn.

Who's who

Developer: Rumford Investments

Architect: Allford Hall Monaghan Morris

Design and build contractor: Laing O'Rourke

Façade design and installation: Dane Architectural

Façade supplier: Kingspan Off-Site

Fire protection: Hilti

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