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Fire protection is inconvenient stuff. It's messy, it's expensive, it can hold up projects and it conceals the steel structure of buildings, to the dismay of architects. But it's an essential part of any building. People need plenty of time to escape from a burning building before it collapses. In many cases, an unprotected steel structure cannot withstand the heat of a blaze long enough without buckling. Extra protective coating is thus required to buy the occupants more time in the event of a fire.

However, a new way of analysing the way that burning buildings perform could drastically reduce the amount of fire protection required around the structural frame. The technique is called "time equivalent analysis" and is based on the behaviour of an entire building in a fire, taking into account how a building is used and what the building contains.

It works by making an allowance for what happens when windows shatter in a fire. In a modern all-glass building, when the windows break some heat escapes, cooling the structure. Traditionally, the amount of fire protection required is calculated by testing structural material in isolation within an enclosed furnace. No allowance is made for the cooling effect of windows shattering – a throwback to the days when buildings had small windows in solid wall facades. The effect of heat on a sample after just 20 minutes in a furnace could be equivalent to the heat that has built up after an hour in an actual building.

Time equivalent analysis demonstrates the amount of fire resistance needed on many tall, glass office buildings can be safely reduced from two hours down to one. This enables fire engineers to use a single 2 mm-thick intumescent coating applied to the steel structure off site instead of the usual messy solution of 25 mm of site-applied spray insulation. This is not only cheaper, it also saves on the expensive add-ons such as protective sheeting for the application process and access scaffolding. Similarly, build times are reduced.

According to Andy Passingham, senior fire safety engineer at consultant Arup, the off-site coating typically costs £20/m2 compared with the thicker, site-applied coating at £50/m2. Neil Butterworth of consulting engineer Buro Happold agrees: "Using off-site intumescent coatings could halve the cost of the structural fire protection."

For developers, the technique will enable tall buildings to be built in less time, for less money. For architects, it will allow more creative freedom to use exposed steelwork because the structure will require less fire protection.

Despite its benefits, securing acceptance for the use of time equivalent analysis has been a long drawn out process. Cautious district surveyors have prevented the theory from being tried since it was first developed. "A lot of district surveyors will say the tables are mandatory, as at the end of the day they have to sign the building off," Passingham says. In fact, the building regulations give designers the option to engineer alternative methods of fire resistance. The only stipulation is that buildings have "reasonable" protection.

The theory behind the method was developed by Margaret Law while she was working at the Fire Research Station in the 1970s. It was only after she moved to Arup as fire consultant in 1974 that she refined the technique into something that could be used in commercial applications.

However, it was 1996 before fire tests on real buildings carried out by BRE and steel producer Corus produced sufficient evidence on the performance of structural steel buildings in fire. This was a useful step in getting surveyors to accept the method, as Barbara Lane, senior engineer at Arup, explains: "They did really serious fires at Cardington and nothing happened to the structure, so when building control officers query this you can show them the pictures and reassure them."

The tests also gave new authority to the technique's inclusion in the European Standard covering design for factors affecting structure, which had sat in a drawer gathering dust since 1995.

The technique is making its debut on one of the most high-profile schemes in London – the spectacular £45m headquarters for the Greater London Authority, under construction on the south bank of the Thames.

But before it got the go-ahead, Arup had to convince Southwark building control that the public's safety would not be put at risk. Local building control manager Bob Jones explains that he went through the European Standard checking the values, but he still had reservations: "Everything hinged on the integrity of the Eurocode and we had to look at this very carefully," says Jones. "I talked to the chairman of the Eurocode committee and he convinced me it was sound." To make doubly sure, Jones also went to an independent fire consultant for verification.

Many London authorities are now taking the technique on board. Arup is using it for schemes in the London boroughs of Camden and Hackney. Wandsworth and Croydon are also apparently happy with the method.

Ultimately, the technique could be embodied in the building regulations. Arup is working on a new British Standard, BS9999 Fire Safety Engineering in Buildings, that will cover all aspects of fire engineering in construction, and Lane says once this principle has been embodied in the standard, it will feed through to future versions of the Building Regulations. And when it does, the revolution will really begin. "The technique may well allow more use of exposed structural steel, which might be bad news for the concrete people," says Passingham.