Eurocodes and fire

The Commission of the European Community began work on the harmonisation of technical specifications for construction in 1975, with the objective of eliminating technical obstacles to trade between member states. Part of this programme of work was the development of a set of harmonised technical rules, the Eurocodes, for the design of construction works, which in the first instance would provide an alternative to national design rules and, ultimately would replace them.

The following standards describe the rules for the fire design of buildings using structural steelwork:

BS EN 1991-1-2 Actions on Structures. Actions on Structures Exposed to Fire.

BS EN 1993-1-2 Design of Steel Structures. General Rules Structural Fire Design.

BS EN 1994-1-2 Design of Composite Steel and Concrete Structures. General Rules Structural Fire Design.

All are available from The British Standards Institution.

The Eurocodes provide common rules for the design of whole structures and component products.  Innovative forms of construction or unusual design conditions are not specifically covered and additional expert consideration will be required by the designer in such cases.

Eurocode standards recognise the responsibility of the regulatory authorities in each member state to define the required levels of safety. Consequently, each member state is required to publish a National Annex to each part of the Eurocode.  The national standards written to implement the Eurocodes will contain the full Eurocode text including annexes, which may be proceeded by a national title page and national foreword and followed by the National Annex. The National Annex may only contain information on those parameters which are left open in the Eurocode for national choice, known as Nationally Determined Parameters. The National Annex may also contain guidance on the application of informative annexes in the Eurocode and references to non-contradictory complementary information to assist the user to apply the design rules in the Eurocode.

At the time of writing, early 2006, the National Annex to BS EN 1991-1-2 is about to be published. This will be followed by a Published Document which will give some of the background to the National Annex and guidance on situations where the Annex cannot be accepted as alternative guidance. The National Annexes to BS EN 1993-1-2 and BS EN 1994-1-2 are expected in 2007. These standards will eventually replace BS5950 Part 8. The Government in the United Kingdom has not given any indication as to when this will take place and it is likely that both codes will be available simultaneously for a period of time.

New European standards have also been developed for fire testing. Existing test standards will also be replaced in the future but, again, the time scale is not known. The new Eurocode equivalent to BS476 Part 20 is BS EN 1363-1:1999. At the time of writing, most intumescent fire protection manufacturers have indicated that they intend to embrace the new European requirements and work only with product performance claims to the new European Standards by mid 2008.Historically, most countries use a fire test standard similar to that outlined in BS476. However, due to differences in the furnace manufacture, fuel used and control mechanisms, different furnaces gave very different results in what was nominally a test carried out to similar parameters. The UK test was recognised as one of the more benign regimes, the German test by contrast was one of the more onerous. The new test standards attempt to solve this problem by imposing a common mechanism of furnace control which will ensure that all furnaces across the European Union give the same results.

Much has been written about the increased severity of the new European harmonised fire test compared to that in widespread use in the United Kingdom. It is considered that the effect will be a general increase in thickness of fire protection but that this is unlikely to have significant cost implications for the steel construction sector.

The new structural design standards have a wider scope than BS5950 Part 8. They open up a number of new design possibilities including the use of what is called the parametric time-temperature curve. This is a mechanism of calculating the actual time-temperature relationship in a compartment of known dimensions and occupancy and removes historic dependence on the standard fire test. It is a major advance in the development of performance based design and forms the basis of the methods used to determine the fire resistance periods in DD9999.