EN 1991-1-2 describes the thermal and mechanical actions for the structural design of buildings exposed to fire, including the following aspects:
Safety requirements
EN 1991-1-2 is intended for clients (e.g. for the formulation of their specific requirements), designers, contractors and relevant authorities.
The general objectives of fire protection are to limit risks with respect to the individual and society, neighbouring property, and where required, environment or directly exposed property, in the case of fire.
Construction Products Directive 89/106/EEC gives the following essential requirement for the limitation of fire risks:
"The construction works must be designed and built in such a way, that in the event of an outbreak of fire
– the load bearing resistance of the construction can be assumed for a specified period of time,
– the generation and spread of fire and smoke within the works are limited,
– the spread of fire to neighbouring construction works is limited,
– the occupants can leave the works or can be rescued by other means,
– the safety of rescue teams is taken into consideration".
According to the Interpretative Document N°2 "Safety in Case of Fire5" the essential requirement may be observed by following various possibilities for fire safety strategies prevailing in the Member States like conventional fire scenarios (nominal fires) or "natural" (parametric) fire scenarios, including passive and/or active fire protection measures.
The fire parts of Structural Eurocodes deal with specific aspects of passive fire protection in terms of designing structures and parts thereof for adequate load bearing resistance and for limiting fire spread as relevant.
Required functions and levels of performance can be specified either in terms of nominal (standard) fire resistance rating, generally given in national fire regulations or, where allowed by national fire regulations, by referring to fire safety engineering for assessing passive and active measures.
Supplementary requirements concerning, for example:
– the possible installation and maintenance of sprinkler systems;
– conditions on occupancy of building or fire compartment;
– the use of approved insulation and coating materials, including their maintenance are not given in this document, because they are subject to specification by the competent authority.
Numerical values for partial factors and other reliability elements are given as recommended values that provide an acceptable level of reliability. They have been selected assuming that an appropriate level of workmanship and of quality management applies.
Design procedures
A full analytical procedure for structural fire design would take into account the behaviour of the structural system at elevated temperatures, the potential heat exposure and the beneficial effects of active and passive fire protection systems, together with the uncertainties associated with these three features and the importance of the structure (consequences of failure).
At the present time it is possible to undertake a procedure for determining adequate performance which incorporates some, if not all, of these parameters and to demonstrate that the structure, or its components, will give adequate performance in a real building fire. However where the procedure is based on a nominal (standard) fire, the classification system, which calls for specific periods of fire resistance, takes into account (though not explicitely) the features and uncertainties described above.
Application of this Part 1-2 is illustrated below. The prescriptive approach and the performance-based approach are identified. The prescriptive approach uses nominal fires to generate thermal actions. The performance-based approach, using fire safety engineering, refers to thermal actions based on physical and chemical parameters.
Design aids
It is expected, that design aids based on the calculation models given in EN 1991-1-2 will be prepared by interested external organizations.
The main text of EN 1991-1-2 includes most of the principal concepts and rules necessary for describing thermal and mechanical actions on structures.
The methods given in this Part 1-2 of EN 1991 are applicable to buildings, with a fire load related to the building and its occupancy.
This Part 1-2 of EN 1991 deals with thermal and mechanical actions on structures exposed to fire. It is intended to be used in conjunction with the fire design Parts of prEN 1992 to prEN 1996 and prEN 1999 which give rules for designing structures for fire resistance.
This Part 1-2 of EN 1991 contains thermal actions related to nominal and physically based thermal actions. More data and models for physically based thermal actions are given in annexes.
This Part 1-2 of EN 1991 gives general principles and application rules in connection to thermal and mechanical actions to be used in conjunction with EN 1990, EN 1991-1-1, EN 1991-1-3 and EN 1991-1-4.
The assessment of the damage of a structure after a fire, is not covered by the present document.
