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EUROPEAN STANDARD
NORME EUROPÉENNE
EUROPÄISCHE NORM

EN 1991-1-2

November 2002

ICS 13.220.50; 91.010.30

Supersedes ENV 1991-2-2:1995
Incorporating corrigendum March 2009

English version

Eurocode 1: Actions on structures - Part 1-2: General actions - Actions on structures exposed to fire

Eurocode 1: Actions sur les structures au teu - Partie 1-2: Actions générales - Actions sur les structures exposées Eurocode 1 - Einwirkungen auf Tragwerke - Teil 1-2: Allgemeine Einwirkungen - Brandeinwirkungen auf Tragwerke

This European Standard was approved by CEN on 1 September 2002.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.

Image

Management Centre: rue de Stassart, 36 B-1050 Brussels

© 2002 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members.

Ref. No. EN 1991-1-2:2002 E

1

Contents

page
Foreword 4
Section 1 General 10
1.1 Scope 10
1.2 Normative references 10
1.3 Assumptions 11
1.4 Distinction between Principles and Application Rules 11
1.5 Terms and definitions 11
  1.5.1 Common terms used in Eurocode Fire parts 11
  1.5.2 Special terms relating to design in general 13
  1.5.3 Terms relating to thermal actions 13
  1.5.4 Terms relating to heat transfer analysis 15
1.6 Symbols 15
Section 2 Structural Fire design procedure 21
2.1 General 21
2.2 Design fire scenario 21
2.3 Design fire 21
2.4 Temperature Analysis 21
2.5 Mechanical Analysis 22
Section 3 Thermal actions for temperature analysis 23
3.1 General rules 23
3.2 Nominal temperature-time curves 24
  3.2.1 Standard temperature-time curve 24
  3.2.2 External fire curve 24
  3.2.3 Hydrocarbon curve 25
3.3 Natural fire models 25
  3.3.1 Simplified fire models 25
    3.3.1.1 General 25
    3.3.1.2 Compartment fires 25
    3.3.1.3 Localised fires 26
  3.3.2 Advanced fire models 26
Section 4 Mechanical actions for structural analysis 27
4.1 General 27
4.2 Simultaneity of actions 27
  4.2.1 Actions from normal temperature design 27
  4.2.2 Additional actions 28
4.3 Combination rules for actions 28
  4.3.1 General rule 28
  4.3.2 Simplified rules 28
  4.3.3 Load level 29
Annex A (informative) Parametric temperature-time curves 30
Annex B (informative) Thermal actions for external members - Simplified calculation method 33
B.1 Scope 33
B.2 Conditions of use 33 2
B.3 Effects of wind 34
  B.3.1 Mode of ventilation 34
  B.3.2 Flame deflection by wind 34
B.4 Characteristics of fire and flames 35
  B.4.1 No forced draught 35
  B.4.2 Forced draught 37
B.5 Overall configuration factors 39
Annex C (informative) Localised fires 41
Annex D (informative) Advanced fire models 44
D.1 One-zone models 44
D.2 Two-zone models 45
D.3 Computational fluid dynamic models 45
Annex E (informative) Fire load densities 46
E.1 General 46
E.2 Determination of fire load densities 47
  E.2.1 General 47
  E.2.2 Definitions 47
  E.2.3 Protected fire loads 48
  E.2.4 Net calorific values 48
  E.2.5 Fire load classification of occupancies 50
  E.2.6 Individual assessment of fire load densities 50
E.3 Combustion behaviour 50
E.4 Rate of heat release Q 51
Annex F (informative) Equivalent time of fire exposure 53
Annex G (informative) Configuration factor 55
G.1 General 55
G.2 Shadow effects 56
G.3 External members 56
Bibliography 59
3

Foreword

This document (EN 1991-1-2:2002) has been prepared by Technical Committee CEN/TC 250 “Structural Eurocodes”, the secretariat of which is held by BSI.

CEN/TC250/SC1 is responsible for Eurocode 1.

This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by May 2003, and conflicting national standards shall be withdrawn at the latest by December 2009.

This document supersedes ENV 1991-2-2:1995.

Annexes A, B, C, D, E, F and G are informative.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom.

Background of the Eurocode programme

In 1975, the Commission of the European Community decided on an action programme in the field of construction, based on article 95 of the Treaty. The objective of the programme was the elimination of technical obstacles to trade and the harmonisation of technical specifications.

Within this action programme, the Commission took the initiative to establish a set of harmonised technical rules for the design of construction works which, in a first stage, would serve as an alternative to the national rules in force in the Member States and, ultimately, would replace them.

For fifteen years, the Commission, with the help of a Steering Committee with Representatives of Member States, conducted the development of the Eurocodes programme, which led to the first generation of European codes in the 1980’s.

In 1989, the Commission and the Member States of the EU and EFTA decided, on the basis of an agreement1 between the Commission and CEN, to transfer the preparation and the publication of the Eurocodes to CEN through a series of Mandates, in order to provide them with a future status of European Standard (EN). This links de facto the Eurocodes with the provisions of all the Council’s Directives and/or Commission’s Decisions dealing with European Standards (e.g. the Council Directive 89/106/EEC on construction products - CPD - and Council Directives 93/37/EEC, 92/50/EEC and 89/440/EEC on public works and services and equivalent EFTA Directives initiated in pursuit of setting up the internal market).

The Structural Eurocode programme comprises the following standards generally consisting of a number of Parts:

EN 1990, Eurocode: Basis of structural design.

EN 1991, Eurocode 1 : Actions on structures.

prEN 1992, Eurocode 2: Design of concrete structures.

prEN 1993, Eurocode 3: Design of steel structures.

1 Agreement between the Commission of the European Communities and the European Committee for Standardisation (CEN) concerning the work on EUROCODES for the design of building and civil engineering works (BC/CEN/03/89).

4

prEN 1994, Eurocode 4: Design of composite steel and concrete structures.

prEN 1995, Eurocode 5: Design of timber structures.

prEN 1996, Eurocode 6: Design of masonry structures.

prEN 1997, Eurocode 7: Geotechnical design.

prEN 1998, Eurocode 8: Design of structures for earthquake resistance.

prEN 1999, Eurocode 9: Design of aluminium structures.

Eurocode standards recognise the responsibility of regulatory authorities in each Member State and have safeguarded their right to determine values related to regulatory safety matters at national level where these continue to vary from State to State.

Status and field of application of Eurocodes

The Member States of the EU and EFTA recognise that EUROCODES serve as reference documents for the following purposes:

The Eurocodes, as far as they concern the construction works themselves, have a direct relationship with the Interpretative Documents2 referred to in Article 12 of the CPD, although they are of a different nature from harmonised product standards3. Therefore, technical aspects arising from the Eurocodes work need to be adequately considered by CEN Technical Committees and/or EOTA Working Groups working on product standards with a view to achieving full compatibility of these technical specifications with the Eurocodes.

The Eurocode standards provide common structural design rules for everyday use for the design of whole structures and component products of both a traditional and an innovative nature. Unusual forms of construction or design conditions are not specifically covered and additional expert consideration will be required by the designer in such cases.

2 According to Art. 3.3 of the CPD, the essential requirements (ERs) shall be given concrete form in interpretative documents for the creation of the necessary links between the essential requirements and the mandates for harmonised ENS and ETAGs/ETAs.

3 According to Art. 12 of the CPD the interpretative documents shall:

  1. give concrete form to the essential requirements by harmonising the terminology and the technical bases and indicating classes or levels for each requirement where necessary;
  2. indicate methods of correlating these classes or levels of requirement with the technical specifications, e.g. methods of calculation and of proof, technical rules for project design, etc.;
  3. serve as a reference for the establishment of harmonised standards and guidelines for European technical approvals.

The Eurocodes, de facto, play a similar role in the field of the ER 1 and a part of ER 2.

5

National standards implementing Eurocodes

The national standards implementing Eurocodes will comprise the full text of the Eurocode (including any annexes), as published by CEN, which may be preceded by a national title page and national foreword, and may be followed by a 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, to be used for the design of buildings and civil engineering works to be constructed in the country concerned, i.e.:

It may also contain:

Links between Eurocodes and harmonised technical specifications (ENs and ETAs) for products

There is a need for consistency between the harmonised technical specifications for construction products and the technical rules for works4. Furthermore, all the information accompanying the CE Marking of the construction products which refer to Eurocodes shall clearly mention which Nationally Determined Parameters have been taken into account.

Additional information specific to EN 1991-1-2

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:

4 See Art.3.3 and Art.12 of the CPD, as well as 4.2, 4.3.1, 4.3.2 and 5.2 of ID N°1.

6

“The construction works must be designed and built in such a way, that in the event of an outbreak of fire

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:

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).

5 See 2.2, 3.2(4) and 4.2.3.3 of ID N°2.

7

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.

Figure 1 — Alternative design procedures

Figure 1 — Alternative design procedures

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.

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National annex for EN 1991-1-2

This standard gives alternative procedures, values and recommendations for classes with notes indicating where national choices have to be made. Therefore the national standard implementing EN 1991-1-2 should have a national annex containing all Nationally Determined Parameters to be used for the design of buildings and civil engineering works to be constructed in the relevant country.

National choice is allowed in EN 1991-1-2 through:

9

Section 1 General

1.1 Scope

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. The assessment of the damage of a structure after a fire, is not covered by the present document.

1.2 Normative references

  1. P This European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text, and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments).

    NOTE The following European Standards which are published or in preparation are cited in normative clauses:

    prEN 13501-2, Fire classification of construction products and building elements - Part 2: Classification using data from fire resistance tests, excluding ventilation services.

    EN 1990:2002, Eurocode: Basis of structural design.

    EN 1991, Eurocode 1: Actions on structures - Part 1-1: General actions - Densities, self-weight and imposed loads.

    prEN 1991, Eurocode 1: Actions on structures - Part 1-3: General actions - Snow loads.

    prEN 1991, Eurocode 1: Actions on structures - Part 1-4: General actions - Wind loads.

    prEN 1992, Eurocode 2: Design of concrete structures.

    prEN 1993, Eurocode 3: Design of steel structures.

    prEN 1994, Eurocode 4: Design of composite steel and concrete structures.

    prEN 1995, Eurocode 5: Design of timber structures.

    prEN 1996, Eurocode 6: Design of masonry structures.

    prEN 1999, Eurocode 9: Design of aluminium structures.

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1.3 Assumptions

  1. P In addition to the general assumptions of EN 1990 the following assumptions apply:

1.4 Distinction between Principles and Application Rules

  1. The rules given in EN 1990:2002, 1.4 apply.

1.5 Terms and definitions

  1. P For the purposes of this European Standard, the terms and definitions given in EN 1990:2002, 1.5 and the following apply.

1.5.1 Common terms used in Eurocode Fire parts

1.5.1.1
equivalent time of fire exposure

time of exposure to the standard temperature-time curve supposed to have the same heating effect as a real fire in the compartment

1.5.1.2
external member

structural member located outside the building that may be exposed to fire through openings in the building enclosure

1.5.1.3
fire compartment

space within a building, extending over one or several floors, which is enclosed by separating elements such that fire spread beyond the compartment is prevented during the relevant fire exposure

1.5.1.4
fire resistance

ability of a structure, a part of a structure or a member to fulfil its required functions (load bearing function and/or fire separating function) for a specified load level, for a specified fire exposure and for a specified period of time

1.5.1.5
fully developed fire

state of full involvement of all combustible surfaces in a fire within a specified space

1.5.1.6
global structural analysis (for fire)

structural analysis of the entire structure, when either the entire structure, or only a part of it, are exposed to fire. Indirect fire actions are considered throughout the structure

11
1.5.1.7
indirect fire actions

internal forces and moments caused by thermal expansion

1.5.1.8
integrity (E)

ability of a separating element of building construction, when exposed to fire on one side, to prevent the passage through it of flames and hot gases and to prevent the occurrence of flames on the unexposed side

1.5.1.9
insulation (I)

ability of a separating element of building construction when exposed to fire on one side, to restrict the temperature rise of the unexposed face below specified levels

1.5.1.10
load bearing function (R)

ability of a structure or a member to sustain specified actions during the relevant fire, according to defined criteria

1.5.1.11
member

basic part of a structure (such as beam, column, but also assembly such as stud wall, truss,...) considered as isolated with appropriate boundary and support conditions

1.5.1.12
member analysis (for fire)

thermal and mechanical analysis of a structural member exposed to fire in which the member is assumed as isolated, with appropriate support and boundary conditions. Indirect fire actions are not considered, except those resulting from thermal gradients

1.5.1.13
normal temperature design

ultimate limit state design for ambient temperatures according to Part 1-1 of prEN 1992 to prEN 1996 or prEN 1999

1.5.1.14
separating function

ability of a separating element to prevent fire spread (e.g. by passage of flames or hot gases - cf integrity) or ignition beyond the exposed surface (cf insulation) during the relevant fire

1.5.1.15
separating element

load bearing or non-load bearing element (e.g. wall) forming part of the enclosure of a fire compartment

1.5.1.16
standard fire resistance

ability of a structure or part of it (usually only members) to fulfil required functions (load-bearing function and/or separating function), for the exposure to heating according to the standard temperature-time curve for a specified load combination and for a stated period of time

12
1.5.1.17
structural members

load-bearing members of a structure including bracings

1.5.1.18
temperature analysis

procedure of determining the temperature development in members on the basis of the thermal actions (net heat flux) and the thermal material properties of the members and of protective surfaces, where relevant

1.5.1.19
thermal actions

actions on the structure described by the net heat flux to the members

1.5.2 Special terms relating to design in general

1.5.2.1
advanced fire model

design fire based on mass conservation and energy conservation aspects

1.5.2.2
computational fluid dynamic model

fire model able to solve numerically the partial differential equations giving, in all points of the compartment, the thermo-dynamical and aero-dynamical variables

1.5.2.3
fire wall

separating element that is a wall separating two spaces (e.g. two buildings) that is designed for fire resistance and structural stability, and may include resistance to horizontal loading such that, in case of fire and failure of the structure on one side of the wall, fire spread beyond the wall is avoided

1.5.2.4
one-zone model

fire model where homogeneous temperatures of the gas are assumed in the compartment

1.5.2.5
simple fire model

design fire based on a limited application field of specific physical parameters

1.5.2.6
two-zone model

fire model where different zones are defined in a compartment: the upper layer, the lower layer, the fire and its plume, the external gas and walls. In the upper layer, uniform temperature of the gas is assumed

1.5.3 Terms relating to thermal actions

1.5.3.1
combustion factor

combustion factor represents the efficiency of combustion, varying between 1 for complete combustion to 0 for combustion fully inhibited

1.5.3.2
design fire

specified fire development assumed for design purposes

13
1.5.3.3
design fire load density

fire load density considered for determining thermal actions in fire design; its value makes allowance for uncertainties

1.5.3.4
design fire scenario

specific fire scenario on which an analysis will be conducted

1.5.3.5
external fire curve

nominal temperature-time curve intended for the outside of separating external walls which can be exposed to fire from different parts of the facade, i.e. directly from the inside of the respective fire compartment or from a compartment situated below or adjacent to the respective external wall

1.5.3.6
fire activation risk

parameter taking into account the probability of ignition, function of the compartment area and the occupancy

1.5.3.7
fire load density

fire load per unit area related to the floor area qt, or related to the surface area of the total enclosure, including openings, qf

1.5.3.8
fire load

sum of thermal energies which are released by combustion of all combustible materials in a space (building contents and construction elements)

1.5.3.9
fire scenario

qualitative description of the course of a fire with time identifying key events that characterise the fire and differentiate it from other possible fires. It typically defines the ignition and fire growth process, the fully developed stage, decay stage together with the building environment and systems that will impact on the course of the fire

1.5.3.10
flash-over

simultaneous ignition of all the fire loads in a compartment

1.5.3.11
hydrocarbon fire curve

nominal temperature-time curve for representing effects of an hydrocarbon type fire

1.5.3.12
localised fire

fire involving only a limited area of the fire load in the compartment

1.5.3.13
opening factor

factor representing the amount of ventilation depending on the area of openings in the compartment walls, on the height of these openings and on the total area of the enclosure surfaces

14
1.5.3.14
rate of heat release

heat (energy) released by a combustible product as a function of time

1.5.3.15
standard temperature-time curve

nominal curve defined in prEN 13501-2 for representing a model of a fully developed fire in a compartment

1.5.3.16
temperature-time curves

gas temperature in the environment of member surfaces as a function of time. They may be:

1.5.4 Terms relating to heat transfer analysis

1.5.4.1
configuration factor

configuration factor for radiative heat transfer from surface A to surface B is defined as the fraction of diffusely radiated energy leaving surface A that is incident on surface B

1.5.4.2
convective heat transfer coefficient

convective heat flux to the member related to the difference between the bulk temperature of gas bordering the relevant surface of the member and the temperature of that surface

1.5.4.3
emissivity

equal to absorptivity of a surface, i.e. the ratio between the radiative heat absorbed by a given surface and that of a black body surface

1.5.4.4
net heat flux

energy, per unit time and surface area, definitely absorbed by members

1.6 Symbols

  1. P For the purpose of this Part 1-2, the following symbols apply.

    Latin upper case letters

    A area of the fire compartment
    Aind,d design value of indirect action due to fire
    Af floor area of the fire compartment
    Afi fire area
    Ah area of horizontal openings in roof of compartment 15
    Ah,v total area of openings in enclosure (Ah,v = Ah + Av)
    Aj area of enclosure surface j, openings not included
    At total area of enclosure (walls, ceiling and floor, including openings)
    Av total area of vertical openings on all walls Image
    Av,i area of window “i”
    Ci protection coefficient of member face i
    D depth of the fire compartment, diameter of the fire
    Ed design value of the relevant effects of actions from the fundamental combination according to EN 1990
    Efi,d constant design value of the relevant effects of actions in the fire situation
    Efi,di,t design value of the relevant effects of actions in the fire situation at time t
    Eg internal energy of gas
    H distance between the fire source and the ceiling
    Hu net calorific value including moisture
    Hu0 net calorific value of dry material
    Hui net calorific value of material i
    Lc length of the core
    Lf flame length along axis
    Lh horizontal projection of the flame (from the facade)
    Lh horizontal flame length
    LL flame height (from the upper part of the window)
    Lx axis length from window to the point where the calculation is made
    Mk,i amount of combustible material i
    O opening factor of the fire compartment Image
    Olim reduced opening factor in case of fuel controlled fire
    Pint the internal pressure
    Q rate of heat release of the fire
    Qc convective part of the rate of heat release Q
    Qfi,k characteristic fire load 16
    Qfi,k,i characteristic fire load of material i
    Image heat release coefficient related to the diameter D of the local fire
    Image heat release coefficient related to the height H of the compartment
    Qk,1 characteristic leading variable action
    Qmax maximum rate of heat release
    Qin rate of heat release entering through openings by gas flow
    Qout rate of heat release lost through openings by gas flow
    Qrad rate of heat release lost by radiation through openings
    Qwall rate of heat release lost by radiation and convection to the surfaces of the compartment
    R ideal gas constant (= 287 [J/kgK])
    Rd design value of the resistance of the member at normal temperature
    Rfi,d,t design value of the resistance of the member in the fire situation at time t
    RHRf maximum rate of heat release per square meter
    T the temperature [K]
    Tamb the ambiant temperature [K]
    T0 initial temperature (= 293 [K])
    Tf temperature of the fire compartment [K]
    Tg gas temperature [K]
    Tw flame temperature at the window [K]
    Tz flame temperature along the flame axis [K]
    W Image width of wall containing window(s) (W1) Image
    W1 width of the wall 1, assumed to contain the greatest window area
    W2 width of the wall of the fire compartment, perpendicular to wall W1
    Wa horizontal projection of an awning or balcony
    Wc width of the core

    Latin lower case letters

    b thermal absorptivity for the total enclosure Image 17
    bi thermal absorptivity of layer i of one enclosure surface
    bj thermal absorptivity of one enclosure surface j
    c specific heat
    deq geometrical characteristic of an external structural element (diameter or side)
    df flame thickness
    di cross-sectional dimension of member face i
    g the gravitational acceleration
    heq weighted average of window heights on all walls Image
    hi height of window i
    heat flux to unit surface area
    net net heat flux to unit surface area
    net,c net heat flux to unit surface area due to convection
    net,r net heat flux to unit surface area due to radiation
    tot total heat flux to unit surface area
    i heat flux to unit surface area due to fire i
    k correction factor
    kb conversion factor
    kc correction factor
    m mass, combustion factor
    mass rate
    in rate of gas mass coming in through the openings
    out rate of gas mass going out through the openings
    fi rate of pyrolysis products generated
    qf fire load per unit area related to the floor area Af
    qf,d design fire load density related to the floor area Af
    qf,k characteristic fire load density related to the surface area Af
    qt fire load per unit area related to the surface area At 18
    qt,d design fire load density related to the surface area At
    qt,k characteristic fire load density related to the surface area At
    r horizontal distance between the vertical axis of the fire and the point along the ceiling where the thermal flux is calculated
    Si thickness of layer i
    Slim limit thickness
    t time
    te,d equivalent time of fire exposure
    tfi,d design fire resistance (property of the member or structure)
    tfi,requ required fire resistance time
    tlim time for maximum gas temperature in case of fuel controlled fire
    tmax time for maximum gas temperature
    tα fire growth rate coefficient
    u wind speed, moisture content
    wi width of window “i”
    wt sum of window widths on all walls (wt = ∑wi); ventilation factor referred to At
    wf width of the flame; ventilation factor
    y coefficient parameter
    z height
    z0 virtual origin of the height z
    z1 vertical position of the virtual heat source

    Greek upper case letters

    Φ configuration factor
    Φf overall configuration factor of a member for radiative heat transfer from an opening
    Φf,i configuration factor of member face i for a given opening
    ΦZ overall configuration factor of a member for radiative heat transfer from a flame
    Φz,i configuration factor of member face i for a given flame
    Γ time factor function of the opening factor O and the thermal absorptivity b
    Γlim time factor function of the opening factor Olim and the thermal absorptivity b 19
    Θm temperature [°C]; Θ [°C] = T[K] - 273
    Θcr,d design value of the critical material temperature [°C]
    Θd design value of material temperature [°C]
    Θg gas temperature in the fire compartment, or near the member [°C]
    Θm temperature of the member surface [°C]
    Θmax maximum temperature [°C]
    Θr effective radiation temperature of the fire environment [°C]
    Ω (Af · (qf,d) / (Av · At)1/2
    Ψi protected fire load factor

    Greek lower case letters

    αc coefficient of heat transfer by convection
    αh area of horizontal openings related to the floor area
    αv area of vertical openings related to the floor area
    δni factor accounting for the existence of a specific fire fighting measure i
    δq1 factor taking into account the fire activation risk due to the size of the compartment
    δq2 factor taking into account the fire activation risk due to the type of occupancy
    εm surface emissivity of the member
    εf emissivity of flames, of the fire
    ηfi reduction factor
    ηfi,t load level for fire design
    λ thermal conductivity
    ρ density
    ρg internal gas density
    σ Stephan Boltzmann constant (= 5,67 · 10–8 [W/m2K4])
    τF free burning fire duration (assumed to be 1 200 [s])
    Ψo combination factor for the characteristic value of a variable action
    Ψ1 combination factor for the frequent value of a variable action
    Ψ2 combination factor for the quasi-permanent value of a variable action
20

Section 2 Structural Fire design procedure

2.1 General

  1. A structural fire design analysis should take into account the following steps as relevant:

    NOTE Mechanical behaviour of a structure is depending on thermal actions and their thermal effect on material properties and indirect mechanical actions, as well as on the direct effect of mechanical actions.

  2. Structural fire design involves applying actions for temperature analysis and actions for mechanical analysis according to this Part and other Parts of EN 1991.
  3. P Actions on structures from fire exposure are classified as accidental actions, see EN 1990:2002, 6.4.3.3(4).

2.2 Design fire scenario

  1. To identify the accidental design situation, the relevant design fire scenarios and the associated design fires should be determined on the basis of a fire risk assessment.
  2. For structures where particular risks of fire arise as a consequence of other accidental actions, this risk should be considered when determining the overall safety concept.
  3. Time- and load-dependent structural behaviour prior to the accidental situation needs not be considered, unless (2) applies.

2.3 Design fire

  1. For each design fire scenario, a design fire, in a fire compartment, should be estimated according to section 3 of this Part.
  2. The design fire should be applied only to one fire compartment of the building at a time, unless otherwise specified in the design fire scenario.
  3. For structures, where the national authorities specify structural fire resistance requirements, it may be assumed that the relevant design fire is given by the standard fire, unless specified otherwise.

2.4 Temperature Analysis

  1. P When performing temperature analysis of a member, the position of the design fire in relation to the member shall be taken into account.
  2. For external members, fire exposure through openings in facades and roofs should be considered.
  3. For separating external walls fire exposure from inside (from the respective fire compartment) and alternatively from outside (from other fire compartments) should be considered when required. 21
  4. Depending on the design fire chosen in section 3, the following procedures should be used:

    NOTE 1 The specified period of time may be given in the national regulations or obtained from annex F following the specifications of the national annex.

    NOTE 2 Limited periods of fire resistance may be set in the national annex.

2.5 Mechanical Analysis

  1. P The mechanical analysis shall be performed for the same duration as used in the temperature analysis.
  2. Verification of fire resistance should be in the time domain:

    tfi,dtfi,requ     (2.1)

    or in the strength domain:

    Rfi,d,tEfi,d,t     (2.2)

    or in the temperature domain:

    ΘdΘcr,d     (2.3)

    where

    tfi,d is the design value of the fire resistance
    tfi,requ is the required fire resistance time
    Rfi,d,t is the design value of the resistance of the member in the fire situation at time t
    Efi,d,t is the design value of the relevant effects of actions in the fire situation at time t
    Θd is the design value of material temperature
    Θcr,d is the design value of the critical material temperature
    22

Section 3 Thermal actions for temperature analysis

3.1 General rules

  1. P Thermal actions are given by the net heat flux net [W/m2] to the surface of the member.
  2. On the fire exposed surfaces the net heat flux net should be determined by considering heat transfer by convection and radiation as

    net = net,c + net,r     [W/m2]     (3.1)

    where

    net,c is given by e.q. (3.2)
    net,r is given by e.q. (3.3)
  3. The net convective heat flux component should be determined by:

    net,c = αc · (ΘgΘm)     [W/m2]     (3.2)

    where

    αc is the coefficient of heat transfer by convection [W/m2K]
    Θg is the gas temperature in the vicinity of the fire exposed member [°C]
    Θm is the surface temperature of the member [°C]
  4. For the coefficient of heat transfer by convection αc relevant for nominal temperature-time curves, see 3.2.
  5. On the unexposed side of separating members, the net heat flux net should be determined by using equation (3.1), with αc = 4 [W/m2K]. The coefficient of heat transfer by convection should be taken as αc = 9[W/m2K], when assuming it contains the effects of heat transfer by radiation.
  6. The net radiative heat flux component per unit surface area is determined by:

    net,r = Φ · εm · εf · σ · [(Θr + 273)4 – (Θm + 273)4]     [W/m2]     (3.3)

    where

    Φ is the configuration factor
    εm is the surface emissivity of the member
    εf is the emissivity of the fire
    σ is the Stephan Boltzmann constant (= 5,67 · 10-8 W/m2K4)
    Θr is the effective radiation temperature of the fire environment [°C]
    Θm is the surface temperature of the member [°C]

    NOTE 1 Unless given in the material related fire design Parts of prEN 1992 to prEN 1996 and prEN 1999, εm = 0,8 may be used.

    23

    NOTE 2 The emissivity of the fire is taken in general as εf = 1,0.

  7. Where this Part or the fire design Parts of prEN 1992 to prEN 1996 and prEN 1999 give no specific data, the configuration factor should be taken as Φ = 1,0. A lower value may be chosen to take account of so called position and shadow effects.

    NOTE For the calculation of the configuration factor Φ a method is given in annex G.

  8. In case of fully fire engulfed members, the radiation temperature Θr may be represented by the gas temperature Θr around that member.
  9. The surface temperature Θm results from the temperature analysis of the member according to the fire design Parts 1-2 of prEN 1992 to prEN 1996 and prEN 1999, as relevant.
  10. Gas temperatures Θg may be adopted as nominal temperature-time curves according to 3.2, or adopted according to the fire models given in 3.3.

    NOTE The use of the nominal temperature-time curves according to 3.2 or, as an alternative, the use of the natural fire models according to 3.3 may be specified in the national annex.

3.2 Nominal temperature-time curves

3.2.1 Standard temperature-time curve

  1. The standard temperature-time curve is given by:

    Θg = 20 + 345 log10 (8 t + 1)     [°C]     (3.4)

    where

    Θg is the gas temperature in the fire compartment      [°C]
    t is the time      [min]
  2. The coefficient of heat transfer by convection is:

    αc = 25 W/m2K

3.2.2 External fire curve

  1. The external fire curve is given by:

    Θg = 660 (1 - 0,687 e-0,32 t - 0,313 e-3,8 t) + 20     [°C]     (3.5)

    where

    Θg is the gas temperature near the member      [°C]
    t is the time      [min]
    24
  2. The coefficient of heat transfer by convection is:

    αc = 25 W/m2K

3.2.3 Hydrocarbon curve

  1. The hydrocarbon temperature-time curve is given by:

    Θg = 1080 (1 - 0,325 e-0,167 t – 0,675 e-2,5 t) + 20     [°C]     (3.6)

    where

    Θg is the gas temperature in the fire compartment      [°C]
    t is the time      [min]
  2. The coefficient of heat transfer by convection is:     (3.7)

    αc = 50 W/m2K

3.3 Natural fire models

3.3.1 Simplified fire models

3.3.1.1 General
  1. Simple fire models are based on specific physical parameters with a limited field of application.

    NOTE For the calculation of the design fire load density qf,d a method is given in annex E.

  2. A uniform temperature distribution as a function of time is assumed for compartment fires. A non-uniform temperature distribution as a function of time is assumed in case of localised fires.
  3. When simple fire models are used, the coefficient of heat transfer by convection should be taken as αc = 35 [W/m2K].
3.3.1.2 Compartment fires
  1. Gas temperatures should be determined on the basis of physical parameters considering at least the fire load density and the ventilation conditions.

    NOTE 1 The national annex may specify the procedure for calculating the heating conditions.

    NOTE 2 For internal members of fire compartments, a method for the calculation of the gas temperature in the compartment is given in annex A.

  2. For external members, the radiative heat flux component should be calculated as the sum of the contributions of the fire compartment and of the flames emerging from the openings.

    NOTE For external members exposed to fire through openings in the facade, a method for the calculation of the heating conditions is given in annex B.

25
3.3.1.3 Localised fires
  1. Where flash-over is unlikely to occur, thermal actions of a localised fire should be taken into account.

    NOTE The national annex may specify the procedure for calculating the heating conditions. A method for the calculation of thermal actions from localised fires is given in annex C.

3.3.2 Advanced fire models

  1. Advanced fire models should take into account the following:

    NOTE 1 Available calculation methods normally include iterative procedures.

    NOTE 2 For the calculation of the design fire load density qf,d a method is given in annex E.

    NOTE 3 For the calculation of the rate of heat release Q a method is given in annex E.

  2. One of the following models should be used:

    NOTE The national annex may specify the procedure for calculating the heating conditions.
    A method for the calculation of thermal actions in case of one-zone, two-zone or computational fluid dynamic models is given in annex D.

  3. The coefficient of heat transfer by convection should be taken as αc = 35 [W/m2K], unless more detailed information is available.
  4. In order to calculate more accurately the temperature distribution along a member, in case of a localised fire, a combination of results obtained with a two-zone model and a localised fire approach may be considered.

    NOTE The temperature field in the member may be obtained by considering the maximum effect at each location given by the two fire models.

26

Section 4 Mechanical actions for structural analysis

4.1 General

  1. P Imposed and constrained expansions and deformations caused by temperature changes due to fire exposure result in effects of actions, e.g. forces and moments, which shall be considered with the exception of those cases where they:
  2. For an assessment of indirect actions the following should be considered:
  3. Design values of indirect actions due to fire Aind,d should be determined on the basis of the design values of the thermal and mechanical material properties given in the fire design Parts of prEN 1992 to prEN 1996 and prEN 1999 and the relevant fire exposure.
  4. Indirect actions from adjacent members need not be considered when fire safety requirements refer to members under standard fire conditions.

4.2 Simultaneity of actions

4.2.1 Actions from normal temperature design

  1. P Actions shall be considered as for normal temperature design, if they are likely to act in the fire situation.
  2. Representative values of variable actions, accounting for the accidental design situation of fire exposure, should be introduced in accordance with EN 1990.
  3. Decrease of imposed loads due to combustion should not be taken into account.
  4. Cases where snow loads need not be considered, due to the melting of snow, should be assessed individually.
  5. Actions resulting from industrial operations need not be taken into account.
27

4.2.2 Additional actions

  1. Simultaneous occurrence with other independent accidental actions needs not be considered.
  2. Depending on the accidental design situations to be considered, additional actions induced by the fire may need to be applied during fire exposure, e.g. impact due to collapse of a structural member or heavy machinery.

    NOTE The choice of additional actions may be specified in the national annex.

  3. Fire walls may be required to resist a horizontal impact load according to EN 1363-2.

4.3 Combination rules for actions

4.3.1 General rule

  1. P For obtaining the relevant effects of actions Efi,d,t during fire exposure, the mechanical actions shall be combined in accordance with EN 1990 “Basis of structural design” for accidental design situations.
  2. The representative value of the variable action Q1 may be considered as the quasi-permanent value Ψ2,1 Q1 , or as an alternative the frequent value Ψ1,1 Q1.

    NOTE The use of the quasi-permanent value Ψ2,1 Q1 or the frequent value Ψ1,1 Q1 may be specified in the national annex. The use of Ψ2,1 Q1 is recommended.

4.3.2 Simplified rules

  1. Where indirect fire actions need not be explicitly considered, effects of actions may be determined by analysing the structure for combined actions according to 4.3.1 for t = 0 only. These effects of actions Efi,d may be applied as constant throughout fire exposure.

    NOTE This clause applies, for example, to effects of actions at boundaries and supports, where an analysis of parts of the structure is performed in accordance with the fire design Parts of prEN 1992 to prEN 1996 and prEN 1999.

  2. As a further simplification to (1), effects of actions may be deduced from those determined in normal temperature design:

    Efi,d,t = Efi,d = ηfi · Ed     (4.1)

    where

    Ed is the design value of the relevant effects of actions from the fundamental combination according to EN 1990;
    Efi,d is the corresponding constant design value in the fire situation;
    ηfi is a reduction factor defined in the fire design Parts of prEN 1992 to prEN 1996 and prEN 1999.
28

4.3.3 Load level

  1. Where tabulated data are specified for a reference load level, this load level corresponds to:

    Efi,d,t = ηfi,t · Rd     (4.2)

    where

    Rd is the design value of the resistance of the member at normal temperature, determined according to prEN 1992 to prEN 1996 and prEN 1999;
    ηfi,t is the load level for fire design.
29

Annex A
Parametric temperature-time curves

(informative)

  1. The following temperature-time curves are valid for fire compartments up to 500 m2 of floor area, without openings in the roof and for a maximum compartment height of 4 m. It is assumed that the fire load of the compartment is completely burnt out.
  2. If fire load densities are specified without specific consideration to the combustion behaviour (see annex E), then this approach should be limited to fire compartments with mainly cellulosic type fire loads.
  3. The temperature-time curves in the heating phase are given by:

    Θg = 20 + 1325 (1–0,324 e–0,2 t* –0,204 e-1,7 t* –0,472 e–19 t*)     (A.1)

    where

    Θg is the gas temperature in the fire compartment [°C]  
    t* = t·Γ [h] (A.2a)

    with

    t time [h]
    Γ = [O/b]2/(0,04/1 160)2 [−]
    b Image  
      with the following limits: 100 ≤ b ≤ 2 200 [J/m2s1/2K]
    ρ density of boundary of enclosure [kg/m3]
    c specific heat of boundary of enclosure [J/kgK]
    λ thermal conductivity of boundary of enclosure [W/mK]
    O opening factor: Image [m1/2]
       with the following limits: 0,02 ≤ O ≤ 0,20  
    Av total area of vertical openings on all walls [m2]
    heq weighted average of window heights on all walls [m]
    At total area of enclosure (walls, ceiling and floor, including openings) [m2]

    NOTE In case of Γ = 1, equation (A.1) approximates the standard temperature-time curve.

  4. For the calculation of the b factor, the density ρ, the specific heat c and the thermal conductivity λ of the boundary may be taken at ambient temperature. 30
  5. To account for an enclosure surface with different layers of material, Image should be introduced as:

    where

    the indice 1 represents the layer directly exposed to the fire, the indice 2 the next layer...

    Si is the thickness of layer i
    bi Image
    ρi is the density of the layer i
    ci is the specific heat of the layer i
    λi is the thermal conductivity of the layer i
  6. To account for different b factors in walls, ceiling and floor, Image should be introduced as:

    b = ((bjAj))/(AtAv)     (A.5)

    where

    Aj is the area of enclosure surface j, openings not included
    bj is the thermal property of enclosure surface j according to equations (A.3) and (A.4)
  7. The maximum temperature Θmax in the heating phase happens for t* = t*max

    t*max = tmax · Γ     [h]     (A.6)

    with tmax = max [(0,2 · 10–3 · qt,d / O); tlim ]     [h]     (A.7)

    where

    qt,d is the design value of the fire load density related to the total surface area At of the enclosure whereby qt,d = qf,d · At / At [MJ/m2]. The following limits should be observed: 50 ≤ qt,d ≤ 1 000 [MJ/m2].
    qf,d is the design value of the fire load density related to the surface area At of the floor [MJ/m2] taken from annex E.
    tlim is given by (10) in [h].

    NOTE The time tmax corresponding to the maximum temperature is given by tlim in case the fire is fuel controlled. If tlim is given by (0,2 · 10–3 · qt,d / O), the fire is ventilation controlled.

    31
  8. When tmax = tlim , t* used in equation (A.1) is replaced by:

    t* = t · Γlim [h]     (A.2b)

    with Γlim = [Olim/b]2 / (0,04/1 160)2     (A.8)

    where Olim = 0,1 · 10–3 · qt,d /tlim     (A.9)

  9. If (O > 0,04 and qt,d < 75 and b > 1 160), Γlim in (A.8) has to be multiplied by k given by:

    Image

  10. In case of slow fire growth rate, tlim = 25 min; in case of medium fire growth rate, tlim = 20 min and in case of fast fire growth rate, tlim = 15 min.

    NOTE For advice on fire growth rate, see Table E.5 in annex E.

  11. The temperature-time curves in the cooling phase are given by:

    Image

    where

    Image

32

Annex B
Thermal actions for external members - Simplified calculation method

(informative)

B.1 Scope

  1. This method allows the determination of:
  2. This method considers steady-state conditions for the various parameters. The method is valid only for fire loads qf,d higher than 200 MJ/m2.

B.2 Conditions of use

  1. When there is more than one window in the relevant fire compartment, the weighted average height of windows heq, the total area of vertical openings Av and the sum of window widths (wt = ∑wi) are used.
  2. When there are windows in only wall 1, the ratio D/W is given by:

    Image

  3. When there are windows on more than one wall, the ratio D/W has to be obtained as follows:

    Image

    where

    W1 is the width of the wall 1, assumed to contain the greatest window area;
    Av1 is the sum of window areas on wall 1;
    W2 is the width of the wall perpendicular to wall 1 in the fire compartment.
  4. When there is a core in the fire compartment, the ratio D/W has to be obtained as follows:

    Image

  5. All parts of an external wall that do not have the fire resistance (REI) required for the stability of the building should be classified as window areas. 33
  6. The total area of windows in an external wall is:
  7. The size of the fire compartment should not exceed 70 m in length, 18 m in width and 5 m in height.
  8. The flame temperature should be taken as uniform across the width and the thickness of the flame.

B.3 Effects of wind

B.3.1 Mode of ventilation

  1. P If there are windows on opposite sides of the fire compartment or if additional air is being fed to the fire from another source (other than windows), the calculation shall be done with forced draught conditions. Otherwise, the calculation is done with no forced draught conditions.

B.3.2 Flame deflection by wind

  1. Flames from an opening should be assumed to be leaving the fire compartment (see Figure B.1):

Figure B.1 — Deflection of flame by wind

Figure B.1 — Deflection of flame by wind

34

B.4 Characteristics of fire and flames

B.4.1 No forced draught

  1. The rate of burning or the rate of heat release is given by:

    Image

  2. The temperature of the fire compartment is given by:

    Image

  3. The flame height (see Figure B.2) is given by:

    Image

    NOTE With ρg = 0,45 kg/m3 and g = 9,81 m/s2 , this equation may be simplified to:
    Image

    Figure B.2 — Flame dimensions, no through draught

    Figure B.2 — Flame dimensions, no through draught

    35
  4. The flame width is the window width (see Figure B.2).
  5. The flame depth is 2/3 of the window height: 2/3 heq (see Figure B.2).
  6. The horizontal projection of flames:
  7. The flame length along axis is given by:

    when LL > 0

    Lf = LL + heq /2     if wall exist above window or if heq ≤ 1,25 wt     (B.12)

    Lf = (LL2 + (LHheq /3)2)1/2 + heq /2     if no wall exist above window or if heq > 1,25 wt     (B.13)

    when LL = 0 , then Lf = 0

  8. The flame temperature at the window is given by:

    Tw = 520/(1 − 0,4725 (Lf · wt/Q)) + T0     [K]     (B.14)

    with Lf · wt /Q < 1

  9. The emissivity of flames at the window may be taken as εf = 1,0
  10. The flame temperature along the axis is given by:

    Tz = (TWT0) (1 − 0,4725 (Lx · wt / Q)) + T0     [K]     (B.15)

    with

    Lx · wt /Q < 1

    Lx is the axis length from the window to the point where the calculation is made
  11. The emissivity of flames may be taken as:

    εf = 1 − e−0,3df     (B.16)

    where df is the flame thickness [m]

  12. The convective heat transfer coefficient is given by:

    αc = 4,67 (1/deq)0,4 (Q/Av)0,6     (B.17)

    36
  13. If an awning or balcony (with horizontal projection: Wa) is located at the level of the top of the window on its whole width (see Figure B.3), for the wall above the window and heq ≤ 1,25 wt, the height and horizontal projection of the flame should be modified as follows:
  14. With the same conditions for awning or balcony as mentioned in (13), in the case of no wall above the window or heq > 1,25 wt the height and horizontal projection of the flame should be modified as follows:

B.4.2 Forced draught

  1. The rate of burning or the rate of heat release is given by:

    Q = (Af · qf,d)/τF     [MW]     (B.18)

  2. The temperature of the fire compartment is given by:

    Image Tf = 1 200 (1 − e−0,00228 Ω) + T0 Image     (B.19)

  3. The flame height (see Figure B.4) is given by:

    Image

    37

    NOTE With u = 6 m/s, LL ≈ 0,628 Q/Avl/2heq

    Figure B.4 — Flame dimensions, through or forced draught

    Figure B.4 — Flame dimensions, through or forced draught

  4. The horizontal projection of flames is given by:

    LH = 0,605 (u2 / heq)0,22 (LL + heq)     (B.21)

    NOTE With u = 6 m/s, Lh = 1,33 (LL + heq) / heq0,22

  5. The flame width is given by:

    wf = Wt + 0,4 LH     (B.22)

  6. The flame length along axis is given by:

    Lf = (LL2 + LH2)1/2     (B.23)

  7. The flame temperature at the window is given by:

    TW = 520 / (1 − 0,3325 Lf (Av)1/2 / Q) + T0     [K]     (B.24)

    with Lf(Av)1/2 /Q < 1

  8. The emissivity of flames at the window may be taken as εf = 1,0
  9. The flame temperature along the axis is given by:

    Image

    where

    Lx is the axis length from the window to the point where the calculation is made
    38
  10. The emissivity of flames may be taken as:

    εf = 1 − e−0,3df     (B.26)

    where df is the flame thickness [m]

  11. The convective heat transfer coefficient is given by:

    αc = 9,8 (1 / deq)0,4 (Q/(17,5 Av)+ u/1,6)0,6     (B.27)

    NOTE With u = 6 m/s the convective heat transfer coefficient is given by: αc = 9,8 (1/deq)0,4 (Q/(17,5 Av) + 3,75)0,6

  12. Regarding the effects of balconies or awnings, see Figure B.5, the flame trajectory, after being deflected horizontally by a balcony or awning, is the same as before, i.e. displaced outwards by the depth of the balcony, but with a flame length Lf unchanged.

    Figure B.5 — Deflection of flame by awning

    Figure B.5 — Deflection of flame by awning

B.5 Overall configuration factors

  1. The overall configuration factor Φf of a member for radiative heat transfer from an opening should be determined from:

    Image

    where

    Φf,i is the configuration factor of member face i for that opening, see annex G;
    di is the cross-sectional dimension of member face i ;
    Ci is the protection coefficient of member face i as follows:
    39
  2. The configuration factor Φf,i for a member face from which the opening is not visible should be taken as zero.
  3. The overall configuration factor Φz of a member for radiative heat transfer from a flame should be determined from:

    Image

    where

    Φz,i is the configuration factor of member face i for that flame, see annex G.
  4. The configuration factors ΦZ,i of individual member faces for radiative heat transfer from flames may be based on equivalent rectangular flame dimensions. The dimensions and locations of equivalent rectangles representing the front and sides of a flame for this purpose should be determined as given in annex G. For all other purposes, the flame dimensions given in B.4 of this annex should be used.
40

Annex C
Localised fires

(informative)

  1. The thermal action of a localised fire can be assessed by using the expression given in this annex. Differences have to be made regarding the relative height of the flame to the ceiling.
  2. The heat flux from a localised fire to a structural element should be calculated with expression (3.1), and based on a configuration factor established according to annex G.
  3. The flame lengths Lf of a localised fire (see Figure C.1) is given by:

    Lf =−1,02 D + 0,0148 Q2/5     [m]     (C.1)

  4. When the flame is not impacting the ceiling of a compartment (Lf < H; see Figure C.1) or in case of fire in open air, the temperature Θ(z) in the plume along the symetrical vertical flame axis is given by:

    Θ(z) = 20 + 0,25Qc2/3(zzo)−5/3 ≤ 900     [°C]     (C.2)

    where

    D is the diameter of the fire [m], see Figure C.1
    Q is the rate of heat release [W] of the fire according to E.4
    Qc is the convective part of the rate of heat release [W], with Qc = 0,8 Q by default
    z is the height [m] along the flame axis, see Figure C.1
    H is the distance [m] between the fire source and the ceiling, see Figure C.1

    Figure C.1

    Figure C.1

    41
  5. The virtual origin z0 of the axis is given by:

    z0 = − 1,02D + 0,00524 Q2/5     [m]     (C.3)

  6. When the flame is impacting the ceiling (LfH; see Figure C.2) the heat flux [W/m2] received by the fire exposed unit surface area at the level of the ceiling is given by:

    = 100 000     if y ≤ 0,30

    = 136 300 to 121 000 y     if 0,30 < y < 1,0     (C.4)

    = 15 000 y−3,7     if y ≥ 1,0

    where

    y is a parameter [−] given by : Image
    r is the horizontal distance [m] between the vertical axis of the fire and the point along the ceiling where the thermal flux is calculated, see Figure C.2
    H is the distance [m] between the fire source and the ceiling, see Figure C.2

    Figure C.2

    Figure C.2

  7. Lh is the horizontal flame length (see Figure C.2) given by the following relation:

    Lh = (2,9 H (Q*H)0,33)−H     [m]     (C.5)

  8. Q*H is a non-dimensional rate of heat release given by:

    Q*H = Q /(1,11·106·H2,5)     [−]     (C.6)

  9. z1 is the vertical position of the virtual heat source [m] and is given by:

    z1 = 2,4 D(QD*2/5QD*2/3) when Q*D < 1,0     (C.7)

    z1 = 2,4D(1,0−QD*2/5) when Q*D ≥ 1,0

    where

    42

    Q*D = Q/(1,11·106·D2,5)     [−]     (C.8)

  10. The net heat flux net received by the fire exposed unit surface area at the level of the ceiling, is given by :

    net = αc · (Θm − 20) − Φ · εm · εf · σ · [(Θm + 273)4 − (293)4]     (C.9)

    where the various coefficients depend on expressions (3.2), (3.3) and (C.4).

  11. The rules given in (3) to (10) inclusive are valid if the following conditions are met:
  12. In case of several separate localised fires, expression (C.4) may be used in order to get the different individual heat fluxes 1, 2… received by the fire exposed unit surface area at the level of the ceiling. The total heat flux may be taken as:

    tot = 1 + 2… ≤ 100 000     [W/m2]     (C.10)

43

Annex D
Advanced fire models

(informative)

D.1 One-zone models

  1. A one-zone model should apply for post-flashover conditions. Homogeneous temperature, density, internal energy and pressure of the gas are assumed in the compartment.
  2. The temperature should be calculated considering:
  3. The ideal gas law considered is:

    Pint = ρg R Tg     [N/m2]     (D.1)

  4. The mass balance of the compartment gases is written as

    Image

    where

    Image is the rate of change of gas mass in the fire compartment
    out is the rate of gas mass going out through the openings
    in is the rate of gas mass coming in through the openings
    fi is the rate of pyrolysis products generated
  5. The rate of change of gas mass and the rate of pyrolysis may be neglected. Thus

    in = out     (D.3)

    These mass flows may be calculated based on static pressure due to density differences between air at ambient and high temperatures, respectively.

  6. The energy balance of the gases in the fire compartment may be taken as:

    Image

    where

    44
    Eg is the internal energy of gas [J]
    Q is the rate of heat release of the fire [W]
    Qout = out c Tf
    Qin = in c Tamb
    Qwall = (AtAh,v) net, is the loss of energy to the enclosure surfaces
    Qrad = Ah,v σ Tf4, is the loss of energy by radiation through the openings

    with:

    c is the specific heat [J/kgK]
    net is given by expression (3.1)  
    is the gas mass rate [kg/s]
    T is the temperature [K]

D.2 Two-zone models

  1. A two-zone model is based on the assumption of accumulation of combustion products in a layer beneath the ceiling, with a horizontal interface. Different zones are defined: the upper layer, the lower layer, the fire and its plume, the external gas and walls.
  2. In the upper layer, uniform characteristics of the gas may be assumed.
  3. The exchanges of mass, energy and chemical substance may be calculated between these different zones.
  4. In a given fire compartment with a uniformly distributed fire load, a two-zone fire model may develop into a one-zone fire in one of the following situations:

D.3 Computational fluid dynamic models

  1. A computational fluid dynamic model may be used to solve numerically the partial differential equations giving, in all points of the compartment, the thermo-dynamic and aero-dynamic variables.

    NOTE Computational fluid dynamic models, or CFD, analyse systems involving fluid flow, heat transfer and associated phenomena by solving the fundamental equations of the fluid flow. These equations represent the mathematical statements of the conservation laws of physics:

45

Annex E
Fire load densities

(informative)

E.1 General

  1. The fire load density used in calculations should be a design value, either based on measurements or in special cases based on fire resistance requirements given in national regulations.
  2. The design value may be determined:
  3. The design value of the fire load qf,d is defined as:

    qf,d = qf,k · m · δq1 · δq2 · δn     [MJ/m2]     (E.1)

    where

    m is the combustion factor (see E.3)
    δq1 is a factor taking into account the fire activation risk due to the size of the compartment (see Table E.1)
    δq2 is a factor taking into account the fire activation risk due to the type of occupancy (see Table E.1)
    Image is a factor taking into account the different active fire fighting measures i (sprinkler, detection, automatic alarm transmission, firemen ...). These active measures are generally imposed for life safety reason (see Table E.2 and clauses (4) and (5)).
    qf,k is the characteristic fire load density per unit floor area [MJ/m2] (see f.i. Table E.4)
    Table E.1 — Factors δq1 , δq2
    Compartment floor area Af [m2] Danger of Fire Activation δq1 Danger of Fire Activation δq2 Examples of Occupancies
    25 1,10 0,78 artgallery, museum, swimming pool
    250 1,50 1,00 offices, residence, hotel, paper Industry
    2 500 1,90 1,22 manufactory for machinery & engines
    5 000 2,00 1,44 chemical laboratory, painting workshop
    10 000 2,13 1,66 manufactory of fireworks or paints
    46
    Table E.2 — Factors δni
    δni Function of Active Fire Fighting Measures
    Automatic Fire Suppression Automatic Fire Detection Manual Fire Suppression
    Automatic Water Extinguishing System Independent Water Supplies

    0 | 1 | 2
    Automatic fire Detection & Alarm Automatic Alarm Transmission to Fire Bridge Work Fire Brigade Off Site Fire Brigade Safe Access Routes Fire Fighting Devices Smoke Exhaust System
    δn1 δn2 by
    Heat
    δn3
    by
    Smoke
    δn4
    δn5 δn6 δn7 δn8 δn9 δn10
    0,61 1,0 | 0,87 | 0,7 0,87 or 0,73 0,87 0,61 or 0,78 0,9 or 1 or 1,5 1,0 or 1,5 1,0 or 1,5
  4. For the normal fire fighting measures, which should almost always be present, such as the safe access routes, fire fighting devices, and smoke exhaust systems in staircases, the δni values of Table E.2 should be taken as 1,0. However, if these fire fighting measures have not been foreseen, the corresponding δni value should be taken as 1,5.
  5. If staircases are put under overpressure in case of fire alarm, the factor δn8 of Table E.2 may be taken as 0,9.
  6. The preceding approach is based on the assumption that the requirements in the relevant European Standards on sprinklers, detection, alarm, smoke exhaust systems are met, see also 1.3. However local circumstances may influence the numbers given in Table E.2. Reference is made to the Background Document CEN/TC250/SC1/N300A.

E.2 Determination of fire load densities

E.2.1 General

  1. The fire load should consist of all combustible building contents and the relevant combustible parts of the construction, including linings and finishings. Combustible parts of the combustion which do not char during the fire need not to be taken into account.
  2. The following clauses apply for the determination of fire load densities:
  3. Where fire load densities are determined from a fire load classification of occupancies, fire loads are distinguished as:

E.2.2 Definitions

  1. The characteristic fire load is defined as:

    Qfi,k = ∑ Mk,i · Hui · Ψi = ∑ Qfi,k,i     [MJ]     (E.2)

    where

    47
    MK,i is the amount of combustible material [kg], according to (3) and (4)
    Hui is the net calorific value [MJ/kg], see (E.2.4)
    [Ψi] is the optional factor for assessing protected fire loads, see (E.2.3)
  2. The characteristic fire load density qf,k per unit area is defined as:

    qf,k = Qfi,k /A     [MJ/m2]     (E.3)

    where

    A is the floor area (Af) of the fire compartment or reference space, or inner surface area (At) of the fire compartment, giving qf,k or qt,k
  3. Permanent fire loads, which are not expected to vary during the service life of a structure, should be introduced by their expected values resulting from the survey.
  4. Variable fire loads, which may vary during the service life of a structure, should be represented by values, which are expected not to be exceeded during 80 % of time.

E.2.3 Protected fire loads

  1. Fire loads in containments which are designed to survive fire exposure need not be considered.
  2. Fire loads in non-combustible containments with no specific fire design, but which remain intact during fire exposure, may be considered as follows:

    The largest fire load, but at least 10 % of the protected fire loads, is associated with Ψi = 1,0.

    If this fire load plus the unprotected fire loads are not sufficient to heat the remaining protected fire loads beyond ignition temperature, then the remaining protected fire loads may be associated with Ψi = 0,0.

    Otherwise, Ψi values need to be assessed individually.

E.2.4 Net calorific values

  1. Net calorific values should be determined according to EN ISO 1716:2002.
  2. The moisture content of materials may be taken into account as follows:

    Hu = Hu0 (1 − 0,01 u) − 0,025 u     [MJ/kg]     (E.4)

    where

    u is the moisture content expressed as percentage of dry weight
    Huo is the net calorific value of dry materials
  3. Net calorific values of some solids, liquids and gases are given in Table E.3. 48
    Table E.3 — Net calorific values Hu [MJ/kg] of combustible materials for calculation of fire loads
    Solids
    Wood 17,5

    Other cellulosic materials

    • Clothes
    • Cork
    • Cotton
    • Paper, cardboard
    • Silk
    • Straw
    • Wool
    20

    Carbon

    • Anthracit
    • Charcoal
    • Coal
    30
    Chemicals

    Paraffin series

    • Methane
    • Ethane
    • Propane
    • Butane
    50

    Olefin series

    • Ethylene
    • Propylen
    • Butene
    45

    Aromatic series

    • Benzene
    • Toluene
    40

    Alcohols

    • Methanol
    • Ethanol
    • Ethyl alcohol
    30

    Fuels

    • Gasoline, petroleum
    • Diesel
    45

    Pure hydrocarbons plastics

    • Polyethylene
    • Polystyrene
    • Polypropylene
    40
    Other products
    ABS (plastic) 35
    Polyester (plastic) 30
    Polyisocyanerat and polyurethane (plastics) 25
    Polyvinylchloride, PVC (plastic) 20
    Bitumen, asphalt 40
    Leather 20
    Linoleum 20
    Rubber tyre 30
    NOTE The values given in this table are not applicable for calculating energy content of fuels.
49

E.2.5 Fire load classification of occupancies

  1. The fire load densities should be classified according to occupancy, be related to the floor area, and be used as characteristic fire load densities qf,k [MJ/m2], as given in Table E.4.
    Table E.4 — Fire load densities qf,k [MJ/m2] for different occupancies
    Occupancy Average 80% Fractile
    Dwelling 780 948
    Hospital (room) 230 280
    Hotel (room) 310 377
    Library 1 500 1 824
    Office 420 511
    Classroom of a school 285 347
    Shopping centre 600 730
    Theatre (cinema) 300 365
    Transport (public space) 100 122
    NOTE Gumbel distribution is assumed for the 80 % fractile.
  2. The values of the fire load density qf,k given in Table E.4 are valid in case of a factor δq2 equal to 1,0 (see Table E.1).
  3. The fire loads in Table E.4 are valid for ordinary compartments in connection with the here given occupancies. Special rooms are considered according to E.2.2.
  4. Fire loads from the building (construction elements, linings and finishings) should be determined according to E.2.2. These should be added to the fire load densities of (1) if relevant.

E.2.6 Individual assessment of fire load densities

  1. In the absence of occupancy classes, fire load densities may be specifically determined for an individual project by performing a survey of fire loads from the occupancy.
  2. The fire loads and their local arrangement should be estimated considering the intended use, furnishing and installations, variations with time, unfavourable trends and possible modifications of occupancy.
  3. Where available, a survey should be performed in a comparable existing project, such that only possible differences between the intended and existing project need to be specified by the client.

E.3 Combustion behaviour

  1. The combustion behaviour should be considered in function of the occupancy and of the type of fire load.
  2. For mainly cellulosic materials, the combustion factor may be assumed as m = 0,8.
50

E.4 Rate of heat release Q

  1. The growing phase may be defined by the expression:

    Image

    where

    Q is the rate of heat release in [W]
    t is the time in [s]
    tα is the time needed to reach a rate of heat release of 1 MW.
  2. The parameter tα and the maximum rate of heat release RHRf , for different occupancies, are given in Table E.5
    Table E.5 — Fire growth rate and RHRf for different occupancies
    Max Rate of heat release RHRf
    Occupancy Fire growth rate tα[s] RHRf [kW/m2]
    Dwelling Medium 300 250
    Hospital (room) Medium 300 250
    Hotel (room) Medium 300 250
    Library Fast 150 500
    Office Medium 300 250
    Classroom of a school Medium 300 250
    Shopping centre Fast 150 250
    Theatre (cinema) Fast 150 500
    Transport (public space) Slow 600 250
  3. The values of the fire growth rate and RHRf according to Table E.5 are valid in case of a factor δq2 equal to 1,0 (see Table E.1).
  4. For an ultra-fast fire spread, tα corresponds to 75 s.
  5. The growing phase is limited by an horizontal plateau corresponding to the stationnary state and to a value of Q given by (RHRf · Afi)

    where

    Afi is the maximum area of the fire [m2] which is the fire compartment in case of uniformly distributed fire load but which may be smaller in case of a localised fire.
    RHRf is the maximum rate of heat release produced by 1 m2 of fire in case of fuel controlled conditions [kW/m2] (see Table E.5).
  6. The horizontal plateau is limited by the decay phase which starts when 70 % of the total fire load has been consumed.
  7. The decay phase may be assumed to be a linear decrease starting when 70 % of the fire load has been burnt and completed when the fire load has been completely burnt. 51
  8. If the fire is ventilation controlled, this plateau level has to be reduced following the available oxygen content, either automatically in case of the use of a computer program based on one zone model or by the simplified expression:

    Image

    where

    Av is the opening area [m2]
    heq is the mean height of the openings [m]
    Hu is the net calorific value of wood with Hu = 17,5 MJ/kg
    m is the combustion factor with m = 0,8
  9. When the maximum level of the rate of heat release is reduced in case of ventilation controlled condition, the curve of the rate of heat release has to be extended to correspond to the available energy given by the fire load. If the curve is not extended, it is then assumed that there is external burning, which induces a lower gas temperature in the compartment.
52

Annex F
Equivalent time of fire exposure

(informative)

  1. The following approach may be used where the design of members is based on tabulated data or other simplified rules, related to the standard fire exposure.

    NOTE The method given in this annex is material dependent. It is not applicable to composite steel and concrete or timber constructions.

  2. If fire load densities are specified without specific consideration of the combustion behaviour (see annex E), then this approach should be limited to fire compartments with mainly cellulosic type fire loads.
  3. The equivalent time of standard fire exposure is defined by:

    te,d = (qf,d · kb · wf) kc or

    te,d = (qt,d · kb · wt) kc     [min]     (F.1)

    where

    qf,d is the design fire load density according to annex E, whereby qt,d = qf,d · Af / At
    kb is the conversion factor according to (4)
    wf is the ventilation factor according to (5), whereby wt = wf · At / Af
    kc is the correction factor function of the material composing structural cross-sections and defined in Table F.1.
    Table F.1 — Correction factor kc in order to cover various materials. (O is the opening factor defined in annex A)
    Cross-section material Correction factor kc
    Reinforced concrete

    Protected steel

    Not protected steel
    1,0

    1,0

    13,7 · O
  4. Where no detailed assessment of the thermal properties of the enclosure is made, the conversion factor kb may be taken as:

    kb = 0,07     [min · m2/MJ]     when qd is given in [MJ/m2]     (F.2)

    otherwise kb may be related to the thermal property Image of the enclosure according to Table F.2.

    For determining b for multiple layers of material or different materials in walls, floor, ceiling, see annex A (5) and (6).

    53
    Table F.2 — Conversion factor kb depending on the thermal properties of the enclosure
    Image
    [J/m2s1/2K]
    kb
    [min · m2/MJ]
    b > 2 500

    720 ≤ b ≤ 2 500

    b < 720
    0,04

    0,055

    0,07
  5. The ventilation factor wf may be calculated as:

    wf = (6,0 / H)0,3 [0,62 + 90(0,4 − αv)4 / (1 + bv αh)] ≥ 0,5     [−]     (F.3)

    where

    αv = Av/Af is the area of vertical openings in the façade (Av) related to the floor area of the compartment (Af) where the limit 0,025 ≤ αv ≤ 0,25 should be observed
    αh = Ah/Af is the area of horizontal openings in the roof (Ah) related to the floor area of the compartment (Af)

    bv = 12,5 (1 +10 αv − αv2) ≥ 10,0

    H     is the height of the fire compartment     [m]

    For small fire compartments [Af < 100 m2] without openings in the roof, the factor wf may also be calculated as:

    wf = O −1/2 · Af / At     (F.4)

    where

    O is the opening factor according to annex A
  6. It shall be verified that:

    te,d < tfi,d     (F.5)

    where

    tfi,d is the design value of the standard fire resistance of the members, assessed according to the fire Parts of prEN 1992 to prEN 1996 and prEN 1999.
54

Annex G
Configuration factor

(informative)

G.1 General

  1. The configuration factor Φ is defined in 1.5.4.1, which in a mathematical form is given by:

    Image

    The configuration factor measures the fraction of the total radiative heat leaving a given radiating surface that arrives at a given receiving surface. Its value depends on the size of the radiating surface, on the distance from the radiating surface to the receiving surface and on their relative orientation (see Figure G.1).

    Figure G.1 — Radiative heat transfer between two infinitesimal surface areas

    Figure G.1 — Radiative heat transfer between two infinitesimal surface areas

  2. In cases where the radiator has uniform temperature and emissivity, the definition can be simplified to : “the solid angle within which the radiating environment can be seen from a particular infinitesimal surface area, divided by 2π.”
  3. The radiative heat transfer to an infinitesimal area of a convex member surface is determined by the position and the size of the fire only (position effect).
  4. The radiative heat transfer to an infinitesimal area of a concave member surface is determined by the position and the size of the fire (position effect) as well as by the radiation from other parts of the member (shadow effects). 55
  5. Upper limits for the configuration factor Φ are given in Table G.1.
    Table G.1 — Limits for configuration factor Φ
      Localised Fully developed
    position effect Φ ≤ 1 Φ = 1
    shadow effect convex Φ = 1 Φ = 1
    concave Φ ≤ 1 Φ ≤ 1

G.2 Shadow effects

  1. Specific rules for quantifying the shadow effect are given in the material orientated parts of the Eurocodes.

G.3 External members

  1. For the calculation of temperatures in external members, all radiating surfaces may be assumed to be rectangular in shape. They comprise the windows and other openings in fire compartment walls and the equivalent rectangular surfaces of flames, see annex B.
  2. In calculating the configuration factor for a given situation, a rectangular envelope should first be drawn around the cross-section of the member receiving the radiative heat transfer, as indicated in Figure G.2 (This accounts for the shadow effect in an approximate way). The value of Φ should then be determined for the mid-point P of each face of this rectangle.
  3. The configuration factor for each receiving surface should be determined as the sum of the contributions from each of the zones on the radiating surface (normally four) that are visible from the point P on the receiving surface, as indicated in Figures G.3 and G.4. These zones should be defined relative to the point X where a horizontal line perpendicular to the receiving surface meets the plane containing the radiating surface. No contribution should be taken from zones that are not visible from the point P, such as the shaded zones in Figure G.4.
  4. If the point X lies outside the radiating surface, the effective configuration factor should be determined by adding the contributions of the two rectangles extending from X to the farther side of the radiating surface, then subtracting the contributions of the two rectangles extending from X to the nearer side of the radiating surface.
  5. The contribution of each zone should be determined as follows:

    Figure G.2 — Envelope of receiving surfaces

    Figure G.2 — Envelope of receiving surfaces

56
  1. receiving surface parallel to radiating surface:

    Image

    where

    a = h / s

    b = w / s

    s is the distance from P to X;
    h is the height of the zone on the radiating surface;
    w is the width of that zone.
  2. receiving surface perpendicular to radiating surface:

    Image

  3. receiving surface in a plane at an angle θ to the radiating surface:

    Image

    Figure G.3 — Receiving surface in a plane parallel to that of the radiating surface

    Figure G.3 — Receiving surface in a plane parallel to that of the radiating surface

    57

    Figure G.4 — Receiving surface perpendicular to the plane of the radiating surface

    Figure G.4 — Receiving surface perpendicular to the plane of the radiating surface

    Figure G.5 — Receiving surface in a plane at an angle θ to that of the radiating surface

    Figure G.5 — Receiving surface in a plane at an angle θ to that of the radiating surface

58

Bibliography

EN ISO 1716:2002, Reaction to fire tests for building products – Determination of the heat of combustion (ISO 1716:2002).

EN 1363-2, Fire resistance tests – Part 2: Alternative and additional procedures.

59