DRAFT FOR DEVELOPMENT DD ENV 1991-2-2:1996

Eurocode 1: Basis of design and actions on structures —

Part 2.2: Actions on structures exposed to fire —

(together with United Kingdom National Application Document)

ICS 13.220.50; 91.040

DD ENV 1991-2-2:1996

This Draft for Development, having been prepared under the direction of the Sector Board for Building and Civil Engineering, was published under the authority of the Standards Board and comes into effect on 15 September 1996

© BSI 03-2000

The following BSI reference relates to the work on this Draft for Development:Committee reference B/525/1

ISBN 0 580 25803 3

Committees responsible for this Draft for Development

The preparation of this Draft for Development was entrusted by Technical Committee B/525, Building and civil engineering structures, to Subcommittee B/525/1, Actions (loadings) and basis of design, upon which the following bodies were represented:

British Constructional Steelwork AssociationBritish Iron and Steel Producers’ AssociationBritish Masonry SocietyConcrete SocietyDepartment of the Environment (Building Research Establishment)Department of the Environment (Property and Buildings Directorate)Highways AgencyInstitution of Structural EngineersNational House Building CouncilRoyal Institute of British ArchitectsSteel Construction Institute

Amendments issued since publication

Amd. No. Date Comments

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Contents

PageCommittees responsible Inside front coverNational foreword iiForeword 2Text of National Application Document iiiText of ENV 1991-2-2 7

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National foreword

This Draft for Development has been prepared by Subcommittee B/525/1 and is the English language version of ENV 1991-2-2:1995 Eurocode 1: Basis of design and actions on structures — Part 2.2: Actions on structures exposed to fire, as published by the European Committee for Standardization (CEN). This Draft for Development also includes the United Kingdom (UK) National Application Document (NAD) to be used with the ENV in the design of buildings to be constructed in England, Wales and Northern Ireland.ENV 1991-2-2:1995 results from a programme of work sponsored by the European Commission to make available a common set of rules for the structural and geotechnical design of building and civil engineering works.This publication is not to be regarded as a British Standard.An ENV is made available for provisional application, but does not have the status of a European Standard. The aim is to use the experience gained to modify the ENV so that it can be adopted as a European Standard.The values for certain parameters in the ENV Eurocodes may be set by individual CEN members so as to meet the requirements of national regulations. These parameters are designated by [ ] in the ENV.During the ENV period reference should be made to the supporting documents listed in the National Application Document (NAD).The purpose of the NAD is to provide essential information, particularly in relation to safety, to enable the ENV to be used for buildings constructed in England, Wales and Northern Ireland. The NAD takes precedence over corresponding provisions in the ENV.The Building Regulations 1991, Approved Document A 1992, draws attention to the potential use of ENV Eurocodes as an alternative approach to Building Regulation compliance.Users of this document are invited to comment on its technical content, ease of use and any ambiguities and anomalies. These comments will be taken into account when preparing the UK national response to CEN on the question of whether the ENV can be converted to an EN.Comments should be sent in writing to the Secretary of Subcommittee B/525/1, BSI, 389 Chiswick High Road, London W4 4AL, quoting the document reference, the relevant clause and, where possible, a proposed revision, within 2 years of the issue of this document.

Summary of pagesThis document comprises a front cover, an inside front cover, pages i to xii, the ENV title page, pages 2 to 32 and a back cover.This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.

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National Application Document for use in the UK with ENV 1991-2-2:1995

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Contents of National Application Document

PageIntroduction v1 Scope v2 References v3 Partial safety factors and other values to be used in ENV 1991-2-2 v4 Reference Standards v5 Additional recommendations viAnnex A (normative) Description of occupancies ixAnnex B (normative) Thermal properties of typical compartment linings xFigure 1 — Definition of building height viiTable 1 — Values to be used in referenced clauses in place of ENV boxed values vTable 2 — Reference in ENV 1991-2-2 to other publications viTable 3 — Fire test correlation factor viTable 4 — Factors quantifying consequences of failure (*q1) to be used in equation (1) viiTable 5 — Factors quantifying risk of failure (*q2) to be used in equation (1) viiiTable 6 — Active protection factor viiiTable 7 — Characteristic variable fire load densities viiiTable 8 — Conversion factor viiiList of references xi

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IntroductionThis National Application Document (NAD) has been prepared by Subcommittee B/525/1. It has been developed from the following.

a) A textual examination of ENV 1991-2-2:1995.b) A calibration against Approved Document B (1992 Edition) of the Building Regulations 1991 (England and Wales).c) Trial calculations.

1 ScopeThis NAD provides information to enable ENV 1991-2-2:1995 (EC1: Part 2.2) to be used for the design of buildings to be constructed in England, Wales and Northern Ireland. Its application does not extend to civil engineering works.

2 References2.1 Normative referencesThis NAD incorporates, by reference, provisions from specific editions of other publications. These normative references are cited at the appropriate points in the text and the publications are listed on page (xi). Subsequent amendments to, or revisions of, any of these publications apply to this NAD only when incorporated in it by updating or revision.

2.2 Informative referencesThis NAD refers to other publications that provide information or guidance. Editions of these publications current at the time of issue of this standard are listed on page (xi), but reference should be made to the latest editions.

3 Partial safety factors and other values to be used in ENV 1991-2-2In the referenced clauses, the values given inTable 1 shall be used for the design of buildings in place of the “boxed” values given in the ENV. Further recommendations on the adoption of the approaches outlined in ENV 1991-2-2 are given in clause 5 of this NAD.

4 Reference standardsReferences in the ENV to national regulations refer to:

a) BUILDING AND BUILDINGS. The Building Regulations 1991. (SI 1991 No. 2768) in England and Wales;b) BUILDING REGULATIONS. The Building Regulations (Northern Ireland) 1990. (SRNI 1990 No. 59) in Northern Ireland.

Reference standards cited in ENV 1991-2-2 are listed in Table 2 of this NAD. Full references are provided on Page (x).

Table 1 — Values to be used in referenced clauses in place of ENV boxed values

ENV Clause Description “Boxed value” UK value

4.1 (4) Configuration factor (Î) 1.0 1.0

4.1 (10) Convection factor on unexposed face (µc) 9.0 9.0

4.2.1 (2) Type of test factor (radiation) (¾n,r) 1.0 0.451.0a

4.2.1 (2) Type of test factor (convection) (¾n,c) 1.0 1.0

4.2.1 (3) Emissivity of fire (¼f) 0.8 0.8

4.2.1 (3) Material emissivity (¼m) 0.7 0.7

4.2.2 (2) Standard curve: coefficient of heat transfer-convection (µc)

25 W/m2 °C 25 W/m2 °C

4.2.3 (2) External curve: coefficient of heat transfer-convection (µc)

25 W/m2 °C 25 W/m2 °C

4.2.4 (2) Hydrocarbon curve coefficient of heat transfer-convection (µc)

50 W/m2 °C 50 W/m2 °C

D.1 (3) Active fire protection factor 0.6 0.60.75a

F.3.1 P (1) Partial safety factor for permanent actions in accidental situation (¾GA)

1.0 1.0

a Guidance on choice of value given in clause 5 of this NAD.

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Table 2 — Reference in ENV 1991-2-2 to other publications

5 Additional recommendationsNOTE 5.1 to 5.7 should be followed when designing in accordance with ENV 1991-2-2.

5.1 Section 1. General

Clause 1.1.2 (1) PENV 1991-2-2 is intended for use in conjunction with the fire design parts of ENV 1992 to ENV 1996 and ENV 1999 which give rules for designing structures for fire resistance. Fire resistance in this context is confined to load bearing function, i.e. the ability of the structure to sustain actions during the relevant fire exposure, according to defined criteria.

5.2 Section 4. Thermal actions

a) Clause 4.2.1 (1)The nominal temperature-time curve considered as appropriate for buildings is the standard temperature-time curve as defined in 4.2.2 of the ENV.

b) Clause 4.2.1 (2)The net heat fluxes due to radiation and convection are calculated in equations (4.1) and (4.2) in a simplistic manner. Accordingly, to correlate the results of the approach given in equations (4.1) and (4.2) with data from fire resistance tests, a factor is applied to each of the net heat flux components, as given in Table 3.The fire test factor is applicable only to the calculation of heat flux for use with the appropriate material thermal models, detailed in ENV 1992 to ENV 1996 and ENV 1999. The factor shall not be used with other numerical models of heat transfer.

Table 3 — Fire test correlation factor

Document referenced in ENV Title Status UK Document

CPD 89/106/EEC Construction products directive EC Directive CPD 89/106/EEC

ID “Safety in the case of fire”

Interpretative document Published in Official Journal of European Communities ref. 94(c)62/01

ENV 1991-1 Basis of design ENV DD ENV 1991-1

ENV 1992-1.2 Design of concrete structures — Structural fire design

ENV ENV 1992-1-2 (BS 8110-2)a

ENV 1993-1.2 Design of steel structures — Structural fire design

ENV ENV 1993-1-2 (BS 5950-8)a

ENV 1994-1.2 Design of composite structures — Structural fire design

ENV ENV 1994-1-2

ENV 1995-1.2 Design of timber Structures — Structural fire design

ENV ENV 1995-1-2

ENV 1996-1.2 Design of masonry structures — Structural fire design

ENV ENV 1996-1-2 (BS 5628-3)a

ENV 1999-1.2 Design of aluminium structures — Structural fire design

In Draft BS 8118-1

ISO 3898 Bases for design of structures — Notations — general symbols

ISO Standard ISO 3898

ISO 1716 Building materials — Determination of calorific potential

ISO Standard ISO 1716

a To be used until DD ENV is published

Mode of heat

transfer

Fire test factor

National value

Construction material

Convection ¾n,c 1.0 All

Radiation ¾n,r 0.45 Steel

Radiation ¾n,r 1.0 Concrete

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5.3 Annex A Parametric fire exposure (informative)

Clause A.2 (2)An approved extinguishing system may be considered in place when the building is fitted throughout with an automatic sprinkler system meeting the relevant recommendations of BS 5306-2, i.e. the relevant occupancy rating together with the additional requirements for life safety.

5.4 Annex B Parametric time-temperature curves (informative)

Annex B (1)The use of parametric temperature-time curves is the subject of current research. At this stage, there has not been sufficient validation of the approach given in equations (B.1) and (B.2). In addition, correlation needs to be established between material temperature response (as calculated in section 4) and recorded experimental data, so that the resulting emissivity and coefficient of convection (in accordance with 4.2.1 and 4.2.2) may be established. Accordingly, the parametric approach detailed in Annex B of ENV 199-2-2 is not yet considered sufficiently proven for adoption in this NAD.

5.5 Annex C Thermal actions for external members (informative)

Clause C.1 (1)Calculations of the maximum temperatures reached in a fire compartment shall not be used for compartments whose construction is of a highly insulating nature with respect to fire conditions. Accordingly, the calculation method shall not be used for compartments with lining materials having thermal inertias (i.e. the parameter b in Table E.1 of Annex E) less than 720 J/m2 S1/2 K.

5.6 Annex D Fire load densities (informative)

a) Clause D.1 (3)The safety factor ¾q is considered to be dependent on both the risk of a fully developed fire occurring and the consequences of structural failure. Thus, ¾q values vary with building type and height. Building types are distinguished by the nature of occupancy. Full details of occupancies are given in Annex A to this NAD. Building height refers to the height of the top storey floor level above ground, as described in Figure 1.

¾q as defined in equation (D.1) is to be given by:

where

Table 4 — Factors quantifying consequences of failure (¾q1) to be used in equation (1)

Figure 1 — Definition of building height

¾q = ¾q1 · ¾q2 (1)

¾q1 and ¾q2 are factors quantifying the risk and consequence of failure and are defined in Table 4 and Table 5.

Occupancy

Building Height (see Figure 1)

k 5 m

k 20 m k 30 m

> 30 mDepth of lowest basement

k 10 m > 10 m

Flats, dwellings, institutional, residential, offices 0.8 1.1 1.6 2.2

Assembly, shops 0.8 1.1

Industrial 0.6

Car parks 0.4 1.6

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Table 5 — Factors quantifying risk of failure (¾q2) factor to be used in equation (1)

The differentiation factor accounting for active protection measures, defined by ¾n in equation (D.1), shall have the values given inTable 6. The active protection factor is dependent on the safety factor ¾q in equation (1).

Table 6 — Active protection factor

For certain building types, additional considerations that are beyond the scope of this NAD may demand that an approved sprinkler system is installed. Further details may be found in the appropriate national regulations.

b) Clause D.2.3 (2)The protected fire load factor, given as Ói in equation (D.2) shall have the value 1.0.c) Clause D.2.5 (2)The combustion factor, given as mi in equation (D.2) shall have the value 1.0.d) Clause D.3 (2)Table 7 gives the fire load densities (related to the floor area of the compartment). These variable fire loads depend on the nature of the compartment’s occupancy, information on which is given in Annex A of this NAD.Where a single fire compartment contains several different occupancies, e.g. a single compartment multi-storey building, the design fire load shall be calculated based on the occupancy with the highest characteristic fire load density.

Table 7 — Characteristic variable fire load densities

5.7 Annex E Equivalent time of fire exposure (informative)

a) Annex E (1)The equivalent time of fire exposure approach should not be used for design of compartments with very low ventilation, i.e. where the ventilation factor wf, defined in equation (E.3), has a value greater than 3.0. The approach has only been validated up to a limiting time equivalent duration of 120 min (without any factoring of fire load density) and should not be used beyond this limit.The provision of sprinklers and other fire protection measures is recommended for certain building types and sizes. Detailed recommendations are given in the relevant national guidance, as referenced in clause 6 of this NAD.b) Annex E (4)Where no detailed assessment of the thermal properties of the enclosure is made, the conversion factor, defined as kb in equation (E.2), to be used is 0.09. Guidance on the thermal properties of a range of typical construction materials is given in Annex B of this NAD.The values assigned to the conversion factors in ENV 1991-2.2 shall be replaced nationally by the values given in Table 8.

Table 8 — Conversion factor

c) Annex E (5)The ventilation factor, defined by wf in equation (E.3), shall be limited to values between 0.5 and 3.0.

Occupancy ¾q2

Flats, dwellings, institutional, offices 1.2

Shops, assembly & recreation, industrial, storage, car parks

0.8

Open car parks (as defined in Annex A of this NAD)

0.4

Active Protection Measures National values for ¾n

¾q k 1.6 ¾q > 1.6

Approved sprinkler system (as defined 5.2)

0.60 0.75

Other 1.0 1.0

Variable fire load density (qf,k) Occupancy

MJ/m2

500 Flats, dwellings, institutional, car parks, offices

750 Shops, assembly & recreation

1 000 Storage, industrial

Thermal inertia(J/m2s1/2K)

kb given in ENV 1991-2-2 kb for use in UK

> 2 500 0.04 0.05

2 500 – 720 0.055 0.07

< 720 0.07 0.09

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Annex A (normative) Description of occupanciesOccupancy is a means of describing the use classification of a building or (where the building is sub-divided into compartments) to a compartment. The occupancy description should describe the main use of the compartment. Where a building contains more than one compartment, with differing occupancy, each compartment may be treated individually, with due regard in each compartment of the possible increased risk from adjacent compartments. In all cases, due regard shall be given to the relevant guidance contained in National Building Regulations with regard to provision of the fire-resisting (separating) function.

Occupancy Description

Flats Flat, maisonette.

Dwellings Dwellinghouse.

Institutional Hospital, nursing home, home for old or children, school with living accommodation, place of detention, where such persons sleep on the premises, hotel, boarding house, residential college, hall of residence.

Offices Offices or premises used for the purposes of administration, clerical work, handling money, communications, radio, television, audio or visual recording or performance (not open to public).

Shops Shops or premises used for a retail trade or business (including sale to members of the public food or drink for immediate consumption on the premises), and premises to which the public is invited to deliver or collect goods in connection with their hire, repair or other treatment.

Assembly & recreation Place of assembly, entertainment and recreation; including bingo halls, broadcasting, recording & film studios open to the public, casinos, dance halls, entertainment–, conference, exhibition & leisure centres, funfairs & amusement arcades, museums & art galleries, non-residential clubs, theatres, cinemas, concert halls, educational, establishments, dancing schools, gymnasia, swimming pool buildings, riding schools, skating rinks, sports pavilions, sports stadia, law courts, churches & other buildings of worship, crematoria, libraries open to the public, non-residential day centres, clinics, health centres & surgeries, passenger stations & termini for air, rail, road and sea travel, public toilets, zoos & menageries.

Industrial Factories and other premises used for manufacturing, altering, repairing, cleaning, washing, breaking-up, adapting or processing any article, generating power or slaughtering livestock.

Storage Place of storage or deposit of goods or materials.

Car parks (open) Car parks designed to admit and accommodate cars, motor cycles and passenger or light goods vehicles weighing no more than 2 500 kg (gross), with no basement storey. Each storey is to be naturally ventilated by permanent openings having an aggregate vent area not less than 5 % of the total floor area, at that level, of which at least 50 % should be on opposing walls.

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Annex B (normative) Thermal properties of typical compartment linings

Nature of Compartment Linings Thermal Inertia(J/m2s1/2K)

Bounding structures of ordinary concrete 2 400

Brickwork 1 500

Bounding structures of lightweight concrete (density = 500 kg/m3) 700

50 % of bounding structures of ordinary concrete and 50 % lightweight concrete 1 500

Ordinary plasterboard 750

Vermiculite plaster 650

Bounded with 33 % lightweight concrete and 67 % plasterboard (2 ×13 mm thick) stud partition

1 000

50 % bounding structures of lightweight concrete, 33 % ordinary concrete and 17 of plasterboard (13 mm thick) on blockwork

1 200

80 % bounding surfaces of sheet steel and 20 % ordinary concrete 2 000

20 % bounding surfaces ordinary concrete and 80 % double plasterboard (2 ×13 mm thick) stud partition

1 320

Wood 450

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List of references (see clause 2)

Normative references

BSI publicationsBRITISH STANDARDS INSTITUTION, London

BS 5306, Fire extinguishing installations and equipment on premises. BS 5306-2:1990, Specification for sprinkler systems.

Informative references

BSI publicationsBRITISH STANDARDS INSTITUTION, London

BS 4422, Glossary of terms associated with fire. BS 4422-1:1987, General terms and phenomena of fire. BS 4422-2:1990, Glossary of terms associated with fire — Structural fire protection. ISO publicationsInternational Organization for Standardization (ISO), Geneva. (All publications are available from BSI Sales.)

ISO 3938:1987, Bases for design of structures — Notations — General symbols. ISO 1716:1973, Building materials — Determination of calorific potential.

Other publications

DoE/WELSH OFFICE. The Building Regulations 1991, Approved Document B, Fire Safety; 1992 Edition.London: HMSO.NORTHERN IRELAND. The Building Regulations (Northern Ireland) 1990. SRNI 1990. No. 59. Belfast: HMSO. CONSIEL INTERNATIONAL DU BATIMENT (CIB). A conceptual approach towards a probability based design guide on structural fire safety. Report of a CIB W14 Workshop. Structural Fire safety. January 1983, published in Fire Safety Journal; No. 1, Vol 6. Elsevier. 1983, ISSN 0379-7112CONSIEL INTERNATIONAL DU BATIMENT (CIB). Design guide — Structural fire safety, published in Fire Safety Journal. No. 1, Vol 9. pp 77–136. Elsevier, 1986.EUROPEAN COMMISSION, Council Directive (89/106/EEC), The Approximation of laws, regulations and administrative provisions of the Member States relating to construction products. 21st December 1988. Official Journal of the European Communities, Vol 32. 1989. ISSN 03786978.LAW M. and O’BRIEN T., Fire safety of bare external steel, Constrado, 1981.

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EUROPEAN PRESTANDARD

PRÉNORME EUROPÉENNE

EUROPÄISCHE VORNORM

ENV 1991-2-2:1995

February 1995

ICS 91.040.00

Descriptors: Buildings, structures, design, computation, fire resistance

English version

Eurocode 1 — Basis of design and actions on structures — Part 2-2: Actions on structures — Actions on structures

exposed to fire

Eurocode 1 — Bases du calcul et actions sur les structures — Partie 2-2: Actions sur les structures — Actions sur les structures exposées au feu

Eurocode 1 — Grundlagen der Tragwerksplanung und Einwirkungen auf Tragwerke — Teil 2-2: Einwirkungen auf Tragwerke — Einwirkungen im Brandfall

This European Prestandard (ENV) was approved by CEN on 1993-06-30 as aprospective standard for provisional application. The period of validity of thisENV is limited initially to three years. After two years the members of CENwill be requested to submit their comments, particularly on the questionwhether the ENV can be converted into an European Standard (EN).CEN members are required to announce the existence of this ENV in the sameway as for an EN and to make the ENV available promptly at national level inan appropriate form. It is permissible to keep conflicting national standards inforce (in parallel to the ENV) until the final decision about the possibleconversion of the ENV into an EN is reached.CEN members are the national standards bodies of Austria, Belgium,Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy,Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland andUnited Kingdom.

CEN

European Committee for StandardizationComité Européen de NormalisationEuropäisches Komitee für Normung

Central Secretariat: rue de Stassart 36, B-1050 Brussels

© 1995 All rights of reproduction and communication in any form and by any means reserved in all countries to CEN and its members

Ref. No. ENV 1991-2-2:1995 E

ENV 1991-2-2:1995

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Foreword

Objectives of the Eurocodes

(1) The “Structural Eurocodes” comprise a group of standards for the structural and geotechnical design of buildings and Civil engineering works.(2) They cover execution and control only to the extent that is necessary to indicate the quality of the construction products, and the standard of the workmanship, needed to comply with the assumptions of the design rules.(3) Until the necessary set of harmonised technical specifications for products and for methods of testing their performance are available, some of the Structural Eurocodes cover some of these aspects in informative annexes.

Background to the Eurocode programme

(4) The Commission of the European Communities (CEC) initiated the work of establishing a set of harmonized technical rules for the design of building and civil engineering works which would initially serve as an alternative to the different rules in force in the various member states and would ultimately replace them. These technical rules became known as the “Structural Eurocodes”.(5) In 1990, after consulting their respective member states, the CEC transferred the work of further development, issue and updating of the Structural Eurocodes to CEN, and the EFTA Secretariat agreed to support the CEN work.(6) CEN Technical Committee CEN/TC250 is responsible for all Structural Eurocodes.

Eurocode programme

(7) Work is in hand on the following Structural Eurocodes, each generally consisting of a number of parts:

EN 1991, Eurocode 1: Basis of design and actions on structures.EN 1992, Eurocode 2: Design of concrete structures.EN 1993, Eurocode 3: Design of steel structures.EN 1994, Eurocode 4: Design of composite steel and concrete structures.EN 1995, Eurocode 5: Design of timber structures.EN 1996, Eurocode 6: Design of masonry structures.EN 1997, Eurocode 7: Geotechnical design.

EN 1998, Eurocode 8: Design of structures for earthquake resistance.EN 1999, Eurocode 9: Design of aluminium alloy structures.

(8) Separate Sub-Committees have been formed by CEN/TC250 for the various Eurocodes listed above.(9) This Part of Eurocode 1 is being published as a European Prestandard (ENV) with an initial life of three years.(10) This Prestandard is intended for experimental application and for the submission of comments.(11) After approximately two years CEN members will be invited to submit formal comments to be taken into account in determining future actions.(12) Meanwhile feedback and comments on this Prestandard should be sent to the Secretariat of CEN/TC250/SC1 at the following address:

or to your National Standards Organization.

National Application Documents (NAD’s)

(13) In view of the responsibilities of authorities in member countries for safety, health and other matters covered by the essential requirements of the Construction Products Directive (CPD), certain safety elements in this ENV have been assigned indicative values which are identified by (“boxed values”). The authorities in each member country are expected to review the “boxed values” and may substitute alternative definitive values for these safety elements for use in national application.(14) Some of the supporting European or International Standards may not be available by the time this Prestandard is issued. It is therefore anticipated that a National Application Document (NAD) giving any substitute definitive values for safety elements, referencing compatible supporting standards and providing guidance on the national application of this Prestandard, will be issued by each member country or its Standards Organization.(15) It is intended that this Prestandard is used in conjunction with the NAD valid in the country where the building or civil engineering works is located.

until end May 1995: from June 1995:SNV/SIA SIS/BSTSelnaustrasse 16 Box 5630Postfach S- 114 86 StockholmCH-8039 ZURICH SWEDENSWITZERLAND

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Matters specific to this Prestandard

(16) The scope of Eurocode 1 is defined in clause 1.1.1 and the scope of this Part of Eurocode 1 is defined in 1.1.2. Additional Parts of Eurocode 1 which are planned are indicated in clause 1.1.3.(17) This Part is complemented by a number of annexes, some normative and some informative. The normative annexes have the same status as the sections to which they relate.(18) The general objectives of fire protection are to limit risks with respect to the individual and society, neighbouring property, and where required, directly exposed property, in the case of fire.(19) 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 capacity 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”.

(20) According to the Interpretative Document “Safety in Case of Fire” the essential requirement may be observed by following various fire safety strategies, including passive and active fire protection measures.

(21) The Structural Eurocodes deal with specific aspects of passive fire protection in terms of designing structures and parts thereof for adequate load-bearing capacity and for limiting fire spread as relevant.(22) Required functions and levels of performance are generally specified by the national authorities — mostly in terms of standard fire resistance rating. Where fire safety engineering for assessing passive and active measures is accepted, requirements by authorities will be less prescriptive and may allow for alternative strategies.(23) It is recognized, however, that fire safety engineering calls for more general fire models than included in this document. Such fire models may be given in future supplements, which will be prepared after prenormative research is completed.(24) On the other hand it is also recognized, that the acceptance of fire models by national authorities differs throughout Europe and that present national regulations may only allow for a design for standard fire resistance requirements.(25) Therefore this document mainly covers thermal actions arising from the standard temperature-time curve and other nominal temperature-time curves. Physically based (parametric) thermal actions are only dealt with where simplified analytical models or direct design data are available; they are given in informative annexes. The field of application for the various thermal actions and design procedures, including national supplements, will be specified by the national authorities.(26) Application of the thermal actions according to this Part and the design of structures according to the fire design Parts of ENV 1992 to 1996 and ENV 1999 is illustrated in Table 1.

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Table 1 — Design procedures

Thermal actionsaccording to national specifications:

design by prescriptive rules/tabulated data

design by calculation models

given in ENV 1991,Part 2.2: for verifying given in ENV 1992–1996,

1999given in ENV 1992–1996, 1999

standard temperature-time curve

standard fire resistance requirements

as relevanta as relevanta

or from fire resistance tests

other nominal temperature-time curves

other nominal fire resistance requirements

mainly from fire resistance tests

as relevanta

standard temperature-time curve

fire resistance— for equivalent time of fire exposure

as relevanta as relevanta

parametric fire exposure

fire resistance— for specified period of time or— for entire fire duration

not applicable as relevanta

a depending on the extent to which prescriptive rules and calculation models are given in the respective fire Parts and the relevant scope of application

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Contents

PageForeword 2Objectives of the Eurocodes 2Background to the Eurocode programme 2Eurocode programme 2National Application Documents (NAD’s) 2Matters specific to this Prestandard 3Section 1. General1.1 Scope 71.1.1 Scope of ENV 1991 — Eurocode 1 71.1.2 Scope of ENV 1991-2-2 Actions on

structures exposed to fire 71.1.3 Further Parts of ENV 1991 71.2 Normative references 71.3 Distinction between principles and

application rules 81.4 Definitions 81.5 Notations 10Section 2. Design procedure and classification of actions 12Section 3. Fire design situations3.1 Accidental situations 133.2 Design fire 133.3 Exposure to fire 133.4 Post-fire situations 13Section 4. Actions for temperature analysis(thermal actions)4.1 General rules 144.2 Nominal temperature-time curves 144.2.1 General 144.2.2 Standard temperature-time curve 154.2.3 External fire curve 154.2.4 Hydrocarbon curve 154.3 Parametric fire exposure 15Section 5. Actions for structural analysis (mechanical actions) 16Annex A (informative) Parametric fire exposure 17Annex B (informative) Parametric temperature-time curves 17Annex C (informative) Thermal actions for external members — simplified calculationmethod 18Annex D (informative) Fire load densities 26Annex E (informative) Equivalent time of fire exposure 29

PageAnnex F (normative) Basis of design — supplementary clauses to ENV 1991-1 for the structural analysis in fire design situations 30Figure C.1 — Deflection of flame by wind 21Figure C.2 — Flame dimensions, no throughdraught 21Figure C.3 — Deflection of flame by balcony 23Figure C.4 — Flame dimensions, through or forced draught 24Figure C.5 — Deflection of flame by awning 25Table 1 — Design procedures 4Table D.1 — Net calorific value Hu of combustible materials 28Table D.2 — Format for fire load classification of occupancies 29Table E.1 — Conversion factor kb depending on the thermal properties of the enclosure 30

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Section 1. General

1.1 Scope1.1.1 Scope of ENV 1991 — Eurocode 1

(1) P ENV 1991 provides general principles and actions for the structural design of buildings and civil engineering works including some geotechnical aspects and shall be used in conjunction with ENV 1992-1999.(2) It may also be used as a basis for the design of structures not covered in ENV 1992-1999 and where other materials or other structural design actions are involved.(3) ENV 1991 also covers structural design during execution and structural design for temporary structures. It relates to all circumstances in which a structure is required to give adequate performance.(4) ENV 1991 is not directly intended for the structural appraisal of existing construction, in developing the design of repairs and alterations or, for assessing changes of use.(5) ENV 1991 does not completely cover special design situations which require unusual reliability considerations such as nuclear structures for which specified design procedures should be used.

1.1.2 Scope of ENV 1991-2-2 Actions on structures exposed to fire

(1)P This Part is concerned with actions on structures exposed to fire. It is intended for use in conjunction with the fire design Parts of ENV 1992 to 1996 and ENV 1999 which give rules for designing structures for fire resistance.(2) Thermal actions given in the main text of this document are mainly confined to nominal thermal actions. Some data and models for physically based thermal actions are given in informative annexes.(3)P This Part provides general principles and actions for the structural design of buildings and civil engineering works and shall be used in conjunction with ENV 1991-1 “Basis of design”, other Parts of ENV 1991 and ENV 1992 to 1996 and ENV 1999.(4)P Application of this Part and the fire design Parts of ENV 1992 to 1996 and ENV 1999 is only valid, if the normal temperature design of structures is in accordance with the relevant Structural Eurocodes.(5) This Part also covers structural design for temporary structures relating to the subjects mentioned in 1.1.2 (1)P. It relates to all circumstances in which a structure is required to give adequate performance in fire exposure.

1.1.3 Further Parts of ENV 1991

(1) Further Parts of ENV 1991 which, at present, are being prepared or are planned are given in 1.2.

1.2 Normative referencesThis European Prestandard incorporates by dated or undated reference, provisions from other standards. These normative references are cited in the appropriate places in the text and publications listed hereafter.ISO 3898:1987, Basis of design for structures — Notations. General symbols.. NOTE The following European Prestandards which are published or in preparation are cited at the appropriate places in the text and publications listed hereafter.ENV 1991-1, Eurocode 1: Basis of design and actions on structures — Part 1: Basis of design. ENV 1991-2-1, Eurocode 1: Basis of design and actions on structures — Part 2.1: Densities, self-weight and imposed loads. ENV 1991-2-3, Eurocode 1: Basis of design and actions on structures — Part 2.3: Snow loads. ENV 1991-2-4, Eurocode 1: Basis of design and actions on structures — Part 2.4: Wind loads. ENV 1991-2-5, Eurocode 1: Basis of design and actions on structures — Part 2.5: Thermal actions. ENV 1991-2-6, Eurocode 1: Basis of design and actions on structures — Part 2.6: Loads and deformations imposed during execution. ENV 1991-2-7, Eurocode 1: Basis of design and actions on structures — Part 2.7: Accidental actions. ENV 1991-3, Eurocode 1: Basis of design and actions on structures — Part 3: Traffic loads on bridges. ENV 1991-4, Eurocode 1: Basis of design and actions on structures — Part 4: Actions in silos and tanks. ENV 1991-5, Eurocode 1: Basis of design and actions on structures — Part 5: Actions induced by cranes and machinery. ENV 1992, Eurocode 2: Design of concrete structures.

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ENV 1993, Eurocode 3: Design of steel structures. ENV 1994, Eurocode 4: Design of composite steel and concrete structures. ENV 1995, Eurocode 5: Design of timber structures. ENV 1996, Eurocode 6: Design of masonry structures. ENV 1997, Eurocode 7: Geotechnical design. ENV 1998, Eurocode 8: Earthquake resistant design of structures. ENV 1999, Eurocode 9: Design of aluminium alloy structures.

1.3 Distinction between principles and application rules(1) Depending on the character of the individual clauses, distinction is made in this Part 2.2 of ENV 1991 between principles and application rules.(2) The principles comprise:

— general statements and definitions for which there is no alternative, as well as— requirements and analytical models for which no alternative is permitted unless specifically stated.

(3) The principles are preceded by the letter P.(4) The application rules are generally recognized rules which follow the principles and satisfy their requirements.(5) It is permissible to use alternative rules different from the application rules given in this Eurocode, provided it is shown that the alternative rules accord with the relevant principles and have at least the same reliability.(6) In this Part 2.2 of ENV 1991 the application rules are identified by a number in brackets, e.g. as this clause.

1.4 DefinitionsFor the purposes of this Prestandard, a basic list of definitions is provided in ENV 1991-1, “Basis of design” and the additional definitions given below are specific to this Part.

1.4.1 configuration factor 9 [–]

ratio between the solid angle by which, from a certain point of the member surface the radiating environment can be seen, and 2 ;

1.4.2 convective heat transfer coefficient !c [W/m2·K]

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

1.4.3 design fire

a specified fire development assumed for design purposes

1.4.4 design fire load density qd [MJ/m2]

the fire load density considered for determining thermal actions in fire design; the value of qd makes allowance for uncertainties and safety requirements

1.4.5 effects of actions E

moments, forces, stresses, deformations (as compared to action effects S: Only forces and moments.)

1.4.6 external fire curve

a 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

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1.4.7 external member

structural members located outside the building enclosure which may be exposed to fire through openings in the building enclosure

1.4.8 fire compartment

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

1.4.9 fire load Q [MJ]

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

1.4.10 fire load density q [MJ/m2]

the fire load per unit area,related to the floor area: qf

related to the surface area of the total enclosure, including openings: qt

1.4.11 fire resistance

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

1.4.12 fire wall

a wall separating two spaces (generally two buildings) which is designed for fire resistance and structural stability, including 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

1.4.13 fully developed fire

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

1.4.14 hydrocarbon fire curve

a nominal temperature-time curve for representing hydrocarbon type fire loads

1.4.15 indirect fire actions

thermal expansions, thermal deformations or thermal gradients causing forces and moments

1.4.16 load bearing function

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

1.4.17 net heat flux hnet [W/m2]

energy per unit time and surface area absorbed by members

1.4.18 normal temperature design

ultimate limit state design for ambient temperatures according to Part 1.1 of ENV 1992 to 1996 and ENV 1999 for the fundamental combination (see Part 1 “Basis of design” of ENV 1991)

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1.4.19 resultant emissivity ¼ [–]

the ratio between the actual radiative heat flux to the member and the net heat flux that would occur if the member and its radiative environment are considered as black bodies

1.4.20 separating function

the ability of a separating member to prevent fire spread by passage of flames or hot gases (integrity) or ignition beyond the exposed surface (thermal insulation) during the relevant fire exposure

1.4.21 separating members

structural and non-structural members (walls or floors) forming the enclosure of a fire compartment

1.4.22 standard fire resistance

the ability of a structure or part of it (usually only members) to fulfill required functions (loadbearing function, and/or separating function), for the standard fire exposure — for a stated period of time. Normally, standard fire resistance requirements are expressed in terms of periods of time such as 30, 60 or more minutes

1.4.23 standard temperature-time curve

a nominal curve for representing mainly cellulosic type fire loads

1.4.24 structural members

the load-bearing members of a structure, including bracings

1.4.25 temperature analysis

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

1.4.26 temperature-time curves

gas temperatures in the environment of member surfaces as a function of time. They may be— nominal, in terms of conventional curves, adopted for classification and verification of fire resistance, e.g. the standard temperature-time curve;— parametric, determined on the basis of fire models and the specific physical parameters defining the conditions in the fire compartment.

1.4.27 thermal actions

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

1.5 Notations(1) For the purpose of this Prestandard, the following symbols apply.NOTE The notations used are based on ISO 3898:1987.

(2) A basic list of notations is provided in ENV 1991-1 “Basis of design” and the additional notations below are specific to this Part.Latin upper case letters

A action from fire exposureAind indirect fire actionE effect of actionsG permanent actionQ variable action

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Latin lower case letters

Rfi load bearing resistance, relevant in fire exposure

h heat flux to unit surface area [W/m2]tfi standard fire resistance (property of the member or structure) [min.]tfi,requ required standard fire resistance time (nominal value) [min.]

Greek upper case letters9 configuration factor [–]G temperature [°C]; G [°C] = T [K] – 273Gcr critical temperature [°C], relevant for steelGr radiation temperature of the environment of the member [°C]Gg gas temperature in fire exposure [°C]Gm surface temperature of the member [°C]Go initial gas temperature [°C]

Greek lower case lettersµ coefficient of heat transfer [W/m2°K]¼res resultant emissivity [–]? load combination coefficients [–]¾ partial safety factor [–]

Indicesc convective component of heat transfercr critical valuefi identifies values relevant for fire designd design valuek characteristic valuer radiative component of heat transfert duration of fire exposure

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Section 2. Design procedure and classification of actions(1)P Structural fire design involves applying actions for temperature analysis and actions for structural analysis according to this Part and other Parts of ENV 1991, to structures which are designed using the rules given in the fire design Parts of ENV 1992 to 1996 and ENV 1999.(2) Depending on the representation of the thermal actions in design, the following procedures are distinguished:

— nominal temperature-time curves which are applied for a specified period of time, and for which structures are designed by observing prescriptive rules, including tabulated data, or by using calculation models;— parametric temperature-time curves, which are calculated on the basis of physical parameters and for which structures are designed by using calculation models.

(3) Verification may be in the time domain:

or in the strength domain:

or in the temperature domain:

where:

(4)P Actions on structures from fire exposure are classified as accidental actions, see ENV 1991-1.

tfi,d U tfi,requ (2.1)

Rfi,d,t U Efi,d,t (2.2)

Gd k Gcr,d (2.3)

tfi,d design value of the standard fire resistance

tfi,requ required standard fire resistance time

Rfi,d,t design value of the load bearing resistance for the fire situation

Efi,d,t design value of the relevant effects of actions for the fire situation

Gd design value of material temperature

Gcr,d design value of the critical material temperature

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Section 3. Fire design situations

NOTE For structures, where the national authorities comprehensively specify structural fire safety requirements, it may be assumed in the design that the relevant fire design situations are accounted for by the requirements.

3.1 Accidental situations(1)P The occurrence of fires, severe enough to cause structural damage, shall be considered as an accidental situation.(2) The relevant design situations and the associated accidental actions of fire should be determined on the basis of a fire risk assessment.(3) Simultaneous occurrence with other independent accidental actions need not be considered.(4) For structures where particular risks of fire arise in the wake of other accidental actions, this risk should be considered when determining the overall safety concept.(5) Time- and load-dependent structural behaviour prior to the accidental situation need not be considered, unless (4) applies.

3.2 Design fire(1)P Fire compartments shall be designed to prevent fire spread to other fire compartments during the relevant fire exposure.(2)P The design fire shall be applied only to one fire compartment of the building at a time.(3) The design fire should represent a fully developed fire within a specified space.

3.3 Exposure to fire(1)P When determining the fire exposure of a member, the position of the design fire in relation to the member shall be taken into account.(2) For verifying the separating function, fire exposure only from one side at a time needs to be applied.(3) For external members, fire exposure through facades or roofs should be considered.(4) For separating external walls fire exposure from inside (from the respective fire compartment) and alternatively from outside (from other fire compartments) should be considered.

3.4 Post-fire situations(1) Post-fire situations after the structure has cooled down need not be considered in design.(2) When designing for a required fire resistance period, the performance of the structure beyond this period need not be considered.

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Section 4. Actions for temperature analysis (thermal actions)4.1 General rules(1)P Thermal actions are given by the net heat flux net [W/m2] to the surface of the member.(2)P The net heat flux hnet shall be determined by considering thermal radiation and convection from and to the fire environment.(3) The radiative heat flux component per unit surface area is determined by:

where:

(4) Where the fire design Parts of ENV 1992 to 1996 and ENV 1999 give no specific data, the configuration factor should be taken as 9 = [1,0].(5) For the resultant emissivity ¼res relevant for nominal temperature-time curves, see 4.2.(6) The radiation temperature Gr may be represented by the gas temperature Gg, see 4.1 (11).(7) The surface temperature Gm results from the temperature analysis of the member according to the fire design Parts of ENV 1992 to 1996 and 1999, as relevant.(8) The convective heat flux component per unit surface area should be determined by:

where:

(9) For the coefficient of heat transfer by convection !c relevant for nominal temperature-time curves, see 4.2.(10) On the unexposed side of separating members, heat flow due to radiation may be neglected and for convection !c = [9] [W/m2°K] may be adopted.(11) Gas temperatures Gg may be:

— adopted as nominal temperature-time curves, see 4.2;— specified in terms of physical parameters, see 4.3.

4.2 Nominal temperature-time curves4.2.1 General

(1) The nominal temperature-time curves given in 4.2.2 to 4.2.4 should be used in accordance with the relevant national field of application.(2) For design to nominal temperature-time curves the net heat flux due to convection and radiation is:

where:

net,r = 9·¼res·5,67·10–8 · [(Gr + 273)4 – (Gm + 273)4] [W/m2] (4.1)

9 configuration factor [–]

¼res resultant emissivity [–]

Gr radiation temperature of the environment of the member [°C]

Gm surface temperature of the member [°C]

5,67 · 10– 8 Stefan Boltzmann constant [W/m2°K4]

net,c = µc·(Gg – Gm) [W/m2] (4.2)

!c coefficient of heat transfer by convection [W/m2°K]

Gg gas temperature of the environment of the member in fire exposure [°C]

Gm surface temperature of the member [°C]

net,d = ¾n,c · net,c + ¾n,r · net,r [W/m2] (4.3)

net,cis given by equ. (4.2)

net,ris given by equ. (4.1)

¾n,c factor to account for different national types of test and equals [1,0]

¾n,r is equal to [1,0] as ¾n,c

h·

h·

h·

h· h· h·

h·

h·

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(3) The resultant emissivity should be introduced as:

where:

4.2.2 Standard temperature-time curve

(1) The standard temperature-time curve is given by:

where:

(2) The coefficient of heat transfer by convection is:

!c = [25] W/m2°K

4.2.3 External fire curve

(1) The external fire curve is given by:

where:

(2) The coefficient of heat transfer by convection is:

!c = [25] W/m2°K

4.2.4 Hydrocarbon curve

(1) The hydrocarbon temperature-time curve is given by:

where:

!c = [50] W/m2°K

4.3 Parametric fire exposure(1) Parametric fire exposures and related data are given in informative annexes to this document for use in accordance with the national field of application.

¼res = ¼f · ¼m [–] (4.4)

¼f emissivity related to fire compartment, usually taken as [0,8]

¼m emissivity related to surface material; where the fire design Parts of ENV 1992 to 1996 and ENV 1999 give no specific data, ¼m should be used as [0,7]

Gg = 20 + 345 log 10(8t + 1) [°C] (4.5)

Gg gas temperature in the fire compartment [°C]

t time [min]

Gg = 660 (1-0,687 e–0,32t – 0,313 e–3,8t) + 20 [°C] (4.6)

Gg gas temperature in the environment of the member

[°C]

t time [min]

Gg = 1 080 (1-0, 325 e–0,167t – 0,675 e–2,5t) + 20 [°C] (4.7)

Gg gas temperature in the fire compartment [°C]

t time [min]

(2) The coefficient of heat transfer by convection is: (4.8)

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Section 5. Actions for structural analysis (mechanical actions)(1) For direct actions, the simultaneity of actions and the combination rules see Annex F.(2)P Imposed and constrained expansions and deformations caused by temperature changes due to fire exposure result in forces and moments, which shall be considered apart from those cases where they:

— may be recognized a priori to be either negligible or favourable;— are accounted for by conservative support and boundary conditions and/or conservatively specified fire safety requirements.

(3) For an assessment of indirect actions the following should be considered:— constrained thermal expansion of the members themselves, e.g. columns in multi-storey frame structures with stiff walls;— differing thermal expansion within statically indeterminate members, e.g. continuous floor slabs;— thermal gradients within cross-sections giving internal stresses;— thermal expansion of adjacent members,e.g. displacement of column head due to the expanding floor slab, or expansion of suspended cables;— thermal expansion of members affecting members outside the fire compartment.

(4) Design values for indirect actions Ad,ind should be determined on the basis of the design values of the thermal and mechanical material properties given in the fire design Parts of ENV 1992 to 1996 and ENV 1999 and the relevant fire exposure.(5) Indirect actions from adjacent members need not be considered when fire safety requirements refer to members.

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Annex A (informative) Parametric fire exposure

A.1 General(1) Gas temperatures for calculating the net heat flux should be determined on the basis of physical parameters considering at least:

— the fire load density;— ventilation conditions.

A.2 Fire models(1) Calculations should be based on the assumption that the relevant fire load is burnt out — except where national specifications allow for limited periods of fire resistance in parametric exposure.(2) For fire compartments with approved extinguishing systems — for which structural fire design is nevertheless required — the design fire load density may be adapted according to Annex D, D.1.(3) With reference to 4.1 of the main text the following applies:

— 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;— For internal members only the contribution of the fire compartment to the radiative heat flux needs to be considered.

(4) For internal members of fire compartments, gas temperatures may be calculated in accordance with Annex B.(5) For external members exposed to fire from openings in the facade, Annex C may be used.(6) Where internal members are designed according to prescriptive rules or tabulated data for the standard temperature-time curve, an equivalent time of fire exposure may be used, see Annex E.

Annex B (informative) Parametric temperature-time curves(1) The following temperature-time curves may be used in accordance with the national field of application. They are valid for fire compartments up to 100 m2 of floor area, without openings in the roof and for a maximum compartment height of 4 m.(2) If fire load densities are specified without specific consideration to the combustion behaviour (see Annex D), 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:

where:

Gg = 1 325 (1 – 0,324 e–0,2t* – 0,204 e–1,7t* – 0,472 e–19t*) (B.1)

Gg temperature in the fire compartment [°C]

t* = t·+ with [h]t time [h]+ = [O/b]2/(0,04/1160)2 [–]

where b = should observe the limits: 1 000 k b k 2 000 [J/m2s1/2K]O opening factor: Av /At with the following limits: 0,02 k O k 0,20 [m1/2]Av area of vertical openings [m2]h height of vertical openings [m]At total area of enclosure (walls, ceiling and floor, including openings) [m2]@ density of boundary of enclosure [kg/m3]c specific heat of boundary of enclosure [J/kgK]2 thermal conductivity of boundary of enclosure [W/mK]

@c2( )

h

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(4) To account for enclosures with different layers of material b = should be introduced as:

where:

(5) To account for different materials in walls, ceiling and floor b = should be introduced as:

where:

(6) The temperature-time curves in the cooling phase are given by:

where:

(7) The resultant emissivity ¼res and the coefficient of heat transfer by convection !c should be in accordance with 4.2.1 and 4.2.2 of the main text.

Annex C (informative) Thermal actions for external members — simplified calculation methodC.1 Scope(1) This method allows the determination of:

— the maximum temperatures of a compartment fire;— the size and temperatures of flame from openings;— radiation and convection parameters.

(2) This method considers steady-state conditions for the various parameters.C.2 Symbols and units

(B.2)

si thickness of layer i

ci specific heat of layer i

2i thermal conductivity of layer i

bi =

b = CbjAtj/CAtj (B.3)

Atj area of enclosure including openings with the thermal property bj

Gg = Gmax – 625 (t* – td*) for td* k 0,5 (B.4)

Gg = Gmax – 250 (3 – td*)(t* – td*) for 0,5 < td* < 2 (B.5)

Gg = Gmax – 250 (t* – td*) for td* U 2 (B.6)

Gmax maximum temperature in the heating phase [°C] for t* = td*

td* = (0,13 · 10–3 qt,d · +)/O [h]

qt,d design value of the fire load density related to the surface area At of the enclosure whereby qt,d = qf,d·Af/At [MJ/m2] the following limits should be observed: 50 k qt,d k 1 000 [MJ/m2]

qf,d design value of the fire load density related to the surface area Af of the floor [MJ/m2]

AF floor area of the fire compartment [m2]

AT total area of floor, ceiling and wall, minus total area of the window [m2]

Aw sum of window area on all walls (Aw = Awi) [m2]

Awi area of window “i” [m2]

d geometrical characteristic of an external structural element (diameter or side) [m]

@c2( )

@ici2i( )

@c2( )

Ci

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C.3 Conditions of use(1) When there is more than one window, the average height, the window area, and the width are given in the relevant fire compartment as follows:

— The weighted average of window heights on all walls:

D depth of the fire compartment [m]

g acceleration due to gravity [m/s2]

h weighted average of window heights on all walls [m]

ha horizontal projection of an awning [m]

hi height of window “i” [m]

l axis length from window to the point where the calculation is made [m]

L fire load (= AF.Q) [kg of wood]

Q fire load density per floor area [kg of wood/m2]

R rate of burning [kg of wood/s]

Ta initial temperature (= 293) [K]

Tf fire temperature [K]

To flame temperature at the window [K]

Tz flame temperature along the axis [K]

u wind speed [m/s]

w sum of window widths on all walls (w = Cwi) [m]

wi width of window “i” [m]

wz width of the flame [m]

W width of wall containing window(s) [m]

x horizontal project of flame (from the facade) [m]

X flame length along axis [m]

z flame height (from the upper part of the window) [m]

Aw h1/2/AT opening factor of the fire compartment [m1/2]

! convective heat transfer coefficient [kW/m2K]

¼ emissivity of flame

@ gas density (assumed to be 0,45) [kg/m3]

2 flame thickness [m]

) AT/Aw h1/2 [m–1/2]

? L/(Aw.AT)1/2 [kg/m2]

EF free burning fire duration (assumed to be 1 200) [s]

(C.1)

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— The sum of window areas on all walls:

— The sum of window widths on all walls:

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

where

(3) When there is a core in the fire compartment, the ratio D/W has to be obtained as follows:— Definition given in C.3 (6) applies;— C1 and C2 are the length and width of the core;— W1 and W2 are the length and width of the fire compartment:

(4) In an external wall, the window is all the part of this wall not having the fire resistance (REI) required for the stability of the building.(5) The total area of the window in an external wall is:

— the total area, according to (4), if it is less than 50 % of the area of the relevant external wall of the compartment;— firstly the total area and secondly 50 % of the area of the relevant external wall of the compartment if, according to (4), the area is more than 50 %. These two situations have to be considered for calculation. When using 50 % of the area of the external wall, the location and geometry of the open surfaces have to be chosen to lead to the worst case.

(6) The size of the fire compartment should not exceed 70 m in length, 18 m in width and 5 m in height.(7) The flame temperature has to be taken as uniform across the width and the thickness of the flame.C.4 Effects of windC.4.1 Mode of ventilation(1) 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 must be done with forced draught conditions. Otherwise, the calculation is done with no forced draught conditions.

Aw = Awi (C.2)

w = wi (C.3)

(C.4)

W1 width of the wall 1, assumed to contain the greatest window area;

Aw1 sum of window areas on wall 1;

W2 width of the wall of the fire compartment, perpendicular to wall 1.

(C.5)

Ci

Ci

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C.4.2 Flame deflection by wind

(1) Flame from an opening has to be assumed to be leaving the compartment fire (Figure C.1):— perpendicular to the facade;— with a deflection, due to the wind effect, of + 45° and – 45° with the facade.

C.5 Characteristics of fire and flameC.5.1 No forced draught

Figure C.1 — Deflection of flame by wind

Figure C.2 — Flame dimensions, no through draught

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(1) Rate of burning:

(2) Temperature of the compartment fire:

(3) Flame height (Figure C.2):

Comment:With Ô = 0,45 kg/m3 and g = 9,81 m/s2, this equation may be simplified to give:

(4) Flame width is the window width (Figure C.2)(5) Flame depth is 2/3 of the window height: 2/3 h (Figure C.2)(6) Horizontal projection of flame:

— If wall above the window:

— If no wall above the window:

(7) Flame length along axis:

(8) Flame temperature at the window:

(9) Emissivity at the window: 1,0(10) Flame temperature along the axis:

where:I axis length from window to the point where the calculation is made

(C.6)

(C.7)

(C.8)

(C.9)

w for h k 1,25 w: x = h/3 (C.10)

w for h > 1,25 w and distance to any other window > 4 w:

x = 0,3 h (h/w)0,54 (C.11)

w other cases: x = 0,454 h (h/2w)0,54 (C.12)

x = 0,6 h (z/h)1/3 (C.13)

— Wall above h k 1,25 w: X = z + h/2 (C.14)

— No wall above or h > 1,25 w:

X = (z2 + (x – h/3)2)1/2 + h/2 (C.15)

To = 520/(1 – 0,027 (X·w/R)) + Ta [K] (C.16)

Tz = (To – Ta) (1 – 0,027 (I · w/R)) + Ta [K] (C.17)

z 12 8 Rw----

2/3– h,=

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(11) Emissivity of flame:

(12) Convective heat transfer coefficient:

(13) If an awning or balcony (with horizontal projection: ha) is located at the level of the top of the window on its whole width, for the wall above the window and h k 1,25 w, the height and horizontal projection of the flame should be modified as follows:

— the flame height z given in (3) is decreased by ;— the horizontal projection of the flame x given in (6), is increased by ha.

(14) With the same conditions for awning or balcony as mentioned in (13), in the case of no wall above the window or h > 1,25 w, the height and horizontal projection of the flame should be modified as follows:

— the flame height z given in (3) is decreased by ha;— the horizontal projection of the flame x, obtained in (6) with the above mentioned value of z is increased by ha.

¼ = 1 – e–0,32 (C.18)

! = 0,026 (1/d)0,4 (R/Aw)0,6 (C.19)

Figure C.3 — Deflection of flame by balcony

ha 2

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C.5.2 Forced draught

(1) Rate of burning:

(2) Temperature of the compartment fire:

(3) Flame height:

Comment:

(4) Horizontal projection of flame:

Comment:

(5) Flame width:

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

R = L/EF (C.20)

Tf = 1 200 (L – e–0,04?) + Ta(C.21)

(C.22)

With u = 6 m/s, z = 11 R/Aw1/2 – h

x = 0,605 (u2/h)0,22 (z + h) (C.23)

with u = 6 m/s, x = 1,33 (z + h)/h0,22

wz = w + 0,4 x (C.24)

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(6) Flame length along axis:

(7) Flame temperature at the window:

(8) Emissivity at the window: 1(9) Flame temperature along the axis:

Where:l axis length from the window to the point where the calculation is made

(10) Emissivity of flame:

(11) Convective heat transfer coefficient:

Comment:

(12) Effect of balcony or awning: After being deflected horizontally by a balcony or awning, the flame trajectory is the same as before, displaced outwards by the depth of the balcony, but the value of X is unchanged.

X = (z2 + x2)1/2 (C.25)

To = 520/(1 – 0,019 X(Aw)1/2/R) + Ta [K] (C.26)

[K] (C.27)

¼ = 1 – e–0,32 (C.28)

! = 0,0098 (1/d)0,4 (R/Aw + u/1,6)0,6 (C.29)

With u = 6 m/s, ! = 0,0098 (1/d)0,4 (R/Aw + 3,75)0,6

Figure C.5 — Deflection of flame by awning

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Annex D (informative) Fire load densitiesD.1 Values for calculation(1) The fire load density used in calculations should be a design value, based on measurements or in special cases a nominal value, based on fire resistance requirements of regulations.(2) The design value may be determined:

— from a national fire load classification of occupancies and/or,— specific for an individual project by performing a fire load survey.

(3) The design fire load density is defined as:

where:

D.2 Determination of fire load densitiesD.2.1 General(1) All combustible building contents and construction elements, including linings and finishings should be accounted for.(2) The following clauses of D.2 apply for the determination of fire load densities

— from a fire load classification of occupancies (see D.3) and/or— specific for an individual project (see D.4).

(3) Where fire load densities are determined from a fire load classification of occupancies, fire loads are distinguished as

— fire loads from the occupancy, given by the classification;— fire loads from the building (construction elements, linings and finishings) which are generally not included in the classification and are then determined according to the following clauses, as relevant.

D.2.2 Definitions(1) The characteristic fire load is defined as:

where:

(2) The characteristic fire load density qk per unit area is defined as:

where

qd = *q · *n · qk (D.1)

qk fire load density determined— from a fire load classification of occupancies and/or— for a specific project;

*q safety factor depending on the consequences of failure and frequency of fires, according to national specifications;

*n differentiation factor accounting for active fire protection measures (if not considered in the fire model) — according to national specifications; for approved fire extinguishing systems *n = [0,6] may be used.

Qfi,k = C Mk,i · Hui · mi · ?i = CQfi,k,i [MJ] (D.2)

Mk,i amount of combustible material [kg], according to (3) and (4)Hui net calorific value [MJ/kg], see (D.2.4)[mi] optional factor describing the combustion behaviour, see (D.2.5)[?i] optional factor for assessing protected fire loads, see (D.2.3)

qk = Qfi,k/A [MJ/m2] (D.3)

A floor area (Af) of the fire compartment or reference space, or inner surface area (Af) of the fire compartment, giving qf,k or qt,k

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(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.D.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 are associated with ?i = 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 ?i = 0,0.Otherwise, ?i-values need to be assessed individually.D.2.4 Net calorific values(1) Net calorific values should be determined according to ISO 1716.(2) The humidity of materials may be taken into account as follows:

where:

(3) Net calorific values of some solids, liquids and gases are given in Table D.1.

Hu = Huo (1 – 0,01 u) – 0,025 u [MJ/kg] (D.4)

u moisture content in % by weight

Huo net calorific value of dry materials

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Table D.1 — Net calorific value Hu of combustible materialssolids [MJ/kg] liquids [MJ/kg]

anthracite 34 gasoline 44asphalt 41 diesel oil 41bitumen 42 linseed oil 39celullose 17 methanol 20charcoal 35 paraffin oil 41clothes 19 spirits 29coal, coke 31 tar 38cork 29 benzene 40cotton 18 benzyl alcohol 33grain 17 ethyl alcohol 27grease 41 isopropyl alcohol 31kitchen refuse 18leather 19linoleum 20paper, cardboard 17paraffin wax 47foam rubber 37rubber isoprene 45rubber tire 32silk 19straw 16wood 19wool 23particle board 18

plastics [MJ/kg] gases [MJ/kg]

ABS 36 acetylen 48acrylic 28 butane 46celluloid 19 carbon monoxide 10epoxy 34 hydrogen 120melamin resin 18 propane 46phenolformaldehyde 29 methane 50polyester 31 ethanol 27polyester, fibre reinforced 21polyethylene 44polystyrene 40petroleum 41polyisocyanurate foam 24polycorbonate 29polypropylene 43polyurethane 23polyurethane foam 26polyvenylchloride 17ureaformaldehyde 15ureaformaldehyde foam 14

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D.2.5 Combustion behaviour(1) The combustion behaviour should be considered in accordance with national rules.(2) For mainly cellulosic materials, the combustion factor may be assumed conservatively as mi = 1,0.D.3 Fire load classification of occupancies(1) Subject to approval and supplement by the national authorities fire load densities should be assumed according to Table D.2 depending on the occupancy of the fire compartment. The fire load densities only cover fire loads from the occupancy and are related to the floor area.(2) Fire loads from the building should be determined according to D.2 to give the total fire load density.Table D.2 — Format for fire load

classification of occupancies

D.4 Individual assessment of fire load densities(1) In cases where national occupancy classes do not apply, fire load densities may be determined specific 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 in consultation with the client, 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.

Annex E (informative) Equivalent time of fire exposure(1) The following approach may be used in accordance with the national field of application. In contrast to Annex B this approach is intended for use where the design of members is by tabulated data or other simplified rules, related to the standard fire exposure.(2) If fire load densities are specified without specific consideration of the combustion behaviour (see Annex D), then this approach should be limited to fire compartments with mainly cellulosic type fire loads.(3) The equivalent time of fire exposure is defined by:

where:

(4) Where no detailed assessment of the thermal properties of the enclosure is pursued kb may be adopted as:

class qf,k [MJ/m2]

I 250

II 500

III 1 000

IV 1 500

V 2 000

te,d = qf,d kb·wf

= qt,d kb·wt [min] (E.1)

qd design fire load density according to Annex D

kb conversion factor according to (4)

w ventilation factor according to (5), whereby wt = wf At/Af

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

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otherwise kb may be related to the thermal property b = of the enclosure according to Table E.1. For determining b for multiple layers of material or different materials in walls, floor, ceiling, see Annex B (4) and (5).Table E.1 — Conversion factor kb depending on the

thermal properties of the enclosure

(5) The ventilation factor wf may be calculated as:

where:

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

where:O opening factor according to Annex B

(6) It shall be verified that:

where:

Annex F (normative) Basis of design — supplementary clauses to ENV 1991-1 for the structural analysis in fire design situationsF.1 General(1) In principle the general format given in ENV 1991-1 for design procedures is applicable.(2) This annex provides supplementary guidance applicable to structures exposed to fire regarding the simultaneity of actions and the combination rules.F.2 Simultaneity of actionsF.2.1 Actions from normal temperature design G, Q(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 situation of fire exposure, should be introduced in accordance with F.3.(3) Decrease of imposed loads due to combustion may not be taken into account.

b =[J/m2s1/2K]

kb[min · m2/MJ]

b > 2 500720 k b k 2 500b < 720

0,040,0550,07

wf = (6,0/H)0,3 [0,62 + 90(0,4 – !v)4/(1 + bv !h)] U 0,5 [–] (E.3)

!v = Av/Af area of vertical openings Av in the facade related to the floor area of the compartment where the limit

0,025 k !v k 0,25 should be observed

!h = Ah/Af area of horizontal openings Ah in the roof related to the floor area of the compartment

bv = 12,5 (1 + 10 !v – !v2) U 10,0

H height of the fire compartment [m]

wf = O–1/2 – Af/At (E.4)

te,d < tfi,d (E.5)

tfi,d design value of the standard fire resistance of the members, assessed according to the fire Parts of ENV 1992 to 1996 and ENV 1999

@c2( )

@c2( )

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(4) Cases where snow loads need not be considered, due to the melting of snow, should be assessed individually.(5) Loads resulting from industrial operations are generally not taken into account, e.g. horizontal forces from a braking crane.F.2.2 Additional actions(1) Depending on the accidental situations according to 3.1 to be considered in design, additional actions may need to be applied during fire exposure, e.g. impact due to collapse of structural elements or heavy machinery.NOTE Design values Ad are specified by the authority or in consultation with the client.

(2) For fire walls a horizontal impact may need to be considered. They should sustain horizontal impact with a design energy, Ad = 3 000 Nm.F.3 Combination rules for actionsF.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 ENV 1991-1 “Basis of design”, using the following accidental combination (given in symbolic form):

where:

F.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 actions combined according to F.3.1 for t = 0 only. These effects of actions may be applied as constant throughout fire exposure.(2) F.3.2 (1) 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 ENV 1992 to 1996 and ENV 1999.(3) As a further simplification to F.3.2 (1), effects of actions may be deduced from those determined in normal temperature design:

where:

(4) Relevant values for )fi are given in the fire design Parts of ENV 1992 to 1996 and ENV 1999.

C *GA·Gk + ?1,1·Qk,1 + C ?2,i·Qk,i + C Ad(t) (F.1)

Gk characteristic values of permanent actions

Qk,1 characteristic value of one (the main) variable action

Qk,i characteristic values of the other variable actions

Ad (t) design values of actions from fire exposure according to sections 4 and 5, as relevant

*GA = [1,0] partial safety factor for permanent actions in the accidental situation

?1,1, ?2,i combination coefficients for buildings according to ENV 1991-1.

Efi,d,t = )fi · Ed (F.2)

Ed the design value of the relevant effects of actions from the fundamental combination according to ENV 1991-1 (including partial factors *F)

Efi,d,t the corresponding design value for the fire situation

)fi = (*GA + ?1,1·K)/(*G + *Q·K) is a reduction factor, depending on K = Qk,1/Gk, which is the global ratio between the main variable and permanent actions applied to the structure

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F.3.3 Load level(1) Where tabulated data are specified for a reference load level, this load level corresponds to:

where:

Efi,d,t = )fi,t Rd (F.3)

Rd the loadbearing resistance of the member, determined according to the Parts 1.1 of ENV 1992 to 1996 and ENV 1999

)fi,t the load level for fire design.

blank

DD ENV 1991-2-2:1996

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