comparison ifeg 2005 vs bs 7974 2001

BS7974 and the International Fire Engineering Guidelines Anthony Ferguson Arup Fire Ove Arup & Partners Ltd 13 Fitzroy Street, London W1T 4BQ July 2006 Summary This report was commissioned by the Scottish Building Standards Agency to compare BS 7974: 2001 ‘Application of Fire Safety Engineering principles to the Design of Buildings’ with the ‘International Fire Engineering Guidelines’ and to assess whether both documents should be cited in the Technical Handbooks.

The Technical Handbooks in support of the Building (Scotland) Regulations 2004 state that fire safety engineering can provide an alternative to the fire safety measures contained in the Technical Handbooks. It refers to BS 7974: 2001 as an appropriate framework to identify one or more fire safety design issues to be addressed using fire engineering. This is however, only one method of achieving compliance with the standards. Fire engineering is a continually developing field with a large degree of international co-operation. A document that aims to embrace the best practise worldwide is the ‘International Fire Engineering Guidelines’, jointly published by the Australian Building Codes Board, the National Research Council of Canada, the International Code Council of the United States of America, and the Department of Building and Housing, New Zealand.

Fire engineering designs can be complex and generally require extensive use of engineering judgement. Therefore, to assist Local Authority Verifiers and Fire and Rescue Services in carrying out an assessment of alternative fire engineered solutions, the report assess the commonality and differences between the two documents to ensure that the guidance we give encompasses best practice worldwide.

Scottish Building Standards Agency BS7947 and the International Fire Engineering GuidelinesReview for Scottish Building Standards Agency

Contents Page

1 Executive summary 1 2 Introduction 2

2.1 Brief 2 2.2 Format of the report 3 2.3 Study method 3

3 The significance of differences between the BS and the IFEG 4 3.1 Procedural issues 4 3.2 Methodology 9 3.3 Data 10

4 Functional standards 11 5 Conclusions and recommendations 12

Appendices Appendix A Process and Methodology Appendix B Data and numerical methods


1 Executive summary The brief for this study is to compare the BS and the IFEG to assess whether both documents should be cited in the Technical Handbooks.

The study has been conducted in two phases. This report covers the second phase, assessing the significance of differences identified between the two documents in the first phase. It also presents the results of the first phase in Appendices A and B.

The general approach advocated by both documents is very similar, and would not present conflicts if both were cited.

The IFEG tends to provide less specific technical detail than the BS. There are also a few detailed technical differences concerning data and methodology.

The IFEG handles procedural issues more graphically and more comprehensively, and might therefore be regarded as more ‘user-friendly’ for those less experienced in fire safety engineering.

The IFEG puts forward a fire service intervention model, based on Australian practice, which the SBSA may wish to review. In the UK it is unusual for fire service intervention to be considered when developing fire safety strategy for a building project.

Each of the four different regulatory bodies that support the publication of the IFEG, has written its own introductory section in Part 0 of the IFEG. They explain how the guidance is intended to be applied in their particular jurisdiction. The following points could be addressed by the SBSA in a Scottish part 0 to the IFEG:-

• Regulatory objectives that should be addressed by a fire engineering brief – the IFEG list issues such as environment protection which may not be relevant under the building regulations [see 3.1.2]

• The importance of sensitivity analysis and the way that assumptions need to be tested in a fire engineering analysis. There are some differences in data and analytical methods [see appendix B] between the BS and the IFEG. These apparent conflicts can be addressed if users appreciate the importance of exploring the effect of different assumptions or methods. Specific instances are:-

o Fire load density and the use of fractiles [see 3.3.1]

o Burning rate [see 3.3.2]

o Ignitability [see 3.3.3]

An issue that the SBSA will need to consider is whether the guidance of a ‘Scottish’ Part 0 to the IFEG will have to be in place before the IFEG is cited. The recommendation of the study’s authors is that this is desirable but not essential, since similar issues arise from citing the BS, which has already been done without the benefit of such clarification.

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2 Introduction

2.1 Brief

The Scottish Building Standards Agency’s brief for the Arup study which is the subject of this report was as follows:-

The Technical Handbooks in support of the Building (Scotland) Regulations 2004 state that fire safety engineering can provide an alternative to the fire safety measures contained in the Technical Handbooks. It refers to BS 7974: 2001 ‘Application of Fire Safety Engineering principles to the Design of Buildings’ as an appropriate framework to identify one or more fire safety design issues to be addressed using fire engineering.

This is however, only one method of achieving compliance with the standards. Fire engineering is a continually developing field with a large degree of international co-operation. A document that aims to embrace the best practice worldwide is the ‘International Fire Engineering Guidelines’, jointly published by the Australian Building Codes Board, the National Research Council of Canada, the International Code Council of the United States of America, and the Department of Building and Housing, New Zealand.

Fire engineering designs can be complex and generally require extensive use of engineering judgement. Therefore, to assist Local Authority Verifiers and Fire and Rescue Services in carrying out an assessment of alternative fire engineered solutions, it would be prudent to assess the commonality and differences between the two documents to ensure that the guidance we give encompasses best practice worldwide.

Aim and Objectives

The aim of this project is to compare BS 7974: 2001 ‘Application of Fire Safety Engineering principles to the Design of Buildings’ with the ‘International Fire Engineering Guidelines’ and to assess whether both documents should be cited in the Technical Handbooks. If this is not possible the areas of conflict need to be highlighted and resolved.

The specific tasks required as part of this project are: • to determine the differences between the two documents, highlighting areas not

covered and identifying alternative approaches; • to highlight areas where the documents may give conflicting guidance; and • to examine and offer views on whether the SBSA could ‘joint badge’ the document

with the International Fire Community and reference it in the Technical Handbook as an appropriate framework for addressing fire safety design issues.

Desired Business Outcome The output from this research will be a report, with an Executive Summary clearly identifying what the differences between the two documents are. The report should identify any critical areas that need to be addressed to allow both documents to be referenced in the Technical Handbooks. The contractor should discuss any particular weakness identified in either document and make appropriate recommendations. The key issue is to determine if it is appropriate to cite both documents in the Technical Handbooks to assist verifiers and the Fire and Rescue Authorities in determining whether the aims of the functional standards have been met.




2.2 Format of the report

The study has been conducted in two phases. In phase one the two references were examined and the differences between them were noted and analysed. This led to an interim report being submitted to the SBSA by the contractor for comment.

In phase two of the study the implications of the identified differences were assessed so that this final report could be prepared.

Because the key issue is the question of whether or not both references could appropriately be cited in the technical handbooks, this report presents the assessment and conclusions first.

The detailed comparison of the two documents is contained in appendices to the report. These deal with:-

• Appendix A - the procedures and methods. The emphasis is on the IFEG document, because BS7974 is already referred to in the guidance on the Building Standards, and the aim is to identify possible conflicts that would arise if the IFEG was also to be a reference document.

• Appendix B - a comparison of the data and numerical methods given in the two documents.

Throughout this report British Standard 7974:2001 “Application of fire safety engineering principles to the design of buildings – Code of Practice” is referred to as BS7974 or the BS. This title includes the set of ‘Published Documents’, PD 7974-1 to -7 associated with the British Standard.

Throughout this report the International Fire Engineering Guidelines are referred to as the IFEG.

The term ‘verifier’ is used in this report to indicate the body responsible for checking or approving proposals.

Text in italics indicates a quotation from the document being referred to.

2.3 Study method

The contractor, Arup, has fire engineering staff with experience of writing fire safety standards, codes and regulations in the UK, USA and Australia, including BS7974 and the International Fire Engineering Guidelines.

The study was conducted in the UK and involved consultation with, and input from, Arup colleagues in the other two countries.

In examining and comparing the two reference documents Arup was able to apply its knowledge of the background and development of both documents, as well as the fire engineering knowledge required to carry out the comparison.




3 The significance of differences between the BS and the IFEG As a general summary the British Standard and the IFEG are essentially equivalent in concept. The BS generally provides rather more detailed information while the IFEG handles procedural issues more graphically and more comprehensively.

Within this generalisation lie a very few detailed differences which are discussed in the following section. However, in the opinion of the authors, they do not prevent the IFEG being cited in the Technical Handbooks.

Fire engineering is not as mature as some other branches of engineering. In a regulatory context there are therefore likely to be more issues of professional judgement made by engineers that have to be assessed by the appropriate authorities, than in some other disciplines. These issues raise questions of training, experience and qualifications, both for the design professions and for the verifiers. The reference to BS7974 in the Technical Handbooks has already presented these issues, and inclusion of the IFEG should not, in our opinion, change the existing situation.

3.1 Procedural issues

The two documents use a very similar approach. Fire engineering embraces a wide range of phenomena, design features and systems, and both documents break the subject down into sub-systems.

Originally the sub-system concept grew from the analogy of a computer processor in which many items of data were passed around and processed under the control a central mechanism; the results of one process often feeding into another.

While this somewhat mechanical view of the process is not entirely realistic, it has allowed some structure to be imposed on a very diverse field. Neither the BS nor the IFEG cling relentlessly to the process analogy, and both make it clear that the illustrations they give are subject to variation, iteration, deletion when applied to any specific project.

In both cases the process begins with an appraisal of the task; called the Qualitative Design Review by the BS, and the Fire Engineering Brief by the IFEG. Figure 1.2 reproduced from the IFEG shows a process for developing a Fire Engineering Brief.

As described, the Fire Engineering Brief [FEB] is very comprehensive; to the extent that some of the factors suggested for consideration are unlikely to be known at the earlier stages of a construction project. The less detailed guidance in the BS does not raise this issue. It will be important for the verifier to understand that it is not always essential that all the elements listed against FEB development in the IFEG should be fully determined.

3.1.1 AHJ’s and Verifiers The term Authority Having Jurisdiction [AHJ] is used in the IFEG to embrace the roles of approver / enforcer. The Scottish term Verifier is used in this report to refer to the ‘approval’ function, noting that the role of enforcement is carried out [at present] by the same Local Authorities who have been appointed as verifiers.




3.1.2 IFEG Part 0 Part 0 in the IFEG document contains introductory sections for each of the national regulatory authorities jointly responsible for publishing these Guidelines. They are the Australian Building Codes Board; the National Research Council of Canada; the International Codes Council of the USA; and the Department of Building and Housing, New Zealand.

Each introductory section explains how the Guidelines are intended to be applied in that jurisdiction. They have not been reviewed in detail for this report because none of them specifically address the circumstances found in Scotland.

This aspect of the IFEG clearly provides an opportunity for any particular considerations relevant to Scotland to be described or highlighted. This would entail the Scottish Building Standards Agency preparing a Scottish Part 0 for the IFEG, assuming that they would wish to become joint participants in the publication of the IFEG.

The following procedural issues could be addressed in a Scottish Part 0. Later in this report other issues, concerning methods and data, are identified as ones which could be addressed using commentary in a Scottish Part 0.

Section 1.2.1.2 of the IFEG notes that the regulatory framework for the design must be understood from the outset. It lists some questions to elicit the relevant information.

Section 1.2.5.1 and .2 identify possible building regulatory objectives for inclusion in a FEB:-

• protecting building occupants • facilitating the activities of emergency services personnel • protecting the property in question • preventing the spread of fire between buildings.

And some other possible regulatory objectives:-

• environmental protection • occupational health and safety • fire services • dangerous goods • land use and other planning matters.

A Scottish Part 0 to the IFEG could make it clear which of these objectives were relevant for purposes of the Scottish Building Standards.




Figure 1; examples from IFEG of acceptance criteria




Given the functional nature of the standards set in the Scottish building regulations, section 1.2.8 of the IFEG is significant:-

“In order to determine the specific objectives or performance requirements it is necessary to determine where the trial designs do not comply with the relevant deemed-to-satisfy or prescriptive provisions. This process will identify the issues that need to be addressed in the analysis of the trial design.

In cases where there are no deemed-to-satisfy or prescriptive provisions, the relevant objectives or performance requirements need to be identified directly (see 1.2.8.2) and the determination of non-compliance issues (Section 1.2.8.1) omitted {bold ed. By Arup}. This situation may occur where the relevant codes comprise objectives or performance requirements only or when general objectives, other than those covered by recognised codes, have been agreed to during the FEB process.”

The verifier will need to be able to identify the underlying objectives or performance requirements of the Functional Standards, so that acceptance criteria can be agreed. A Scottish Part 0 to the IFEG could be used to give assistance here by giving examples of the selection of relevant performance requirements.

The SBSA may wish to consider whether this kind of modification has to be made to the IFEG before it can be called up for use in Scotland. Arguably the need already arises with BS7974, which is already cited, and therefore incorporation of Scottish examples in the IFEG does not have to precede it being cited in the guidance, although it is clearly desirable that it should.

3.1.3 Acceptance criteria The IFEG does not set acceptance criteria, and given the range of possible cases it is not possible to do so. It does give some examples in section 1.2.10 of performance parameters relevant to certain common fire safety objectives.

Factors of safety are also discussed in this section, at a very general level.

The passage emboldened in the extract from 1.2.8 of the IFEG reproduced above was to draw attention to the importance of determining acceptance criteria, in a functional-based system, rather than simply identifying non-compliances.




3.2 Methodology

3.2.1 Sub-system on fire service intervention The BS reflects British practice in a largely qualitative way, while the IFEG presents the Australian Fire Brigade Intervention Model as a method for quantifying this intervention.

In England and Wales there has been reluctance to take fire service intervention into account when the fire strategy for a building has been put forward for regulatory approval.

Similarly in Scotland, while various facilities are expected to be provided to assist the firefighters to access the building, it is not customary to reduce some aspect of a building’s performance in fire in recognition of fire brigade activity.

The SBSA may wish to consider including some reference to the account that may or may not be taken of fire service actions, should they decide to write a Scottish Part 0 to the IFEG.

3.2.2 Changes in the state of the art Fire safety engineering is a relatively new branch of engineering and advances in understanding of fire phenomena, and development of new analytical methods, happen frequently.

The BS was set up with the detailed technical material in a set of Published Documents because this makes it easier to revise parts of the whole body of knowledge and information as necessary.

The IFEG reduces its exposure to content becoming out of date by giving less detailed technical information, and calling up other sources. However this makes the IFEG more dependent on outside sources and gives the publishers less control, unless they choose to add material specifically to address new developments.




3.3 Data

3.3.1 Fire load Both the BS and the IFEG refer to the CIB W14 report on fire loading. Fire loads are given as ranges, for various types of occupancy.

However the BS recommends that the 80% fractile of the range of fire load should be used while the IFEG recommends that the 95% fractile should be used.

If one is following the guidance in BS7974 to calculate a post flash-over fire then it would be inappropriate to use the 95% fractile in favour of the recommended 80% one. The 95% fractile is very conservative when compared with other fire loads recommended elsewhere, e.g. EuroCode1, Law and O’Brien on external steelwork; and measured in real fire tests such as the Cardington office series.

While the SBSA might consider addressing this question if they prepare a ‘Scottish’ Part 0 to the IFEG, the essential point, which applies to any aspect of fire engineering analysis where assumptions are being made, is that sensitivity studies should be carried out to ensure that a solution's acceptability is not critically dependent on some assumption, such as fire load.

3.3.2 Rate of heat release The guidance in the two documents on the subject of heat release or burning rates in fuel bed controlled conditions [i.e. where the rate of burning is not restricted by a limited air supply] is different, as summarised in the table below.

Topic IFEG BS7974

Fuel bed controlled HRR

No equations are suggested. References are made to Babrauskas’ section in the SFPE handbook and Sardqvists “Initial fires”. It is recommended that “appropriate engineering judgement” should be applied when setting fire rates.

An effective fire duration of 20 minutes can be assumed in houses, offices and shops. Burning rate is based on the assumption that the total initial fire load burns in 1200 seconds Another equation for fuel bed controlled fires is presented with no reference to its origins. The time to reach burnout after flashover is shown as two times the mass of fuel left when flashover occurs, divided by peak mass burning rate.

The BS guidance is an engineering approximation to a complex situation. The SFPE reference called up by the IFEG discusses these complications, but it requires a higher level of understanding of fire dynamics to make use of the advice given. This should not be considered as a weakness of the IFEG.

The fundamental point, which applies to any aspect of fire engineering analysis where assumptions are being made, is that sensitivity studies should be carried out to ensure that a solution's acceptability is not critically dependent on some assumption, such as release rate.




3.3.3 Ignitability In data associated with sub-systems 3 ‘structural response’, the two references give different advice on spontaneous or auto-ignition temperatures for timber elements.

Topic IFEG BS7974 Heat flow by radiation

Various references to publications regarding external fire spread. Some data on ignitability limits under radiant heat flux. The spontaneous ignition criterion for wood is set to 250-400°C.

Standard radiation relationships shown. 12.6kW/m2 is mentioned as a criterion, giving “some factor of safety” It is possible to base analysis on the increase of surface temperature of the object exposed. For organic solids a surface temp. criterion of 600°C is suggested for spontaneous ignition, and 300-410°C for ignition by flying brands under a radiative heat flux..

The range of values offered by both documents overlap. They reflect the fact that this is a very complex subject. The value depends on many variables, such as the nature of the heat transfer mechanism, the specimen thickness and period of exposure to heating. The measurement of specimen surface temperature is technically difficult. It is suggested that this is a relatively trivial issue in the overall question of whether the IFEG is a suitable reference.

It might have been better if the BS had adopted the IFEG approach of simply referring to other sources, without attempting to summarise a complicated topic. The IFEG gives less data and relies more on other references.

4 Functional standards The Scottish building regulations identify 15 functional standards.

It is obviously essential that the two documents, BS7974 and IFEG, do address all of the Functional Standards.

In Appendix A section 4 the scope of both the BS and the IFEG have been compared to the Functional Standards.

This confirms that the functional standards are capable of being addressed by following the guidance in the two reference documents.




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5 Conclusions and recommendations The brief for this study is to compare the BS and the IFEG to assess whether both documents should be cited in the Technical Handbooks.

The general approach advocated by both documents is very similar, and would not present conflicts if both were cited.

The study has identified a difference in the general character of the IFEG – it tends to provide less specific technical detail than the BS – and a few detailed technical differences concerning data and methodology.

The IFEG handles procedural issues more graphically and more comprehensively, and might therefore be regarded as more ‘user-friendly’ for those less experienced in fire safety engineering.

The IFEG puts forward a fire service intervention model, based on Australian practice, which the SBSA may wish to review. In the UK it is unusual for fire service intervention to be considered when developing fire safety strategy for a building project. Normally the safety of building occupants in case of fire is regarded as a matter of ‘self-help’ without reliance on outside intervention.

Each of the four different regulatory bodies that support the publication of the IFEG, has written its own introductory section in Part 0 of the IFEG. They explain how the guidance is intended to be applied in their particular jurisdiction.

The following points could be addressed by the SBSA in a Scottish part 0 to the IFEG:-

• Regulatory objectives that should be addressed by a fire engineering brief – the IFEG list issues such as environment protection which may not be relevant under the building regulations [see 3.1.2]

• The importance of sensitivity analysis and the way that assumptions need to be tested in a fire engineering analysis. There are some differences in data and analytical methods [see appendix B] between the BS and the IFEG. These apparent conflicts can be addressed if users appreciate the importance of exploring the effect of different assumptions or methods. Specific instances are:-

o Fire load density and the use of fractiles [see 3.3.1]

o Burning rate [see 3.3.2]

o Ignitability [see 3.3.3]

An issue that the SBSA will need to consider is whether the guidance of a ‘Scottish’ Part 0 to the IFEG will have to be in place before the IFEG is cited. Arguably the need already arises with BS7974, which is already cited, and therefore incorporation of a ‘Scottish’ Part 0 in the IFEG does not have to precede it being cited in the guidance.

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n

Appendix A Process and Methodology

Scottish Building Standards Agency BS7974 and the International Fire Engineering Guidelines Review for Scottish Building Standards Agency

A1 BS7974 BS7974 is in effect a headcode under which sit a set of Published Documents [PD’s]. This study embraces the PD’s along with the BS7974.

The BS code of practice:

“provides a framework for developing a rational methodology for design of buildings using a fire safety engineering approach based on the application of scientific and engineering principles to the protection of people, property and the environment from fire”.

It may be applied to new or existing buildings, to show that regulatory requirements can be met.

It is intended to be applied in three main stages:-

1. Qualitative design review [QDR]; in which the scope and objectives of the fire safety design are defined, performance criteria established and one or more potential design solutions proposed.

2. Quantitative analysis; engineering methods are used to evaluate the potential solutions identified in the QDR

3. Assessment against criteria; the output of the quantitative analysis is compared to the acceptance criteria identified in the QDR

The BS7974 provides guidance on these procedures. The sub-systems in the PD’s provide data and analytical methods for tackling the relevant quantitative analysis, and advice on acceptance criteria and suitable design approaches.

The document structure with the sub-systems is illustrated in figure 1.


Page A1 Ove Arup & Partners LtdRev A 3 July 2006


BS7974 Code of Practice –

Application of fire safety engineering principles to the design of buildings

BSPD7974-0

BSPD7974-1

BSPD7974-2

BSPD7974-3

BSPD7974-4

BSPD7974-5

BSPD7974-6

BSPD7974-7

Guide to design framework and fire safety engineering procedures

Initiation and development of fire within enclosure of origin

Spread of smoke and toxic gases within and beyond the enclosure of origin

Structural response and fire spread beyond the enclosure of origin

Detection of fire and activation of fire protection systems

Fire service intervention

Evacuation Probabilistic risk assessment

Figure A1 structure of sub-systems in BS7974 Note that 0 and 7 are not sub-systems as such, ie they do not address characteristics of fire or safety systems. PD0 provides guidance on procedure and PD7 provides guidance on risk assessment techniques, both being applicable to any of the other subsystems.

Qualitative Design Review

Quantitative analysis

Assessment against criteria

Figure A2; the engineering approach described in BS7974




A2 The International Fire Engineering Guidelines The guidelines document and approach uses a very similar sub-systems break-down of the subject to that used in BS7974. The guidelines are derived from an earlier Australian document [the draft National Building Fire Safety Systems code]. In the early 1990’s the original consultant team commissioned to draft the document that eventually became BS7974 in the UK, were in contact with members of the team who were working on the first edition of the Australian Fire Engineering Safety Systems code at the same time. There was cross-fertilisation between these groups. The UK group picked up the Australian sub-system concept and the Australian group adopted the UK QDR concept (though some of the terminology was altered).

It is assumed that Scotland would prepare an introductory section [Part 0] for a new edition of the IFEG, should they wish to cite the IFEG, in a similar fashion to the other regulatory authorities who have “adopted” the IFEG. The present study does not examine Part 0 of the IFEG document as these are written for other ‘national’ jurisdictions.

The structure of the IFEG after the ‘national’ introductory sections, is in three parts:

1. process

2. methodologies

3. data

A2.1 IFEG Process

The first stage in the Guidelines is the preparation of a Fire Engineering Brief [FEB]. The process follows the following sequence:-

Prepare FEB Carry out analysis

Collate and evaluate results

Draw conclusions

Prepare report

FigureA3; sequence of the fire engineering process in the IFEG

The “Process” section of the IFEG offers guidance on what issues should be addressed in the Fire Engineering Brief [FEB].

The FEB is a process as well as a document. It defines the scope of the fire engineering analysis, and the basis on which that analysis will be undertaken. All interested parties, including the Authority Having Jurisdiction [AHJ], have to be involved, since key components of the FEB include acceptance criteria. These criteria are likely to be more detailed than the Functional Standards of building regulations.

This section of the IFEG gives an illustration [fig.1.2 see below] of a process for developing a FEB. Clearly this is only illustrative as the particular characteristics of a project will determine its content to some extent. The IFEG notes that the FEB for an analysis to evaluate a simple departure from some prescriptive guidance in a code or standard, may be a much shorter document than the FEB for a major project with many departures from Code.

The steps shown in fig 1.2 may be re-ordered, omitted or an iterative process introduced.




A practical criticism of the FEB principle is that it is generally impossible to follow in a real project. This is essentially because there are many unknowns in the early stages. The IFEG acknowledges this in noting that there may well be iterative loops in its development, and in accepting that there may be preliminary ‘test’ calculations/analyses to establish the likelihood of success before trial designs are defined ready for fuller analysis.

Typically there may be some exploratory ‘hand calculations’ before the fire engineer advises the design team to take a particular approach, after which a more time-consuming analysis may be carried out to test the approach, once the design has been further developed.

The FEB is not necessarily fixed [1.2.14]:-

“Sometimes, as the analysis of a design proceeds or as a project develops, it may be appropriate to revise the FEB, adopting the same consultative approach as with the original. The 'final' FEB will be incorporated into the overall report”

A2.1.1 Regulatory requirements Section 1.2.1.2 of the IFEG notes that the regulatory framework for the design must be understood from the outset. It lists some questions to elicit the relevant information.

Section 1.2.5.1 and .2 identify possible building regulatory objectives for inclusion in a FEB:-

• protecting building occupants • facilitating the activities of emergency services personnel • protecting the property in question • preventing the spread of fire between buildings.

And some other possible regulatory objectives:-

• environmental protection • occupational health and safety • fire services • dangerous goods • land use and other planning matters.

A2.1.2 Trial designs Section 1.2.7 describes activity during the development of trial designs. It notes that each of these should be clearly identified and all its features, including fire safety features, should be recorded. Sections 1.2.3 and 1.2.6.2 list the types of feature to be included.



Scottish Building Standards Agency BS7974 and the International Fire EReview for Scottish Building Standards Agenc

ngineering Guidelines y



A2.1.3 Given the functional nature of the Scottish Standards section 1.2.8 of the IFEG is significant:-

“In order to determine the specific objectives or performance requirements it is necessary to determine where the trial designs do not comply with the relevant deemed-to-satisfy or prescriptive provisions. This process will identify the issues that need to be addressed in the analysis of the trial design.


In cases where there are no deemed-to-satisfy or prescriptive provisions, the relevant objectives or performance requirements need to be identified directly (see 1.2.8.2) and the determination of non-compliance issues (Section 1.2.8.1) omitted {bold text ed. Arup}. This situation may occur where the relevant codes comprise objectives or performance requirements only or when general objectives, other than those covered by recognised codes, have been agreed to during the FEB process” .

The verifiers will need to be able to identify the underlying objectives or performance requirements of the Functional Standards, so that acceptance criteria can be agreed.

Another issue raised by this section is whether the FEB has to show equivalent performance to the solutions given in guidance/codes, or whether it is acceptable to demonstrate compliance with the functional/performance standard. From our understanding of the Scottish regulatory system, both options would be available.

Reflecting the importance of this section, the IFEG gives examples of the selection of relevant performance requirement in Australia, USA, Canada and New Zealand. Presumably an example under the Scottish regulatory system could be included as part of the process of ‘adopting’ the IFEG, if so-desired.

The SBSA will need to consider whether it is necessary for this kind of modification to be made to the IFEG before it can be called up for use in Scotland.

A2.1.4 Selection of analytical approaches The Process section includes a discussion of the selection of the approaches and methods of analysis, section 1.2.9. It gives useful advice on the principles involved, but is not a substitute for experience and training in fire engineering. It is probably more helpful than BS7974 in this area, and certainly goes into more detail than the somewhat cursory section 6.4.6 in the BS, although similar information can be gleaned from other parts of the BS and its PD’s.

A2.1.5 Acceptance criteria The IFEG does not set acceptance criteria, and given the range of possible cases it is not possible to do so. It does give some examples in section 1.2.10 of performance parameters relevant to certain common fire safety objectives. See illustration Figure A4.

Factors of safety are also discussed in this section, at a very general level.



Scottish Buildy

ing Standards Agency BS7974 and the International Fire Engineering Guidelines Review for Scottish Building Standards Agenc



Figure A4; examples from IFEG of acceptance criteria


A2.1.6 Sub-systems The sub-system approach is introduced in section 1.3.1 of the IFEG document. As noted the IFEG sub-systems bear a very close resemblance to those used in BS7974. They are set out in figure Figure A5.

The following quote from IFEG 1.3.2 is important in that it qualifies the importance of the whole sub-system principle:-

“Typically, each building project is unique and similarly, each fire engineering evaluation is unique. It is not sensible, therefore, to set down detailed guidance on how the fire safety analysis should be undertaken. Instead, it is the responsibility of the fire engineer to plan the analysis for the particular project, based on the decisions taken during the preparation of the FEB as discussed in Chapter 1.2.”

Subsystem A Subsystem B Subsystem C Subsystem D Subsystem E Subsystem F

Fire initiation and development and control of fire within enclosure of origin as well as enclosures to which fire subsequently spreads

Development and spread of smoke within the building, and its control

Spread of fire beyond the enclosure of origin, impact on structure and how spread and impact may be controlled

Fire detection warning and suppression. Enables suppression effectiveness to be estimated

Occupant evacuation and control. Enables estimate of time to reach place of safety

Fire services intervention. Effectiveness of intervention including suppression.

Figure A5; the IFEG subsystems

BS7974 Code of Practice –

Application of fire safety engineering principles to the design of buildings

BSPD7974-0

BSPD7974-1

BSPD7974-2

BSPD7974-3

BSPD7974-4

BSPD7974-5

BSPD7974-6

BSPD7974-7

Guide to design framework and fire safety engineering procedures

Initiation and development of fire within enclosure of origin

Spread of smoke and toxic gases within and beyond the enclosure of origin

Structural response and fire spread beyond the enclosure of origin

Detection of fire and activation of fire protection systems

Fire service intervention

Evacuation Probabilistic risk assessment

Figure A6; the BS7974 sub-systems repeated for ease of comparison

The point is made that the sub-systems actually used will depend on the non-compliance issues identified and the specific objectives established in the FEB. The FEB is therefore integral to the overall process.




A2.1.7 Sub-system Flow charts Each sub-system description includes flow charts indicating how analysis may be undertaken. IFEG Section 1.4.1 notes that these charts are only for guidance, and do not necessarily cover all the factors which may be relevant to a particular case. An example from sub system 1 ‘fire initiation and development’ is shown as an illustration in Figure A7 below.






Figure A7: flow chart from IFEG for sub-system on fire initiation and development


A2.1.8 Preparation of the Fire Engineering brief The IFEG gives more information about the documentation of the fire engineering work than the BS.

The BS lists information that may be appropriate to include in the report.

A3 Methodologies Part 2 of the IFEG is devoted to methodologies that may be appropriate for the preparation of the FEB and for the analysis in each subsystem

It touches on the:-

• Identification and definition of fire scenarios

• Use of event trees for scenario identification.

PD7 of the BS has a section on these techniques, in the context of probabilistic approaches generally, as they may be employed in any sub-system.

A comparison of the data and methodologies is provided in Appendix B.

A4 Functional standards The Scottish building regulations identify 15 functional standards, reproduced below.

Standards n.1 and n.13 do not apply to domestic buildings and Standard n.11 only applies to a building which is:- a dwelling; or is a residential building; or is an enclosed shopping centre. Standard n.15 applies only to a building which is an enclosed shopping centre; is a residential care building; is a high rise domestic building; or forms the whole or part of a sheltered housing complex.

The IFEG and BS7974 do not discriminate between domestic and other types of building work. The procedures defined in the two documents are applicable to dwellings and to other buildings.

It is obviously essential that the two documents, BS7974 and IFEG, do address all of the Functional Standards.

This section is to confirm that all the Functional Standards are capable of being addressed by following the guidance in the two reference documents

A4.1 Functional standard 2.1

Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, fire and smoke are inhibited from spreading beyond the compartment of origin until any occupants have had the time to leave that compartment and any fire containment measures have been initiated.

Limitation

This standard does not apply to domestic buildings.

Sub-systems relevant to this functional standard

BS7974 IFEG

SS1, SS2, SS3, SS4, SS5, SS6 SSA, SSB, SSC, SSD, SSE, SSF





Every building, which is divided into more than one area of different occupation, must be designed and constructed in such a way that in the event of an outbreak of fire within the building, fire and smoke are inhibited from spreading beyond the area of occupation where the fire originated.


BS7974 IFEG

SS1, SS2, SS3, SS4 SSA, SSB, SSC, SSD


Every building must be designed and constructed in such a way that in the event of outbreak of fire within the building, the load-bearing capacity of the building will continue to function until all occupants have escaped, or been assisted to escape, from the building and any fire containment measures have been initiated.


BS7974 IFEG

SS1, SS3, SS4, SS5, SS6 SSA, SSC, SSD, SSE, SSF


Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the unseen spread of fire and smoke within concealed spaces in its structure and fabric is inhibited.


BS7974 IFEG

SS2, SS3, SS4 SSB, SSC, SSD


Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the development of fire and smoke from the surfaces of walls and ceilings within the area of origin is inhibited.


BS7974 IFEG

SS1, SS2, SS4, SSA, SSB, SSD





Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the spread of fire to neighbouring buildings is inhibited.


BS7974 IFEG

SS1, SS2, SS3, SS4, SS5 SSA, SSB, SSC, SSD, SSF


Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, or from an external source, the spread of fire on the external walls of the building is inhibited.


BS7974 IFEG

SS1, SS2, SS3, SS5 SSA, SSB, SSC, SSF


Every building must be designed and constructed in such a way that in the event of an outbreak of fire in a neighbouring building, the spread of fire to the building is inhibited.


BS7974 IFEG

SS2, SS3, SS4, SS5 SSC, SSD, SSF


Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the occupants, once alerted to the outbreak of the fire, are provided with the opportunity to escape from the building, before being affected by fire or smoke.


BS7974 IFEG

SS1, SS2, SS3, SS4, SS5, SS6 SSA, SSB, SSC, SSD, SSE, SSF





Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, illumination is provided to assist in escape.


BS7974 IFEG

SS1, SS2, SS4, SS6 SSA, SSB, SSD, SSE


Every building must be designed and constructed in such a way that in the event of an outbreak of fire within the building, the occupants are alerted to the outbreak of fire.

Limitation

This standard applies only to a building which:

(a) is a dwelling;

(b) is a residential building; or

(c) is an enclosed shopping centre.


BS7974 IFEG

SS2, SS4, SS6 SSB, SSD, SSE


Every building must be accessible to fire appliances and fire service personnel.


BS7974 IFEG

SS5, SS6 SSE, SSF


Every building must be provided with a water supply for use by the fire service.

Limitation

This standard does not apply to domestic buildings.


BS7974 IFEG

SS5 SSF







Every building must be designed and constructed in such a way that facilities are provided to assist fire-fighting or rescue operations.


BS7974 IFEG

SS2, SS3, SS4, SS5, SS6 SSB, SSC, SSD, SSE, SSF


Every building must be designed and constructed in such a way that, in the event of an outbreak of fire within the building, fire and smoke will be inhibited from spreading through the building by the operation of an automatic life safety fire suppression system.

Limitation

This standard applies only to a building which:

(a) is an enclosed shopping centre;

(b) is a residential care building;

(c) is a high rise domestic building; or

(d) forms the whole or part of a sheltered housing complex.


BS7974 IFEG

SS1, SS2, SS4 SSA, SSB, SSD

Appendix B Data and numerical methods


B1 Data and numerical methods The following series of tables compares the guidance given on input data for each sub-system in the two documents under review [BS7974 including PD’s, and the IFEG]

The object of the assessment has been to identify possible conflicts that might arise if both the reference documents are afforded equal status as sources of guidance for satisfying the Scottish Building Standards.

Potential conflicts identified below are discussed in section 3.3 of the main report.

Sub-system 1- Initiation and development of fire within the enclosure of origin. Design Calculations-Pre-flashover IFEG 7974-1:2003 Conclusion

Allowed to be assessed by surveys.

Allowed to be assessed by surveys.

Identical. Both use the same equation for fire load density.

Generic data-Swiss data collected 1967-1969, it is also reproduced in Warrington-BCC’s “Fire resistant barriers and structures (2000)” The CIB W14 workshop report is also referred to.

Generic data-The CIB W14 workshop report is referred to.

Similar. IFEG provides more information.

Fire load densities

Where the CIB W14 workshop figures are utilised, it is recommended the 95% fractile value should be taken as the fire load.

Where the CIB W14 workshop figures are utilised, it is recommended that in the UK the 80% fractile value should be taken as the fire load.

Contradicting

Ignition It is appreciated that in most cases a deterministic approach is utilised and a fire initiation is a presumption for the fire engineered analysis. The use of event trees to determine fire ignition and spread is recognised. Some information is provided on ignition characteristics. Time to ignition of second object is discussed. The time to flame contact is given as a conservative value. For fire spread through radiation Babrauskas relationship between mass loss rate and ignition distance is shown. Data is provided on ignitability limits for common fuels for both piloted ignition and spontaneous ignition. Extensive references to Babrauskas “Ignition Handbook”

A list of common ignition sources is provided.

NA. The IFEG is more detailed and also provides more references for additional information.


Page B1 Ove Arup & Partners LtdRev A 3 July 2006



Convective fraction is approximated to 70% of total heat release.

Data for convective heat release fractions rates refers to SFPE handbook

Heat release rates

No recommendation on an appropriate heat release model.

Q*-Dimensionless heat release rate as described by Zukoski, referred to Drysdale-An introduction to fire dynamics.

NA

“Growth times” referenced to NFPA 204

Fire growth parameters as described in NFPA92B

Similar/Identical Characteristic fire growth curves-t²

Occupancy related fire growth times referenced to NFPA 204

Picture gallery-slow Dwelling-medium Office-medium Hotel reception-medium Hotel bedroom-medium Shop-fast Industrial storage or plant room-Ultra-fast

Similar/Identical

Heat release rates per unit area

No recommendations on peak heat release rates

Shops-550kw/m2

Offices-290kw/m2

Hotel rooms-250kw/m2

Industrial (excl. storage) – 90-620kw/m2

NA-More info in 7974

Smouldering fires Equation developed by Quintere et al. (1982)

Equation developed by Quintere et al. (1982).

Identical

Heat release within enclosure for flashover

Walton & Thomas (2002) equation for heat release rates needed to induce flash-over.

Walton & Thomas (2002) equation for heat release rates needed to induce flash-over.

Identical. Noted misprint in IFEG on definition of terms

Temperature within enclosure prior to flashover

No recommendations Equation presented by McCaffrey et al. 1981 recommended.

NA

Flame length for axi-symmetric fire source.

Flame length is estimated with the McAffrey and Heskestad equations

Flame length according to Cox and Chitty, 1980. (0.2*Q^(2/5))

Dissimilar, but not contradicting

Flame length for line sources

No recommendations The equation shown is referenced to DD240-1.

NA-7974 provides more information

Flame lengths for corner room and wall fires.

No recommendations “Corner room fires are likely to increase flame heights by 75% and wall fires by 32%” this is referenced to Zukoski.


Flame temperature Heskestad (2002) equations No recommendations NA-IFEG provides greater detail

Flame radiation & flame emissivity

Standard radiation calculations. The emissivity can be conservatively set to 1

If the flame length is over 1m and the flame is luminous it is common to assume black body behaviour. Emissivity = 1 Standard radiation calculation with view factor. It is suggested that the influence of air flow should be taken into account

Identical

Smoke yield No relationships are given for mass conversion factors. A basic equation is shown.

Smoke mass conversion factors for flaming and non-flaming combustion. The smoke mass conversion factors are referenced to the SFPE handbook.

NA-7974 provides more information.





The light depletion equations is Bouguer’s law. It is however shown in the fire detection section

The light depletion equations is Bouguer’s law.

Optical density

Optical density data required for smoke detector activation is expressed in dB/m.

Optical density given in dB/m.

Identical

Mass optical density

No discussion on mass optical density.

Relations for mass optical density for different fuels is shown. Referenced to SFPE handbook


Visibility No discussion on visibility of signage etc.

S=(10/D), S=visibility distance, D=optical density db/m If a sign is back illuminated its visibility distance can be increased by a factor of 2.5


Mass production of CO and other species

CO yield factors referenced to “part three of these guidelines” no data is however found in the appendices. The equations shown are basic concentration equations.

The mass conversion factor for CO is given as 0.013mf.. This value, and other conversion factors, is referenced to the SFPE handbook.


Design Calculations-Fully developed fire IFEG 7974-1:2003 Conclusion

Flashover occurs when the hot layer temperature reaches approximately 600°C or when radiation at floor level from the hot smoke layer reaches 20kW/m2.

“Flashover can be assumed to occur when sustained flaming from combustibles reaches that ceiling and the temperature of the hot gas layer is between 550°C and 600°C. If flames from the combustibles do not reach the ceiling, or the temperature remains below 550°C, flashover can be assumed to be unlikely.”

Similar Time to flashover

When 80% of the fuel has been consumed the fire can be assumed to decay either: -linearly -at rate determined experimentally -at any rate than can be justified

For design purposes it may be assumed that heat release rates remain constant until 80% of the fuel has been consumed and the decay phase starts. Kawagoe and Sekine equation for linear decline.

Similar

Heat release rate at flashover

Thomas (1981) for no consideration of wall thermal properties. No recommendations for thermal effects of enclosures.

Walton & Thomas (2002) for no consideration to wall thermal properties. McCaffrey for when thermal effects of enclosures is considered.

Identical for cases where no consideration is taken for thermal effects of enclosures. 7974 provides further information.

Steady state fires IFEG 7974-1:2003 Conclusion Mass burning rate in ventilation controlled conditions

Uses Drysdales’ equation for mass flow, with a reasonable and referenced assumption regarding underventilated fires.

Uses Thomas,1973, equation for the mass flow in an underventilated fire or an unreferenced equation for fuel mass flow (it is identical to the one in Drysdale 1999).

Similar




Sub-system 1- Initiation and development of fire within the enclosure of origin. Design Calculations-Pre-flashover IFEG 7974-1:2003 Conclusion Mass burning rate in fuel bed controlled conditions

No equations are suggested. References are made to Babrauskas section in the SFPE handbook and Sardqvists “Initial fires”. It is recommended that “appropriate engineering judgement” should be applied when setting fire rates.

An effective fire duration of 20 minutes can be assumed in houses, offices and shops. Burning rate is based on assessment that the total initial fire load burns in 1200 seconds Another equation for fuel bed controlled fires is presented with no reference to its origins. Time to reach burnout after flashover is shown as two times the mass of fuel left at flashover divided by peak rate mass burning rate.

Different

Standard temperature-time curve

7974 recognises the ISO and BS 476 temperature-time curve

Large pool fire, in accordance with BS 476-20

Hydrocarbon temperature-time curve Temperature curve in

accordance with BS EN 1991-1-2:2002

Slow heating curve Two heating curves for slow heating fires. Reference to BS 1363-2:1999.

Maximum temperature curve

Equation referenced to M.law 1978

Ventilation controlled temperature-time curve

Short discussion on the existence of empirical time-temperature curves. Reference given to Lie (1994).

Kawagoe and Sekine equation dependant on opening factor.

NA-The 7974 provides many equations and data whilst the information found in IFEG is very limited.

Summary Both documents provide quite comprehensive quantitative guidance on the subject. BS7974 however provides the most information.




Sub-system 2- Spread of Smoke and toxic gases within and beyond the enclosure of origin. IFEG 7974-2:2002 Conclusion

Visible and non visible products of combustion or pyrolysis and entrained air.

‘airborne’ products of combustion, solid or liquid particulates within a gaseous mass.

Similar/Identical Hazards of smoke

“CO, CO2 and HCN are often considered for life safety criteria”.

Most fire deaths from smoke inhalation. CO2, H2O, CO, HCN. Further pre-amble of smoke dangers.

Similar.

Smoke Dynamics

Influence of buoyancy and combustion generated products. Amount of air entrained greatly exceeds mass flow of fuel burned.

Initial flow influenced by air currents; fuel controlled fire creates a plume, smoke rises to ceiling, then radially spreads. Air entrainment increases volume and decreases temperature. Fire growth may be limited by limited ventilation.

Dissimilar, but not contradicting.

Smoke Control IFEG 7974-2:2002 Conclusion

Evaluate effect on Means of Escape [MoE]

Protection of MoE – clear layer solutions

Identical

Temperature control mentioned with regards to fire spread.

Temperature Control – protects materials within the smoke zone

Similar – both outline advantages of controlling temperatures.

Evaluate effect on FF operations

Assist fire fighting operations – prevent hot smoky layers occurring in certain situations.

Identical

Design Objectives

Property Protection – limiting heat flux on structure through exhaust.

N/A – No mention in IFEG of limiting heat fluxes.

Containment mentioned. Smoke containment – physical measures to prevent the spread of hot and smoky products – smoke curtains, walls etc.

Similar

Extraction mentioned. Smoke clearance – removal of smoke after smoke has finished being produced.

Similar

Dilution mentioned. Smoke Dilution – mixing smoke with clean air to reduce the concentration of toxic products and increase visibility.

Similar

Natural ventilation mentioned. Smoke exhaust ventilation – natural or mechanical means of removing smoke from top of layer.

Similar

Zone pressurisation mentioned. Pressurization – effectively contains smoke. Uses pressure differences over openings.

Similar

Techniques

Depressurisation – limiting smoke movement by pressure differentials. Fans pull air out of designated spaces rather than supplying it.

N/A – depressurisation not mentioned in IFEG

Design Procedure IFEG SS-C 7974-2:2002 Conclusion Inputs Building characteristics, heat

release rate profile, smoke yield, characteristics of smoke management equipment, time to smoke detection, environmental effects.

Building Characteristics Occupant characteristics Design fire – sub system 1 Environmental influences – wind, internal air movement, stack effect. Active systems activation time.

Identical.

Analysis IFEG SS-C 7974-2:2002 Conclusion Heat content Qc=0.7Q Qp=XQ where X is the fraction of heat Dissimilar, but not




Sub-system 2- Spread of Smoke and toxic gases within and beyond the enclosure of origin. IFEG 7974-2:2002 Conclusion of plume as convection (0.4 – 0.9). table

provided for different fuels. contradicting. More information in 7974.

Mean flame height and virtual origin mentioned.

Luminous flame height – Cox and Chitty or Heskestad – whichever is more onerous. Calculations outlined for flame height and mass flow rate of smoke and entrained air.

Dissimilar, but not contradicting. More detail in BS 7974.

McCaffrey Model – equations given for mass entrainment rate for flame region, intermittent flame region and buoyant plume.

Axi-symmetric plumes: Discussion about the movement of smoke and air entrainment.

Dissimilar, but not contradicting. BS 7974 has greater detail and commentary.

Not mentioned. Line Plume: Where L=5W of fire base. Flame height, mass flow of smoke. Dependant on length of side and HRR.

N/A –not mentioned in IFEG

References the use of reflection (Mowrer and Williamson 1987). No calculation given.

Effect of Adjacent Walls: the reduction of entrained air from the perimeter causes the flame height to lengthen. Flame height and mass floor of smoke given for fire against wall and in corner.

Dissimilar, but not contradicting. More detail in BS 7974.

Not mentioned. Fire induced winds: Inlet air velocity causes the flame jet to move away from opening. Mass flow of smoke can be calculated.

N/A – BS 7974 has more information.

Smoke plumes above fire source

Stack effect makes reference made to Klote and Milke (2002). Equation given for vertical smoke flow rate (kg/s).

Stratification of Smoke: two equations for stratification of smoke rise (m). Dependant on temperature and height of rise.


Ceiling jet mentioned in Detection sub system. Short explanation.

Plume impingement on ceiling. Ceiling jets are typically 5-12% of fire source to ceiling height in depth. Maximum velocities and temperatures occur in first 1% of fire source to ceiling height.

Dissimilar, but not contradicting – BS 7974 goes into more detail.

Axi-symmetric ceiling jet: temperatures and velocities in unconfined spaces discussed. Equations outline the maximum temperature rise and maximum gas velocities and is dependant on the radial distances and height of ceiling above the fire source. (Alpert 1972).

Axi-symmetric ceiling jet: temperatures and velocities in unconfined spaces discussed. Equations outline the maximum temperature rise and maximum gas velocities and is dependant on the radial distances and height of ceiling above the fire source. (Alpert 1972).

Identical.

Ceiling Jets

References Delichatsios 1981. Two-dimensional ceiling jet: Where beams or corridors inhibit plume spread, the velocity and temperature rises will be different to unenclosed spaces. The velocity and temperature rises are dependant on the width of the corridor and the distance to a point which wants to be found. (Delichatsios 1981)

Identical references – BS 7974 goes into more detail.

Flow from enclosure openings

Rockett (1976) and Edmonds (2002) equation given for mass flow out of an opening. Dependant on density of smoke and opening.

Calculation of mass flow of smoke from a vertical opening before the onset of flashover is considered (Thomas 1992). This is based on the temperature rise, air density, depth of smoke layer and the profile correction factor. Depth of smoke layer is presented based on a constant of proportionality.






Smoke spread from other than the enclosure of fire origin is stated as being difficult using hand calculations are rarely used although SFPE handbook has some calculations.

Spill Plumes: discusses the effect of large spill areas. Large uncertainties can be involved. The mass flow rates include the effect of the width of the opening. Calculations for mass flow of smoke presented.

Dissimilar, but not contradicting. BS 7974 provides greater discussion and provides hand calculations.

Flow through a horizontal vent references Klote and Milke (2002). Equation given for vertical smoke flow.

Flow of hot gases through natural horizontal vents: calculation given to determine the mass flow rate through a horizontal vent (Thomas et al 1963).

Similar – Different equations with same basis used.

Replacement Air

Briefly mentioned. Essential for inlet to be provided, maximum speed 5m/s.

BS 7974 provides more detail.

Upper temperature of layer from McCaffrey. Dependant on openings, materials in room and fire size.

Temperature of the hot gases: represented by the relationship between fire size and mass flow of smoke.


Not mentioned. Smoke volume flow rate: well mixed smoke layer volume flow rate represented by temperature and mass flow of the smoke.

N/A – BS 7974 goes into more detail.

Optical density of smoke: expression given on the way light is attenuated in respect to source intensity and optical density of smoke.

Optical density of smoke: expression given on the way light is attenuated in respect to source intensity and optical density of smoke. The optical density of smoke is a function of the total volume of smoke and the mass optical density of the fuel.


Visibility through smoke is not given. Optical density per unit length can be found.

Visibility through smoke: visibility through the smoke is one over the optical density per unit length (Tewarson 1995).

Similar – BS 7974 goes into more detail.

Short discussion on the use of gas species concentrations. Consideration required for certain toxins when related to life safety.

Gas species mass concentrations: discussion about the means by which the mass concentration of a particular species can be found.

Dissimilar, but not contradicting. 7974 allows calculation of species concentration by mass.

Properties of Smoke

Not mentioned. Gas volume concentrations: dependant on the density of species.


Smoke Reservoir Size

No information given, references made to; Drysdale (1999), SFPE Handbook (DiNenno 2002), Klote and Milke (2002), Evans and Klote (2003). Referes to NFPA92B and NFPA 204.

Limits for smoke reservoir sizes in the absence of computer modelling to 2000m2 for MoE, 2600m2 for powered and 3000m2 for property.

Dissimilar, but not contradicting. Greater detail in BS 7974.

Minimum number of exhaust Ventilators

Refers to NFPA92B and NFPA 204.

The phenomenon of plug holing is discussed and the calculation for critical exhaust rate of ventilators away form a wall is given from BRE 368. The number of vents can be found from the mcrit and the mass flow entering the layer.


Interactions of sprinklers and smoke ventilation

No mentioned. References BRE 368 to determine whether sprinklers will affect the designed smoke control system and the effect the temperature control will have on the sprinkler system.


Not mentioned. Discussion on the problems associated with free hanging smoke curtains and horizontal deflections.


Free hanging smoke curtains

Not mentioned. Curtains containing a smoke layer: the deflection of the smoke curtain






can be calculated from the parameters of the curtain and projected smoke layer. Length of curtain required is iterative.

Not mentioned. Curtains closing an opening: deflection of curtain and length can be found.


Fire Safety Management IFEG SS-C 7974-2:2002 Conclusion Management Suggest management

procedures for active systems particularly and consideration required for passive systems.

Defines the use of BS 9999: 4 to determine frequency of maintenance.

IFEG goes into more detail, 7974 references a management document.

Data IFEG SS-C 7974-2:2002 Conclusion Convected fractions

0.7 referred to as standard. Convected fractions for various materials


Means of determining via use of extinction coefficient.

Mass optical densities and CO yield of various products.

N/A – BS 7974 goes into more detail. Mass optical density

Not mentioned. Mass optical densities and CO yield of various materials.


Computer Modelling IFEG SS-C 7974-2:2002 Conclusion Mentioned as a means of analysis, no advice given.

Discussion of model types, zone models, CFD, thermal radiation etc.


Conclusions IFEG SS-C 7974-2:2002 Conclusion Where calculations and

concepts are not given, reference one of a number of books/papers. Good flow chart of procedures. Some details are brief. Some information in other sub-systems.

Provides defined areas to provide smoke ventilation and smoke control in enclosures and large spaces.

Both provide the answers, although only BS 7974 provides them within the document. IFEG references other document heavily, some widely-used calculations are not present.




Sub-system 3- Structural response and fire spread beyond the enclosure of origin IFEG 7974-3:2003 Conclusion

General Recognition of fire tests

It is appreciated that the standard fire test curves do not represent a real fire time-temperature curve.

Information from standard tests is reasonably well understood. In most cases this allows a rapid appraisal of an element’s ability to resist fire spread and maintain structural function.

Dissimilar, but not contradictory

Time equivalence

Recognises and shows the Eurocode1 approach. The recommended kb value (0.08-0.045) is however higher than the recommendations given in EC1. This is referenced to Kirby (1999)

Recognises and shows the Eurocode1 approach. kb is set in a range of 0.09-0.05 with a recommendation for UK for 0.07. This is higher than the values found in EC1.

The recommendations given are similar between the two publications. They do however differ from the EC1. The EC1 suggests a kb ranging between 0.04 and 0.07.

Fire severity IFEG 7974-3:2003 Conclusion

Maximum temperature equation shown, as well as a similar equation for through draught conditions.

Determination of fire conditions through engineering calculations

Basic heat balance and references to simple relationships.

Transient fire conditions equations shown from DD ENV 1991-2-2


Structural Performance IFEG 7974-3:2003 Conclusion General Much of the information given

on this subject seems to be taken from a standard presented by the American Society of Civil Engineers. ASCE/SFPE 29, 1999.

Very detailed on the structural performance of different construction units in fire conditions.


Empirical equations based on the standard time temperature curve to predict temperature profiles within concrete members

Concrete Simplified design processes for reinforced concrete members are referenced to a number of national standards from Australia, New Zeeland, Eurocode. Information given on thermal

elongation and shrinkage, specific heat capacity, thermal conductivity, density and emissivity.

NA-7974 contains a lot of practical guidance. IFEG references to other sources and only provides a rough commentary.

Section factors from BS 5950-8 and temperature rise within a steel member is calculated from DD ENV 1993 1-2.

Eurocode 3-Design of Steel structures is recommended as a suitable guide for steel design. Guidance is given on when FEM methodology should be used over simpler methodologies. Information given on thermal

elongation, specific heat capacity, thermal conductivity, density and emissivity.

NA-IFEG provides a fair bit of information on existing standards. No practical guidance is found in the document. BS7974 provides more data and guidance in the document but other sources will still need to be studied to perform an analysis.

Protection to external steel member is referenced to Law and O’Brien (1981) and EC1 and EC3

Protection to external steel member is referenced to Law and O’Brien (1981).

Identical

Steel

Short discussion on the possible fire protection measures available for steel structures.

Detailed recommendations of calculation methodologies for protected steel.

NA-7074 provides more practical guidance.

Timber Confirms a charring line equal The charring rate is estimated Dissimilar, but not contradictory-





using Hadvigs (1981) equations. Equations for time to maximum charring rate and time dependant charring rates shown. Charring rates from BS 5268-4.1 and DD ENV 1995-1-2 is shown. It is suggested, in accordance with BS 5268-4.1, that charring rates to columns should be increased by 25% compared to a beam.

to the 300°C line of heating. Refers to White (2002) and an Australian Standard. EC 5 is mentioned as a source of charring rate equations

Information given on thermal elongation and shrinkage, specific heat capacity, thermal conductivity, density and emissivity.

IFEG only provides a very short commentary of timber behaviour in fire, with references to external sources. BS7974 provides more data and practical guidance, but studies of external sources is still necessary for a complete analysis.

Masonry Reference for methodologies given to Australian Standard AS 3700

Information given on thermal elongation and shrinkage, specific heat capacity, thermal conductivity, density and emissivity.

NA-7974 provides information that is more related to thermal properties rather than structural design. IFEG appreciates that there is not much guidance available but still references a national standard for some guidance.

Lightweight Timber/ Steel Frame assemblies

References given to thermal calculations on lightweight timber walls performed by Clancy (1999), Collier (1996) and others. Lightweight steel frame guidance is referenced to Gerlich et al.

General description on the fire performance of these constructions. The structural performance is referenced to BS 5268.

NA-IFEG does not provide any data or practical guidance but refers to a number of sources.

Plastics No information given Information given on thermal elongation and shrinkage, specific heat capacity, thermal conductivity, density and emissivity.

NA-7974 provides more information, mostly on the thermal properties but some also on structural performance.

Aluminium No information given Information given on thermal elongation and shrinkage, specific heat capacity, thermal conductivity, density and emissivity. Some guidance on structural stress behaviour in raised temperatures.

NA-7974 provides more information, mostly on the thermal properties but some also on structural performance.

Summary of information on structural performance

7974 provides a great deal of information on the structural performance of most the common building materials. IFEG is very limited in its guidance and refers to other sources.

Fire spread IFEG 7974-3:2003 Conclusion General The recommended approach

to determining the appropriate fire resistance of barriers is to utilise the time equivalence model and then use a barrier that can achieve the resulting fire period.

Design guidance on openings into fire enclosure: -doors should be assumed open if enclosure has no other openings -doors should be assumed closed if the enclosure has other openings -all enclosure surfaces (including glazed openings) may be assumed to be imperforate for the duration of fire provided analysis hasn’t proved otherwise. -Monte Carlo analysis is recommended to evaluate combinations of openings

NA

Heat flow by conduction

No information given Designer should take “great care” if deciding to use a criterion of a surface temperature on the unexposed side in

NA-7974 provides quantified guidance.





excess of 200°C Heat flow by convection

No information given Criteria of 500°C can be used when establishing likelihood of spontaneous ignition due to convection only. Piloted ignition is assumed to be probable in the region 400-450°C Some criteria given for human tolerability levels, 60°C saturated air is mentioned as intolerable.

NA-7974 provides quantified guidance.

Heat flow by radiation

Various references to publications regarding external fire spread. Some data on ignitability limits under radiant heat flux. The spontaneous ignition criterion for wood is set to 250-400°C.

Standard radiation relationships shown. 12.6kW/m2 is mentioned as a criterion, giving “some factor of safety” Possible to base analysis on the increase of surface temperature of the object exposed. For organic solids a surface temp. criterion of 600°C is suggested for spontaneous ignition, and 300-410°C for ignition by flying brands under a radiative heat flux..

NA-7974 provides quantified guidance. IFEG provides a short commentary and references to other guidance documents. Only very brief quantified guidance on ignitability.. Some dissimilarity in the criteria for ignition of solids.

Presence of flying brands hard to determine with any certainty. Should be considered as piloted ignition leads to lower necessary surface temperatures.

Heat flow by mass transfer

BS 476-3 is recommended for a methodology assessing the ignitability of roof coverings subject to radiative heat fluxes and flying brands Design care should be taken to mass

flow of burning liquids.

NA-IFEG provides a very short commentary, but does reference a test method for assessing ignitability of surfaces exposed to flying brands. 7974 does not provide any quantified guidance.

Heat flow by direct pyrolysis and reaction to fire

No information given A reasonable design approach is to assume that all combustibles within enclosure will at some point become involved in the fire. Any part of continuous combustible construction that extends outside the enclosure the enclosure should be viewed as permitting fire spread beyond that enclosure.

NA-Some practical guidance from 7974. No guidance in IFEG.

Fire spread in large enclosures

It is recognised that assuming simultaneous combustion in enclosures over 150m² leads to unrealistically high temperatures in the enclosure. It is recommended that the floor area should be sub-divided into smaller grids (10-50m²) and that fire spreads from one grid to another.

It is recognised that the size of the enclosure influences the potential fire severity and that a fire in a large compartment is more likely to be fuel bed controlled than fires in smaller compartments.

Similar-The IFEG suggests a quantified value, whilst 7974 only provides a qualitative comment.

Computer models

Provides information on the use of computer models in the design process, and what one should keep in mind when utilising computational modelling. The models discussed are zone and field models used to establish fire severity. The use of FEM models is also discussed.

No information NA- IFEG provides more information.

Summary It seems that 7974 provides comprehensive quantified guidance to many aspects of structural performance in fires. The section regarding thermal properties is extensive but the information is effectively very simple physical properties. IFEG is more qualitative and often only suggest other sources for where the information can be found.




Sub-system 4-Detection of fire and activation of fire protection systems. IFEG 7974-4:2003 Conclusion General Extensive References to BS 5839 and

BS EN 54

Type of detectors IFEG 7974-4:2003 Conclusion

Two models mentioned: Optical density and Heat detector equivalence

Mentions the research performed regarding the temperature rise needed to activate a smoke detector.

Smoke detectors is assumed to activate when the temperature is raised 13°C above ambient. (Heskestad 1981)

13°C above ambient is mentioned.

Identical

For flaming fires, DD 240-1 is referenced for the equation showed for smoke detector activation time. It does also require the detectors specific sensing threshold. Point-type smoke detectors need a surrounding air velocity of at least 0.15m/s to be able to detect fire.

Smoke

For the optical density detection model only brief information is provided, and a simple correlation between light depletion and detector threshold. It is stated that calculations of the optical density should be performed for the plume or preferably the ceiling jet.

For non-flaming fires alternative method will have to be sought

Dissimilar, but not contradicting. IFEG does not really provide any calculations on the activation of smoke detectors. 7974 provides more practical information, especially on the heat detector equivalence.

The concept of RTI is described.

The concept of RTI is described. Identical

BS EN 54-5 is referenced for tables showing detector response times

Heat detectors

Alpert (1972) ceiling jet model for gas temperature and gas velocity predictions. Additional equations shown for special applications such as high ceilings or partially confined ceilings. These are referenced to NFPA 92B. Quintere et al. (1982) model for temp.

rise in the hot layer. This is suggested as a worst case scenario for combined fixed-temperature/ heat-rise detectors. Qualitative commentary on cases where smoke spread is confined by beams and narrow corridors etc.

Dissimilar, but not contradicting. It should be noted that the equations shown for heat detector activation are quite dissimilar, it is however hard to determine how much of an impact this has on the estimation of activation time.

Beam detectors

An unreferenced equation is shown for the optical density required to cause activation of a beam detector.

A relationship for the obscuration is shown. This is referenced to an EN standard in draft. EN 54-12

Similar-The equations shown are almost the same, but they differ by a factor 10. One would think that 7974 would therefore be expressed in bel rather than decibel, but this does not seem to be the case. It is therefore unclear if the references used in the two guides are interchangeable.

Manufacturers specifications and SS-B “smoke development and control” parameters

British Fire Protection Systems Association “COP for Category 1 Aspirating Detection Systems” (1996) is referenced for information.

NA Aspirating detectors

Each sampling point can be modelled as an individual point detector. Long detection time delays in large

When considering location of smoke sampling points, the best analogy is to consider them as individual point detectors. Long detection time delays in

Identical




Sub-system 4-Detection of fire and activation of fire protection systems. IFEG 7974-4:2003 Conclusion

systems. large systems. Linear heat detectors

No information A brief discussion of the applicability of linear detectors. The most practical way of assessing their performance is recommended to be by regarding them as a continuous line of heat detectors.


Flame detectors

It is recommended that normal radiation and view factor equations should be utilised to calculate the radiation impinged on the detector.

SFPE handbook relationship for the level of radiation impinged on the detector. The SFPE refers to standard curves for fire size and distance. The BS EN 54-10 standard is mentioned.

Dissimilar, but not contradicting.- 7974 provides quantitative guidance.

Gas detectors No acceptable methodology available for detection times.

Carbon monoxide detectors mentioned, with a relationship for the mass flow of CO as a function of total mass flow. A threshold value of 40 ppm is mentioned.


Manual detection

No information It is stated that manual call points should be provided to aid in raising an alarm.


Spacing of detectors IFEG 7974-4:2003 Conclusion No information given It is recognised that siting and spacing of

detectors to a standard template (BS 5839-1 mentioned) is not likely to provide the optimum performance and that engineered layouts can provide a more effective system.

NA

Automatic suppression IFEG 7974-4:2003 Conclusion Sprinklers Madrzykowski and Vittori (1992)

relationship for heat release after sprinkler initiation. Evans (1993) NIST relationship between spray density and heat release. An extended radius is recommended to incorporate a degree of conservatism in the detection time equations.

Evans (1993) NIST relationship between heat release and spray density. This is presented as a conservative estimate. Bs 5306-2 is referred to for engineering guidance

Similar

Water mist Referred to applicable national standard.

General discussion on the subject. Reference to NFPA 750 for more information

NA-7974 provides more information, mostly qualitative but with some guidance on high, low or medium pressure systems.

Gaseous suppression system

Referred to applicable national standard.

General discussion on the subject. Reference to BS ISO 14520 for more information

NA-7974 provides more information, such as the impact of fire growth.

Foam system No information given General discussion on the subject. Reference to SFPE handbook for more information

NA-7974 provides more information, such as the impact of fire growth.

Activation of fire barrier system IFEG 7974-4:2003 Conclusion No information given General discussion on the subject,

including failure modes. NA-7974 provides more information, such as the impact of fire growth.




Sub-system 4-Detection of fire and activation of fire protection systems. IFEG 7974-4:2003 Conclusion Activation of smoke control systems

IFEG 7974-4:2003 Conclusion No information given General discussion on the subject,

including failure modes NA-7974 provides more information

Summary 7974 provides more practical information and quantified guidance. It also addresses issues such as choosing the right detection system with regards to false alarms. The IFEG keeps the quantified guidance to a minimum, and the equations shown are often very basic physical relationships.

Sub-system 5-Fire service intervention.

IFEG 7974-5:2002 Conclusion The Australian FBIM (Fire Brigade Intervention Model) Model) is presented as an appropriate method for quantification of fire service intervention.

The time for fire service attendance is referenced to the Home Office, and a table of recommended time limits is shown for different areas depending on the areas risk classification.

The FBIM employs a structured decision-based framework necessary both to determine and measure fire service activities on a time-line basis.

The only details to support a quantified analysis are the recommended time limits and a notation that the initiation of fire tackling will take “upwards 10 minutes from the time of arrival”

The fire service operation is split up into 16 flowcharts.

A detailed description of what is expected of fire service provisions installed in a building, but their respective relation to fire service operations is not thoroughly explained.

The description of the FBIM is very much an overview, and the IFEG does not cover any technical details of fire service provisions and operations. The FBIM (2004) is referenced for quantified estimates for each flowchart.

Very little information on where the reader can find more information about quantified analysis of fire service operations.

NA-IFEG provides a model or a framework for fire service intervention. 7974 provides more information, but this is qualitative to a great extent.

Summary The IFEG effectively refers all of its recommendations to the FBIM. It also appreciates that the FBIM is a unique document as Australia is the only country that has produced such an extensive quantified guide. It is also appreciated that the guidance given in FBIM is developed with Australian conditions in mind, and that the guidance given in the document may not be directly applicable to other countries. It is however suggested that the quantitative guidance in FBIM can be used as a semi-quantitative utility in other locations. 7974-5 is highly qualitative and does not provide any model for setting up a quantified model for fire service intervention. Some quantified guidance on the likely fire service response times as a function of the areas UK risk category.




Sub-system 6-Occupant evacuation, behaviour and condition. IFEG 7974-6:2004 Conclusion

The Required Time for Escape (RSET) is divided into a detection phase and a movement phase.

A description of Available Safe Escape Time (ASET) and Required Safe Escape Time (RSET).

It is recommended that Fire engineered Solutions should be based on data in publications such as the SFPE handbook and other scientific publications.

A quantified strategy is proposed, separating RSET into sub-elements, and guidance is given on quantified values for the time needed in the different sub-elements.

Very little quantitative guidance on the sub-elements of the escape time. A list of information sources is however presented.

Extensive quantified guidance on time to detection, travel speeds, evacuation times etc. given in appendices.

General

A model for travel times is referenced to Nelson & Mowrers’ work presented in the SFPE handbook.

A tenability criterion is given for zero exposure. This is given as a clear layer height of 2.5m and a smoke layer temperature not exceeding 200°C.

NA- the two documents are similar in such that they both appreciate the basic model for evaluating egress time, but 7974 provides more information in regards to the different parameters.

Summary The IFEG provides only qualitative guidance and refers extensively to other sources for guidance on several subjects in regards to evacuation. 7974 provides a mainly qualitative commentary on many different aspects of evacuation times and evacuation behaviour. Some quantified guidance is provided, most of the figures originates and relates from the UK.




Sub-system 6-Occupant evacuation, behaviour and condition. IFEG 7974-7:2003 Conclusion

The use of a probabilistic approach is recognised and described in the Overview section of Part 1.

One method of probabilistic risk assessment is shown. This method is based on Beck and Yung’s work, presented in1994.

Three method categories are described in some detail: -simple statistical analysis -logic tree analysis -sensitivity analysis A section also discusses complex analysis tools.

It is recognised that the acceptable risk can be of absolute type or comparative type. For life safety the result is shown as Occupant safety and Occupant number of deaths.

Acceptance criteria are shown as absolute or comparative. A number of examples of criteria is shown but it is highlighted that there is not a generally accepted criteria for fire risk in the UK. .

It is appreciated that risk analysis can be used to estimate financial loss. Fire Cost Expectation is mentioned.

A brief discussion on the financial aspects of probabilistic risk assessment. An example of cost-benefit analysis is shown.

An event tree technique is utilised to show different fire scenarios and establish the risk parameters.

A similar methodology is shown for estimations of monetary risk.

General

No information given on the cost-benefit side of fire protection or any target values for acceptable fire risk.

Data and information given on many of the parameters needed in a Probabilistic Fire Risk Assessment.

NA, but it is clear that 7974-7 provides more detail than IFEG

Summary 7974 provides the most guidance, both qualitative and quantitative, on the subject of risk analysis. Different techniques are described and the probability of different aspects of fire scenario models is discussed. IFEG provides some information on setting up a fire risk assessment and the results of such an analysis. Some quantitative guidance is provided on some parameters of fire scenarios, such as ignition frequencies, fire loads and detection/suppression system reliability. In general the 7974 provides “better” quantitative guidance as the guidance for several parameters is shown as a distribution rather than a point estimate or a mean value.



comparison ifeg 2005 vs bs 7974 2001

Documents

engineering guidelinesreview

engineering designs

safety engineering principles

technical handbooks

department of building

functional standards

detailed technical differences

building scotland regulations