IP RESEARCH REPORT IGNITION PROBABILITY REVIEW, MODEL DEVELOPMENT AND LOOK-UP CORRELATIONS

IP RESEARCH REPORT IGNITION PROBABILITY REVIEW, MODEL DEVELOPMENT AND LOOK-UP CORRELATIONS

January 2006

Published by ENERGY INSTITUTE, LONDON The Energy Institute is a professional membership body incorporated by Royal Charter 2003 Registered charity number 1097899

The Energy Institute gratefully acknowledges the financial contributions towards the scientific and technical programme from the following companies: BG Group BHP Billiton Limited BP Exploration Operating Co Ltd BP Oil UK Ltd Chevron ConocoPhillips Ltd ENI ExxonMobil International Ltd Kuwait Petroleum International Ltd Maersk Oil North Sea UK Limited Murco Petroleum Ltd Nexen Shell UK Oil Products Limited Shell U.K. Exploration and Production Ltd Statoil (U.K.) Limited Talisman Energy (UK) Ltd Total E&P UK plc Total UK Limited

Copyright 2006 by the Energy Institute, London: The Energy Institute is a professional membership body incorporated by Royal Charter 2003. Registered charity number 1097899, England All rights reserved No part of this book may be reproduced by any means, or transmitted or translated into a machine language without the written permission of the publisher. The information contained in this publication is provided as guidance only and while every reasonable care has been taken to ensure the accuracy of its contents, the Energy Institute cannot accept any responsibility for any action taken, or not taken, on the basis of this information. The Energy Institute shall not be liable to any person for any loss or damage which may arise from the use of any of the information contained in any of its publications. The above disclaimer is not intended to restrict or exclude liability for death or personal injury caused by own negligence.

ISBN 978 0 85293 454 8 Published by the Energy Institute Further copies can be obtained from Portland Customer Services, Commerce Way, Whitehall Industrial Estate, Colchester CO2 8HP, UK. Tel: +44 (0) 1206 796 351 email: sales@portland-services.com

CONTENTSPageForeword..vii Acknowledgements.......ix Overview....xi SECTION 1 - Phase 1 Report - Ignition probability review and model development .................................... 1 1.1 Introduction ............................................................................................................................................... 1 1.2 Literature review ....................................................................................................................................... 2 1.2.1 Review of historical ignition probability data............................................................................. 2 1.2.2 Ignition models and related issues .............................................................................................. 6 1.3 HCR OIR12 ignition event analysis........................................................................................................ 13 1.3.1 OIR12 2001 ignition data.......................................................................................................... 13 1.3.2 OIR12 2000 leak and ignitions data.......................................................................................... 17 1.3.3 OIR12 analysis - Summary ....................................................................................................... 24 1.4 Ignition modelling and related topics...................................................................................................... 24 1.4.1 Gas dispersion within plant areas.............................................................................................. 24 1.4.2 Gas dispersion outside plant areas ............................................................................................ 26 1.4.3 Ignition probability methods..................................................................................................... 27 1.4.4 Self-ignition .............................................................................................................................. 30 1.4.5 Ignition modelling and dispersion summary............................................................................. 31 1.5 Review conclusions and implications for ignition modelling ................................................................. 32 1.5.1 Model approach ........................................................................................................................ 32 1.5.2 Ignition data and simple probability correlations...................................................................... 32 1.5.3 Ignition timing and fire-explosion probabilities for use in QRA .............................................. 33 1.5.4 Release source modelling.......................................................................................................... 34 1.5.5 Control factors .......................................................................................................................... 35 1.5.6 Ignition timing and explosion probabilities Model implications ........................................... 35 1.5.7 Categorisation of fluid types ..................................................................................................... 36 1.5.8 Model development Initial concept........................................................................................ 36 1.6 Model description.................................................................................................................................... 38 1.6.1 Model structure ....................................................................................................................................... 38 1.6.2 Input data .................................................................................................................................. 41 1.6.3 Model output............................................................................................................................. 50 1.6.4 Model process detailed description........................................................................................... 51 1.6.5 Workbook model overview....................................................................................................... 63 1.7 Model benchmarking............................................................................................................................... 64 1.8 Model conclusions and recommendations .............................................................................................. 66 1.9 Issues for future work.............................................................................................................................. 66 Annex Annex 1.A References........................................................................................................................................ 67 Figures Figure 1.1 Simple correlation of fraction of liquid not raining out vs. discharge pressure based on RELEASE model estimates ................................................................................................................................... 10 Figure 1.2 Simple correlation of fraction of liquid not raining out vs. discharge pressure based on cyclohexane test data................................................................................................................................................ 11 Figure 1.3 Cumulative event based ignition probabilities - based on average release rate................................... 21 Figure 1.4 Cumulative event based ignition probabilities - based on maximum release rate ............................... 21 Figure 1.5 Ratio between maximum (initial) release rate and averaged release rate for 294' cut of OIR12 data 22 Figure 1.6 Cumulative event distribution for 294 data cut................................................................................. 22 Figure 1.7 Gas build-up JIP workbook - Output for selected typical module configurations .............................. 25 Figure 1.8 A comparison of different indicators for gas dispersion...................................................................... 26

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Figure 1.9 A comparison of ignition probabilities assigned by various models for some selected scenarios....... 30 Figure 1.10 Ignition modelling Areas.................................................................................................................... 37 Figure 1.11 Ignition modelling Areas.................................................................................................................... 39 Figure 1.12 Alternative ignition modelling Areas approach ................................................................................. 39 Figure 1.13 Ignition model structure ..................................................................................................................... 40 Figure 1.14 Ignition modelling Areas.................................................................................................................... 44 Figure 1.15 Ignition modelling Areas Cloud areas............................................................................................. 45 Figure 1.16 Alternative ignition modelling Areas approach ................................................................................. 45 Figure 1.17 Gas build-up JIP workbook correlation ............................................................................................. 57 Figure 1.18 Liquid release aerosol formation correlation ..................................................................................... 59 Figure 1.19 Release maximum vs. average release rate Decay factor................................................................ 61 Figure 1.20 Model comparison Gas releases...................................................................................................... 65 Figure 1.21 Model comparison Liquid releases ................................................................................................. 65 Tables Table 1.1 Analysis of offshore ignition sources ...................................................................................................... 2 Table 1.2 Generic ignition probabilities .................................................................................................................. 2 Table 1.3 Generic explosion probabilities (given ignition) ..................................................................................... 2 Table 1.4 Ignition sources for industrial plant......................................................................................................... 3 Table 1.5 Generic ignition probabilities (CMPT).................................................................................................... 3 Table 1.6 Generic ignition probabilities (Cox et al) ................................................................................................ 3 Table 1.7 Ignition delay probabilities...................................................................................................................... 3 Table 1.8 Judged ignition probabilities for a range of offshore scenarios............................................................... 4 Table 1.9 Proposed generic ignition probabilities for typical offshore hydrocarbon releases................................. 4 Table 1.10 Suggested method for assigning ignition timings.................................................................................. 5 Table 1.11 Ignition timings - Based on an analysis of LPG releases ...................................................................... 5 Table 1.12 Probability of explosion given ignition - Based on offshore data ......................................................... 5 Table 1.13 Onshore gas pipeline leak ignition probabilities ................................................................................... 6 Table 1.14 Onshore gasoline pipeline leak ignition probabilities ........................................................................... 6 Table 1.15 Ignition source densities (per hectare)................................................................................................... 8 Table 1.16 Ignition parameters for area based model ........................................................................................... 9 Table 1.17 Estimated rain-out fractions for flammable liquid releases (RELEASE model) ................................... 9 Table 1.18 Analysis of all ignitions by cause and source of ignition .................................................................... 13 Table 1.19 Analysis of OIR12 MAH related ignition events ................................................................................ 14 Table 1.20 Analysis of OIR12 database large releases.......................................................................................... 17 Table 1.21 Analysis of OIR12 database large releases - more bands.................................................................... 18 Table 1.22 Analysis of OIR12 database large releases - 499 events by maximum and average release rate basis ................................................................................................................................................. 19 Table 1.23 Analysis of OIR12 database large releases - comparison with cumulative basis ................................ 20 Table 1.24 Analysis of large liquid releases.......................................................................................................... 23 Table 1.25 Analysis of OIR12 database - Ignition timing..................................................................................... 23 Table 1.26 Analysis of OIR12 database - Ignited events ...................................................................................... 24 Table 1.27 CHAOS based model from DNV TDIM JIP - Appendix G - Gives average gas concentration in module vs. time ................................................................................................................................... 25 Table 1.28 DNV TDIM - Recommended ignition source densities ...................................................................... 27 Table 1.29 Application of DNV TDIM ignition sources to a typical module ....................................................... 27 Table 1.30 Selected results for a typical offshore module based on the WS Atkins on-site ignition methodology ........................................................................................................................................ 28 Table 1.31 Comparison of ignition probabilities assigned by various models to selected scenarios .................... 29 Table 1.32 Self-ignition probabilities.................................................................................................................... 31 Table 1.33 Generic ignition probabilities (Cox et al and Revised)..................................................................... 32 Table 1.34 Ignition timings overview.................................................................................................................... 33 Table 1.35 Relative incidences of ignited events .................................................................................................. 33 Table 1.36 Pool spill sizes ..................................................................................................................................... 35 Table 1.37 IP fluid categories................................................................................................................................ 36 Table 1.38 Relationship between IP fluid categories and petroleum classes ........................................................ 36 Table 1.39 Ignition model input data..................................................................................................................... 41 Table 1.40 Ignition area types set up in model...................................................................................................... 43 Table 1.41 Release types - Data entry ................................................................................................................... 49

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Table 1.42 Model output data and format ............................................................................................................. 50 Table 1.43 Model output information.................................................................................................................... 51 Table 1.44 Ignition source densities for onshore offsite areas .............................................................................. 53 Table 1.45 Typical ignition source densities for onshore plant............................................................................. 53 Table 1.46 Hot work ignition characteristics......................................................................................................... 54 Table 1.47 DNV TDIM - Recommended ignition source densities ...................................................................... 54

SECTION 2 - Phase 2 Report Look-up correlations..................................................................................... 69 2.1 Introduction ............................................................................................................................................. 69 2.2 Model description.................................................................................................................................... 69 2.2.1 Model structure ......................................................................................................................... 69 2.2.2 Input data .................................................................................................................................. 71 2.3 Phase 2 overview and representative scenarios....................................................................................... 73 2.4 General basis and assumptions................................................................................................................ 74 2.4.1 Fluids considered ...................................................................................................................... 74 2.4.2 Release rates.............................................................................................................................. 75 2.4.3 Windspeed ................................................................................................................................ 76 2.4.4 Liquid pool sizes ....................................................................................................................... 76 2.4.5 Onsite offices and administration areas .................................................................................... 76 2.4.6 Liquid only spills No flashing or atomisation........................................................................ 76 2.4.7 Pressures ................................................................................................................................... 77 2.4.8 Module geometry and orientation factor................................................................................... 77 2.4.9 Areas 2 and 3 Confinement.................................................................................................... 78 2.4.10 Storage area ignition parameters............................................................................................... 80 2.5 Scenario specific configurations ............................................................................................................. 80 2.5.1 Onshore pipeline (cross-country).............................................................................................. 80 2.5.2 Onshore small plant .................................................................................................................. 81 2.5.3 Onshore large plant ................................................................................................................... 81 2.5.4 Onshore storage ........................................................................................................................ 82 2.5.5 Offshore NUI ............................................................................................................................ 83 2.5.6 Offshore FPSO.......................................................................................................................... 83 2.5.7 Offshore wellhead module ........................................................................................................ 84 2.5.8 Offshore process or compression module................................................................................. 84 2.5.9 Offshore riser ............................................................................................................................ 84 2.5.10 Offshore release engulfing the platform ................................................................................... 85 2.6 Ignition modelling results........................................................................................................................ 88 2.6.1 Results presentation .................................................................................................................. 88 2.6.2 Onshore pipelines ..................................................................................................................... 88 2.6.3 Onshore plant............................................................................................................................ 88 2.6.4 Onshore storage ........................................................................................................................ 88 2.6.5 Offshore NUIs........................................................................................................................... 88 2.6.6 Offshore FPSOs ........................................................................................................................ 88 2.6.7 Offshore risers........................................................................................................................... 89 2.6.8 Offshore releases engulfing the platform.................................................................................. 89 2.6.9 Results discussion ..................................................................................................................... 89 2.7 Look-up correlations ............................................................................................................................... 91 2.7.1 Look-up correlation characteristics........................................................................................... 91 2.7.2 Look-up correlation selection ................................................................................................... 92 2.8 Ignition timing and outcome probability distributions .......................................................................... 100 2.8.1 Modelling ignitions in QRA ................................................................................................... 100 2.8.2 Ignition timing ........................................................................................................................ 100 2.8.3 Ignition outcome distribution.................................................................................................. 101 2.8.4 Ignition timing vs. ignited event outcomes ............................................................................. 102 2.8.5 Addressing ignition outcomes in QRA ................................................................................... 103 Annexes Annex 2.A References...................................................................................................................................... 106

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Annex 2.B Ignition modelling results figures and look-up correlation figures for scenario specific configurations ................................................................................................................................. 107 Figures Figure 2.1 Ignition modelling Areas................................................................................................................... 70 Figure 2.2 Ignition model structure .................................................................................................................... 70 Figure 2.3 Model results for onshore pipeline Oil......................................................................................... 108 Figure 2.4 Model results for onshore pipeline LPG ...................................................................................... 108 Figure 2.5 Model results for onshore pipeline Gas ....................................................................................... 109 Figure 2.6 Model results for small onshore plant Open plant area................................................................ 109 Figure 2.7 Model results for small onshore plant Confined/ congested plant area........................................ 110 Figure 2.8 Model results for large onshore plant Open plant area ................................................................ 110 Figure 2.9 Model results for large onshore plant Confined/ congested plant area ........................................ 111 Figure 2.10 Model results for onshore tank farm LPG Passive dispersion ................................................ 111 Figure 2.11 Model results for onshore tank farm Oil Passive dispersion................................................... 112 Figure 2.12 Model results for onshore tank farm LPG Release treated as momentum jet ......................... 112 Figure 2.13 Model results for onshore tank farm Oil Release treated as momentum jet............................ 113 Figure 2.14 Model results for offshore process module Oil releases ............................................................ 113 Figure 2.15 Model results for offshore wellhead Oil releases....................................................................... 114 Figure 2.16 Model results for offshore NUI..................................................................................................... 114 Figure 2.17 Model results for offshore FPSO process module ........................................................................ 115 Figure 2.18 Model results for offshore FPSO process module behind transverse wall................................. 115 Figure 2.19 Model results for offshore process module Gaseous releases.................................................... 116 Figure 2.20 Model results for offshore wellhead and compression modules Gaseous releases .................... 116 Figure 2.21 Model results for offshore riser Release near to edge of installation ......................................... 117 Figure 2.22 Model results for offshore riser Release away from edge of installation................................... 117 Figure 2.23 Model results for offshore release engulfing platform.................................................................. 118 Figure 2.24 Cox, Lees and Ang ignition probabilities for comparison ............................................................ 118 Figure 2.25 Look-up vs. model results for offshore NUI................................................................................. 119 Figure 2.26 Look-up vs. model results for offshore process module Gas ..................................................... 119 Figure 2.27 Look-up vs. model results for offshore process module Gas Congested or mechanically ventilated module.......................................................................................................................... 120 Figure 2.28 Look-up vs. model results for offshore risers ............................................................................... 120 Figure 2.29 Look-up vs. model results for offshore FPSO no wall............................................................... 121 Figure 2.30 Look-up vs. model results for offshore FPSO with transverse wall .......................................... 121 Figure 2.31 Look-up vs. model results for offshore release engulfing platform .............................................. 122 Figure 2.32 Look-up vs. model results for offshore process module Liquid ................................................ 122 Figure 2.33 Look-up vs. model results for onshore pipelines Gas/ LPG ...................................................... 123 Figure 2.34 Look-up vs. model results for onshore pipelines Liquid............................................................ 123 Figure 2.35 Look-up vs. model results for onshore small plant Gas/ LPG ................................................... 124 Figure 2.36 Look-up vs. model results for onshore small plant Liquid......................................................... 124 Figure 2.37 Look-up vs. model results for onshore large plant Gas/ LPG .................................................... 125 Figure 2.38 Look-up vs. model results for onshore large plant Liquid ......................................................... 125 Figure 2.39 Look-up vs. model results for onshore storage Gas/ LPG ......................................................... 126 Figure 2.40 Look-up vs. model results for onshore storage Liquid............................................................... 126 Figure 2.41 Look-up correlations (best fit) for onshore liquid releases ........................................................... 127 Figure 2.42 Look-up correlations (best fit) for onshore gas/LPG releases....................................................... 127 Figure 2.43 Look-up correlations (best fit) for offshore liquid releases........................................................... 128 Figure 2.44 Look-up correlations (best fit) for offshore gas releases............................................................... 128 Figure 2.45 Look-up correlations (best fit) for offshore engulfing release and riser release ........................... 129 Tables Table 2.1 Ignition model input data.................................................................................................................... 71 Table 2.2 Ignition area types set up in model..................................................................................................... 73 Table 2.3 Release materials and properties ........................................................................................................ 75 Table 2.4 Release mass flow rates used.............................................................................................................. 75 Table 2.5 Scenarios pressures used .................................................................................................................... 78 Table 2.6 Offshore module f4 geometry and orientation factor assessment....................................................... 79 Table 2.7 Storage ignition parameters ................................................................................................................ 80 Table 2.8 Ignition probability scenario configurations....................................................................................... 86

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Table 2.9 Look-up correlation characteristics .................................................................................................... 93 Table 2.10 Look-up correlation selection guide................................................................................................. 96 Table 2.11 Ignition timings overview............................................................................................................... 101 Table 2.12 OIR 12 data ignition timings .......................................................................................................... 101 Table 2.13 OIR 12 data ignition outcome distribution by media ..................................................................... 102 Table 2.14 OIR 12 data ignition outcome distribution by leak severity........................................................... 102 Table 2.15 Plant ignition timings distribution .................................................................................................. 103 Table 2.16 Ignition source densities (per hectare)............................................................................................ 104 UKOOA ignition model workbook single scenario format Worksheets Read me User guide Results record Summary Area 1 plant area Areas 2-4 Area 2 ign Area 3 ign Area 4 ign Area 1 liquid Area 2 liquid Area 3 liquid UKOOA ignition model workbook multirun format Worksheets Read me User guide Data file Results record Chart_all Summary Area 1 plant area Areas 2-4 Area 2 ign Area 3 ign Area 4 ign Area 1 liquid Area 2 liquid Area 3 liquid Look-up correlations workbook Worksheets Read me User guide Examples Look-up factors Full test Select Chart select Basis Data Chart_all Chart_onsh_tank_pipe Chart_onsh_plant Chart_offsh

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FOREWORDThe probability of ignition of flammable releases from onshore and offshore installations is a key factor in determining the risks such installations present to people, assets and the environment. Yet, data and practical models available to enable assessors to assign suitable ignition probability distributions in quantified risk analysis (QRA) have been lacking. IP Ignition probability review, model development and look-up correlations provides the findings of a United Kingdom Offshore Operators Association (UKOOA)/ Health and Safety Executive (HSE)/ Energy Institute (EI) co-sponsored project undertaken by ESR Technology (formerly the Engineering Safety and Risk Business of AEA Technology) to improve the modelling of ignition probabilities in onshore and offshore installation QRAs. Specifically, the project reviewed current data and models, developed an ignition probability model for assigning ignition probabilities in QRA, and developed a simple basis and guidance for assigning ignition probabilities to generic scenarios. Phase 1 of the project reviewed knowledge and research in the field of ignition probability estimation in support of QRA. This was evaluated, together with the usefulness of the UK offshore industry hydrocarbon release data, as a basis for developing an improved ignition probability model. The review concluded that the commonly applied approach of adopting generic correlations based on the mass release rate for the probability of ignition was overly simplistic, and may lead to unrealistic and very conservative estimates in some situations. Further, some of the correlations in use do not reflect recent ignition probability data and knowledge. An ignition probability model was developed that combined recent work on the dispersion of flammable vapours in process areas with the identification of ignition characteristics in offshore and onshore plant areas and other relevant onsite and offsite land use types. It has been benchmarked against historical ignition probability data. The model made available as a functional workbook provides a means to estimate the overall ignition probability and an approximate time/ location distribution for specific release scenarios. It can also provide an insight into the main ignition factors and allows sensitivity analysis and 'what-if' analysis, which may help designers to change the plant layout or process conditions to reduce the ignition potential. Recognising that the number of factors taken into account by the model means it may be too onerous to apply for some risk assessments, Phase 2 of the project involved development of a series of simple, mass release rate based, ignition probability look-up correlations for a selected range of representative onshore and offshore plant and storage release scenarios. These correlations made available as a functional workbook provide users with a simple and convenient introductory means to incorporate more appropriate ignition probability data in many typical QRAs. Their scope includes liquid and vapour release correlations; in addition, two-phase releases can be assessed by combining the liquid and vapour results. The look-up correlations are supported by guidance on selecting the appropriate correlation to use in a given situation, and details of the underlying basis and assumptions used in deriving them. Note that the full model should be run for complex scenarios or where additional detail is required. Some guidance is provided on ignition timing and estimating the likelihood of an explosion given ignition. Note that the model and look-up correlations are intended to assess the ignition potential of momentum driven releases of hydrocarbons; however, they are not suited to the ignition probability assessment of refrigerated liquefied gases, vaporising liquid pools, sub-sonic gas releases, or non-momentum driven releases, such as those following catastrophic storage vessel failure. IP Ignition probability review, model development and look-up correlations should be drawn to the attention of safety practitioners, risk analysts and designers who need to determine or evaluate ignition probabilities in QRA, such as where required for safety cases or safety reports. The project sponsors believe that the model and look-up correlations provide a more appropriate means for assigning ignition probabilities in QRA as they take better account of the release type and plant characteristics, and results better align with historical data including the UK offshore industry hydrocarbon release data. However, their use requires expert judgement and results should be used and interpreted with a degree of caution, in particular where they are less conservative than former approaches. In addition, those preparing or revising safety cases or safety reports should include details of pertinent assumptions and input data that support the derived ignition probabilities. The information contained in this IP Research Report is provided as guidance only and while every reasonable care has been taken to ensure the accuracy of its contents, the Energy Institute, the project cosponsors, the developer and the technical representatives listed in the acknowledgements, cannot accept any

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responsibility for any action taken, or not taken, on the basis of this information. The Energy Institute shall not be liable to any person for any loss or damage which may arise from the use of any of the information contained in any of its publications. The information contained in this IP Research Report may be reviewed from time to time. It would be of considerable assistance in any future revision if users would send comments (e.g. on the performance of the model and the look-up correlations) or suggestions for improvement to: The Technical Department Energy Institute 61 New Cavendish Street London W1G 7AR e: technical@energyinst.org.uk

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ACKNOWLEDGEMENTSThe project was undertaken by David Mansfield ESR Technology1 (formerly the Engineering Safety and Risk Business of AEA Technology) and co-ordinated by a joint industry steering group drawn from the project sponsors, petroleum operating companies and senior risk assessment consultants working in the field of onshore and offshore QRA: David Aberdeen Brian Bain Gerry Burke Stephen Connolly Howard Crowther Tim Davenport Alastair Gunn Richard Jones Robert Kyle Colin Morgan Mark Scanlon Chris Venn BP (Chairperson) DNV WS Atkins Health and Safety Executive Consultant Shell ExxonMobil Acona United Kingdom Offshore Operators Association ESR Technology Energy Institute WS Atkins

The Institute wishes to record its appreciation of the work carried out by them and others who participated during the technical review, for example by testing the draft deliverables. Affiliations refer to the time of participation. Co-sponsorship of this project by UKOOA and HSE is gratefully acknowledged.

1

ESR Technology, Whittle House, 410 The Quadrant, Birchwood Park, Warrington, WA3 6FW, United Kingdom. Telephone +44 (0)1925 843400. Facsimile +44 (0)1925 843500

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OVERVIEWThis IP Research Report comprises the following project deliverables: Phase 1 report: Ignition probability review and model development (provided as part of this Adobe Acrobat document) (issued to project sponsors as AEAT/NOIL/27780001/001(R) Issue 1); UKOOA ignition model workbooks (Version D1) in single scenario and multirun formats (provided as Microsoft Excel workbooks) (issued to project sponsors as Ukooa_Ignition_model_D1 Version D1 and Ukooa_Ignition_model_D1_multirun Version D1, respectively); Phase 2 report: Look-up correlations (provided as part of this Adobe Acrobat document) (issued to project sponsors as AEAT/NOIL/28129001/002(R) Issue 1); Look-up correlations workbook (Version D1) (provided as a Microsoft Excel workbook) (issued to project sponsors as Ukooa_pign_lookup_function_D1 Version D1).

Given that the project was carried out in two phases, some aspects of the Phase 1 report have been superseded by the Phase 2 report. In addition, the workbooks and Phase 1 report refer to earlier versions of the workbooks. Furthermore, the process of preparing the project deliverables for publication necessitated some editorial changes to the versions issued to the project sponsors. Notwithstanding this, none of these issues should affect the technical integrity of this IP Research Report. Phase 1 report: Ignition probability review and model development The Phase 1 report reviews knowledge and research in the field of ignition probability estimation in support of QRA. This was evaluated, together with the usefulness of the UK offshore industry hydrocarbon release data, as a basis for developing an improved ignition probability model. The review concluded that the commonly applied approach of adopting generic correlations based on the mass release rate for the probability of ignition was overly simplistic, and may lead to unrealistic and very conservative estimates in some situations. Further, some of the correlations in use do not reflect more up-to-date historical ignition probability data and knowledge. The report describes the basis for the ignition probability model, which combined recent work on the dispersion of flammable vapours in process areas with the identification of ignition characteristics in offshore and onshore plant areas and other relevant onsite and offsite land use types. The model has been structured to consider the ignition of hydrocarbons within the immediate area where the leak occurs, and any additional probability of ignition were the flammable vapour cloud or liquid to spread to adjacent areas or beyond. The model can provide an insight into the main ignition factors and allows sensitivity analysis and 'what-if' analysis, which may help designers to change the plant layout or process conditions to reduce the ignition potential. The report also describes benchmarking of the model against historical ignition probability data. UKOOA Ignition model workbooks The ignition probability model, which is referred to as the UKOOA Ignition model is provided in single scenario and multirun formats as Microsoft Excel workbooks (Version D1); the main difference being that the latter also includes a macro to run the model for a variety of user defined scenarios and release rates. The model input data consists of basic information on the release, the four Areas being considered and their ignition characteristics, and a number of options for modelling the release and any subsequent dispersion beyond the immediate area of release. The model provides an estimate of the overall probability of ignition for the scenario, together with contributions to the probability from vapour and liquid components of the release for each of the four Areas represented in the model. It also provides an approximate time distribution of the ignition probability as it spreads across them. The Microsoft Excel workbooks also include user notes and change records. Phase 2 report: Look-up correlations Recognising that the number of factors taken into account by the ignition probability model means it may be too onerous to apply for some risk assessments, the Phase 2 report describes use of the model to prepare a series of

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mass release rate based, ignition probability look-up correlations for a selected range of representative onshore and offshore plant and storage release scenarios. These correlations provide users with a simple and convenient introductory means to incorporate more appropriate ignition probability data in many typical QRAs. Their scope includes liquid and vapour release correlations; in addition, two-phase releases can be assessed by combining the liquid and vapour results. The look-up correlations are supported by guidance on selecting the appropriate correlation to use in a given situation, and details of the underlying basis and assumptions used in deriving them. However, users are cautioned that there will be situations where the nature or complexity of the scenario or the detail of the assessment means that the look-up correlations will not be sufficient. In these cases the full model should be used to estimate the relevant ignition probabilities. The Phase 2 report also offers guidance on ignition timing and estimating the likelihood of an explosion given ignition. In addition, it describes several improvements which were made to the model, primarily to provide additional error traps and to better represent plant storage area ignition characteristics. Look-up correlations workbook A Microsoft Excel workbook (Version D1) enables the ignition probability to be determined from the look-up correlations using a simple cell function formula requiring mass flow rate and scenario type inputs, linked to a visual basic module in the workbook. The workbook also contains other worksheets with information and useful supporting features related to the look-up correlations, such as a help guide to selecting the most suitable release type for a given situation, and the basis and characteristics of the correlations. Its functionality enables users to view all look-up correlation charts, those of similar types (e.g. onshore plant) or user-defined combinations.

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