OFFSHORE HYDROCARBON RELEASES STATISTICS, 2001 HID STATISTICS REPORT HSR

OFFSHORE HYDROCARBON RELEASES STATISTICS, 2001 HID STATISTICS REPORT HSR 2001 002 Date of Issue: January 2002 Health & Safety Executive

Preface This is the sixth report on statistics obtained from the HCR database, and is the fourth since the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995 (RIDDOR 95) came into force offshore on 1 st April 1996. The report presents data on hydrocarbon releases that have been reported for the period 1 st October 1992 to 31 st March 2001 inclusive. It should also be noted that the report is now part of a new (HID Statistics Report HSR) series to replace the OTO series, which is to be discontinued. Copies of this report can be obtained free of charge from: Health and Safety Executive Hazardous Installations Directorate Central Division CD4C Data Management Room 201b Merton House Stanley Road Bootle Merseyside L20 3DL Tel: 0151 951 3099 Fax: 0151 951 4980 e-mail : HCR.Admin@hse.gsi.gov.uk Copies of this report can also be downloaded free of charge from HSE s website at http://www.hse.gov.uk/hid/osd/hsr2001/contents.htm 2

OFFSHORE HYDROCARBON RELEASES STATISTICS, 2001 (FOR THE PERIOD 1-10-92 TO 31-3-01 INCLUSIVE) CONTENTS Page EXECUTIVE SUMMARY 5 1.0 INTRODUCTION 7 2.0 DATA CATEGORIES 9 3.0 STATISTICS 10 3.1 Hydrocarbon type 10 3.2 Reporting frequency 11 3.3 Severity analysis 11 3.4 Systems 13 3.5 Equipment 15 3.6 Drilling/Well Operations 16 3.7 Installation type and location 16 3.8 Ignitions 18 3.9 Means of Detection 19 3.10 Emergency actions 20 3.11 Causation & Operating Mode 21 4.0 TABLES (See separate section index) 23 5.0 FIGURES (See separate section index) 95 Appendix 1 - OSD PROCESS INTEGRITY INITIATIVE 105 Appendix 2 - SEVERITY CLASSIFICATION 107 FEEDBACK QUESTIONNAIRE 111 3

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EXECUTIVE SUMMARY An agreed target under the Government s Revitalising Health and Safety initiative is to reduce the number of major and significant releases by 50% over the next three years to March 2004, with 1999/2000 figures as baseline data. The total number of major releases in 2000/2001 shows a substantial decrease, down from 12 to 8 (33%) on last year s figure, and the total number of significant releases has also decreased from 126 to 117 (7%) over the same period. The combined total for major and significant releases has therefore shown a reduction of 10% on the baseline target. During the past year OSD undertook to investigate all hydrocarbon releases reported to OSD as part of a three-part Process Integrity initiative (see Appendix 1). This project was commissioned in the context of the sustained plateau in the number of hydrocarbon releases evidenced in the data up to 1999/2000, with a view to achieving a significant decrease. The results of these investigations are presented in OTO 2001 055 1, including an assessment of immediate and underlying causation factors, which supplements the information given in this statistics report. Reported minor releases have increased by 50% over the past year, from 96 to 145, but there is good evidence that this increase is as a result of publicity related to the Process Integrity Initiative, and does not represent an increase in the number of minor releases occurring. There were 13 reported ignitions in 2000/2001 none of which were major releases. Although there have been no ignited major releases since the launch of the HCR database, of the total 131 reported ignitions over the period 1 October 1992 to 31 March 2001, 40 of these (30.5%) have been significant releases (16 gas and 24 liquids). Failure rates for individual systems and for individual items of equipment are published in alternate years, and the failure rate data in this report updates that provided in the 1999 Hydrocarbon Statistics Report, OTO 1999 079. 1 Offshore Technology Report OTO 2001 055, OSD Hydrocarbon Release Reduction Campaign Report on the hydrocarbon release incident investigation project 1/4/2000 to 31/3/2001. 5

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1. INTRODUCTION The purpose of this report is to provide the offshore industry with data from the Hydrocarbon Releases (HCR) Database for their use in connection with the preparation and revision of offshore safety cases, particularly in quantified risk assessment (QRA), as recommended by Lord Cullen in his report on the Piper Alpha disaster (Cullen Recommendation 39). The HCR Database contains data on offshore hydrocarbon release incidents, supplementary details of which are reported voluntarily to the Health and Safety Executive, Hazardous Industries Directorate, Offshore Division (OSD) on form OIR/12. These data have been technically checked against the parent RIDDOR (OIR/9B) details, and then entered into the database by OSD since database startup on 1 October 1992. This report, HSR 2001 002, covers the period 1 October 1992 to 31 March 2001. It is the sixth report on statistics obtained from the HCR Database, and is the fourth since the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995 (RIDDOR 95) came into force offshore on 1 April 1996. Criteria for severity classification (i.e. major, significant, minor), first introduced in 1997, were refined in 1999 to include release rates (see Appendix 2). The limited accuracy of the systems and equipment population data estimates, and the voluntary nature of the information supplied on form OIR/12, should all be taken into consideration when drawing conclusions from the statistics contained in this report. The main thrust of this report is to advise industry of the bare statistics. Nevertheless, some discussion has been added where appropriate. This report also contains statistics on detection modes, emergency actions, and causation, but offers no root cause analysis at this stage. However, in view of the reporting plateau evidenced in data up to 1999/2000, and the absence of any downward trend to that time, OSD began a 3-part Process Integrity initiative (see Appendix 1) aimed at raising industry awareness to the problem and identifying their root causes, with a view to achieving a significant break through in the existing plateau. 7

An agreed target under the Government s Revitalising Health and Safety initiative is to reduce the number of major and significant releases by 50% by March 2004. Detailed failure rate tables are published in alternate years, and the latest versions of (a) System Failure Rates & Severity / Hole Size Distribution; and (b) Equipment Failure Rates & Severity / Hole Size Distribution are included in this report. The failure rate data in this report therefore updates that provided in the 1999 Hydrocarbon Statistics Report, OTO 1999 079. Feedback on the contents of this statistics report for 2001 would be appreciated. This can be provided by completing the single page questionnaire form at the back of the report and returning it to HSE Hazardous Installations Directorate, at the address indicated on the form. 8

2. DATA CATEGORIES This section describes the categories of data available from the HCR Database, statistics from which are contained in section 3.0. Section 4.0 contains the data tables referred to in the report, all of which are listed in a separate section 4.0 index. Section 5.0 contains the figures referred to in the report, all of which are listed in a separate section 5.0 index. The statistics, tables, and figures show the breakdown of data using the following sort categories: v Type of hydrocarbon, viz. liquids (oil/condensate/non-process 2 ), gas, or 2-phase v Severity of release, i.e. major, significant, or minor (Appendix 2) v Type of installation, viz. fixed (including Floating Production Systems [FPS]), mobile or subsea v Location of installation on the UK Continental Shelf (UKCS) viz. Northern (above 59 0 Latitude), Central (56 0 to 59 0 Latitude) or Southern area (below 56 0 Latitude, including Irish Sea and English Channel) v Year of occurrence (12 month periods from 1 April to 31 March unless noted otherwise) Each release has a single system type allocated to it and an individual equipment type within that system (well type and/or well operation for drilling activities). Most tables show the number of releases occurring, sorted by one or more of the above categories. Statistics for other reported features such as ignitions, mode of detection, emergency actions taken, causation factors etc., are also given in Section 3.0. 2 Non-process hydrocarbon liquids include diesel, helifuel, lubricants, methanol, etc. 9

3. STATISTICS A total of 2071 hydrocarbon release incident reports have been received, checked and input during the 8½ year period since the start-up of the Hydrocarbon Releases (HCR) Database on 1 October 1992, up to 31 March 2001 inclusive. The following subsections comprise detailed discussion of the statistics shown in the tables and figures in sections 4.0 and 5.0 respectively. Caution should be exercised when interpreting these statistics, in view of the limited accuracy of population data, the voluntary nature of the information supplied on form OIR/12, and the small number of releases involved in some cases. 3.1 Hydrocarbon type Figure 1, in section 5.0, shows the breakdown of reported releases by hydrocarbon type. It can be seen from this pie-chart that gas releases constituted, by far, the largest proportion of releases reported, i.e. 1150 out of 2071 (55.5%). The other types, ranked in decreasing order, were oil 347 (16.8%), non-process 239 (11.5%), 2-phase 184 (8.9%) and condensate 151 (7.3%). The higher proportion of gas releases may have arisen from the fact that almost all offshore installations handle gas, but only 37% of installations handle hydrocarbon production liquids (see also section 3.7 - Installations ). Other contributing factors to the higher incidence of gas releases could be that gas is usually subjected to higher pressures and temperatures than other forms of hydrocarbon, hence there are greater challenges associated with gas containment. 10

3.2 Reporting frequency Figure 2, in section 5.0, shows the monthly reporting frequencies since October 1992 up to the end of March 2001. Major milestones which occurred during the reporting period are also listed. Reporting reached a peak of 325 in 1994/1995, probably attributable to more detailed reporting following the issue of the OIR/12 form in August, 1992, and to comprehensive guidance 3 in August, 1993. There then followed a substantial drop down to 212 in 1995/96, ostensibly due to the safety case regime and improved safety management systems taking effect. Thereafter, the number of incidents seemed to have reached a plateau with the annual totals for the following years being 226 (1996/1997), 218 (1997/1998), 234 (1998/1999) and 234 (1999/2000), and the monthly reporting rate fluctuated between 18 to 20 in the same period. Although the number of major and significant releases has decreased to 125 (from 138 in 1999/2000) the total number of reported releases has increased to 270 for 2000/2001, reflecting a marked increase in the number of minor releases, with the monthly average increasing to 22.5. The increase in the number of minor releases reported has been attributed to the effects of raised awareness during the investigation phase of the Process Integrity initiative, which was carried out during 2000/2001. 3.3 Severity analysis 3.3.1 All releases All releases have been classified according to agreed severity criteria. (See Appendix 2). Table 4 in Section 4.0 shows that, of the 2071 reported releases to 31 March 2001, 143 were classified major (6.9% of all leaks), 1173 were significant releases (56.6%) and the remaining 755 were minor (36.5%). 3 Revised in Nov 96 to encompass RIDDOR 95 Revised Guidance on Reporting Offshore Hydrocarbon Releases OTO 96 956, is available free on request from HSE on tel :0151-951-3099 or fax: 0151-951-3098 or e-mail: HCR.Admin@hse.gsi.gov.uk or downloaded free from the HSE website: http://www.hse.gov.uk/research/frameset/oto/1996/index.htm 11

Figure 3 in section 5.0 shows the reporting patterns by year for major, significant and minor releases in both tabular and line graph form. The overall number of major releases in 2000/2001 decreased from last year s figures (down from 12 to 8), and the number of significant releases also decreased (from 126 to 117) over the same period. In contrast, the overall number of minor 4 releases reported in 2000/2001 increased in comparison with last year's figure (up from 96 to 145). 3.3.2 Gas releases Figure 4 in section 5.0 shows the reporting patterns by year for major, significant and minor gas releases in both tabular and line graph form. The upward trend in the annual number of reported gas releases continued in 2000/2001, with a further increase of 3.6% over the previous year (up from 136 to 141). However, the number of major gas releases went down for the first time since the low of 6 in 1997/98 having decreased to 7 in 2000/2001 from 11 in 1999/2000. Similarly, significant gas releases also dropped from 79 to 74 in the same period. The combined number of major and significant gas releases has decreased from 90 in 1999/2000 to 81 in 2000/2001. This is the lowest full-year figure for combined major and significant releases since the start-up of the HCR database. However, the number of minor gas releases has shown a year in year increase since 1995/1996, again going up from 46 to 60 in the past year. 3.3.3 Liquid releases Figure 5 in section 5.0 shows the reporting patterns by year for major, significant and minor liquid releases in both tabular and line graph form. It can be seen from these that the annual numbers of reported liquid releases (i.e. oil, condensate and nonprocess combined) have fluctuated over the years since database start-up, with no discernible trend. The number of minor releases has however increased from 47 in 1999/2000 to 79 in 2000/2001, reflecting the overall increase in minor releases over this period. 4 It is important to note that reports of minor releases only cover those reportable under RIDDOR definitions which are based on the potential for fire/explosion. It should also be noted that all ignitions offshore are reportable, however minor. 12

3.3.4 2-phase releases Figure 6 in section 5.0 shows the reporting patterns by year for major, significant and minor 2-phase releases in both tabular and line graph form. From these, it can be seen that the numbers of reported 2-phase releases have also fluctuated over the years since database start-up. As with liquid releases, there is no discernible trend. 3.4 Systems 3.4.1 Failure rates and severity / hole size distribution Table 1 in section 4.0 gives details of failure rates and severity / hole size distributions for all system types (in alphabetical order) contained in the database, whether any releases were reported for the system type or not. It should also be noted that Drilling in this case only involves those releases from permanent drilling equipment, and does not include those releases related to drilling activities and well operations such as workover. Information on severity and hole size distribution for drilling and well operations is given in section 3.6 of this report, and in Table 3 below. (a) Failure Rates: The population in system years is given in the table (SYSYEARS=summation of the total years of that type of system that has been on each installation), together with the number of releases reported against that system type (LEAK) for each year since the start-up of the database in October 1992. The failure rate for any system is given by the total leaks divided by the total system years, and is expressed as a rate per system year. If no releases were reported, then a rate has not been calculated (see notes on table). It is recognized that there are methods of estimating failure rates, even given a zero occurrence, but it is left to the practitioner to select the method appropriate to the scenario under analysis. (b) Severity Distribution: The total number of releases for each system has been broken down into the three classes of severity i.e. major, significant or minor (see Appendix 2 for details), and a fractional distribution has been calculated for each. 13

(c) Hole Size Distribution The total number of leaks for each system has been broken down into seven hole size categories, together with the fractional distribution for each band or range of hole size. It should be noted that hole size is not considered applicable to some scenarios involving open topped vessels (e.g. shale shakers, wemco units, tilted plate separators, etc.), and certain other scenarios involving liquid carry-over, so these have been assigned to a separate category (N/A), in addition to the six ranges shown. IMPORTANT: The severity distribution may be used to find the proportion of major, significant or minor releases within any system failure rate. Similarly, the hole size distribution may be used to determine the proportion of releases within each hole size band. It is very important to note, however, that only one of these distributions should be used at any one time, and that it is incorrect to apply both distributions together on failure rates. For example, the proportion of hole size <10mm for major releases can NOT be found by multiplying the two relevant factors together. 3.4.2 Systems : highest 15 failure rates The barchart in figure 7, section 5.0, shows the failure rates in leaks per system year for the highest ranked 15 release rates out of a total of 52 system types. The system with the highest failure rate is gas compression with a failure rate of 3.00 x 10-1 leaks per system year. High operating temperatures and pressures, vibration, and the consequent effects of these on vulnerable equipment items such as seals, instruments, and small bore pipework items etc. are considered to be major contributors to the frequency of hydrocarbon releases from this system type, and these factors have been taken into account in the current Process Integrity initiative (Appendix 1). The next highest system failure rate was for subsea gas injection wells (1.67 x 10-1 leaks per system year). Caution should however be exercised when interpreting this rate, as the calculation is based on a very small equipment population. 14

The next highest ranking systems were oil export (1.44 x 10-1 leaks per system year), and fuel gas (1.39 x 10-1 leaks per system year). 3.5 Equipment 3.5.1 Failure rates and severity / hole size distribution Table 2 in section 4.0 portrays equipment failure rates, severity and hole size distributions in similar fashion to those described for systems, and so it is important to read sections 3.4.1 (a), (b), (c) above in relation to equipment items also. Again, it is very important to note that only one of the distributions should be used at any one time, and that it is incorrect to apply both distributions together on any failure rates. The relationship between systems and individual items of equipment in them has been omitted due to the relatively small number of releases reported compared to the large number of system / equipment type combinations involved. 3.5.2 Equipment : highest 15 failure rates The barchart in figure 8, section 5.0, shows the failure rates in leaks per equipment year for the highest ranked 15 release rates out of a total of 119 equipment types. The major equipment items with the highest failure rates are dual fuel turbines at 7.24 x 10-2 leaks per equipment year, and reciprocating compressors at 6.50 x 10-2 leaks per equipment year. These indicate strong links with the high gas compression system leak rates shown above. It should be noted that the equipment items having the highest numbers of reported leaks were instruments (316 total), and pipework items such as valves, flanges and piping. Their respective population numbers are also very large and thus their respective failure rates in the rankings are reduced. However, the problems (with 15

small bore tubing in particular) have been recognised and guidelines 5 have been produced for addressing loss of containment, etc. 3.6 Drilling/Well Operations activities versus release type and severity 3.6.1 Severity / hole size distribution Table 3 in section 4.0 portrays Drilling and Well Operations activities due to the different population data requirements i.e. per activity per rig year, rather than per system year or equipment year. Drilling activities are sorted by well type i.e. exploration, appraisal, development, completion, etc. Well operations are sorted by operation type i.e. wireline, coiled tubing, etc. as shown. It should be noted that, due to the lack of suitable population data, failure rates cannot be provided for drilling / well operations activities. Therefore, only severity and hole size distributions are shown in the table. Again, it is very important to note that only one of the distributions should be used at anyone time, and that it is incorrect to apply both distributions together. 3.7 Installation type/location versus release type and severity Table 5 in section 4.0 summarises the breakdown of all reported releases by hydrocarbon type versus installation type, i.e. fixed which includes floating production systems (FPS), mobile including both drilling and accommodation units, and subsea. Each installation also has an associated location in either the Northern (above 59 0 Latitude North), Central (56 0 to 59 0 Latitude North), or Southern (below 56 0 Latitude North, including Irish Sea and English Channel) areas of UKCS. The total current population and the estimated number of installation years (as at 31 March 2001) is also given for each installation type on the UKCS by area. 5 Guidelines for the Management, Design, Installation and Maintenance of Small Bore Tubing Systems. ISBN 0 85293 275 8. Published in 2000 by the Institute of Petroleum. 16

3.7.1 Installation type The breakdown by installation type showed that fixed installations were responsible for 1994 (96.3%) of releases reported. In contrast, only 77 releases (3.7%) were reported by mobile drilling and accommodation installations. These proportions are not considered unusual, because there is constant exposure to hydrocarbons on fixed installations whereas the exposure on mobile installations is intermittent. 3.7.2 Fixed installation failure rates Failure rates have been calculated in terms of leaks per installation year, for each type of installation, by dividing the total number of leaks for that type by the total number of installation years. Floating Production Systems (including FPSO and FSU) had the highest overall leak rate of 2.8 leaks per installation year, with 5.9% major releases. Fixed attended installations in the Northern North Sea had the next highest leak rate of 2.5 leaks per installation year, with 5.2% of these being major releases. Central fixed attended installations were next, with 2.3 leaks per installation year, with 5.2% major releases. Southern fixed attended installations had a leak rate of 0.4 leaks per installation year, with 8.7% major, and Southern normally unattended installations (NUI) leak rate was 0.2 leaks per installation year, with 20.5% major releases. The production equipment on the larger attended oil production platforms in the Northern and Central areas is more complex and subject to much greater fluctuation of operating parameters than on the simpler and smaller gas production platforms in the Southern area. It is reasonably foreseeable, therefore, that there may be a greater propensity for hydrocarbon releases of all types on the larger installations. In view of the smaller numbers of the larger installations, it is also expected that failure rates would be much greater than those in the Southern Sector. 3.7.3 Mobile installation failure rates Using the population data held in the HCR database, leak rates have been calculated in terms of leaks per installation year, for each type of mobile installation. However, in the absence of accurate rig years data, it was necessary to assume that each unit was present on the UKCS for the entire period since their arrival, and so 17

these leak rates must be considered very approximate (and tending toward best case) as a result. Combining Southern and Central release figures gave an overall leak rate for jack-up mobile drilling and accommodation units of 0.4 leaks per installation year, with 7.3% major releases. Northern and Central release figures combined gave an overall leak rate for semi-submersible mobile drilling and accommodation units of 0.3 leaks per installation year, with 19.4% major releases. 3.8 Ignitions 3.8.1 Ignition summary Table 6, section 4.0, summarises the numbers of ignitions for each year versus the number of releases for each type of hydrocarbon. It is important to note that the percentages shown are ignition rates (i.e. percentage of releases ignited) and NOT ignition probabilities (i.e. the likelihood of a particular release igniting). There was a grand total of 131 reported ignitions (i.e. 6.3% of all releases) over the 8½ year period, none of which were major. There were 40 gas ignitions (30.5% of all ignitions), of which 16 were classed as significant releases (ignition rate 2.2%), and 24 as minor (ignition rate 7.7%). There were no major ignited gas releases. There were 91 liquid ignitions (69.5% of all ignitions) of which 24 were classed as significant releases (ignition rate 8.0%), and 67 as minor (ignition rate 15.9%). There were no major ignited liquids releases. There have been no reported 2-phase ignitions to date. The higher ignition rates in the case of minor releases, and liquids releases in particular, is considered to be due to the fact that reports of unignited minor releases cover only those reportable under RIDDOR definitions based on the potential for fire/explosion, but that ALL ignitions are reportable no matter how minor. 18

3.8.2 Ignition details Table 7, section 4.0, comprises three parts, which contain full details of every ignition reported in the 8½ years to 31 March 2001. The three parts cover the following details : (a) Release parameters (b) Mode of operation/ignition sources/ignition sequences, and (c) Detection mode/emergency actions taken. Each individual record has a unique number and so it is possible to read all three parts for one ignition incident to obtain the full picture. The purpose of this report is to provide statistics only, so any analysis of ignitions has been excluded here. 3.9 Means of detection 3.9.1 Summary Table 8 in section 4.0, summarises the modes of detection employed during an incident versus the type of hydrocarbon and severity of release. The modes comprise heat, smoke, flame, gas and other. It should be noted that more than one means of detection may be reported for any one release, and so the totals for each column may be more than the total number of releases reported. There were 2212 detection modes connected with the total 2071 reported releases, more than one mode being effective on some releases. Gas detectors detected 41.8% of all releases (58.7% of gas releases), and the remaining releases were mainly detected by means other than equipment designed for the purpose (see 3.9.2 below). 3.9.2 Other detection modes A breakdown of the other category which includes detection by visual means, by sound, by smell etc., is shown in table 9, section 4.0. It is considered important to have a separate table for these, since they have made a substantial contribution to the overall detection of offshore releases. 19

Of the total 2212 modes, 1267 (57.3% of modes) involved means of detection other than by dedicated detection systems. Of these 1267 other means of detection 975 (77%) were visually detected, of which 49 (5% of visual detection) involved major releases, 521 (53% of visual detection) involved significant releases, and 405 (42%) minor releases. Specific detection details for all reported ignitions are included in table 7 (c). 3.10 Emergency actions versus release type & severity Table 10, section 4.0, shows a breakdown of the various types of emergency actions taken against the types and severity of releases involved. These actions include either automatic or manual initiation of shutdown, blowdown, deluge, and/or CO 2 /Halon systems, plus whether any musters and/or any other emergency actions were carried out. Nearly two-thirds of releases (1355) required shutdown action (404 automatic, 951 manual), of which 103 (7.6% of shutdowns) were for major releases. Blowdown operated on 629 (255 auto, 374 manual = 30.4% of all releases) of which 64 (10.2% of blowdowns) were for major releases. There were 560 musters (520 at stations, 40 at lifeboats = 27.0% of all releases), 58 of which (10.4% of musters) were for major releases. In contrast, deluge only operated on 41 releases (2.0% of all releases), of which 11 (26.8% of deluge) were for major releases, and only 52 (2.5% of all releases) involved the use of CO 2 /Halon systems, of which only 1 was for a major release. There were a total of 62 releases (5 major, 35 significant, 22 minor) where no reported emergency actions were taken. This represents 3.0% of all major releases, 3.0% of significant releases, and 2.9% of minor releases. This indicates that, regardless of severity, 97.0% of all reported releases involved some sort of 20

emergency action. Specific emergency actions taken for all ignitions reported to 31 March 2001 are included in table 7(c). 3.11 Causation & operating mode versus release type & severity Table 11, section 4.0, summarises the breakdown of all types of release into the four main causation categories (i.e. design, equipment, operational and/or procedural faults) plus details of the mode of operation in the area at the time of the incident. It should be noted that more than one category may be involved in any one incident, and so caution should be exercised when interpreting the figures shown. The most frequently reported factor was equipment fault at 1362 (65.8% of incidents). Operational faults were next with 1116 (53.9% of incidents), procedural faults 588 (28.4% of incidents), and design faults 321 (15.5% of incidents). The proportion of releases occurring during normal production was 48.8% compared to that during intervention type activities such as start-up / reinstatement (18.1%), drilling / workover (9.5%), and maintenance / construction (9.7%). These proportions have generally been maintained throughout each year since database start-up in October 1992. The causation factor involved in most incidents was mechanical failure which occurred on 920 occasions (44.4% of all incidents), followed by improper operation that occurred on 495 occasions (23.9% of all incidents). A detailed analysis of the causation factors involved in the investigation phase of the Process integrity Initiative (see Appendix 1) is contained in OTO 2001 055. 21

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4.0 TABLES CONTENTS (All single page tables unless noted otherwise) Table 1. System failure rates and severity / hole size distribution (9 pages) 2. Equipment failure rates and severity / hole size distribution (24 pages) 3. Drilling and Well operations, severity / hole size distribution 4. Severity analysis (7 Pages) 5. Installation type/location versus release type & severity (2 pages incl. notes) 6. Ignitions : summary 7. Ignitions : details (3 tables of 5, 6 and 5 pages, plus 1 page of notes) 8. Means of detection : summary 9. Means of detection : other 10. Emergency actions versus release type & severity 11. Causation & operating mode versus release type & severity 23

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TABLE 1 : SYSTEM FAILURE RATES & SEVERITY / HOLE SIZE DISTRIBUTION SYSTEM (ALL TYPES) NOTES: 1. Previous = Total for all previous years from 1 October 1992 to 31 March 1999 2. Rate = Total Leaks divided by Total System Years. If no leaks reported, then Rate is not calculated. 3. Hole size is not applicable for some scenarios e.g. where open vessels such as shale shakers are involved or for liquid carry-over incidents, etc. YEAR SYSYEARS (Note 1) SEVERITY DISTRIBUTION HOLE SIZE DISTRIBUTION MAJOR SIGNIFICANT MINOR TOTAL <10 mm 10<25 mm 25<50 mm 50<75 mm 75<100 mm >=100 mm N/A RATE (note 3) (PER YEAR) (Note 2) Overall rate may be multiplied by the severity distribution factor Leak rate may be multiplied by hole size distribution factor to obtain rate for various hole sizes. shown to obtain rate for leaks of different severities CAUTION : DO NOT USE SEVERITY AND HOLE SIZE DISTRIBUTION FACTORS TOGETHER. BLOWDOWN DRAINS, CLOSED, DRAINS, OPEN, DRILLING EXPORT, CONDENSATE, EXPORT, GAS, Previous 1137 0 6 0 6 3 1 0 1 0 1 0 1999/00 193 1 0 0 1 0 1 0 0 0 0 0 2000/01 196 0 1 0 1 1 0 0 0 0 0 0 Total: 1526 1 7 0 8 5.24E-03 4 2 0 1 0 1 0 0.13 0.88 0.00 < DISTRIBUTION > 0.50 0.25 0.00 0.13 0.00 0.13 0.00 Previous 1317 2 20 5 27 8 3 3 1 0 8 4 1999/00 222 0 2 4 6 4 1 0 0 0 0 1 2000/01 225 0 3 5 8 7 1 0 0 0 0 0 Total: 1764 2 25 14 41 2.32E-02 19 5 3 1 0 8 5 0.05 0.61 0.34 < DISTRIBUTION > 0.46 0.12 0.07 0.02 0.00 0.20 0.12 Previous 1436 0 21 15 36 19 7 3 3 1 3 0 1999/00 248 0 3 4 7 5 1 1 0 0 0 0 2000/01 252 0 5 8 13 7 4 1 0 0 1 0 Total: 1936 0 29 27 56 2.89E-02 31 12 5 3 1 4 0 0.00 0.52 0.48 < DISTRIBUTION > 0.55 0.21 0.09 0.05 0.02 0.07 0.00 Previous 863 1 9 2 12 0 0 3 5 0 2 2 1999/00 138 0 0 0 0 0 0 0 0 0 0 0 2000/01 138 0 0 0 0 0 0 0 0 0 0 0 Total: 1139 1 9 2 12 1.05E-02 0 0 3 5 0 2 2 0.08 0.75 0.17 < DISTRIBUTION > 0.00 0.00 0.25 0.42 0.00 0.17 0.17 Previous 113 0 6 4 10 8 2 0 0 0 0 0 1999/00 17 0 0 1 1 1 0 0 0 0 0 0 2000/01 18 0 1 2 3 3 0 0 0 0 0 0 Total: 148 0 7 7 14 9.46E-02 12 2 0 0 0 0 0 0.00 0.50 0.50 < DISTRIBUTION > 0.86 0.14 0.00 0.00 0.00 0.00 0.00 Previous 1225 7 26 10 43 31 7 1 2 1 1 0 1999/00 203 0 3 1 4 4 0 0 0 0 0 0 2000/01 206 0 4 0 4 4 0 0 0 0 0 0 Total: 1634 7 33 11 51 3.12E-02 39 7 1 2 1 1 0 0.14 0.65 0.22 < DISTRIBUTION > 0.76 0.14 0.02 0.04 0.02 0.02 0.00 25

TABLE 1 : SYSTEM FAILURE RATES & SEVERITY / HOLE SIZE DISTRIBUTION SYSTEM (ALL TYPES) NOTES: 1. Previous = Total for all previous years from 1 October 1992 to 31 March 1999 2. Rate = Total Leaks divided by Total System Years. If no leaks reported, then Rate is not calculated. 3. Hole size is not applicable for some scenarios e.g. where open vessels such as shale shakers are involved or for liquid carry-over incidents, etc. YEAR SYSYEARS (Note 1) SEVERITY DISTRIBUTION HOLE SIZE DISTRIBUTION MAJOR SIGNIFICANT MINOR TOTAL <10 mm 10<25 mm 25<50 mm 50<75 mm 75<100 mm >=100 mm N/A RATE (note 3) (PER YEAR) (Note 2) Overall rate may be multiplied by the severity distribution factor Leak rate may be multiplied by hole size distribution factor to obtain rate for various hole sizes. shown to obtain rate for leaks of different severities CAUTION : DO NOT USE SEVERITY AND HOLE SIZE DISTRIBUTION FACTORS TOGETHER. EXPORT, OIL, FLARE, HP, FLARE, LP, FLOWLINES, GAS FLOWLINES, OIL FLOWLINES, OTHER, (CONDENSATE, METHANOL ETC) Previous 687 4 47 52 103 74 14 3 0 2 7 3 1999/00 119 0 4 5 9 8 1 0 0 0 0 0 2000/01 119 0 6 15 21 18 2 0 0 0 0 1 Total: 925 4 57 72 133 1.44E-01 100 17 3 0 2 7 4 0.03 0.43 0.54 < DISTRIBUTION > 0.75 0.13 0.02 0.00 0.02 0.05 0.03 Previous 676 2 11 10 23 9 2 4 1 1 1 5 1999/00 120 1 2 0 3 1 1 0 0 1 0 0 2000/01 121 0 4 2 6 5 1 0 0 0 0 0 Total: 917 3 17 12 32 3.49E-02 15 4 4 1 2 1 5 0.09 0.53 0.38 < DISTRIBUTION > 0.47 0.13 0.13 0.03 0.06 0.03 0.16 Previous 753 2 7 2 11 2 0 2 2 0 2 3 1999/00 135 1 4 0 5 0 0 0 2 0 1 2 2000/01 137 0 0 0 0 0 0 0 0 0 0 0 Total: 1025 3 11 2 16 1.56E-02 2 0 2 4 0 3 5 0.19 0.69 0.13 < DISTRIBUTION > 0.13 0.00 0.13 0.25 0.00 0.19 0.31 Previous 6011 14 43 6 63 54 6 2 0 0 1 0 1999/00 979 4 8 2 14 10 4 0 0 0 0 0 2000/01 989 0 5 2 7 5 2 0 0 0 0 0 Total: 7979 18 56 10 84 1.05E-02 69 12 2 0 0 1 0 0.21 0.67 0.12 < DISTRIBUTION > 0.82 0.14 0.02 0.00 0.00 0.01 0.00 Previous 5643 6 38 25 69 63 0 2 0 0 4 0 1999/00 992 1 3 5 9 8 1 0 0 0 0 0 2000/01 992 1 8 7 16 15 1 0 0 0 0 0 Total: 7627 8 49 37 94 1.23E-02 86 2 2 0 0 4 0 0.09 0.52 0.39 < DISTRIBUTION > 0.91 0.02 0.02 0.00 0.00 0.04 0.00 Previous 4885 1 1 1 3 2 0 0 1 0 0 0 1999/00 763 0 0 0 0 0 0 0 0 0 0 0 2000/01 763 0 0 0 0 0 0 0 0 0 0 0 Total: 6411 1 1 1 3 4.68E-04 2 0 0 1 0 0 0 0.33 0.33 0.33 < DISTRIBUTION > 0.67 0.00 0.00 0.33 0.00 0.00 0.00 26

TABLE 1 : SYSTEM FAILURE RATES & SEVERITY / HOLE SIZE DISTRIBUTION SYSTEM (ALL TYPES) NOTES: 1. Previous = Total for all previous years from 1 October 1992 to 31 March 1999 2. Rate = Total Leaks divided by Total System Years. If no leaks reported, then Rate is not calculated. 3. Hole size is not applicable for some scenarios e.g. where open vessels such as shale shakers are involved or for liquid carry-over incidents, etc. YEAR SYSYEARS (Note 1) SEVERITY DISTRIBUTION HOLE SIZE DISTRIBUTION MAJOR SIGNIFICANT MINOR TOTAL <10 mm 10<25 mm 25<50 mm 50<75 mm 75<100 mm >=100 mm N/A RATE (note 3) (PER YEAR) (Note 2) Overall rate may be multiplied by the severity distribution factor Leak rate may be multiplied by hole size distribution factor to obtain rate for various hole sizes. shown to obtain rate for leaks of different severities CAUTION : DO NOT USE SEVERITY AND HOLE SIZE DISTRIBUTION FACTORS TOGETHER. GAS COMPRESSION. IMPORT, CONDENSATE IMPORT, GAS, IMPORT, OIL, MANIFOLD, GAS MANIFOLD, OIL Previous 835 16 172 51 239 181 36 9 0 3 5 5 1999/00 141 2 37 10 49 44 4 1 0 0 0 0 2000/01 145 1 26 21 48 44 2 1 1 0 0 0 Total: 1121 19 235 82 336 3.00E-01 269 42 11 1 3 5 5 0.06 0.70 0.24 < DISTRIBUTION > 0.80 0.13 0.03 0.00 0.01 0.01 0.01 Previous 60 0 0 0 0 0 0 0 0 0 0 0 1999/00 9 0 0 0 0 0 0 0 0 0 0 0 2000/01 9 0 0 0 0 0 0 0 0 0 0 0 Total: 78 0 0 0 0 Note 2 0 0 0 0 0 0 0 0 0 0 < DISTRIBUTION > 0 0 0 0 0 0 0 Previous 1231 2 12 4 18 14 2 1 0 0 1 0 1999/00 185 0 0 2 2 2 0 0 0 0 0 0 2000/01 188 0 1 1 2 2 0 0 0 0 0 0 Total: 1604 2 13 7 22 1.37E-02 18 2 1 0 0 1 0 0.09 0.59 0.32 < DISTRIBUTION > 0.82 0.09 0.05 0.00 0.00 0.05 0.00 Previous 802 1 13 8 22 16 1 2 0 0 2 1 1999/00 139 0 2 0 2 2 0 0 0 0 0 0 2000/01 139 0 0 1 1 1 0 0 0 0 0 0 Total: 1080 1 15 9 25 2.31E-02 19 1 2 0 0 2 1 0.04 0.60 0.36 < DISTRIBUTION > 0.76 0.04 0.08 0.00 0.00 0.08 0.04 Previous 1728 3 13 2 18 16 2 0 0 0 0 0 1999/00 281 0 1 1 2 2 0 0 0 0 0 0 2000/01 283 2 0 0 2 1 1 0 0 0 0 0 Total: 2292 5 14 3 22 9.60E-03 19 3 0 0 0 0 0 0.23 0.64 0.14 < DISTRIBUTION > 0.86 0.14 0.00 0.00 0.00 0.00 0.00 Previous 1417 3 17 3 23 17 2 2 0 0 2 0 1999/00 253 0 5 4 9 8 1 0 0 0 0 0 2000/01 253 0 1 2 3 3 0 0 0 0 0 0 Total: 1923 3 23 9 35 1.82E-02 28 3 2 0 0 2 0 0.09 0.66 0.26 < DISTRIBUTION > 0.80 0.09 0.06 0.00 0.00 0.06 0.00 27

TABLE 1 : SYSTEM FAILURE RATES & SEVERITY / HOLE SIZE DISTRIBUTION SYSTEM (ALL TYPES) NOTES: 1. Previous = Total for all previous years from 1 October 1992 to 31 March 1999 2. Rate = Total Leaks divided by Total System Years. If no leaks reported, then Rate is not calculated. 3. Hole size is not applicable for some scenarios e.g. where open vessels such as shale shakers are involved or for liquid carry-over incidents, etc. YEAR SYSYEARS (Note 1) SEVERITY DISTRIBUTION HOLE SIZE DISTRIBUTION MAJOR SIGNIFICANT MINOR TOTAL <10 mm 10<25 mm 25<50 mm 50<75 mm 75<100 mm >=100 mm N/A RATE (note 3) (PER YEAR) (Note 2) Overall rate may be multiplied by the severity distribution factor Leak rate may be multiplied by hole size distribution factor to obtain rate for various hole sizes. shown to obtain rate for leaks of different severities CAUTION : DO NOT USE SEVERITY AND HOLE SIZE DISTRIBUTION FACTORS TOGETHER. MANIFOLD, OTHER, (CONDENSATE, METHANOL ETC) METERING, CONDENSATE, METERING, GAS, METERING, OIL, PROCESSING, GAS, CHEMICAL INJECTION PROCESSING, GAS, DEHYDRATION Previous 1781 0 2 0 2 1 0 0 1 0 0 0 1999/00 281 0 0 0 0 0 0 0 0 0 0 0 2000/01 281 0 0 0 0 0 0 0 0 0 0 0 Total: 2343 0 2 0 2 8.54E-04 1 0 0 1 0 0 0 0.00 1.00 0.00 < DISTRIBUTION > 0.50 0.00 0.00 0.50 0.00 0.00 0.00 Previous 309 0 5 8 13 11 2 0 0 0 0 0 1999/00 50 0 1 1 2 2 0 0 0 0 0 0 2000/01 52 0 0 1 1 1 0 0 0 0 0 0 Total: 411 0 6 10 16 3.89E-02 14 2 0 0 0 0 0 0.00 0.38 0.63 < DISTRIBUTION > 0.88 0.13 0.00 0.00 0.00 0.00 0.00 Previous 1087 1 20 8 29 23 5 0 0 0 0 1 1999/00 186 0 5 2 7 7 0 0 0 0 0 0 2000/01 188 0 5 2 7 6 1 0 0 0 0 0 Total: 1461 1 30 12 43 2.94E-02 36 6 0 0 0 0 1 0.02 0.70 0.28 < DISTRIBUTION > 0.84 0.14 0.00 0.00 0.00 0.00 0.02 Previous 640 2 10 11 23 15 5 0 1 1 1 0 1999/00 117 0 4 2 6 5 1 0 0 0 0 0 2000 117 0 0 2 2 2 0 0 0 0 0 0 Total: 874 2 14 15 31 3.55E-02 22 6 0 1 1 1 0 0.06 0.45 0.48 < DISTRIBUTION > 0.71 0.19 0.00 0.03 0.03 0.03 0.00 Previous 707 0 1 3 4 3 0 1 0 0 0 0 1999/00 125 0 0 0 0 0 0 0 0 0 0 0 2000/01 126 0 0 0 0 0 0 0 0 0 0 0 Total: 958 0 1 3 4 4.18E-03 3 0 1 0 0 0 0 0.00 0.25 0.75 < DISTRIBUTION > 0.75 0.00 0.25 0.00 0.00 0.00 0.00 Previous 571 2 29 15 46 33 4 3 3 1 0 2 1999/00 98 1 3 5 9 6 2 1 0 0 0 0 2000/01 99 0 2 2 4 4 0 0 0 0 0 0 Total: 768 3 34 22 59 7.68E-02 43 6 4 3 1 0 2 0.05 0.58 0.37 < DISTRIBUTION > 0.73 0.10 0.07 0.05 0.02 0.00 0.03 28

TABLE 1 : SYSTEM FAILURE RATES & SEVERITY / HOLE SIZE DISTRIBUTION SYSTEM (ALL TYPES) NOTES: 1. Previous = Total for all previous years from 1 October 1992 to 31 March 1999 2. Rate = Total Leaks divided by Total System Years. If no leaks reported, then Rate is not calculated. 3. Hole size is not applicable for some scenarios e.g. where open vessels such as shale shakers are involved or for liquid carry-over incidents, etc. YEAR SYSYEARS (Note 1) SEVERITY DISTRIBUTION HOLE SIZE DISTRIBUTION MAJOR SIGNIFICANT MINOR TOTAL <10 mm 10<25 mm 25<50 mm 50<75 mm 75<100 mm >=100 mm N/A RATE (note 3) (PER YEAR) (Note 2) Overall rate may be multiplied by the severity distribution factor Leak rate may be multiplied by hole size distribution factor to obtain rate for various hole sizes. shown to obtain rate for leaks of different severities CAUTION : DO NOT USE SEVERITY AND HOLE SIZE DISTRIBUTION FACTORS TOGETHER. PROCESSING, GAS, LPG/ CONDENSATE PROCESSING, GAS, METHANOL (INJECTION) PROCESSING, GAS, PROD. WATER TREATMENT. PROCESSING, GAS, SOUR (H2S/CO2) TREATMENT. PROCESSING, OIL, CHEMICAL INJECTION PROCESSING, OIL, METHANOL (INJECTION) Previous 542 0 19 19 38 31 5 1 0 1 0 0 1999/00 90 0 1 2 3 3 0 0 0 0 0 0 2000/01 92 0 0 2 2 2 0 0 0 0 0 0 Total: 724 0 20 23 43 5.94E-02 36 5 1 0 1 0 0 0.00 0.47 0.53 < DISTRIBUTION > 0.84 0.12 0.02 0.00 0.02 0.00 0.00 Previous 739 0 5 5 10 8 1 1 0 0 0 0 1999/00 132 0 0 2 2 2 0 0 0 0 0 0 2000/01 134 0 1 2 3 3 0 0 0 0 0 0 Total: 1005 0 6 9 15 1.49E-02 13 1 1 0 0 0 0 0.00 0.40 0.60 < DISTRIBUTION > 0.87 0.07 0.07 0.00 0.00 0.00 0.00 Previous 409 0 5 1 6 5 1 0 0 0 0 0 1999/00 69 0 0 0 0 0 0 0 0 0 0 0 2000/01 69 0 0 1 1 1 0 0 0 0 0 0 Total: 547 0 5 2 7 1.28E-02 6 1 0 0 0 0 0 0.00 0.71 0.29 < DISTRIBUTION > 0.86 0.14 0.00 0.00 0.00 0.00 0.00 Previous 59 0 2 2 4 2 0 1 0 0 1 0 1999/00 9 0 0 0 0 0 0 0 0 0 0 0 2000/01 10 0 0 0 0 0 0 0 0 0 0 0 Total: 78 0 2 2 4 5.13E-02 2 0 1 0 0 1 0 0.00 0.50 0.50 < DISTRIBUTION > 0.50 0.00 0.25 0.00 0.00 0.25 0.00 Previous 1123 0 2 1 3 2 1 0 0 0 0 0 1999/00 191 0 0 0 0 0 0 0 0 0 0 0 2000/01 192 0 0 0 0 0 0 0 0 0 0 0 Total: 1506 0 2 1 3 1.99E-03 2 1 0 0 0 0 0 0.00 0.67 0.33 < DISTRIBUTION > 0.67 0.33 0.00 0.00 0.00 0.00 0.00 Previous 240 0 1 1 2 1 0 1 0 0 0 0 1999/00 51 0 0 0 0 0 0 0 0 0 0 0 2000/01 52 0 0 1 1 1 0 0 0 0 0 0 Total: 343 0 1 2 3 8.75E-03 2 0 1 0 0 0 0 0.00 0.33 0.67 < DISTRIBUTION > 0.67 0.00 0.33 0.00 0.00 0.00 0.00 29

TABLE 1 : SYSTEM FAILURE RATES & SEVERITY / HOLE SIZE DISTRIBUTION SYSTEM (ALL TYPES) NOTES: 1. Previous = Total for all previous years from 1 October 1992 to 31 March 1999 2. Rate = Total Leaks divided by Total System Years. If no leaks reported, then Rate is not calculated. 3. Hole size is not applicable for some scenarios e.g. where open vessels such as shale shakers are involved or for liquid carry-over incidents, etc. YEAR SYSYEARS (Note 1) SEVERITY DISTRIBUTION HOLE SIZE DISTRIBUTION MAJOR SIGNIFICANT MINOR TOTAL <10 mm 10<25 mm 25<50 mm 50<75 mm 75<100 mm >=100 mm N/A RATE (note 3) (PER YEAR) (Note 2) Overall rate may be multiplied by the severity distribution factor Leak rate may be multiplied by hole size distribution factor to obtain rate for various hole sizes. shown to obtain rate for leaks of different severities CAUTION : DO NOT USE SEVERITY AND HOLE SIZE DISTRIBUTION FACTORS TOGETHER. PROCESSING, OIL, OIL TREATMENT, PROCESSING, OIL, PROD. WATER TREATMENT, SEPARATION, GAS PRODUCTION SEPARATION, GAS TEST SEPARATION, OIL PRODUCTION SEPARATION, OIL TEST Previous 250 1 16 9 26 21 3 0 1 0 1 0 1999/00 48 0 1 0 1 1 0 0 0 0 0 0 2000/01 48 0 0 3 3 2 1 0 0 0 0 0 346 1 17 12 30 8.67E-02 24 4 0 1 0 1 0 0.03 0.57 0.40 < DISTRIBUTION > 0.80 0.13 0.00 0.03 0.00 0.03 0.00 Previous 471 2 18 22 42 14 8 4 2 0 3 11 1999/00 84 0 1 5 6 4 0 0 0 0 0 2 2000/01 85 0 2 3 5 3 1 0 0 0 0 1 Total: 640 2 21 30 53 8.28E-02 21 9 4 2 0 3 14 0.04 0.40 0.57 < DISTRIBUTION > 0.40 0.17 0.08 0.04 0.00 0.06 0.26 Previous 865 5 8 6 19 15 2 1 0 1 0 0 1999/00 131 0 1 0 1 1 0 0 0 0 0 0 2000/01 134 1 2 1 4 1 1 1 0 0 0 1 Total: 1130 6 11 7 24 2.12E-02 17 3 2 0 1 0 1 0.25 0.46 0.29 < DISTRIBUTION > 0.71 0.13 0.08 0.00 0.04 0.00 0.04 Previous 425 2 2 3 7 6 0 0 1 0 0 0 1999/00 65 0 1 0 1 1 0 0 0 0 0 0 2000/01 66 0 2 0 2 2 0 0 0 0 0 0 Total: 556 2 5 3 10 1.80E-02 9 0 0 1 0 0 0 0.20 0.50 0.30 < DISTRIBUTION > 0.90 0.00 0.00 0.10 0.00 0.00 0.00 Previous 662 3 38 20 61 46 6 2 0 0 3 4 1999/00 116 0 2 0 2 0 2 0 0 0 0 0 2000/01 116 0 5 3 8 7 1 0 0 0 0 0 Total: 894 3 45 23 71 7.94E-02 53 9 2 0 0 3 4 0.04 0.63 0.32 < DISTRIBUTION > 0.75 0.13 0.03 0.00 0.00 0.04 0.06 Previous 435 5 16 7 28 19 4 2 0 1 0 2 1999/00 80 0 2 1 3 3 0 0 0 0 0 0 2000/01 80 0 4 1 5 4 1 0 0 0 0 0 Total: 595 5 22 9 36 6.05E-02 26 5 2 0 1 0 2 0.14 0.61 0.25 < DISTRIBUTION > 0.72 0.14 0.06 0.00 0.03 0.00 0.06 30

TABLE 1 : SYSTEM FAILURE RATES & SEVERITY / HOLE SIZE DISTRIBUTION SYSTEM (ALL TYPES) NOTES: 1. Previous = Total for all previous years from 1 October 1992 to 31 March 1999 2. Rate = Total Leaks divided by Total System Years. If no leaks reported, then Rate is not calculated. 3. Hole size is not applicable for some scenarios e.g. where open vessels such as shale shakers are involved or for liquid carry-over incidents, etc. YEAR SYSYEARS (Note 1) SEVERITY DISTRIBUTION HOLE SIZE DISTRIBUTION MAJOR SIGNIFICANT MINOR TOTAL <10 mm 10<25 mm 25<50 mm 50<75 mm 75<100 mm >=100 mm N/A RATE (note 3) (PER YEAR) (Note 2) Overall rate may be multiplied by the severity distribution factor Leak rate may be multiplied by hole size distribution factor to obtain rate for various hole sizes. shown to obtain rate for leaks of different severities CAUTION : DO NOT USE SEVERITY AND HOLE SIZE DISTRIBUTION FACTORS TOGETHER. UTILITIES, GAS, FUEL GAS, UTILITIES, GAS, POWER GEN. TURBINES. UTILITIES, OIL, DIESEL. UTILITIES, OIL, HEAT TRANSFER OIL UTILITIES, OIL, HELI-FUEL / JET FUEL UTILITIES, OIL, POWER GEN. TURBINES. Previous 767 7 59 44 110 75 17 10 2 1 3 2 1999/00 127 1 5 4 10 6 1 0 1 0 0 2 2000/01 129 0 9 13 22 21 1 0 0 0 0 0 Total: 1023 8 73 61 142 1.39E-01 102 19 10 3 1 3 4 0.06 0.51 0.43 < DISTRIBUTION > 0.72 0.13 0.07 0.02 0.01 0.02 0.03 Previous 1580 1 21 18 40 33 3 0 0 0 0 4 1999/00 269 0 2 2 4 1 0 0 0 0 1 2 2000/01 272 0 1 3 4 3 1 0 0 0 0 0 Total: 2121 1 24 23 48 2.26E-02 37 4 0 0 0 1 6 0.02 0.50 0.48 < DISTRIBUTION > 0.77 0.08 0.00 0.00 0.00 0.02 0.13 Previous 2287 1 27 36 64 44 9 4 3 0 3 1 1999/00 386 0 7 13 20 18 2 0 0 0 0 0 2000/01 390 0 3 12 15 14 0 1 0 0 0 0 Total: 3063 1 37 61 99 3.23E-02 76 11 5 3 0 3 1 0.01 0.37 0.62 < DISTRIBUTION > 0.77 0.11 0.05 0.03 0.00 0.03 0.01 Previous 316 0 3 8 11 7 2 2 0 0 0 0 1999/00 63 0 1 0 1 1 0 0 0 0 0 0 2000/01 64 0 0 1 1 1 0 0 0 0 0 0 Total: 443 0 4 9 13 2.93E-02 9 2 2 0 0 0 0 0.00 0.31 0.69 < DISTRIBUTION > 0.69 0.15 0.15 0.00 0.00 0.00 0.00 Previous 996 0 2 1 3 1 1 1 0 0 0 0 1999/00 164 0 0 2 2 1 1 0 0 0 0 0 2000/01 165 0 0 1 1 1 0 0 0 0 0 0 Total: 1325 0 2 4 6 4.53E-03 3 2 1 0 0 0 0 0.00 0.33 0.67 < DISTRIBUTION > 0.50 0.33 0.17 0.00 0.00 0.00 0.00 Previous 3092 0 4 5 9 6 2 1 0 0 0 0 1999/00 540 0 1 2 3 2 0 0 0 0 0 1 2000/01 540 1 0 1 2 1 0 1 0 0 0 0 Total: 4172 1 5 8 14 3.36E-03 9 2 2 0 0 0 1 0.07 0.36 0.57 < DISTRIBUTION > 0.64 0.14 0.14 0.00 0.00 0.00 0.07 31

TABLE 1 : SYSTEM FAILURE RATES & SEVERITY / HOLE SIZE DISTRIBUTION SYSTEM (ALL TYPES) NOTES: 1. Previous = Total for all previous years from 1 October 1992 to 31 March 1999 2. Rate = Total Leaks divided by Total System Years. If no leaks reported, then Rate is not calculated. 3. Hole size is not applicable for some scenarios e.g. where open vessels such as shale shakers are involved or for liquid carry-over incidents, etc. YEAR SYSYEARS (Note 1) SEVERITY DISTRIBUTION HOLE SIZE DISTRIBUTION MAJOR SIGNIFICANT MINOR TOTAL <10 mm 10<25 mm 25<50 mm 50<75 mm 75<100 mm >=100 mm N/A RATE (note 3) (PER YEAR) (Note 2) Overall rate may be multiplied by the severity distribution factor Leak rate may be multiplied by hole size distribution factor to obtain rate for various hole sizes. shown to obtain rate for leaks of different severities CAUTION : DO NOT USE SEVERITY AND HOLE SIZE DISTRIBUTION FACTORS TOGETHER. VENT, HP, VENT, LP, WELL CONTROL WELL, GAS INJECTION, SUBSEA WELL, GAS INJECTION, SURFACE WELL, GAS PRODUCTION, SUBSEA Previous 1052 3 14 9 26 11 2 1 4 0 4 4 1999/00 177 0 0 0 0 0 0 0 0 0 0 0 2000/01 179 0 0 0 0 0 0 0 0 0 0 0 Total: 1408 3 14 9 26 1.85E-02 11 2 1 4 0 4 4 0.12 0.54 0.35 < DISTRIBUTION > 0.42 0.08 0.04 0.15 0.00 0.15 0.15 Previous 1441 2 4 5 11 3 2 2 1 1 1 1 1999/00 247 0 0 3 3 1 1 0 0 0 0 1 2000/01 249 0 0 2 2 2 0 0 0 0 0 0 Total: 1937 2 4 10 16 8.26E-03 6 3 2 1 1 1 2 0.13 0.25 0.63 < DISTRIBUTION > 0.38 0.19 0.13 0.06 0.06 0.06 0.13 Previous 837 0 0 0 0 0 0 0 0 0 0 0 1999/00 134 0 0 0 0 0 0 0 0 0 0 0 2000/01 134 0 0 0 0 0 0 0 0 0 0 0 Total: 1105 0 0 0 0 Note 2 0 0 0 0 0 0 0 0 0 0 < DISTRIBUTION > 0 0 0 0 0 0 0 Previous 2 0 0 0 0 0 0 0 0 0 0 0 1999/00 2 0 0 0 0 0 0 0 0 0 0 0 2000/01 2 0 1 0 1 1 0 0 0 0 0 0 Total: 6 0 1 0 1 1.67E-01 1 0 0 0 0 0 0 0.00 1.00 0.00 < DISTRIBUTION > 1.00 0.00 0.00 0.00 0.00 0.00 0.00 Previous 344 0 2 0 2 2 0 0 0 0 0 0 1999/00 54 0 0 0 0 0 0 0 0 0 0 0 2000/01 54 0 0 1 1 1 0 0 0 0 0 0 Total: 452 0 2 1 3 6.64E-03 3 0 0 0 0 0 0 0.00 0.67 0.33 < DISTRIBUTION > 1.00 0.00 0.00 0.00 0.00 0.00 0.00 Previous 190 1 1 0 2 0 1 0 0 0 1 0 1999/00 31 0 0 0 0 0 0 0 0 0 0 0 2000/01 31 0 0 0 0 0 0 0 0 0 0 0 Total: 252 1 1 0 2 7.94E-03 0 1 0 0 0 1 0 0.50 0.50 0.00 < DISTRIBUTION > 0.00 0.50 0.00 0.00 0.00 0.50 0.00 32