OGP Ignition Probabilities 434-6

Risk Assessment Data Directory Report No. 434 – 6.1 March 2010

Ignition probabilities International Association of Oil & Gas Producers

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RADD – Ignition probabilities

contents 1.0

Introduction ........................................................................ 1

2.0 2.1 2.2

Summary of Recommended Data ......................................... 1 Ignition Probability Curves ......................................................................... 1 Blowout Ignition Probabilities .................................................................. 16

3.0 3.1 3.2

Guidance on use of data .................................................... 17 General Validity.......................................................................................... 17 Alternative Approaches ............................................................................ 17

3.2.1 3.2.2

Releases addressed by datasheets in Section 2.0 ............................................ 17 Other releases ....................................................................................................... 20

3.3

Uncertainties .............................................................................................. 20

4.0

Review of data sources ...................................................... 20

5.0

Recommended data sources for further information ........... 22

6.0

References ......................................................................... 22

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RADD – Ignition probabilities

Abbreviations FPSO LPG NAP NUI QRA UKOOA

2

Floating Production Storage and Offloading (Installation) Liquefied Petroleum Gas Normal Atmospheric Pressure Normally Unmanned Installation Quantitative Risk Assessment United Kingdom Offshore Operators Association

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RADD – Ignition probabilities

1.0

Introduction

The data presented in section 2 provide estimates of the probabilities of hydrocarbon releases igniting to result in an explosion and/or a sustained fire. These data may be applied to any on the leak types described in the Process Release Frequencies datasheet1. The values presented relate to “total” ignition probability, which can be considered as the sum of the probabilities of immediate ignition and delayed ignition. Immediate ignition can be considered as the situation where the fluid ignites immediately on release through auto-ignition or because the accident which causes the release also provided an ignition source. Delayed ignition is the result of the build-up of a flammable vapour cloud which is ignited by a source remote from the release point. It is assumed to result in flash fires or explosions, and also to burn back to the source of the leak resulting in a jet fire and/or a pool fire. These probabilities are considered appropriate for use in QRA studies where a relatively coarse assessment is acceptable. Section 3.2 refers to a more detailed approach for QRAs where this is considered to be required.

2.0

Summary of Recommended Data

2.1

Ignition Probability Curves

Data presented in this section come in the form of 28 mathematical functions drawn from the UKOOA look-up correlations (see section 4.0) which relate ignition probabilities in air2 to release rates for typical scenarios both onshore and offshore. The various scenarios are summarised in Table 2.1,

1

With the exception of “zero pressure” releases, where the limited inventory and hence cloud size would result in a lower ignition probability than would be predicted using this approach. 2 Ignition probabilities in other atmospheres, e.g. oxygen enriched or chlorine, are outside the scope of this datasheet.

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RADD – Ignition probabilities

Table 2.2 and Table 2.3. The functions themselves are given in both tabular and graphical form in the data sheets which follow. The curves of ignition probability vs. release rate comprise between two and four sections, each a straight line when plotted on log-log axes. These curves represent “total” ignition probability. The method assumes that the immediate ignition probability is 0.001 and is independent of the release rate. As a result, all the curves start at a value of 0.001 relating to a release rate of 0.1 kg/s. Users of the data may wish to adopt this value and to obtain delayed ignition probabilities by subtracting 0.001 from the total ignition probability, e.g. an ignition probability value of 0.004 obtained from the look-up correlations can be considered as an immediate ignition probability of 0.001 and a delayed ignition probability of 0.003.

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Table 2.1 Onshore Ignition Scenarios Scenario No. 1 2 3

4 5 6 7

8 9 10

Look-up Release Type

Application

Pipe Liquid Industrial (Liquid Releases from onshore pipeline in industrial area) Pipe Liquid Rural (Liquid Releases from onshore pipeline in industrial area) Pipe Gas LPG Industrial (Gas or LPG release from onshore pipeline in an industrial area) Pipe Gas LPG Rural (Gas or LPG release from onshore pipeline in a rural area) Small Plant Gas LPG (Gas or LPG release from small onshore plant) Small Plant Liquid (Liquid release from small onshore plant) Small Plant Liquid Bund Rural (Liquid release from small onshore plant where the spill is bunded) Large Plant Gas LPG (Gas or LPG release from large onshore plant) Large Plant Liquid (Liquid release from large onshore plant) Large Plant Liquid Bund Rural (Liquid Released from large onshore plant where spill is bunded)

Releases of flammable liquids that do not have any significant flash fraction (10% or less) if released from onshore cross-country pipelines running through industrial or urban areas. Releases of flammable liquids that do not have any significant flash fraction (10% or less) if released from onshore cross-country pipelines running through rural areas. Releases of flammable gases, vapour or liquids significantly above their normal (Normal Atmospheric Pressure (NAP)) boiling point from onshore cross-country pipelines running through industrial or urban areas. Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from onshore cross-country pipelines running through rural areas. Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from small onshore plants (plant area up to 1200 m2, site area up to 35,000 m2). Releases of flammable liquids that do not have any significant flash fraction (10% or less) if released from small onshore plants (plant area up to 1200 m2, site area up to 35,000 m2) and which are not bunded or otherwise contained. Releases of flammable liquids that do not have any significant flash fraction (10% or less) if released from small onshore plants (plant area up to 1200 m2, site area up to 35,000 m2) and where the liquid releases from the plant area are suitably bunded or otherwise contained. Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from large onshore outdoor plants (plant area above 1200 m2, site area above 35,000 m2). Releases of flammable liquids that do not have any significant flash fraction (10% or less) if released from large onshore outdoor plants (plant area above 1200 m2, site area above 35,000 m2) and which are not bunded or otherwise contained. Releases of flammable liquids that do not have any significant flash fraction (10% or less) if released from large onshore outdoor plants (plant area above 1200 m2, site area above 35,000 m2) and where the liquid releases from the plant area are suitably bunded or otherwise contained.

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RADD – Ignition probabilities Scenario No. 11

12

Look-up Release Type

Application

Large Plant Congested Gas LPG (Gas or LPG released from a large confined or congested onshore plant) Tank Liquid 300m x 300m Bund (Liquid release from a large confined or congested onshore plant)

Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from large onshore plants (plant area above 1200 m2, site area above 35,000 m2), where the plant is partially walled/roofed or within a shelter or very congested.

13

Tank Liquid 100m x 100m Bund (Liquid release from onshore tank farm where spill is limited by small or medium sized bund)

14

Tank Gas LPG Plant (gas or LPG release from onshore tank farm within the plant)

15

Tank Gas LPG Storage Industrial (Gas or LPG released from onshore tank farm sited adjacent to a plant or away from the plant in an industrial area) Tank Gas LPG Storage Only Rural (Gas or LPG released from onshore tank farm sited adjacent to a plant or away from the plant in an industrial area)

16

Releases flammable liquids that do not have any significant flash fraction (10% or less) if released from very large onshore outdoor storage area 'tank farm' (e.g. spill in a large multitank bund over 25,000 m2 area). See curve No. 30 “Tank Liquid – diesel, fuel oil’ if liquids are stored at ambient conditions below their flash point. Releases of flammable liquids that do not have any significant flash fraction (10% or less) if released from onshore outdoor storage area 'tank farm' (e.g. spill in a large tank bund containing four or fewer tanks, or any other bund less than 25,000 m2 area). See curve No. 30 “Tank Liquid – diesel, fuel oil’ if liquids are stored at ambient conditions below their flash point. Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from onshore outdoor storage tanks located in a 'tank farm' entirely surrounded by plants. For tank farms adjacent to plants use curve No. 15 “Tank Gas LPG Storage Industrial” or Curve No. 16 “Tank Gas LPG Storage Only Rural” look-up correlations. Releases from process vessels or tanks inside plant areas should be treated as plant releases. Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from onshore outdoor storage tanks located in a 'tank farm' adjacent to plants or situated away from plants in an industrial or urban area.

Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from onshore outdoor storage tanks located in a 'tank farm' adjacent to plants or situated away from plants in a rural area.

Source: Energy Institute [1]

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Table 2.2 Offshore Ignition Scenarios Scenario No. 17 18 19

20

Look-up Release Type Offshore Process Liquid (Liquid release from offshore process module) Offshore Process Liquid NUI (Liquid release from offshore process area on NUI) Offshore Process Gas Open Deck NUI (Gas release from offshore process open deck area on NUI) Offshore Process Gas Typical (Gas release from typical offshore process module)

21

Offshore Process Gas Large Module (gas release from typical offshore process module)

22

Offshore Process Gas Congested or Mechanical Vented Module (Gas released from a mechanically ventilated or very congested offshore process module) Offshore Riser (Gas release from typical offshore riser in air gap)

23

Application Releases of flammable liquids that do not have any significant flash fraction (10% or less) if released from within offshore process modules. Releases of flammable liquids that do not have any significant flash fraction (10% or less) if released from within offshore process modules or decks on NUIs. Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from an offshore process weather deck/ open deck on NUIs. Can also be used for open/uncongested weather decks with limited process equipment on larger attended integrated platforms. Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from within offshore process modules or decks on integrated deck / conventional installations). Process modules include separation, compression, pumps, condensate handling, power generation, etc. If the module is mechanically ventilated or very congested – see curve No. 22 “Offshore Process Gas Congested or Mechanical Vented Module”. Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from within large offshore process modules or decks on integrated deck / conventional installations (module greater than 1000 m2 floor area). Process modules include separation, compression, pumps, condensate handling, power generation, etc. If the module is mechanically ventilated or very congested – see curve No. 22 'Offshore Process Gas Congested or Mechanical Vented Module'. Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from within offshore process modules or decks on integrated deck / conventional installations: applies where the module is enclosed and has a mechanical ventilation system or is very congested (volume blockage ratio => 0.14 and less than 25% of area of the end walls open for natural ventilation) Releases from offshore installation risers in the air gap area where there is little chance of the release entering process areas on the installation (e.g. solid decks, wind walls). Applies to partial flashing oil or gas releases. May also be used for blowouts with well positioned diverters directing any release away from the installation (see also curve No. 27 “Offshore Engulf – blowout riser”).

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RADD – Ignition probabilities Scenario No. 24

25

26

27

Look-up Release Type Offshore FPSO Gas (Gas release from offshore FPSO process module) Offshore FPSO Gas Wall (Gas release from offshore FPSO process module behind a transverse solid wall) Offshore FPSO Liquid (Liquid release from typical offshore FPSO process module) Offshore Engulf – blowout – riser (Major release which can engulf an entire offshore installation)

Application Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from within offshore process modules or decks on FPSOs. See curve No. 25 “offshore FPSO Gas Wall” if the release is from an area downwind of a transverse wall across the FPSO deck. Releases of flammable gases, vapour or liquids significantly above their normal (NAP) boiling point from within offshore process modules or decks on FPSOs. This correlation applies if the release is from an area downwind of a transverse wall across the FPSO deck. Releases of flammable liquids that do not have any significant flash fraction (10% or less) if released from within offshore process modules or decks on FPSOs Releases from drilling or well working blowouts or riser failures under open grated deck areas where the release could engulf the entire installation and reach into platform areas: applies to partial flashing oil or gas releases. (see also curve No. 23 “Offshore Riser” for riser releases and blowouts with divertors)

Source: Energy Institute [1]

Note. Curve Nos. 28 and 29 related to Cox, Lees and Ang formulation which were included in the document for comparison

Table 2.3 Special (Derived) Ignition Scenarios Scenario No. 30

Look-up Release Type

Application

Tank Liquid – diesel fuel oil (Liquid Release from onshore tank farm of liquids below their flash point, e.g. diesel or fuel oil)

Releases of combustible liquids stored at ambient pressure and at temperatures below their flash point (e.g. most gas, oil, diesel and fuel oil storage tanks) from onshore outdoor storage area “tank farm”. This look-up correlation can be applied to releases from tanks and low pressure transfer lines or pumps in the tank farm/ storage area. However, it should not be used for high-pressure systems (over a few barg): in these situations use curve No. 12 “Tank Liquid 300m x 300m Bund” or curve No. 13 “Tank Liquid 100 x 100m Bund”

Source: Energy Institute [1]

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Data Sheet 1: Scenarios 1 – 4

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Data Sheet 2: Scenarios 5 – 7

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Data Sheet 3: Scenarios 8 – 11

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Data Sheet 4: Scenarios 12, 13 & 30

10

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Data Sheet 5: Scenarios 14 – 16

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Data Sheet 6: Scenarios 17 & 18

12

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Data Sheet 7: Scenarios 19 – 22

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Data Sheet 8: Scenarios 24 – 26

14

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Data Sheet 9: Scenarios 23 & 27

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RADD – Ignition probabilities

Notes: 1. A flammable substance above its auto-ignition temperature is likely to ignite on release and should be modelled as having an ignition probability of one. 2. Very reactive substances are unlikely to found in oil and gas processing operations but if present it is suggested that the values given in the look-up correlations are doubled, subject to a maximum of 1. Such substances include hydrogen, acetylene, ethylene oxide and carbon disulphide. 3. High flash point (>55°C) liquids stored at or near ambient conditions are significantly less likely to ignite than suggested in the look-up correlations. It is suggested that an ignition probability from the look-up correlations is multiplied by a factor of 0.1 subject to a minimum of 0.001 and taking account of the 0.001 immediate ignition probability. 4. For liquids with flash fractions above 10% it is suggested that the ignition probability is estimated by combining the relevant liquid ignition probability with a suitable gas/LPG ignition probability. The appropriate release rates should be obtained from the flash fraction, e.g. a 10 kg/s release with a 20% flash fraction should give rise to an equivalent 2 kg/s gas release and 8 kg/s liquid release. The two probabilities can be combined using the following equation;

Alternatively the higher of the two ignition probabilities can be used on the basis that the areas covered by the liquid and gas are likely to have considerable overlap. 5. Since the correlations are based on typical combinations of ignition sources, it follows that they should not be used in situations where particularly strong sources such as fired heaters are present. In this case the full UKOOA ignition model is more appropriate.

2.2

Blowout Ignition Probabilities

An alternative to the blowout ignition probabilities given by the UKOOA look-up correlations can be obtained from Scandpower’s interpretation of the blowout data provided by SINTEF 2. This is given in Table 2.4. The most significant category is that for deep blowouts which indicates an early ignition probability of 0.09. For the purposes of QRA studies this can be taken as occurring immediately on release. The report also gives a delayed ignition probability of 0.16 although all of these are taken to occur more than one hour after the start of the release. Conservatively, this could be taken as occurring shortly after the initial release and result in an explosion. Table 2.4 Ignition Probabilities for Blowouts and W ell Releases on Platform s

16

Release Type

Early ignition (< 5 min)

Shallow Gas Blowout Deep Blowout Deep Well Release

0.07 0.09 0.03

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Delayed ignition (5 – 60 min) 0.11 -

Very Delayed ignition (> 60 min) 0.07 0.16 -

RADD – Ignition probabilities

3.0

Guidance on use of data

3.1

General Validity

The correlations are considered to provide an acceptable approach for use in typical QRA studies. For more detailed analysis it is recommended that the full spreadsheet UKOOA ignition model is used so that the specific circumstances with regard to layout and ignition sources can be more accurately represented. The correlations were developed for UKOOA member companies with the intention of providing representative probabilities for installations operating in UK waters. They may be applied to the analysis of hydrocarbon releases in other regions which comply with recognised industry good practice, as it is applied in the UKCS. The forward to the Energy Institute report states that the model and look-up correlations “are not suited to the ignition probability assessment of refrigerated liquefied gases, vapourising liquid pools, sub-sonic gas releases, or non-momentum driven releases, such as those following catastrophic storage vessel failure.” Despite this note, flashing liquid releases are covered by a number of the correlations and analysts may further modify them by combining them with a gas or LPG ignition probability in suitable proportions as suggested in note 4 of section 2.1. Atmospheric storage tanks are dealt with in the Storage Incident Frequencies data sheet. Low momentum and sub-sonic gas releases are uncommon in process systems. An approach to the scenarios for which the correlations are not valid is suggested in Section 3.2.2.

3.2

Alternative Approaches

3.2.1

Releases addressed by datasheets in Section 2.0

The initial task for the analyst is to determine which of the scenarios given in Table 2.1 to

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RADD – Ignition probabilities

Table 2.2 and Table 2.3 best matches the scenario under consideration. There may be situations where the scenario under consideration lies between two of the described scenarios, in which case the analysts may attempt to interpolate between two curves. The data presented in the tables in Section 2.0 can be used in three ways: 1. Estimate from the graphs 2. Obtain probability based on the tabulated values 3. Use values in Table 3.1 to calculate the probability. Note that, in interpolating between the data points, it is necessary to take logarithms of the release rate and probabilities, interpolate between these to find the logarithm of the required probability and then obtain the value itself, i.e.:

where Pign

is the required ignition probability corresponding to release rate Q is the ignition probability at a release rate of Qlower (the lower bound of the relevant curve section), and is the ignition probability at a release rate of Qupper (the upper bound of the relevant curve section)

The third of these options is the recommended approach and the analyst may find it convenient to construct a spreadsheet or some other computer programme to carry this out. The data used to generate the lines on the graphs in the datasheets (Section 2.1) are shown in Table 3.1. This has been derived from Table 2.9 in the Institute of Energy report 1, which provides further explanation on the derivation of the lines. This specifies the release rates and ignition probabilities relating to each of the points bounding the segments as indicated in Figure 3.1. Some information on the timing of ignitions is also available in 1. Figure 3.1 Typical Ignition Probability Curve

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A more accurate assessment may be obtained by the use of the full UKOOA ignition model which is described in 1. This has been implemented in a spreadsheet tool which is made available on a CD which accompanies the report. This allows the user to input specific data relating to release conditions, platform layout and ignition sources. However, this requires more effort on the part of the analyst and the availability of more installation specific data compared with the relative ease with which the look-up functions can be used.

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RADD – Ignition probabilities

Table 3.1 Data for Look-up Correlations Scenario No.

Type

1 2 3 4 5 6 7 8 9 10

Pipe Liquid Industrial Pipe Liquid Rural Pipe Gas LPG Industrial Pipe Gas LPG Rural Small Plant Gas LPG Small Plant Liquid Small Plant Liquid Bund Rural Large Plant Gas LPG Large Plant Liquid Large Plant Liquid Bund Rural Large Plant Congested Gas LPG Tank Liquid 300x300 Bund Tank Liquid 100x100 Bund Tank Gas LPG Plant Tank Gas LPG Storage Only Industrial Tank Gas LPG Storage Only Rural Offshore Process Liquid Offshore Process Liquid NUI Offshore Process Gas Open Deck NUI Offshore Process Gas Typical Offshore Process Gas Large Module Offshore Process Gas Congested or Mechanically Vented Module Offshore Riser Offshore FPSO Gas Offshore FPSO Gas Wall Offshore FPSO Liquid Offshore Engulf – Blowout Riser

11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 30 20

Tank Liquid - Diesel and Fuel Oil

Point 1 Release Probability rate 0.1 0.001 0.1 0.001 0.1 0.001 0.1 0.001 0.1 0.001 0.1 0.001 0.1 0.001 0.1 0.001 0.1 0.001 0.1 0.001

Point 2 Release Probability rate 70.00 0.07 0.30 0.00 1000.01 1.00 10.00 0.00 1.00 0.00 1.00 0.00 1.00 0.00 1.00 0.00 1.00 0.00 1.00 0.00

Point 3 Release Probability rate 70.00

0.01

23408.55 3.00 100.00 8.05 260.00 109.99 42.49

1.00 0.01 0.10 0.01 0.65 0.13 0.05

Point 4 Release Probability rate

498.99

0.60

0.1

0.001

1.00

0.00

70.00

0.43

325.03

0.70

0.1 0.1 0.1

0.001 0.001 0.001

1.00 1.00 1.00

0.00 0.00 0.00

7.00 7.00 102.84

0.00 0.00 1.00

519.62 49.03

0.12 0.02

0.1

0.001

1.00

0.00

100.00

0.23

988.11

1.00

0.1

0.001

1.00

0.00

10.00

0.02

52551.35

0.50

0.1 0.1

0.001 0.001

100.00 24.73

0.02 0.01

0.1

0.001

1.00

0.00

31.42

0.03

0.1

0.001

3.00

0.01

37.01

0.04

0.1

0.001

5.00

0.03

30.00

0.05

0.1

0.001

1.00

0.01

92.63

0.04

0.1 0.1 0.1 0.1

0.001 0.001 0.001 0.001

38.27 1.00 0.30 100.00

0.03 0.00 0.00 0.03

50.00 10.00

0.15 0.15

0.1

0.001

100.00

0.10

0.1

0.001

1.00

0.00

7.00

0.00

25.55

0.00

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3.2.2

Other releases

As noted in Section 3.1, the UKOOA ignition model cannot be considered valid for all types of release. In particular, it does not refrigerated releases that form evaporating liquid pools. Analysis of these and the other scenarios referred to there may require a more fundamental treatment by calculating likely cloud sizes for the given release, material and weather conditions and estimating the number and strength of ignition sources which the flammable part of the cloud may reach. There is no generally recognized method for determining ignition source strength for use in QRAs. Some values are given in the “Purple Book” [3] but these are estimates based on engineering judgment and do not have any more scientific basis.

3.3

Uncertainties

The assessment of ignition probability is subject to a large degree of uncertainty. The spreadsheet model produced under phase I of the joint industry project is itself subject to uncertainties in the analytical approach taken and in the data used. The adoption of the lookup correlations based on this model introduces more uncertainties because a compromise has to be made in selecting the most appropriate curve and these curves themselves are approximations to the curves produced by the model itself. Ignition probabilities are influenced by design layout, the number and separation of ignition sources, the quality of maintenance of equipment, and thereby the control of ignition sources. Despite these uncertainties, the approach is considered to be an advance on other formulations which relate ignition probability to release rate only with no regard for the presence of ignition sources, the nature of the fluids or the layout of the plant.

4.0

Review of data sources

The data presented in Section 2 are largely a reproduction of data from the Energy Institute Research Report [1], published on behalf of the joint industry project sponsors UKOOA (Now Oil and Gas UK), the HSE and the Energy Institute. The report reviews existing models and develops a new model which could be applied to both onshore and offshore scenarios. The work was undertaken in two phases. The first phase involved developing a model for assigning ignition probabilities in QRA studies and to further the understanding of scenario specific ignition probabilities. The work was undertaken by AEA Technology (now ESR Technology) and co-ordinated by a joint industry steering group drawn from UKOOA member representatives, the HSE and consultants working in the field of onshore and offshore QRA. The report summarised the current status of knowledge and research in the field of ignition probability estimation in support of QRA. It evaluated this, together with the usefulness of the UK HSE’s hydrocarbon release database as a basis to develop an improved ignition model for use in QRA. The end result is a spreadsheet model for estimating the ignition probability of process leaks offshore and also attempts to include the capability to assess the ignition probability of most typical onshore hydrocarbon leak scenarios. The spreadsheet attempts to model the ignition

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probability by considering the size of the gas cloud which would be formed by the release and taking into account the number and type of ignition sources which the cloud, at sufficient concentration, might reach. As a result of the complexity of the model, users are required to obtain and enter a significant amount of data relating to the platform configuration and the distribution of ignition sources. Having completed the work to establish a model, a second phase was commissioned to consider representative scenarios which would generate look-up correlations which could be used in QRA studies without the need for the user to gather the data required for the full model. The following summarises the release types considered. •

Gas releases

•

LPG (flashing liquefied gas) releases

•

Pressurised liquid oil releases – leading to a spray release with flashing/ evaporation/ aerosol formation

•

Low pressure liquid oil releases – leading to a spreading pool only (no aerosol formation or flashing)

•

Release rates from 0.1 to 1000 kg/s – (graphs shown in the data sheets are extended to 10000 kg/s where the probability function does not reach a maximum below 1000 kg/s)

The configurations considered are given in Table 2.1 to Table 2.3. A large number of analyses were carried out to produce graphs of ignition probability against release rate. Figure 4.1 shows a typical set of curves. In the final stage of the process, groups of similar curves were considered and grouped into the scenarios listed in Table 2.1 to Table 2.3. These scenarios were then examined and a representative curve assigned to them. These curves consist of between two and four segments each of which appears as a straight line when plotted on logarithmic axes. It is these curves which are depicted in the data sheets. Figure 4.1 Exam ple of Ignition Probability Curve Calculated by UKOOA ignition m odel

Source: Energy Institute [1]

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Prior to the introduction of the UKOOA ignition model approach outlined above, the formulation attributed to Cox, Lees and Ang 4 was widely used. This gained acceptance largely because of the proportion of analysts using it rather than because of the rigour of the theory underlying it. Ignition probabilities predicted by this method were in excess of what was found to occur in practice and this was partly responsible for instigating the work which resulted in the UKOOA ignition model. References in this report to “UKOOA (spreadsheet) model” and “UKOOA look-up correlations” relate respectively to the output from the two phases of the project [1].

5.0

Recommended data sources for further information

For further information, on the ignition probability curves presented in this document, the Energy Institute report 1 should be consulted.

6.0

References

1. Ignition Probability Review, Model Development and Look-Up Correlations, Research Report published by the Energy Institute, January 2006. ISBN 978 0 85293 454 8 2. Scandpower Risk Management AS 2006. Blowout and Well Release Frequencies – Based on SINTEF Offshore Blowout Database, 2006, Report No. 90.005.001/R2. 3. Guidelines for quantitative risk assessment (Purple book), Part 1, Establishment, CPR18 E, Committee for the Prevention of Disasters (CPR), National Institute of Public Health and Environment (RIVM), Ministry of Transport, Public Works & Water Assessment Management, AVIV Adviserend Ingenieurs Save Ingenieurs (Adviesbureau), 1999. 4. Cox, Lees and Ang, 1991. Classification of Hazardous Locations, Rugby: Institution of Chemical Engineers, ISBN 0 85295 258 9.

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209-215 Blackfriars Road London SE1 8NL United Kingdom Telephone: +44 (0)20 7633 0272 Fax: +44 (0)20 7633 2350 165 Bd du Souverain 4th Floor B-1160 Brussels, Belgium Telephone: +32 (0)2 566 9150 Fax: +32 (0)2 566 9159 Internet site: www.ogp.org.uk e-mail: [email protected]