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Preliminary Hazard Analysis Appendix H

Prepared for BOC Limited, 1 April 2009 J:\JOBS\43283480\6 Deliv\DPEMP\BOC Westbury LNG Facility (Final) V10.doc

H Preliminary Hazard Analysis

BOC Westbury LNG Preliminary Hazard Analysis

for BOC Limited

26 February 2009

Reference: AUS0073607 Issue: 2

BOC Westbury LNG: Preliminary Hazard Analysis

Document History and Authorisation

Issue Date Changes

A

0

1

2

February

10 February 2009

19 February 2009

26 February 2009

Initial draft for comment.

Formal Issue: incorporating comments

Formal Issue: incorporating additional comments

Formal Issue: incorporating further comments

Compiled by: John Paul Maiorana

Signed: ................................................................................... Date: 26 February 2009

Verified by: Philip Skinner


Approved by: Howard Lister


Distribution List

Name Organisation From (Issue)

To (Issue)

Kevin Peakman BOC 1 2

Project File Lloyd’s Register 1 2

Uncontrolled copies as required (BOC Westbury LNG PHA Rev 2)

This document was prepared for BOC Limited. The information herein is confidential and shall not be divulged to a third party without the prior permission of BOC Limited.

Lloyd’s Register Rail, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as the ‘Lloyd’s Register Group’. The Lloyd’s Register Group assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Lloyd’s Register Group entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.

© BOC Limited 2009


Summary

Lloyd’s Register was commissioned by BOC to undertake a Preliminary Hazard Assessment (PHA) of the proposed Westbury LNG Facility in Westbury, TAS.

This PHA has been undertaken in accordance with the guidance provided by the NSW Department of Planning (DOP) in Hazardous Industry Planning Advisory Paper (HIPAP) No. 6 - Guidelines for Hazard Analysis. An assessment of the risk has been undertaken in accordance with the criteria published by the DOP in HIPAP No. 4 - Risk Criteria for Land Use Safety Planning. The NSW guidelines and risk criteria were adopted for this study as they are the most stringent of state guidelines and therefore consistent with BOC’s best practice approach to risk reduction across their facilities.

Conclusions The proposed LNG Facility in Westbury, TAS complies with all the risk criteria published by the NSW DOP.

• The fatality risk at the boundary of the site is below 50 in a million p.a.

• The fatality risk at the nearest commercial development, Tasmanian Alkaloids is less than 1 in a million p.a.

• The risk of heat radiation exceeding 4.7 kW/m2 or explosion overpressure exceeding 7 kPa at the western site boundary is less than 5 in a million p.a., which is 10 times less than acceptable risk criterion for residential areas.

• The risk of heat radiation exceeding 4.7 kW/m2 or explosion overpressure exceeding 7 kPa at the Tasmanian Alkaloids site is less than 0.5 in a million p.a., which is 100 times less than acceptable risk criterion for residential areas.

• The risk of heat radiation exceeding 23 kW/m2 or explosion overpressure exceeding 14 kPa at the western site boundary is less than 1 in a million p.a., which is 50 times less than acceptable risk criterion for neighbouring industrial facilities.

• The risk of heat radiation exceeding 23 kW/m2 or explosion overpressure exceeding 14 kPa at the Tasmanian Alkaloids site is less than 5 in a million p.a., which is 10 times less than acceptable risk criterion for neighbouring industrial facilities.

Page 1 Reference: AUS0073607 Issue: 2


Contents

1 Introduction................................................................................................................... 8 1.1 Background............................................................................................................. 8 1.2 Study Objectives ...................................................................................................... 8 1.3 Study Scope ............................................................................................................ 8

2 The Site and Surrounding Land Uses............................................................................... 9 2.1 Facility Location and Surrounding Land Uses ........................................................... 9 2.2 Meteorology............................................................................................................ 9

3 Facility Description ....................................................................................................... 11 3.1 Facility Overview.................................................................................................... 11 3.2 Operating Hours.................................................................................................... 11 3.3 Product Movements .............................................................................................. 11 3.4 Pre-Purification Unit............................................................................................... 13 3.5 Natural Gas Liquefaction ....................................................................................... 13 3.6 Storage Vessels...................................................................................................... 13 3.7 Tanker Loading Bay ............................................................................................... 13 3.8 Flare System .......................................................................................................... 13 3.9 Safety Features for LNG Facility.............................................................................. 14

4 Methodology ............................................................................................................... 15 4.1 Study Scope .......................................................................................................... 15 4.2 Study Methodology............................................................................................... 15 4.3 Software Used....................................................................................................... 19

5 Hazard Identification.................................................................................................... 21 5.1 Introduction .......................................................................................................... 21 5.2 Hazardous Material ............................................................................................... 21 5.3 Hazardous Material - MRG .................................................................................... 24 5.4 HAZID Workshop................................................................................................... 25 5.5 Failure Modes........................................................................................................ 26 5.6 Major Accident Event Register ............................................................................... 27 5.7 Hydrocarbon Release Scenarios ............................................................................. 28 5.8 Rule Set for Failure Scenarios................................................................................. 30 5.9 Fires 31 5.10 Vapour Cloud Explosion (VCE)............................................................................... 31 5.11 Summary of Incident Scenarios Carried Forward.................................................... 31

6 Hazard Consequence Analysis ...................................................................................... 33 6.1 Isolatable Inventories ............................................................................................. 33 6.2 Software Used....................................................................................................... 34 6.3 LNG Release Scenarios........................................................................................... 34 6.4 LNG Fires............................................................................................................... 38 6.5 Vapour Cloud Explosion ........................................................................................ 39 6.6 Summary of Consequence Analysis Results............................................................ 39

7 Frequency Analysis ....................................................................................................... 40 7.1 General ................................................................................................................. 40 7.2 Base Failure Rate Data ........................................................................................... 40



7.3 Hole Size Distribution ............................................................................................ 40 7.4 Event Tree Analysis ................................................................................................ 41 7.5 Ignition Probability................................................................................................. 41 7.6 Probability of Explosion Given Ignition................................................................... 42 7.7 Detection & Shutdown .......................................................................................... 42 7.8 LNG Wall Impingement ......................................................................................... 42

8 Risk Criteria ................................................................................................................. 43 8.1 Individual Fatality Risk............................................................................................ 43 8.2 Injury Risk.............................................................................................................. 43 8.3 Risk of Property Damage and Accident Propagation .............................................. 44

9 Risk Assessment........................................................................................................... 45 9.1 Individual Fatality Risk............................................................................................ 45 9.2 Injury Risk.............................................................................................................. 46 9.3 Property Risk ......................................................................................................... 47

10 References ................................................................................................................... 48 Appendices

Appendix A Hazard Identification Tables

Appendix B Meteorological Data

B.1 Data Source

B.2 Wind Speed/Weather Stability

Appendix C Isolatable Sections

Appendix D Consequence Analysis

D.1 Pool Fires Results

D.2 Jet Fire Results

D.3 Flash Fire Results

D.4 VCE Results

Appendix E Base Failure Frequency

E.1 Base Failure Frequencies (All Industries)

E.2 LNG Failure Frequencies modification

Appendix F Parts Count

Appendix G Total Likelihood of Release

Appendix H Ignition Probability

Appendix I Risk Results

I.1 Individual Risk Contour

I.2 Injury Risk Contour

I.3 Property Damage Risk Contour





B.1 Data Source







D.4 VCE Results










I.3 Property Damage Risk Contour List of Figures

Figure 1 Land Use Zoning for Westbury .............................................................................. 10 Figure 2 BOC Westbury Site Layout..................................................................................... 12 Figure 3 Typical Risk Analysis Methodology......................................................................... 16 Figure 4 Example Event Tree ............................................................................................... 41 Figure 5 Westbury Site Individual Risk Contour ................................................................... 45 Figure 6 Westbury Site Injury Risk Contour.......................................................................... 46 Figure 7 Westbury Site Property Damage Risk Contour ....................................................... 47 List of Tables

Table 1 Product Movements in Site................................................................................... 11 Table 2: Codes and Standards considered applicable to the LNG project............................. 14 Table 3 Injury Criteria for Fires and Explosions.................................................................... 18 Table 4 Physical Properties ................................................................................................. 21 Table 5 Physical Properties of MRG .................................................................................... 24 Table 6 List of Nodes for Hazard Identification Workshop .................................................. 26 Table 7 Failure Mode Prompts for Hazard Identification Workshop .................................... 27



Table 8 Summary of Major Accident Events ....................................................................... 27 Table 9 List of Incident Scenarios Carried Forward for Analysis........................................... 32 Table 10 Isolatable Inventories Summary.............................................................................. 33 Table 11 Hazard Consequence Software used in the Study.................................................. 34 Table 12 Representative LNG (Liquid) Release Scenarios...................................................... 35 Table 13 Representative LNG (Vapour) Release Scenarios..................................................... 36 Table 14 Hole Size Distribution for Pipework........................................................................ 40 Table 15 Ignition Probability................................................................................................. 42 Table 16: HAZID Attendees ......................................................................................... 51 Table 17: HAZID Table................................................................................................. 52 Table 18 Criteria for Rationalisation of Meteorological Data ....................................... 65 Table 19 Rationalised Wind Weather Data for Powranna Weather Station.................. 65 Table 20: Pool Fire – Distance to 22.5kW/m2 .............................................................. 69 Table 21: Jet Fire – Distance to 22.5kW/m2................................................................. 69 Table 22: Flash Fire – Distance to LFL ........................................................................... 71 Table 23: VCE – Distance to 14 kPa ............................................................................. 73 Table 24: Parts Count Table......................................................................................... 77 Table 25: Release Frequency....................................................................................... 79 Table 26: Ignition Probabilities..................................................................................... 80



Notation

Abbreviation Description

BOC BOC Limited

C2H6 Ethane

C4H10 Butane

C5H12 Pentane

CH4 Methane

CO2 Carbon Dioxide

DOP Department of Planning

ESD Emergency Shutdown

F&G Fire and Gas

GLP Gas Liquid Processing

H2S Hydrogen Sulfide

HAZID Hazard Identification

HIPAP Hazardous Industry Planning Advisory Paper

HP High Pressure

IR Individual Risk

ISIR Individual Specific Individual Risk

LFL Lower Flammability Limit

LNG Liquefied Natural Gas

LR Lloyd’s Register

LSIR Location Specific Individual Risk

MAE Major Accident Event

MRG Mixed Refrigerant Gas

NB Nominal Bore

NG Natural Gas

OSHA Occupational Safety Health Authority

P&ID Piping and Instrumentation Drawing



Abbreviation Description

PFD Process Flow Diagram

PHA Preliminary Hazard Analysis

pmpy Per Million Per Year

PPU Pre-Purification Unit

PSV Pressure Safety Valve

QA Quality Assurance

QRA Quantitative Risk Assessment

RPT Rapid Phase Transition

UFL Upper Flammability Limit

VCE Vapour Cloud Explosion



1 Introduction

1.1 Background

Lloyd’s Register (LR) has undertaken a Preliminary Hazard Assessment (PHA) of the proposed LNG Facility to be constructed at Westbury, Tasmania.

This report includes an assessment of the proposed operations including the potentially hazardous materials. This assessment has been undertaken with reference to the Department of Planning’s (DOP)

Hazardous Industry Planning Advisory Paper (HIPAP) No. 6, “Guidelines for Hazard Analysis”. An assessment of the risk has been undertaken with reference to DOP’s HIPAP No. 4, “Risk Criteria for Land Use Planning” for proposed facilities.

The NSW guidelines and risk criteria were adopted for this study as they are considered the most stringent of state guidelines and therefore consistent with BOC’s best practice approach to risk reduction across their facilities.

1.2 Study Objectives

The aim of the study was to assess the risk to safety of people living and working in the neighbourhood surrounding the LNG Facility.

The specific objectives of the study were to:

• Identify the hazardous incidents that relate to the operation of the facilities.

• Assess the significance of each incident in terms of its potential off-site impact.

• Assess and quantify the off-site levels of risk to people, property and the environment due to the proposed upgraded terminal operations, using iso-risk levels (individual risk contours).

• Provide a clear, concise report of the analysis in line with the requirements of HIPAP No. 6 [1].

1.3 Study Scope

The study covered the following:

• Identification of the hazards present on the site and development of incident scenarios.

• Assessment of the consequences of the identified potential events.

• Estimation of the frequency of identified events.

• An assessment of risk in relation to established risk guidelines.



2 The Site and Surrounding Land Uses

This section of the report includes a description of the facilities included in the scope of the Preliminary Hazard Analysis. A summary of the plant operations is presented together with a description of the surrounding land uses and a detailed description of the design and operation of proposed safety systems.

2.1 Facility Location and Surrounding Land Uses

The plant will be located in a proposed industrial subdivision (subject to rezoning) adjacent to Birralee Road and directly north of the Tasmanian Alkaloids factory in Westbury, Meander Valley municipality. The high pressure Tasmanian Gas Pipeline traverses the rear of the proposed site.

The northern boundary of the township of Westbury is located approximately one kilometre south of the subject site as shown in Figure 1

2.2 Meteorology

The meteorological data for the study was based on the data for Powranna Weather Station, this being closest to the Westbury site. The information obtained from the Bureau of Meteorology was processed into representative wind speed/ weather stability classes. Details are given in Appendix B.



Proposed BOC LNG Facility Tasmanian Alkaloids

Scale 1 km

Figure 1 Land Use Zoning for Westbury



3 Facility Description

3.1 Facility Overview

The BOC Westbury LNG facility will consist of two vacuum insulated vessels (VIE), of 200 te capacity. A site layout diagram is shown in Figure 2.

Natural gas (NG) will enter the site, from an off take of the Tasmanian Gas Pipeline, on the southern side of the site adjoining the pipeline easement. The natural gas is first let down to a facility pressure of 2500 kPa abs from its supply pressure of 9900 kPa abs at the let down skid. After the pressure is let down the NG is then conditioned in the amine plant where carbon dioxide (CO2) and any traces of hydrogen sulphide (H2S) are removed from the gas and then any moisture removed in the molecular sieve dryers. The NG is the liquefied using refrigeration process and stored for B-double tanker loading.

The facility includes:

• NG Letdown Skid

• Amine Plant

• Molecular Sieve Dryers

• MRG System (including compression)

• Cold Box (NG liquefaction unit)

• 2 x 120 te LNG vessel

• 1 LNG pump for tanker loading (80 mm NB)

• 1 B-Double tanker loading bay

• Other NG, LNG pipework, pneumatics, electrical equipment and instrumentation, and fire protection system for the installation of the above.

3.2 Operating Hours

The plant will be operating continuously with onsite personnel during normal daytime operating hours and a 24 hour process monitoring from both BOC’s Sydney Control Centre and the Cryogenic Centre in Dandenong, Victoria.

B-Double tanker filling will occur in the tanker bay area. The tanker filling will be undertaken by the tanker driver, who will be trained accordingly.

3.3 Product Movements

The expected product movements are given in Table 1.

Table 1 Product Movements in Site

No. Movement Mode Type of Truck Size of Parcel Frequency 1 Tanker loading B-Double Tanker 36 t 2/ day



Figure 2 BOC Westbury Site Layout



3.4 Pre-Purification Unit

The pre purification unit conditions the natural gas feed, entering the site from the Tasmanian Gas Pipeline, to the liquefaction process.

After the pressure is let down from the pipeline supply pressure of ~10MPa the NG is then fed through the Amine Plant. CO2 and any trace H2S is removed by solvent absorption. The entrained gases are then stripped from the rich solvent and superheated as a part of the sulphur treatment to remove H2S and then vented to atmosphere through the LP Flare.

The NG is finally dried to remove any moisture in a molecular sieve adsorber.

3.5 Natural Gas Liquefaction

A refrigeration process, through a “Cold Box” liquefies the purified NG. The cold box is essentially a heat exchanger that cools the NG to below its boiling point. The refrigerant system is a basic compression and condensing refrigeration loop. The Mixed Refrigerant Gas (MRG) in the refrigerant loop is constantly made up with gas that is dosed into the system..

3.6 Storage Vessels

The two 120 te vessels are approximately 5 m outside diameter, and 25m high and will be continuously fed LNG from the NG liquefaction process. The storage vessels are constructed of an inner stainless steel wall with an outer carbon steel wall. To provide insulation, for the tanks the void between the two walls is filled with a perlite material and maintained under constant vacuum.

The storage area is bounded by three walls deliberately designed to both contain any potential LNG releases and minimise the likelihood of any jet releases beyond the storage area. In addition, all pipework in and out of the vessels will be located at a low elevation to take advantage of the protection provided by the walls.

All LNG spills within the containment area will drain to a specially designed containment pit, 5m x 5m x 1m which allows for a controlled response to any release.

3.7 Tanker Loading Bay

Two B-double road tankers will be loaded per day on a 7 day per week basis. The road tanker fill time is expected to be approximately 1hr. The tanker loading bay has a wall running parallel to the road to contain any potential releases from the tanker loading process. The tanker loading bay also drains to the LNG containment pit.

3.8 Flare System

The Westbury site has an enclosed ground flare installed to safely vent any gases from the process. All relief valves vent to this system via a series of headers. Any venting that may contain liquid, particularly heavy hydrocarbons, is first sent to a dump pot where they are heated to ensure only vapours are sent to the flare. The pilot flames on the flare are fed via a continuous bleed of methane from the storage vessel boil off gas.



3.9 Safety Features for LNG Facility

The safety features proposed to be provided at the BOC Westbury LNG Facility have been based upon experience with similar industrial facilities.

LNG has a long and excellent safety record. The potential safety hazards of LNG are very well understood and measures to preclude them have been universally deployed. Extensive research has gone into understanding the behaviour of LNG and how to control its associated hazards. Furthermore the LNG industry operates under an umbrella of strict design codes and regulations which ensure that LNG facilities are constructed and operated to exacting standards.

It is intended that this project will adopt the best approaches from AS/NZ and international codes and standards as shown in Table 2:

Table 2: Codes and Standards considered applicable to the LNG project Risk Level Criteria (Siting)

Hazardous Industry Planning Advisory Paper No.4 (HIPAP 4) Risk Criteria for Land Use Safety Planning 1990 (NSW Department of Planning,

Risk Methodology AS/NZS 4360: Standard for Risk Management (Standards Australia, 2004,

Plant Layout AS 3961: Liquefied Natural Gas Storage and Handling

Equipment Standards AS 3961: Liquefied Natural Gas Storage and Handling

NFPA 59A: Standard for the Production, Storage, and Handling of Liquefied Natural Gas (LNG)

Emergency Response Plan

Hazardous Industry Planning Advisory Paper No.1 (HIPAP 1) Industry Emergency Planning Guidelines 1990 (NSW Department of Planning)

Training CSA-Z276-01:2001 Liquefied Natural Gas (LNG) - Production, Storage, and Handling

In general, for LNG the NFPA standard is prescriptive whereas the Australian standard is performance based with flexibility using risk-based design. For plant layout the relevant Australian Standard, AS 3961, was adopted. For example, the distance from the edge of trenches/bunds for LNG containment to the boundary is 0.7 times the tank diameter as prescribed in NFPA 59A, while AS 3961 determines the distance to the boundary based on thermal radiation levels from pool fires.

In the design of the actual processing equipment, a combination of both NFPA 59A and AS 3961 was used based on the applicability of the standards to the relative applications.

The proposed safety measures are captured in Appendix A.



4 Methodology

4.1 Study Scope

The study assessed the risks to the public arising from both normal operations and atypical occurrences associated with the storage and handling of hazardous materials at the site.

The scope of the study included the following tasks:

1 Hazard Identification (HAZID) for the proposed Westbury LNG facility; and

2 Preliminary Hazard Analysis of the proposed Westbury LNG facility.

4.2 Study Methodology

The PHA methodology used in this study is that of “classical” risk assessment. This is a systematic approach to the analysis of what can go wrong in complex industrial systems. The normal conditions of operation of the system are defined and then the following questions asked:

• What accidental events can occur in the system?

• What are the consequences of each event?

• How likely is each event to occur?

• What are the total risks (likelihood x consequence) of the system?

• What is the significance of the calculated risk levels?

These questions correspond to the five basic components of a PHA. Once a system has been analysed, if the risks are assessed to be too high according to some criteria, the system can be modified in various ways to attempt to reduce the risks to a tolerable level, and the risk levels recalculated. The process may therefore be viewed as iterative, where the design of the system may be changed until it complies with the needs of society. By objectively quantifying the risks from each part of the system, a quantitative risk analysis enables identification of the most effective measures to reduce risks.

The methodology used follows the following steps:

• System definition, in which information on the facility is collected and assimilated.

• Hazard identification, in which site events and external events are identified which may lead to the release of hazardous material.

• Consequence modelling, in which all the possible consequences of each event are estimated.

• Frequency estimation, in which the frequency (i.e. likelihood per year of occurrence) of each of the accidental events is estimated, based on historical failure data.

• Risk estimation, in which the frequencies and consequences of each event are combined to determine levels of fatality risk.

• Risk assessment, in which the risks calculated are compared with risk criteria.

Figure 3 shows the project flow by task.



TASK 1Kick-Off Meeting

TASK 4Hazard Identification

(Accident Case Development)

TASK 3Background Data,

Collection and Analysis

TASK 2Familiarisation, and

Data Collection.(System Description)

TASK 5 Frequency Analysis TASK 6

Consequence Analysis

TASK 7Risk Calculations

TASK 8 Risk Criteria TASK 9

Risk AssessmentTASK 10

Iterative Calculations

TASK 11Risk Mitigation

TASK 12Report Production

and ResultsPresentation

Figure 3 Typical Risk Analysis Methodology

4.2.1 Hazard Consequence Analysis

The physical consequences of an LNG release are dependent on the quantity released, the rate of release and, for fire and explosion events, when ignition occurs:

The quantity of release depends on the size of release (assumed equivalent hole diameter) and duration of release (how soon can the release be detected and isolated).



The release rate from a hole is assumed to be from a circular orifice of equivalent diameter. This is the maximum flow-rate for a given hole area and is used because it can be calculated readily and with confidence and will also produce the maximum release rate for a given hole area.

An LNG liquid release may form an evaporating pool and generates vapour. Ignition of the vapour arising from the LNG pool would result in a flash back and a pool fire, causing intense thermal radiation around the burning pool.

If the evaporating pool does not ignite immediately, the generated vapour forms a cloud and disperses in ambient air. The dispersion rate depends on the wind speed and atmospheric stability conditions. Being cold (release temperature -160C), the vapour is heavier than air and tends to stay close to the ground, until the vapour is sufficiently dilute and warm by mixing with air and disperse as a neutrally buoyant gas, and finally as buoyant gas. The flammable gas is methane.

The dispersion of LNG vapour up to its lower flammability limit (LFL) is modelled to produce a flammable gas concentration profile in three dimensions (downwind, crosswind and elevation). For releases that are constant over time, this can be represented by a set of contours of constant concentration (isopleths) on a plan drawing and/or summarised in a tabular format.

If ignition of the methane gas-air mixture occurs, then the result would be a flash fire or a vapour cloud explosion. VCEs of LNG vapour do not occur in open air. Even in partially confined and/or congested plant areas the explosion impact is low because of the low flame speed of methane and the absence of significant turbulence in the dispersing vapour cloud. Any impact would be localised with no impact outside the immediate areas of confinement or congestion.

If the release is of LNG vapour under pressure, an ignition would produce a jet fire. The jet fire would generate heat radiation, which can be modelled using the surface emissivity of the flame to produce contours of heat radiation levels. In addition, a jet flame impinging on adjacent equipment may cause structural failures and incident escalation.

The Consequence analysis for the MAEs was carried out using the PHAST software package for releases on land.

4.2.2 Impairment Criteria

Impairment criteria for injury have been developed for explosions, fires and unignited releases as shown in Table 3. These criteria are taken from Ref: 6

Value Damage

Explosions (kPa)

7 Probability of injury is 10%. No fatality.

35 50% chance of fatality for a person

70 100% chance of fatality for a person

Fire (kW/m2)

4.7 Injury to person who cannot escape or seek shelter after 30s exposure.

6 10% probability of fatality. The criterion does not specify exposure duration, but some duration is implied.



Value Damage

12.6 First degree burns in 10s. 50% probability of fatality. The criterion does not specify exposure duration, but some duration is implied.

23 Probability of fatality is 100% within 60s of exposure.

Vapour cloud fire (Flash fire)

Within flammable cloud

The extent depends on the flammable gas content of the cloud and duration of combustion. Probability of fatality is estimated using thermal radiation intensity and duration of exposure for a normally clothed person.

100% probability of fatality

Table 3 Injury Criteria for Fires and Explosions

4.2.3 Incident Frequency and Likelihood Analysis

Once the consequences of the various accident scenarios have been estimated, it is necessary to estimate the likelihood of each scenario. In a QRA, the likelihood must be estimated in quantitative terms (i.e. occasions per year). Exponential notation (e.g. 5.2 x 10-6 per annum) is normally used because the likelihood of an MAE is usually a low number (i.e. much less than 1).

For very low frequency events for which historical occurrences have been rare, the likelihood values cannot be estimated directly based on historical data. Most of the representative release scenarios are summations of many individual events (e.g. rupture of a pipeline could occur at flanges, bends, junctions, etc. due to a variety of causes). The total likelihood of the rupture scenario is estimated based on the number potential release sources, i.e. number of flanges, bends and junctions, coupled with the historical likelihood of pipeline rupture for those fittings. Further, this is only possible because data on such incidents has been collected by various organisations over a number of years in the process industry and oil and gas industry.

It is important to note that use of historical data to forecast the future assumes that the conditions in the future will be similar to those that existed in the past. For operational incidents, e.g. overfilling a tank, it may be necessary to develop a fault tree, using the fill frequency and failure of level measuring equipment and independent overfill protection failure.

There is no data on equipment failure rates specific to the LNG industry. The use of generic failure data for process industries is highly conservative when applied to LNG facilities as some of the failure modes are not present in LNG terminals (e.g. corrosion).

The frequency of the MAEs was estimated from the following generic reliability database:

• Classification of Hazardous Locations (Cox, Lees and Ang) [Ref: 8]. This was used for piping, valves and pumps, and for probability of ignition.

The frequency analysis data and results are summarised in Section 7.

In this study an attempt has been made to identify the relative contributions of various failure modes to the total failure frequency so that the generic frequency can be adjusted to remove those failure modes that do not exist in LNG installations.



The frequency of each possible outcome is normally derived using event tree analysis. Starting with the initial event of hydrocarbon release, the event tree follows various possible outcomes such as ignition, exposure of persons within the impact radius, and injury or fatality. Probabilities are ascribed at each node of the event tree, based on the detection and mitigation measures, and exposure probability.

The frequency / likelihood analysis step in a QRA contributes to the most uncertainty in the estimated risk. It may sometimes be necessary to undertake a sensitivity analysis to identify and analyse the significance of variation to the frequency / likelihood data to the risk results.

4.2.4 Risk Analysis and Assessment

Risk analysis and assessment are separate tasks although they are often undertaken at the same time. Risk analysis requires the scenario consequence and likelihood estimates to be combined and then summed across all the accident scenarios to generate a complete picture of the risk.

Part of this analysis will be to determine the most appropriate way of presenting the risk results. The risk measures commonly used are:

Individual Risk of Fatality

• Location-specific individual risk (LSIR) - These are fatality iso-risk contours, superimposed on a plan of a site. Risk levels that are often shown as iso-risk contours include the 1 x 10-6 per annum (p.a.), 1 x 10-5 p.a. and 5 x 10-5 p.a. levels. The Centre for Chemical Process Safety (CCPS) [Ref. 12] explains that individual risk contours show the geographical distribution of individual risk. The risk contours show the expected frequency of an event capable of causing a specified level of harm at a specified location, regardless of whether or not anyone is present at that location to suffer that harm. Thus, individual risk contour maps are generated by calculating individual risk at every geographic location, assuming that somebody will be present and at the given location 100% of the time (i.e. peak individual risk with no allowance for escape).

• Individual-specific individual risk (Risk to nominated individual) (ISIR) - This is applied to a specific employee population on-site, and is an estimate of the likelihood of a specific individual (e.g. a nominated plat operator) sustaining fatal injury. Unlike location-specific individual risk, this risk estimate takes account of the fraction of time that the nominated person spends at different locations in the facility. Typical risk estimates are 1 x 10-5 p.a., 1 x 10-4 p.a. and 1 x 10-3 p.a.

The assessment of risk results involves comparing the results against risk criteria. In some cases, this assessment may be a simple listing of each criterion together with a statement that the criterion is met. In other, more complex cases, the risk criteria may not be met and additional risk mitigation controls may be required to reduce the risk.

4.3 Software Used

The PHAST software package was used for both flammable gas cloud and pool/jet fire modelling. PHAST was selected for the consequence analysis because it includes a model for releases of liquefied gases (an important consideration for this QRA) and independent evaluation of this model indicates that it is appropriately conservative.

The risk contours were generated using the proprietary software package ORCA (On-Shore Risk and Consequence Analysis).



The basic structure of the ORCA package simulates the approach used in classical risk analysis. The conceptual flow of data through the various steps follows logically through failure case definition, consequence modelling and impact assessment to the final calculation of individual risk and societal risk results.

Although ORCA includes some consequence models, the results from PHAST are readily imported into the ORCA software (which has been designed to allow the input of results from different consequence analysis software).



5 Hazard Identification

5.1 Introduction

The major objective of the HAZID process was to identify the potential MAEs associated with the BOC Westbury LNG facility. A HAZID was carried out through a review of the PFDs, engineering documents and available literature and through a consultative workshop with Stakeholders.

The HAZID results are given in full in Appendix A. From this, the MAEs were developed. An MAE is an event with the potential to cause harm to people as a result of a release of hazardous material (NG, LNG, and MRG), or to escalate the primary event to a larger event, thus affecting safety.

5.2 Hazardous Material

5.2.1 Physical Properties

NG or LNG is principally used as a fuel. It typically contains 95 to 97% methane (CH4). As the name implies, LNG is the liquid form of NG.

The physical properties of NG and LNG are listed below:

Properties

Parameter NG LNG

Boiling Point -162 °C -162 °C

Density 5-16 kg/m3 (vapour) 415-435 kg/m3 (liquid)

Lower Flammability 5.3% 5.3% (liquid)

Upper Flammability 14% 14%

Main composition (>95%) Methane Methane

Table 4 Physical Properties

5.2.2 Hazardous Properties

Hazardous properties of LNG are as follows:

• vapour is flammable;

• liquid is flammable when released because the vapours burn on ignition and flash back to the liquid surface;

• vapour is heavier than air at vapour temperatures below about –113°C;

• vapour is colourless, odourless and non-toxic, with a potential for asphyxiation at higher concentrations due to oxygen depletion; and

• liquid is cryogenic, requiring special materials of construction due to the intense cold, and special Personal Protection Equipment (PPE) is required to prevent cold burns.

It should be noted that NG vapour at ambient conditions (predominantly methane) is lighter than air and so will tend to rise and disperse into the atmosphere. However, vapour arising from a spill of LNG is heavier than air because of its low temperature until it gains sufficient heat from the ambient air.



Injury may result due to exposure to:

• The low temperature liquid (e.g. skin contact) - To transport LNG at atmospheric pressure, it is refrigerated at approximately -162 ºC.

• Overpresssure from a rapid phase transition.

• Asphyxiation – Although non-toxic, LNG (vapour) has the potential to cause asphyxiation, particularly if exposure occurs in a confined space.

• Heat radiation, and/or direct flame contact, from a jet fire, pool fire or flash fire.

• Overpressure from a vapour cloud explosion or an explosion in a confined space.

Exposure to Cryogenic Liquid

Natural gas may be liquefied at atmospheric pressure if it is cooled to -162 ºC. At this temperature, it forms a clear, colourless liquid with a density about half that of water. Due to its low temperature, LNG can cause severe cryogenic burns to exposed skin.

Cryogenic burns are more severe for liquid exposure than for vapour exposure. On contact with skin, the liquid removes more heat (viz. sensible heat and latent heat of vaporisation) from the skin.

For the QRA, the potential for fatality was not considered wherever direct exposure to a liquid release might occur as no LNG pools form off site and therefore would not contribute to the off-site risk.. Cryogenic exposure was only considered to generate a severe injury.

Rapid Phase Transition

There may be a rapid change of phase (from liquid to vapour), when low temperature LNG (liquid) is released onto warmer water. The corresponding increase in volume (an approx. 600-fold increase) can lead to the phenomenon known as a ‘rapid phase transition’ (RPT) explosion and generation of a potentially hazardous overpressure.

Although a type of explosion, there is no flame associated with a RPT, and the overpressure is localised. Damaging overpressures only occur very close to the source and ignition of the vapour has never been observed during an RPT. However, ignition of the gas cloud has occurred due to the RPT causes damage to neighbouring equipment or instrumentation.

Although energy releases equivalent to several kilograms of TNT have been observed [Ref: 16] the impacts of this phenomenon will be localized near the spill source and should not cause extensive structural damage [Ref: 16] or pose any direct threat to safety outside of the immediate area of the spill itself.

The effects of RPT explosions are not included in the QRA. This is consistent with standard QRA practice for LNG facilities to-date and the absence of experimental (or incident) data that can be used to predict the consequences of an RPT explosion.

Asphyxiation

Methane is a simple asphyxiant with low toxicity to humans. If a release of LNG does not ignite, then the potential exists for the LNG vapour concentration to be high enough to present an asphyxiation hazard to personnel nearby.

An atmosphere with marginally less than 21% oxygen can be breathed without noticeable effects. However, at 19.5% (which is OSHA's lower limit for confined space entry in 29 CFR 1915.12) there is a rapid onset of impairment of mental activity.



An oxygen concentration of about 15% will result in impaired coordination, perception and judgment. This may prevent a person from performing self-rescue from a confined space.

The potential for unconsciousness and fatality is only significant at less than 10% oxygen. However, to reduce the oxygen concentration to 10% requires a relatively high methane concentration of approximately 342,000 mg/m3 or 52% v/v.

Oxygen deficiency from vaporization of an LNG spill should not be a major issue because the flammability limits (the LFL for methane is approximately one-tenth of the fatal asphyxiant concentration) and fire hazards are usually the dominant effects in most locations [Ref: 16].

Asphyxiating concentrations only occur close to the release point and do not pose a threat offsite. Therefore, the potential for fatality from asphyxiation was not carried forward to the likelihood and risk estimation steps of the QRA .

Jet Fire

Combustion of NG or LNG (vapour) released from an orifice (e.g. hole in a pipe) may create a jet fire.

The potential for fatality due to exposure to heat radiation from a jet fire was included in the QRA.

Pool Fire

If ignited, LNG (liquid) released from an orifice (e.g. hole in a pipe) onto the ground may result in a pool fire.

The potential for fatality due to exposure to heat radiation from a pool fire was included in the QRA.

Flash Fire

Methane is flammable between concentrations of approximately 5.3% (LFL) and 14% (UFL) by volume when mixed with air. However, methane is a low reactivity gas and only a powerful spark or very hot surface (above 540 °C) will ignite the vapour if it is between these limits.

For low reactivity fuels such as LNG, combustion of an unconfined gas cloud will usually progress at low velocities and will not generate a significant overpressure. Ignition of the gas cloud will cause the vapour to burn back to the spill source. This is a flash fire and has the potential to cause injuries or fatalities for individuals within the ignited gas cloud.

The potential for fatality due to direct exposure to a flash fire was included in the QRA.

Vapour Cloud Explosion

VCEs of LNG vapour do not occur in open air. Even in partially confined and/or congested plant areas an explosion impact is low because of the low flame speed of methane and the absence of significant turbulence in the dispersing vapour cloud. In order to produce high flame speeds (i.e. > 100 m/s) in a methane gas cloud, a high degree of confinement and congestion is required. This may occur in and around buildings, process plant and pipework. However, ignition trials on dispersed unconfined LNG gas clouds have confirmed that no significant overpressures are developed. Flame speeds are of the order of 10 m/s and measured overpressures less than 1 mbar (or 0.1 kPa).

The potential for fatality due to exposure to overpressure from a vapour cloud explosion was included in the QRA for large NG releases within the covered area of the PPU.



5.3 Hazardous Material - MRG

5.3.1 Physical Properties

MRG is the refrigerant gas used to cool the NG down to cryogenic temperatures. It typically contains methane (CH4), ethane (C2H6), butane (C4H10) and iso-pentane (C5H12).

The physical properties of MRG are listed below:

Properties

Parameter MRG Vapour MRG Liquid

Main composition (~35%) Methane and Ethane Pentane

Density 5-20 kg/m3 (vapour) 500 kg/m3 (liquid)

Lower Flammability 2.8% 1.6% (liquid)

Upper Flammability 13.4% 9.1%

Table 5 Physical Properties of MRG

5.3.2 Hazardous Properties of MRG

Hazardous properties of MRG are as follows: • vapour is flammable;

• liquid is flammable when released because the vapours burn on ignition and flash back to the liquid surface;

• vapour is colourless, odourless and non-toxic, with a potential for asphyxiation at higher concentrations due to oxygen depletion; and

• liquid is cryogenic, requiring special materials of construction due to the intense cold, and special Personal Protection Equipment (PPE) is required to prevent cold burns.

Injury may result due to exposure to:

• The low temperature liquid (e.g. skin contact)

• Heat radiation, and/or direct flame contact, from a jet fire, pool fire or flash fire.

• Overpressure from a vapour cloud explosion or an explosion in a confined space.

Exposure to Cryogenic Liquid

Due to its low temperature, MRG liquid can cause severe cryogenic burns to exposed skin. Cryogenic burns are more severe for liquid exposure than for vapour exposure. On contact with skin, the liquid removes more heat (viz. sensible heat and latent heat of vaporisation) from the skin.

For the QRA, the potential for fatality was not considered wherever direct exposure to a liquid release might occur (i.e. for persons caught within a pool of MRG liquid).

Jet Fire

Combustion of MRG (vapour) released from an orifice (e.g. hole in a pipe) may create a jet fire.

The potential for fatality due to exposure to heat radiation from a jet fire was included in the QRA.



Pool Fire

If ignited, MRG (liquid) released from an orifice (e.g. hole in a pipe) onto the ground may result in a pool fire.

The potential for fatality due to exposure to heat radiation from a pool fire was included in the QRA.

Flash Fire

MRG is flammable between concentrations of approximately 2.8% (LFL) and 13.4% (UFL) by volume when mixed with air. A flash fire is possible with the ignition of the gas cloud and ignition will cause the vapour to burn back to the spill source.

The potential for fatality due to direct exposure to a flash fire was included in the QRA.

Vapour Cloud Explosion

A flammable vapour cloud of MRG can form a VCE in partially confined and/or congested areas of plant. The presence of C2’s and C4’s with methane, in MRG, allows for the generation of higher flame speeds than for 100% methane vapour clouds.

The potential for fatality due to exposure to overpressure from a vapour cloud explosion from an MRG release was included in the QRA.

Confined Explosion

If a confined MRG-air mixture is ignited, then high flame speeds can occur with damaging overpressures. However, the only enclosed space where a MRG release could occur is within the Cold Box which is mechanically ventilated and equipped with gas detection equipment. Even if a confined explosion were to occur in this room, the overpressure would be damaging but restricted to within the confined region, decaying rapidly in the unconfined part of the cloud.

Therefore, releases of MRG that ignite in or around this structure were included in the QRA as flash fires rather than confined explosions.

The potential for fatality due to exposure to overpressure from a confined gas explosion was not included in the QRA.

5.4 HAZID Workshop

A hazard identification workshop was held at BOC’s offices in Preston, Victoria on 25 November 2008. The objective of this workshop was to identify credible causes of NG, LNG and MRG releases at the facility. For each identified specific cause, the consequences, prevention measures and mitigation measures were also identified and recorded.

The facility was split into the following sections (or nodes):



Node Description

1 Natural Gas Let Down

2 Pre-Purification Unit

3 Cold Box (Liquefaction)

4 LNG Storage and tanker loading

5 Flare System

6 General

Table 6 List of Nodes for Hazard Identification Workshop

The hazard log developed from the hazard identification workshop is included in Appendix A.

5.5 Failure Modes

The following list of typical failure modes was then used as a prompt for identifying the specific causes, consequences, prevention measures and mitigation measures at each node:

Failure Mode Notes

Mechanical / Electrical Failure

Includes all component failures that may result in a release of NG, LNG, or MRG (e.g. gasket failure, flange leaks, equipment malfunction due to fatigue, aging, lack of maintenance, material failure etc.). The potential for release is minimised by preventive maintenance and inspections.

Material selection and QA in procurement and installation to minimise the risk of this failure mode occurring.

Natural Hazards Includes adverse weather conditions leading to failure (e.g. lightning strike).

Corrosion - Applicable for all carbon steel equipment and pipework used in non- LNG service.

- Not applicable to LNG equipment and pipework since LNG is non-corrosive. Construction materials are nickel alloys which are corrosion resistant. Unlike carbon steel, corrosion underneath insulation would not occur because the piping is stainless steel.

Escalation Includes events that may escalate and cause a secondary release of NG, LNG or MRG.

Impact The potential is minimised by control of onsite movements within the facility and permit to work systems for lifting loads, etc.

Material defect in fabrication

Qualified and certified welders and QA in fabrication minimise the risk of this failure mode occurring

Incorrect installation Quality assurance (QA) and testing minimise the risk of this failure mode occurring.

Human Error Includes procedural errors that may result in a release of NG, LNG, or MRG.

Overpressure Unintended high pressure leading to equipment failure.



Failure Mode Notes

Overfill This failure mode applies for loading the road tanker. Level monitoring and independent high-high level protection instrumentation reduce this risk to very low levels.

Open Pathway Operational/maintenance errors create an open pathway to atmosphere.

Table 7 Failure Mode Prompts for Hazard Identification Workshop

From Table 7, it is clear that not all failure modes in the process industries are applicable to the LNG industry. When generic failure rates for the petrochemical industry are used in risk assessment, care should be taken to adjust the generic data for absent failure modes, provided that the failure rate data by distribution of failure modes are available.

5.6 Major Accident Event Register

The hazard log from the hazard identification workshop (Refer to Appendix A) was used to develop the following representative Major Accident Events (MAEs).

MAE Description

1 Release of HP NG (vapour) from Site boundary to Letdown Skid

2 Release of HP NG (vapour) at the Letdown Skid

3 Release of NG (vapour) from the Amine Plant equipment and piping

4 Release of NG (vapour) from the Dryer Unit equipment and piping

5 Release of NG (vapour) from the feed to Cold Box

6 Release of LNG (liquid) from equipment and piping to LNG Storage

7 Release of LNG (liquid) from Storage Vessel T85A

8 Release of LNG (liquid) from Storage Vessel T85B

9 LNG to tanker filling

10 Release of NG (vapour) from tanker loading vapour return line

11 Release of MRG (vapour) return from Cold Box to Compressor equipment and piping

12 Release of MRG (vapour) in equipment and piping to Cold box

13 Release of MRG (liquid) in equipment and piping to Cold box

14 Release of NG (vapour) in Regeneration Gas Return equipment and piping

15 Release of NG (vapour) in Dryer Unit Regeneration

16 Release of LNG (vapour) during tanker Loading

17 Release of LNG (liquid) from Cold Box

Table 8 Summary of Major Accident Events

These MAEs were carried forward to the consequence, likelihood and risk analysis steps of the QRA.

The Major Accident Events (MAEs) are listed in more detail in Appendix B.



5.7 Hydrocarbon Release Scenarios

Hydrocarbon releases can occur from either equipment failures or operational failures. The causes of failures are described below, with comments on their applicability to the proposed site.

5.7.1 Overpressure

LNG Storage An overpressuring of a vessel could only occur if overfilling takes place, the vessel is overheated, and the relief valve fails to discharge at the same time or from tank roll over.

Both storage vessels are fitted with a high level alarm and a high high level trip which trips the feed to the tank. Therefore, the chance of an overfill is very low.

The vessels are double walled and vacuum insulated with a perlite material, and not subject to fluctuations in ambient temperatures. Therefore, overheating of the vessel is not possible.

Any rupture of the internal wall would result in release of LNG into the void between the two walls of the tank breaking the vacuum and causing the PSV on the void to activate. Such an incident would be readily noticeable as the perlite would be seen discharging from the PSV. The failure of the inner wall is only considered credible as a manufacturing defect and should be identified during vessel fabrication QC and the commissioning process. Given the inner wall being constructed out of stainless steel and no reported failures of these vessels in cryogenic service this scenario was considered non-credible and not carried forward into the QRA.

Multiport relief valves are installed in the tanks, with four valves in the assembly. The chance of a relief valve failing to open itself is very low as these valves are on clean duty, and are tested and maintained at regular intervals. Even in such an event, the chance of more than one port failing to open is considered to be non-credible.

Tank roll over occurs when there is a large product density differential and stratification within the storage tank during loading. The difference in densities causes a roll over of material which creates vapour at a much higher rate than can be discharged by the PSV’s. The scenario has been considered non credible due to:

1 The tall thin vessel design – historically this event has only occurred in a large diameter

vessel.

2 High product change over and QC – historically this event has occurred in large storage vessels receiving LNG via ship transfer with variable product specification and large intervals between vessel filling which allows stratification to occur.

The scenario of vessel failure from overpressure is therefore no longer considered as credible.

The pressure in the pipe work could increase if liquid LNG is trapped between isolation valves, and it is heated by the sun. Hydrostatic relief valves are installed on all pipe work, between two isolation valves, where liquid can be trapped.



5.7.2 Corrosion

LNG is a clean liquid and is non-corrosive. Therefore, the chance of internal corrosion is negligible. All pipe work is painted with a corrosion resistant paint, and inspected externally on a regular basis. The chance of a major failure of LNG vessels and pipe work due to corrosion is considered negligible.

Corrosion on NG pipework has been considered given both the carbon steel material selection and the presence of water and CO2 in the NG feed.

5.7.3 Mechanical Damage

The site is protected by a security gate, and normally there is no vehicular access to the storage vessels.

The system does not require frequent maintenance, and any crane access to the site is rare. Even then no heavy objects are moved over the vessels or pipe work, and hence the chance of a mechanical damage due to impact is low. The access road for road tankers to the loading bay will be designed with a straight run section on approach without any bends.

For the LNG service, the pipe work has minimum flanged connections, and is mostly welded. No instruments are provided on the piping. The hydrostatic relief valves have an orifice and hence, even if accidentally damaged, the leak would be minimal.

5.7.4 Failures of Gaskets/ Flanges

A gasket failure would vary from a weeping leak to a small section of gasket being blown away (typically the section between two adjacent bolts). The maximum possible hole size for such failures was postulated as 9 mm, based on the distance between bolts and the gasket thickness.

For all failures except those on the first flange on vessel nozzles, the leak could be minimised by activating the ESD.

5.7.5 External Leaks from Valves

The type of failures that could be encountered include a gland leak to atmosphere (weep), a body/ bonnet gasket leak to atmosphere (weep), and a significant body/bonnet gasket leak to atmosphere (Blything and Reeves, 1988).

Most of the leaks would be small. The maximum possible hole size for a significant leak was taken as 9 mm.

5.7.6 LNG Hose Failure

The likelihood of this incident is low due to the following reasons:

• The hoses are pressure tested at regular intervals to 1.5 times the maximum operating pressure.



• The construction of the transfer hose incorporates a double walled hose, with the outer hose provided with pinholes at regular intervals along its full length. Should a failure of the inner hose occur, then atmospheric moisture would condense on the outer wall of the hose, providing an immediate detection method of a failure. The hose would then be decommissioned.

• There have been inner hose failures in the past, but these were identified due to ice formation on the outer wall, and the hose was discarded. No loss of containment has been reported.

• There has been two reported cases of failure of the joint between the rubber hose and the metal casing in the last 20 years of operation (Robbins, 1994). This has resulted in a full bore failure and the excess flow valve on the tanker had shut resulting in a total loss of less than 5 litres. The integrity of the hose testing in the LNG industry has significantly improved since these events.

Since the failure of the hose is a credible scenario (based on past incidents), it has been included in the analysis.

5.7.7 Operational Failures

The key operational failure identified is an overfill of the B-double road tanker during tanker filling.

Overfill of road tankers is controlled by the following procedures:

• The tanker filling control system is governed by weigh scales which are monitoring the filling process.

• The driver who is in attendance during the fill will monitor the liquid flow and shutdown the pump if necessary.

• The loading bay will be fitted with a “dead man switch” to ensure the operator is in attendance during filling.

Based on the above arguments, major LNG releases from potential operational deviations have not been included in the analysis.

5.8 Rule Set for Failure Scenarios

The following rule sets were therefore developed for the release scenarios:

• Significant leaks for carbon steel piping (NG service) distributed to 9, 20, 50mm and full

bore representative hole size.

• Leak from the LNG pipework equivalent to 80mm hole based on the largest nozzle size.

• Significant flange leaks in liquid and vapour lines, and manway cover, equivalent to 9 mm hole.



• Significant leak from gasket on valve body/ bonnet, equivalent to 9 mm hole and 20mm for small bore fittings.

Flange/ valve leaks on pipe work can be isolated by operating the ESD. This is done either by the operator, if present, or by the fire and gas detection system. If isolated, the leak duration would be limited as the isolated inventory is low.

A prolonged leak would occur;

• if the operator were not present and the leak did not ignite, or

• if the leak ignited and the emergency isolation valve failed to close on ESD activation.

5.9 Fires

Three types of fires are possible with NG, LNG, MRG.

1. A jet fire. This could occur if a gas leak or a liquid leak from a pipe is ignited.

2. A flash fire. A flash fire is the result of ignition of a well mixed air-methane cloud. A liquid/two-phase leak of LNG would evaporate and disperse into atmosphere forming a flammable air-vapour mixture on ignition, depending on the degree of congestion and confinement in the flame front, a vapour cloud explosion may result. In its absence, a flash fire would be the result.

3. A pool fire. After flashing off a portion, the remaining leaked LNG may form a pool and if ignited, would form a pool fire. All areas of the facility where LNG is in service drain towards a containment pit. A containment pit poolfire has been considered for all liquid release scenarios.

5.10 Vapour Cloud Explosion (VCE)

If a liquefied flammable gas is released to atmosphere, there is a possibility that the ignition of the flammable cloud may result in an explosion, and it is referred to as a Vapour Cloud Explosion (VCE). For a VCE to occur the cloud must have sufficient mass and confinement.

The areas of partial confinement for NG dispersion are primarily in the undercover area of the PPU. The confinement is not significant and hence any explosion overpressure generated is likely to be small.

5.11 Summary of Incident Scenarios Carried Forward

The incident scenarios that have been carried forward for further assessment are listed in Table 9

Not all the NG, LNG and MRG releases are expected to result in a risk impact. The consequence analysis of releases is described in the next section (Section 6). Using the results of the consequence analysis, those events that were determined as not contributing to risk by virtue of having only localised effect without escalation, were excluded from further consideration.



No. Event Possible Consequence 1 Loss of vessel contents in LNG

storage Jet fire, Flash fire, Containment Pit Pool fire.

2 Loss of vessel contents in tanker loading bay

Jet Fire, Flash fire, Containment Pit Pool fire.

3 Fittings leak at tanker loading bay Jet fire, Flash fire, Containment Pit Pool fire.

4 Flange/gasket external valve leak in liquid lines

Flash fire, spray/jet fire

5 Flange/gasket external valve leak in vapour lines

Jet fire, Flash Fire, possible VCE depending on leak location and confinement,

6 LNG loading hose failure Jet fire, Flash Fire, possible VCE depending on leak location and confinement

7 Flange/gasket external valve leak in MRG lines

Jet fire, Flash Fire

Table 9 List of Incident Scenarios Carried Forward for Analysis



6 Hazard Consequence Analysis

6.1 Isolatable Inventories

Pipework or equipment failures could occur with leak sizes varying from pin-hole leaks to full-bore ruptures. However, as it would be impractical to analyse a large number of leak sizes in detail, it is standard practice in a QRA to select a limited number of hole/orifice diameters to represent the full range. In some cases, only one representative hole/orifice diameter may be relevant, but typically 2-3 hole/orifice diameters are sufficient for each isolatable section.

Seventeen isolatable sections were identified for the Westbury LNG facility. It is a general assumption that simultaneous failure of multiple equipment items (e.g. Compressors) is non-credible.

The isolatable sections are listed in Table 10. For each isolable section, the inventory of LNG within the equipment item, or the inventory that would be trapped between shutdown valves, is also listed.

Section Description Approximate Inventory, kg Phase

1 HP NG line from Site boundary to LD Skid 117.0

V

2 HP NG feed to let down skid 117.0

V

3 NG through Amine Plant 187.5

V

4 Dryer Unit 186.5

V

5 NG to Cold Box 141.6

V

6 LNG to Storage 192.2

L

7 LNG Storage T85A 120,000

L

8 LNG Storage T85B 120,000

L

9 LNG to tanker filling 1318.7

L

10 Vapour return line 18.3

V

11 MRG return from Cold Box to Comp 81.0

V

12 MRG vapour to Cold box 163.7

V

13 MRG liquid to Cold box 505.3

L

14 Regen Gas Return 32.8

V

15 Dryer Unit Regeneration 60.2

V

16 LNG Tanker Loading 1318.7

L

17 Cold Box 773.1

L

Table 10 Isolatable Inventories Summary



6.2 Software Used

The following software were used for hazard consequence analysis.

Table 11 Hazard Consequence Software used in the Study

No. Hazardous Consequence Software and Model Used

1 LPG Release and dispersion DNV PHAST 6.51 – Release Model

2 Jet Fire DNV PHAST 6.51 – Jet Fire Model

3 Vapour Cloud Explosion DNV PHAST 6.51 – TNO Multi-energy model

4 Pool Fire DNV PHAST 6.51 – Pool Fire Model

6.3 LNG Release Scenarios

A set of representative releases was developed that are considered most appropriate to an LNG installation as follows:

• flange releases are equivalent to a 9 mm diameter hole;

• releases from glands, pump seals or valve bodies are equivalent to a 9 mm diameter hole;

• failures of instrument connections on pipework are equivalent to a 20 mm diameter hole;

• Major failures of pipework/ equipment equivalent to 50 mm hole; and

• Full-bore failure equivalent largest nozzle size or a large small bore rupture (eg. 80mm for LNG storage).

In most cases, the leak quantity depends on the estimated release rate and the time taken to isolate the leak (e.g. by ESD activation), plus the trapped inventory between the shutdown valves.

The following representative LNG (liquid) release scenarios, in Table 12 were selected for the identified MAEs and isolatable sections:

Scenario ID MAE Description

MAE6_9mm 9mm release of LNG from equipment and piping to LNG Storage

MAE6_20mm 20mm release of LNG from equipment and piping to LNG Storage

MAE6_80mm

6

80mm release of LNG from equipment and piping to LNG Storage

MAE7_9mm 9mm release of LNG (liquid) from Storage Vessel T85A

MAE7_80mm

7

80mm release of LNG (liquid) from Storage Vessel T85A

MAE8_9mm 9mm release of LNG (liquid) from Storage Vessel T85B

MAE8_80mm

8

80mm release of LNG (liquid) from Storage Vessel T85B

MAE9_9mm 9 9mm release of LNG in tanker filling transfer line




MAE9_80mm 80mm release of LNG in tanker filling transfer line

MAE16_9mm 9mm release of LNG during tanker Loading

MAE16_80mm

16

80mm release of LNG during tanker Loading

MAE17_9mm 9mm release of LNG from Cold Box

MAE17_20mm 20mm release of LNG from Cold Box

MAE17_80mm

17

80mm release of LNG from Cold Box

Table 12 Representative LNG (Liquid) Release Scenarios

Similarly, the following representative NG or MRG (vapour) release scenarios were selected for the identified MAEs and isolatable sections:


MAE1_9mm 9mm release of HP NG from Site boundary to Letdown Skid

MAE1_20mm 20mm release of HP NG from Site boundary to Letdown Skid

MAE1_50mm

1

50mm release of HP NG from Site boundary to Letdown Skid

MAE2_9mm 9mm release of HP NG at the Letdown Skid

MAE2_20mm 20mm release of HP NG at the Letdown Skid

MAE2_50mm

2

50mm release of HP NG at the Letdown Skid

MAE3_9mm 9mm release of NG from the Amine Plant equipment and piping

MAE3_20mm 20mm release of NG from the Amine Plant equipment and piping

MAE3_50mm

3

50mm release of NG from the Amine Plant equipment and piping

MAE4_9mm 9mm release of NG from the Dryer Unit equipment and piping

MAE4_20mm 20mm release of NG from the Dryer Unit equipment and piping

MAE4_50mm

4

50mm release of NG from the Dryer Unit equipment and piping

MAE5_9mm 9mm elease of NG from the feed to Cold Box

MAE5_20mm 20mm elease of NG from the feed to Cold Box

MAE5_50mm

5

50mm elease of NG from the feed to Cold Box

MAE10_9mm 9mm release of NG from tanker loading vapour return line

MAE10_20mm 20mm release of NG from tanker loading vapour return line

MAE10_50mm

10

50mm release of NG from tanker loading vapour return line

MAE11_9mm 11 9mm release of MRG return from Cold Box to Compressor equipment and piping




MAE11_20mm 20mm release of MRG return from Cold Box to Compressor equipment and piping

NAE11_100mm 100mm release of MRG return from Cold Box to Compressor equipment and piping

MAE12_9mm 9mm release of MRG (vapour) in equipment and piping to Cold box

MAE12_20mm 20mm release of MRG (vapour) in equipment and piping to Cold box

MAE12_100mm

12

100mm release of MRG (vapour) in equipment and piping to Cold box

MAE13_9mm 9mm release of MRG (liquid) in equipment and piping to Cold box

MAE13_20mm 20mm release of MRG (liquid) in equipment and piping to Cold box

MAE13_100mm

13

100mm release of MRG (liquid) in equipment and piping to Cold box

MAE14_9mm 9mm release of NG in Regeneration Gas Return equipment and piping

MAE14_20mm 20mm release of NG in Regeneration Gas Return equipment and piping

MAE14_50mm

14

50mm release of NG in Regeneration Gas Return equipment and piping

MAE15_9mm 9mm release of NG in Dryer Unit Regeneration

MAE15_20mm 9mm release of NG in Dryer Unit Regeneration

MAE15_50mm

15

9mm release of NG in Dryer Unit Regeneration

Table 13 Representative LNG (Vapour) Release Scenarios

Once the representative release scenarios are defined, the release modelling was undertaken using the PHAST software. The initial output of this modelling is an estimate of the rate of release of LNG (liquid or vapour) from the containment system (pipework, tank, etc.).

To determine the rate of release, the PHAST software also requires inputs of the physical and chemical properties of the released material, and other source terms such as the storage or operating conditions.

The physical and thermodynamic properties of released material (e.g. molecular weight, phase, boiling point, heat of vaporization, etc.) determine how the chemical behaves at the point of release. For example, the liquid may form a pool or it may immediately flash to vapour. In this case, the material was modelled as pure methane and the default physical and thermodynamic property data in PHAST was adopted.



6.3.1 Rate of Release

The holes sizes and operating pressures used to determine the release rate are tabulated in Appendix C. The release rates estimated for each of the representative release scenario are also tabulated in Appendix C.

6.3.2 Duration of Release

The duration of release is a function of the release rate, available inventory and time for intervention to occur (e.g. activation of the ESD system).

The ESD may be activated automatically (gas or fire detection) or by LNG facility personnel. If activated automatically, it is assumed that isolation would occur within 1 minute from activation. If manual activation is necessary, it is assumed that isolation would be achieved within 10 minutes.

The ESD system is not applicable for a direct release from a storage tank (MAE 7 and 8). In this case, the release duration is a function of the release rate and available inventory.

6.3.3 General Gas Dispersion

PHAST models gas dispersion using the unified dispersion model (UDM). The UDM can model the dispersion of ground-level or elevated un-pressurised or pressurised releases and it allows for continuous, instantaneous, constant finite-duration, and general time-varying release cases. It also includes a unified model for jet, heavy and passive dispersion including possible droplet rainout and pool spreading/evaporation on land or water.

All of the dispersion calculations for the QRA were undertaken using the PHAST UDM. For each representative release scenario:

• The NG and MRG (vapour) is assumed to be released horizontally at 1 m above ground level (This is the minimum release height permitted in the PHAST software).

• The LNG (liquid) is assumed to be released at a 45 degree angle at 1 m above ground level.

• The dispersion analysis was undertaken using representative meteorological conditions (Refer to Section 2.2) and average ambient air and water conditions for the Westbury area.

• The dispersion analysis was undertaken using a surface roughness value of 0.1. This value is typical for relatively flat open areas, such as those surrounding the site.

6.3.4 Dispersion of Vaporized LNG

Due to its low temperature, a release of LNG onto land results in rapid vaporisation, which produces a plume of cold dense methane gas. This gas plume is often visible as a white cloud (or fog) due to the presence of condensed water vapour from the atmosphere.

Initially, the gas plume remains near ground level because the cold methane is denser than the surrounding air. Over time, as the gas warms up and mixes with air (which is assisted by the wind), the gas concentration at ground level decreases. At ambient temperatures, methane gas is less dense than air. Therefore, as it warms the gas cloud will eventually become buoyant and will rise into the atmosphere.

Due to the rapid evaporation of LNG, particularity over large surface areas, no pool fires were considered for releases that are not contained within the walls of the storage and tanker loading bay



are. The gas cloud generated creates a dispersion that is a combination of both the pool evaporation and direct flashing from the release point.

For all releases of LNG contained within the walls there are two possible simultaneous outcomes i) flashing within the storage or loading bay areas ii) evaporation of liquid containment in the containment pit.

6.4 LNG Fires

6.4.1 Jet Fire

The heat radiated from a jet fire is a function of the radiant heat flux of the flame (i.e. kW per m2 of flame surface) and the dimensions of the flame. In PHAST, the flame envelope for a jet fire is modelled as a truncated cone.

The calculated distances to a heat radiation flux of 22.5 kW/m2 are tabulated in Appendix D for each of the representative LNG release scenarios. These distances range from approximately 15 to 70 m for 50 mm and larger representative holes. Within the QRA model, 6 and 12.5 kW/m2 heat radiation fluxes have also been included for 10 and 50% probability of fatality respectively.

6.4.2 Pool Fire

The heat radiated from a fire on a pool of LNG is a function of the radiant heat flux of the flame (i.e. kW per m2 of flame surface) and the dimensions of the flame. If a small pool of LNG is ignited on land, then a non-smoky luminous flame will be produced and the surface emissive power is relatively high.

As the diameter of the pool increases, the surface emissive flux of the flame will increase (due to the increased evaporation rate and rate of combustion). However, the surface emissive flux of the flame does not increase indefinitely. A limiting value of approximately 220 kW/m2 is typical for LNG due to the increased formation of soot (which acts as a heat sink) as the pool diameter increases and incomplete combustion becomes more dominant.

In PHAST, the flame envelope for a pool fire is modelled as a cylinder, tilted in the direction of the wind. Due to the containment arrangement only poolfires within the containment pit area have been considered as all other unconfined pools flash rapidly forming vapour clouds.

The calculated distances to a heat radiation flux of 22.5 kW/m2 are tabulated in Appendix D for each of the representative LNG release scenarios. These distances range from approximately 9 to 17 m for 80 mm representative hole size scenarios for an uncontained pool. A pool fire in the containment pit will result in a fatal heat flux at 6m Within the QRA model, 6 and 12.5 kW/m2 heat radiation flux have also been included for 10 and 50% probability of fatality respectively.

6.4.3 Flash Fire

The extent of a flash fire is determined by the distance to the lower flammability limit (LFL) concentration in air (i.e. c. 5% (v/v) for methane). The maximum distance to the LFL concentration was calculated using PHAST as described in Section 6.3.3.

The calculated downwind distances to the LFL concentration are tabulated in Appendix D for each of the representative LNG release scenarios and each of the representative wind stability class – wind speed conditions.



6.5 Vapour Cloud Explosion

Explosion overpressures from VCEs were calculated using the TNO correlation model (CCPS 1989). It is generally accepted that some confinement is required to cause a VCE. Based on the level of confinement in the PPU covered area a curve number of 5 was used with a fill volume of 30%. Due to the lack of confinement the maximum calculated overpressure that can be produced from a curve number 5 TNO model is 20kPa. The impairment criteria of 35kPa, for 50% fatality, was not reached.

Details of explosion overpressure distances for the various release rates are listed in Appendix D.

6.6 Summary of Consequence Analysis Results

A summary of the consequence analysis results for each representative release scenario is provided in Appendix D.



7 Frequency Analysis

7.1 General

The likelihood of each representative release scenario was estimated using:

• Generic historical frequency data – The base failure data (selected from various sources) used for the QRA is listed in Appendix E.

• Parts count data (Refer to Appendix F) – This includes pipe lengths, number of flanges and valve etc, for the Westbury facility. The number of tanker loading operations (although not strictly a ‘parts count’) is also relevant as this was used to determine the likelihood (per year) where the base failure rate data is reported per operation.

The estimated frequency (per year) of each representative release scenario is reported in Appendix G.

The likelihood of each potentially hazardous outcome (i.e. jet fire, pool fire, etc.) was then estimated using event tree analysis (Refer to Section 7.4) and representative ignition probabilities (Refer to Section 7.5 and Appendix H).

7.2 Base Failure Rate Data

The base failure frequency data used for the QRA is listed in Appendix E. This data covers both stainless steel and carbon steel piping and equipment and is based on whether the equipment is in cryogenic service. This data includes:

• The likelihood (per item per year) of leaks from flanges, valves, and instrument piping

• The likelihood (per m per year) of release from piping

7.3 Hole Size Distribution

7.3.1 Pipework

The Westbury facility consists of both carbon steel and stainless steel pipework depending on whether being used for NG, MRG or LNG service. For pipework, the appropriate (based on materials of construction) base failure (leak) rate data is applicable for all (non-trivial) hole sizes. Therefore, the following hole size distribution was assumed.

Representative Hole Diameter (mm) 9 20 50 Full Bore

Probability 0.82 0.09 0.08 0.01

Table 14 Hole Size Distribution for Pipework

A full bore rupture of pipework, for pipework larger than 100 mm, has been modelled based on the largest nozzle size or an equivalently sized small bore rupture (relative to the pipe diameter). Historically full bore ruptures of pipework have a very low likelihood driven predominantly by the failure modes required for the scenario to occur (guillotine of pipework).



7.4 Event Tree Analysis

The likelihood of each potentially hazardous outcome (i.e. jet fire, pool fire, etc.) was estimated using event tree analysis.

Each branch in the event tree was assigned a probability to determine the probability of a specific outcome. The total probability for each branch must add up to 1.0 (e.g. if the probability of early ignition = 0.1, then the probability that there is not early ignition = 1.0 – 0.1 = 0.9).

The outcome probability is the product of each probability for each branch leading to that event. Therefore, this was multiplied by the likelihood (per year) of the representative release scenario to determine the likelihood (per year) of each potentially hazardous outcome.

The two principal factors that dictate the potentially hazardous outcome/s for a release are:

• Whether there is early or delayed ignition; and

• The time taken for detection and shutdown to occur.

The following is an example of event tree that was used for the QRA

Figure 4 Example Event Tree

7.5 Ignition Probability

Early ignition of a release of LNG is more likely to result in a pool or jet fire than a flash fire, whereas delayed ignition is more likely to result in a flash fire which may flash back to a pool or jet fire. For the QRA, all early ignition events were modelled as pool or jet fires and all delayed ignition events were modelled as flash fire events.

Ignition probabilities may be site specific. For example, a release of LNG may have a relatively high ignition probability if strong ignition sources such as naked flames from open flares or gas fired boilers are nearby. At the Westbury facility, there are no obvious strong ignition sources and numerous



controls are in place to control other ignition sources. Therefore, the following generic historical ignition probability data was used:

Early Ignition Probability Delayed Ignition Probability Gas/Liquid Release Rate or

Evaporation Rate Gas Release Liquid Release Gas Release Liquid Release

< 1 kg/s 0.02 0.02 0.01 0.01

1 – 50 kg/s 0.04 0.04 0.07 0.07

> 50 kg/s 0.09 0.09 0.3 0.3

Table 15 Ignition Probability

7.6 Probability of Explosion Given Ignition

The probability of a vapour cloud explosion, given that ignition occurs, was taken from the data provided by Cox et al. (1990) and is considered to be an industry accepted generic value.

An explosion or a flash fire may occur if the released gas ignites. For the QRA, 7% of all delayed ignitions were modelled as vapour cloud explosions and 93% of all delayed ignitions were modelled as flash fires.

7.7 Detection & Shutdown

Based on full coverage of all process, storage and tanker loading areas by fire and gas detection for the Westbury site the following probabilities have been postulated:

• Probability of successful detection of gas release 0.9

• Probability of successful activation and closure of ESDV 0.98

7.8 LNG Wall Impingement

Releases of LNG within the storage and tanker loading areas have the potential to be deflected by a number of walls provided to contain the release. The probability of a release being contained has been defined as 0.33.



8 Risk Criteria

8.1 Individual Fatality Risk

The individual fatality risk imposed by a proposed industrial activity should be low relative to the background risk. This forms the basis for the following individual fatality risk criteria adopted by DOP in New South Wales.

Land Use Risk Criterion

[per million per year]

Hospitals, schools, child care facilities and old age housing developments 0.5

Residential developments and places of continuous occupancy, such as hotels and tourist resorts

1

Commercial developments, including offices, retail centres, warehouses with showrooms, restaurants and entertainment centres

5

Sporting complexes and active open space areas 10

Industrial sites 50 *

* HIPAP 4 does allow for some flexibility in the interpretation of this criterion. For example, ‘where an industrial site involves only the occasional presence of people, such as in the case of a tank farm, a higher level of risk may be acceptable’.

8.2 Injury Risk

In HIPAP 4, injury risk criteria are presented for exposure to toxic gas/vapour/smoke, heat radiation and explosion overpressure.

8.2.1 Acute Toxic Exposure: Serious Injury

The first acute toxic exposure risk criterion is concerned with serious injury, as follows:

Toxic concentrations in residential areas should not exceed a level which would be seriously injurious to sensitive members of the community following a relatively short period of exposure at a maximum frequency of 10 in a million per year. This is not applicable to this facility

8.2.2 Acute Toxic Exposure: Irritation or Other Physiological Response

The second acute toxic exposure risk criterion is concerned with lower concentration effects that may result in an acute physiological response (e.g. irritation) rather than serious injury. This risk criterion is as follows:

Toxic concentrations in residential areas should not cause irritation to eyes or throat, coughing or other acute physiological responses in sensitive members of the community over a maximum frequency of 50 in a million per year. This is not applicable to this facility

8.2.3 Heat Radiation or Explosion Overpressure

The risk of heat radiation exceeding 4.7 kW/m2 or explosion overpressure exceeding 7 kPa should not exceed fifty chances in a million (50 x 10-6) per year at residential areas.



8.3 Risk of Property Damage and Accident Propagation

Heat radiation exceeding 23 kW/m2 may cause unprotected steel to suffer thermal stress that may cause structural damage and an explosion overpressure of 14 kPa can cause damage to piping and low-pressure equipment. The risk of heat radiation exceeding 23 kW/m2 or explosion overpressure exceeding 14 kPa should not exceed 50 in a million (50 x 10-6) per year at the boundary to neighbouring industrial facilities.



9 Risk Assessment

In this section, the results of the analysis are assessed against the criteria presented in Hazardous Industry Planning Advisory Paper No. 4. As the surrounding land is zoned “Industrial” with commercial developments, offices and warehouses, the risk contours have been limited to 5 x 10-6 pa in this section. The full set of risk contours, based on HIPAP No. 4 criteria, can be found in Appendix I.

9.1 Individual Fatality Risk

The cumulative individual fatality risk results for the proposed Westbury LNG facility are presented in Figure 5.

Figure 5 Westbury Site Individual Risk Contour

The 50 x 10-6 p.a. (or 50 chances per million per year) contour, which is applicable for industrial uses, is not reached and therefore is not exceeded off-site. The 5 x 10-6 p.a. contour, the criteria for commercial developments etc, is contained within the site boundary. At the site boundary with Tasmanian Alkaloids, the risk is 0.5 x 10-6 p.a. (or 0.5 chances per million per year), as shown in Appendix I, which is the risk level for hospitals, schools and aged care facilities

BOC LNG

--- 10 pmpy --- 5 pmpy

Tasmanian Alkaloids



9.2 Injury Risk

The cumulative injury risk results for the proposed Westbury LNG facility are presented in Figure 6.

The risk of heat radiation exceeding 4.7 kW/m2 or explosion overpressure exceeding 7 kPa at the site boundary with Tasmanian Alkaloids is 0.5 x 10-6 p.a. (or 0.5 chances per million per year). This is 100 times less than that the risk criterion for a residential area. The injury criterion of 50 x 10-6 p.a was not reached on site.

BOC LNG

--- 10 pmpy --- 5 pmpy

Tasmanian Alkaloids

Figure 6 Westbury Site Injury Risk Contour



9.3 Property Risk

The cumulative property damage risk results for the proposed Westbury LNG facility are presented in Figure 7.

The risk of heat radiation exceeding 23 kW/m2 or explosion overpressure exceeding 14 kPa at the site boundary is less than 5 x 10-6 p.a. (or 5 chances per million per year), which is 10 time less than the risk criterion for neighbouring industrial facilities. The property damage risk criterion of 50 x 10-6 p.a was not reached on site.

Figure 7 Westbury Site Property Damage Risk Contour

--- 10 pmpy --- 5 pmpy

BOC LNG

Tasmanian Alkaloids



10 References

1 NFPA 59A – Standard for the Production, Storage, and handling of Liquefied natural Gas (LNG), National Fire Protection Association, Quincy, MA, 2006.

2 British Standard European Norm BS EN 1473 – Installation and equipment for liquefied natural gas – Design of onshore installations, BSI, 1997.

3 1NSW Department of Planning (1990): “Hazardous Industry Planning Advisory paper No.1 – Industry Emergency Planning Guidelines”, Sydney, Australia.

4 IChemE 1992, Nomenclature for Hazard and Risk Assessment in the Process Industries, Institution of Chemical Engineers, Rugby, UK.

5 NSW Department of Planning (1996): Hazardous Industry Planning Advisory Paper No. 6 - Guidelines for Hazard Analysis

6 NSW Department of Planning (1990): Hazardous Industry Planning Advisory Paper No. 4 - Risk Criteria for Land Use Planning

7 Cameron, I. and Raman, R. (2005): Process Systems Risk Management, Elsevier Academic Press.

8 Cox, A.W., Ang, M.L., and F.P. Lees, 1990, Classification of Hazardous Locations, IChemE, Rugby, UK.

9 Balasubramanian, S.G. and Louvar, J.F. 2002, ‘Study of major accidents and lessons learned’, Process Safety Progress, vol. 21, no. 3, September, pp. 237- 244

10 OREDA, 2002, Offshore Reliability Data Handbook, Prepared by SINTEF Industrial Management, Distributed by Det Norske Veritas, Hovik, Norway.

11 Lees, F.P., “Loss Prevention in the Process Industries”, Vol.2, Edition 2, Butterworths-Heinemann, Oxford, 1996.

12 HSE, Hazardous Installation Directorate, SPC/TECH/OSD/24, 2004.

13 TNO, VROM, Guidelines for Quantitative Risk Assessment, CPR18E, 3rd Edition.

14 CCPS, 1989, Guidelines for Chemical Process Quantitative Risk Analysis.

15 CCPS, 2003, Guidelines for Investigating Chemical Process Incidents.

16 Sandia National Laboratories, Guidance on Risk Analysis and Safety Implica ions of a Large Liquefied Natural Gas (LNG) Spill Over Water, 2004.

t




Appendices




A Hazard Identification (HAZID) study was undertaken for the LNG PLANT. The study required the following inputs:

The first step in a Quantitative Risk Analysis (QRA) is the identification of hazardous scenarios. This step is carried out using established hazard identification techniques including literature review, consultations and workshops with stakeholders. The workshop participants are listed in Table 16

Table 17 records the following: Table 17 shows the Hazard Identification (HAZID) results for the BOC Westbury LNG facility.

The focus was on the identification of site specific hazards, covering loss of containment from process areas from failures of pumps, compressors, heat exchangers, vessels and pipework.

The focus was on the identification of all possible hazardous scenarios with no pre-judgement of their contribution to the QRA.

• Consultation with a multi-disciplinary group covering; design, operations, engineering and safety.

• Stream data for compositions of the various streams to identify combustion characteristics

• The Westbury Site Layout

• Actions for further assessment where appropriate.

• The safeguards (prevention, detection, and mitigation);

• The causes of the incident;

• The consequences of the incident;

• The hazardous incident;

Table 16: HAZID Attendees

Attendee Organisation

Kevin Peakman BOC

Simon Smith BOC

Alistair Hewson BOC

Colin McDonald BOC

Ross Hargreaves BOC

Andrew Wesley BOC

David Wilson BOC

Jason Garrett Process Control Solutions

Paul Nield GLP

Marcus Jones GLP

Duncan Whitford GLP

John Paul Maiorana (Facilitator) LR


Table 17: HAZID Table

Safeguards No

Incidents/ Hazardous Events

Potential Consequence/ Effects

Threats/ Causes

Prevention Detection Mitigation

Comments

Unit – Generic

Natural GasRelease (generic)

Jetfire, VCE, asphyxiation, flash fire,

Gasket, valve gland leaks, small bore fitting failure, piping/ equipment failures, mechanical impact, drain/bleed valve left open, corrosion, operator error,

- material selection - preventative maintenance, - JSA, PTW - Inspection and Test Plan (ITP’s) - Maintenance procedures - Code Compliance - Operating procedures - Training -physical barriers (bollards) - cathodic protection -process alarms and trips - overpressure protection

-gas detectors (LEL 10-20%), -IR (flame detection) - operator surveillance (smell and sound) - process deviation alarms

- earthing - HAC - Flare system - ESD - Fire monitors - minimal manning - industrial zoning

1. Potential for deluge system in covered area for NG processing



Safeguards No



Threats/ Causes


Comments

LNG (Generic) Poolfire, VCE, jet fire, flashfire, asphyxiation, cold burns, fracture of other material,

Gasket, valve gland leaks, small bore fitting failure, piping/ equipment failures, mechanical impact, drain/bleed valve left open, corrosion, embrittlement, cold fatigue fracture, operator error

- material selection - preventative maintenance, - JSA, PTW - Inspection and Test Plan (ITP’s) - Maintenance procedures - Code Compliance - Operating procedures - Training -physical barriers (bollards) -process alarms and trips - overpressure protection

-gas detectors (LEL 10-20%), -IR (flame detection) - operator surveillance (sight) - process deviation alarms

- containment pit - earthing - HAC - Flare system - ESD - minimal manning - industrial zoning - physical barriers - safety showers - PPE

Note: 1. flange guards, 2. Fusible links, 3. Establish the need for barriers.



Safeguards No



Threats/ Causes


Comments

MixedRefrigerant release (Generic)

Poolfire, VCE, jet fire, flashfire, asphyxiation, cold burns, fracture of other material, toxic vapour and toxic liquid

Gasket, valve gland leaks, small bore fitting failure, piping/ equipment failures, mechanical impact, drain/bleed valve left open, corrosion, embrittlement, cold fatigue fracture, operator error, Mechanical seals (pump and compressor), -contamination with air (post maintenance)



- earthing - HAC - Flare system - ESD - minimal manning - industrial zoning - physical barriers - safety showers - PPE - bunded

Unit - Gas Let down



Safeguards No



Threats/ Causes


Comments

Natural GasRelease from gas let down system






Natural gasingress into CW

-explosive atmosphere at cooling tower - over pressure CW pipework

- Tube failure from HE 21 - maintenance error

- design codes - cooling water treatment -materials selection -maintenance procedures

-sight glass - operating surveillance

- EXn motor on CT fan - PSV on CW pipework venting to flare KO pot

- Consider a standpipe on the CW tower.



Safeguards No



Threats/ Causes


Comments

Natural gas intohot oil

- overpressure oil system

- Tube failure from HE 20

- design codes -materials selection -maintenance procedures

- operating surveillance - sight glass - PAH after heater

- PSV on hot oil return line venting to flare KO pot - PSV on oil tank to grade -PSV on oil heater to grade

- Consider venting to safe location (i.e. flare)

High Noiselevels

- non compliance with regulations (250m 35dB, Ops 85dB)

- pressure reduction valve

none Noise monitoring PPE (ops) - pipe insulation -valve trim - silencer

Over pressurisefacility

Over pressurise pipework and vessels (100bar NG supply)

PCV-20-4 fails open -valve maintenance -material selection

- PAHH 20-4 - PSV-20-2 vents full flow to flare.

Unit - PPU



Safeguards No



Threats/ Causes


Comments

Natural GasRelease from

- Jetfire - VCE - asphyxiation - flash fire - Escalation to adjoining process equipment


- material selection - preventative maintenance, - JSA, PTW - Inspection and Test Plan (ITP’s) - Maintenance procedures - Code Compliance - Operating procedures - Training -physical barriers (bollards) - cathodic protection -process alarms and trips - overpressure protection - ESD system - size of inventory



Over pressurethe stripper

- over pressurise the stripper

-loss of liquid seal (bottom of absorber)

- level control LIC-21-02 with LSLL 21-6 to trip upstream SDV. -PCV 24-1

-LAL on absorber

-PSV 24-1 -PSV 22-1

Release ofamine

-Personal Injury -Environmental

Pump seal failure, drain valve leaks, flange leaks, screwed fitting leaks, HX seal failure, gasket leaks

-material selection -maintenance -ops and maint procedures

-operator surveillance -LAL 22-5,

-PPE -Bunded -safety showers -man down system

Emergency Response Plan



Safeguards No



Threats/ Causes


Comments

Confinedexplosion in PPU

VCE NG release in the area Note: to be modelled

Over pressuringof PPU system

-vessel or pipework rupture

- isolation of HP safety valve header.

-limit switch interlocked to ESD

- alarm on limit switch Consider pressure measurement on HP safety valve header

Unit – Cold Box

Natural GasRelease








Safeguards No



Threats/ Causes


Comments

LNG Poolfire, VCE, jet fire, flashfire, asphyxiation, cold burns, fracture of other material,

Gasket, valve gland leaks, small bore fitting failure, piping/ equipment failures, mechanical impact, drain/bleed valve left open, corrosion, embrittlement, cold fatigue fracture, operator error



- containment pit - earthing - HAC - Flare system - ESD - minimal manning - industrial zoning - physical barriers - safety showers - PPE

NG/LG releaseinto cold box

- flammable atmosphere within cold box - over pressuring the cold box - brittle fracture of the cold box

Splitting of the internal pipework of the cold box

- design standards - operating procedures

- visual inspection -N2 purging - Over pressure relief

Consider a LEL detector on the cold box vent

Erosion of coldbox internals

- flammable atmosphere within cold box - over pressuring the cold box - brittle fracture of the cold box

- internal leak within the cold box creating abrasive flow

- fully welded - visual inspection -N2 purging - Over pressure relief

To be confirmed



Safeguards No



Threats/ Causes


Comments

to MRG releaseinto cold box

- flammable atmosphere within cold box - over pressuring the cold box - brittle fracture of the cold box - toxic exposure

- internal leak within the cold box creating abrasive flow

- fully welded - visual inspection -N2 purging - Over pressure relief

To be confirmed

MRG release - Compressor casing rupture - leaking shaft seal

- liquid carry over into compressor (iso pentane)

- demister pad in SP 36 - LAHH on SP 36

-high vibration trip

MRG releaseinside compressor enclosure -

- Flammable mixture created within enclosure with explosion potential

MRG released while enclosure fans not running

- Flow sensors interlocked to trip compressor on loss of flow -LEL detector

- flow switch

- process trip -isolation of power to

- Air fan – zone 1 - All other equipment zone 2

Unit – LNG Storage and tanker loading

Rollover withinstorage vessel

- high rates of vapour generation in excess of PSV capacity

- variable density of material during storage tank filling

- continuous production and feed into tank with a high turnover of inventory - feed stoke material specification constant - VIE geometry



Safeguards No



Threats/ Causes


Comments

Boil-off of LNG in storage

-rapid boiling of LNG -pressure rise in storage vessel

-loss of vacuum - vacuum checks - PAH - PCV 850-10 to flare

Vessel rupture Not consideredcredible

Vessel leak - embrittlement fractures on external vessel and structure

- loss of vacuum and pressure increase - manufacturing fault - Fracture of weld - Heating cooling cycle material fatigue

-cold shock the vessel using liquid n2 prior to charging with LNG - codes for pressure vessel

- Vacuum relief valve lifts - cold patch

- increased relief to flare from inner vessel. - liquid leak flow to containment pit. - management of inventory into separate tank or road tanker.

Tow away - hose/ pipeworkpulled out from facility

- driver drives off while still connected to LNG lines

- LNG release - poolfire -jet fire - Tyres burst - Cold burns to driver

- brake interlocks - driver procedures (dedicated and trained drivers) - -

- F+G system - low pressure on pump discharge - visual damage

- break away coupling - instrument gas from plant used for tanker valve control and pump discharge valve control - liquid drains to the containment pit



Safeguards No



Threats/ Causes


Comments

Hose release - LNG release - poolfire -jet fire - Tyres burst - Cold burns to driver

Hose fails - condition monitoring of the hose (pre use) - material selection - annual hose test.

- F+G system with ESD - visual

- containment pit

Consider “dead man” switch

Hose couplingleak

- LNG release - poolfire -jet fire - Tyres burst - Cold burns to driver

Hose fails - condition monitoring of the hose (pre use) - material selection - annual hose test.

- F+G system with ESD - visual

- containment pit

Tanker overfill - LNG release through tanker safety valves (not designed for liquid) - tanker rupture

- weigh scale fails - automatic filling valve stuck open

- preventative maintenance for weigh scale - control system diagnostics

- F+G with ESD. -visual - liquid level gauge on tanker

- drains to containment pit

- consider draining back to the dump pot. - consider top fill to be at trycock level.

Unit – Flare System

Liquid carry over to the flare

- embrittlement of flare header

- - high level trip on dump pot -TALL on line to the flare - suitably designed dump pot

- visual (frosting) -

- - consider avapouriser on the dump pot

Loss of pilot flame on flare

- potential release of gas to atmosphere

- nitrogen slug - Detector failure -CO2 slug

- backup pilot gas

- LEL detectors on the site

- Flame out detection with ESD



e: AUS0073607 : 2

Safeguards No



Threats/ Causes


Comments

Unit - General

- HAC across the site - control of ignition sources - Restricted access - UPS backup - SPOC 24 control - loan worker requirement (man down alarm)

-site securityneeded - ESD contacts local ER -deluge system

Enclosures(MCC, Control room, analyser hut)

- Fire and smokedetection. - Split system on recycle (AC) -LEL and O2 monitoring (Analyser Hut)

ReferencIssue

Loss ofcontainment of hot oil. (Enviro)

- bunded

Lightning strike - lightning rods

Earthing - earthing mat -pipework continuity checks

ESD (pushbutton) locations

- local-remote



B.1 Data Source

The following source of meteorological data was used in the study;

Wind weather data (mean cloud cover, temperature, wind speeds) collected by the Bureau of Meteorology at the Powranna weather station from 1991 to 2008. This raw data was rationalised in a form appropriate for vapour dispersion calculations.

Powranna weather station was selected as being closest to the subject site.


The dispersion of gas releases is strongly dependent upon the prevailing wind speed and atmospheric stability. Information regarding wind weather for input into the dispersion model was extracted from the meteorological data.

Wind speed data and wind rose data were combined to obtain annual averages. Pasquil stability classes of A, B, C, D, E and F have been evaluated using an estimation of lapse rates, from mean cloud cover and maximum/ minimum temperatures. The wind rose was divided into each stability class.

The data has been processed into a rationalised form consisting of six wind speed/stability group classes arranged into sixteen wind direction groups. The arrangement into wind speed/stability group classes followed the criteria set out below in Table 18 and the rationalised wind weather data is shown in Table 19.



Table 18 Criteria for Rationalisation of Meteorological Data

Original Data Allocated Allocated

Stability Group

Wind Speed Group Wind/Stability Group Class

Wind Speed m/s

A & B C & D E & F

All speeds <2m/s 2 - 7m/s > 7m/s < 2m/s > 2m/s

B D D D F E

3.0 1.5 5.0 9.0 1.5 3.0

Table 19 Rationalised Wind Weather Data for Powranna Weather Station

Wind Weather Class Wind Direction (FROM) B3 D1.5 D5 D9 E3 F1.5

Total

N 1.9 3.0 5.6 5.0 3.1 0.9 19.5 NNE 1.0 1.8 3.0 2.5 1.8 0.8 10.9 NE 0.2 0.5 0.4 0.0 0.6 0.7 2.4 ENE 0.2 0.5 0.3 0.0 0.5 0.7 2.2 E 0.1 0.5 0.3 0.0 0.5 0.7 2.1 ESE 0.3 1.0 0.7 0.1 1.0 0.7 3.7 SE 0.4 1.5 1.1 0.2 1.5 0.8 5.3 SSE 0.5 1.4 1.5 0.5 1.5 0.8 6.2 S 0.6 1.4 2.0 0.8 1.5 0.8 7.0 SSW 0.4 0.9 1.2 0.5 1.0 0.7 4.7 SW 0.2 0.4 0.4 0.2 0.5 0.7 2.4 WSW 0.2 0.5 0.4 0.2 0.5 0.7 2.6 W 0.2 0.5 0.5 0.3 0.6 0.7 2.8 WNW 0.6 1.1 1.4 0.7 1.1 0.8 5.6 NW 0.9 1.6 2.3 1.2 1.6 0.8 8.4

Prob

abili

ties

(%)

NNW 1.4 2.3 3.9 3.1 2.4 0.8 13.9 Total 9.3 18.9 25.0 15.2 19.7 12.0 100.0




The following isolatable sections have been carried forward into the QRA

Scenario ID Failure

Scenario

Release Pressure (barg)

Hole Size

(mm)

Release Rate (kg/s)

Consequence/s Modelled

MAE1_9mm 9 9.62e-1 JTF, FFR

MAE1_20mm 20 4.75e+0 JTF, FFR

MAE1_50mm

Leak 98.99

50 2.97e+1 JTF, FFR

MAE2_9mm 9 9.62e-1 JTF, FFR, VCE

MAE2_20mm 20 4.75e+0 JTF, FFR, VCE

MAE2_50mm

Leak 98.99

50 2.97e+1 JTF, FFR, VCE



MAE3_50mm

Leak 21.38




MAE4_50mm

Leak 21.38




MAE5_50mm

Leak 21.38


MAE6_9mm 9 3.47e-01 PLF, FFR

MAE6_20mm 20 1.71e+01 PLF, FFR

MAE6_80mm

Leak 0.98

80 2.74e+01 PLF, FFR

Reference: AUS0073607 Page 66 Issue: 2


Scenario ID Failure

Scenario


Hole Size

(mm)

Release Rate (kg/s)


MAE7_9mm _contained

9 3.47e-01 PLF, FFR

MAE7_80mm

Leak 1.99

80 2.74e+01 PLF, FFR


MAE8_80mm

Leak 1.99

80 2.74e+01 PLF, FFR


MAE9_80mm

Leak 4.53

80 5.89e+01 PLF, FFR



MAE10_50mm

Leak 21.38

50 6.58e+0 JTF, FFR


MAE11_20mm 20 2.08e-01 JTF, FFR

NAE11_100mm

Leak 2.3

100 5.20e+0 JTF, FFR



MAE12_100mm

Leak 19.4

100 3.13e+01 JTF, FFR


MAE13_20mm

Leak 19.4

20 5.47e+01 JTF, FFR



Scenario ID Failure

Scenario


Hole Size

(mm)

Release Rate (kg/s)


MAE13_100mm 100 1.37e+01 JTF, FFR



MAE14_50mm

Leak 20.38

100 5.18e+02 JTF, FFR, VCE



MAE15_50mm

Leak 20.38



MAE16_80mm

Leak 4.53

80 5.89e+01 PLF, FFR


MAE17_20mm 20 1.71e+01 PLF, FFR

MAE17_80mm

Leak 0.98

80 2.74e+01 PLF, FFR





Table 20: Pool Fire – Distance to 22.5kW/m2

Stability Class – Wind Speed

F1.5 D1.5 D5 D9 B3 E3 Scenario ID

Distance (m) to 22.5 kW/m2

MAE6_9mm - - - - - -

MAE6_20mm 0.33 0.58 0.02 - - -

MAE6_80mm 17.4 17.2 12.1 9.0 14.8 15.3

MAE7_9mm _contained

1.3 1.3 1.1 1.0 1.1 1.1

MAE7_80mm _contained

5.6 5.6 5.6 5.6 5.6 5.6

MAE8_9mm _contained

1.3 1.3 1.1 1.0 1.1 1.1


5.6 5.6 5.6 5.6 5.6 5.6

MAE9_9mm 2.0 1.9 1.7 1.6 1.8 1.8

MAE9_80mm 5.6 5.6 5.6 5.6 5.6 5.6

MAE16_9mm 2.0 1.9 1.7 1.6 1.8 1.8

MAE16_80mm 5.6 5.6 5.6 5.6 5.6 5.6

MAE17_9mm - - - - - -

MAE17_20mm 0.33 0.58 0.02 - - -

MAE17_80mm 17.4 17.2 12.1 9.0 14.8 15.3


Table 21: Jet Fire – Distance to 22.5kW/m2




MAE1_9mm 12.1 12.1 12.6 13.1 13.0 13.0

MAE1_20mm 27.1 27.1 28.9 30.9 27.9 27.9

MAE1_50mm 61.9 61.9 66.7 71.4 64.1 64.1






MAE2_9mm 12.1 12.1 12.6 13.1 12.3 12.3

MAE2_20mm 27.1 27.1 28.9 30.9 27.9 27.9

MAE2_50mm 61.9 61.9 66.7 71.4 64.1 64.1

MAE3_9mm - - - - - -

MAE3_20mm 12.6 12.6 13.1 13.8 12.9 12.9

MAE3_50mm 31.6 31.6 33.9 36.2 32.6 32.6

MAE4_9mm - - - - - -

MAE4_20mm 12.6 12.6 13.1 13.8 12.9 12.9

MAE4_50mm 31.6 31.6 33.9 36.2 32.6 32.6

MAE5_9mm - - - - - -

MAE5_20mm 12.6 12.6 13.1 13.8 12.9 12.9

MAE5_50mm 31.6 31.6 33.9 36.2 32.6 32.6

MAE10_9mm - - - - - -

MAE10_20mm 12.6 12.6 13.1 13.8 12.9 12.9

MAE10_50mm 31.6 31.6 33.9 36.2 32.6 32.6

MAE11_9mm - - - - - -

MAE11_20mm - - - - - -

NAE11_100mm 27.4 27.4 30.5 33.4 28.8 28.8

MAE12_9mm - - - - - -

MAE12_20mm 13.1 13.1 13.6 14.2 13.3 13.3

MAE12_100mm 39.4 39.4 45.1 51.2 41.1 41.1

MAE13_9mm 38.7 38.7 42.9 46.9 40.6 40.6

MAE13_20mm 48.2 48.2 53.4 57.1 49.1 49.1

MAE13_100mm 48.2 48.2 53.4 57.1 49.1 49.1

MAE14_9mm - - - - - -

MAE14_20mm 11.2 11.2 11.7 12.2 11.4 11.4

MAE14_50mm 28.2 28.2 30.2 32.2 29.1 29.1

MAE15_9mm - - - - - -

MAE15_20mm 11.2 11.2 11.7 12.2 11.4 11.4






MAE15_50mm 28.2 28.2 30.2 32.2 29.1 29.1


Table 22: Flash Fire – Distance to LFL


F1.5 D1.5 D5 D9 B3 E3

Maximum Downwind and Crosswind Distance (m) to LFL Concentration Scenario ID

Downwind Downwind Downwind Downwind Downwind Downwind

MAE1_9mm - - - - - -

MAE1_20mm 20.6 19.2 17.2 14.8 17.1 18.9

MAE1_50mm 67.1 63.3 35.2 66.7 61.9 65.4

MAE2_9mm - - - - - -

MAE2_20mm 20.6 19.2 17.2 14.8 17.1 18.9

MAE2_50mm 67.1 63.3 35.2 66.7 61.9 65.4

MAE3_9mm - - - - - -

MAE3_20mm - - - - - -

MAE3_50mm 26.3 24.9 22.6 20.0 22.2 24.0

MAE4_9mm - - - - - -

MAE4_20mm - - - - - -

MAE4_50mm 26.3 24.9 22.6 20.0 22.2 24.0

MAE5_9mm - - - - - -

MAE5_20mm - - - - - -

MAE5_50mm 26.3 24.9 22.6 20.0 22.2 24.0

MAE6_9mm 20.6 12.4 8.2 4.6 10.5 12.3

MAE6_20mm 52.1 52.9 32.2 24.6 35.7 40.5

MAE6_80mm 220.8 185.8 130.9 113.4 125.2 174.7

MAE7_9mm _contained

59.25 14.2 14.1 11.4 12.9 17.1

MAE7_80mm 226.9 212.5 100.5 - 124.4 151.3




F1.5 D1.5 D5 D9 B3 E3



_contained

MAE8_9mm _contained

59.25 14.2 14.1 11.4 12.9 17.1


255.3 64.0 64.9 68.5 50.5 80.6

MAE7_9mm _uncontained

- - - - - -


226.9 212.5 100.5 - 124.4 151.3


- - - - - -


226.9 212.5 100.5 - 124.4 151.3

MAE9_9mm 85.7 20.9 22.1 21.6 18.9 26.2

MAE9_80mm 252.9 120.0 81.3 87.2 70.2 153.0

MAE10_9mm - - - - - -

MAE10_20mm - - - - - -

MAE10_50mm 26.3 24.9 22.6 20.0 22.2 24.0

MAE11_9mm - - - - - -

MAE11_20mm - - - - - -

MAE11_100mm 19.8 18.6 16.1 13.6 16.2 18.0

MAE12_9mm - - - - - -

MAE12_20mm - - - - - -

MAE12_100mm 13.8 10.9 22.5 17.3 15.7 28.1

MAE13_9mm 37.8 35.8 34.1 31.6 33.8 35.8

MAE13_20mm 50.8 65.1 32.4 32.2 41.1 38.2

Mae13_100mm 50.8 65.1 32.4 32.2 41.1 38.2

MAE14_9mm - - - - - -

MAE14_20mm - - - - - -

MAE14_50mm 20.4 19.1 17.3 15.2 17.1 18.9




F1.5 D1.5 D5 D9 B3 E3



MAE15_9mm - - - - - -

MAE15_20mm - - - - - -

MAE15_50mm 20.4 19.1 17.3 15.2 17.1 18.9

MAE16_9mm 85.7 20.9 22.1 21.6 18.9 26.2

MAE16_80mm 252.9 120.0 81.3 87.2 70.2 153.0

MAE17_9mm 20.6 12.4 8.2 4.6 10.5 12.3

MAE17_20mm 52.1 52.9 32.2 24.6 35.7 40.5

MAE17_80mm 220.8 185.8 130.9 113.4 125.2 174.7

D.4 VCE Results

Table 23: VCE – Distance to 14 kPa



Distance (m) to 14 kPa

MAE2_9mm 12.1 12.0 11.9 - 11.9 12.0

MAE2_20mm 55.2 45.0 44.5 44.2 44.6 44.9

MAE2_50mm 125.5 134.3 134.4 143.9 123.4 134.7

MAE3_20mm 12.2 12.1 11.9 - 12.0 12.0

MAE3_50mm 56.6 56.2 55.8 55.2 55.8 56.0

MAE4_20mm 12.2 12.1 11.9 - 12.0 12.0

MAE4_50mm 56.6 56.2 55.8 55.2 55.8 56.0

MAE5_20mm 12.2 12.1 11.9 - 12.0 12.0

MAE5_50mm 56.6 56.2 55.8 55.2 55.8 56.0

MAE14_20mm 12.0 12.0 - - 11.7 11.8-

MAE14_50mm 45.5 35.1 34.7 34.3 34.7 45.3

MAE15_20mm 12.0 12.0 - - 11.7 11.8-

MAE15_50mm 45.5 35.1 34.7 34.3 34.7 45.3

Note: Explosion distance does not reach 35 kPa as the maximum overpressure for curve 5 is 20 kPa.




The LNG industry has been in operation for over 40 years. Most LNG releases have been small and the effects contained wholly within the facility boundary. Further, no failure rate data is available in the public domain for process equipment and pipework in LNG facilities.

In the absence of LNG industry-specific data the following approach was adopted:

• Gather failure rate data for equipment and pipework from generic frequency databases for petrochemical industries available in the public domain.

• Since specific failure modes such as material defects, corrosion etc. are not present in LNG service, assess the contributions of these failure modes from available data and subtract from the petrochemical industry data.

Use the adjusted frequency for likelihood analysis for the study. While the above approach may not fully represent the LNG industry, it provides a ‘cautious best estimate’. Use of petrochemical industry data without eliminating the failure modes absent in LNG service would make the assessment unrealistic.


9 mm Flange Leak

(per flange per yr)

9 mm Valve Leak

(per valve per yr)

20 mm Leak from Instrument Piping

(per section per yr)

1.82E-04 2.00E-04 1.00E-04

Ref: HSE, Hazardous Installation Directorate, SPC/TECH/OSD/24, 2004.

Piping Failure Frequency (per m per year)

D <= 4" 4"< D <= 8” 8" < D <= 12" 12" < D <= 16" D >16"

1.26E-05 2.69E-06 1.92E-06 3.21E-06 1.07E-06

Ref: HSE, Hazardous Installation Directorate, SPC/TECH/OSD/24, 2004.

Equipment Item Equivalent Leak Size Diameter (mm) Leak Frequency (per item-year)

Pump 9 3.00E-03

Reciprocating compressor 9 1.70E-02

9 2.00E-05

20 1.00E-05

50 1.00E-05

Pressure Vessel

catastrophic 2.00E-06



Equipment Item Equivalent Leak Size Diameter (mm) Leak Frequency (per item-year)

20 1.2 x 10-5

50 7 x 10-6

Fin Fan heat exchanger

catastrophic 6 x 10-6


Historical data in the process industries over a 40-year period gave the following split of contributions to failure (Balasubramanian, and Louvar, Ref. 9):

• Corrosion - 19% (petrochemical) to 36% (oil refining)

• Material failures (e.g. gaskets and seals)- 11% (petrochemical) to 13% (oil refining)

• Other - remaining (human error, natural events, seal failures etc.)

From the above it is clear that on average 40% of the failures are caused by corrosion and material defects. Because we can eliminate these two failure modes for LNG we have 60% of the generic frequency that is applicable to LNG industry.

In the absence of LNG industry specific data, the values for pipework in the above table were multiplied by a factor of 0.6 and the results applied to the LNG facility.


ReferencIssue

BOC Westbu

e: AUS0073607 Page 77 : 2

ry LNG: Preliminary Hazard Analysis

Table 24: Parts Count Table

MAE Description

Pipe Diameter / Tank Diameter (mm)

Pipe Length (m)

No of flanges assumed

No of Valves assumed

No of instrument piping assumed

Vessels/Road Tanker**

Pumps H Exch Comp

1 HP NG from Site boundary to LD Skid 50 30 10 7 0

2 HP NG feed to let down skid 100 20 21 7 4 2 3 NG through Amine Plant 80 40 48 14 12 1 4 Dryer Unit 100 10 19 6 3 1 5 NG to Cold Box 100 40 30 15 11 1 2 6 LNG to Storage 100 80 18 6 4 7 LNG Storage T85A 80 40 32 15 4 1 8 LNG Storage T85B 80 40 32 15 4 1 9 LNG to tanker filling 80 30 18 7 2 1 10 Vapour return line 80 80 14 6 1 1

11 MRG return from Cold Box to Comp 350 40 18 5 4 1 1

12 MRG vapour to Cold box 250 30 22 3 4 1 1 1 13 MRG liquid to Cold box 100 30 44 9 3 1 2 1 14 Regen Gas Return 50 50 40 17 3 2 1 15 Dryer Unit Regeneration 100 10 23 6 5 1 16 LNG Tanker Loading** 100 20 24 10 4 1 17 Cold Box 100 40 22 6 3 1 1

ReferencIssue

BOC Westbu

e: AUS0073607 Page 79 : 2

ry LNG: Preliminary Hazard Analysis

Table 25: Release Frequency

MAE Description 9mm (Pipe/ Equip)

20mm (Pipe/ Equip)

50mm (Pipe/ Equip)

Full bore rupture (Pipe/Equip)

9mm for flanges leak

9mm for Valves leak

20mm for instru piping

9mm (Pumps)

9mm (Comp)

9mm (Vessel)

20mm (Vessel)

50mm (Vessel)

FBR (Vessel)

1

HP NG from Site boundary to LD Skid 1.20E-04 3.00E-05 1.50E-05 N/A 3.00E-04 4.90E-03 N/A N/A N/A N/A N/A N/A N/A

2 HP NG feed to let down skid 3.00E-04 3.00E-05 3.00E-06 3.60E-05 6.30E-04 4.90E-03 4.00E-04 N/A N/A 4.00E-05 2.00E-05 2.00E-05 4.00E-06

3 NG through Amine Plant 6.00E-04 6.00E-05 6.00E-06 7.20E-05 1.44E-03 9.80E-03 1.20E-03 3.00E-03 N/A N/A N/A N/A N/A

4 Dryer Unit 1.50E-04 1.50E-05 1.50E-06 1.80E-05 5.70E-04 4.20E-03 3.00E-04 N/A N/A 2.00E-05 1.00E-05 1.00E-05 2.00E-06

5 NG to Cold Box 6.00E-04 6.00E-05 6.00E-06 7.20E-05 9.00E-04 1.05E-02 1.10E-03 N/A N/A 6.00E-05 3.00E-05 3.00E-05 6.00E-06

6 LNG to Storage 8.2E-04 8.2E-05 8.2E-06 9.8E-05 3.28E-03 1.20E-03 4.00E-04 N/A N/A N/A N/A N/A N/A

7 LNG Storage T85A 4.1E-04 4.1E-05 4.1E-06 4.9E-05 5.82E-03 3.00E-03 4.00E-04 N/A N/A 2.00E-05 1.00E-05 1.00E-05 2.00E-06

8 LNG Storage T85B 4.1E-04 4.1E-05 4.1E-06 4.9E-05 5.82E-03 3.00E-03 4.00E-04 N/A N/A 2.00E-05 1.00E-05 1.00E-05 2.00E-06

9 LNG to tanker filling 2.6E-05 2.6E-06 2.6E-07 3.1E-06 2.73E-04 1.17E-04 1.67E-05 3.00E-03 N/A N/A N/A N/A N/A

10 Vapour return line 1.20E-03 1.20E-04 1.20E-05 1.44E-04 4.20E-04 4.20E-03 1.00E-04 3.00E-03 N/A N/A N/A N/A N/A

11

MRG return from Cold Box to Comp 1.0E-04 1.0E-05 1.0E-06 1.3E-05 3.28E-03 1.00E-03 4.00E-04 N/A N/A 4.00E-05 2.00E-05 2.00E-05 4.00E-06

12 MRG vapour to Cold box 4.7E-05 4.7E-06 4.7E-07 5.6E-06 4.00E-03 6.00E-04 4.00E-04 N/A 1.70E-02 4.00E-05 2.00E-05 2.00E-05 4.00E-06

13 MRG liquid to Cold box 3.1E-04 3.1E-05 3.1E-06 3.7E-05 8.01E-03 1.80E-03 3.00E-04 6.00E-03 N/A 4.00E-05 2.00E-05 2.00E-05 4.00E-06

14 Regen Gas Return 2.00E-04 5.00E-05 2.50E-05 N/A 1.20E-03 1.19E-02 3.00E-04 N/A N/A 6.00E-05 3.00E-05 3.00E-05 6.00E-06

15 Dryer Unit Regeneration 1.50E-04 1.50E-05 1.50E-06 1.80E-05 6.90E-04 4.20E-03 5.00E-04 N/A N/A 2.00E-05 1.00E-05 1.00E-05 2.00E-06

16 LNG Tanker Loading** 1.7E-05 1.7E-06 1.7E-07 2.0E-06 3.64E-04 1.67E-04 3.33E-05 N/A N/A 1.67E-06 8.33E-07 8.33E-07 1.67E-07

17 Cold Box 4.1E-04 4.1E-05 4.1E-06 4.9E-05 4.00E-03 1.20E-03 3.00E-04 N/A N/A 4.00E-05 2.00E-05 2.00E-05 4.00E-06



The probabilities used for ignition and fire/or explosion of releases was estimated from a hazardous industry study by Cox et al. (1990). However, the presence of ignition sources at installations surrounding the facility was examined as the distance to lower flammability limit often exceeded the site boundary. For such cases, particularly for large releases, the probability of ignition was based on the probability of wind direction towards the source of ignition. Thus, the ignition probabilities were based on both the release rates as provided by Cox et al., and an assessment of the prevailing wind direction.

The ignition probabilities used are listed in Table 26.

Table 26: Ignition Probabilities

Early Ignition Probability Delayed Ignition Probability Gas/Liquid Release Rate or

Evaporation Rate Gas Release Liquid Release Gas Release Liquid Release

< 1 kg/s 0.02 0.02 0.01 0.01

1 – 50 kg/s 0.04 0.04 0.07 0.07

> 50 kg/s 0.09 0.09 0.3 0.3





--- 10 pmpy --- 5 pmpy --- 1 pmpy --- 0.5 pmpy

BOC LNG

Tasmanian Alkaloids




I.3 Property Damage Risk Contour


BOC LNG

Tasmanian Alkaloids

BOC LNG


Tasmanian Alkaloids




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