Appendix A documents the basis for the QRA of the Stavanger LNG Base Load Plant. The actual Assumption Sheets are presented in Table 19.
Table 19: List of assumption sheets Subject Area Assumption
Sheet No. Assumption Sheet Topic Revision No. / Revi- sion Date Page No. Remarks
HC-1 Main area definitions Rev0 / 2008.05.26
58
HC-2 Release Rates Rev1 /
2008.07.31
59
HC-3 Hydrocarbon Releases Rev1 /
2008.07.31
60
HC-4 Gas Dispersion Rev0 /
2008.05.26
61
HC-5 Gas Fire Modelling Rev0 /
2008.05.26
62
HC-6 Liquid Fire Modelling Rev1 / 2008.07.31
63
HC-7 Vapour Clod Explosion Modelling Rev0 / 2008.05.26 64 HC-8 Non-Process Rev0 / 2008.05.26 65
HC-9 Loading Frequency Rev0 /
2008.05.26
66
HC-10 Ship Transport Acci- dents Rev1 / 2008.07.31 67 Hazard Identification / Consequence Analysis
HC-11 Occupational Risk Rev0 /
2008.05.26
68
FA-1 Inventory Count Rev1 /
2008.06.02
69
FA-2 Frequency Database Rev0 /
2008.05.26
70 Frequency
Analysis
FA-3 Leak Frequency (LNG Storage Tank)
Rev1/ 2008.07.31
71
RA-1 Event Tree
Probabilities
Rev0 / 2008.06.02
72
RA-2 Ignition Sources – Probabilities
Rev0 / 2008.06.02
74
RA-3 Fire and Gas Detection Rev1 / 2008.07.31 76 RA-4 ESD/Blowdown System-Duration Time Rev0 / 2008.06.02 77
RA-5 Vulnerabilities Rev0 /
2008.06.02
79
RA-6 Heat Radiation Mitigation
Rev0 / 2008.06.02
80
RA-7 Active and Passive Fire Protection Rev1 / 2008.07.31 82 Risk Assessment
RA-8 Escape Ways and Safe Haven
Rev2 / 2008.08.25
MI-1 Acceptance Criteria Rev0 / 2008.07.31
84
MI-2 Meteorological Data / Parameters
Rev0 / 2008.07.31
86 Miscellaneous
MI-3 Manning Levels / Population Distribution
Rev1 / 2008.08.25
Stavanger LNG Base Load Plant
Date: 2008.05.26
Assumption No.:
HC-1 Revision: 0
Subject Area: Hazard Identification/Consequence Analysis
Topic: Main area definitions
Assumption/Rule Set
The Stavanger LNG Base Load Plant has been divided into the following main areas:
Main area definition Description
Inventory Loop 1 Feedgas Purification Inventory Loop 2A NG Liquefication Gas
Inventory Loop 2B1 NG Liquefication Liquid_103 bar System Inventory Loop 2B2 NG Liquefication Liquid_19 bar System Inventory Loop 3A LNG Storage Return Gas
Inventory Loop 3B LNG Storage Inventory Loop 4 LNG Truck Loading
Inventory Loop 5A LNG Ship Loading Tank Top Inventory Loop 5B1/2/3 LNG Ship Loading Line Inventory Loop 5C LNG Ship Loading Jetty
Inventory Loop 6A1 Refrigeration Gas System_4 bar System Inventory Loop 6A2 Refrigeration Gas System_18 bar System Inventory Loop 6A3 Refrigeration Gas System_40 bar System Inventory Loop 6B1 Refrigeration Liquid 25-HX-101/103 System Inventory Loop 6B2 Refrigeration Liquid 25-VA-101 System
Inventory Loop 6B3 Refrigeration Liquid 25-VA-102/25-HX-102 System Inventory Loop 6B4 Refrigeration Liquid 25-VL-102 System
Inventory Loop 7 Propane Storage Inventory Loop 8 Pentane Storage Inventory Loop 9 Butane Storage
Inventory Loop 10A Ethylene Storage Gas System Inventory Loop 10B Ethylene Storage Liquid System Inventory Loop 11 Hot Oil System
Inventory Loop 12 Feedgas Fiscal Metering Inventory Loop 13 Tailgas Fiscal Metering
Implication of assumption:
Impact on safety function impairment.
Reference:
Prepared by: Sign: CAN Date: 2008.05.26
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.05.26
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.07.31
Assumption No.:
HC-2 Revision: 1
Subject Area: Hazard Identification/Consequence Analysis
Topic: Release Rates
Assumption/Rule Set
Only releases of hydrocarbons are considered. A release of MDEA in the Solvent Regenera- tion system is not considered, as it is used in a not flammable aqueous solution. CO2/H2S leaks from pipelines to Regenerative Thermal Oxidation (RTO) due to a low operating pres- sure are not considered, but discussed qualitatively (see Appendix B: Hazard Identification). Releases have been analysed in terms of four characteristic hole sizes:
• Small: 1-10 mm • Medium: 10-50 mm • Large: 50-100 mm
• Very Large (Full bore): taken to be hole equivalent to the largest diame- ter pipework in that inventory ( > 100 mm)
Releases from pipelines, flanges, pumps etc. are modelled as liquid, gas, or two-phase re- leases. Where an inventory comprises significant liquid and gas sections, e.g. in a vessel, then both are modelled.
The representative release height for all cases is taken 1 m; except for the LNG Tank, where 30 m are applied, since the leak sources (flanges) by the LNG Tank are expected on the tank top.
Release rates are assumed to be constant throughout the release duration time and calcu- lated with isolation (ESD System), and with blowdown (see Assumption Sheet RA-4). Accord- ing to EN 1473, the isolated sections shall be depressurised to 50 % of design pressure in 15 minutes or to 7 barg in 30 minutes. Based on this, the calculated time to detect and initiate is 600 s. An average blowdown time of 900 s is used in the calculation. Release rates of gas systems with small gas volume are limited by flow controlled gas supply. Liquid release rates are limited by pump rates.
However, the times to detect will vary, depending on leak size, release rate, location of re- lease, etc. In practice, some releases may be isolated much quicker, but it is assumed that this represents a “realistic worst case” value.
Implication of assumption:
Releases of hydrocarbons affect the fire and explosion risk.
Reference:
Prepared by: Sign: CAN Date: 2008.07.31
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.07.31
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.07.313
Assumption No.:
HC-3 Revision: 1
Subject Area: Hazard Identification/Consequence Analysis
Topic: Hydrocarbon Releases
Assumption/Rule Set
Outdoor Releases of hydrocarbons (gas/liquid or two phases) are considered from the count- ing equipment (see Assumption Sheet FA-1). Hole sizes are defined in Assumption Sheet HC-2. Release duration time is based on the fire and gas detection and ESD&Blowdown Sys- tem (see Assumption Sheets RA-3 and RA-4).
Hydrocarbon leaks in buildings, which contain Hydrocarbons, are defined as explosion group zone 1 and are assumed to have a minor contribution to risk compared to outdoor releases due to forced ventilation. Hydrocarbon entering in a building is prevented by adequate gas detection and closing the air-intake. Therefore Hydrocarbon leaks in buildings are not ana- lysed, but are discussed qualitatively (see Appendix B: Hazard Identification).
Implication of assumption:
Outdoor hydrocarbon releases affect the fire and explosion risk.
The buildings are specified with explosion group zone 1. Gas entering in a building is pre- vented by adequate gas detection and closing the air-intake. Therefore the risk of internal explosion is not considered.
Reference:
Prepared by: Sign: CAN Date: 2008.07.31
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.07.31
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.05.26
Assumption No.:
HC-4 Revision: 0
Subject Area: Hazard Identification/Consequence Analysis
Topic: Gas Dispersion
Assumption/Rule Set
The gas dispersion is calculated by the UDM model implemented in the PHAST / PHAST RISK software. This model considers only free field dispersion, so that any local air stream effects at equipment/ buildings are not included in the dispersion calculation. Dispersion gen- erally is modelled as horizontal releases.
A representative gas cloud size to 50% of lower flammable limit (LFL fraction) has been used to determine the magnitude / extent of flash fires / explosions.
Implication of assumption:
Gas dispersion affects the consequence calculations associated with the fire and explosion risk.
Reference:
Prepared by: Sign: CAN Date: 2008.05.26
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.05.26
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.05.26
Assumption No.:
HC-5 Revision: 0
Subject Area: Hazard Identification/Consequence Analysis
Topic: Gas Fire Modelling
Assumption/Rule Set
Gas fires resulting from ignited hydrocarbon releases are modelled as jet fire, flash fire and fire ball for each release scenario.
For unimpinged gas releases the jet fire is calculated using the Shell model. The original Shell model uses the Chamberlain correlation for calculation of the flame length as function of the release rate, which was developed for near-vertical vapour-phase releases. This correlation was modified by Cook et al. to describe the shape of jets that contain liquid. Therefore the option DNV Recommended has been used, that means the PHAST / PHAST RISK program will use the correlation that is most appropriate for the release-conditions.
For impinged releases the fireball diameter is calculated from the release rate using the corre- lation given in Dutch Yellow book.
For delayed ignition the flash fire limit is the distance to ½ LFL.
Implication of assumption:
This assumption affects the fire risk. See also the assumption sheet RA-6.
Reference:
Methods for the calculation of physical effects (Yellow Book), CPR14E
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Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.05.26
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.07.31
Assumption No.:
HC-6 Revision: 1
Subject Area: Hazard Identification/Consequence Analysis
Topic: Liquid Fire Modelling
Assumption/Rule Set
Fires resulting from ignited liquid releases are modelled as a pool or a jet fire.
Pool fire dimensions are modelled using the spill rate to compute pool development with al- lowance for burning (if ignited) or boil off. The maximum pool sizes are defined either by hit- ting a dike wall or by reaching a minimum thickness. The minimum thickness depends on sur- face and is set by the PHAST / PHAST RISK program to 5 mm for a concrete surface.
For pool fires the effects are calculated for an early and late ignition. The late pool fire is as- sumed to occur when the pool reaches its maximum radius. For early pool fires pool size evo- lution is based on ignition occurring at 10 sec.
Jet flame lengths and radiation effects distances are calculated as per gas fires (refer to HC- 5).
The bund around the pentane tank is implemented in the calculation. The effect of an LNG pit at the storage tank and at the jetty is implemented in the LNG PLANT QRA calculations as a bund around the tank (Inventory Loop 3B) and around the jetty (Inventory Loop 5C), since the PHAST RISK program can not directly simulate such a pit. The bunds limit the pool spread- ing.
Implication of assumption:
This assumption affects the fire risk.
The LNG pool fires around storage tank and around the jetty loading are limited by a pit in each case (modelled as bund). This reduces the pool spreading and thus the heat radiation.
Reference:
Prepared by: Sign: CAN Date: 2008.07.31
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.07.31
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.05.26
Assumption No.:
HC-7 Revision: 0
Subject Area: Hazard Identification/Consequence Analysis
Topic: Vapour Cloud Explosion Modelling
Assumption/Rule Set
The TNT model is used to calculate vapour cloud explosion effects. The explosion efficiency is set to 10 %. For gases lighter than air an air burst is assumed. For gases heavier than air a ground burst is taken into account. Then the PHAST / PHAST RISK program multiplies the explosion efficiency by factor two, to account for the effects of reflection on the overpressure. The flammable mass is calculated as mass between LFL and UFL. The explosion location criterion is the cloud front (1/2 LFL fraction). Vapour cloud explosion effects are calculated if the minimum explosion energy of 5 x 10^6 kJ (DNV default value) is exceeded.
Implication of assumption:
This assumption affects the explosion risk.
Reference:
Prepared by: Sign: CAN Date: 2008.05.26
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.05.26
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.05.26
Assumption No.:
HC-8 Revision: 0
Subject Area: Hazard Identification/Consequence Analysis
Topic: Non-Process
Assumption/Rule Set
Non-process events include: loss of utilities (failure leads to fail safe conditons), utilities re- leases, non-hydrocarbon fires (e.g. transformer fire in electrical/instrument room). They are not included in the LNG PLANT QRA due to their low frequency and low consequence and active and passive fire protection , but discussed qualitatively (see Appendix B: Hazard Identi- fication).
Implication of assumption:
This assumption has none impact on fire and explosion risk in the LNG PLANT QRA.
Reference:
Prepared by: Sign: CAN Date: 2008.05.26
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.05.26
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.05.26
Assumption No.:
HC-9 Revision: 0
Subject Area: Hazard Identification/Consequence Analysis
Topic: Loading Frequency
Assumption/Rule Set
Loading operations are assumed to be 1 cargo ship loading every 5th day (filling time 6h) and truck loading 10 times in a day (filling time 1.2 h).
Implication of assumption:
This assumption reduces the release and ignition probabilities.
Reference:
Prepared by: Sign: CAN Date: 2008.05.26
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.05.26
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.07.31
Assumption No.:
HC-10 Revision: 1
Subject Area: Hazard Identification/Consequence Analysis
Topic: Ship Transport Accidents
Assumption/Rule Set
Types of accidents are not a part of LNG PLANT QRA.
A ship collision risk assessment is recommended (important risk). As it has an impact on third party population risk. A ship collision with jetty could be significant with respect to 1st risk.
Implication of assumption:
This assumption could have impact on fire and explosion risk in the LNG Plant. Collision inci- dents per port visit - while mooted at jetties, berths etc or within locks, enclosed harbours etc. is 3.7 X 10-5 [LMIS database]. Therefore, such accidents can be neglected.
Reference:
Lyod’s Maritime Information Services (LMIS).
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Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.07.31
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.05.26
Assumption No.:
HC-11 Revision: 0
Subject Area: Hazard Identification/Consequence Analysis
Topic: Occupational Risk
Assumption/Rule Set
The occupational accidents have been not included in the acceptance criterion, and are there- fore not considered in the LNG Plant QRA.
Implication of assumption:
This assumption has none impact on harm/death risk in the LNG Plant QRA.
Reference:
OGP, Safety Performance Indicators – 2006 data, Report no. 391, June 2007 Section 2.2 & 4.1
Prepared by: Sign: CAN Date: 2008.05.26
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.05.26
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.06.02
Assumption No.:
FA-1 Revision: 1
Subject Area: Frequency Analysis
Topic: Inventory Count
Assumption/Rule Set
For each inventory the leak frequencies are estimated using a full parts count of the equip- ment shown on the P&ID. Typically this includes:
• Flanges (not to consider in welded pipelines) • Valves
• Small bore fittings • Pipelines • Pressure vessels • Heat exchangers • Pumps • Compressors • Atmospheric Tanks
Equipment counts assumptions are detailed below:
• Drums and other vessels that are primarily gas (e.g. cycle compressor interstage drum) or liquid (e.g. cold MRC separator) are conservatively treated as 100% gas or liquid, respectively
• Relief valves to flare and blow down valves are counted as normal valves and assumed to be closed in normal operation. Therefore down- stream equipment are not considered
• Flanges and small bore fittings in pipelines are not counted since the failure of flanges is included in the failure frequency of the pipeline [Purple Book]
• For jetty, a double flange per valve connections and associated flanges are counted
• Flanges and small bore fittings at vessels and at the LNG Tank are not counted since their failure frequencies are included in the failure fre- quency of the vessels and tanks [Purple Book]
Further details are given in Appendix C: Equipment Count.
Implication of assumption:
The amount of inventories as leakage sources affects the release frequency.
Reference:
Guidelines Risk calculations (Purple Book) BEVI Module C, Version 3.0 Date 1 January 2008: Modelling specific BEVI categories.
BEVI is the abbreviation of the decree implementing the SEVESO directive.
Prepared by: Sign: CAN Date: 2008.06.02
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.06.02
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.05.26
Assumption No.:
FA-2 Revision: 0
Subject Area: Frequencies Analysis
Topic: Frequency Database
Assumption/Rule Set
As Linde AG has not received a database from the Client, the leak sizes and- frequencies, are calculated with DNV Software Leak 3.2. The generic failure data used as the basis of the frequency analysis is the UK HSE Offshore Hydrocarbon Release Statistic 1992-2006, or HCRD [Ref. A]. This is a DNV recommended database for Hydrocarbon releases. To reflect the LNG plant, which is considered a clean service and an onshore facility, leak frequencies for pipelines, vessels and the LNG Storage Tank are applied as given in the Purple Book [Ref. B]. Accordingly, failures of flanges in pipelines or at vessels are included in the failure frequency of the pipeline or of the vessel (see Assumption Sheet FA-1).
Further details are given in Appendix D: Results of Leak 3.2. Calculations.
Implication of assumption:
Key influence on the risks (i.e. risk is directly proportional to frequency).
Reference:
A: HSE, 2000. Offshore Hydrocarbon Release Statistics, 1999, Offshore Technology Report OTO 079, HSE Offshore Safety Division (OSD), January 2000.
B: Guidelines Risk calculations (Purple Book) BEVI Module C, Version 3.0 Date 1 January 2008: Modelling specific BEVI categories.
BEVI is the abbreviation of the decree implementing the SEVESO directive.
Prepared by: Sign: CAN Date: 2008.05.26
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.05.26
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.07.31
Assumption No.:
FA-3 Revision: 1
Subject Area: Frequencies Analysis
Topic: Leak Frequency (LNG Storage Tank)
Assumption/Rule Set
Acc. to EN 1473 roof collapse/tank collapse is considered negligible for full containment tanks. Therefore, a very large leak (full rupture) associated with the full containment LNG tank is not considered in Inventory Loop 3A “LNG Storage Return Gas” (refer to the Assumption Sheet HC-1).
Further details are given in Appendix D: Results of Leak 3.2. Calculations.
Implication of assumption:
The leak frequency is directly proportional to risk.
Reference:
Prepared by: Sign: CAN Date: 2008.07.31
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.07.31
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.06.02
Assumption No.:
RA-1 Revision: 0
Subject Area: Risk Assessment
Topic: Event Tree Probabilities
Assumption/Rule Set
The development of a release is largely defined by the stage at which ignition occurs, where the immediate and delayed ignition may give an explosion, or a flash fire, or a fireball. These different developments are represented in a diagram called an “event tree”, and the probabili- ties for the developments are known as “event tree probabilities” or “event tree parameters”. The sum of the probabilities for Fireball, Flash Fire, Explosion and Pool Fire alone is usually 100%. An example risk model event tree for a continuous release with rainout (with probability of a pool fire) is shown in Figure 23.
Figure 23: Example Risk Model Event Tree Structure
0.6 0.3* 0.15 1.0 1.0 1.0 0.4 0.6 0.6 0.3* 0.15 1.0 1.0 1.0 0.4 0.6
* The default probability of immediate ignition (0.3) has not been used to account the effects of fluid properties (e.g. reactivity) and source strength on the ignition probability.
If no immediate ignition occurs, the program models the dispersion of the cloud through a succession of time steps until it has diluted below a hazardous concentration. At each time step the program models the effects of delayed ignition of the cloud, calculating the probability of delayed ignition by considering the ignition sources (see the Assumption Sheet RA-2) within the flammable area of the cloud during that time-step.
Implication of assumption:
The event tree is a key aspect of the QRA model and affects of fire and explosion risk de- pending on the timing and type of ignition.
Reference:
Prepared by: Sign: CAN Date: 2008.06.02
Internal Verification: Sign:
BAUMGARTNER/RATH
Date: 2008.06.02
Comment from Lyse:
Stavanger LNG Base Load Plant
Date: 2008.06.02
Assumption No.:
RA-2 Revision: 0
Subject Area: Risk Assessment
Topic: Ignition Sources – Probabilities
Assumption/Rule Set
The ignition sources are defined by ignition probability and time period. The ignition probabil- ity is the probability that the ignition source will ignite a flammable cloud if the cloud is ex- posed to the source for the specified time period, which is assumed 10 s (default value in PHAST RISK).
The expected ignition sources and their probabilities are listed in following table:
Ignition Source Ignition Probability Traffic Density Average Speed
[Fraction] [day] [kph]
Flare 54-FC-101 0.5 Fired Heater for Hot Oil 52-FA-101 0.1 H2S Conventer (Incinerator) 20-XT-101 0.1 Electrical Substation 0.1
Traffic (Truck Loading) 0.1 10 30 Maintenance Traffic 0.1 1 30 Parking Area Traffic 0.1 20 20
It is assumed that all electrical equipment will be EX-safe (Explosion Protection). Due to fire and gas detection, the Regenerative Thermal Oxidation (RTO) Incinerator and all the not ex- safe units will be isolated by closing the damper at the air inlet. Therefore the ignition prob- abilities have been reduced to 0.1 expect for the flare.
The flare pilots will burn with a pilot flame continuously. Due to the fact that the flare pilots are