Quantitative Risk Assessment for the Nubaria – Meet Nama ...
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The Egyptian Natural Gas Company
Prepared by:
Executive Summary
The Nubaria-Metnama Natural Gas pipeline starts from Al-Nubaria power station passing by North Giza power station and ends at Metnama area. This pipe line is used to feed this area with Natural Gas for power plants to be used in the production of electricity.
EcoConServ was assigned to prepare a Quantitative Risk Assessment (QRA) study for the proposed Nubaria-Metnama Natural Gas pipeline, on behalf of the The Egyptian Natural Gas Company (GASCO). This report is the main deliverable of this assignment.
This document sets out the Nubaria-Metnama Natural Gas pipeline QRA in order to identify the key hazards and risks associated with the new pipeline. The study focuses on the major, worst-case hazards, essentially in order to prioritize the potential impacts to the public.
Risk Criteria
Individual risks are the key measure of risk acceptability for this type of study, where it is proposed that:
• Risks to the public can be considered to be broadly acceptable if below 10-6 per year. Although risks of up to 10-4 per year may be considered acceptable if shown to be ALARP.
• Risk in the range of 10-6 to 5 x 10-7 may cause injury to persons who could not find a shelter within 30 seconds.
Risk Results – Public
From the day of construction and until 20 years of operation, only two villages will be affected by the 5 x 10-7 risk of injury contour which are Izbt Masjid Ar-Rahman and Al-Baradah villages, with no real risk for the residents of the villages.
After 20 and until 30 years of operation, five villages will be affected, but again only by the 5 x 10-7, which means that they are no real risk too.
After 30 years, the 1x10-6 risk appears but does not reach any villages except Al-Baradah village; also the 5 x 10-7 reaches 7 villages with no real risk to the residents.
Concerning Al-Baradah village, GASCO ensures that they performed a field visit and that the exact placement of the pipeline will be based on real conditions according to real ground situation. This will decrease the risk at Al-Baradah village to a high extent. Furthermore, all villages which may be affected in the future will be repeatedly visited by the GASCO team to ensure that populations are not exposed to unacceptable risk. Special attention will be paid to the village of Al-Baradah.
Recommendations
The results of this QRA report show that the 1 x 10-6 risk contour (which is the risk of fatality to the public) does not appear except after 30 years of operation and even then has a negligible effect. However the 5x10-7 risk of injury contour appears but with a limited effect and it is acceptable for population to exist within its vicinity.
GASCO will take all possible actions to organize building construction and encroachment around both banks of the pipeline. Also, they are committed to coordinate with local authorities about any new projects to be constructed in the area of the project. This will limit the effect of any accident to a great extent.
The emphasis on risk reduction should be on preventative measures, i.e. to minimize the potential for leaks to occur. This would chiefly be achieved through appropriate design (to recognized standards) and through effective inspection, testing and maintenance plans / procedures. All of these measures are already included in the pipeline design and mitigation measures to be followed strictly by GASCO.
Rapid isolation of significant leaks will not eliminate the risks but will help to further minimize the hazards and, particularly, the ignition probability (by limiting the total mass of flammable gas released). For isolation to be effective first requires detection to occur. Close monitoring and rapid shutdown of the pipeline in case of an emergency are important to limiting the effects of leaks.
Contents
Executive Summary 1
Risk Criteria 1
Risk Results – Public 1
Recommendations 2
Abbreviations 8
1 Introduction 9
1.1 Background 9
1.2 Objectives and Scope 9
1.3 Layout of Study 9
2 Site Description 11
2.1 Location 11
2.2 Land Use 11
2.3 Location of Valve Rooms 12
2.4 Meteorological Conditions 15
3 Project Description 17
3.1 Pipeline Description 17
3.2 Pipeline Specifications 17
3.3 Mitigations for Construction and Pipeline Operation 17
4 Risk Acceptance Criteria 19
4.1 Risk Assessment Framework 19
4.2 Individual Risk Criteria 20
4.3 Societal Risk Criteria 21
5 Methodology 22
5.1 Data Collection 22
5.2 Hazard Identification (HAZID) 23
5.3 Frequency Analysis 23
5.4 Consequence Analysis 23
5.5 Risk Calculations 23
5.6 Risk Software Tools 24
6 Frequency Analysis 25
6.1 General 25
6.2 Basic Failure Frequencies 26
6.3 External Interference Factors Adjustments 27
6.3.1 Marker Tape 27
6.3.2 Depth of Cover 27
6.3.3 Wall Thickness 28
6.4 Ground Movement Factors Adjustments 28
6.5 Adjusted Failure Frequencies 29
6.6 Probability of Pipeline Ignition 30
7 Assumptions 31
7.1 Introduction 31
7.2 Background Assumptions 31
7.2.1 Weather Categories 31
7.2.2 Wind Direction 32
7.2.3 Atmospheric Parameters 32
7.3 Vulnerability/ Impact Criteria Assumption for Jet Fire 33
7.4 Failure Case Definition Assumptions 33
7.4.1 Failure Cases - Definition 33
7.4.2 Failure Cases - Parameters 34
7.4.3 Failure Cases - Release Types 34
7.5 Consequence Analysis Assumptions 35
7.5.1 General 35
7.5.2 Fire Modeling 35
8 Hazard Identification 36
8.1 General Hazards 36
8.2 Hazardous Properties of Natural Gas 39
8.3 Detailed Hazards Identification 39
8.3.1 Natural Gas Line 39
9 Failure Case Definitions 42
9.1 Introduction 42
9.2 Methodology 42
10 Consequence Assessment 44
10.1 Consequence of Jet Fire Accidents 44
11 Risk Assessment 45
11.1 Calculated Risk due to Jet Fire 45
12 Risk Results 47
12.1 Frequency Estimation 47
12.2 Individual Risk Contours 48
12.3 Risks to the Public 49
12.4 Recommendations 50
13 Bibliography 68
A1 Risk Acceptance Criteria 70
A1.1 Introduction 70
A1.2 Basis for Criteria 70
A1.2.1 Need for Criteria 70
A1.2.2 Principles for Setting Risk Criteria 70
A1.2.3 Framework 71
A1.3 Proposed Risk Criteria 73
A1.3.1 Individual Risk 73
A1.3.2 Societal Risk 75
List of Figures
Figure 2-1: A Google Earth image showing the Nubaria–Metnama pipeline with valve rooms locations and power plants on the line 14
Figure 5-1: QRA Methodology 22
Figure 6-1: Average contribution of incident causes for all categories of pipelines 26
Figure 6-2: General Contribution of Failure Causes In Case of Full-Bore Rapture 26
Figure 7-1: Wind Rose (Probability of Wind Direction) 32
Figure 10-1: ALOHA jet fire Output at 70 bar 44
Figure 11-1: Risk at 70 bar pressures as afunction of distance from center of pipeline at 1.2 m depth of cover 46
Figure 12-1: Pipeline path general view showing the fourteen villages around the pipeline 52
Figure 12-2: Less than 20 years Individual Risk Contours at Izbt Masjid Ar-Rahman (10-6 risk contour does not appear) 53
Figure 12-3: Less than 20 years Individual Risk Contours at Al-Baradah Village (10-6 risk contour does not appear) 54
Figure 12-4: 20 – 30 years Individual Risk Contours at Izbt Masjid Ar-Rahman Village (10-6 risk contour does not appear) 55
Figure 12-5: 20 – 30 years Individual Risk Contours at Izbt Sidi Ibrahim(10-6 risk contour does not appear) 56
Figure 12-6: 20 -30 years Individual Risk Contours at Izbt Jamal Al-Fransawi (10-6 risk contour does not appear) 57
Figure 12-7:20 - 30 years Individual Risk Contours at Kafr Mansour Village (10-6 risk contour does not appear) 58
Figure 12-8: 20 – 30 years Individual Risk Contours at Al-Baradah Village (10-6 risk contour does not appear) 59
Figure 12-9: 30 -40 years Individual Risk Contours at Izbt As-Sukhna Al-Jadida 60
Figure 12-10: 30 – 40 years Individual Risk Contours at Izbt Masjid Ar-Rahman 61
Figure 12-11: 30 – 40 years Individual Risk Contours at Izbt Sidi Ibrahim 62
Figure 12-12: 30 – 40 years Individual Risk Contours at Izbt Jamal Al-Fransawi 63
Figure 12-13: 30 – 40 years Individual Risk Contours at Kafr Mansour 64
Figure 12-14: 30 – 40 years Individual Risk Contours at Darawa Village 65
Figure 12-15: 30-40 years Individual Risk Contours at Al-Baradah Village 66
Figure 12-16: F-N curve marking the ALARP zone and the frequency for less than and greater than 20 years of operation 67
Figure A- 1: "ALARP" Framework for Risk Criteria 73
Figure A- 2: An interpretation of UK HSE Societal Risk Criteria (F-N Curve) 76
List of Tables
Table 2-1: Location of Valve Rooms 12
Table 2-2: Temperature and humidity for North Giza area 15
Table 6-1: Base Frequencies for Pipeline Release 26
Table 6-2: Base Frequency for pipelines in the diameter category of 29” – 35” 27
Table 6-3: Reduction Factor Related to the Depth of Cover 28
Table 6-4: Frequency Reduction Factor related to Wall Thickness 28
Table 6-5: Sub causes of Ground Movement and their Contributions 28
Table 6-6: Final Frequency after Adjustments for three years Categories 29
Table 6-7: Probability of Ignition Following a Release from Pipe 30
Table 7-1: Atmospheric Parameters 32
Table 7-2: Summary of Ignited Release Outcomes, or Hazard Types 35
Table 8-1: Hazard causes, consequences and proposed or inherent safeguards 37
Table 12-1 : Frequencies used for all the cases at the three operation years categories 47
Abbreviations
|AIChE |American Institute of Chemical Engineers |
|ALARP |As Low As Reasonably Practicable |
|ALOHA |Areal Locations of Hazardous Atmospheres |
|API |American Petroleum Institute |
|BP |British Petroleum |
|CCPA |Center for Chemical Process Safety |
|CCTV |Closed Circuit Television |
|CIA |Central Intelligence Agency |
|DNV |Det Norske Veritas |
|EGIG |European Gas Pipeline Incident Data Group |
|EGPC |Egyptian General Petroleum Company |
|EPA |Environmental Protection Agency |
|ESD |Electrostatic Discharge |
|F/N |Frequency – Number of Fatalities Curve |
|FM200 |Dupont waterless fire suppression system |
|FRED |Fire, Release, Explosion and Dispersion |
|GASCO |Egyptian Natural Gas Company |
|HAZID |Hazard Identification |
|HCRD |Hydrocarbon Release Database |
|HRSG |Heat Recovery Steam Generator |
|HSE |Health and Safety Executive |
|HVAC |Heating, Ventilation and Air Conditioning |
|IP |Intermediate Pressure |
|LFL |Lower Flammability Limit |
|LP |Low Pressure |
|MAOP |Maximum Allowable Operating Pressure |
|NFPA |National Fire Protection Association |
|NG |Natural Gas |
|NOAA |National Oceanic and Atmospheric Administration |
|OEM |Office of Emergency Management |
|QRA |Quantitative Risk Assessment |
|UK |United Kingdom |
Introduction
1 Background
Nubaria-Metnama Natural Gas pipeline is planned to be constructed between Nubaria Power Station and Metnama area for the transfer of natural gas through the West of the Nile Delta area. The design of the project is performed by the Egyptian Natural Gas Company (GASCO).
EcoConServ was assigned to prepare a Quantitative Risk Assessment (QRA) study for the proposed Nubaria-Metnama Natural Gas pipeline, on behalf of GASCO. This report is the main deliverable of this assignment.
2 Objectives and Scope
The main objectives of this QRA study are:
• To identify and quantify the major hazards associated with the proposed pipeline
• Assess the acceptability of the risks to people (any nearby residential areas), against internationally recognized criteria.
The scope covered is for a QRA, which is focused on the worst-case hazards, and associated risks, in order to assess the key risks.
3 Layout of Study
The layout of the remainder of this document consists of the following sections:
• Section 2 and Section 3 describe the site of the pipeline and the give details about the project, and the mitigation measures adopted by GASCO.
• Section 4 sets out the risk criteria proposed for this study, on which the determination of acceptability will be based. This is covered in detail by Appendix A1.
• Section 5 clarifies the methodology adopted while carrying out the risk assessment and the tools used for the study.
• Section 6 describes the frequency analysis and the effect of the preservative measures on the frequency
• Section 7 summarizes the assumptions undertaken in this study in detail (detailed assumptions / failure case definition).
• Section 8 and Section 9 summarize the outcome of the Hazard Identification step and enumerate the failure cases.
• Section 10 describes the Consequence Assessment steps and presents its results.
• Section 11 describes the Risk Assessment steps and presents its basic results.
• Section 12 details the final risk results, which are primarily based around the individual risk contours. These are discussed with respect to the potential risks to the public. It also presents the Conclusions and Recommendations of the analysis.
Site Description
1 Location
The Nubaria-Metnama Natural Gas pipeline starts from Al-Nubaria power station passing through several villages and agricultural land in the West of the Delta, near its end it passes by North Giza power station and ends at Metnama area. The pipeline is 104 Km long and passes through the Bhaira, Menofia, Giza and Qalyubiyah Governorates. Figure 2-1 shows the Google earth image for the pipeline showing the valve rooms locations and numbers, Al-Nubaria power station as the starting point of the line, and North Giza power station that benefits from the pipeline.
2 Land Use
The pipeline passes through agricultural land, and moves adjacent to the agricultural area border where possible. First part of the pipeline is located to the West bank of Al-Rayyah An-Nasiri canal, after valve-room 7 the line crosses the canal to North Giza power plant. After this, the pipeline crosses the Rashid Branch, the Damietta Branch of the Nile and several other canals.
It is memorable to note that the detailed maps on which the pipeline was placed are old dating back to 1992, on the other hand the Google earth images are based on the satellite photos taken within 2010. During this time some villages extended and the pipeline now passes through one of them, namely Al-Baradah village (see Figure 12-1).
GASCO ensures that they have done a physical survey of the entire route and that they will not construct a pipeline passing through villages, only through agricultural land, and that the exact placement of the pipeline will be based on real conditions according to real ground situation. Limited accuracy due to drawing the pipeline on the Google Earth image or during measuring distances from the actual maps may account for the difference than the real case.
The pipeline passes beside several Villages; these Villages are listed from the North (beginning of the line) and moving South then East with the line. The villages are:
• Al-Iman – قرية الإيمان
• Salah Al-Din – قرية صلاح الدين
• Badr - بدر
• Umar Makram–قرية عمر مكرم
• Umar Shahin–قرية عمر شاهين
• Izbt As-Sukhnah Al-Jadida–عزبة السخنة الجديدة
• Izbt Masjid Ar-Rahman–عزبة مسجد الرحمن
• Al-Khatatba - الخطاطبة
• Izbt Sidi Ibrahim–عزبة سيدي إبراهيم
• Izbt Jamal Al-Fransawi–عزبة جمال الفرنساوي
• Ar-Raml - الرمل
• Al-karadi - الكرادي
• Kafr Mansour–كفر منصور
• Sheshaa - شعشاع
• Darawah - داراوة
• Kafr Ash-Shurfa Al-Gharbia–كفر الشرفة الغربية
• Al-Baradah - البرادعة
• As-Sabah and Kafr ash-Shaheed – الصباح وكفر الشهيد
3 Location of Valve Rooms
Table 2-1 shows the approximate location of each of the 12 valve rooms placed on the pipeline according to Geographical coordinates from Google earth.
Table 2-1: Location of Valve Rooms
|Location Name |North |East |Distance to Valve Room (km between valve |
| | | |rooms) |
|Valve Room 1 |30° 42’ 16.88” |30° 40’ 12.77” |0 |
|Valve Room 2 |30°35 38.02” |30° 42’ 49.77” |13 |
|Valve Room 3 |30° 32’ 29.54” |30° 45’ 58.70” |8 |
|Valve Room 4 |30° 29’ 43.12” |30° 48’ 15.81” |8 |
|Valve Room 5 |30° 25’ 34.84” |30° 48’ 56.89” |8 |
|Valve Room 6 |30° 20’ 17.17” |30° 48’ 17.59” |10 |
|Valve Room 7 |30° 14’ 55.05” |30° 55’ 07.53” |15 |
|Valve Room 8 |30° 14’ 48.49” |30° 56’ 33.74” |4 |
|Valve Room 9 |30° 12’ 12.10” |31° 00’ 25.64” |10 |
|Valve Room 10 |30° 14’ 09.06” |31° 05’ 51.72” |10 |
|Valve Room 11 |30° 14’ 08.57” |31° 11’ 08.57” |9 |
|Valve Room 12 |30° 12’ 42.76” |31° 16’ 00.60” |9 |
[pic]
Figure 2-1: A Google Earth image showing the Nubaria–Metnama pipeline with valve rooms locations and power plants on the line
4 Meteorological Conditions
The meteorological conditions for the pipeline were taken as the meteorological data for the of North Giza Power Plant site, as the pipeline feeds the plant and the meteorological conditions of the area through which the pipeline pass is nearly constant. The meteorological data for the North Giza Power Plant were obtained from the Giza Meteorological Station, and cover the area of 50 km around the station.
Table 2-2shows the annual temperature and humidity variation around the site. The wind rose for the area is shown in Figure 2-2. The wind rose shows that wind blows mainly from the North and that the wind speed seldom increases over 10 knots.
Table 2-2: Temperature and humidity for North Giza area
|Month |Av. Temperature (oC) |Relative |
| |Av. |Av. |Highest Daily Max. |Lowest Daily Min. |Humidity |
| |Daily Max. |Daily Min. | | |(%) |
|January |19.8 |6.9 |31.5 |3.3 |66 |
|February |21.2 |7.6 |36.2 |2.0 |61 |
|March |24.1 |9.8 |39.0 |1.2 |59 |
|April |28.7 |13.1 |43.5 |3.5 |51 |
|May |32.5 |16.7 |48.0 |7.9 |48 |
|June |34.8 |19.8 |48.0 |11.9 |51 |
|July |35.3 |21.5 |45.5 |15.0 |58 |
|August |34.8 |21.6 |42.9 |15.3 |62 |
|September |33.0 |19.6 |44.0 |11.9 |61 |
|October |30.6 |17.0 |44.5 |8.9 |62 |
|November |25.7 |12.7 |38.8 |3.4 |67 |
|December |21.1 |8.6 |36.3 |-1.1 |68 |
|Annual-average |28.46 |14.58 | | |59.5 |
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Project Description
1 Pipeline Description
The pipeline is 104 km long starting at Al-Nubaria power station and feeds the North Giza power plant along its path. The line has 12 valve rooms to act as a safeguard for the pipeline.
2 Pipeline Specifications
The pipe diameter is 32 inch with a daily average flow-rate of 8 MMscmd, an inlet gas pressure is in the range 60-70 bar. The pipeline will be buried at a depth of 1.2 m and has marker tapes to indicate its path.
3 Mitigations for Construction and Pipeline Operation
The following mitigation measures are followed by GASCO during the construction and operation of the pipeline:
• The Quality Control ISO 9001 is applied throughout the project,
• International codes and criteria are used during the choice of the path and the design of the pipeline,
• Direct and accurate supervision on all the construction phases will be present through the company’s engineers and technicians,
• Engineering inspection will be done during all the project phases,
• Pipelines must successfully pass the hydrostatic test at a pressure of 1.5 times the maximum operating pressure before the starting to operate,
• The gases being transmitted must not contain any corrosive materials,
• The pipelines have corrosion resistant internal lining,
• The pipelines are externally coated with three layers of polyethylene and checked before the pipes are put down and buried,
• Cathodic protection systems are applied as soon as the line is put in the ground,
• The most up-to-date internal testing systems are applied to discover any defects and address them early, if any. (On-Line Inspection technique).
• The internal testing system is repeated periodically and the results are compared against the previous test results.
• The SCADA system, available at the National Control Center (NATA), will be used to control and isolate the areas at risk immediately in case of emergencies in order to ensure a speedy control and minimize the damage,
• The choice of the main pipelines paths to be outside the residential areas,
• The thickness of the pipeline is chosen to match the population class near the highly populated areas,
• The valve rooms are distributed on the pipeline in a way that decreases the amount of confined gas and enables easy discharge in case of emergency.
• Coordination with the local authorities and the concerned authorities about the pipeline path and maps to be taken into consideration when approving any new projects or constructions,
• Increasing the awareness about the pipeline in the nearby communities through the patrol squads.
Risk Acceptance Criteria
In the absence of Egyptian legislation setting definite limits for acceptable risk, the risks evaluated within this study were referenced against internationally accepted criteria, in order to determine the acceptability of the risks and any need for risk reduction measures to be implemented within the design process. The EGPC does have its own standards for risk acceptance, but it was considered more conservative in this case to apply the internationally accepted criteria.
The risk criteria proposed to be used are drawn from the widely used framework set out by the UK’s HSE, using the As Low As Reasonably Practicable (ALARP) principle, and proposes risk acceptance criteria to be used as guidance for this study.
1 Risk Assessment Framework
The following measures of acceptability should be evaluated in assessing the risks from any hazardous activity:
• Individual risk criteria should be used to limit risks to members of the public.
• Cost-benefit analysis should be used to ensure that, once the above criteria are satisfied, an optimum level of safety measures is chosen for the activity, taking costs as well as risks into account. (Note that this is outside the scope of this study.)
The simplest framework for risk criteria is a single risk level which divides tolerable risks from intolerable ones. Such criteria give attractively simple results, but they need to be used very carefully, because they do not reflect the uncertainties both in estimating risks and in assessing what is tolerable. For instance, if applied rigidly, they could indicate that an activity which just exceeded the criteria would become acceptable as a result of some minor remedial measure which in fact scarcely changed the risk levels.
A more flexible framework specifies a level, usually known as the maximum tolerable criterion, above which the risk is regarded as intolerable whatever the benefit may be, and must be reduced. Below this level, the risks should also be made As Low As Reasonably Practicable (ALARP). This means that when deciding whether or not to implement risk reduction measures, their cost may be taken into account, using cost-benefit analysis. In this region, the higher the risks, the more it is worth spending to reduce them. If the risks are low enough, it may not be worth spending anything, and the risks are then regarded as negligible.
This approach can be interpreted as dividing risks into three tiers (as is illustrated in Appendix A1):
• An upper band where risks are intolerable whatever the benefit the activity may bring. Risk reduction measures or design changes are considered essential.
• A middle band (or ALARP region) where the risk is considered to be tolerable only when it has been made ALARP. This requires risk reduction measures to be implemented if they are reasonably practicable, as evaluated by cost-benefit analysis.
• A negligible region where the risks are negligible and no risk reduction measures are needed.
2 Individual Risk Criteria
Individual risk is widely defined as the risk of fatality (or serious injury) experienced by an individual, noting that the acceptability of individual risks should be based on that experienced by the most exposed (i.e. ‘worst-case’) individual.
The most widely-used criteria for individual risks are the ones proposed by the UK HSE, noting that these have also been interpreted for projects in Egypt.
These criteria are:
• The acceptable criterion, for the public, corresponding to the level below which individual risks can be treated as effectively negligible, is 10-6 per year (i.e. 1 in 1,000,000 years)
• If the risk calculated from heat radiation at residential areas exceeds 5 x 10-7per year, this will cause injury after 30 seconds of direct exposure to the heat. The risk of injury in this case is 5 x 10-7 (i.e. 5injuries in 10,000,000 years), which may considered negligible.
In terms of the acceptability of individual risks, it should be noted that:
• Individual risks are typically presented as contours that correspond to the risk experienced by a person continuously present, outdoors, at each location.
• While people are unlikely to remain “continuously present, outdoors” at a given point, the individual risk levels used to assess residential developments are not modified to account for any presence factor or the proportion of time spent indoors. That is, it should be conservatively assumed that dwellings are occupied at all times and that domestic properties offer no real protection against the potential hazards.
• It should also be noted that lower criteria are often adopted with respect to vulnerable populations, such that schools and hospitals, for example, should be located such that the individual risks are well below 10-6 per year.
3 Societal Risk Criteria
A proposed criterion for Societal Risk is set out in Appendix A1in the form of an F-N curve, which gives the cumulative frequency (F) of exceeding a number of fatalities (N).
It is, however, important to note that the acceptability of societal risks can be subjective and depends on a number of factors (such as the benefits versus the risks that a facility provides). There is not a single established indicator in terms of societal risk.
The proposed societal (F-N) criteria are considered to provide useful guidance on the acceptability of the societal risk, although it should be emphasized that the criteria are not as widely accepted as individual risk and should be used as guidance only.
Methodology
QRA is a well-established methodology to assess the risks of industrial activities and to compare them with risks of normal activities. The QRA methodology used is shown in Figure 5-1.
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Figure 5-1: QRA Methodology
1 Data Collection
This study is based on information sent to EcoConServ by email in addition to the general pipeline path map and detailed terrain maps, which were obtained from (GASCO).
2 Hazard Identification (HAZID)
The hazard identification process is important for any risk analysis. A HAZID was been performed in the course of preparing the QRA depending on historical data for gas transportation accidents. The HAZID study for the pipeline has enabled us to identify and enumerate the failure cases that require further analysis.
3 Frequency Analysis
Failure frequencies were determined for each event in order to perform a probabilistic risk assessment. Generally, a number of techniques are available to determine such frequencies. The approach relies on generic data. This provides failure frequencies for equipment items where data has been obtained from failure reports from a range of facilities. Frequency assumptions are detailed in Chapter 7.
4 Consequence Analysis
For each identified hazard scenario, consequence analysis tools were used to determine consequence effect zones for each hazard. In general the different possible outcomes could be:
• Dispersing of Hydrocarbon Vapor Cloud
• Explosion
• Flash Fire
• Jet Fire
The particular outcomes modeled depend on source terms (conditions like fluid, temperature, pressure etc.) and release phenomenology. The current understanding of the mechanisms occurring during and after the release is included in our consequence analysis models and tools. These models and tools are explained in Section 5.6.
5 Risk Calculations
The outcome of the risk analysis is risk terms presented in form of risk curves, where the location of specific individual risk measurements is displayed.
The individual risk is the risk for a hypothetical individual assumed to be continuously present at a specific location. The individual at that particular location is expected to sustain a given level of harm from the realization of specified hazards. It is usually expressed in risk of death per year. Individual risk is presented in form of risk contours.
Risk contours were generated using the tools described in Section 5.6
6 Risk Software Tools
A collection of freely available software and in-house developed programs were used to estimate the risk in this study. This approach has enables a deep understanding of the risk calculations methodology. The use of this risk software tools enables the users to have control over the modeling and hence the majority of the assumptions are covered in the inputs to, rather than within, the software.
Consequence modeling is done using ALOHA, a tool developed by EPA’s Office of Emergency Management (OEM) and the National Oceanic and Atmospheric Administration Office of Response and Restoration (NOAA), to assist front-line chemical emergency planners and responders. ALOHA is an atmospheric dispersion model used for evaluating releases of hazardous chemical vapors. ALOHA allows the user to estimate the downwind dispersion of a chemical cloud based on the toxicological/physical characteristics of the released chemical, atmospheric conditions, and specific circumstances of the release. ALOHA can estimate threat zones associated with several types of hazardous chemical releases, including toxic gas clouds, fires, and explosions. The input to ALOHA is mainly the conditions at the release source, and the output is a graph showing the release effect at the specified standard radiation levels or overpressure according to the type of release. The graphs from ALOHA are then turned into a digital format in the form of a table showing the distances in all directions at each radiation level.
The general principles of consequence identification are:
• Dispersion results are drawn in from ALOHA software, taking flammable and toxic hazard ranges separately. These are used for delayed ignition hazards, such as toxic impacts and flash fires.
Similarly, the way the risks are calculated, via event trees, is part of the user-defined input. The risk assessment software is written using a programming language that takes the digitized graphs from ALOHA as an input, taking into consideration the frequency of occurrence and the probability of ignition of each type of release. The inputs are consequences in the form specified above, where each will have an event frequency together with an immediate ignition probability or a background delayed ignition probability. The probability of weather category and wind direction is determined as per Assumptions of Chapter 7, as are the ignition and explosion probabilities (as discussed further in Chapter 7). All other variations on the outcome frequency are defined before input, e.g. the probability of isolation failure or variation in release orientation. The risk from all different releases is then added to give the final total risk contours graph, which is presented on a Google Earth image for the pipelines.
Frequency Analysis
1 General
The failure data of release are derived from the European Gas Pipeline Incident Data Group (EGIG, 2008). The European data is derived based on a significant exposure experience in terms of kilometer years experienced from 1970 – 2007 in fifteen European countries, which is a statistically significant base for estimating release frequencies. The general statistical data is averaged on all the fifteen countries without taking the regional differences, such as population density and geological conditions, into consideration, which makes the data more reliable for use. The frequency also takes into consideration a number of variable factors such as: wall thickness, depth of cover, probability of ignition, etc.
The operating conditions of the pipeline that will be constructed by GASCO between the Nubaria and Metnama are covered well in the statistical data used in the report of EGIG about pipelines, these conditions are the operating pressure, pipe diameter, wall thickness, depth of cover and coating material.
The analysis of the main incident causes for all categories of pipelines (different diameters, thicknesses, pressures, etc.) shows that the main cause of incidents is through external interference followed by construction defect / Material Failure then corrosion as can be seen in Figure 6-1.
[pic]
Figure 6-1: Average contribution of incident causes for all categories of pipelines
2 Basic Failure Frequencies
The average data derived from EGIG for all pipelines are shown in Table 6-1, where they are categorized by the cause of the incident and gives the frequency of each cause. For more specification, only the data for pipes of diameters greater than 29” will be used during the calculations of the frequency. Also the frequency of material defects will be calculated according to the year of construction as more advanced measure. Figure 6-2 shows the contribution of failure causes in case of full-bore rupture before the specific measures applied for this case.
[pic]
Figure 6-2: General Contribution of Failure Causes In Case of Full-Bore Rapture
Table 6-1: Base Frequencies for Pipeline Release
|Cause |Pipeline General Base frequency by Cause and Hole Size |
| |(Per 1000 km-year) |
| |Hole |Full-Bore Rupture |
| |(10 mm < d < 50 mm) | |
|External Interference |0.1 |0.03 |
|Construction/Material Defect |0.015 |0.01 |
|Corrosion |0.0025 |0 |
|Ground Movement |0.008 |0.009 |
|Other/Unknown |0.003 |0 |
|Total |0.1285 |0.049 |
The failure data indicate that for pipelines with a diameter from 29” to 35”, only full rupture can occur at this diameter with the frequency shown in Table 6-2. Table 6-2 also shows the change in the construction defect/ material failure based on the number of years that passed since the construction, for this study three categories are adopted, the first is since the construction till 20 years, the second is the period of 20-30 years since construction and the third is 30-40 years since construction. More measures will be applied later to account for all the mitigation measures taken by GASCO and the difference between the Egyptian and European geographical terrain.
Table 6-2: Base Frequency for pipelines in the diameter category of 29” – 35”
|Pipeline Full Bore Rupture Base frequency for 29” – 35” Diameter Class |
|(Per 1000 km-year) |
|Years since construction |Less than 20 years |20 – 30 years |30 – 40 years |
|Cause | | | |
|External Interference |0.0048 |0.0048 |0.0048 |
|Construction/Material Defect |0 |0.0029 |0.0039 |
|Corrosion |0 |0 |0 |
|Ground Movement |0.009 |0.009 |0.009 |
|Other/Unknown |0 |0 |0 |
|Total |0.0138 |0.0167 |0.0177 |
3 External Interference Factors Adjustments
The base frequencies in Table 6-2 are adjusted to account for the additional preservative measures taken for each pipeline, such as: Pipeline depth, wall thickness and the presence of Marker Tape. These measures will result in decreasing the likelihood of external interference; therefore it is the main factor that is going to be affected.
1 Marker Tape
Corder (Corder, 1995) has reported that a damage reduction factor of 1.67 was achieved when marker tape is provided above pipelines based on experimental data derived from testing undertaken by British Gas. This factor will be used in this study to reduce the frequency of impacts resulting from external interference for sensitivity cases with marker tape.
2 Depth of Cover
The depth of cover presents the depth at which the pipeline will be buried, as the depth of cover increase the reduction factor decrease and so the frequency decrease. The depth of 1.11 m has no reduction factor where for depths below this value the frequency increases and above it the frequency decrease. These data were originally available to the depth of 1.4 m, which were extrapolated to reach a value of 2.0 m and are shown in Table 6-3.
Table 6-3: Reduction Factor Related to the Depth of Cover
|Depth of Cover (m) |Reduction Factor |
|0.8 |1.30 |
|1.0 |1.11 |
|1.2 |0.92 |
|1.4 |0.73 |
|1.6 |0.54 |
|1.8 |0.35 |
|2.0 |0.157 |
Thus a reduction factor of 0.92 (for 1.2 m depth) will be used in this study.
3 Wall Thickness
The (EGIG, 2008) database summarizes pipeline failure frequencies by wall thickness. Based on the data, the factors in Table 6-4 are used for pipes with varying wall thicknesses.
Table 6-4: Frequency Reduction Factor related to Wall Thickness
|Pipe Wall |Puncture |Rupture |
|Thickness (mm) |(Hole) |(Full-Bore) |
|2.5 (0-5 mm) |2.4 |5.8 |
|7.5 (5-10 mm) |1.0 |1.0 |
|12.5 (10-15 mm) |0.5 |0.5 |
Note that GASCO uses an additional conservative measure which is increasing the pipe thickness from the usual 0.5” (12.7 mm) to 0.625” (16 mm) near the areas with low population and to 0.75” (19 mm) near the highly populated areas, all the road and river crossings. Therefore, it is convenient to assume a wall thickness higher than 15 mm for population areas near the pipeline and roads and rivers which decreases the corrosion probability to its minimum.
4 Ground Movement Factors Adjustments
The factors that compromise the ground movement frequency are not all experienced in Egypt due to the difference in the geographical terrain, although Europe is near enough; therefore these factors are either removed or reduced to match the earthquake categories of Egypt versus Europe. Table 6-5 shows the factors that contribute in the base ground movement frequency.
Table 6-5: Sub causes of Ground Movement and their Contributions
|Sub-Causes of Ground Movement |Percent Contribution |
|Land Slide |55% |
|Flood |19% |
|River |6% |
|Mining |5% |
|Dike break |1% |
|Lightning |3% |
|Other |2% |
|Unknown |9% |
The factors that were removed are flood, mining, dike break and lightning while the land slide factor was reduced to the third of its value to take into consideration that the delta areas is far enough from the tectonic plates boundaries, which are the main earthquakes reason, unlike some of the contributing countries in the EGIG data like Italy and Spain.
5 Adjusted Failure Frequencies
The effect of release from a hole in the pipe was found to be negligible compared to the release from full-bore rupture; as the pipe diameter class indicates according to the statistical data from EGIG. Also the preservative mitigation measures taken by GASCO, such as the polyethylene coating, the cathodic protection and the hydrostatic test on the pipe at 1.5 its maximum operating pressure, eliminate the possibility of corrosion which is the main reason for hole rupture. Therefore, the effect of hole-release is not carried forward.
The frequency of full-bore rupture after taking into account the marker tape and depth of cover in the external interference factor and adjusting the ground movement factor is shown in Table 6-6.
Table 6-6: Final Frequency after Adjustments for three years Categories
|Pipeline Full Bore Rupture Base frequency for 29” – 35” Diameter Class |
|(Per 1000 km-year) |
|Years since construction |Less than 20 years |20 – 30 years |30 – 40 years |
|Cause | | | |
|External Interference |0.0026 |0.0026 |0.0026 |
|Construction/Material Defect |0 |0.0029 |0.0039 |
|Corrosion |0 |0 |0 |
|Ground Movement |0.002 |0.002 |0.002 |
|Other/Unknown |0 |0 |0 |
|Total |0.0138 |0.0167 |0.0177 |
It is important to note that the construction/ material defect factor will not appear as a considerable factor except after 20 years since the pipeline was built and will only slightly increase after 10 more years. Therefore three calculations were made to take into consideration the change in this factor.
6 Probability of Pipeline Ignition
The probability of ignition of holes and ruptures used in the frequency assessment was based on the (EGIG, 2008) Report Section 3.4.3, summarized in Table 6-7. The probability differs in case of rupture according to the pipe diameter.
Table 6-7: Probability of Ignition Following a Release from Pipe
|Hole size |Ignition Probability |
|Hole (50 mm) |2% |
|Rupture (d 406 mm) |33% |
Possible sources of ignition include but are not limited to: direct heat (Smoking, cooking, etc.), electrical current (lights, irrigation pumps, tractors, cars, etc.), lightning, etc.
Assumptions
1 Introduction
The basic aim of this Assumptions chapter is to document the details underpinning this QRA study.
Background data:
The site-specific aspects that apply (or potentially apply) to each of the release scenarios (failure cases) modeled are referred to as ‘background data’. This covers the meteorological conditions and the potential ignition sources that are specific to the site, and the potentially exposed populations.
General assumptions:
The basic methodology adopted for studies of this kind is set out in the following sections, in order to describe the basis for the defined scenarios and modeling approach. It should be emphasized that elements of these sections are generic and are intended to define the broad approach only.
2 Background Assumptions
1 Weather Categories
As well as the wind direction, the actual weather conditions, in terms of the wind speed and the stability (a measure of atmospheric turbulence), determine how quickly the flammable plume disperses to lower non-hazardous concentrations.
In the absence of detailed meteorological data (i.e. covering the stability categories), two representative weather conditions are applied to model the dispersion of each release scenario. These are D5 and F2 conditions, which are widely adopted (such as by NFPA and the UK HSE) as broadly representative of ‘typical’ and ‘worst-case’ dispersion conditions, respectively:
• D5 – neutral stability (D) and 5 m/s wind speed.
• F2 – stable (F) conditions and 2 m/s wind speed.
UK HSE guidance suggests that good practice for QRA studies is to assume that D5 conditions apply for 80% of the time and F2 for the remaining 20% - again, in the absence of detailed data only.
Although based on the experience of conducting QRA worldwide suggests that this provides a reasonably representative (and slightly conservative) basis when compared against local weather conditions.
2 Wind Direction
The wind rose for the region where the pipeline will be constructed is given below.
[pic]
Figure 7-1: Wind Rose (Probability of Wind Direction)
Please note that the above figure is based on the True North. The data provided is based on annual averages and, hence, is applied to the risk model as being the same for all time periods (e.g. day and night).
3 Atmospheric Parameters
The representative atmospheric parameters that are applied to the consequence modeling are summarized in Table 7-1, below.
Table 7-1: Atmospheric Parameters
|Parameter |Value |Unit |Notes |
|Air temperature |22 |°C |The range of min/max temperatures is 2 to 41 °C, where 20 °C is taken as a representative base |
| | | |value in case of absence of representative data. |
|Surface temperature |22 |°C |Taken as the same as air temperature, above. |
|Relative humidity |60 |% |Assumed. Note that its influence on dispersion / consequences is minor. |
|Surface roughness |1 |m |Representative parameter for regular large obstacles based on TNO Purple Book guidance. |
|Solar radiation |1 |kW/m2 |Assumed. Note that its influence on dispersion / consequences is negligible. |
|Atmospheric pressure |1.013 |bar |Negligible influence on dispersion /consequences. |
As indicated in the above table, assumptions such as surface roughness can significantly affect the hazard ranges predicted for the worst-case release scenarios. However, the influence on most releases is minor and the purpose of the risk study is to determine the frequency of the most representative outcomes. Hence, the overall risks will be reasonable robust to the above assumptions.
3 Vulnerability/ Impact Criteria Assumption for Jet Fire
The basis for the jet fire impact levels and criteria is summarized below.
• The levels at which impairment from fires occurs are defined for three radiation levels, of greater than 37.5 kW/m2, 12.5 kW/m2 and 4.7 kW/m2which are referenced within the risk model as ‘flame’, ‘radiation’ and ‘Injury’ impacts, respectively.
• A fatality rate of 100% is assumed at radiation levels of 37.5 kW/m2 or greater and 50% for 12.5 kW/m2 or greater for personnel outdoors that are exposed to radiation effects from jet fires. These values involve a degree of judgment, but are consistent with standard practice (and slightly conservative).
• For the 4.7 kW/m2 radiation level the risk of injury assigned is 50 chances in million years.
4 Failure Case Definition Assumptions
1 Failure Cases - Definition
The key factors in selection of the representative sections (i.e. the generic failure cases) are:
• Gas released.
• Flow conditions (temperature and pressure).
• Release location (the area in which the release occurs, including the height).
• Isolation.
For each of the pipe sections, up to five representative release sizes are considered:
• Full-bore rupture (where the hole diameter is larger than the diameter of the pipeline, based on the most representative line size within each section)
• Large leaks (e.g. due to connection failures) - 75 mm (3”) equivalent diameter
• Medium, Small and Very Small leaks (e.g. due to corrosion, impact and other such cases) – 25, 12 and 2 mm (1”, ½” and 1/10”) equivalent diameter leaks respectively.
2 Failure Cases - Parameters
For each of the release scenarios to be modeled, the key inputs to the derivation of release parameters are the flow conditions, flow-rate and location, where the parameters are derived as follows:
• Flow conditions (temperature and pressure) were obtained through GASCO as mentioned in section 3.2, where the pressure drops through the whole pipeline from about 70 bar to about 30 bar. However, according to GASCO’s request, the pressure in the pipe is taken to be 70 bar along the pipeline, representing no-flow conditions, as a conservative measure.
• Release location: The release location selected is necessarily representative as it is taken to be at any point along the pipeline. The release is modeled at a depth of 1.2 m from the surface of the ground, which is the depth of cover of the pipeline, also the presence of marker tape is taken into account as stated by GASCO.
3 Failure Cases - Release Types
The outcome, and hence the way in which the discharge and subsequent dispersion parameters are modeled are listed below:
• In case of immediate ignition after the release the result is jet fire.
• If the release is not followed by immediate ignition, it will result in a flash fire. The flash fire consequence is negligible compared to the jet fire consequence and is not carried forward for further assessment.
• Toxicity. Natural gas has no known toxic or chronic physiological effects (that is, it is not poisonous). Exposure to a moderate concentration may result in a headache or similar symptoms due to oxygen deprivation but it is likely that the sound accompanying the release would be heard well in advance of concentrations being high enough for this to occur.
5 Consequence Analysis Assumptions
1 General
For each release event defined, dispersion modeling and fire size calculations are conducted within ALOHA modeling software tool. These consequence results are used directly by the risk modeling software.
The consequences are input to the risk model in groups of hazard type, which depend upon the type of release and when ignition occurs, as summarized Table 7-2 below. Note that this table addresses flammable impacts only; toxic impacts will also apply for unignited releases depending on the composition.
Table 7-2: Summary of Ignited Release Outcomes, or Hazard Types
|Release Type |Hazard Type (Consequence) |
| |Immediate Ignition |Delayed Ignition |
|Gas release |Jet fire (or fireball for short duration release)|Flash fire/explosion |
2 Fire Modeling
Based on the derivation of the release parameters, the determination of the initial fire effects is handled by the ALOHA as follows.
• All immediately ignited releases are modeled as jet fires.
• All delayed ignition events are modeled as flash fires or VCEs (not applicable for this study).
• Flash fires are based on the LFL (Lower Flammability Level) distance (not applicable for this study).
Hazard Identification
1 General Hazards
The first step in any risk assessment is to identify all hazards. The merits of including the hazard for further investigation are subsequently determined by its significance, normally using a cut-off or threshold quantity.
Once a hazard has been identified, it is necessary to evaluate it in terms of the risk it presents to the neighboring community. In principle, both probability and consequence should be considered, but there are occasions where if either the probability or the consequence can be shown to be sufficiently low or sufficiently high, decisions can be made on just one factor.
Table 8-1 shows the general hazards that were found for the N.G. pipeline, along with possible causes, expected consequences and proposed or inherent safeguards.
Table 8-1: Hazard causes, consequences and proposed or inherent safeguards
|Site Area |Hazard Cause |Hazard Consequence |Proposed / Inherent Safeguard |
|Pipeline |External interference |Leak/rupture, ignition, jet fire, flash |pipeline marker signs to be installed at regular intervals |
| | | |The national control center (NATA) will be used to control and isolate the areas at risk |
| | | |immediately in case of emergencies |
| | | |The choice of the main pipelines paths to be outside the residential areas |
| | | |Increasing the awareness about the pipeline in the nearby communities through patrol squads |
| | | |Coordination with the local authorities and the concerned authorities about the pipeline path and |
| | | |maps to be taken into consideration when approving any new projects or constructions |
| | | |The thickness of the pipeline is chosen to match the population class near the highly populated |
| | | |areas |
|Pipeline |Construction error |Leak/rupture, ignition, jet fire, flash |hydrostatic test at a pressure of 1.5 times the maximum operating pressure before operating |
| | | |The most up-to-date internal testing systems are applied to discover any defects and fix them |
| | | |early |
| | | |The internal testing system is repeated periodically and the results are compared against the |
| | | |previous test results |
|Pipeline |Corrosion |Leak/rupture, ignition, jet fire, flash |External coating system corrosion protection |
| | | |Corrosion resistant internal lining |
| | | |Gases transmitted must not contain any corrosive materials |
| | | |Cathodic protection systems are applied |
|Pipeline |Ground Movement, Earthquake |Leak/rupture, ignition, jet fire, flash |land is flat with no subsidence potential |
| | | |Use of Horizontal Directional Drilling as a construction method for water way crossings |
| | | |Use of steel pipes which are flexible enough to take the shape of the ground beneath it |
|NG Valve rooms |Equipment failure causing leaks due to|Gas release |Inherent flexibility and strength of gas transmission pipelines and equipment |
| |corrosion or defects |Jet fire if ignited |Closed rooms for security |
| | |Flash fire if ignition is delayed |QA, welding inspection |
| | | |Hydrostatic testing of equipment |
| | | |Radiography of circumferential welds – ultrasonic on pipes |
| | | |Maintenance/inspection |
2 Hazardous Properties of Natural Gas
The inherent hazards of the fitting line arise from the flammability of the natural gas, and the pressure at which it is transmitted and processed in the station. The types of hazardous incident which may occur, in theory at least, would all require a leak in the fitting line or associated equipment (e.g. valves, meters, flanges, etc.). They are: Jet fire and flash fire.
It is noted that natural gas is lighter than air (i.e. a buoyant gas) and if released tends to rise and disperse rather than accumulate forming a flammable cloud thus it is not possible for Vapor Cloud Explosion to occur.
3 Detailed Hazards Identification
The following section constitutes detailed qualitative hazard identification for those incidents listed in Table 8-1.
1 Natural Gas Line
The following fitting line design and operational details, below, were used:
• Inlet Pressure – 70 bar
• Outlet Pressure – 70 bar
• Length – 104 km
• Diameter – 32 inch (8128 mm); and
• Wall thickness – varying according to the population density in each area (from 0.5” to 0.75” (12.7mm -19mm)), therefore, taken as above 15mm.
There is historical evidence of gas transmission pipeline failure. Historical evidence (Bolt & Horalek, 2004)indicates that there are a number of factors that can lead to fitting line leak and subsequent release of gas. The details below summarize those incidents that have historically led to fitting line failure and gas release:
• External Interference – external interference accounts for the majority of release incidents in gas transmission fitting lines (Bolt & Horalek, 2004).
• Flood Damage – this may occur where the fitting line traverses river beds or water courses. The potential for fast running water could lead to scouring above the fitting line exposing the pipe to potential impact from rocks and debris moving in the water stream. In addition, surface flooding could lead to the fitting line floating from the trench, leading to fitting line damage. A review of the fitting line route indicates that the fitting line will be laid away from flood areas. Additionally, Horizontal Directional Drilling will be used as a construction method for waterway crossings. Hence, this hazard has not been carried forward for further analysis.
• Subsidence Damage – where fitting lines are installed near or in banks and levees, wash away may expose the fitting line and uneven weight could cause severe fitting line damage. However, the fitting line is not installed in a bank or levee and therefore, incidents resulting from subsidence have not been carried forward for further analysis
• External Corrosion Damage – many soils are acidic and fitting lines installed without external protection are susceptible to corrosion and eventual failure (leaks). The fitting line is installed underground and hence is exposed to acidic soils increasing the potential for external corrosion. Therefore, polyethylene coating is applied for protection as well as cathodic protection. Incidents involving external corrosion (excluding impact) have not been carried forward for further analysis.
• Internal Corrosion Damage – the introduction of corrosive gas to the fitting line could result in accelerated corrosion or moisture in the gas could lead to corrosion impact on the pipe internal surface. However, gas fed is dry and non-corrosive, having passed many kilometers through this line, also internal lining is used to protect the pipe. Hence, the likelihood of corrosion from this source is considered negligible. Incidents as a result of corrosion have therefore not been carried forward for further analysis.
• Faulty Material – the use of faulty materials, such as fitting line with manufacturing defects, could lead to premature fitting line failure resulting in rupture. However, pipe material will be purchased from a quality assured organization (i.e. ISO9001), which minimizes the potential for faulty materials. Further, the fitting line will be fully tested in accordance with the appropriate requirements, including a pressure test to prove fitting line will operate safely and without failure at maximum allowable operating pressure (MAOP). The quality assurance testing regime minimizes the potential for fitting line failure as a result of material defects. These measure are strictly followed, therefore the faulty material frequency will not start to affect the flow except after 20 years of operation, which could be minimized through regular check of the pipeline.
• Faulty Construction – like the faulty materials incidents detailed above, faulty construction can also lead to failure of the fitting line. For example, faulty welding can lead to premature failure and gas release. However, fitting line welds will be subjected to X-Ray inspection minimizing the potential for failure from this source. Further, the fitting line will be subjected to a testing regime, further minimizing the potential for faulty construction failure. Additional construction problems, such as poor support or alignment in the pipe rack will be minimized by strictly following the appropriate requirements. These measure are strictly followed, therefore the faulty material frequency will not start to affect the flow except after 20 years of operation, which could be minimized through regular check of the pipeline.
• Ground Movement – this may occur where fitting lines are installed in an earthquake zone. Earthquakes and excessive ground movement may lead to damaged pipe racks and buckled pipework or, in the worst case, rupture. However, the fitting line would not be installed in an earthquake zone. Delta area is relatively stable and earthquakes of the magnitude that could result in fitting line rupture are rare. The risk of ground movement is slightly taken into consideration in the frequency of pipe rupture, as not all the ground movement factors are present for the proposed pipeline.
• “Hot Tap” by Error “– “hot tap” is the connection to a live gas line during operation. When this is conducted by expert personnel the risk is negligible. However, failure to identify a live gas fitting line and attempts, by error, to connect to this fitting line could lead to fitting line breach and gas release. To identify gas fitting line, marker signs will be installed on the fitting line in accordance with the appropriate requirements. This incident therefore, has not been carried forward for further analysis.
The above analysis is supported by the results of studies conducted by the European Gas Pipeline Incident Data Base (Bolt & Horalek, 2004), which conducts research into gas pipeline incidents both in Europe and overseas. The results of these studies indicate that the majority of pipeline incidents 50% occur as a result of external interference, 17% due to material defects and 15% due to corrosion.
Failure Case Definitions
1 Introduction
The basic aim of the Failure Case Definition stage is to identify the failure cases, or major accident hazards, that will have the potential to result in risks to populations around the pipeline path, and hence will be inputs to the risk modeling.
The basic approach adopted is summarized in Section 9.2.
Note that the failure case definition presented in this section is underpinned by the methodology set out in Section 7.
2 Methodology
For the purposes of this risk assessment it is not necessary (or practical) to attempt to model all of the potential hazards associated with all the points of the pipeline. The basic approach adopted instead is summarized below.
• 70 bar pressure will be used over the whole pipeline as a conservative measure.
• The scenario is carried out at the valve rooms and then extended over the whole pipeline length
• Two risk values were considered 1 x 10-6 and 5 x 10-7 per year, where the first value represents the risk of fatality and the second represents the risk of injury.
• These failure cases are then superimposed upon the image of the pipeline on Google Earth to define the populated areas that are at risk from this line.
Note that the general methodology adopted in deriving the initial failure cases, and the subsequent development of each, is detailed in Section 7 . Note also that the subsequent modeling approach is also described in Section 7.
The failure cases derived for each unit are presented in the following section. The section includes a basic description of the failure case, as well as the representative flow conditions and the primary hazard outcome(s) of each release.
Due to the insignificance of the risk due to the hole compared to the full-bore rupture, as detailed in Section 7, therefore the hole consequence is not carried forward for investigation.
Consequence Assessment
The consequence of the failure cases were estimated using the methodology of Section5 and the assumptions detailed in Chapter7. Consequences presented here are jet fire consequence as the flash fire consequence was found to be negligible compared to the jet fire consequence.
1 Consequence of Jet Fire Accidents
The failure case which result in jet fire, has the following calculated data by ALOHA, where the hole diameter is equal to the pipe diameter: The total amount burned in 1 hr is 237,173 kg and the flame length is 91 m.
A sample jet fire output is shown in Figure 10-1shows radiation contours of 37.5, 12.5 and 4.7 kW/m2 for 70 bar jet fire scenarios. Note that ALOHA figures assume that the wind blows towards the positive x-axis
[pic]
Figure 10-1: ALOHA jet fire Output at 70 bar
Risk Assessment
The Risk assessment is based on the data presented in Section6. Before calculating the risk, the rupture was first assumed to be at every point in the pipeline each representing a separate case. Then during the risk assessment the risk for each heat radiation contour was calculated, and the risks of all cases were added to reach the final result which shows the risk as a function of the distance from the center of the pipeline.
1 Calculated Risk due to Jet Fire
The collected Risk calculated for each section is shown as a function of the distance from the center of the pipeline. Figure 11-1shows the calculated risk from the center of the pipeline at 70 bar with distance for the time of construction of less than 20 years, then between 20 - 30 years and after 30 – 40 years in operation.
The distance from the center of the pipe to the 1 x 10-6 and 5 x 10-7 risk contours (fatality and injury) was obtained from the Risk – Distance curve (Figure 11-1). From the time of construction and until 20 years the 1 x 10-6 risk contour does not appear and the distance for the 5 x 10-7 risk contour is 80 m in average. Between 20 – 30 years of operation the 1 x 10-6 risk contour does not appear again and the distance for the 5 x 10-7 risk contour is 180 m in average. Between 30 - 40 years of operation the 1 x 10-6 risk contour has an average distance of 35 m and 190 m for the 5 x 10-7 risk contour.
[pic]
Figure 11-1: Risk at 70 bar pressures as afunction of distance from center of pipeline at 1.2 m depth of cover
Risk Results
The risks were calculated from the results of the consequence analysis of the failure cases and the estimation of the frequencies of those cases. The frequencies were estimated based on the assumptions; data and practices explained in Sections 6&7 and are presented in Section 12.1.
Individual risks are the key measure of risk acceptability for this type of study, where it is proposed that:
• Risks to the public can be considered to be broadly acceptable if below 10-6 per year, although noting that societal risk factors should also be considered (including the type of population potentially exposed). Although risks of up to 10-4 per year may be considered acceptable if shown to be ALARP.
Individual risks are presented in Section 12.2, while risk to the public is presented in Section.12.3
1 Frequency Estimation
Table 12-1 shows the frequencies calculated for each of the cases identified during the hazards identification phase at the three operating years categories.
Table 12-1 : Frequencies used for all the cases at the three operation years categories
|Years of Operation |Fire accident type |Basis for Frequency Calculations |Frequency of |Frequency of Injury |
| | | |Fatality | |
|Less than 20 years |Jet Fire |1.52 x 10-6 from Section 6x 1 |1.52 x 10-6 |1.78 x 10-8 |
| | |probability of fatality for 37.5 kW/m2 | | |
| | |and x 0.5 probability of fatality for | | |
| | |12.5 kW/m2 | | |
| | |Frequency of injury is at 4.7 kW/m2 | | |
|20 – 30 years |Jet Fire |2.48 x 10-6 from Section 6x 1 |2.48 x 10-6 |2.90 x 10-8 |
| | |probability of fatality for 37.5 kW/m2 | | |
| | |and x 0.5 probability of fatality for | | |
| | |12.5 kW/m2 | | |
| | |Frequency of injury is at 4.7 kW/m2 | | |
|30 – 40 years |Jet Fire |7.2 x 10-6 from Section 6x 1 |2.64 x 10-6 |3.09 x 10-8 |
| | |probability of fatality for 37.5 kW/m2 | | |
| | |and x 0.5 probability of fatality for | | |
| | |12.5 kW/m2 | | |
| | |Frequency of injury is at 4.7 kW/m2 | | |
2 Individual Risk Contours
At this stage in the risk assessment the most useful measure of risk is individual risk, which is presented in the form of contours. The individual risk contours for the risk assessment are presented for each village at risk alone to emphasize the type of risk that will affect the residents and to what extent. The individual risk contours give the risk of fatality (or serious injury) experienced by a person continuously present, outdoors and the risk of injury that can be experienced by a person if he did not find a shelter within 30 seconds.
Figure 12-1 shows the villages that are present around the pipeline with their positions as a reference, these villages are:
• Al-Iman
• Badr
• Umar Makram
• Umar Shahin
• Izbt As-Sukhna Al-Jadida
• Izbt Masjid Ar-Rahman
• Izbt Sidi Ibrahim
• Izbt Jamal Al-Faransawi
• Izbt Ar-Raml
• Kafr Mansour
• Sheshaa
• Darawah
• Al-Shurfa Al-Gharbia
• Al-Baradah
At 1.2 m depth of cover and in the operating time till 20 years, Figure 12-2 and Figure 12-3 represent the two affected villages which are Izbt Masjid Ar-Rahman and Al-Baradah consecutively, these villages are affected by the 5x10-7 risk of injury contour only.
Between 20 – 30 years of operation, 5 villages are expected to be affected, also by the 5x10-7 risk of injury contour only. These villages are shown in Figure 12-4 to Figure 12-8, and in order they are: Izbt Masjid Ar-Rahman, Izbt Sidi Ibrahim, Izbt Jamal Al-Faransawi, Kafr Mansour and Al-Baradah.
The expected villages to be affected between 30-40 years of operation are 7 villages as shown in Figure 12-9 to Figure 12-15. These 7 villages are mainly affected by the 5x10-7 risk contour, and the 1x 10-6 although appearing does not affect any villages except Al-Baradah. The seven villages are: Izbt As-Sukhna Al-Jadida, Izbt Masjid Ar-Rahman, Izbt Sidi Ibrahim, Izbt Jamal Al-Faransawi, Kafr Mansour, Darawa and Al-Baradah
3 Risks to the Public
As discussed above, Figure 12-2 and Figure 12-3are focused on the villages that fall within the risk contours at the first 20 years of operation, where it can be seen that:
• The 10-6 individual risk contour does not exist
• The 5 x 10-7 touches Izbt Masjid Ar-Rahman and covers small part of Al-Baradah village
Figure 12-4 to Figure 12-8 are focused on the villages that fall within the risk contours after 20 years of operation and until 30 years, where it can be seen that:
• The 10-6 individual risk contour does not exist
• The 5 x 10-7 passes through Izbt Masjid Ar-Rahman, Izbt Sidi Ibrahim, Izbt Jamal Al-Faransawi, Kafr Mansour and Al-Baradah villages.
Figure 12-9 to Figure 12-15 are focused on the villages that fall within the risk contours after 30 years of operation and until 40 years, where it can be seen that:
• The 10-6 individual risk contour just barely exists and does not affect any nearby villages except Al-Baradah village (see note below regarding this village)
• The 5 x 10-7 passes through Izbt As-Sukhna Al-Jadida, Izbt Masjid Ar-Rahman, Izbt Sidi Ibrahim, Izbt Jamal Al-Faransawi, Kafr Mansour, Darawa and Al-Baradah villages.
Concerning Al-Baradah village, GASCO ensures that they performed a field visit and that the exact placement of the pipeline will be based on real conditions according to real ground situation. This will decrease the risk at Al-Baradah village to a high extent. Furthermore, all villages which may be affected in the future will be repeatedly visited by the GASCO team to ensure that populations are not exposed to unacceptable risk. Special attention will be paid to the village of Al-Baradah.
From the above results it is apparent that the 1x10-6 risk of fatality contour will not appear except after more than 30 years of operation, and even then, its effect will be negligible and is expected not to reach any of the nearby villages. However, it is recommended to put this risk in consideration for future expansion of the areas adjacent to the pipeline.
The F-N curve, Figure 12-16, gives the cumulative frequency (F) of exceeding a number of fatalities (N). In the region between the red and the green lines the risks are acceptable only if demonstrated to be As Low As Reasonably Practicable (ALARP).
The maximum frequency is marked by a black line for the operating periods: less than and greater than 20 years. The figure indicates that the number of fatalities is the number of individuals present outdoors in the fire area with no barrier separating them from the accident source. The Figure shows that:
• For the first 20 years of operation: the risk is considered to be negligible if less than 65 individuals are present outdoors near the accident source, while the risk is considered to be ALARP if 6500 individuals are present outdoors near the accident source.
• After 20 years of operation: the risk is considered to be negligible if less than 40 individuals are present outdoors near the accident source, while the risk is considered to be ALARP if 4000 individuals are present outdoors near the accident source.
Based on the low population density along the path of the pipeline, and the small affected area by the 10-6 contour, it is to be concluded that the risk will never exceeds the ALARP border for the whole lifetime of the pipeline, resulting in an acceptable level of risk.
4 Recommendations
The results of this QRA report show that the 1 x 10-6 risk contour (which is the risk of fatality to the public) does not appear except after 30 years of operation and even then has a negligible effect. However the 5x10-7 risk of injury contour appears but with a limited effect and it is acceptable for population to exist within its vicinity.
GASCO will take all possible actions to organize building construction and encroachment around both banks of the pipeline. Also, they are committed to coordinate with local authorities about any new projects to be constructed in the area of the project. This will limit the effect of any accident to a great extent.
The emphasis on risk reduction should be on preventative measures, i.e. to minimize the potential for leaks to occur. This would chiefly be achieved through appropriate design (to recognized standards) and through effective inspection, testing and maintenance plans / procedures. All of these measures are already included in the pipeline design and mitigation measures to be followed strictly by GASCO.
Rapid isolation of significant leaks will not eliminate the risks but will help to further minimize the hazards and, particularly, the ignition probability (by limiting the total mass of flammable gas released). For isolation to be effective first requires detection to occur. Close monitoring and rapid shutdown of the pipeline in case of an emergency are important to limiting the effects of leaks.
[pic]
Figure 12-1: Pipeline path general view showing the fourteen villages around the pipeline
[pic]
Figure 12-2: Less than 20 years Individual Risk Contours at Izbt Masjid Ar-Rahman (10-6 risk contour does not appear)
[pic]
Figure 12-3: Less than 20 years Individual Risk Contours at Al-Baradah Village (10-6 risk contour does not appear)
[pic]
Figure 12-4: 20 – 30 years Individual Risk Contours at Izbt Masjid Ar-Rahman Village (10-6 risk contour does not appear)
[pic]
Figure 12-5: 20 – 30 years Individual Risk Contours at Izbt Sidi Ibrahim(10-6 risk contour does not appear)
[pic]
Figure 12-6: 20 -30 years Individual Risk Contours at Izbt Jamal Al-Fransawi (10-6 risk contour does not appear)
[pic]
Figure 12-7:20 - 30 years Individual Risk Contours at Kafr Mansour Village (10-6 risk contour does not appear)
[pic]
Figure 12-8: 20 – 30 years Individual Risk Contours at Al-Baradah Village (10-6 risk contour does not appear)
[pic]
Figure 12-9: 30 -40 years Individual Risk Contours at Izbt As-Sukhna Al-Jadida
[pic]
Figure 12-10: 30 – 40 years Individual Risk Contours at Izbt Masjid Ar-Rahman
[pic]
Figure 12-11: 30 – 40 years Individual Risk Contours at Izbt Sidi Ibrahim
[pic]
Figure 12-12: 30 – 40 years Individual Risk Contours at Izbt Jamal Al-Fransawi
[pic]
Figure 12-13: 30 – 40 years Individual Risk Contours at Kafr Mansour
[pic]
Figure 12-14: 30 – 40 years Individual Risk Contours at Darawa Village
[pic]
Figure 12-15: 30-40 years Individual Risk Contours at Al-Baradah Village
[pic]
Figure 12-16: F-N curve marking the ALARP zone and the frequency for less than and greater than 20 years of operation
Bibliography
Abdul Rosyid, O. (2006). System-analytic Safety Evaluation of the Hydrogen Cycle for Energetic Utilization. Otto-von-Guericke-University.
Alcock, J. (2001). Compilation of existing safety data on hydrogen and comparative. EIHP2 Report.
API. (1995). Management of Hazards Associated With Location of Process Plant Buildings (First Edition ed.). API Recommended Practice 752.
Bolt, R., & Horalek, V. (2004). European Gas pipeline Incident Data Group Pipeline Incident Database. 13th Colloquium Reliability of HP Steel Pipes. Prague, Czech Republic.
CCPS, A. (1999). Guidelines of Consequence Analysis of Chemical Releases. New York: American Institute of Chemical Engineers.
Corder, I. (1995). "The Application of Risk Techniques to the design and operations of pipelines". IMechE.
Eggen, J. (1995). GAME: development of guidance for the application of the Multi-Energy Model. TNO Report PML.
EGIG, E. G. (2008). 7th EGIG Report 1970 - 2007, Gas Pipeline Incidents Data Group (EGIG). Report Number -B.0502.
HSE, U. (1999). Offshore Hydrocarbon Release Statistics. Offshore Technology Report. UK HSE.
LASTFIRE. (1997). Large Atmospheric Storage Tank Fire Project – LASTFIRE. Technical Working Group.
Technica. (1990). Atmospheric Storage Tank Study for Oil and Petrochemical Industries Technical and Safety Committee. Singapore.
TNO. (1997). Methods for the calculation of physical effects, (3 ed., Vol. 2). The Hague: Committee for the Prevention of Disasters.
Witlox, H., & Bowen, P. (2001). Flashing liquid jets and two-phase dispersion – A review. HSE.
APPENDICES
Risk Acceptance Criteria
1. INTRODUCTION
This appendix introduces the concept of risk acceptance criteria and the As Low As Reasonably Practicable (ALARP) principle, and proposes risk acceptance criteria to be used as guidance for this study. It should be emphasized that the selection of criteria is open to interpretation, in the absence of any formal local regulations, but where the intention of this study is to use criteria that are consistent with internationally accepted practice.
• Section A1.2 describes the basis for the risk criteria, introducing the widely accepted As Low As Reasonably Practicable (ALARP) concept.
• Section A1.3sets out the criteria that are proposed for this study, covering both individual and societal risk criteria.
2. Basis for Criteria
1. Need for Criteria
A risk analysis provides measures of the risk resulting from a particular facility or activity. However, the assessment of the acceptability (or otherwise) of that risk is left to the judgment and experience of the people undertaking and/or using the risk analysis work. The normal approach adopted is to relate the risk measures obtained to acceptable risk criteria.
A quantitative risk analysis produces only numbers, which in themselves provide no inherent use. It is the assessment of those numbers that allows conclusions to be drawn and recommendations to be developed. The assessment phase of a study is therefore of prime importance in providing value from a risk assessment study.
2. Principles for Setting Risk Criteria
Given that society accepts hazardous activities in principle, and does not have limitless resources to devote to their safety, the following set of principles is considered by some to be appropriate when making decisions about their acceptability in specific cases:
1. The activity should not impose any risks which can reasonably be avoided.
2. The risks should not be disproportionate to the benefits (in terms of jobs, tax revenues and finished products) which the activity produces.
3. The risks should be equitably distributed throughout the society in proportion to the benefits received.
4. The risks should be revealed in minor accidents which the emergency services can cope with, rather than in catastrophes.
In reality, principles such as these are impossible to achieve. In fact, when resources are limited, such principles may be in conflict with each other. For example, reducing catastrophic risks may require expenditure that could have saved more lives from low-fatality accidents.
The following approach is proposed for assessing the risks from any hazardous activity, being the nearest practical approach to the ideal situation:
• Individual risk criteria should be used to limit risks to individual workers and members of the public. These address the equity requirement (3) above insofar as it applies to individuals.
• Societal risk criteria should be used to limit risks to the affected population as a whole. These attempt to address requirement (2) above, although in a necessarily crude fashion since the benefits of hazardous activities are even more difficult to quantify than their risks. They also address the equity requirement (3) above insofar as it applies to communities. By expressing societal risk criteria on a frequency-fatality (FN) curve, they can also address the catastrophe risk in requirement (4) above.
• Cost-benefit analysis should be used to ensure that, once the above criteria are satisfied, an optimum level of safety measures is chosen for the activity, taking costs as well as risks into account. This addresses requirement (1) above.
An activity is said to have tolerable risks if it satisfies all three aspects of this approach, and intolerable risks if it fails to meet any of them.
Leaving aside other inputs to the decision, an activity with tolerable risks would generally be regarded as acceptable to the company, the regulatory authority and the public, while an activity with intolerable risks would generally be regarded as unacceptable.
3. Framework
The simplest framework for risk criteria is a single risk level which divides tolerable risks from intolerable ones (i.e. acceptable activities from unacceptable ones). Such criteria give attractively simple results, but they need to be used very carefully, because they do not reflect the uncertainties both in estimating risks and in assessing what is tolerable. For instance, if applied rigidly, they could indicate that an activity which just exceeded the criteria would become acceptable as a result of some minor remedial measure which in fact scarcely changed the risk levels.
A more flexible framework specifies a level, usually known as the maximum tolerable criterion, above which the risk is regarded as intolerable whatever the benefit may be, and must be reduced. Below this level, the risks should also be made as low as reasonably practicable (ALARP). This means that when deciding whether or not to implement risk reduction measures, their cost may be taken into account, using cost-benefit analysis. In this region, the higher the risks, the more it is worth spending to reduce them. If the risks are low enough, it may not be worth spending anything, and the risks are then regarded as negligible.
This approach can be interpreted as dividing risks into three tiers as is illustrated in Figure A- 1.
• An upper band where risks are intolerable whatever the benefit the activity may bring. Risk reduction measures or design changes are considered essential.
• A middle band (or ALARP region) where the risk is considered to be tolerable only when it has been made ALARP. This requires risk reduction measures to be implemented if they are reasonably practicable, as evaluated by cost-benefit analysis.
• A negligible region where the risks are negligible and no risk reduction measures are needed.
There is some consensus on this three-band approach, and versions are used by the UK, Dutch, Swiss and US Santa Barbara criteria.
[pic]
Figure A- 1: "ALARP" Framework for Risk Criteria
3. Proposed Risk Criteria
1. Individual Risk
Individual risk is widely defined as the risk of fatality (or serious injury) experienced by an individual, noting that the acceptability of individual risks should be based on that experienced by the most exposed (i.e. ‘worst-case’) individual.
The most widely-used criteria for individual risks are the ones proposed by the UK HSE (Reference 1), noting that these can also be used for projects in Egypt.
These criteria are:
• The maximum tolerable individual risk for workers is taken as 10-3 per year (i.e. 1 in 1,000years).
• The maximum tolerable individual risk for members of the public is 10-4 per year (i.e. 1 in10,000 years).
• The acceptable criterion, for both workers and public, corresponding to the level below which individual risks can be treated as effectively negligible, is 10-6 per year (i.e. 1 in1,000,000 years)
• Between these criteria the risks are in the ‘ALARP’ or tolerability region. In this region the risks are acceptable only if demonstrated to be As Low As Reasonably Practicable (ALARP).
In terms of the acceptability of individual risks, it should be noted that:
• Individual risks are typically presented as contours that correspond to the risk experienced by a person continuously present, outdoors, at each location.
• While people are unlikely to remain “continuously present, outdoors” at a given point, the individual risk levels used to assess residential developments are not modified to account for any presence factor or the proportion of time spent indoors. That is, it should be conservatively assumed that dwellings are occupied at all times and that domestic properties offer no real protection against the potential hazards. Hence, the individual risks contours can be used directly with respect to the public, while for workers it is more appropriate to consider the most exposed individual (accounting for the time they spend in different areas, indoors, away from the hazards, etc).
• The individual risk criteria proposed for the public correspond to an individual having a chance of death or serious injury (due to the hazards assessed) of between 1 in 10,000and 1,000,000 years. To put these risks into context, note that the risk of death in the UK due to road accidents is just over 1 in 10,000 years, while the risk of an individual being struck by lightning is widely quoted as being 1 in 10,000,000 years.
• For risks approaching the maximum tolerable individual risk level for the public of 10-4peryear (1 in 10,000 years) to be considered to be acceptable, it should be demonstrated that all reasonably practicable measures to minimize the risks have been, or will be, taken. The same applies for risks closer to the acceptable criterion of 10-6per year, but where the degree of effort (and expenditure) that would be considered to be practicable would be less.
It should be emphasized that a variety of individual risk criteria are used worldwide, as shown by selected examples given below:
For risks to the public a lower / tolerable criterion of 10-6per year is widely accepted. However, lower values are adopted by some companies and legislators. For example, Statoil have a lower criterion of 10-7 per year and where for new facilities the Dutch authorities use 10-6 per year as the upper / maximum criterion.
It should also be noted that lower criteria are often adopted with respect to vulnerable populations, such that schools and hospitals, for example, should be located such that the individual risks are well below 10-6 per year.
The maximum criterion for the public varies between 10-3 and 10-5 per year (or lower in some cases – as indicated above). The UK HSE value of 10-4 per year is maintained in this study as a representative maximum. However, it should be emphasized that this is a maximum value and it would be extremely rare for this level to be considered acceptable for a new facility / development. That is, there is unlikely to be sufficient justification that there are no practicable methods of reducing this level of risk. In fact, it is considered to be best practice to treat 10-6 per year as the target criterion, while risks of up to 10-5 per year would require strong justification and risks above 10-5 per year should be avoided with respect to the public.
It should, in any case, be emphasized that risks above 10-6 per year are acceptable only if shown to be ALARP.
In summary, it is proposed that:
• Risks to the public can be considered to be broadly acceptable if below 10-6 per year, although noting that societal risk factors should also be considered (including the type of population potentially exposed). Although risks of up to 10-4 per year may be considered acceptable if shown to be ALARP, it is recommended that 10-5 per year is adopted for this study as the maximum tolerable criterion.
2. Societal Risk
A proposed criterion for Societal Risk is set out in Figure A- 2 in the form of an F-N curve, which gives the cumulative frequency (F) of exceeding a number of fatalities (N).
It is important to note that the acceptability of societal risks can be subjective and depends on a number of factors (such as the benefits versus the risks that a facility provides). There is not a single established indicator in terms of societal risk. For example, the UK HSE does not apply specific societal risk criteria in general, although they are applied to particular sites such as ports. Instead, the emphasis is placed on demonstrating that the risks are ALARP, where judgment on the ultimate acceptability of the risks is determined on a case by case basis.
However, the UK HSE do quote a single point risk criterion which has been interpreted to form an F-N criterion, as shown in Figure A- 2. The maximum tolerable risk line is based on a standard 1:1 slope through the UK HSE’s quoted intolerable societal risk level of “50 or more fatalities occurring with a frequency of 1 in 5000 years” (N=50 and F=2 x 10-4 per year). The minimum (broadly acceptable) risk line is simply assumed to be two orders of magnitude lower.
This is considered to provide a useful guidance on the acceptability of societal risk, although it should be emphasized that the criteria are not as widely accepted as individual risk and should be used as guidance only.
[pic]
Figure A- 2: An interpretation of UK HSE Societal Risk Criteria (F-N Curve)
-----------------------
Nubaria-Metnama
Natural Gas Pipeline,
Egypt
E2818 v7
QUANTITATIVE RISK ASSESSMENT
June 2011
Final Report
4
5
6 Dahshour-Atfeeh and Nubaria-Metnama gas pipelines, Egypt
RESETTLEMENT POLICY FRAMEWORK
Draft Report
February 2011
Room 4
Room 3
Room 2
Room 12
Room 11
North Giza Power Station
Room 7
Room 8
Al-Nubaria Power Station
Room 10
Room 9
Room 6y 2011
Room 4
Room 3
Room 2
Room 12
Room 11
North Giza Power Station
Room 7
Room 8
Al-Nubaria Power Station
Room 10
Room 9
Room 6
Room 5
Room 1
Figure 2-2: Wind rose of North Giza (wind speed in Knots)
Badr
Darawah
Izbt Ar-Raml
Al-Shurfa Al-Gharbia
Al-Baradah
Sheshaa
Izbt As-Sukhna Al-Jadida
Kafr Mansur
Izbt Jamal Al-Faransawi
Izbt Sidi Ibrahim
Izbt Masjid Ar-Rahman
Al-Iman
Umar Makram
Umar Shahin
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Izbt Masjid Ar-Rahman
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Al-Baradah Village
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Izbt Masjid Ar-Rahman
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Izbt Sidi Ibrahim
Izbt Jamal Al-Fransawi
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Kafr Mansur
Al-Baradah
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Izbt As-Sukhna Al-Jadida
A
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Izbt Masjid Ar-Rahman
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Izbt Sidi Ibrahim
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Izbt Jamal Al-Fransawi
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Kafr Mansour
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Darawa Village
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
NG Pipeline
1 x 10-6 Risk Level
5 x 10-7 Risk Level
Al-Baradah
Al-Baradah
................
................
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