This document outlines the quantitative risk assessment (QRA) methodology used to identify and quantify hazards and risks from a natural gas pipeline. The QRA methodology includes: 1) identifying hazards such as fires, explosions, and toxicity exposures; 2) determining base and modified failure frequencies from industry databases; 3) analyzing consequences using simulation software to model hazards; 4) evaluating and summarizing risks; and 5) recommending risk mitigation measures such as emergency response planning, monitoring systems, and procedure updates. The QRA provides a framework to minimize risks and hazards from the natural gas pipeline.

1. Quantitative Risk Assessment
Methodology

2. Introduction
Purpose of QRA:
1. Identify and quantify hazards and risks
2. Determine individual risks (IR)
3. Recommend measures to minimize/eliminate
hazards/risks
4. Facilitate development of emergency response plans

3. Types of Hazard Zones Criteria
 Fire (Thermal Radiation)
- 37.5kW/m2 heat radiation hazard zone (1)
- 4kW/m2 heat radiation hazard zone (2)
- 3% fatality / 500 Thermal Dose Unit (for a fire < 30secs)
 Explosion (overpressure)
- 5psi, 1psi and 0.5psi
 Toxicity Exposure
- 3% fatality
Note:
1) Heat load capable of causing damages to equipment
2) Unbearable pain to human being upon exposure

4. QRA Hazard Zones Criteria

5. Individual Risk Criteria

6. Requirements of QRA Report
1. Hazard Identification
2. Base Frequency
3. Modified Frequency
4. Consequence Analysis
5. Risk Summation and Evaluation
6. Recommended Risk Mitigation

7. QRA Methodology

8. 1. Hazard Identification
 Hazards of natural gas
 Occupational hazards
 Other hazards:
 Earthquake
 Lightning
 Aircraft crash
 Heavy vehicle impact
 External fire

9. Hazards of Natural Gas
JF = jet fire, FF = flash fire, EX = explosion

10. 2. Base Frequency
From UKOPA Pipeline Fault Database

11. 3. Modified Frequency
 Based on BSI PD 8010:3-2009
 Physical Risk Mitigation Measures:
 Wall thickness and design factor
 Slabbing
 Depth of cover
 Procedural Risk Mitigation Measures:
 Additional surveillance
 Additional liaison visits
 Additional high visibility pipeline marker posts

12. 3. Modified Frequency

13. 3. Modified Frequency

14. 4. Consequence Analysis
• Jet Fire vs. Flash Fire
• Explosion vs. Fire
Using DNV PHAST 6.53.1

15. Fire (Thermal Radiation)

16. Explosion (Overpressure)

17. 4. Risk Summation & Evaluation

18. 5. Recommended Risk Mitigation
 Provide adequate ventilation
 Install suitable gas monitoring system
 Update relevant operating procedures e.g. maintenance
and inspection
 Update Emergency Response Plan (ERP)
 Communicate updated procedures and ERP to
maintenance personnel