Gerald Laheij | March 8 th 2006

1. Gerald Laheij | March 8th 2006 Risk assessment on pipelines The Dutch approach Workshop UN ECE

2. High pressure natural gas pipelines Total length: 12000 kilometre Main transport pipelines • 18- 48 inch (66 bar) • Average depth of cover 1.75 meter Regional transport pipelines • 2-16 inch (40 bar) • Average depth of cover 1.2 meter Workshop UN ECE

3. Prevention of accidents • Risk reduced as much as is reasonably practicable through measures at the source • Number of people exposed is reduced by a risk based zoning policy • Individual risk, creates distance between potential hazardous source and its surroundings • Societal risk, limits the population density around the potential hazardous source

4. Risk measures Individual risk • Chance that an unprotected person residing permanently at a fixed location is killed as a result of an accident • Presented as risk contours on a map • Limit for dwellings and vulnerable destinations, guidance value for less vulnerable destinations (10-6 per year) Workshop UN ECE

5. Risk measures Societal risk • Chance that in a single accident a certain number of victims is exceeded • Presented in a F-N curve • Justification of new developments • Guidance value, per km pipeline Workshop UN ECE

6. Standardised method Guidelines for quantitative risk assessment (QRA) are given in the Purple Book • loss of containment events • source term and dispersion • exposure and damage • calculation and presentation of results Guideline is reviewed, use of a single computer code Workshop UN ECE

7. Current building distances • Building distances derived in 1984 • Building distance depends on diameter, pressure of pipeline, and vulnerability of objects (4 – 60 meter) • Construction (wall thickness) of new pipelines depends on area classification • Building distances are currently under revision Workshop UN ECE

8. Loss of containment • Full bore ruptures dominate the risk of natural gas pipelines • External interference main cause of failure • Failure frequency depends on depth of cover and wall thickness Workshop UN ECE

9. Source term and dispersion • Pipeline rupture results in vertical jet which can ignite • Source term, average release (first 20 seconds) • Exposure dominated by effects of heat radiation Workshop UN ECE

10. Probability of ignition • Casuistic available for rural areas, depends on diameter and pressure (5-80%) • Influence build-up area not known • Large scale experiments are planned

11. Consequences Example for a 12 inch pipeline Workshop UN ECE

12. Additional measures Building distances (1984) normative distance for new building developments, additional measures at source may be necessary • Obligatory one-call system • Supervision of pipeline operator (dangerous substance) • Concrete slabs and warning tapes • Warning marks, camera surveillance For new pipelines depth of cover and wall thickness are chosen such that distance to individual risk contour of 10-6 per year is less or equal to building distance of 1984. Workshop UN ECE