A Spill Risk Assessment of the Enbridge Northern Gateway Project
A Spill Risk Assessment of the Enbridge Northern Gateway Project
A Spill Risk Assessment of the Enbridge Northern Gateway Project
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Appendix A -‐ Detailed Summary <strong>of</strong> ENGP <strong>Spill</strong> <strong>Risk</strong> Analysis<br />
This appendix provides a detailed summary <strong>of</strong> <strong>the</strong> methodologies used by <strong>Enbridge</strong> and its<br />
consultants to estimate spill likelihood for ENGP tanker, terminal, and pipeline spills. This<br />
summary relies on <strong>the</strong> same regulatory documents referenced in section 3 in <strong>the</strong> main<br />
body <strong>of</strong> <strong>the</strong> report.<br />
1. <strong>Spill</strong>s from Tanker Traffic Accessing Kitimat Terminal<br />
DNV determines spill return periods for tanker traffic accessing Kitimat Terminal in <strong>the</strong><br />
Marine Shipping Quantitative <strong>Risk</strong> Analysis prepared for <strong>the</strong> Nor<strong>the</strong>rn <strong>Gateway</strong> <strong>Project</strong><br />
on behalf <strong>of</strong> <strong>Enbridge</strong>. DNV uses a per-‐voyage methodology to forecast spills in <strong>the</strong><br />
marine shipping QRA based on nautical miles (nm) travelled by tankers within <strong>the</strong><br />
study area. The methodology consists <strong>of</strong> <strong>the</strong> following steps:<br />
• Determine base incident frequencies per nm<br />
• Apply scaling factors to base incident frequencies to adjust for local conditions<br />
• Determine conditional spill probabilities from an assessment <strong>of</strong> incident<br />
consequences<br />
• Calculate unmitigated spill return periods based on scaled incident frequencies<br />
and conditional probabilities<br />
• Conduct sensitivity analysis<br />
• Identify mitigation measures and recalculate spill return periods based on<br />
mitigation<br />
Base Incident Frequencies<br />
As part <strong>of</strong> <strong>the</strong> per-‐voyage methodology, DNV determines base incident frequencies from<br />
historical tanker incident data and uses various assumptions to estimate incident<br />
frequencies per nm. DNV determines frequencies for international tanker incidents<br />
based on data from Lloyds Register Fairplay (LRFP) for <strong>the</strong> period 1990-‐2006<br />
(Brandsæter and H<strong>of</strong>fman 2010 p. 5-‐49). DNV examines four types <strong>of</strong> potential<br />
incidents associated with tanker traffic:<br />
1. Powered and drift grounding, whereby a tanker runs aground ei<strong>the</strong>r with<br />
functional mechanical and navigation equipment (powered) or as a result <strong>of</strong><br />
failed propulsion equipment (drift)<br />
2. Collisions, whereby <strong>the</strong> navigational failure <strong>of</strong> one or both vessels results in a<br />
collision<br />
3. Foundering, whereby a tanker sinks due to structural failure <strong>of</strong> <strong>the</strong> hull from<br />
wea<strong>the</strong>r or structural defects<br />
4. Fire and/or explosion.<br />
As shown in Table A-‐1, DNV calculates LRFP incident frequencies per nm based on <strong>the</strong><br />
following assumptions <strong>of</strong> <strong>the</strong> average distance travelled by a tanker per year for each<br />
tanker incident type:<br />
84