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Study examines Cook Inlet marine mishaps Oil tankers have ‘lowest baseline spill rate’ of vessels plying inlet, but they pose top spill risk, says citizens council report Wesley Loy For Petroleum News
The Cook Inlet Regional Citizens Advisory Council has released a new analysis of vessel accidents and spills as part of an ongoing maritime risk assessment project.
Not surprisingly, the study found that crude oil and petroleum product tankers pose the greatest risk in Cook Inlet.
“Tank ship risk is primarily attributed to their greater oil capacity and their concentrated operations in the middle region of the inlet. They also showed a high likelihood for a structural failure,” concludes the study from contractor The Glosten Associates of Seattle.
The report, titled “Spill Baseline and Accident Causality Study,” builds on a previous report examining Cook Inlet vessel traffic. The Cook Inlet RCAC released the vessel traffic study in February.
Hundreds of scenarios The Cook Inlet RCAC is a Kenai-based, congressionally mandated organization formed after the 1989 Exxon Valdez oil spill in Prince William Sound. The council says its mission is promoting safe marine transportation and oil facility operations in Cook Inlet.
The Glosten study examines 16 years of data, from 1995 through 2010, on spills and the types of incidents leading to spills in Cook Inlet. During that period, 121 incidents occurred involving all sorts of vessels, from tankers to tugs to barges to offshore supply boats. Of these 121 incidents, 60 involved spills, the data show.
The study’s authors analyze incident and spill rates according to vessel type and then forecast spill risk as far out as the year 2020.
They run hundreds of spill scenarios using a range of factors: vessel type, incident type, location in Cook Inlet, whether vessels are moving or moored, whether ice is present in the inlet, the type of oil aboard the vessels, and spill volume. The researchers also consider the positive effect of the shift to double hulls for tankers and tank barges.
Incident types include allision (one ship striking another), bilge discharge, collision, equipment failure, fire, drift grounding, powered grounding, operations error, structural failure or transfer error.
Low spill rate, high risk “The workboat vessel type had the highest baseline spill rate: 0.96 spills per year,” the study found. “Tank ships have the lowest baseline spill rate, but have the most risk from an oil spill in Cook Inlet.”
The Cook Inlet vessel traffic study released in February tallied 480 ship port calls or transits during 2010, with 15 ships accounting for 80 percent of them. These ships regularly called at Homer, Nikiski or Anchorage, the state’s largest city.
The 15 ships included five oil tankers — the Overseas Boston, the Overseas Martinez, the Overseas Nikiski, the Seabulk Pride and the Seabulk Arctic — operating between the Drift River oil terminal on the west side of Cook Inlet and the Nikiski community on the east side, home to the Tesoro refinery.
Find the spill baseline, accident causality report as well as the vessel traffic study at www.cookinletriskassessment.com.
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