Responding to comments on its report on methods for evaluating the hazards of LNG leaks from tankers, FERC staff said it was modifying certain analysis elements and would continue to use updated methodologies in individual cases as new technical information becomes available.

The staff paper was made public Wednesday, responding to a torrent of comments criticizing the methodologies set out of either seriously underestimating or overestimating on the very controversial topic of the hazards of LNG tanker accidents or attacks (see Daily GPI, June 2 and June 3 ). It was clear from the comments there was some misunderstanding of the scope and intent of the very technical report. Staff stressed that the initial report,”Consequence Assessment Methods for Incidents Involving Releases from Liquefied Natural Gas Carriers,” prepared for FERC by ABS Consulting Inc. (AD04-6), was simply to recommend modeling methods to be used in the review of proposed LNG import facilities and was not meant to set generic standards for locating import terminals.

FERC staff noted that possible “worst case” scenarios for an LNG vessel accident or attack described in the report were not meant to set the limits for location of a facility “given the conservatisms in the models and the level of damage required to yield such large scale releases… Rather the ‘worst case’ scenarios provide guidance in developing the operation restrictions for LNG vessel movements within each shipping channel, as well as in establishing potential impact areas for emergency response and evacuation planning.” Actual relevant and credible worst case scenarios have and will be used in individual cases.

The report was on methodologies, Staff emphasized, and the size of the holes in the tankers used in the analysis was taken from other studies and was not meant to set a range of damage scenarios. A study by Lloyds Register North America and other studies currently under way examine credible ship damage and effects. Likewise the probability of potential incidents or the ongoing operation of existing LNG import terminals are not within FERC’s jurisdiction. “The operational safety of LNG ships is under the jurisdiction of the U.S. Coast Guard,” which has stated it believes LNG tanker operations continue to be safely conducted in U.S. ports,” the staff paper said.

The study is a starting point in developing consequence assessment methodology that will be modified as additional research becomes available, the staff response said. “In effect, the development of our consequence models will be ongoing.” As to whether the assumptions in the analysis were overconservative or underconservative, the Commission staff said “the lack of large-scale historical incidents and the need to extrapolate small-scale field test data lead to the use of conservative assumptions.”

Responding to technical questions raised, staff said it was modifying portions of the analysis: “The orifice discharge coefficient for calculating spill rates has been changed from 1.0 to 0.65; the approximate pool shape of an uncontained LNG spill on water is now represented as a semicircle instead of a circle; the estimated effects of friction between the LNG pool and the water surface on pool spread have been reduced; the relationship between decreasing spill rate and pool size has been refined; the rate of heat influx from water has been set at 85 kW/m2; and the solid flame model has been modified to represent a two-zone pool fire.”

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