Over the past decade, the United States has become a major producer of natural gas. As a result, federal regulators have approved the construction of new liquified natural gas (LNG) export terminals on the Atlantic and Gulf coasts that were built using standard industry safety calculations. Engineers all over the world are now saying those calculations grossly underestimate the potential force of a vapor cloud explosion.
The threat of a vapor cloud explosion comes from the heavier hydrocarbons (knows as refrigerants) that the export terminals use to chill the natural gas until it turns into a liquid. A typical export terminal may have 50-tons of refrigerants on site. A leak occurring when there is no wind is the most dangerous because the vapor that forms as the liquid evaporates won’t disperse. It will gather in a ground-hugging cloud that will continue to grow until the leak stops or all the liquid spills. At that point, any spark could cause a catastrophic explosion.
Jerry Havens, retired director of the Chemical Hazards Research Center at the University of Arkansas, said “If something doesn’t get corrected, there might be some terrible accidents.” Despite his efforts to raise alarms about this potential danger for over five years, he said “I can’t get anybody to do anything about it.”
PHMSA issued a statement that said, in part, “The agency keeps safety at the forefront as we review LNG facility applications and operations — including factoring in the most up to date hazard modeling — and ensuring operators are doing the same. Our work over the last few years on VCE [vapor cloud explosions] has continued and evolved with broad input from researchers and stakeholders….Regulations are one tool in PHMSA’s toolbelt to ensure safety in the design and operations processes — and under new leadership we have been immediately focused on building out our capacity to more quickly develop and implement new regulations. This is particularly important given the dozens of new regulatory mandates passed in the bipartisan PIPES Act of 2020 (last December) — with updates to the LNG facilities rules being one of our top regulatory priorities.”
PHMSA has already approved the safety plans for three proposed LNG export terminals. During the permit process, all three projects submitted calculations that addressed vapor cloud explosions from small potential spills but critics feel they lowballed the shock wave emanating from the blast.
The dynamics of a vapor cloud as it forms and spreads, and the calculation of overpressures, can seem dauntingly arcane. Engineers even have different words for different potential explosions, which are determined by the amount of vapor involved, and act differently. Industry calculations are based on weaker “deflagrations.” Critics worry about much stronger “detonations.”
Vapor clouds with a diameter exceeding 100 meters, or about 110 yards, are especially dangerous, based on a survey of a representative selection of incidents, HSE, the British agency, said in a statement provided to The Post. It is difficult to find examples of such a large cloud that did not explode. “There may be an element of underreporting, especially where no one is killed, but it still seems appropriate to work on the basis that there is a fairly high probability of explosion for these very large vapor clouds,” it said.
The statement suggested that the model used to assess explosion risks is not fundamentally flawed but is only as good as the assumptions made by its users, regarding not only the size of the vapor cloud but its turbulence, the speed with which it forms and the probability of ignition, among other factors. “Experience has shown,” the statement said, following on a 2019 study, that different users “can produce quite different results for the same scenario.”
The model is a subset of a software program called FLACS, for Flame Acceleration Simulator, developed by a company called Gexcon. The sub-model for vapor cloud explosions has been dubbed Q9, and this is what has drawn critics’ attention.
Vincent Tam of Warwick University in Britain was the lead author of a paper critical of Q9 published this year in Eng, a peer-reviewed journal. “The results in this paper showed that Q9 systematically underpredicts” the force of vapor explosions, he wrote.
In a follow-up email, Tam wrote that industry risk assessments usually do not consider windless conditions because modeling them is too difficult. (Both the San Juan and Venezuelan explosions occurred in what engineers call nil-wind situations.) PHMSA said it is reviewing Tam’s paper.
Gexcon points to studies by former company engineers that support the Q9 model. One of those engineers, Filippo Gavelli, used Q9 in writing the vapor cloud sections of environmental impact statements for several proposed LNG terminals. He now works for Blue Engineering and Consulting, in Ellicott City, Md.
“Every hazard modeling tool that Blue utilizes has been widely used worldwide and accepted by numerous regulatory agencies,” Gavelli wrote in an email. “Blue’s work products comply with all federal regulations and applicable codes and standards.” – By Will Englund for The Washington Post.
Engineers raise alarms over the risk of major explosions at LNG plants
