COLLEGE STATION, Texas, Nov. 18, 2008 – Tankers transporting liquefied natural gas (LNG) have yet to experience a major accident but with more of the energy source being transported than ever before and in a post-Sept. 11 environment, preparing for a potential disaster is critical, says a Texas A&M University authority on disaster mitigation and process safety.
Spearheading a collaboration of more than 40 experts from industry, academia and various regulatory agencies, M. Sam Mannan, professor in the Artie McFerrin Department of Chemical Engineering, is working to develop models that can help predict the behavior of the intense fires resulting from a potential LNG tanker spill.
The group’s findings are detailed in a white paper developed by the Mary Kay O’Connor Safety Process Center, of which Mannan serves as director. The paper, which is the result of a workshop sponsored by the Center for Liquefied Natural Gas, is available to a variety of private entities and regulatory agencies and can be downloaded at http://psc.tamu.edu/links/lng-white-paper-on-pool-fire-modeling.
Liquefied natural gas is natural gas that has been cooled to the point that it condenses to a liquid. That process reduces its volume by about 600 times, making it more economical to transport. For a fire or hazardous situation to occur, LNG must be ignited after first vaporizing and mixing with air in the proper proportions. That conversion can happen very quickly once a spill occurs, Mannan said.
“With LNG, as soon as you release it into the environment it starts to evolve vapor because of its chemical properties,” Mannan explained. “That vapor is the problem, as it is what creates the fire.”
While the United States has federal regulations in place that address potential spills from land-based LNG facilities, regulations do not exist for LNG spills on water, despite the primary mode of transportation being sea-faring vessel, Mannan said.
He believes much of this can be attributed to the fact that large-scale transportation of LNG has not occurred until recently. Increased worldwide demand for energy has resulted in greater amounts of LNG being transported with greater frequency between continents, Mannan noted. In addition, little thought was given to the possibility of an intentionally caused catastrophic release of LNG from a tanker prior to Sept. 11, Mannan said.
The result has been a void of knowledge when it comes to understanding how these potential fires will react with their environment if they occur over water, he said. It’s a troubling scenario if the spill is intentionally caused in a populated coastal area. That’s why Mannan’s group went to work, producing detailed mathematical calculations that explain and project the behavior of these fires.
“I think it’s very important to have something like this laid out not only for the science discussed but to give people in industry and government a way of doing the right calculations for these fires,” Mannan said. “I think it sets the stage for not only people to understand what it is we can do today based on the available knowledge but also what future direction we need to take.
“I think it would irresponsible of us to wait for an incident to happen. We have to find the knowledge to understand these potential phenomena better.”
Working to develop a consensus approach in modeling these potential fires, Mannan said the group examined numerous factors, including the size of the spill, its dispersion in water and the intensity of the heat radiation generated from a fire if the spill is ignited.
These are all aspects of a pool-based LNG fire that will vary greatly from one that occurs over land, Mannan explained.
“The heat transfer characteristics are going to be different between a land-based spill and a spill on water,” he said. “The water itself, depending on the temperature, may cause the LNG to vaporize faster.”
Another difference, he said, is in the containment of such spills. Mannan pointed out that a LNG spill on land would most likely be from a storage tank built to engineering standards and also contained within a diked area that would limit the spill. However, a water-based spill wouldn’t be contained as easily since tankers obviously can’t be diked.
While the complexities of water-based LNG spills have been recognized by various groups in industry and government there has been little agreement on a systematic, structured approach for addressing such scenarios, Mannan said. He believes the findings and calculations provided by his group will help change that.
“If you have knowledge of how big a spill could be and what the consequences could be, then you can develop a prevention program to prevent that from happening in the first place,” Mannan said. “But more importantly, once we know the nature of the spill and the consequences then we can do planning with regard to response. Whether it’s intentional or unintentional, this could happen, and we want to know how to respond to it.”
-30-
Contact: M. Sam Mannan at (979) 862-3985 or via email: mannan@tamu.edu or Ryan A. Garcia at (979) 845-9237 or via email: ryan.garcia99@tamu.edu
