Abstract
On September 27, 2001, the liquefied natural gas (LNG) tanker Matthew, operated by a Norwegian shipping company, was denied entry into Boston Harbor, where it had a scheduled delivery. “One of my functions,” explained Coast Guard Port of Boston Captain Brian Salerno, “is to provide for safe and secure transportation of maritime traffic in Boston Harbor. Since September 11 the dynamics of that role have changed.” But what are the connections between the dangers of shipping LNG and terrorism?
There are only four LNG import terminals in the United States: Chesapeake Bay, Maryland; Lake Charles, Louisiana; Elba Island, Georgia; and Everett, Massachusetts. Tankers traveling to Everett, in Boston Harbor, pass near heavily populated areas. Along both inbound and outbound routes, LNG ships travel within several hundred yards of the Boston waterfront, past the end of the Logan International Airport runway from which two planes left for the World Trade Towers, and under a busy bridge. Even now, ships coming into Everett are subjected to greater scrutiny than before September 11.
LNG is already a major source of energy in Japan and Korea, and its use appears to be again increasing in the United States. The remoteness of the world's primary gas reserves means that large amounts of gas are transported across the oceans. Although underwater pipelines are used in some locations, transoceanic movement of liquefied gas is primarily by ship. As many as a dozen new import terminals are planned in the continental United States, and the infrastructure to supply those terminals is largely complete in the Middle and Far East.
The LNG carrier Matthew passes under the bridge at Boston Harbor.
The last time there was so much interest in LNG was in the 1970s, when the four current continental U.S. LNG import terminals were built. At that time three terminals were also proposed for southern California alone–at Los Angeles, Point Conception, and Oxnard. From environmental and health impacts to the consequences of a catastrophic event, each site was evaluated on the basis of public safety. The studies identified four areas of concern for catastrophic accident events:
vapor cloud explosions,
pool fires on the surface of the water or on land,
flammable vapor clouds that can form if a spill does not ignite immediately, and
rapid phase transition (RPT) accidents from rapid mixing of LNG with water.
The three California projects were shelved for economic reasons along with their safety studies, but not before raising public concern. As a result, Congress authorized approximately $40 million to study the four catastrophic scenarios.
Assessing the danger
In the 1970s I took a sabbatical from the University of Arkansas and spent a year as a technical adviser to the Coast Guard's Office of Merchant Marine Safety in Washington, D.C. I was soon assigned to review several predictions, then the subject of congressional hearings, of the vapor cloud hazards that might follow the nearly instantaneous release of LNG onto water from a single ship-board storage tank. A typical tank contained (then as today) approximately 6.5 million gallons of LNG.
At that time the Coast Guard had been advised that a hazardous vapor cloud from this type of spill could extend as far as 75 miles. Updated estimates have reduced the risk area to under 10 miles, still indicating the need to use care in the future siting of onshore LNG import terminals. Even the updated models, however, are based on idealized mathematical models that may exaggerate risk.
U.S. regulations spell out the requirements for estimating vapor cloud hazard exclusion distances and fire radiation exclusion distances. The present regulations were not in force when the existing terminals were built, however, and all of the facilities built in the 1970s are operating under the regulations' grandfather clauses. In fact, the regulations only apply directly to the onshore facilities and do not require estimates to be made for catastrophic tanker spills. Further, the regulations covering onshore facilities focus on “credible” scenarios. For example, a less serious “guillotine break” in a large transfer line is much more likely to occur than a tank failure and instantaneous release of gas. As a result, hazard exclusion zones are usually made substantially smaller and often do not extend beyond a plant's boundaries. Such a zone would not be large enough to protect people from one of the low-probability, high-consequence disaster scenarios.
I have continued to study all of these concerns and believe there is a consensus regarding the relative risk of each.
What do we know about the hazards of such pool fires? There have been no experiments with fires of such magnitude. By marine cargo standards, LNG marine carriage is relatively new, and there is no evidence of any pool fires on water larger than experimental spills of about 10,000 gallons performed during the 1970s and 1980s. These experiments resulted in roughly cylindrical fires approximately 50 feet wide and 250 feet high.
Although large-model extrapolations (from 10,000 gallons to 6.5 million gallons) can raise significant questions, it is reasonable to be concerned about the damage potential of such fires. Most predictions suggest that even the largest LNG tankers (typically more than 900 feet in length) might be completely enveloped in a pool fire following a complete spill of a single 6.5 million gallon tank. This raises questions about the vulnerability of the ship and the potential for additional releases. A typical LNG tanker contains as many as five tanks with a combined capacity of 33 million gallons.
We do know some things about such fires. They could not be extinguished and would have to burn themselves out. Unlike some other flammable liquids such as crude oil, the gas would burn itself out only when it was totally consumed. And such fires would be expected to burn more rapidly and with greater intensity than crude oil or even gasoline fires.
After September 11
That's pretty much where the industry stood regarding catastrophic releases of LNG as it entered the new millennium, and nothing changed significantly until the attacks of September 11. As in so many other areas, risk assessment in the LNG business must now include the possibility of terrorism. It's a difficult problem, but something that must be considered in the future siting of LNG terminals.
Before the attacks on the World Trade Towers and the Pentagon, the idea that terrorists would use aircraft to attack targets on the ground was regarded as too unlikely for serious consideration. Today we know this is not the case.
Today, accounting for less probable events such as terrorist attack is, and must continue to be, an important consideration in the planning of LNG facilities. For example, an initial report completed in January of an LNG import terminal proposed for Mare Island, in San Francisco Bay, includes discussion of catastrophic risks as well as consideration of potential terrorist threats. The initial report does not yet incorporate a scientific risk assessment but requires that one be completed if the project enters the next phase. At press time, the Mare Island project appears to be on hold.
For nearly 50 years now, all discussions of risk and probability in LNG transport have focused on how to account for human errors. The new reality is that we must now consider malicious acts as well.
A “direct hit” as shown by Brig. Gen. Vincent Brooks of Central Command.
