LNG Tanker Safety
LNG tank ships are designed with safety and security in mind. They must meet tough international and U.S. Coast Guard standards. These are high-tech ships, using special materials and designs to safely handle the very cold LNG. Most ships have two hulls, in effect a double ship that protects the cargo in the event of a collision, grounding, or a terrorist act. Even before the ship construction has begun, government safety experts review the plans. The ships are inspected during construction and are periodically inspected after completion. International and US Coast Guard rules cover just about every safety feature of these ships, as well as crew training standards.
Everyone involved in liquefied natural gas transportation takes safety very seriously. There are many lives and a great deal of money at stake. Government and industry work together to make sure these ships are designed, maintained, and manned with safety in mind; industry maintains them with oversight by periodic government inspection, and government sets the standards for crew training. This has resulted in an outstanding safety record. Over the last 30 years, there have been about 33,000 LNG voyages worldwide, and on none of these has there been a significant LNG spill. Currently, there are approximately 180 LNG ships with about 110 more being built. They are so well designed that, even when a submarine surfaced directly under an LNG ship, there was no damage to the LNG tanks, even though there was damage to the tank ship's bottom.
No fuel or petroleum product is completely safe: not coal, oil, or liquefied natural gas, all of which are carried on ships. LNG is a fuel, and, when it becomes a gas and mixes with air, it will burn. One can never consider anything that burns completely safe, even fairly innocuous materials like wood and cooking oil. But some are worse than others, and liquefied natural gas is far from the worst. When LNG vapor reaches an open flame, it easily catches fire and will burn everything within the vapor-air mixture; the same as when natural gas burns. Due to the extra care in designing, maintaining, and operating LNG ships, they all have excellent safety records. There have been some fires at shore facilities, but those are rare events. However, if a ship catches fire, it could be very serious. That's why the LNG industry and the Coast Guard are very careful about the movement of liquefied natural gas.
LNG contains a great deal of energy, but so does a pile of coal. The claim that LNG tankers contain more energy than 50 atom bombs and are attractive terrorist targets is based on the incorrect and misleading premise that the magnitude of an explosion can be estimated based on the available chemical energy. Following the same logic, a tanker full of wood could also be said to contain the chemical energy of multiple atom bombs.
LNG is a liquid that won't burn until it becomes a vapor, and the vapor won't burn until it mixes with air and becomes diluted to between 5 percent and 15 percent LNG vapor in air. Above 15 percent, there's not enough air for it to burn, and below 5 percent, there's not enough LNG vapor to burn. LNG vapor clouds burn when they are in the 5-15-percent dilution range, but they don't explode. US Coast Guard tests have demonstrated that unconfined LNG vapor clouds do not detonate, they only burn.
In 1941 the first commercial LNG plant was built in Cleveland, Ohio. This plant ran without incident until 1944. That year, the plant expanded and added an additional LNG tank. This tank was added during World War II, when stainless steel alloys were scarce. Therefore, low-nickel alloy (3.5-percent nickel) was substituted in the construction of the tank. Low-nickel steel does not have the same properties as stainless steel, and, shortly after going into service, the tank failed.
At the time of failure, the tank had been filled to capacity, and the failure caused the contents of the entire tank to be emptied into the streets and sewers of the surrounding city. When the vapors from this spill ignited, the ensuing fire engulfed the nearby tanks and surrounding areas. Within 20 minutes of the initial release of LNG, a second spherical tank failed, due to the weakening from the fire. During the entire incident, 128 people were killed, 225 were injured, and 475 surrounding acres were directly impacted.
Since the Cleveland event, there are only four other land-based LNG incidents that resulted in any fatalities. The incidents occurred in Arzew, Algeria, 1977; Cove Point, Md., 1979; Bontang, Indonesia, 1983; and Skikda, Algeria, 2004. These fatalities were strictly limited to plant and facility personnel. The incidents caused no damage or harm to people of the surrounding community.
The January 19, 2004, explosion at the Skikda, Algeria, liquefaction facility impacted approximately 2 percent of the world's liquefaction capacity and caused 27 fatalities. The Skikda accident was caused by a hydrocarbon leak of unknown origin, which was ingested into the boiler of the liquefaction line. The boiler explosion is believed to have initiated a larger explosion.
The safety record for LNG transportation by vessel has a history that is enviable by almost all other heavily transported dangerous commodities. Since 1959, when the commercial transportation of liquefied natural gas began, there has never been a shipboard death involving liquefied natural gas. The LNG tank ship fleet of 180 carriers has safely delivered over 33,000 shiploads, while covering more than 60 million miles. As of 2006, eight marine incidents worldwide had resulted, involving the accidental spillage of liquefied natural gas. In these cases, only minor hull damage occurred, and there were no cargo fires. Seven additional marine-related incidents have occurred, with no significant cargo loss.
In the worst grounding accident of a loaded LNG tanker, the El Paso Kayser ran onto rocks and grounded at 19 knots in the Straits of Gibraltar in June 1979, loaded with 99,500 m3 of LNG. The Kayser suffered heavy bottom damage over the whole length of the cargo spaces, as well as flooding to the starboard double bottom and wing ballast tanks. However, the membrane cargo containment was not breached, and no liquefied natural gas was spilled.
In 1984, during the Iran-Iraq war, three Maverick missiles were launched from an aircraft at the Gaz Fountain, a prismatic tanker that was carrying butane and propane. Although the attack caused a fire, the tanker survived this intentional attack.
Some cargoes are more hazardous, and some are less. Some cargoes are so bad that the Coast Guard doesn't allow them on tank ships. Liquefied chlorine is an example of one of these that the Coast Guard will not allow on tank ships, because it is too dangerous. On the other hand, the Coast Guard allows gasoline in tanks that are built to much less stringent design requirements than liquefied natural gas tanks. Because LNG's hazards are in between gasoline's hazards and liquefied chlorine's hazards, the Coast Guard allows it on tank ships (unlike chlorine) but with strict safety measures (more than those for gasoline).
LNG ships have emergency shutdown systems that can identify potential safety problems and shut down operations. This significantly limits the amount of liquefied natural gas that could be released. Fire and gas detection and fire fighting systems help address the risk of fire. Special operating procedures, training, and maintenance further contribute to safety. LNG vessels also have equipment to make ship handling safer. This equipment includes sophisticated radar and positioning systems that enable the crew to monitor the ship's position, traffic, and identified external hazards. A global maritime distress system automatically transmits signals if an onboard emergency occurs that requires external assistance. In addition, some LNG ships use velocity meters to ensure safe speeds when berthing. When moored, automatic line monitoring helps keep ships secure. When connected to the onshore system, the instrument systems and the shore-ship LNG transfer system act as one, allowing emergency shutdowns of the entire system both from ship and from shore.
The most likely hazards to people and property would be thermal hazards from an LNG fire. Cryogenic and fire damage to an LNG ship were also identified as concerns that could cause additional damage to LNG cargo tanks following an initial cargo tank breach, though the additional impact on public safety would be limited.
Accident events resulting in the spillage of 12,500 m3 of are expected to provide an ignition source, such that a pool fire occurs and the likelihood of a large unignited release of LNG is unlikely. The 37.5 kW/m2 and 5 kW/m2 values are thermal flux values commonly recognized for defining hazard distances for LNG. The 37.5 kW/m2 is a level suggesting severe structural damage and major injuries if expected for over 10 minutes. The 5 kW/m2 is a level suggesting second-degree skin burns on exposed skin if expected for periods of over about 20 seconds, and is the value suggested as the protection standard for people in open spaces. The lower flammability limit (LFL) is the lowest level at which liquefied natural gas will burn. This value is commonly used as the maximum hazard distance for a vapor dispersion fire. The results suggest that thermal hazards will occur predominantly within 1600 meters of an LNG spill, with the highest hazards generally in the near field (approximately 250-500 meters of a spill). While thermal hazards can exist beyond 1600 meters, they are generally lower in most cases.
Nonetheless, the estimate of two to three miles of flammable vapor cloud travel that could result from an unignited spill of LNG from a single containment is at once reasonable and sufficient for regulatory planning purposes. Indeed, given the uncertainties involved, the point of diminishing returns has been reached on this scenario for vapor dispersion from a 12,500 m3 LNG spill on water.
A number of international and US safety and design standards have been developed for LNG ships to prevent or mitigate an accidental LNG spill over water. These standards are designed to prevent groundings, collisions, and steering or propulsion failures. They include traffic control, safety zones around the vessel while in transit within a port, escort by Coast Guard vessels, and coordination with local law enforcement and public safety agencies. These efforts have been exemplary, and, in more than 40 years of LNG marine transport operations, there have been no major accidents or safety problems either in port or on the high seas.
After the 9/11 terrorist attacks occurred, concern over liquefied natural gas (LNG) carriers rose as these were feared to be prime targets for terrorists. In fact, as an immediate precaution the LNG terminal near Boston, owned by Tractebel, was temporarily shut down pending an evaluation of security measures and the risks associated with bringing LNG tankers into Boston Harbor.
The Everett LNG import facility was located in a densely populated area, and vessels transiting to that facility passed through a restricted waterway that converged with waterfront businesses, residential communities, and Logan International Airport. The local fire chiefs of Everett, Chelsea, and Boston had unsuccessfully fought the siting decision for the facility in the 1970s when the plant went into operation. The safety concerns they had at that time were translated to security concerns and revisited with a new eye toward "malicious intent."
Eventually, additional security measures were implemented and the facility was reopened, but security concerns raised by local communities have become a major issue for many of the proposed shore-side LNG terminals. Since September 11, 2001, additional security measures have been implemented to reduce the potential for intentional LNG spills over water. They include earlier notice of a ship's arrival (from 24 hours to 96 hours), investigation of crew backgrounds, at-sea boardings of LNG ships, special security sweeps, and positive control of a liquefied natural gas ship during port transit.
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