.
Site categories

FAQ about Basic Facts, Safety and Security Clarifications of Liquefied Natural Gas

This section is structured in the form of answers to frequently asked questions (FAQ) about LNG posed by those with little or no previous understanding of the LNG industry.

Background of LNG

Liquefied Natural Gas (LNG) is the liquid form of natural gas. LNG is a natural gas, just like the gas produced and delivered by pipelines to energy markets around the world.

It is called liquefied natural gas because it is a liquid. When natural gas is cooled at atmospheric pressure to very low temperatures (about -162 °C, or about -260 °F, depending on the composition of the natural gas) it condenses into a liquid. The critical temperature and pressure of natural gas are around -82 °C and 46 bar, again depending upon the exact composition of the gas.

Natural gas is composed primarily of methane (typically at least 90 %), but may also contain some heavier hydrocarbons such as ethane, propane, or butane, and typically less than 1 % nitrogen. Prior to liquefaction natural gas is typically conditioned to remove any oxygen, carbon dioxide, sulfur com-pounds, other trace impurities (such as mercury), and water. Removal of these impurities eases the handling of the LNG formed by minimizing corrosion or damage to materials used for its containment.

Why LNG?

It typically takes about 600 m3 of natural gas to yield 1 m3 of LNG, with 1 tonne of LNG holding the energy equivalent of some 50,000 cubic ft of natural gas. Exact conversions depend upon the composition of the natural gas in question. It is the large contraction in volume from the gaseous state to the liquid state that makes LNG much easier and more economical to transport over large distances and store in large quantities.

Is LNG explosive?

LNG is not at all explosive or flammable in its liquid state.

What happens when LNG is warmed?

As LNG vapor warms above -160 °F (-106.7 °C), it becomes lighter than air and will rise and disperse rather than collect near the ground. However, it is not explosive unless flammable concentrations of gas occur in enclosed or otherwise confined spaces.

How much energy does it take to make LNG from natural gas?

Typically about 10 to 20 % of gas delivered into an LNG supply chain is consumed in the process and transportation facilities. This is comparable with long-distance high-pressure gas pipelines.

What are the advantages of storing gas as LNG?

LNG facilities offer two clear advantages over alternative gas storage options:

  • Because LNG facilities can be located above ground, operators and/or owners have many more opportunities for locating LNG facilities in comparison with traditional underground gas storage alternatives that depend on underground geological conditions such as depleted reservoirs, aquifers, and salt caverns;
  • LNG facilities are often constructed with a higher degree of “deliverability” (the amount of gas the facility can send out under peak conditions relative to stock in inventory) than traditional underground storage facilities. This deliverability provides the opportunity to meet demand spikes, sometimes called “needle peaks.”

What is the history of LNG?

LNG has been used for more than 50 years, especially in Asia, Europe, and the United States. Improved technology is now making it more economical to produce, transport, and store LNG in large quantities. These economies of scale have opened up wider markets for its use where it can compete effectively on price with other sources of fuel.

LNG fed by gas from large gas fields remote from gas markets has become an increasingly attractive alternative to oil or piped gas (natural gas transported from its country of origin through pipelines). Natural gas as a “clean” source of energy is becoming the fuel of choice or preference in many regions if significant volumes can be brought reliably and at competitive prices into a market enabling it to compete with coal, oil, and petroleum products for power generation and industrial and commercial fuels.

Read also: Fundamentals of Liquefied Natural Gas

There is an increasing need globally for diversification of energy supplies due to politics, eco¬nomics, and reserves. LNG carriers can be diverted to a number of LNG consuming countries easily providing higher confidence in security of supply for major gas-importing nations.

How can we keep LNG cold?

LNG is stored in large insulated tanks that are designed to minimize any heat ingress. The insulation of the tanks, as efficient as it is, does not keep the temperature of LNG at cryogenic temperatures by itself. LNG will stay at near constant temperature if kept at constant pressure. This phenomenon is called auto-refrigeration.

As long as the LNG vapor boil-off is allowed to leave the tank in a safe and controlled manner, the auto-refrigeration process will keep the temperature constant. This vaporization loss is typically collected as it leaves the tank and either reliquefied, sent to the gas line connecting to a gas distribution network, or used as fuel on the site or to power an LNG carrier ship.

What are the differences between LNG and LPG or LNG and NGL?

All are light liquid hydrocarbons that can be used as fuel. To most nonengineers, the terminology is confusing. Liquefied petroleum gas (LPG) is composed primarily of propane (upward of 95 %) and smaller quantities of butane. This is quite different from the primarily methane composition of LNG. LPG is used primarily as residential fuel, petrochemical feedstock and often is used as vehicle fuel. In fact LPG is a cleaner burning liquid fuel than gasoline.

Natural gas liquid (NGL) is a light hydrocarbon mixture that may also consist of ethane, propane, butane and traces of condensate (heavier gasoline range hydrocarbon) components. Ethane can be used for petrochemical production and the remaining portion can be sold as LPG.

LPG can be maintained as a liquid by means of elevated pressure alone or by chilling to tem-peratures to around -40 °C. On the other hand, it is not possible to liquefy natural gas (methane) at ambient temperature even at elevated pressure.
Despite perceived safety concerns, LNG is also safer to handle than LPG in most circumstances. Because LPG is heavier than air, it “hangs” low to the ground if leaks occur in storage facilities. A leaked, low-lying cloud of LPG is more easily ignited than LNG. In contrast, LNG vapor (primarily methane) is lighter than air. As a result, the revaporized gas stream in an uncontained condition typically floats away into the atmosphere and poses a much lower threat of fire or explosion.

What are the sources of LNG?

Qatar, Indonesia, Australia, Malaysia, Trinidad, Algeria and Nigeria are leading exporters of LNG. There are in total some nineteen countries that export LNG. LNG is imported by many countries and in particularly large quantities by Japan and South Korea and some European countries with China and India increasing their demand for LNG quite rapidly.

Growth in LNG applications depends on expansion of current facilities and new construction and infrastructure investment along the LNG supply chains. The industry has experienced growth of some 7.5 % per year for the past 20 years and investment commitments suggest this rate of growth will continue for the next decade at least.

The continued expansion and diversification of LNG supply indicates that sources of LNG will become more readily available in gas consuming markets around the world. The emergence of new LNG import markets in South America (i.e., Argentina, Brazil, and Chile) and the Middle East (i.e., Dubai, Kuwait) in recent years is testament to the diversification of the industry.

Floating regasification and LNG storage units have enabled smaller markets to secure LNG imports quickly (i.e. in less than a year) without building land-based LNG receiving terminals. This approach has now become popular with countries seeking to import occasional or seasonal LNG cargoes.

Demand for LNG is expected to increase as emission restrictions favor gas over coal for power gen-eration, and gas supply companies make inroads into niche markets such as road vehicular fuel, as a marine vessel fuel, and as LNG replaces propane as a fuel for facilities not connected to the pipeline gas grid.

LNG supply chain

The LNG supply chain includes all the facility and equipment involved in taking natural gas from an underground reservoir, liquefying it, and transporting to an end-user customer of natural gas.

That supply chain is typically long in terms of distance and expensive in terms of the capital costs of the equipment and facility involved. The components of the supply chain typically include:

  • Gas field production infrastructure;
  • Feed gas pipeline to gas processing and conditioning plant;
  • A large-scale refrigeration plant involving heat exchangers to liquefy the feed gas;
  • LNG storage and port loading facilities: everything must be kept cold;
  • LNG marine tankers;
  • LNG receiving terminal including port unloading, LNG storage, regasification, and gas sendout compression facilities;
  • Connection to a natural gas transmission and distribution network to deliver gas to customers;
  • In some cases distribution of LNG by truck to small, remote off-grid gas customers.

Can LNG compete commercially with pipeline gas?

Yes. An LNG supply chain (i.e., gas field development, liquefaction plant, transportation by LNG carrier, LNG terminal) is generally set up when pipeline transmission is too expensive due to the long distances involved or the technical/political difficulties of pipeline construction, or to enable the gas to be delivered to more than one geographic market location. LNG supply chains are much more flexible than gas pipelines, being able to serve different markets at different times and to avoid the political and geopolitical instability of transit countries that transcontinental gas pipelines have to deal with.

What are the commercial terms?

In traditional LNG markets, buyers and sellers are generally linked by long-term contracts (i.e., 10 to 25 years duration typically) for predefined quantities of LNG produced in a liquefaction plant and received at an LNG terminal specified in the contract.

There are usually penalties for the customer not taking the contracted quantitiesdtake-or-pay. The contracts usually specify a price often linked to benchmark gas prices or to other fuel (crude oil) prices or inflated from an initial floor price.

Rapidly growing short-term markets are changing this as more uncontracted LNG carrier vessels enter the market. However, the LNG market will remain dominated by long-term contracts for the foreseeable future. Short-term LNG cargo sales amount to about 15 % of the overall LNG supply.

LNG regasification terminals

An LNG regasification terminal is where the LNG is delivered to the end users, which typically comprises the LNG unloading jetty and LNG storage and sendout facility, along with heating to reconvert LNG back to natural gas. The regasification process is a heating process typically using ambient temperature heat sources. Most terminals use seawater for heating, and in some terminals ambient air is also used. In cold climate regions, fuel gas is necessary to supplement heating during the winter months.

The LNG terminals typically unload the LNG shipment in 10 to 12 hours, in order to minimize the docking times for the ships and reduce the operating cost of the ship.

How are terminals designed?

All LNG storage facility designs must comply with stringent regulations as required by national planning legislation codes (e.g., in the United States: the US Department of Transportation (DOT)’s safety standards in Title 49 Code of Federal Regulations (CFR) Part 193dLiquefied Natural Gas Facilities: Federal Safety Standards and National Fire Protection Association (NFPA) 59Ad Standard for the Production, Storage, and Handling of LNG).

In accordance with safety standards, vapor dispersion distances must be calculated to determine how far downwind a natural gas cloud could travel from an onshore storage facility and still be flammable. As required by these regulations, these exclusion zones must not reach beyond a property line where other development could occur.

Since a fire would burn with intense heat, each onshore LNG container and LNG transfer system must also have thermal exclusion zones established in accordance with prevailing safety standards. These exclusion zones must be legally controlled by the LNG facility operator, or a government agency, to ensure adequate separation between members of the public and the heat from a fire.

Seismic design requirements

LNG facilities must meet stringent standards to ensure public safety and plant reliability in the event of an earthquake. Extensive studies of the geological conditions and earth history of a proposed LNG site are required to determine appropriate design loads on the critical components of the LNG plant, such as the design of the LNG storage tanks.

What gas markets do LNG regasification facilities serve?

Some LNG facilities have the flexibility to participate in several markets at once. For example, some fill both base load and peak shaving roles. Some also provide LNG for commercial vehicle fuel which is growing in demand since the LNG fuel cost is significantly less than petroleum fuel that has been escalating in price.

How long can LNG be stored at LNG regasification terminals?

Scheduling for both the arrival of the LNG shipment and the dispatch of the regasified product generally is necessary to maintain an optimum operation of the LNG facility. A balance of multiple sources of LNG supply and storage capacity to match the variations in consumption is essential to minimize the inventory shortages that might be brought about by weather or tanker-scheduling problems.

Typically, the regasified LNG is sent out to customers on a routine schedule under a contract that calls for a set daily volume. Consequently, the LNG may be in storage at a marine import terminal for only a few days and, depending on the terms of individual contracts and the time of the year, is seldom held for more than a few months, unless it is held only for emergency back-up.

What is an LNG peak shaving plant?

Such facilities typically involve a small liquefaction unit linked with a large LNG storage tank and gas sendout facilities to a gas distribution network capable of responding to gas demand peaks or supply crises. However, some peak shaving plants receive their LNG in liquid form by ship or by truck from other LNG facilities and do not have liquefaction facilities of their own.

Typically, gas is taken from a pipeline supply and liquefied and stored as LNG at the peak shaving plant. LNG remains in storage for several months and in most cases is only used to supply the extreme demand periods or needle peaks of just a few days each winter.

Read also: International trade of Liquefied Natural Gas in maritime industry

Peak shaving plants are used by gas utilities and regional pipeline companies as a means of storing gas in liquid form for peak periods and emergency backup. They are usually located at strategic points within the supply network to enable rapid delivery of gas to key markets.

Are there air emissions from an LNG regasification terminal?

During the operation of an LNG regasification terminal, atmospheric emissions are mainly combustion emissions resulting from the burning sulfur-free natural gas.

LNG terminals are typically subject to regulations set by a government environment agency. Authorization for a specified level of emissions is typically granted by such agencies once they are satisfied that best available techniques are being employed in the operation and the terminal to eliminate, minimize, and render harmless any resultant emissions to the environment.

LNG’s safety records

The LNG industry has a long and excellent safety record, due to strict industrial safety standards applied worldwide. Up to 2012 there have been some 50,000 LNG carrier voyages, without a sig¬nificant accident or safety problem (i.e., loss of containment) either in port or on the high seas.

Two major accidents have impacted the LNG industry:

  • Cleveland LNG storage facility, located in the United States, in 1944;
  • and, Skikda liquefaction plant, located in Algeria, in 2004. These incidents are described together in the following, with lessons learned.

In most jurisdictions “safety case” and environmental impact study” reports are required by the government’s regulatory authorities before consent for building an LNG facility is granted. The safety case considers all aspects of management, handling facilities, and operation of the plant, particularly on potential accidents and how major accidents would be prevented. Fires are more likely at lique¬faction plants than regasification terminals, but are extremely rare; for example, a fire shut down the seventh train of the Malaysian MLNG Tiga plant (Bintulu), with a capacity of 3.4 MTPA, for seven months.

As part of the safety case and environmental impact studies, “credible” LNG spill incidents are the subject of risk analyses to review and assess the suitability of the site and the design of an LNG facility and any access waterway and road network. Modern LNG facilities are designed and operated such that persons not involved in the operation of the facility (including ships) that are outside the clearly designated safety and exclusion zones would not be at risk should these credible incidents occur. Rapid response planning to potential incidents by emergency services and training of responders is also part of the safety systems put in place for LNG facilities.

What caused the Cleveland LNG tank failure in 1944?

The East Ohio Gas Company built the world’s first LNG peak shaving facility in Cleveland in 1941. It consisted of three small spherical LNG storage tanks covered by cork insulation and a mild steel outer shell. The tanks were supported by uninsulated mild steel legs. The facility adjoined a residential neighborhood. The facility was run without incident until 1944, when a larger new tank was added. Since stainless steel alloys were scarce because of shortages resulting from World War II, the new tank was built using a toro-segmented design using low-nickel content (3.5 %) alloy steel.

Shortly after going into service, on October 20, 1944, the tank failed. LNG spilled into the street and storm sewer system where vaporizing gas ultimately met an ignition source and ignited. The resultant fire killed 128 people.

The US Bureau of Mines investigation (1946) that followed showed that the accident was due to the low-temperature embrittlement of the inner shell of the cylindrical tank. The inner tank was made of 3.5 %-nickel steel, a material now known to be susceptible to brittle fracture at LNG storage tem¬perature (-260 °F). Had the fourth Cleveland tank been built using appropriate materials, the investi¬gation concluded that the tragic accident would not have happened. LNG tanks constructed around the world of 9 %-nickel steel have never had a brittle crack failure over decades of subsequent operations.

Clearly there is no reason why such an accident should be repeated.

What caused the Skikda liquefaction train fire in 2004?

On January 19, 2004, a leak in the hydrocarbon refrigerant system at one of the natural gas liquefaction units (Train 40) in Skikda, Algeria formed a vapor cloud that was ingested into the inlet of the combustion fan of a steam boiler. The hydrocarbon acted as increased fuel to the boiler causing a rapidly rising pressure within the steam generating equipment. The rapidly rising pressure quickly exceeded the capacity of the boiler’s safety valve and the steam drum ruptured, tearing apart the boiler fire box and housing. The flames from the boiler firebox ignited the leaked refrigerant gas, which was confined by the equipment and structures in the area producing an explosion and an ensuing fire.

The explosion, along with the shrapnel from the ruptured steam drum, caused further damage to the process piping and pressure vessels in the immediate area leading to additional flammable fluid release. The fire took eight hours to extinguish. The explosions and fire destroyed a portion of the LNG plant and caused 27 deaths and injury to 72 more. No one outside the plant was injured nor were the LNG storage tanks damaged by the hydrocarbon explosions.

A joint report issued by the US Federal Energy Regulatory Commission (FERC) and the US Department of Energy (DOE) was issued in April 2004. The findings in that report indicate that:

  • There were ignition sources in the process area;
  • There was a lack of “typical” automatic equipment shutdown devices required by modern design codes;
  • There was a lack of hazard detection devices, which should have provided advanced warning of the refrigerant leak and helped to prevent the explosion.

While Skikda liquefaction trains 10, 20, and 30 had been upgraded in the late 1990s, Skikda train 40 was, in fact, of an obsolete design and scheduled for demolition at the time of the incident. Train 40 was originally built in 1981 and not well maintained. The poor maintenance, obsolete design, and poor general condition of Skikda train 40 suggest that such an incident should not be repeated in a modern liquefaction plant. Nevertheless, the incident highlights the need for comprehensive maintenance schedules and appropriate hazard detection systems at LNG facilities.

What other serious incidents have occurred at LNG regasification terminals?

In addition to Cleveland, there have been two other incidents attributed to LNG.

A construction accident on Staten Island in 1973 has been cited by some parties as an “LNG accident” because the construction crew was working inside an (empty, warm) LNG tank.

In another case, the failure of an electrical seal on an LNG pump in 1979 permitted gas (not LNG) to enter an enclosed building. A spark of indeterminate origin caused an explosion in the building. As a result of that incident, the electrical code was revised for the design of electrical seals used with all flammable fluids under pressure.

This record suggests that LNG offers a safe and reliable source of natural gas and facilities can be located close to urban areas with confidence that they do not pose https://sea-man.org/lng-safety.htmlsignificant safety risks.

LNG carriers

LNG carriers have double-hulled containment systems to limit loss of containment in cases of collision or grounding. LNG carrier safety equipment includes sophisticated radar and positioning systems that alert the crew to other traffic and hazards around the ship. A number of distress systems and beacons will automatically send out signals if the ship is in difficulty. The cargo system safety features include an extensive instrumentation package that safely shuts down the system if it starts to operate out of predetermined parameters.

Ships are also equipped with gas and fire detection systems. Crews are extensively trained to maintain high levels of onboard safety and how to handle emergency situations if they should arise.

Three LNG cargo tank types currently used in LNG carrier ships are self-supporting spherical, self¬supporting prismatic SPB, and membrane. The membrane tanks are the most common in vessels built over the past decade and very few vessels have been built with self-supporting prismatic tanks, although there is renewed interest in such designs for floating liquefaction vessels.

For all cargo tank types, penetrating one or more LNG cargo tanks in a collision or grounding requires the penetration of all of the following:

  • The ship’s outer hull;
  • The 3-meter or so space between the outer and inner hulls (the water ballast tanks);
  • The inner hull;
  • The insulation system around the LNG cargo tank;
  • The secondary containment of the individual LNG cargo tank;
  • The insulation system around the primary containment;
  • The primary containment vessel wall of the individual LNG cargo tank.

What are the sizes of an LNG carrier and an LNG terminal?

LNG import terminals are equipped with storage tanks capable of holding at least one tanker load of LNG, and most modern facilities typically have a capacity of at least two tanker loads.

Modern large LNG carrier ships or tankers commonly hold some 145,000 cubic meters of LNG in liquid form, which equates to about 3 Bcf (about 80 mcm) in gaseous form. LNG vessels range in capacity from 19,000 to 265,000 m3. The largest (Q-max) vessels of up to 265,000 m3 have come into service since 2008 as part of Qatar’s LNG supply chains.

LNG carriers are large double-hulled ships, several hundred meters in length, which travel at average speeds of 17 to 20 knots (18 knots is 33 km/h). It takes around 10 hours to fill an LNG tanker with a capacity of 120,000 m3. Larger vessels require higher capacity loading infrastructure to enable rapid loading of cargoes.

Although the storage tanks at an LNG marine terminal often function as LNG storage facilities, the principal operation of an import terminal is not for gas storage, but rather for receiving the water-borne LNG imports and then regasifying LNG for shipment via pipelines to customers.

Have LNG carrier groundings and collisions occurred?

Very few incidents involving LNG ships have occurred and those that have occurred have not resulted in loss of containment. The following example illustrates the robustness of these vessels and that the piercing or breaching an LNG ship tanks is extremely difficult.

In 1979, the El Paso Paul Kayser, loaded with about 125,000 m3 of LNG, was steaming out of the Mediterranean Sea from an Algerian port. It was traveling at approximately 19 knots off the coast of Gibraltar when it struck a rock outcropping below surface and gouged a 750-foot long scar in its hull. This serious marine incident did not involve a loss of cargo, nor did it result in a breach of an LNG tank. The grounding did not even penetrate the outer hull. Another ship was brought alongside; the cargo was pumped out of the El Paso Paul Kayser into the second ship. The El Paso Paul Kayser was righted and sent to the shipyard for repairs and eventually returned to service.

LNG spills

In order to be ignited, LNG must first be vaporized (heated and returned to a vapor state), mixed with between 5 to 15 % air, and come in contact with an ignition source.

Were LNG to be released onto the ground as a consequence of a leak from a storage tank, the heat from the ground surface would initially cause very rapid boiling of the LNG. As the ground cools the boiling rate of the LNG would reduce. The amount of vapor formed would be in direct proportion to the amount of LNG released, the rate of release, and the surface area covered in the release.

In an unconstrained open-air environment the cold gas vapor will condense most of the water (humidity) in the surrounding air forming a white vapor cloud. If unhindered, the cloud will drift in the direction of the wind, further mixing with the air and picking up heat from both the ground and the air as it moves. As the vapor cloud warms up, it will become buoyant (lighter than air) and rise into the atmosphere where typically it will gradually disperse without ignition.

LNG released on water acts very similarly to the initial release on land. Assuming a large volume of water, the vapor formation rate will remain high as the surface water that is cooled by the LNG sinks and is replaced by warmer water.

Hence, in unconstrained scenarios spilled LNG should not typically ignite. Ignition is possible only in certain zones of an LNG vapor cloud where mixing with air would produce a flammable gas in the to 15 % concentration in air range. At the center of the cloud the air quantity is too low for ignition; at the outer limits of the cloud the air quantity is too high for ignition. Natural gas has an auto-ignition temperature range of approximately 590 °C to 650 °C (1 100 °F to 1 200 °F), which is higher than LPG and significantly higher than gasoline. Those other fuels also ignite with lower concentrations in air. For example, gasoline has a lower flammability limit (LFL) of only 1.4 % and propane is 2.1 %, meaning that both can be ignited with significantly lower concentrations in air than natural gas (which has an LFL of 5 %). If the limited flammable portion of a natural gas vapor cloud in an unconstrained environment met an ignition source, it would burn but not explode.

In order for the ignition of an LNG vapor cloud to result in an explosion, the gas must first be uniformly mixed with air in the 5 to 15 % range, confined in an enclosed space, and then ignited through contact with an ignition source. It is extremely unlikely that such conditions could all occur together in a modern LNG facility.

What are the likely impacts of large LNG spills?

Over the course of the past decade Sandia National Laboratories (New Mexico, USA) have conducted a series of detailed risk analysis studies and provided safety guidance associated with the conse¬quences of a large LNG spill over water from a marine vessel. The studies examine the vulnerability of LNG tankers and the impact of an intentional or accidental event that spills a large amount of LNG into a carrier or onto the water. As part of the research, Sandia in December 2009 intentionally set a very large LNG fire in a 120 meter-diameter pool in New Mexico that was made for that purpose. The test LNG spill was 83 m in diameter and created a 56 m diameter fire. The test also showed that the fire would likely stay attached to the ship instead of floating away.

Modeling associated with Sandia’s 2011 studies showed that about 40 % of spilled LNG could stay within the ship, causing cryogenic and heat damage. At high temperatures the strength of the steel on the ship is much reduced. On the other hand the extreme cold temperature of LNG is likely to cause fractures in all structural elements in and around the ship that come into contact with LNG. The largest intentional breach events modeled would cause significant damage and make the vessel unseaworthy. The study considered a wide range of events, including shoulder-fired weapons, stinger missiles, backpack explosives, underwater events, and small aircraft.

The estimated thermal hazard distances, even from a pool fire associated with the largest capacity LNG carriers in operation, involve significant impacts to public safety and property contained within approximately 500 m of a spill, with lower public health and safety impacts at distances beyond approximately 1 600 m. However, the studies found that pool fire and vapor dispersion hazard distances are significantly influenced by site-specific environmental, topographical, climatic, and operational conditions including the breach and spill size.

What should be done if there is spill from an LNG delivery truck?

Truck loading and transport of LNG carries a higher risk than normal pipeline delivery, but involves a relatively small, limited amount of LNG. First responders need to be trained to treat such a spill because pouring water on an LNG pool results in a large increase in LNG vaporization. A better approach is to confine a spill with quick, simple methods such as placing sand bags in ditches.

Application of firefighting foam is not too effective once an LNG pool fire is ignited, but it can limit the evaporation rate of a pool prior to ignition. Blocking traffic is important to reduce ignition sources from hot engines and mufflers. If ignition occurs, an explosion is very unlikely unless the vaporized LNG cloud drifts indoors into buildings.

What are the safety concerns of LNG spills?

Because of its cryogenic temperature (atmospheric boiling point approximately -260 °F), LNG poses exposure concerns to employees, facility structure, and equipment. The design and operation of LNG terminals minimize ignition sources; thus, cryogenic exposure is more likely than a fire incident. This is particularly true in the high-pressure processing areas where the fluid inventory is lower but where the higher pressure creates greater potential for cryogenic exposure.
Cryogenic exposure can cause freeze burns to employees. Gas from LNG vaporization is extremely cold and can produce irreparable burns on delicate tissues such as those of the eyes. Therefore unprotected parts of the body should not be allowed to touch uninsulated pipes or vessels containing LNG.

The cold LNG vapor can also cause embrittlement to carbon steel, thus possibly resulting in structural failure. Protection from cryogenic exposure with insulation, as well as from fire exposure, is installed in the facility. Protective measures should be chosen that are effective for both fire and cryogenic exposure.

The other safety concern is asphyxiation. The normal oxygen content of air is 20.9 % in volume. Atmosphere containing less than 18 % are potentially asphyxiant. In the case of gas leakage, the high concentration of gas can cause nausea or dizziness from anoxia. In an LNG facility, oxygen and hydrocarbon content of the atmosphere are constantly monitored to detect any gas leakage. For maintenance of equipment, the operator is equipped with instruments to ensure sufficient oxygen is present before entry to any equipment.

How would an LNG facility be safeguarded against damages from an LNG spill?

Direct contact of LNG with structural steel can rapidly cool the material to below embrittlement temperature and may quickly cause failure in a short time. For this reason, the construction and protection system material is selected to withstand cold temperatures and must comply with the most stringent LNG safety standards. Insulation, shielding, and detection systems are provided in the facility to limit the volume of LNG release and mitigate the spread of LNG over a greater area. In the United States, NFPA-59A is one of the key design documents for the design of the LNG facilities. In Europe, BS EN-1473 is normally used. Both US NFPA-59A (2009) and BS EN-1473 (2007) require that equipment and structures whose failure would result in incident escalation must be protected from cryogenic embrittlement.

Security for LNG facilities and ships

Each country has its own regulations and agencies responsible for marine vessel security. For example, in the United States FERC is among several federal agencies overseeing the security of LNG terminals and peak shaving plants. The Coast Guard has responsibility for LNG shipping and marine terminal security. DOT’s Pipeline and Hazardous Materials Safety Administration (PHMSA) and the Department of Homeland Security’s Transportation Security Administration (TSA) have security authority for LNG peak shaving facilities. In addition to federal agencies, state and local authorities provide security assistance at LNG facilities.

Security measures for both onshore and offshore portions of marine terminals are required by Coast Guard regulations under the Maritime Transportation Security Act. Requirements for maintaining security of LNG import terminals are in the Coast Guard regulations at 33 CFR Part 105. The Coast Guard keeps other ships and boats from getting near LNG vessels while in transit or docked by enforcing Regulated Navigation Areas and security zones. The Coast Guard performs a number of important security and safety checks before allowing an General information and Rules for Ships carrying LNG and LPGLNG tanker to enter a port and unload its LNG. Facilities are required to have a written security plan and an emergency response plan. FERC, DOT, and the Coast Guard require LNG companies to contact and coordinate procedures with local response organizations.

Risk of terrorism adds new dimension to LNG safety risk

The LNG business has an admirable safety record overall but a whole new dimension has been introduced since the terrorist attacks of September 11, 2001.

By their nature, LNG import terminals are likely to be near centers of population, and issues of public protection and public acceptance of new terminal proposals have high community profiles.

How much LNG could conceivably be released in a major incident? How quickly and how far might the pool spread? How fast does it vaporize to gaseous methane? And, what is the maximum size and intensity of any resulting fire? These are the questions typically addressed in accessing the potential impact of terrorist attacks. These are questions typically addressed in the planning, siting and design of modern LNG import terminals.

Footnotes
Sea-Man

Did you find mistake? Highlight and press CTRL+Enter

Июнь, 23, 2022 125 0
Add a comment


Notes
Text copied
Favorite articles
Loading

Here will store all articles, what you marked as "Favorite". Articles store in cookies, so don't remove it.

Article added to "Favorite list"! Reload...
Вставить формулу как
Блок
Строка
Дополнительные настройки
Цвет формулы
Цвет текста
#333333
Используйте LaTeX для набора формулы
Предпросмотр
\({}\)
Формула не набрана
Вставить