Environmental Impact of Liquefied Natural Gas

An LNG spill can have severe consequences (environmental impact), including the potential for contamination of water bodies and harm to marine life. The release of liquefied natural gas can also lead to the formation of flammable vapor clouds, posing risks to nearby ecosystems and human populations. Cleanup efforts for LNG spills are complex and can require extensive resources to mitigate the damage caused.

Reference: SIGTTO “LNG Shipping Suggested Competency Standards”, Sections:

1 Have an awareness of the potential environmental impact of LNG operations:

• Release to atmosphere;
• Consequences of cargo spillage.

2 Know and understand the potential environmental impacts of LNG operations:

Release to atmosphere

LNG is odourless, non-toxic and non-corrosive. As it warms, LNG vapour rises and dissipates into the atmosphere.

The use of LNG as a fuel may be considered “environmentally friendly” as while it does not offer zero-emissions, it does offer a substantial reduction over other hydrocarbons. LNG vapour (methane) released to atmosphere spreads evenly, taking approximately 10 years to disperse in the atmosphere.

At minus 110 °C (-110 °C), LNG vapour becomes lighter than air but at colder temps (-110 °C to -161 °C), it is heavier.

Methane is a simple asphyxiant but has low toxicity to humans. In a large scale LNG release, the cryogenically cooled LNG would begin to vaporise. If the vaporising LNG did not ignite, the potential exists for the LNG vapour concentrations in the air to be high enough to present an asphyxiation hazard. Although oxygen deficiency from vaporisation of an LNG spill should be considered when evaluating potential consequences, flammability limits and fire concerns would be the dominant effects in most emergency situations.

LNG vapour clouds can ignite within the portion of the cloud where the concentration of natural gas is between a 5-15 % (by volume) mixture with air. However, in order to ignite, this portion of the vapour cloud must encounter an ignition source or it will dissipate into the atmosphere. Because of its tremendous radiant heat output, an ignited LNG vapour cloud is very dangerous. When an LNG vapour cloud ignites, the flame can burn back towards the LNG source, ultimately burning the quickly evaporating natural gas immediately above the pool. This results in a “burning pool” or “pool fire”.

An LNG pool fire can cause extensive damage to life and property. Unless the source can be isolated, it may be very difficult, or even impossible, to extinguish the fire.

Environmental consequences of cargo spillage

If LNG is spilled into the sea, it will disperse faster than a spillage on deck or ashore as there is limited opportunity for containment. In addition, LNG vaporises more quickly when spilled into the sea as the expanse of water provides an enormous heat source, resulting in “rapid phase transition”.

If LNG is spilled into water it evaporates, leaving no residue or harmful after effects. There is no environmental cleanup needed for LNG spillage on water. If spilled, a vapour layer forms above the water. The LNG expands by 600 times while changing state from a liquid to a vapour.

In laboratory tests, when LNG is added to water and boils off (evaporates), all that is left is the water, which is unaffected.

An LNG facility has minimal Environmental aspects in Liquefied Natural Gas productionenvironmental impacts with regard to air emissions, but there is some concern about cold water discharges.

LNG facilities do not usually flare natural gas and every effort is made to capture BOG and use it productively, either on board the LNGC or within the receiving facility’s operations. However, a terminal, will have a pressure rise as loading begins to empty tanks and this is usually reliquefied, although occasionally it may be “flared”.

Environmental impact of general shipping

Ships produce a variety of emissions. These include CO₂ SOx, NOx, particulate matter, oil, sludge, ballast water, bilge water and sewage. Some emissions, in particular air emissions, depend on the type of propulsion system fitted (i. e. diesel).

Air emissions are regulated by MARPOL Annex VI internationally, as well as by regional and local (port State) regulations. Monitoring of emissions to ensure compliance with regulatory requirements is carried out by Port State Control inspection. Regulations set out mandatory emission levels. For example, on 1 January 2020, the sulphur emission level was set at 0,1 % inside a Sulphur Emissions Control Area (SECA) and 0,5 % globally. Other geographical areas may impose their own sulphur restrictions.

In most cases,the monitoring of emissions is through ,checking the fuel used on the LNGC. For example, SOx emissions are directly dependent on the sulphur content of the fuel. Bunker delivery notes (BDN) can be inspected, along with samples of the fuel on board (note that carriage of heavy fuel oil (HFO) for use as a fuel was banned 1^st March 2020). However,some ships may use higher sulphur fuel, such as where an approved exhaust gas cleaning system (EGCS), known as a scrubber, is fitted. However, scrubber wash water release may be limited by local regulation.

For other types of emissions, monitoring is more complicated. NOx emissions, for example, are set according to the engine installation parameters and depend on engine type, year of build, etc. Different levels (tiers) of control apply based on the ship construction date. This information is surveyed and detailed in the Engine International Air Pollution Prevention (EIAPP) Certificate of the ship.

Read also: Environmental Control on Liquefied Gas Carriers

For CO₂ emissions, the IMO established a data collection system that began on 1^st January 2019. Regional regulations also apply.

For example, in the European Union, the Monitoring, reporting and verification (MRV) of CO₂ emissions has been mandatory since 1^st January 2018. Companies must submit verified annual emissions reports.

Other emission types, such as sewage and oil, are controlled under the MARPOL Convention. A key exception is ballast water, which is controlled under the International Convention for the Control and Management of Ships Ballast Water and Sediments (BWM Convention) since its entry into force on 8^th September 2017.

Action to be taken to reduce environmental impact in the event of release

The most significant impact affecting public safety exists within about a 500 m radius of an LNG spill. This is the thermal hazard from any resulting fire, with a reduced health and safety impact at distances of beyond 1 600 m.

A large, unignited LNG vapour release is an unlikely hazard. However, if a release did occur and it did not ignite, the resulting vapour clouds could spread over a large distance, extending the hazard range. The actual hazard distances will depend on breach and spill size, site-specific conditions and environmental conditions.

Methane, which is a “greenhouse gas” has a short lifespan of ~10 years and it is 20 times more effective than CO₂ in trapping heat in the atmosphere.

However, it should be noted that 60 % of the methane released into the atmosphere originates from:

• Waste landfill sites;
• Agricultural activities;
• Coal mining;
• Petroleum production.

The remaining balance occurs from natural resources (wetlands, termites and hydrates on the seabed of the oceans). By far the largest source of industrial releases of methane occurs through the breakdown of garbage in waste landfill sites. LNG vapour released from the LNG industry accounts for only a small percentage overall.