Liquefied natural gas (LNG) is often regarded as extremely dangerous and toxic with container ships. Natural gas vapors are flammable, and LNG typically contains methane, ethane and propane. LNG presents safety hazards that must be managed. When LNG spills, it vaporizes quickly and leaves behind no residues. As LNG vaporizes, the vapor cloud can ignite if there is a source of ignition, but otherwise LNG dissipates completely.
To handle LNG safely, it is stored in industry standard tanks (double walled, insulated, of proper metals according to the relevant EU (CEN) standards, or to the US standards, e.g. NFPA59) transferred in closed systems with redundant controls. LNG facilities and equipment are designed with special features to ensure containment of LNG and its vapors.
Hazards of a LNG spill
Hazards of a large LNG spill over water includes asphyxiation, cryogenic burns and cryogenic damage to the ship from the LNG, dispersion, fires, and explosions. Thermal hazards occur too from the fire that breaks out during a spill. Cryogenic and fire damage to an LNG ship cause further damage to LNG cargo tanks following an initial cargo tank breach, though the additional impact on public safety would be limited.
Risk management approaches
Risks and hazards from a potential marine LNG spill can be reduced through a combination of approaches, including reducing the potential for a spill, reducing the consequences of a spill, or improving LNG transportation safety equipment, security, or operations to prevent or mitigate a spill. Other approaches include:
- improvements in ship and terminal safety/security systems including improved surveillance, tank and insulation upgrades, tanker standoff protection systems;
- modifications and improvements in LNG tanker escorts, extension of vessel movement control zones, and safety operations near ports and terminals;
- improved surveillance and searches of tugs, ship crews, and vessels;
- redundant or offshore mooring and offloading systems; and
- improved emergency response systems to reduce fire and dispersion hazards and improved emergency response coordination and communication.
Risk prevention and mitigation techniques are especially useful in zones where the potential impact on public safety and property can be high. The hazards of brittle fracture, rapid phase transitions, and explosions in confined ship spaces, as well as cascading events that may result from the extreme fire exposure.
In the case of a leakage or spillage of LNG, the following general procedure should be followed:
- Isolate source of LNG. If loading/discharging, the ESD system should be activated.
- Summon assistance.
- Protect the hull from risk of cold fracture.
- Speed vaporisation to minimise ignition risk.
The exact procedure will depend upon the nature of the incident, inclusive of size of spill, location, ambient conditions and ignition risks.
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