Explainer-What are the risks of an LNG tanker explosion?

LONDON, July 8 - A Qatari tanker loaded with liquefied natural gas (LNG) was at risk of exploding, one source said, after it sustained significant damage in an attack on the Omani side of the Strait of Hormuz on Tuesday.

While the LNG industry has experienced a few accidents at onshore facilities, there has never been a catastrophic LNG cargo-tank explosion on a commercial LNG carrier at sea. Recent targeting of energy shipping vessels by belligerents in both the Ukraine and Iran wars has raised concerns, however.

Tuesday's incident involving the tanker Al Rekayyat marks the second case this year of an LNG vessel being caught up in a war-related attack. In March, the Russian LNG tanker Arctic Metagaz caught fire in the Mediterranean after it was struck by Ukrainian naval drones, forcing its crew to abandon ship, according to Russia's transport ministry.

WHAT IS LNG AND HOW IS IT STORED AND TRANSPORTED?

LNG is natural gas that has been cooled to around minus 162 degrees Celsius (minus 260 degrees Fahrenheit). Cooling turns the gas into a liquid and shrinks its volume by around 600 times, making it economical to transport by ship.

LNG is stored in heavily insulated cryogenic tanks that keep it at extremely low temperatures. At export terminals, it is loaded into specialised LNG carriers. These ships have double hulls and highly insulated cargo tanks designed to keep the LNG cold throughout the voyage.

A small amount of LNG naturally evaporates during transport. If left unmanaged, the so-called boil-off gas increases the volume and pressure inside storage tanks. It is often captured and fed directly into the ship's engines as a primary fuel source.

WHAT ARE THE MAIN RISKS?

LNG itself does not burn in its liquid form. Risks, however, can arise if LNG leaks, warms into a gas, mixes with air in the right proportion and reaches an ignition source.

To reduce that risk, LNG ships use double-hull construction, multiple containment barriers, gas detection systems, pressure-relief equipment, emergency shutdown systems, firefighting equipment, strict operating procedures and crew training.

COULD THE QATARI TANKER EXPLODE?

The Al Rekayyat tanker reported a fire in the vessel's engine room, and a source said the ship was at risk of exploding, though there was no indication that its LNG tanks had been breached. The crew were evacuated safely.

In theory, any LNG carrier faces a risk if damage leads to a major LNG release and formation of a flammable gas cloud and ignition.

But modern LNG carriers are designed with multiple layers of protection to prevent any ignition from reaching the cargo tanks. And industry experts say a fire in an engine room does not automatically mean the tanker will explode.

The risk would increase if the fire spread to cargo systems, damaged containment tanks or triggered a significant LNG leak.

One industry source said on Wednesday that as long as Al Rekayyat was not subject to any further attack, it was likely to remain in its current state and not explode. REUTERS