Tuesday, December 29, 2009

The Care and Handling of Liquefied Natural Gas

This "Chemical of the Quarter" excerpt is from the U.S. Coast Guard “Proceedings of the Marine Safety & Security Council” magazine, by Dr. Alan Schneider, U.S. Coast Guard Office of Operating and Environmental Standards.

Liquefied Natural Gas

What is it?
Natural gas is a flammable gas we use to heat our homes, cook our food, and make electricity. It is made up of over 90 percent methane. The U.S. no longer produces enough natural gas to meet our needs, so we import it as liquefied natural gas (LNG) in tank ships.

How is it shipped?
Natural gas must be converted to a liquid before you can put it on a ship. If you didn’t, you’d need 600 ships to carry the same amount as a gas! Natural gas cannot be liquefied by compressing; it must be cooled to below its boiling point, -258°F.

Why should I care?
Shipping concerns. Engineers design LNG tank ships with special metals and materials placed where LNG makes contact (cargo tanks, pumps, piping). They do this because liquefied natural gas is so cold that it will crack ordinary steels. For example, whenever you make or break a line, you need to put a drip pan made of a material that is not brittle at LNG temperatures underneath. Aluminum makes a great drip pan.

Health concerns. As noted, liquefied natural gas is extremely cold, and will give you frostbite if you get even a small amount on you. Additionally, LNG is an asphyxiation concern in unventilated areas; as it vaporizes, it pushes air out of the space. Great care needs to be taken when entering an area containing LNG that does not receive air exchanges on a timely basis.

Fire or explosion concerns. LNG is very flammable. If spilled on water, it will boil off and form a potentially flammable vapor cloud. If it catches fire (on land or water), it will rapidly burn with a tall, hot flame.

Does that mean that an LNG ship is a “floating bomb”? No. LNG won’t burn unless it is a vapor, and only then if it is diluted to between five and 15 percent LNG vapor in air. LNG does not explode, even if it catches fire.

What’s the Coast Guard doing about it?
LNG’s safety record is excellent due to the high safety standards that have been implemented throughout the industry. The Coast Guard normally escorts LNG carriers in and around ports and also routinely creates a restricted area around moving LNG tank ships and shoreside terminals.

For more information:
Full article and “Environmental Protection” edition of USCG Proceedings is available at http://www.uscg.mil/proceedings/Winter2008-09//.

Subscribe online at http://www.uscg.mil/proceedings/subscribe.asp.

Online survey available at: http://www.uscg.mil/proceedings/survey.asp.

Direct requests for print copies of this edition to: HQS-DG-NMCProceedings@uscg.mil.