Independent classification societies such as the American Bureau of Shipping and Lloyd's Register routinely inspect and certify ships, as well as issue safety and pollution prevention documents on behalf of the states where the ships are registered, or "flagged".[i] These certificates are necessary for the ship to operate in international shipping. In order to obtain a certificate of classification from a society, ship owners must demonstrate that their vessel complies with the society's rules.[ii]
The International Maritime Organization (IMO), a branch of the United Nations, establishes international safety and design standards for shipping - which classification societies follow. One of the IMO's most important instruments to promote tanker safety is the International Convention for the Prevention of Pollution from Ships (MARPOL). MARPOL is the main international convention intended to prevent marine pollution by requiring ships to be designed and maintained according to MARPOL standards.
A number of environmental disasters involving tankers over the past 35 years prompted revisions to the MARPOL convention. One of the amendments requires single-hulled tankers to be phased out and replaced with double-hulled tankers by 2010.[iii] Double-hulled tankers have a second, outer steel shell intended to lessen the likelihood of an oil spill in the event of a collision. Even if the outer hull is breached, a spill could be averted if the inner hull remains intact. The space between the outer and inner hull is used for ballast.[iv] The area is empty during the transport of cargo, and it is filled with water to maintain the ship's stability when the cargo holds are empty.
Caption: A pictoral diagram of a typical oil tanker
Another MARPOL amendment requires cargo tanks in oil tankers to be divided into separate compartments so that a hull breach in one area will not result in the loss of the entire cargo. Vessels greater than 160,000 DWT are typically divided width-wise into three tanks. Vessels less than 160,000 DWT may be arranged as a single tank or two tanks across.[v]
[i] European Maritime Safety Agency, Glossary. Online. Available: http://www.emsa.europa.eu/end645d002.html. Accessed: April 23, 2008.
[ii] Interview with individuals from an ExxonMobil affiliate, Austin, TX, November 28, 2007.
[iii] International Maritime Organization, Revised phase-out schedule for single-hull tankers enters into force. Online. Available: http://www.imo.org/About/mainframe.asp?topic_id=1018&doc_id=4801. Accessed: April 4, 2008.
[iv] National Research Council, Commission on Engineering and Technical Systems, Committee on Oil Pollution Act of 1990, Double-Hull Tanker Legislation: An Assessment of the Oil Pollution Act of 1990 (Washington, DC: National Academy Press, 1998), p. 118. Online. Available: http://www.nap.edu/openbook.php?record_id=5798&page=117. Accessed: December 4, 2007.
[v] National Research Council, Commission on Engineering and Technical Systems, Committee on Oil Pollution Act of 1990, Double-Hull Tanker Legislation: An Assessment of the Oil Pollution Act of 1990 (Washington, DC: National Academy Press, 1998), p. 117. Online. Available: http://www.nap.edu/openbook.php?record_id=5798&page=117. Accessed: December 4, 2007.
This page last modified in August 2008