The U.S. Coast Guard (USCG) Wednesday afternoon was responding to an explosion and fire aboard a mobile offshore drilling unit 42 miles southeast of Venice, LA, in the Gulf of Mexico (GOM). The explosion occurred about 10 p.m. Tuesday aboard Transocean Ltd.'s semisubmersible Deepwater Horizon.

Of the 126 people on board, 115 had been accounted for. Seventeen injuries were reported with three of them said to be critical. As of Wednesday afternoon some of the injured had been released from the hospital. Eleven people remained missing.

The rig is in Mississippi Canyon Block 252, Transocean said. According to press reports, it is listing and may be in danger of toppling.

USCG established a safety zone in the area that requires USCG approval for entry. Additionally, airspace restrictions include a five-nautical-mile radius around Deepwater Horizon and 4,000-foot elevation. The cause of the explosion is under investigation. Initial indications show that it was not a terrorist incident. The investigation is a cooperative effort of the Minerals Management Service and USCG.

USCG Rear Admiral Mary Landry, who heads the Eighth Coast Guard District, said search and rescue efforts were continuing. "We have the capability to search throughout the night...We have no idea where the 11 unaccounted for personnel are at this time, and we're going to continue to search."

The response effort includes helicopters, airplanes and cutters. Coast Guard cutters Pompano and Zephyr were on scene and cutters Razorbill, Pelican and Cobia were en route to assist.

Transocean emergency and family response teams are working with the USCG and lease holder BP Exploration & Production Inc. to care for rig personnel and search for the missing workers. Of those on board at the time of the explosion, 79 were Transocean employees, six worked for BP, and the remaining 41 worked for third-party service providers, said Transocean Vice President Adrian Rose.

Landry said there was "minimal, minimal sheening in the water. Most of the product is burning off." She said there was the potential for a pollution problem, though.

David Rainey, BP vice president of GOM exploration, said seven oil spill response vessels were en route to the scene, including one of the largest such vessels in the world. The oil fire was still burning and was described as a "hot" fire by Rainey, who said it was coming up a riser pipe to the rig.

The Transocean rig was drilling an exploration well on BP's Macondo prospect. A BP spokesman would not say whether the rig was targeting oil, natural gas or both. During a press briefing Wednesday officials would not speculate on the cause of the blast but said a full investigation would take place.

BP said it offered its full support to Transocean, noting that it stood ready to assist in responding to the incident. "Our concern and thoughts are with the rig personnel and their families," said BP plc CEO Tony Hayward. "We are also very focused on providing every possible assistance in the effort to deal with the consequences of the incident."

Video of the USCG operations is posted on a USCG website. A next of kin hotline has been set up at (832) 587-8554.

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