Eleven people were injured in the production platform blast and oil spillage was minimal, according to the Coast Guard. NBC's Brian Williams reports.

Updated at 5:56 p.m. ET: Coast Guard crews continued searching Saturday evening for two workers missing after an explosion and fire aboard a Gulf of Mexico oil rig on Friday that was apparently triggered by workers using a blow torch to cut a pipe.

Eleven workers on the rig were airlifted to hospitals after the accident some 17 miles southeast of Grand Isle, La. Four of the injured were in critical condition.

The fire was extinguished a few hours after the blast and Coast Guard Capt. Ed Cubanski told reporters that the platform appeared to be structurally sound. Twenty-two people had been aboard the rig at the time of the accident.

The search and rescue operation is making use of an 87-foot surface vessel assisted by a helicopter, the U.S. Coast Guard told NBC News Saturday night.

The platform was not actively producing oil and a sheen spotted in the water was probably from an estimated 28 gallons of oil that could have spilled when a pipe ruptured, Cubanski said Friday.

It does not appear the incident could lead to a major environmental disaster, added Coast Guard Capt. Peter Gautier.

Gerald Herbert / AP Damage from the fire aboard a Gulf of Mexico oil rig is seen Friday after the fire was put out.

He said initial reports suggested that the explosion occurred when maintenance workers using a torch cut into a pipe with oil inside.

The platform is a shallow-water production platform, unlike BP's Macondo well that blew out in 2010 in mile-deep water. The Macondo explosion killed 11 workers and caused the worst offshore oil spill in U.S. history.

The owner of the platform is Houston-based Black Elk Energy. On its website, the company stated that this month it was starting to drill the first of 23 new wells in the Gulf of Mexico.

Last Sunday, The Houston Chronicle named Black Elk Energy one of the top small businesses to work for in Houston based on employee surveys.

In August, the oil and gas company was named one of the fastest-growing privately held companies by Inc. Magazine.

The explosion came a day after BP settled criminal charges in the Macondo disaster by agreeing to pay $4.5 billion in penalties. It still faces up to $20 billion in civil fines.

Black Elk Energy was investigated last August by the federal Bureau of Ocean Energy Management Regulation and Enforcement for an incident in which two employees were dropped 60 feet into Gulf of Mexico waters due to a crane malfunction, Reuters reported. No injuries were reported.

Black Elk also paid a $300,000 civil fine in September, related to a site inspection in 2011 of one of its facilities that revealed it was not complying with regulations.

Federal data also shows a small fire occurred at a Black Elk platform in February of 2011 in the Gulf of Mexico, but was quickly contained.

The company's chief executive, John Hoffman, formerly worked for BP Amoco, according to a report earlier this year in the Houston Business Journal. Hoffman founded Black Elk in 2007, the report said.

Friday's incident could reignite a national debate over safety standards for offshore drilling. After the Horizon spill, the government overhauled offshore drilling regulations and imposed a ban on drilling that lasted for several months.

"BP and the government may have settled criminal matters yesterday, but today's incident shows that increasing safety of offshore drilling and for hard-working men and women is still not a settled matter," Rep. Ed Markey, the ranking Democrat on the House National Resources Committee, said in a statement.

NBC's Edgar Zuniga Jr. as well as Reuters and The Associated Press contributed to this report.

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