Story highlights About 28 gallons of fuel spilled, Coast Guard official says

11 injured, including four critically

The platform is for production and not drilling, authorities say

The fire has been put out, the Houston-based firm in charge of the platform says

An explosion tore through an oil platform in the Gulf of Mexico on Friday, triggering a fire and injuring at least 11 people, authorities said.

Rescue planes and helicopters are searching for at least two crew members who are still missing.

The incident happened roughly 20 miles off the coast of Grand Isle, Louisiana, on a platform used for production, not drilling. About 28 gallons of fuel spilled into the region, according to Coast Guard Response Division Chief Ed Cubanski. A half-mile oil sheen reportedly stretched near the area.

The 11 injured were airlifted off the platform, and nine additional crew members were safely evacuated off the platform, according to the Coast Guard. Four of the injured were taken to West Jefferson Medical Center in Louisiana where they were listed in critical condition, a hospital spokeswoman told CNN. Once they stabilized, they were scheduled to be transferred to the Baton Rouge General Burn Center.

The fire has been extinguished, according to a spokesman for Black Elk Energy, the Houston-based firm in charge of the platform. Federal authorities are investigating what triggered the explosion.

Map: Grand Isle, Louisiana

The incident comes a day after the Justice Department announced that oil company BP would plead guilty to manslaughter charges stemming from the 2010 Deepwater Horizon explosion and oil spill in the Gulf of Mexico.

The London-based oil giant BP has agreed to pay $4.5 billion in government penalties.

Working in the oil industry is a dangerous business. The fatality rate for oil and gas workers is 15.8 deaths per 100,000 employees, according the Bureau of Labor Statistics. That's nearly five times the national average.

In 2011, there were 11 fatalities in the oil and gas industry, according to BLS.

Most of the deaths were accidental, and criminal charges are never filed. The manslaughter charges brought against BP and two of its employees Thursday were rare. Only a handful of all workplace deaths in the United States result in criminal cases, according to the union AFL-CIO.