The liquefied natural gas (LNG) facility of U.S. olefins producer Williams at Plymouth, Washington, was rocked by an explosion and fire on Mar. 31.

The company said the facility, owned by its subsidiary Northwest Pipeline, was immediately shut down and personnel evacuated. An area of about two miles around the plant also was evacuated, reports said. One employee is believed to have been treated for injuries.

This was the second explosion and fire at a Williams facility in less than a year. In June 2013, two people died and more than 70 were injured at its cracker in Geismar, Louisiana, at the time engaged in a maintenance turnaround.

The US Occupational Safety and Hazard Administration (OSHA) cited the company for six safety violations and fined $99,000. In February 2014, a class action suit was filed on behalf of some of the injured.

Williams said the Mar. 31 incident, which it added had not impacted supply, was  not a natural gas pipeline rupture, but rather occurred within the LNG storage facility.

"We believe that only natural gas was released and it evaporated into the atmosphere. There is no hazardous vapor drifting toward residents in the area. The tanks involved were about one-third full of liquefied natural gas," the company said in a statement.