The Coast Guard marine safety office and OSHA were investigating.

PORTLAND (AP) – One worker was killed and two others were injured Tuesday when a lifeboat drill aboard one of two massive oil rigs went awry, causing the boat to plummet into Portland Harbor, officials said.

The lifeboat with three people aboard was being lifted back to its 75-foot-high perch when it dropped from an unknown height at 11:15 a.m., said Jeff Monroe, city director of ports and transportation.

The three were fished from the water by co-workers and a Portland fire boat.

One of the victims was pronounced dead at the scene; two others were taken to Maine Medical Center for treatment, Monroe said.

The workers, whose identities were not immediately released, were members of the crew of the Pride Rio de Janeiro, one of two oil rigs that arrived nearly two years ago on the Portland waterfront.

It was unclear if the workers were employed by Brazil-based Petrodrill, which owns the rigs, or by someone else. They were not part of the Cianbro crews who had outfitted the rig, officials said.

The Coast Guard marine safety office and the Occupational Safety and Health Administration were investigating.

The oil rig was in deep water undergoing tests as part of the commissioning process. Before the accident, it had been scheduled to leave Portland Harbor in a few weeks for ocean tests, officials said.

Pittsfield-based Cianbro was responsible for outfitting the structures, which were brought to Portland from separate Gulf Coast yards after the companies that were building them sank into bankruptcy.

Cianbro had completed most of the work on the Pride Rio de Janeiro and there were only a few Cianbro workers aboard when the accident occurred Tuesday, said Alan Burton, director safety and human resources for Cianbro.

A sister rig, Pride Portland, remains at dockside as it continues to be outfitted by Cianbro workers, Burton said.

Before the accident, the three workers on Pride Rio de Janeiro had successfully lowered the 20-foot-long lifeboat into the water and had motored around the harbor to test the vessel, Burton said.

Investigators will have to determine what went wrong when the vessel was being raised back into position, he said.

It’s the second death this winter at the work site. A South Portland man was killed Dec. 4 on a tugboat that was working with one of the two rigs. OSHA officials are investigating that accident, as well.

Despite the two deaths, Cianbro’s safety record of more than 2 million hours of work without time lost to injury remains intact because the victims worked for other companies, said spokeswoman Dottie Hutchins.