TRAVERSE CITY, Mich. (AP) -- A Michigan regulatory panel said Thursday that it needs more information about safety risks before it can rule on Enbridge Energy's plan to extend an oil pipeline through a tunnel beneath a waterway linking two of the Great Lakes.
The state Public Service Commission voted 3-0 to seek further details about the potential for explosions and fires involving electrical equipment during construction of the tunnel beneath the Straits of Mackinac.
The commission's approval would be required for Enbridge to replace two existing Line 5 pipes in the straits, which connect Lake Huron and Lake Michigan, with a new segment that would run through the proposed underground tunnel.
"This has been an extensive process," Chairman Dan Scripps said. "We want to make sure that we get it right."
Enbridge and the state of Michigan are mired in legal battles over Line 5. The 69-year-old underground pipeline carries Canadian oil and natural gas liquids used for propane through northern Michigan and Wisconsin to refineries in Sarnia, Ontario.
A 4-mile-long (6.4-kilometer-long) section divides into dual pipes that cross the bottom of the straits.
Enbridge is defying Michigan Gov. Gretchen Whitmer's 2020 order to shut down the line, a move long sought by environmental groups and Native American tribes who fear a rupture would devastate the lakes. The company says the line is in good condition and contends in a federal lawsuit that the Democratic governor doesn't have the jurisdiction to shut it down.
Enbridge, based in Calgary, Alberta, reached a deal with former Republican Gov. Rick Snyder in 2018 to build the $500 million tunnel. Enbridge has obtained permits from the Michigan Department of Environment, Great Lakes and Energy and awaits word from the U.S. Army Corps of Engineers as well as Michigan Public Service Commission.
The commission said last year it would not pass judgment on whether the entire 645-mile (1,038-kilometer) line should continue operating, focusing instead on the underwater section.
Its three members are Whitmer appointees. Scripps and Tremaine Phillips are Democrats, while Katherine Peretick is an independent.
In its order Thursday, the commission said testimony, exhibits and briefings included too little about tunnel engineering and hazards.
Also lacking is information about safety and maintenance of the dual pipelines, "including leak detection systems and shutdown procedures," the order said.
Interviewed by telephone after the meeting in Lansing, Scripps said Enbridge had pegged the likelihood of an oil release from the tunnel pipe as "one in a million." The commission wants to know how the figure was calculated, he said, as well as steps to eliminate even that possibility.
In a statement, Enbridge said it already had provided "extensive" material on those matters but would answer further questions.
"The engineering and design of the tunnel has been developed in accordance with the tunnel agreement entered with the state, and in close coordination with the Mackinac Straits Corridor Authority to ensure its safety and design life," the company said.
The corridor authority was created under Snyder to oversee building and operation of the tunnel.
Pipeline critics praised the commission's push to learn more.
"Enbridge has not proven feasibility or safety for this project," said Beth Wallace of the National Wildlife Federation. "Enbridge has proven time and again that they cannot be trusted to operate Line 5 and they should not be trusted to blast a tunnel through the Great Lakes."
The commission's decision was the latest of many delays for the tunnel, which the company originally pledged to complete by 2024. The Army Corps is conducting a lengthy environmental impact study.
Enbridge said it remains committed to the project.
The Great Lakes Michigan Jobs Coalition, which represents industry and labor groups, urged the commission to "get back to work, move the tunnel project forward and protect tens of thousands of Michigan jobs."