Saturation diving operation on Line 5 Straits of Mackinac crossing is a Great Lakes first

Coating inspections, dent repairs, cathodic protection testing, anchor support work will strengthen Line 5 safety measures

They’re living in a highly pressurized environment for a full month. And they’re making history as they do it.

This month, a team of four divers with Ballard Marine Construction is stationed in Michigan’s Straits of Mackinac, along with a larger team of about 40 marine professionals performing inspection and repair work on Enbridge’s Line 5 pipeline that travels across the bottom of the Straits.

This four-diver team is making repairs to three dents on the dual Line 5 pipes about 235 feet below the water’s surface, after an anchor strike in April that also damaged electrical cables in the Straits.

As they move from diving suits to an enclosed diving bell to a pressure chamber on board their barge, the divers are kept in the same pressurized environment for four weeks as they perform repair work. It’s known as saturation diving, and it’s believed to be the first such operation ever undertaken in the Great Lakes.

“To our knowledge—and we’ve asked no less than a dozen people in the industry, some with decades of experience—nobody has heard of a saturation diving system being worked in the Great Lakes,” says senior project manager Chris Bauer of Ballard Marine. “We believe this is the first.”

With shifts around the clock, the saturation diving team is able to work 16 hours out of a 24-hour cycle—far more than a traditional mixed-gas operation, which severely limits a diver’s time at greater depths, and demands a rigorous process while ascending and descending.

Saturation diving is also ultimately safer, says Bauer.

“Decompression sickness is the riskiest part of the job. Even if you’re doing everything right, and running a perfect decompression schedule, the statistics tell us that 2 to 4 percent of dives may result in some sort of decompression symptoms,” he says.

“With gas diving, if you work for 30 days with three dives a day, you have 90 decompression events. With saturation diving, you’ve got four guys who go in the system and live in that environment for 28 days, and are then decompressed once. Instead of 90 events, you’ve got four.”



With simultaneous saturation and mixed-gas diving operations ongoing in the Straits, this summer’s Line 5 work includes:

Safety is the very foundation of Enbridge’s business, and we take multiple safety precautions to prevent an incident on our Line 5 Straits of Mackinac crossing—which has never experienced a leak.

At the same time, we are also working with the State of Michigan to enhance protection of the Great Lakes, while continuing to safely meet Michigan’s energy needs. Part of our agreement with the State included exploring two feasible Line 5 replacement options at the Straits—an open-cut installation with secondary containment, and a tunnel bored under the lakebed.

We’re also evaluating further measures to prevent unintentional anchor strikes, including enhanced marine communications and a protective cover of engineered rock and gravel.


Protection measures would enhance Line 5 in the Straits of Mackinac and beyond
Enbridge presents three additional reports to the State of Michigan