The odds of a resident of Delaware or Chester Counties who lives near Sunoco's Mariner East pipelines dying in an explosion from those lines are about one in 81,000, according to a grassroots-funded study.

For context, that's a probability sandwiched between dying in a car crash (one in 8,513) and from complications in a medical procedure (one in 125,000).

Still, the findings — the first quantitative analysis of the risk presented by Mariner East 2 and its pipeline brethren buried throughout the suburban counties — are being hailed as vindication by local activists and other longtime pipeline critics.

"Sunoco has decided that the risk of these deaths is acceptable against their bottom line," said George Alexander, a member of Del-Chesco United for Pipeline Safety, the group that commissioned the study after obtaining crowdfunding of nearly $50,000. "But accidents happen, and when they involve highly volatile liquids, the consequences can be catastrophic."

The findings were unveiled last week by Jeff Marx, a senior engineer with Quest Consultants, who is overseeing the risk-analysis project. A final version of Marx's analysis will be made available later this month, according to members of Del-Chesco United.

Sunoco did not comment on the specific findings. Previously, a spokesperson said the Mariner East project has followed all mandated safety analyses and risk assessments required by state and federal authorities, and has worked with local municipalities to coordinate "emergency preparedness efforts."

Mariner East 2, designed to carry propane and other highly volatile liquids to a refinery at Marcus Hook, is nearing completion after state-mandated shutdowns and safety violations. Sunoco estimates that Mariner East 2 will be operational by the "third quarter of 2018," according to a statement on its website. A secondary, 16-inch pipeline dubbed Mariner East 2X, will be completed next year.

Two weeks ago, a contractor excavated sections of the pipeline in Edgmont Township, Delaware County. Lisa Dillinger, a spokesperson for Energy Transfer Partners, Sunoco's parent company, said that work was part of the company's "regular construction process, which is constantly checked and rechecked."

The pipe was replaced, she added, as a "preventative measure" because the coating did not meet Sunoco's standards.

"Our primary goal has been and continues to be to build a pipeline that is constructed to the highest standards," Dillinger said.

Using publicly available data, including the diameter of the pipeline, its route, and weather patterns, Marx modeled how likely Mariner East 2 and its sister pipeline, Mariner East 1, are to rupture or leak, and how far the material released by a hypothetical breach would travel.

The results of that model ranged from a 120-foot cloud of flammable gas vapor from a quarter-inch hole in the pipeline, to a 2,130-foot cloud from a complete rupture, according to Marx. Accidental "releases" of pipeline materials can also spark "jet fires" that can burn as far as 1,000 feet, depending on the size of the rupture, his report said.

Residents in the direct vicinity of the pipeline and its pump stations face the greatest risk, with the danger dropping to "essentially zero" a half-mile away from Mariner East 2 and a quarter-mile away from Mariner East 1.

Marx also calculated, using incident reports from the Pipeline and Hazardous Materials Safety Administration, that a leak or rupture is likely to occur once every 79 years along the 35 miles of pipeline in Delaware and Chester Counties. That frequency would jump to about once every three years when looking at the 1,000 miles of Mariner East 1 and 2 stretching across Pennsylvania.

Another effort at analyzing the risks presented by the pipeline is underway. After eight months of debate, the Delaware County Council voted in July to commission a risk-analysis study by G2 Integrated Solutions LLC.

Work on that study is moving forward, according to Brian Zidek, a Democratic county councilman and a supporter of the study.

"This is an increased risk for our community, and it's up to us as a community to determine if that risk is worth any benefits derived from it," Zidek said. "I expect rational minds will come to different conclusions on that front."