FOLLANSBEE, W.Va. — There was no smell, no sound, and no warning before the pipeline exploded on the far side of Ed Dillon's pasture, causing him, his family, and four grazing horses to instinctively conduct what the government euphemistically calls a "self-evacuation" — they ran for their lives.

"It got so hot, so quick," said Dillon, 67, recalling that winter morning three years ago. Though the 20-inch diameter high-pressure pipeline rupture was located more than two football fields away, the heat was so intense it cracked the windows on his house and warped the vinyl siding.

"I've never been involved with anything of that magnitude before," said Larry Rea, 60, the fire chief in Follansbee, which is about four miles from the Pennsylvania border in West Virginia's northern panhandle. "It sounded like a damn jet engine, and the flame was huge."

The ATEX Pipeline accident on Jan. 26, 2015, which caused no injuries, involved the same highly volatile liquids from Marcellus Shale natural gas that Sunoco Pipeline plans to ship on its Mariner East 2 line, now under construction across Pennsylvania. The Mariner project has aroused a growing chorus of protests, especially where the pipeline threads through densely populated Chester and Delaware Counties, as close as 20 feet from some houses.

Mariner East opponents have cited the accident in West Virginia, which involved a pipeline that had been in service only 13 months, as well as Sunoco's own spotty record, in calling for a formal risk assessment of the Sunoco project.

"We just want a scientific, impartial, independent assessment of the risk," said Eric Friedman, a Thornbury resident and spokesman for the Middletown Coalition for Community Safety in Delaware County. Pipeline resisters say a public discussion on safety never took place when the project was approved.

Sunoco Pipeline, a subsidiary of Energy Transfer Partners LP, says its $5.1 billion Mariner East project meets or exceeds all federal safety standards. The project aims to transport gas liquids — mostly ethane, propane, and butane — through three adjacent pipelines to an industrial complex and export terminal in Marcus Hook.

"It is important to note that safety and risk reduction are built into the strict federal regulations that pipeline operators have to follow, and we have performed the required safety analyses for our systems and shared information with our regulators and emergency services officials," Sunoco spokesman Jeff Shields said in an email response to questions.

Problems with the ongoing construction have done little to lift public confidence in Sunoco's project. The Pennsylvania Department of Environmental Protection on Thursday fined Sunoco $12.6 million after lifting its five-week suspension of construction permits for "egregious and willful violations."

And now the project is taking on political dimensions. After voters ousted Republican officials in two Chester County communities in November, elected officials stepped up calls for a risk analysis, and the Delaware County Council is considering a vote to commission such a study. A coalition of opposition groups has launched an online campaign to raise $50,000 to pay for its own study, which would quantify the project's risk to human life and property.

"The citizens are smart enough to realize that now is the time for a risk assessment and to start the discussion because in November half of the Senate, the whole House, and the governor will be running for reelection," said State Sen. Andy Dinniman (D., Chester). Dinniman, along with State Sen. John Rafferty (R., Montgomery), has introduced a package of bills that would increase pipeline oversight and assess an impact fee on pipeline operators.

Richard Kuprewicz, an independent pipeline safety expert, questioned the value of a quantitative risk assessment (QRA). Though European pipeline regulators require a risk assessment, he said, no legal standards have been set in this country on how to measure the risk, which would require a regulatory authority to set an acceptable mortality rate for a pipeline.

"I'll be real blunt here, but what is your acceptable kill threshold?" he said. "That's a hard way to look at that, and it's not an issue that you can get a yes or no answer to. … If you're on the receiving end of a pipeline, and you don't want it, you're probably going to take a position that the threshold should be zero."

Kuprewicz said he did not think a risk assessment would solve anything. "It's just going to make the opponents angrier or more fearful, and Sunoco could argue they are not under any obligation," he said.

The U.S. Pipeline and Hazardous Materials Safety Administration (PHMSA) tallied 13 fatalities and 42 injuries in 26 "serious" incidents between 1998 and 2017 involving pipelines that carry "highly volatile liquids," a category that includes the ethane, butane, and propane that will be transported through the Mariner East system.

Chester and Delaware Counties are crisscrossed with no fewer than 10 pipelines transporting natural gas or natural gas liquids, Sunoco said. "They safely pass close to schools, hospitals, senior living facilities, and homes," said Shields, the company spokesman. "They have done so for decades and do so today because of the strict regulations that protect our communities."

The Mariner East system is unique in size and proximity to population, opponents  say. The three pipelines, including the eight-inch diameter Mariner East 1 that is already in service, will carry as much as 675,000 barrels of gas liquids a day, under high pressure. If the liquids leak and lose pressure, they vaporize into a heavier-than-air gas cloud that collects at ground level. The gas itself is not poisonous, but it can suffocate if it displaces enough oxygen. The primary risk is explosion.

While the Mariner East 2 pipeline in Chester County is similar in size to the ATEX Pipeline in West Virginia, the similarities end there. Brooke County, W.Va., is a largely rural area with shuttered steel mills, retired coal mines, and about 30 new shale-gas well sites drilled since the fracking boom took off. Its economy is built on natural resources.

"We're a coal-mining state, and although it's very terrible and may affect us, it's just part of the business," said Chuck Jackson, former Brooke County sheriff who responded to the 2015 explosion. "You accept the risk. The people, that's their money. That's their bread and butter."

The 1,265-mile ATEX line, which carries ethane from Western Pennsylvania to Texas, is underlain by abandoned coal mines in Brooke County, which cause subsidence that may have contributed to the accident.

It's not clear how long the ATEX Pipeline was leaking before it exploded on Jan. 26, 2015. The pipeline operators, Enterprise Products Partners L.P., reported a sudden drop in pressure at 9:38 a.m. consistent with what inspectors later found: The pipe had broken at a failed welded joint.

The rupture occurred 12 feet underground, in an area filled with coal-mine debris, according to PHMSA's 2016 inspection report. The pipeline had sunk three feet since it was built, and the weight of the soil caused the weld to fail.

A high-tension power line passed directly over the site of the rupture, and local authorities speculated that an electrical arc ignited the gas cloud. When it exploded, it created a crater around the broken pipeline, forcing most of the flame upward. About five acres of woods burned.

"I'm not minimizing the extent of the rupture and the accident, but it was an isolated area and the dead of winter, so we really didn't have to worry about any fires in the surrounding wooded area," said Rea, the fire chief.

Though the operator shut down flow immediately, a large fireball continued to burn for several hours before subsiding into a smaller fire that was extinguished the following day. PHMSA said 30,565 barrels of ethane were released, and estimated the damage at $6.9 million.

The PHMSA report says the pipeline rupture was located about 2,000 feet from Dillon's house. But an aerial photo of the site in the agency's report, as well as a Google Earth view and video of the fire, suggest the distance was closer to 700 feet. Even at that distance, the heat was intense.

"It was just a freak accident," Dillon said.

The pipeline company put his family up in a suite at the Hampton Inn for three nights, and told him they would make a generous settlement if he did not sue. Dillon says he can't discuss the settlement, but it covered the cost of home repairs, with enough left over to buy a third Harley motorcycle for his collection, a motor home, and a new pickup truck for a son, and paid off the student loans of his second son.

"I can't complain," said Dillon. "They treated us good." The company sends a surveyor every month to his property to make sure the pipeline is stable.

Dillon recognizes that circumstances might have been different. His family's deer hunting stand was located about 60 feet from the pipeline rupture. The explosion turned it to ash. The day before the accident, Dillon had been cutting firewood a few feet from the spot that 24 hours later erupted into an inferno.

"If I was 100 feet from that explosion," he said, "I wouldn't be here today."