A worker who heard gas flowing from an open valve on a Susquehanna County compressor engine pulled an emergency shutdown switch as he evacuated the station, stopping the flow of gas to the building just before it exploded, according to a report by Williams Partners released Friday by state regulators.

The report detailing events before and after the blast and fire at the Lathrop compressor station in Springville Twp. on March 29 was submitted to the Department of Environmental Protection on April 7.

Williams said a worker did not properly lock down a compressor when he was away from the engine during maintenance and two other workers, who assumed the work was done, began to turn the engine back on.

Although the account revealed new details about the incident, it left unanswered some questions sought by state environmental regulators and raised new ones.

The report does not explain what ignited the gas trapped in the compressor.

It also appears to contradict earlier reports from Williams that automatic shutdown procedures were triggered by the flow of gas into the building. According to the report, "One of the workers pulled the (emergency shutdown) button on his way out of the building."

DEP responded to the report with more than a dozen questions for Williams to clarify, a department spokeswoman said Friday.

Williams' explanation of the shutdown procedure and missing information about the source of the explosion were among the areas of concern highlighted by the agency, spokeswoman Colleen Connolly said.

No one was injured in the blast and fire at the station, but the explosion tore part of the roof and sides from the building, rattled nearby homes and drew emergency response crews from three counties - including the Chinchilla Hose Company's specialized foam trailer that had to travel there from South Abington Twp.

The incident also raised concerns about the safety and oversight of the natural gas infrastructure which, because it is in a rural area, is not regulated like pipelines and compressors in more populated places. DEP and Williams will hold a public briefing about the explosion on Tuesday evening at Montrose High School.

Williams spokeswoman Helen Humphreys said Friday that there are "multiple manual switches, multiple gas detectors and multiple fire detectors" at the Lathrop compressor building "any one of which could have triggered the emergency shutdown system."

Although Williams initially thought the gas detection system triggered the shutdown, she said, it found during its investigation that a manual switch was pulled first, "within seconds of the release" of gas.

The report revealed a clearer picture of the scene at the station on the day of the blast: After workers mistakenly turned on the engine that was shut down for maintenance, three workers training on a nearby engine heard the leaking gas and left the building.

The manual shutdown switch pulled by a worker stopped gas from entering or leaving the station and vented natural gas out of the compressors. But the gas trapped in the building ignited and burned out in about 30 minutes while a second fire fed by the oil in the engine burned for two-and-a-half hours before it was put out by firefighters.

The compressor where the explosion originated "suffered severe damage" and is being replaced. A second compressor had wiring damage but was otherwise in "good working order."

The report also detailed new worker training and compressor lockout protocols and the steps Williams took over several days to restart the compressors safely.

It did not address why engines were turned on after DEP instructed the company not to.

Williams has called it a "misunderstanding."

"We asked them to not resume running gas until we had a written report and an inspector out to the site," Connolly said. "We are not satisfied with the answer that Williams gave to DEP on when they restarted the compressor station."

The director of the Clean Air Council, an environmental group, also faulted Williams for restarting its engines without DEP permission and insisted that DEP complete its own investigation.

"Regardless of whether or not engines are functioning properly now," Joseph Otis Minott said, "this lack of concern for DEP's authority calls into question the company's attitude toward compliance with rules or orders designed to protect public health and safety."

Contact the writer: llegere@timesshamrock.com