The point of origin for a deadly home explosion in Plum on Aug. 12 came from inside the house at 141 Rustic Ridge, the Allegheny County Fire Marshal’s Office said Friday.

Officials continue to investigate the explosion that occurred just less than a month ago in Plum’s Rustic Ridge subdivision, the Fire Marshal’s Office said. Paul and Heather Oravitz, Kevin Sebunia, Mike Thomas and Casey and Keegan Clontz were killed in the explosion.

Three homes were destroyed by the blast; 10 homes have been identified as possibly being structurally compromised.

The home at 141 Rustic Ridge was owned by Paul and Heather Oravitz, and all six victims were inside that home when it exploded.

“All potential outside factors like wells, pipelines, ground gas propagation and other utilities were all inspected and tested at several levels by each of the associated agencies and companies,” the statement said. “All findings to date confirm that there are no factors external to the home that exploded that led to the explosion.”

The Fire Marshal’s Office said several levels of testing and sampling have been completed, and results of those tests were reviewed and discussed during joint investigative meetings.

Some testing included soil gas monitors, mobile leak survey, electric resistivity training that looks for variations in the ground, multichannel analysis that looks for changes in the ground’s subsurface, ground-penetrating radar that looks for underground utilities and frequency domain electromagnetic scans, which looks for abandoned wells, the fire marshal said.

Per state law, the Fire Marshal’s Office will determine the explosion’s origin and cause at the end of its investigation. There is no time frame for when the investigation will be complete. As of Friday, the Fire Marshal’s Office had completed scene safety and security, additional agency notifications, witness statements and interviews, and processing of the incident site.

On-scene investigative efforts also have been completed, the Fire Marshal’s Office said. Joint investigative efforts with agencies including the state’s Department of Environmental Protection and Public Utility Commission, Plum police, Peoples natural gas company and several insurance carriers continue.

The Department of Environmental Protection announced Friday that its investigators have completed an analysis of preliminary test results from its stray gas investigation. Those results do not indicate a stray gas migration incident.

The DEP said inspectors found detectible concentrations of combustible gas throughout the Rustic Ridge area on Aug. 14, but the gas is no longer detectible in soil near the incident. Isotopic samples, which help to identify molecular signatures, were collected Aug. 14 by the DEP and Peoples from soil and a nearby Peoples meter.

Eighteen points of interest were investigated, the DEP said. Gas samples were collected for isotopic analysis from five of those locations, including the area around a leaking gas pipeline, gas in the soil near a Peoples meter and under the foundation of the home.

“The findings suggest that concentrations of gas detected on Aug. 14 came from (a) single inundation event, likely the explosion itself,” the DEP’s statement said.

Investigators inspected seven conventional oil and gas wells and two gathering pipelines after the explosion and ruled they were all in compliance. Those wells and pipelines were within a 2,500-foot radius of the home.

One of the two pipelines, a suction line to a compressor station, was known to be leaking but was taken out of commission a week before the explosion, the DEP said. The other pipeline, a gathering line that ties into the suction line, was taken out of service immediately after the explosion “out of an abundance of caution.” On Aug. 15, that gathering line passed a pressure test with no leaks detected.

On Aug. 25, the DEP helped to distribute combustible gas detectors to the 227 houses in Rustic Ridge. The DEP estimated about 90% of the units were picked up for houses in the community, and remaining residents will be contacted by the Rustic Ridge Homeowners Association to collect their detectors if they want them.

The property at 141 Rustic Ridge will be turned over to the property owners and representatives. The fire marshal said it will continue to work with local officials on further remediation efforts to make the scene safe.

Officials are conducting follow-up interviews with some responders and witnesses, which is normal for such investigations, the fire marshal said. They continue to investigate the cause of the incident with further analysis of the interviews and physical evidence.

The process to confirm the origin and cause may include interviews, investigative photography or videography, drone imagery and 3D scans, debris layering, scene reconstruction and examining all utility connections and circuitry, the fire marshal said.

The Fire Marshal’s Office also encouraged homeowners to install combustible gas detectors and reminded residents that if they smell natural gas to not turn on appliances or light switches and exit the home and go to a safe area away from the house. People should call 911 and the gas company from outside the house, not reenter it and wait for first responders to arrive.

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