charting an accident using the Change, Barrier, or Analytic Tree Approach Accident Report.

Select a Pipeline, Marine, Aviation, or Railroad Accident Report from the NTSB Accident Docket Search.Links to an external site.

First, provide a descriptive summary of the accident and the investigation conclusions (do not cut/paste from the official accident investigation report). Describe how change, barrier, fault, or one of the analytic tree approaches could have been used in this particular investigation. You can explain by charting the accident investigation or by deconstructing and explaining it in paragraph form.

On June 28, 2021, about 3:35 p.m. local time, natural gas ignited causing an explosion during routine maintenance activities involving the insertion of an in-line inspection tool (pig) into a launcher, near Farmersville, Texas.1 (See figure.) The pig ejected from the pipeline shortly after it was inserted into the launcher while employees were manually removing the metal insertion tool.2 Before the insertion tool was completely removed, employees at the site heard a loud sound, and one employee observed a flash near the open launcher door. Employees from Atmos Energy Corporation (Atmos), FESCO, Ltd., and Bobcat Contracting L.L.C. were onsite at the time of the accident performing work for Atmos. The explosion was directed toward four employees, injuring all of them, two fatally. Three employees working nearby were not injured.

An Atmos employee onsite called 9-1-1 following the accident. The Collin County assistant fire marshal was the first responder to arrive and assist the injured. When the assistant fire marshal arrived, he observed no fire. The Collin County Sheriffs Office took control of the site, provided aid to the victims, and documented the accident scene. Additional emergency responders arrived on scene to provide aid to the victims. The Collin County Sheriffs Office called the Federal Bureau of Investigation to investigate for any criminal activity; none was found.

Later that day, inspectors from the Railroad Commission of Texas responded to the explosion requesting Atmos conduct a leak survey of the area. No leak indications were found along the flare flow line or around the launcher.3 However, natural gas was detected at the flare tip. Similar leak survey results were obtained by the National Transportation Safety Board (NTSB) investigative team.

Preliminary information indicates that natural gas was leaking into the launcher, through the flare flow line, and venting through the flare tip following the explosion.4 There were two valves that connected the launcher to the gas transmission system, which was owned and operated by Atmos. The NTSB retained these two valves as evidence for further evaluation.

The NTSB investigative team examined the site where the explosion occurred, gathered preliminary information, conducted interviews, and inspected equipment while on-scene. The NTSBs investigation into this accident is ongoing. Future investigative activity will focus on causal factors and pipeline safety.

Parties to the investigation include the Pipeline and Hazardous Materials Safety Administration, Railroad Commission of Texas, Collin County Sherriffs Office, City of Farmersville Police Department, Atmos, Bobcat Contracting, and FESCO.