Probe details cause of blast

A broken gas-line connection caused by a Flathead Electric Cooperative backhoe operator was to blame for a May 6 natural-gas explosion in Columbia Falls that killed a man and destroyed a home, a NorthWestern Energy investigation has determined.

Longtime NorthWestern Energy gas serviceman Jim Hilton, 53, of Kalispell was killed in the explosion and the home of Ted and Myrtle Langton on the southwest corner of Second Avenue West and 12th Street West in Columbia Falls was destroyed.

In a report released Wednesday, NorthWestern said the accident investigation established that while using a backhoe to dig a hole for a street-light pole, a Flathead Electric Cooperative worker snagged a 3/4-inch gas service line, pulling it off of its welded connection to a service tee on the nearby gas main.

Gas from the broken connection migrated through the soil along the path of a sewer line and into the basement of the house, where it found an unidentified source of ignition and exploded.

When the explosion occurred, NorthWestern Energy employees were repairing the underground service line that had been damaged earlier that day by Flathead Electric Cooperative.

Two service gas lines branch perpendicularly off of the main running under Second Avenue West. The service line to the Langtons’ home tees off of the main and runs west to the meter on the south side of that house, the report said. ELM Locating and Utility Services had located and marked the service line to that house the previous week.

A second service line — the line that was damaged — tees off of the main and provides service to the neighboring house to the west. That line runs west, parallel to Second Avenue West on the north side of the house that exploded. ELM reportedly had not located that service line prior to the accident, according to NorthWestern’s investigation.

Flathead Electric Cooperative had sent a request to the UDIG center a week prior to the job near the Langtons’ home, cooperative spokeswoman Wendy Ostrom Price said. UDIG sent Flathead Electric confirmation that it had received the request.

UDIG is the recognized One Call Locate Center serving all of Flathead County, most of Lincoln County and parts of Sanders and Lake counties. The UDIG system is administered by the Flathead Valley Utility Coordinating Council.

“When our crew got to the job, there was locate paint on our pole that said ‘OK,’” Ostrom Price said, adding that the paint is an indicator that there are no obstacles in the ground. “That line that was hit was not marked.”

Ostrom Price said the backhoe operator followed state procedure “to a T” by immediately contacting the co-op’s dispatcher. The dispatcher, in turn, called 911 and immediately alerted NorthWestern Energy, she said.  

Investigators for all of the parties involved conducted initial site documentation and surveying in the days immediately following the accident.

On May 27 investigators reassembled at the site and cleared debris from the basement of the Langtons’ house to conduct gas migration tests.

Compressed air was used to identify the general path of the gas from the broken gas line near the street into the basement of the house. Those tests indicated that the gas escaping from the broken weld generally had followed the soil around the sewer line from the leak to the foundation of the house that exploded, NorthWestern maintained.

After completing the gas migration testing, investigators began excavating the gas piping where the service line for 218 12th St. W. connected to the gas main line near the southwest corner of the intersection.

Most of the gas service line was exposed that day, but the area where the service line connected to the gas main was left buried and covered with a tarp overnight to protect it from the elements, NorthWestern’s investigation indicated.

The ground above the service line/gas main connection was unburied the next day to expose the service line connection to the main. Visual inspection of the exposed line confirmed that the service line had been torn off of the service tee on the gas main line when the service line was snagged by the backhoe on May 6.

The fracture was documented in place and then digging continued to remove and preserve the damaged sections of gas main and service line, NorthWestern’s report said. After the damaged sections of gas piping had been removed, additional non-destructive documentation of the fracture surfaces was performed. 

The basement and exposed sewer lines associated with the house that had been destroyed were documented, and the interior gas piping and boiler collected from the house debris earlier that day were documented and retained. Soil samples also were taken adjacent to the leak site.

“The investigation confirmed that gas migrated from the separation into the home where it exploded,” NorthWestern President and Chief Executive Officer Bob Rowe said in a prepared statement. “While the investigation has ended, the lengthy healing process continues for the Langton and Hilton families and for everyone else who was touched by this tragedy.”

Price echoed that concern.

“It’s been hard for everyone,” she said. “We feel for everyone involved.”

Features editor Lynnette Hintze may be reached at 758-4421 or by e-mail at lhintze@dailyinterlake.com.