West Knox County, TN –

The Knoxville Utilities Board has concluded it could not determine a cause in the deadly house explosion in West Knox County last December.

But as KUB releases its final report, which leaves many questions unanswered, a fire investigator is releasing his report as well, which provides a theory as to exactly how the explosion happened.

Mike Dalton, a fire investigator for the Knox County Sheriff’s Office, has concluded that a natural gas leak, from outside the home, led to the explosion and subsequent fire.

On Dec. 9, 2009, an early morning explosion destroyed the home of Steve and Sue Krzeski on Grey Pointe Lane. The Krzeskis were blown from their second-floor bedroom into the backyard. Their 18-year-old son, Nick, whose bedroom was in the basement, died in that fire.

In his report, Dalton writes that the gas likely entered the home on that basement level where Nick’s bedroom was located and made it into the utility room, where it was ignited.

He ruled out a number of sources of ignition, including smoking, electrical failure, lightning, cooking, open flames, and an intentionally set fire.

Dalton also told 10News that, because the leak came from outside the home, it rules out the possibility that any of the home’s interior appliances, including the much-discussed fireplace, could have caused the explosion.

“It was determined that the gas appliances in the structure would have had to (have) leaked for a significantamount of time and been discovered by residents before reaching the level to have caused this type of explosion,” he wrote.

The report concludes that the gas migrated from “the gas main at the street into the structure and filled the mechanical room where it could be ignited by the furnace.

“Examination of the furnace in the center of the room showed indicators that the combustion chamber was bent outward.

“The ignition source and the reason the gas escaped its pipeline and (found) its way into the structure is not known at this time.”

Meanwhile, KUB’s report was much less conclusive.

After extensive testing of the pipeline, air and soil, KUB’s final report says the “apparent cause of the natural gas incident is unknown.”

Crews did find a problem at the connection site of the Krzeskis’ service line to KUB’s main pipeline, where a small fire occurred.

“We did discover that the bolts on the particular fitting did fail, although the inconclusive component of that is that we do not know whether they failed before the incident or as a result of the incident,” said Chris Spencer, KUB regulatory specialist.

That fitting is known as a “tee” fitting.

Jim Wright, the attorney for the manufacturer of that particular fitting, Elster Perfection Corp., said the problem really began during installation.

The “tee” itself is fine,” Wright said. “It’s been taken apart and been inspected by a number of experts. The “tee” works properly, it just simply was not connected all the way to pipe by the installer.”

That fitting is known as a “self-tapping tee.” The fitting is clamped around the main gas pipeline, secured with four screws, and then locked into place by a large screw that is inserted from the top. Wright said that the evidence showed that top screw never made it into the Krzeskis’ pipe, which means it was not secured properly.

While experts say they still don’t know if the fire at the site of the pipe fitting happened before or after the explosion, KUB is taking some proactive steps.

Spencer says crews will replace all 1,500 of the “tee” fittings installed throughout the coverage area between the 1997 and 2001.

The new fittings will be connected using a heat fusion process, rather than the “self-tapping tee.”

Also, over the next year, workers will inspect the more than 14,000 other fittings installed during that five-year period to ensure everything is safe and working properly.

Spencers estimates the cost of this work to be between $2 million and $4 million, but he adds that that cost will not be transferred to customers.

Meanwhile, the state agency that regulates KUB is looking into the incident.

Larry Borum, the chief of the Tennessee Regulatory Authority Natural Gas Pipeline Safety Division says he is reviewing reports and documents to come up with a conclusion as to what happened.

On Wednesday afternoon, he was not yet ready to make a determination.

When he is, TRA will submit a final report to the Department of Transportation’s Pipeline and Hazardous Materials Safety Administration.