Public Utility Commission investigators blame a stress fracture in a 36 -year-old plastic pipe for a gas explosion that destroyed a Kingsbury Grade home a year ago.
A report released last week found no evidence Southwest Gas was to blame for the October 2000 blast, but it does recommend changes in safety inspection procedures and when to order a home evacuated because of a suspected leak.
The blast occurred while inspectors were outside the home of Hans and Suzanne Rosevold at 370 Andria Drive trying to find the source of the leak.
Suzanne, 48, was playing piano and was thrown upward against the ceiling, suffering a broken bone in her back and a fractured heel. Hans, 59, was blown through window of the home and landed in the yard, but escaped with bruises and a cut over one eye.
Inspectors Dennis Sax and Mike Gaylord of Health Consultants, which does safety inspections under contract to Southwest Gas, detected the gas leak while doing a special survey ordered as part of an erosion control project by the Kingsbury General Improvement District.
The PUC report cannot, by law, be used as evidence in a lawsuit. Incident reports are designed to help the PUC determine whether to order changes in construction, inspection and safety regulations to prevent similar problems in the future.
According to the PUC incident report, released last week by the PUC under a new law which makes all incident reports public information, Sax's instruments detected a leak close to the meter outside the house and some gas beneath it.
He warned the Rosevolds three times not to turn on any light, use any electric devices or do anything that would bring about an open flame -- for fear of creating a spark. He continued to investigate but didn't order them to evacuate because he didn't detect gas in the home itself.
After detecting gas concentrations up to 40 percent at the riser pipe connected to the meter, Sax called in a "Grade 1" -- hazardous gas leak -- alert, asking Southwest's dispatch center to send a construction crew to the home.
No sooner had he made the call than something ignited a pocket of gas in the crawl space beneath the home. Half of the structure was destroyed by the blast.
The investigative report said the PVC gas pipe was leaking where it was broken completely in half just inches from where it connected to the metal pipe below the gas meter. It said the underground pipe had been bent downward more than 5 inches over an 18-inch distance.
"The most probable cause of the fracture was mechanical failure caused by high bending stresses at the PVC to steel transition," it says.
According to the report, it wasn't possible to determine whether it was installed that way, caused by slumping earth or a later construction or yard project at the home. It said the pipe might have been bent for years before it failed, but that investigators found no violations by Southwest Gas Corp.
Investigators who went to the scene after the blast found gas had permeated the ground in a wide area around the leak.
"Given the spread and concentration of natural gas in the ground after the explosion, staff believes that the line break occurred well before the explosion," the report says.
The report says the incident shows inspectors should move more quickly to underground testing to determine the size of gas leaks. It says that would almost certainly have shown enough gas to warrant evacuation of the Rosevolds' home.
It recommends reviewing training for field personnel on when to order evacuation of an area when a gas leak is discovered. It also recommends evaluating procedures for how to conduct inspections of leaks in and around structures.
A review of "when should an investigation be abandoned in order to protect the safety of occupants or survey personnel" was also suggested by the report.