SOUTHWEST GAS CORP — Gas distribution — incident on 2008-01-12

Gas distribution incident in SOUTH LAKE TAHOE, ELDORADO County, CA. Reported cause: 10. Reported consequences: 0 fatalities, 0 injuries, $504,909 reported property damage. Operator-reported incident data submitted to PHMSA, generally within 30 days. Records may be supplemented or corrected and do not represent final agency causal findings.

Report number: 20080013.

Operator ID: 18536.

Reported incident date: 1/12/2008.

Cause detail: FIRE/EXPLOSION AS PRIMARY CAUSE

Cause detail: ON JANUARY 9, 2008, A ROOFING CONTRACTOR SHOVELED WET SNOW OFF OF THE ROOF AND PILED IT ON TOP OF THE GAS METER. THE WET SNOW AND ICE THAT WAS PILED BETWEEN THE STRUCTURE AND THE GAS FACILITIES EXPANDED DUE TO ITS PARTIAL MELTING AND SUBSEQUENT FREEZING (A FREEZE/THAW CYCLE). THE FREEZE/THAW CYCLE(S) IMPOSED A HORIZONTAL LOADING ONTO THE GAS FACILITIES AND CAUSED THE METER PIPING TO BREAK DOWNSTREAM OF THE SHUT-OFF VALVE AND UPSTREAM OF THE SERVICE REGULATOR SOMETIME BETWEEN JANUARY 9 AND JANUARY 12, 2008. ESCAPING GAS ENTERED THE STRUCTURE THROUGH EAVE VENTS AND CONTINUED TO BUILD UP UNTIL IT REACHED AN IGNITION SOURCE. UPON IGNITION, STRUCTURAL DAMAGE WAS SUSTAINED TO THE REAR PORTION OF THE RESTAURANT AND SEVERAL GLASS WINDOWS BROKE INSIDE AND OUTSIDE OF THE STRUCTURE. FLYING GLASS DEBRIS CAUSED MINOR INJURIES TO TWO CONFIRMED CUSTOMERS AND ONE UNCONFIRMED. THEY WERE TREATED AND RELEASED AT THE SCENE. THE EXPLOSION WAS GENERATED FROM A FLASH FIRE ONLY WITH NO SUSTAINED COMBUSTION, AND THEREFORE NO FIRE DAMAGE TO THE STRUCTURE. ***SUPPLEMENTAL*** THE PREVIOUS FINAL REPORT SUBMITTED ON FEBRUARY 17, 2009 WAS PREPARED BEFORE AN ANALYSIS WAS UNDERTAKEN BY AN INDEPENDENT METALLURGICAL ENGINEER RETAINED BY SOUTHWEST GAS CORPORATION. THAT ANALYSIS DETERMINED THAT THE FAILURE WAS NOT CAUSED BY THE WEIGHT OF THE WET SNOW THAT WAS SHOVELED ONTO ON THE GAS FACILITIES. INSTEAD, THE FAILURE WAS CAUSED BY THE FREEZE/THAW CYCLE(S) ACTING UPON THE LARGE AMOUNT OF WET SNOW (AND ICE) THAT HAD BEEN SHOVELED ONTO THE GAS FACILTIES WHICH INDUCED HORIZONTAL FORCES ON THE GAS FACILITIES AND CAUSED THEM TO FAIL.

PHMSA trend classification: not significant, not serious, fire-first incident.

PHMSA standardized cause: OTHER OUTSIDE FORCE DAMAGE — FIRE/EXPLOSION AS PRIMARY CAUSE.

PHMSA indexed costs: $504,909 reported total cost, $281,333.682 in 1984 dollars, $692,132.664 in current-year dollars.

PHMSA trend flags, standardized causes, and indexed costs are analytical fields added to operator-reported incident data. They do not represent final agency causal findings.