NORTHERN NATURAL GAS CO — Gas transmission and gathering — incident on 2017-12-07

Gas transmission and gathering incident in Not Within a Municipality, SAUK County, WI. Reported cause: EQUIPMENT FAILURE. Reported consequences: 0 fatalities, 0 injuries, 3396 NATURAL GAS released, $0 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: 20170120.

Operator ID: 13750.

Reported incident date: 12/7/2017 2:15.

Location detail: MP 40.75

Cause detail: MALFUNCTION OF CONTROL/RELIEF EQUIPMENT

Cause detail: ON DECEMBER 7, 2017, AT APPROXIMATELY 0357 HOURS, THE SAUK COUNTY SHERIFF'S OFFICE NOTIFIED THE OPERATIONS COMMUNICATION CENTER THAT A LOUD NOISE WAS OBSERVED AT THE SPRING GREEN COMPRESSOR STATION. OPERATIONS RESPONDED AND FOUND NO ISSUES WITH THE UNIT OR STATION THAT WOULD HAVE CAUSED A HIGH PRESSURE SITUATION. THE RELIEF VALVE IS SET AT 880 PSIG BUT ACTUATED AT 798 PSIG. THE VALVE WAS DISASSEMBLED FOR INSPECTION AND A BUILDUP OF ICE IN THE PILOT WAS DISCOVERED. THE RELIEF VALVE WAS REPAIRED AND PLACED BACK IN SERVICE.

PHMSA trend classification: not significant, not serious.

PHMSA standardized cause: EQUIPMENT FAILURE — MALFUNCTION OF CONTROL/RELIEF EQUIPMENT.

PHMSA indexed costs: $9,621 reported total cost, $9,135.325 in 1984 dollars, $11,216.791 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.