NTSB Safety Recommendation P-70-040

NTSB safety recommendation P-70-040.

THE NTSB RECOMMENDS THAT IOWA SOUTHERN UTILITIES, INC., TAKE THE FOLLOWING ACTION: DEVELOP A WRITTEN, COMPREHENSIVE REGULATOR MAINTENANCE AND TESTING PROCEDURE TO ASSURE PROPER OPERATION DURING NORMAL USE AND IN THE EVENT OF EMERGENCIES, PENDING ANY GOVERNMENT-ORIGINATED REQUIREMENTS. APPROPRIATE RECORDS OF MAINTENANCE WORK PERFORMED SHOULD BE MADE.

Priority: CLASS II

Overall Status: Closed - Acceptable Action

Issued Date: 1970-10-14

Adopted Date: 1970-10-14

Overall Date Closed: 1976-07-20

Synopsis: ON NOVEMBER 6, 1969, DURING A HIGHWAY CONSTRUCTION PROJECT IN BURLINGTON, IOWA, A BULLDOZER WEIGHING 70,000 POUNDS DROVE OVER AND PARTIALLY COLLAPSED THE STEEL COVERS OF A GAS REGULATOR PIT, DAMAGING THE REGULATOR. WHILE THE PRESSURE WAS PARTIALLY CONTROLLED BY A MONITORING OR SAFETY REGULATOR, GAS, REPORTEDLY AT FOUR TO FIVE TIMES THE NORMAL OPERATING PRESSURE, ENTERED THE DISTRIBUTION SYSTEM. GAS CUSTOMERS IN THE AFFECTED AREA STARTED REPORTING HIGH GAS PILOTS AND FIRES TO ISU AND THE FIRE DEPARTMENT. THE HIGH-PRESSURE GAS SOURCE WAS TURNED OFF BUT FIRES CONTINUED TO BE REPORTED, THE FIRES WROUGHT MAJOR DAMAGE TO THE INTERIORS OF 10 HOUSES AND MINOR DAMAGE TO KITCHENS AND APPLIANCES IN 42 OTHERS. PROPERTY DAMAGE WAS ESTIMATED AT $80,000.

Probable Cause: The probable cause of the fires in the houses was the continued overpressure condition of the low-pressure distributions system for an extended period of time, which allowed pressure to build up until high gas flames ignited nearby objects. The initiation of the overpressure was caused by a bulldozer which damaged the largest primary working regulator which, with other regulators, controlled the gas pressure entering the low-pressure systems; and by inadequate performance of the monitoring regulator which failed to operate to limit the gas pressure to a safe level.

Ntsbnumber: DCA70MP001

Report Number: PAR-70-01

Addressee Name: Iowa Southern Utilities, Inc.

Addressee Status: Closed--No Longer Applicable

Addressee Date Closed: 1976-07-20

Addressee Acronym: ISU

Addressee Organization Type: P-Private Industry

Communication Date: 1971-07-07

Communication Type: Official Correspondence

Communication Contents: THE BOARD WAS INFORMED BY LETTER THAT THE FOLLOWING ACTION HAS BEEN TAKEN: A REGULATOR STATION INSPECTION PROCEDURE HAS BEEN WRITTEN AND SUBMITTED TO THE BOARD. CORRESPONDENCE DOCUMENTATION INCOMPLETE.

Addressee Acronym: ISU

Addressee Organization Type: P-Private Industry

Communication Date: 1971-06-02

Communication Type: Official Correspondence