NTSB Safety Recommendation P-70-037

NTSB safety recommendation P-70-037.

THE NTSB RECOMMENDS THAT IOWA SOUTHERN UTILITIES, INC., TAKE THE FOLLOWING ACTION: REVIEW ITS OWN REGULATOR DESIGN, MAINTENANCE, AND TRAINING PROCEDURES TO DETERMINE WHETHER ITS GAS CONSUMERS WILL BE PROPERLY PROTECTED AGAINST OVERPRESSURIZATION IN THE EVENT OF A MALFUNCTION OF A PRIMARY REGULATOR.

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.

Keywords: Maintenance, Training and Education

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Addressee Status: Closed--No Longer Applicable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: AN ENGINEERING CONSULTANT WAS HIRED TO MAKE A STUDY OF REGULATOR STATIONS ON THE LOW PRESSURE SYSTEM IN BURLINGTON, IOWA, AND TO MAKE RECOMMENDATIONS TO PROPERLY PROTECT THE SYSTEM AGAINST OVERPRESSURIZATION AND RECOMMENDED SET POINTS OF MONITOR REGULATORS. MONITOR REGULATORS ON THE SYSTEM WERE PILOT LOADED TO PROVIDE MORE SENSITIVE CONTROL UPON FAILURE OF WORKING REGULATORS. AN OVERPRESSURE WARNING DEVICE WAS INSTALLED AND LOCATED IN THE DISPATCHING OFFICE. CONCRETE-FILLED STEEL POSTS HAVE BEEN INSTALLED AROUND BOTH REGULATOR PITS FOR ADDED PROTECTION. THE CONTROL LINE TO THE MONITOR REGULATOR HAS BEEN RELOCATED OUTSIDE THE REGULATOR PIT AND AT A LOWER DEPTH. CORRESPONDENCE DOCUMENTATION INCOMPLETE.

Addressee Acronym: ISU

Addressee Organization Type: P-Private Industry

Communication Date: 1971-06-02

Communication Type: Official Correspondence