NTSB Safety Recommendation P-70-041

NTSB safety recommendation P-70-041.

THE NTSB RECOMMENDS THAT THE IOWA STATE HIGHWAY COMMISSION TAKE THE FOLLOWING ACTION: REVISE ITS PROCEDURES SO THAT ITS INSPECTORS, WHO WILL BE ASSIGNED TO A CONSTRUCTION JOB, ARE AWARE OF THE VARIOUS ASPECTS OF THE PROJECT AND PROBLEMS OF INTERFERENCE WITH UTILITIES.

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: State of Iowa, Highway Commission

Addressee Status: Closed--No Longer Applicable

Addressee Date Closed: 1976-07-20

Addressee Organization Type: S-State Government

Communication Date: 1970-12-21

Communication Type: Official Correspondence

Communication Contents: LETTER FROM DIRECTOR OF IOWA STATE HIGHWAY COMMISSION: WE CERTAINLY CAN MAKE SOME EFFORT IN THIS AREA. WE WILL MAKE EVERY ATTEMPT TO HAVE THE INSPECTION FORCES WELL INFORMED AT ALL TIMES ON ALL THE FACTORS OF THE PROPOSED CONSTRUCTION.