NTSB Safety Recommendation P-70-031

NTSB safety recommendation P-70-031.

THE NTSB RECOMMENDS THAT THE OFFICE OF PIPELINE SAFETY OF THE DEPARTMENT OF TRANSPORTATION TAKE THE FOLLOWING ACTION: CONDUCT A STUDY TO DETERMINE WHAT CONSTITUTES A SAFE MAXIMUM OPERATING PRESSURE FOR LOW-PRESSURE DISTRIBUTION SYSTEMS. FURTHER, USE THE RESULTS OF SUCH STUDY IN FORMULATING MINIMUN FEDERAL SAFETY STANDARDS, SO THAT THE DESIRED PRESSURE AND THE CORRECT FUNCTIONING OF MONITORING REGULATORS AND OTHER OVERPRESSURE PROTECTION DEVICES WILL BE DEFINED.

Priority: CLASS II

Overall Status: Closed - Acceptable Alternate Action

Issued Date: 1970-10-14

Adopted Date: 1970-10-14

Overall Date Closed: 1976-09-10

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: RSPA

Addressee Status: Closed - Acceptable Alternate Action

Addressee Date Closed: 1976-09-10

Addressee Acronym: RSPA

Addressee Organization Type: G-Federal Government

Communication Date: 1975-06-17

Communication Type: Official Correspondence

Communication Contents: 5/7/71 - LETTER FROM DOT: SECTION 192.623 ADDRESSES ITSELF TO MINIMUM AND MAXIMUM ALLOWABLE OPERATING PRESSURES. HOWEVER, IT WILL BE IMPORTANT TO STUDY THIS AREA TO INSURE THAT OUR RULE IS EFFECTIVE. 6/17/75 - STATUS REPORT FROM OPS STATED, OUR EXPERIENCE TO DATE HAS NOT INDICATED A SAFETY NEED FOR REVISIONS TO THE REGULATIONS IN THIS AREA. EXISTING SECTIONS 192.201 REQUIRED CAPACITY OF PRESSURE RELIEVING AND LIMITING STATIONS, 192.195 PROTECTION AGAINST ACCIDENTAL OVERPRESSURE, 192.623 MAXIMUM AND MINIMUM ALLOWABLE OPERATING PRESSURE: LOW PRESSURE DISTRIBUTION SYSTEMS, AND 192.743 PRESSURE LIMITING AND REGULATING STATIONS; TESTING OF RELIEF DEVICES MAY BE ADEQUATE. CORRESPONDENCE DOCUMENTATION INCOMPLETE.

Addressee Acronym: RSPA

Addressee Organization Type: G-Federal Government

Communication Date: 1971-07-17

Communication Type: Official Correspondence