​​​On June 3, 1969, a series of explosions and fires occurred in the natural gas distribution system in the western half of the Glen Park residential subdivision of Gary, Indiana. There were no fatalities, but nine residents and five firemen were injured. Seven houses were destroyed, and 45 others incurred damage extending from minor to virtual destruction. Total property damage was about $350, 000.

We find the probable cause of this accident was a combination of personnel error and system inadequacy. Involved were the inadvertent opening of a separation valve by a gas company employee allowing gas at 20 p. s. i. g. to flow into a l / 4 p. s. i. g. system and a system which could not control adequately such an increase in pressure owing to the lack of overpressure protection devices. Thereafter, the increase in pressure caused the failure of a regulator diaphragm which allowed an 80-fold overpressure in the low-pressure system to become continuous for 30 to 45 minutes.

Significant contributing causal factors were:

1. ​The inaccessibility of the shutoff valve for the regulator which failed.
2. The lack of a systematic review of the hazards in the conversion operation which could have revealed the hazardous condition in which one human error could produce catastrophe, coupled with the lack of a written plan for the conversion.
3. The absence in Code B31. 8 of any specification of safe­ guards to be employed at separation (isolation) valves during pressure conversions.
4. The lack of complete leakage surveys, before and during the pressure increase in the eastern area, which would have probably disclosed the lea.king condition of the pipe and avoided the major leaks which occurred on June 3, 1969.