At 3:30am an explosion followed by an intense natural gas-fed fire destroyed two apartments at 3022 North 37th Street in Phoenix, AZ. Of the 12 persons injured in the fire, 5 persons died. After the fire was extinguished, the 1 1/2 inch diameter acrylonitrile butadiene styrene (ABS) plastic main supplying gas to the destroyed apartments was excavated and a 3 inch long longitudinal split was discovered in the bottom of the pipe 18 feet from the has meters on the apartment building. Gas at 30 psig had escaped through the longitudinals split, migrated into and under the apartments, ignited, exploded and burned.
We determined that the probable cause of the accident was the deterioration and ensuring rupture of a 1 1/4 inch diameter ANS plastic pipe due to weakening from internal environmental stress cracking that resulted from a chemical reaction between the pipe and liquid entrapped in a low spot in the pipe, which allowed natural has at 30 npsig to escape from the failed pipe and to migrate through the adjacent soil into and under two apartments where it accumulated and was ignited by the has pilot light of a furnace.
Contributing to the accident was the failure of persons who had detected gas odors earlier to report those odors to the gas company or to the fire department. Also contributing to the accident was the absense of a gas company program to analyze the cause of leaks as they occurred.
As a result of this investigation, we issued 15 new recommendations. We issued recommendations to:
- the Southwest Gas Corporation
- Phoenix Fire Department
- the Research and Special Programs Administratoin of the US Department of Transportation
- Committee on Gas of the National Association of Regulatory Commissioners
- to the American Gas Association
- to the Plastic Pipe Institute
