Gas Explosion and Fire
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A gas explosion and fire destroyed a residential duplex late one January night, injuring two occupants. 60 feet away from the building, a gas leak was discovered in a six-inch main under the street. The gas service for the duplex was connected to a separate, twelve-inch main. It was not clear there was any connection between the leak and the explosion. Subsequently, scene investigators discovered a large crack in the foundation on the origin side of the duplex.
Through the process of scene documentation, it was determined the HVAC system was improperly designed and installed in violation of the Massachusetts state building code. Through 3D modeling and on-site testing, a multidisciplinary team of investigators concluded the non-compliant HVAC system created negative pressure in the basement. This condition pulled gas from the ground into the basement where it entered an open-ended return air duct and was circulated through the building until the gas/air concentration reached the explosive limit.