One issue found in states that allow legalized marajuana is that some folks will use butane to extract hash oil from the buds, and butane leaks will fill the basement with explosive gas mixture.
Another issue can be the meth labs. Still another one that is more relevant to engineers is the use of manual bypasses around the pressure regulating valve at the city gates ,for cities that have natural gas. The insurance investigator would likely review the records of main pressure vs time prior to the incident.
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick