Last Thursday, a 30-inch gas “transmission line” ruptured beneath suburban San Bruno, south of San Francisco. A massive fireball shot 1,000 feet into the air, destroying 37 homes and killing at least four people. The National Transportation Safety Board (NTSB) has launched an investigation into the cause of the explosion. While it may seem like a freak accident, this incident is only one of a number of natural gas disasters this year. How many gas lines are there in residential neighborhoods? Are there sufficient safety precautions in place?