General service tank cars are used to transport a wide variety of liquid and solid materials, both hazardous and non-hazardous. Although they are classified as DOT-111 “nonpressure” by the U.S. Department of Transportation, general service tank cars are equipped with pressure relief devices that protect against excess internal pressure as well as prevent a vacuum from forming within the tank. The emergency conditions that would activate a pressure relief device include exposure to fire, hydrostatic pressure from overloading, a build-up of pressure from exothermic reactions in the lading, and pressure spikes caused by surging liquids during over-speed impacts.
