Railroad cars that are used to transport hazardous materials are, in many cases, similar to their highway counterparts, but they have much larger capacities. The primary types of railcars are box, hopper, bulk, tank, flat and tube. Types of hazardous materials carried by rail are much like those...
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Railroad tank cars, as previously mentioned, are built to DOT specifications for hazardous materials transportation. Certain markings are required to be stenciled on each tank car as a part of the specification requirements.
Of particular interest to emergency responders is the requirement that names of certain commodities be stenciled on both sides of the tank car in four-inch-high letters. Some 50 materials require name stenciling; these include anhydrous ammonia, chlorine and liquefied petroleum gas. Additionally, if a material is an “Inhalation Hazard,” that too must be stenciled on the container above the commodity name.
A tank containing hazardous materials will bear a DOT specification including DOT followed by the tank car type, such as 111, or DOT-111. Next to the tank car type will be a letter designating the type of protection the pressure car has for accidents or flame exposure:
- A – the tank has top and bottom shelf couplers.
- S – the tank has A plus head puncture resistance.
- J - the tank has A and S and jacket thermal protection.
- T - the tank has A, S, J and spray-on thermal protection.
If the tank is a pressure container, following the letters will be a number indicating the tank test pressure. Following the test pressure will be letters designating the type of material in which the tank is constructed: Al designates aluminum, N nickel, and C, D and E for stainless steel. Non-pressure tanks will not have the test pressure information.
Unless they are carrying certain poison gases, such as hydrocyanic acid, pressure tanks have relief valves designed to relieve excess pressure caused by increases in ambient temperature. These relief valves are not designed to relieve the pressure created from radiant heat from a fire or other source or direct flame impingement.
Many accidents have occurred over the years from boiling liquid expanding vapor explosions (BLEVEs) when pressure containers have had excess pressure buildup. These accidents have resulted in many firefighter and civilian deaths and injuries when pressure relief valves could not keep up with internal pressure buildup and the tanks failed.
Boxcars are also used to transport hazardous materials. Individual container sizes inside boxcars are 119 gallons or less and, in many cases, 55 gallons or less. Potentially, any class of hazardous material may be included in boxcar shipments.
Flat cars are used to ship pallets of hazardous materials, including small containers. Flat cars are also used to carry “intermodal containers,” which can be box containers or any type of bulk tank container. Intermodal containers get their name from the fact that they are shipped by highway, rail and water. They can carry any class of hazardous material and the quantities will be smaller than ordinary highway or rail containers. There can, however, be multiple intermodal containers that can present a quantity problem during an accident.
Hopper cars do not always contain hazardous materials, but the physical state of the materials in the container may present a hazard. When suspended in air, fine powders and dusts can become a dust explosion hazard. An accident could cause the materials to be airborne; if an ignition source is present, a dust explosion can occur.
Response personnel who have railroads that transport hazardous materials through their jurisdictions should be familiar with types of rail cars and the hazardous materials they contain. NFPA 472, 1997 edition, lists the competencies that a hazmat technician with a railroad tank car specialty should have.
Robert Burke, a Firehouse® contributing editor, is the fire marshal for the University of Maryland. He is a certified Hazardous Materials Specialist, and has served on state and county hazmat response teams. Burke is a veteran of over 18 years in the fire service, in career and volunteer fire departments, having attained the ranks of lieutenant and assistant chief, and served as deputy state fire marshal. He has an associate’s degree in fire protection technology and a bachelor’s degree in fire science, and is pursuing a master’s degree in public administration. Burke is an adjunct instructor at the National Fire Academy. He is the author of the books Hazardous Materials Chemistry For Emergency Responders, published in 1997, and Counter-Terrorism For Emergency Responders, published in 1999. Burke can be reached on the Internet at email@example.com.