Hazardous Materials Containers: Part 2 – Railroad Cars

Railroad cars that are used to transport hazardous materials are, in many cases, similar to their highway counterparts, but they have much larger capacities.


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 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 transported on highways, but again a primary difference is the increased amount of product being transported in individual containers. Additionally, there may be more than one tank car of the same product, or multiple products.

Highway emergencies usually involve single amounts or small amounts of several chemicals, but rail incidents can involve from one to 100 or more tanks of the same or varying types of hazardous materials. Increased amounts of hazardous materials only compound the situation, making the work of response personnel difficult.

Railroad tank cars contain bulk quantities of hazardous materials and are the primary concern of emergency responders in derailments or other types of rail accidents. In fact, over 80% of all hazardous materials are transported by rail and tank cars account for 70% of the total. Most serious railroad hazmat incidents involve tank cars; therefore, they will be the focus of most of this column.

Cargoes Vary Greatly

More than 200,000 tank cars are used in rail transportation in the U.S. Most tank cars are not owned by railroads, but by private companies. Over 1,200 are owned by the U.S. government and supervised by the military. Government cars are used to transport jet fuels, nitrogen-tetroxide (a rocket fuel) and materials used in weapons production. The amounts of a hazardous material in a tank car can range from a few hundred gallons to as much as 34,500 gallons. (No tank car is considered empty unless it has been purged of the product and cleaned.)

Railroad tank cars are assigned identification numbers that identify the type of tank – pressure, non-pressure, cryogenic or miscellaneous. Tank cars transporting hazardous materials can be identified through 100-series numbers regulated by the U.S. Department of Transportation (DOT). Tank cars that carry non-hazardous commodities such as corn syrup and cooking oil bear 200-series numbers and are regulated by the Association of American Railroads (AAR), are not considered hazardous materials containers.

Numerical designations for tank car designs are as follows:

  • Pressure Tank Car Designations – DOT 105, 109, 112, 114 and 120.
  • Non-Pressure Tank Car Designations – DOT 103, 104, 111 and 115; and AAR 201, 203, 206 and 211.
  • Cryogenic Tank Car Designations – DOT 113; AAR 204 and 204XT.
  • Miscellaneous Tank Car Designations – DOT 106, 107 and 110; and AAR 207 and 208.

While the numbering system for railroad cars identifies particular types of tanks, the numbers may not be readily visible to emergency responders from a safe distance.

The most important concern for emergency responders about a tank car is whether it is a pressure or non-pressure tank. Pressure tanks present a much more difficult and dangerous situation for response personnel than non-pressure cars.

Pressure tank cars and non-pressure tank cars can be differentiated by looking at the locations of valves and other piping on the tops of the cars. On a pressure car all valves and piping are enclosed within a dome at the top center of the tank car. The dome is designed to prevent damage during a derailment. Non-pressure cars can have unprotected valves and piping on tops of the tanks or, in some cases, on top of the domes. Non-pressure tanks may also have bottom fittings and washouts.

Pressure tanks are top loaded through the dome assembly and generally are used to transport flammable and non-flammable gases and poison gases. The tanks may be insulated or non-insulated, and are hydrostatically tested for pressures of 100 to 600 psi. Pressure tank cars present a much more significant hazard to response personnel than do non-pressure cars under heat or flame impingement conditions.

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