Intermodal Tank Containers: Often Forgotten but Ever Present

It is an undeniable fact that hazardous materials responders should possess a thorough knowledge of the containers that hazardous materials are transported in. When we focus our attention towards the realm of hazardous materials transportation, we often think about the “usual suspects” of railcar transportation and the MC/DOT specification series of highway transportation trailers and vessels. The one area of hazardous materials transportation containers that is usually overlooked is that of intermodal tank containers, as we usually do not encounter such containers on incident scenes or in training as often as other highway or rail transportation containers. Intermodals are by their very nature present in the transportation realm, but also are encountered at fixed facilities. If we as hazardous materials response professionals overlook intermodal containers, we are doing ourselves and the citizens we protect a huge disservice.

A major consideration in responses to intermodal tank container incidents in present-day times is that intermodal tank containers may not only be present on highway, rail, or maritime transportation conveyances; but may also be present at facilities as temporary, semi-permanent or permanent bulk containers.

Intermodal containers are named as such because they are containers surrounded by a frame that allows them to be placed on multiple modes of transportation, e.g. a highway transportation flatbed trailer, a flatbed railcar, or waterborne transportation such as a ship. Intermodals are also known as isotainers (short for ISO container) due to the fact that the International Organization for Standardization (ISO) develops the specifications to which the containers are constructed to in international transportation. As a side note, the International Maritime Organization (IMO) stipulated such specifications through 2001. Although the broad description of intermodal containers includes both intermodal tanks and intermodal box (or “conex”) containers, we will concentrate our discussion on intermodal tank containers.

We will first turn our attention to the product identification markings that are specific to intermodal tank containers. While intermodal containers should possess the usual placarding as required by Department of Transportation (DOT) regulations and the UN/NA Identification Number appropriate for the product transported either on a placard or by itself in an orange rectangle, there is also an identification system specific to intermodal containers that are shipped internationally that allows us to determine what the container is carrying and the hazards of the product therein. This identification system consists of two orange rectangles stacked atop each other. The bottom rectangle contains the UN/NA Identification Number of the product, which allows us to determine the product inside utilizing the Emergency Response Guidebook or other research sources. The top rectangle contains a Hazard Identification Number (HIN), also known as a “Kemler Code.” If the HIN begins with an “X” it indicates that the product is water reactive. The numbers comprising the HIN then indicate the hazard or hazards presented by the contents, which can then be researched in the Emergency Response Guidebook in the pages dedicated to intermodal containers (pages 16 through 19 in the 2016 ERG). For example, a code of “8” corresponds to a general hazard of corrosivity. The doubling of a digit indicates that the hazard is intensified. If the HIN is comprised of a single numerical digit, it will be followed by a zero. A third numerical digit provides additional information. A code of “80” would then correspond to a corrosive substance, while a code of “88” corresponds to a highly corrosive substance. A code of “886” corresponds to a substance that is a highly corrosive toxic substance, all of which are delineated in the Emergency Response Guidebook.

As stated above, the previous IMO specification system for tank containers was succeeded internationally by the ISO “T Code” system that was introduced in 2001. The T Code system classifies intermodal tank containers by test pressure, shell thickness, pressure relief device or devices, and bottom opening requirements. For example, a “T12” tank container has a test pressure of 6 bar (87 psi), a shell thickness of at least 6mm, has a pressure relief device and rupture disc; and three shut off devices (internal, external; and a cap or blank). While the T Code system is currently in use internationally, we will discuss intermodal tank containers in greater detail by their current DOT domestic IM specification, as that is still in use domestically and is what most responders in the United States remain most familiar with.

The IM-101 and IM-102 intermodal tanks (formerly known as IMO 1 and IMO 2 in international transportation) are considered to be nonpressure tanks, which is a misnomer because their working pressure can be up to 100 psi. I often envision them as being closely akin to low pressure (general service) rail tank cars and/or DOT 406/407 highway transportation tank trailers. IM-101 tanks have maximum working pressures of 25.4 psi to 100 psi, while IM-102 tanks have maximum working pressures of 14.5 psi to 24.4 psi. The hazardous materials transported in IM-101 tanks include toxics, corrosives, and flammable liquids with flash points below 32 degrees Fahrenheit in quantities from 5,000 gallons to 6,300 gallons. IM-102 tanks contain commodities such as alcohols, corrosives, solvents, and flammable liquids with flash points from 32 degrees Fahrenheit to 140 degrees Fahrenheit in quantities from 5,000 gallons to 6,300 gallons.

The tank container fittings that may be present somewhat resemble those found on low pressure (general service) rail tank cars and/or DOT 406/407 series highway tank trailers, such as a top manway (often surrounded by a spillbox), a dipstick level gauge, top loading valves, bottom discharge valves, air line connections for pressure offloading, and pressure relief/vacuum relief devices. IM-101 and IM-102 tank containers transporting hazardous materials are required to have two bottom outlet valves for redundancy that are externally operated and a liquid-tight closure such as a screw cap, blind flange or other type of cap.

Pressure intermodal tank containers are termed DOT Spec. 51 containers in the U.S. and were formerly termed IMO Type 5 containers in international transportation. Such containers closely resemble MC 331 highway transportation tank trailers surrounded by a frame. As with any intermodal tank container, the frame may run continuously along the length of the container (“box type”) or may only exist at the ends of the tank with the tank itself providing structural rigidity (“beam type”). The working pressure of Spec. 51 containers ranges between 100 psi and 500 psi, with normal internal quantities ranging from 4,500 gallons to 5,500 gallons. Commonly transported commodities include LP gas, anhydrous ammonia and chlorine. Tank fittings commonly resemble pressure railcar and/or MC 331 highway tank trailer fittings such as liquid and vapor lines/valves; excess flow devices, sample lines, thermometer wells, and pressure relief devices.

Other specialized intermodal tank containers that are in use include intermodal cryogenic tanks (formerly known as IMO Type 7 and now internationally known as ISO T75 tanks) that transport gases liquefied by cooling (e.g. liquid helium and oxygen) and resemble MC 338 cryogenic highway tank trailers surrounded by a frame. Tube module intermodals transport compressed gases in high pressure cylinders reminiscent of compressed gas tube highway trailers surrounded by a frame, with working pressures of 3,000 psi to 5,000 psi. Materials transported include oxygen, nitrogen, and helium.

A major consideration in responses to intermodal tank container incidents in present-day times is that intermodal tank containers may not only be present on highway, rail, or maritime transportation conveyances; but may also be present at facilities as temporary, semi-permanent or permanent bulk containers. A facility can rent the intermodal container and then incorporate it into a plant system for a cost-effective means of product storage. Such storage methods can lead to big surprises if we do not effectively perform our proper pre-incident planning.

In conclusion, many hazardous materials responders dismiss the need for developing a thorough knowledge of intermodal tank containers, as responses involving such containers normally occur on an infrequent basis. The truth is that intermodal tank containers are present in many of our response districts and may be encountered in both transportation and fixed facility settings. As such, we should continue to develop our knowledge base regarding intermodal tank containers to remain on our hazmat “A Game.”

As always, stay safe out there and be sure to visit the North Carolina Association of Hazardous Materials Responders website at

Glenn Clapp is a past president of the North Carolina Association of Hazardous Materials Responders and has over 22 years of fire service and emergency management experience. He is currently an Improvement Specialist with the Industry Expansion Solutions Division of North Carolina State University and is a volunteer firefighter with the Fairview Fire Department. He is also a Technician-Level Hazmat Instructor, an Executive Fire Officer, a Certified Hazardous Materials Manager and a Certified Fire Protection Specialist.

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