Are You Using Proper Tank Truck Lingo?

Here's a look at some of the key terms tank truck operators should use to create a unified industry language
Are You Using Proper Tank Truck Lingo?
A specification plate shows that this trailer was built under a special permit.

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Every industry has its own language — the lingo you use to discuss truck parts and tank components. The tank truck industry is certainly no exception. Ask a mechanic in one part of the country to check the Christmas tree on the trailer and you’d receive a blank stare. But a mechanic in another part of the country would know immediately to inspect fittings on the dome cover. 

While local jargon might be your go-to, it is not appropriate when discussing U.S. DOT cargo tank regulatory requirements. Let’s take a look at some of the key terms that should be used consistently by tank truck operators, shippers, regulators, manufacturers and repair facilities to create a unified industry language standard.

Spec vs. non-spec

A specification cargo tank must be built, inspected, tested, maintained or repaired to DOT standards. Specification cargo tanks are mandated for most, but not all, hazardous materials. 

The most common specification cargo tank is the DOT406 used for petroleum products, the DOT407 general chemical tank, and the DOT412 tank used for acids and corrosives. Less common tanks are the MC331 for compressed gases like propane or anhydrous ammonia, and the MC338 tanker used for cryogenic liquids. 

A specification tank carries a specification plate, which includes information on the manufacturer, capacity and construction material. Any tanker that has a specification plate must remain in compliance with the specification regardless of the product hauled. All DOT inspections must be up to date if you have a spec plate on the tanker, even if you are hauling water. The spec plate describes the tank, not the product. 

A non-spec tank is not built to any specific DOT regulation, though most of these are very similar to DOT406 tankers. With just a few exceptions like diesel fuel hauled only in the U.S., non-spec tanks are used for nonhazardous materials such as food products or wastewater. 

A specification tanker can be converted to a non-spec tank by removing or covering up the spec plate and submitting the appropriate paperwork. Covering the plate rather than removing it is recommended if there is a possibility that the tank may someday be recertified as a spec tank. 

Code tanker

Specification cargo tanks are often referred to as code tankers. The difference is important in trailer specification and repair, as well as in initial and ongoing costs. The DOT requires certain specification cargo tanks be constructed and certified in accordance with Section VIII of American Society of Mechanical Engineers code. Factors such as operating pressure and material of construction are considered when determining if an ASME code tank trailer is required. 

The DOT is currently considering allowing the use of ASME code Section XII as an alternative to Section VIII. That change should not have an immediate impact on tank truck operators. Manufacturers of specification cargo tanks must hold an ASME U-stamp and must build trailers in accordance with the ASME code, but need not certify the spec tanker to the code. 

Remember, all code tankers are specification tanks, but not all specification tanks are code tankers. 

Special permits and exemptions

DOT’s Pipeline and Hazardous Materials Safety Administration is authorized to grant a special permit (SP) to allow a person to perform — or not perform — a function not currently authorized under the regulations. That function must meet or exceed the requirements of the affected regulation. The term exemption was used prior to 2005 when it was replaced with special permit. You will still hear people refer to exempt tankers, but that term is no longer accurate.

The most common SPs in the tanker industry allow for the use of materials of construction not otherwise authorized (FRP or some stainless steels), for different product loading or unloading systems, or to allow a product to be transported in a tanker not otherwise allowed. 

A tank constructed under an SP must have the SP number displayed on the spec plate. Any tanker operated under a special permit must have a DOT SP marking followed by the number of the permit. A copy of the SP also must be carried on the truck or tractor. 

Anyone involved in cargo tank operations should have a current copy of the DOT regulations. Both general and hazardous materials regulations are available online or in print from the government or from commercial suppliers. A cargo tank specific bulk hazardous materials regulatory compliance guide is available from National Tank Truck Carriers. 

About the Author

John Conley is past president of National Tank Truck Carriers and former editor of Modern Bulk Transporter magazine. He is president of ConleyComm LLC in Chester, Maryland. Contact him at


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