A Comprehensive Guide to DOT 406, 407, 412 and MC-331 Tanker Trailers

The role of the Department of Transportation (DOT) and the Federal Motor Carrier Safety Administration (FMCSA)

The Department of Transportation (DOT) is a federal agency responsible for ensuring the safety and efficiency of the United States transportation system. The Federal Motor Carrier Safety Administration (FMCSA), a division of the DOT, is tasked with promoting the safety of commercial motor vehicles (CMVs) and their drivers. This includes developing and enforcing regulations, conducting safety audits and investigations, administering safety programmes and funds, and providing education and outreach to the industry and public. The FMCSA also maintains a database of safety performance data for motor carriers and drivers, which is used to identify and address potential safety concerns. Together, the DOT and FMCSA promote a safe, efficient transportation system, with the FMCSA focusing on commercial motor vehicles.

DOT Codes vs MCC (Motor Carrier Code)

The US DOT (Department of Transportation) code is a unique identifier assigned by the Federal Motor Carrier Safety Administration (FMCSA) to carriers engaged in operating commercial motor vehicles in interstate commerce. This code is used for regulatory and monitoring purposes to track the carrier's safety performance, compliance with federal regulations, and other important information related to their operations. All vehicles conducting interstate commerce, with a gross vehicle weight rating of over 10,000 pounds, that transport more than 8 passengers (including the driver) for compensation, more than 15 passengers not for compensation, or any amount of hazardous materials, must be registered and have a DOT number.

On the other hand, the MC (Motor Carrier) code is also assigned by the FMCSA but specifically to carriers who transport regulated commodities in interstate commerce. Regulated commodities refer to items that are subject to federal regulation, such as hazardous materials and household goods, pharmaceuticals, agriculture commodities, and other specialized cargo. The MC code is used to monitor the carrier's compliance with federal regulations related to the transportation of these regulated commodities. It includes adherence to rules and requirements related to vehicle safety, driver qualifications, hours of service, hazardous materials transportation, and more. For example, vehicles may need to meet certain safety standards, such as having properly functioning brakes, tires, and lights, and drivers may need to meet licensing, training, and medical certification requirements.

In essence, both the US DOT and MC numbers are unique identifiers assigned by the FMCSA to carriers engaged in interstate commerce. The US DOT number is used to track carriers engaged in commercial motor vehicle operations, while the MC number is used to identify carriers who transport regulated commodities for hire in interstate commerce. Therefore, all commercial vehicles may need a DOT number, but only certain types of commercial activities require an MC number.

DOT 406: Non-Pressurized Tankers for Flammable Liquids

DOT 406 / MC 306 tank trailers are primarily designed for the safe transportation of highly flammable liquids such as gasoline, diesel, Jet fuel, and others. These trailers are commonly used in the transportation industry to deliver fuel to gas stations, airports, and other fuel-dependent businesses. Constructed primarily from lightweight aluminum, these trailers feature a heavily reinforced top that is excavated to contain small spills. They typically consist of three to four compartments, each with its own hatch for easy access. The tanks are elliptical in shape when viewed from the rear, with oval or egg-shaped cross-sections and flat or nearly flat ends with an average hauling capacity of 9000 gallons. DOT 406/ MC 306 tanker trailers have bottom discharge options for safe and easy loading and unloading of flammable liquids. While adhering to DOT safety regulations, these trailers have various safety features like highly engineered manlids/manholes, vapor recovery systems, emergency internal valves, and electronic stability control (ESC) systems to ensure human and environmental safety on roadways.

Here are some of the general specifications of DOT 406/MC306 tank trailers. However, the specific features may vary based on the manufacturer and the intended cargo.

• Built Material: Primarily constructed from aluminum.
• Pressure: Minimum design pressure is typically 3 pounds per square inch gauge (psig).
•  Design: Elliptical with straight bottom & double taper bottom variants
• Loading/Unloading: Typically equipped with bottom loading facilities to ensure safe and efficient loading/unloading of materials. 
•  Compartments: Single-compartment and multi-compartment designs
• Emergency Features: Emergency venting facilities, emergency shutoff-drivers side front, rollover rail protection to protect the tank's top fittings in a rollover and more.
• Capacity range: 9000 to 9500 gallons 

DOT 407: Chemical Tankers

The DOT 407 / MC 307 chemical tank trailers are durable stainless steel tank trailers, designed to efficiently secure and transport non-corrosive chemical liquids and related products, particularly solvents and petroleum-based chemicals. These trailers are the workhorse for the chemical industries with a standard hauling capacity ranging between 5000 to 7000 US Gallons, while the largest tank trailer can haul up to 8000 Gallons. With a pressure of up to 40 psi at 70 degrees Fahrenheit, these chemical tank trailers are used in a variety of industries, including the chemical manufacturing industry, petroleum industry, and agricultural industry, requiring strict adherence to DOT safety regulations to prevent spills, leaks, or accidents. That is why these trailers are equipped with safety features such as pressure relief valves, emergency shut-off valves, and spill containment systems.

In addition, tank trailers can be fitted with extended manways, platforms, ladders, and hydraulic guardrails for ease of use and maintenance.

Here are some of the general specifications of DOT 407 tank trailers. However, the specific features may vary based on the manufacturer and the intended cargo.

• Built Material: Generally made from stainless steel.
• Pressure: Design pressure typically around 25-40 psig
•  Design: Round or Elliptical shape with straight bottom & double conical bottom design.
• Loading/Unloading: Equipped with top and/or bottom loading facilities.
•  Compartments: Single-compartment and multi-compartment designs
• Emergency Features: Emergency venting facilities, emergency shutoff-drivers side front, rollover rail protection to protect the tank's top fittings in a rollover and more.
• Capacity range: Average from 7000 to 8000 Gallons for tandem axles
• Other Features: Insulated and non-insulated variants.

DOT 407: Crude Oil Tank Trailers

The DOT 407 / MC 307 crude oil tank trailers are robust aluminum or stainless steel trailers designed to handle the specific challenges and hazards associated with the transportation of thick, unrefined oils. These trailers are often used in the oil and gas industry to move crude oil from its source to refineries. With an average hauling capacity of 8400 to 13000 US gallons, these trailers are available in double conical tank designs, typically with one compartment, and often are standard as non insulated, but in colder climates trailers will be insulated.

These trailers are also equipped with safety features such as pressure relief valves, emergency shut-off systems, and venting systems to handle the expansion and contraction of cargo. This is crucial for preventing accidents, especially when transporting volatile substances like crude oil.

The following are some general specifications of DOT 407 crude oil tank trailers. Although, the specific features may vary based on the manufacturers and models.

• Construction Material: Generally made from aluminium.
• Pressure: 25 PSI Operating Pressure
•  Design: Double conical, 12" drop is a common design.
• Loading/Unloading: Typically equipped with bottom loading facilities to ensure safe and efficient loading/unloading of materials.
•  Compartments: Typically built in a single compartment
• Emergency Features: Emergency venting facilities, emergency shutoff driver-side front, rollover rail protection to protect the tank's top fittings in a rollover, overfill monitor system, and more.
• Capacity range: Average from 8,000 to 13,000 Gallons for different designs. Tandem trailers usually 8400 (200 bbl) to 8820 (210 bbl) Gallons.
• Other Features: Non-insulated and insulated variants depending on climate zones.

DOT 412: Corrosive Material Tankers

DOT 412/ MC 312 tank trailers are used for transporting the toughest corrosive and acidic chemical liquids such as hydrochloric acid, sulfuric acid, nitric acid, ammonium hydroxide, and more. These vessels are generally made up of stainless or carbon steel with FRP (fiberglass reinforced plastic) corrosion-resistant lining to protect the tank from corrosive liquids in the long run. With a maximum average capacity of 5,500 US Gallons, these trailers are used in chemical manufacturing, petroleum refining, and transportation of hazardous materials.

Designed to meet safety standards set by DOT, these trailers are equipped with features such as double-wall construction, emergency venting, and spill containment systems to ensure the safe transport of hazardous materials. Below are the general specifications of DOT 412:

• Built Material: Made from stronger variety of stainless steel or carbon steel and then lined with materials such as rubber or other corrosion-resistant materials
• Pressure: Higher than the 35-50 psig range and high vapor pressure.
•  Design: Round shape
• Loading/Unloading: Equipped with top and/or bottom loading facilities.
•  Compartments: Single-compartment and multi-compartment designs
• Emergency Features:Emergency venting facilities,Vapor Recovery System, internal valves, overfill protection, rollover rail protection to protect the tank's top fittings in a rollover and more.
• Capacity range: 3,500 to 5,500 gallons

MC-331: High-Pressure Cargo Tankers for Compressed Gasses

MC 331 tanker trailers, also known as high-pressure cargo tanks, are specifically designed to transport pressurized gasses that are liquefied at room temperature, such as propane, butane, Ammonia, Propylene, Dimethyl Ether, liquefied petroleum gasses (LPGs), Isobutane, and Butadiene. They play a critical role in various industries, including residential heating, commercial cooking, and industrial processes by providing a safe and efficient method of transporting these gasses over long distances. The MC 331 specification has stringent safety requirements due to the high pressure and volatility of the transported materials. In Addition, MC 331 regulations specify that the tanks must be designed and built to accommodate the physical and chemical properties of the gasses they carry.

These MC 331 tankers are usually made up of steel and have single-compartment designs with a hauling capacity ranging from 5200 - 19600 US Gallons. The MAWP ( Maximum Allowable Work Pressure) of these gas tank trailers ranges up to 100 psi to 500 psi. Equipped with safety features to avoid or minimize impact in case of accidents. These tankers are equipped with pressure relief devices or safety relief valves to keep the tank from over-pressurizing. They also have reinforced recessed skid and protected gauge wells to protect gauges for temperature, pressure, liquid level, etc. in case of a rollover. Significant configurations of MC 331 are as follows:

• Built Material: Typically made from quenched and tempered steel for the high-pressure containment needed for pressurized gasses. Some tanks can also be made from aluminum or other materials depending on the specific gas being transported.
• Pressure: Have a high design pressure, often exceeding 250 psi (pound per square inch).
•  Design: Typically cylindrical in shape, which helps evenly distribute the high pressure of the gasses they contain.
• Loading/Unloading: Equipped with specific loading and unloading facilities that allow for safe and efficient transfer of the pressurized gasses they carry.
•  Compartments: Single-compartment
• Emergency Features: All valves, gauges, and piping are protected against damage from rollovers. Equipped with pressure relief devices, emergency shut-off valves, overpressure protection and more.
• Capacity range: 10,600 - 11,600 US Gallons

Enforcement of DOT and FMCSA Codes

DOT and FMCSA codes are enforced through various methods, including roadside inspections, compliance reviews, and audits. Inspectors and auditors may examine drivers' logs, vehicle maintenance records, and other paperwork to ensure that carriers are complying with regulations.

What and When of Tanker Inspections: Key Focus Areas and Timelines

These tank trailers are typically required to undergo an annual inspection as mandated by the Federal Motor Carrier Safety Administration (FMCSA). The annual inspection ensures that commercial motor vehicles (CMVs) are in good working condition and comply with all the necessary safety standards. The inspection covers various vehicle components and systems to prevent mechanical failures and accidents on the road. Furthermore, trailers that transport hazardous materials are required to undergo more frequent inspections, such as every six months or every three months. This includes:

• External Visual Inspection (V)
• Internal Visual Inspection (I)
• Lining Inspection (L)
• Leakage Test (K)
• Pressure Test (P)
• Thickness Test (T)

Each cargo tank, as per the specifications, needs to undergo tests and inspections by a qualified inspector at periodic intervals as specified on the following table (source: www.govinfo.gov):

Periodic test and inspection periods for cargo tank trailers.