IMO Type 5 containers are portable tanks specifically designed to transport non-refrigerated liquefied gases under pressure, operating at pressures between 100 and 500 psi. They are the highest-pressure intermodal tank containers in the IMO classification system, built to carry some of the most hazardous materials moved by sea and land. Under current international regulations, they correspond to the T50 portable tank instruction in the IMDG Code.
What IMO Type 5 Containers Carry
These tanks are purpose-built for liquefied gases that remain in liquid form through pressure rather than refrigeration. The cargo types they handle fall into several high-hazard categories: high vapor pressure flammable liquids, highly toxic poison liquids or gases, and pyrophoric liquids (substances that ignite spontaneously on contact with air). This makes them fundamentally different from lower-numbered IMO tank types, which handle less volatile liquids and chemicals at much lower pressures.
The gases transported in Type 5 tanks are classified as Class 2 dangerous goods under international shipping regulations. Examples include liquefied petroleum gas, chlorine, ammonia, and other compressed gases that exist as liquids inside the pressurized tank but would rapidly expand into gas if released.
Pressure Rating and Construction
The defining physical feature of an IMO Type 5 tank is its ability to contain internal pressures of 100 to 500 psi. This is substantially higher than IMO Type 1 or Type 2 tanks, which handle atmospheric or low-pressure cargoes. The tank itself is a horizontal cylinder housed inside a rectangular steel frame, sized to fit standard intermodal shipping dimensions so it can move between ships, trucks, and rail cars.
Construction standards are strict. Aluminum cannot be used for the shell of any portable tank carrying non-refrigerated liquefied gases. The minimum shell thickness is 4 mm (about 0.2 inches) for the cylindrical body, heads, and manhole covers, regardless of material. For tanks with a diameter of 1.8 meters or less, the minimum thickness increases to 5 mm in reference steel, or an equivalent thickness if another approved metal is used. These requirements reflect the forces involved in containing pressurized liquefied gas during transport, including thermal expansion, sloshing, and the potential for rapid pressure changes.
Pressure Relief and Safety Systems
Every IMO Type 5 tank must be fitted with pressure relief devices. This is part of the formal definition in the IMDG Code: “a portable tank fitted with pressure-relief devices which is used for non-refrigerated liquefied gases of class 2.” These relief valves are designed to vent gas in a controlled way if internal pressure exceeds safe limits, preventing catastrophic tank failure.
Relief valve settings can vary depending on where the tank is traveling. U.S. Coast Guard regulations require higher stress factors for certain tank designs entering U.S. territorial waters, which translates to lower maximum allowable relief valve settings than those permitted under the international IGC Code. In practice, this means some tanks must carry two sets of pressure relief valve settings and switch between them when crossing into U.S. waters. Tanks built and certified under the 1993 edition of the IGC Code (with amendments through December 1996) by an authorized classification society may use the international settings throughout.
How T50 Replaced the IMO Type 5 Label
The “IMO Type 5” designation is a legacy classification. Since January 1, 2003, the international dangerous goods shipping rules have used a system of T-codes instead. Non-refrigerated liquefied gases are now assigned to portable tank instruction T50, which specifies the design, testing, and operational requirements for these tanks. The T50 instruction covers the same territory that IMO Type 5 once did, with updated and more detailed technical provisions.
Older IMO Type 5 tanks certified and approved before 2003 under the rules in effect as of July 1, 1999 (IMDG Code Amendment 29) can still be used in service. The condition is that they continue to pass their required periodic inspections and tests. The IMDG Code retains the IMO Type 5 definition explicitly for reference, acknowledging that many of these tanks remain in active use worldwide.
How to Recognize One
Visually, an IMO Type 5 container looks like a large horizontal cylinder mounted inside a blue or otherwise colored rectangular steel frame. The frame matches standard intermodal container dimensions, with corner castings that allow it to be stacked, locked onto a chassis, or lifted by crane. Compared to standard box containers or even lower-pressure tank containers, the cylinder walls are noticeably thicker, and the tank will have visible pressure relief valves, gauges, and specialized fittings on top or at the ends. Placards indicating Class 2 dangerous goods and the specific UN number of the cargo will be displayed on the exterior.