A High Pressure Shipping Situation

As hazmat professionals, when we think of the phrase “under pressure,” we typically think of cylinders filled with gasses like helium, oxygen, or chlorine. But gasses aren’t the only kind of hazardous material shipped under pressure.

In 2012, the US DOT recognized that shippers often used classification and naming conventions for compressed gasses, liquefied gasses, and aerosols to describe materials that don’t necessarily fit the bill: liquids, powders, and  pastes packaged in cylinders dispensed under pressure; and products like foams, adhesives, coatings, and cleaners combined with a gas to dispense the contents.

Because these materials are a combination of solids or liquids combined with a gas, the use of compressed gas as the Proper Shipping Name does not adequately describe the shipment. And while the US DOT’s definition of aerosols does include liquids, pastes, or powders expelled by a gas under pressure (49 CFR 171.8), Aerosols are limited to a capacity of 1 liter or less and must be self-closing and non-refillable—properties not common to larger compressed gas containers.

New Shipping Names for Chemicals Under Pressure

Consequently, in 2013 (January 7, 2013; 78 FR 988), DOT finalized a new Rule to address the concerns created by these materials and to maintain harmonization with international regulations. The Final Rule established the following new Proper Shipping Names and rules for chemicals under pressure, n.o.s.:



Special Provision 362 defines chemicals under pressure as liquids, pastes or powders pressurized with a propellant that is a flammable or non-flammable gas (49 CFR 173.115). SP 362 also states that materials packaged in small (1 liter or less), non-refillable, self-closing aerosol dispensers are not "chemicals under pressure."

How to Classify Chemicals Under Pressure

To classify a chemical under pressure, shippers must consider all of the material’s components.

If any of the material’s components is flammable—whether the propellant or the material being dispensed—the primary hazard class of the material will be Division 2.1 flammable gas.

There are three scenarios in which shippers can select this hazard class to describe the shipment:

1. The material meets the definition of a flammable liquid in Special Provision 362: a liquid with a flash point of less than or equal to 200°F (93°C). Note that the definition of “flammable” in this special provision differs from the definition of flammable liquid found at 49 CFR 173.120, which carries a more stringent threshold (less than or equal to 140°F (60°C)).
2. The material meets the definition of flammable solid found at 49 CFR 173.124.
3. The material meets the definition of a flammable gas at 49 CFR 173.115.

Otherwise, the primary hazard will be Division 2.2, non-flammable gas.

Shipping Subsidiary Hazards 6.1 and 8 Under Pressure

Division 6.1 (poison) or Class 8 (corrosive) may sometimes be selected as a subsidiary hazard for shipments of chemical under pressure.

If the material that is being dispensed meets the definition of a Division 6.1 poison as defined at 49 CFR 173.132 and 173.133 at the Packing Group II or III level, the material will be assigned a subsidiary hazard of 6.1.

Similarly, if the material being dispensed meets the definition of a Class 8 corrosive material as defined at 49 CFR 173.136 and 173.137 at the Packing Group II or III level, the material will be assigned a subsidiary hazard of 8.

If the material being dispensed is non-hazardous but the shipment meets the definition of a compressed gas at 49 CFR 173.115, then the material will be classified as Division 2.2.

Important: If the material is a Division 6.1, PG I or Class 8, PG I, the shipper may not use the Proper Shipping Name “Chemical under pressure, n.o.s.”

Packaging Hazmat Chemicals Under Pressure

Non-bulk cylinders (water capacity of 1,000 lbs. or less) must meet the general requirements as described in 49 CFR 173.335. The general requirements are compatibility, filling limits, minimum service pressure, and periodic inspection requirements. Cylinders also need to be authorized and meet additional requirements, such as being placed in a strong outer package and in some instances placed in UN specification tested packages, such as wooden crates. Rules for DOT specification packages are located in 49 CFR 173.301, 173.301a, 173.302, 173.302a, and 173.305. Rules for UN pressure receptacles are located in 49 CFR 173.301, 173.301b, and 173.302b.

Bulk cylinders (water capacity > 1,000 lbs.) must meet design specifications for minimum design pressure, location of openings, pressure relief devices, and maximum filling density (49 CFR 173.313). Special Provisions T50 and TP40 must also be followed.

IATA and IMDG Rule for Chemicals Under Pressure 

Shipments by air following the International Air Transport Association (IATA) regulations are similar, with two notable exceptions. IATA rules require all cylinders to be placed in a strong outer package and to have a capacity of 50 liters or less. Also, shipments of chemicals under pressure are only authorized on cargo aircraft. Vessel shipments prepared using the International Maritime Dangerous Goods (IMDG) regulations are basically consistent with DOT rules, except that the required packaging instruction, P206, limits the maximum capacity at 50 liters.

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Tags: DOT, hazmat shipping