Q1. You ask whether a grouping of seamless DOT specification cylinders (longer than 2 meters) within a frame can also meet the definition of a MEGC for domestic transportation.

A1. The answer is no. In accordance with the definition in § 171.8, a "Multiple-element gas container or MEGC" is defined in the HMR as "assemblies of UN cylinders, tubes, or bundles of cylinders interconnected by a manifold and assembled within a framework." The requirements for the use of MEGCs in § 173.312 specify that certain requirements for UN cylinders in part 173 must be followed. Section 173.312 also requires that MEGCs meet the design, construction, inspection, and testing requirements in § 178.75 and be marked in accordance with § 178.75(j). Therefore, for purposes of the HMR, DOT specification cylinders connected by a manifold and assembled within a framework are not considered MEGCs. However, bundles of DOT specification cylinders may be mounted on frames in accordance with the requirements of § 173.301(i)."

Q2. You ask whether DOT 3T and 3AAX cylinders mounted in frames which conform to the design requirements for a MEGC (other than those specific to cylinders meeting certain UN/ISO standards) can be transported in accordance with § 173.301(i), provided the requirements for both sections are met.

A2. The answer is yes, provided the frame is not visibly marked in accordance with the MEGC marking requirements in § 178.75(j) during transportation. The markings specified in § 178.75(j) certify that the MEGC meets the design and approval requirements in part 178. Therefore, MEGCs which display the marking in accordance with § 178.75(j) are only authorized for transportation with UN/ISO cylinders. See A1.

Q3. You ask for confirmation of your understanding that DOT permits bundles of DOT cylinders to be transported in accordance with international standards as authorized in part 171 subpart C. You note that the United Nations (UN) Recommendations on the Transport of Dangerous Goods do not specify the cylinder design type required for a bundle of cylinders or MEGCs. Rather, cylinders must be of a type "approved by the Competent Authority."

A3. Hazardous materials may be transported to, from, or through the United States under the International Civil Aviation Organization's Technical Instructions for the Safe Transport of Dangerous Goods by Air (ICAO TI), the International Maritime Dangerous Goods (IMDG) Code, Transport Canada's Dangerous Goods (TDG) Regulations, or the International Atomic Energy Agency (IAEA) Regulations when the requirements of part 171 subpart C are met. The United Nations Recommendations on the Transport of Dangerous Goods recognize the transport and use of pressure receptacles other than those that bear the "UN" certification mark when approved by the Competent Authority of the countries of transport and use (see §107.1 definition of Competent Authority). This recognition is reflected also in the IMDG Code and the European ADR under certain conditions. Therefore, bundles of DOT cylinders are authorized for transportation in accordance with the requirements in 49 CFR 173.301(i) and applicable international standards.