Q1. You ask if a DOT 3AA cylinder is subject to the hammer test requirement in § 180.209(b)(1)(iii) at the time of refill. You note that your company interprets the meaning of "refill" as it applies to § 180.209(b) as filling an oxygen cylinder when it contains less than 50 psi.

A1. The answer is yes. If your company wishes to requalify a DOT 3AA cylinder every 10 years instead of every 5 years, as outlined in § 180.209(b)(1), the cylinder must meet all applicable requirements, including the hammer test, prior to being refilled. The HMR is silent on the definition of "refill" for this exception, but generally "refill" has meant the filling of a cylinder regardless of the pressure at the time of refill.

As it is currently written in the HMR and as a condition to allow a 10-year requalification period instead of a 5-year period, the cylinder must pass the hammer test in accordance with CGA C-6 before each refill. The test protocol calls for the cylinder to be empty prior to performing the hammer test. For the purposes of the HMR, a cylinder containing a permanent Division 2.2 gas is empty when the pressure is less than 29.0 psig at 20 ºC.

Q2. You ask if an internal inspection is required each time you refill a DOT 3AA cylinder.

A2. The answer is no. There is no regulatory requirement to conduct an internal inspection each time a cylinder is refilled. However, there is a requirement to internally inspect a DOT 3AA cylinder at the time of requalification. Specifically, § 180.205(f)(1) requires that a steel cylinder be visually inspected in accordance with CGA C-6, which requires an internal inspection be conducted each time a cylinder is requalified or if the cylinder fails the hammer test.

Please note that if the cylinder is subject to the hammer test at the time of refill, such as is required in § 180.209(b)(1), failure of the hammer test may present conditions rendering the cylinder unsafe and subject to testing and inspection in accordance with § 180.205(d)(1).

Q3. You ask if it was PHMSA's intention in the HM-234 NPRM [81 FR 48977] to remove the authorization to requalify a DOT 3AA cylinder every 10 years. Specifically, you reference the table in § 180.209(a), which proposes to list a 5- or 12-year requalification period for a DOT 3AA cylinder.

A3. The answer is no. The § 180.209(a) table should specify a 5-, 10-, or 12-year requalification period for a DOT 3AA cylinder. This was an inadvertent error and will be amended in the publication of the final rule.

Q4. You ask if it was PHMSA's intention in the HM-234 NPRM to restrict those cylinders removed from aircraft from the 10-year requalification period exception as outlined in § 180.209(b)(1).

A4. The answer is no. It is not PHMSA's intention to restrict cylinders removed from aircraft from the 10-year requalification in § 180.209(b). This will be addressed in the final rule.