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Interpretation Response #16-0111 ([MansourGavin, LPA] [Mr. Jeffrey Embleton, Esq])

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: MansourGavin, LPA

Individual Name: Mr. Jeffrey Embleton, Esq

Location State: OH Country: US

View the Interpretation Document

Response text:

April 05, 2017

Mr. Jeffrey M. Embleton, Esq.
MansourGavin, LPA
1001 Lakeside Avenue, Suite 1400
Cleveland, OH 44114

Reference No. 16-0111

Dear Mr. Embleton,

This letter is in response to your June 21, 2016, letter on behalf of your client requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the inspection of threads on DOT 3A, 3AX, and 3E seamless steel cylinders. You state that in order to ensure the threads are built "to gauge," your client uses a statistical sampling size of C = 0, AQL = 1.5% (per Acceptance Number Sampling Plans, N.L. Squeglia, ASQC, 4th Edition), along with additional processes identified in an established quality plan. You also provide examples of more stringent statistical sampling sizes, such as C = 0, AQL = 0.4% and C = 0, AQL = 0.1%, and specifically ask which is the most appropriate method for the inspection of cylinder threads.

In accordance with §§ 178.36(h)(1) and 178.42(e)(1), the threads on a DOT 3A, 3AX, or 3E cylinder are required to be "clean cut, even, without checks, and to gauge." It is the manufacturer's responsibility determine how best to ensure the threads on each cylinder meet the appropriate specification, whether by testing each or by some sample set according to a quality plan.

Please note that a DOT 3A, 3AX, or 3E cylinder is also required to be inspected and analyzed by an inspector as designated in § 178.35(b)1. Specifically, the designated inspector is required in accordance with § 178.35(c)(3)(vi) to "verify threads by gauge" to determine cylinder compliance with the applicable specification. Furthermore, § 178.35(c)(4) requires that the inspector's report be prepared in accordance with Compressed Gas Association (CGA) C-11. Specifically, CGA C-11 requires that for seamless cylinders, "threaded openings in each cylinder shall be inspected and gauged for compliance with the design specification as well as quality. Performance of this inspection shall be verified by the inspector." Therefore, in addition to the manufacturer's responsibility, the designated inspector must inspect the cylinders in order to verify and assure that the threads are built "to gauge."

I hope this information is helpful. Please contact us if we can be of further assistance.



Dirk Der Kinderen
Chief, Standards Development Branch
Standards and Rulemaking Division

178.36(h)(1), 178.42(e)(1), 178.35(b), 178.35(c)(4), 178.35(c)(3)(vi)


1 As specified in § 178.35(b), a DOT 3A or 3AX cylinder must be inspected and verified by an Independent Inspection Agency (IIA). A DOT 3E cylinder must be inspected and verified by either an IIA or a competent inspector of the manufacturer.

Regulation Sections

Section Subject
178.35 General requirements for specification cylinders
178.36 Specification 3A and 3AX seamless steel cylinders
178.42 Specification 3E seamless steel cylinders