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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #18-0036

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

Interpretation Response Details

Response Publish Date:

Company Name: Association of American Railroads

Individual Name: Kenneth B. Dorsey

Location State: DC Country: US

View the Interpretation Document

Response text:

September 18, 2018

Kenneth B. Dorsey
Association of American Railroads
425 Third Street, SW
Washington, DC  20024

Reference No. 18-0036

Dear Mr. Dorsey:

This letter is in response to your March 13, 2018, letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to specifications for DOT-111 and DOT-117 series tank cars.

We have paraphrased and answered your questions as follows:

Q1. You ask whether a DOT-111 tank car manufactured after October 1, 2015, is eligible to be retrofitted to DOT-117R or DOT-117P specification.

A1. The answer is no.  In accordance with § 174.310(a)(4), a newly manufactured tank car used to transport flammable liquids must be built to the new DOT-117 or DOT 117P specifications.

Q2. Certain jacketed DOT-111 tank cars are equipped with fiberglass insulation, which is not an approved thermal protection system, in accordance with § 179.18(c).  You ask whether these tank cars being retrofitted to the DOT-117 specification require documentation of a worst-case thermal analysis for crude oil and ethanol to show that they are capable of achieving the performance standard in § 179.18(a).

A2. The answer is yes.  When converting jacketed DOT-111 tank cars equipped with a thermal protection system not on the verification list, a thermal analysis must be provided that demonstrates the tank car can achieve the performance standard in § 179.18(a).  In accordance with § 179.202-12(a), only cars that show they can meet this performance standard will be eligible for conversion to DOT-117P specification and need additional approval from Associate Administrator for Railroad Safety/Chief Safety Officer, Federal Railroad Administration (FRA).

Q3. You ask if the minimum plate thickness requirements for DOT-117R specification can be based on the minimum plate thickness requirement at the time of original construction.
A3. The answer is yes.  In accordance with § 179.202-13(c), the minimum plate thickness for all tank cars manufactured to the DOT-117R is 7/16 of an inch.  However, DOT-111 tank cars manufactured to the Association of American Railroads CPC-1232 standard have a minimum plate thickness of ½ an inch.  Additionally, when calculating minimum allowable tank shell thickness in accordance with § 180.509(f), the original plate thickness at time of construction must be used for these calculations.

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

174.310(a)(4), 179.18(c), 179.18(a), 179.202-12(a), 179.202-13(c), 180.509(f)

Regulation Sections

Section Subject
179.18 Thermal protection systems
179.202-12 Performance standard requirements (DOT-117P)
179.202-13 Retrofit standard requirements (DOT-117R)
180.509 Requirements for inspection and test of specification tank cars