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Interpretation Response #07-0077 ([UPS Aircraft Maintenance Hangar] [Mr. Robert A. Stewart])

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

Interpretation Response Details

Response Publish Date:

Company Name: UPS Aircraft Maintenance Hangar

Individual Name: Mr. Robert A. Stewart

Location State: KY Country: US

View the Interpretation Document

Response text:

July 7, 2009



Mr. Robert A. Stewart

UPS Component Shop Supervisor

UPS Hydrostatic Shop

UPS Aircraft Maintenance Hangar

750 Grade Lane

Louisville, KY 40213

Reference No. 07-0077

Dear Mr. Stewart:

This is in further reference to your follow-up letters inquiring about the cylinder requalification requirements contained in § 180.205 of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180). Specifically, you ask about the methods used to calibrate the pressure test system. I apologize for the delay in responding.

Your questions are paraphrased and answered below:

Q1. What tolerances apply to permanent expansion of a calibrated cylinder?

A1. None. 49 CFR § 180.205, paragraph (g)(3) requires a cylinder requalifier to use a calibrated cylinder or other method authorized in writing by the Associate Administrator for Hazardous Materials Safety to verify the accuracy of a hydrostatic retest system, including both the Pressure Indicating Device and the Expansion Indicating Device (EID). Paragraph (g)(4) specifies that the calibrated cylinder must show "no permanent expansion." This is a separate requirement and is not related to the test equipment ±1.0% accuracy requirement. Thus, the HMR do not specify a tolerance in the determination of permanent expansion of a calibrated cylinder when used to demonstrate the accuracy of a retest system. Any permanent expansion may indicate entrapment of air or other malfunction of the equipment.

Q2. Does the requirement that the calibrated cylinder show no permanent expansion hold a requalifier who utilizes digital equipment, which measures expansion to a high degree of resolution, to a different standard than a requalifier who utilizes less sophisticated methods?

A2. The requirement is the same regardless of the type of equipment used. The calibrated cylinder must show "no permanent expansion." This means that the water level in the burette or the weigh bowl must return to the same point where it began " not slightly higher or lower. Rounding is not permitted when determining whether the calibrated cylinder has shown permanent expansion. After depressurization of the calibrated cylinder, all of the displaced water must return to the water jacket. Any volume of water measured in the EID above zero (or the original reading) indicates permanent expansion of the calibrated cylinder. If this occurs, the equipment has not been proven to be accurate in accordance with the HMR.

I hope this information is helpful. Please contact us if you have additional questions.

Sincerely yours,

Hattie L. Mitchell

Chief, Regulatory Review and Reinvention

Office of Hazardous Materials Standards


Regulation Sections

Section Subject
180.205 General requirements for requalification of specification cylinders