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Interpretation Response #14-0144 ([Engineer Trainee] [Mr. Terrance Douglas])

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

Interpretation Response Details

Response Publish Date:

Company Name: Engineer Trainee

Individual Name: Mr. Terrance Douglas

Location State: FL Country: US

View the Interpretation Document

Response text:

September 16, 2014

Mr. Terrance Douglas
Engineer Trainee
1903 Sterling Palms Court, Apt. 102
Brandon, FL 33511

Reference No. 14-0144

Dear Mr. Douglas:

This is in response to your July 27, 2014 letter requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the calibration and certification of gauges used for pressure testing cylinders.  Your questions are paraphrased below:

Q1. Your customers pressure gauge is of 0 to 11,000 PSI scale with a 0.25% accuracy grade (27.5 PSI max error).  When compared to your certified master gauges, the customer’s pressure gauge reports a +40 PSI error (5,040) at 5,000 PSI and a +70 PSI error (8,070) at 8,000 PSI.  You ask if the pressure indicating device may show tolerance errors that exceed its accuracy grade?

A1. As required by § 180.205(g)(3)(i) the pressure indicating device, itself, must be certified as having an accuracy of ±0.5%, or better, of its full range.  In the scenario described, the tolerances read at both 5,000 and 8,000 PSI exceed the accuracy of ±0.5%.  In this case, the pressure indicating device would not be authorized for use without recertification of its accuracy to of ±0.5%, or better, of its full range.  

Q2. Section 180.205(g)(3)(i) states that the pressure-indicating device, as part of the retest apparatus, is accurate within ±1.0% of the prescribed test pressure of any cylinder tested that day. You ask if a pressure indicating device is reporting a 70 PSI error (or 1%), that a pressure test of less than 7,000 PSI should not be conducted that day?

A2. A pressure test at 7,000 PSI could be completed that day.  For additional tests to be conducted that day, the pressure-indicating device, as part of the retest apparatus, must be accurate within ±1.0% of each individual test pressure to be tested that day. However, if the pressure indicating device, itself, is not in compliance with an accuracy of ±0.5%, or better, of its full range, retesting is not permitted on that day.

Q3. Your customer uses a digital scale for the expansion indicating device. This digital scale has a range from 0 to 1,000 grams with a 0.01% accuracy grade (0.1 gram max error).  When compared to your certified 100 gram weight, the customer’s digital scale shows 100.4 grams.  You ask if this 0.4 gram weight difference is too large?  

A3. As required by § 180.205(g)(3)(ii) the expansion-indicating device itself must have an accuracy of ±0.5%, or better, of its full scale, therefore, the digital scale described could be used as it has an accuracy of  0.4% unless the accuracy exceeds ±0.5% at any point of its full scale.  

Q4. For the scenario described in Q3), if the error is 0.4 grams, should tests conducted that day be limited to cylinders that produce less than 40 g/ml total expansion?

A4. Each day before restesting, the retester shall confirm that the expansion-indicating device, as part of the retest apparatus, gives a stable reading of expansion and is accurate to ±1.0% of the total expansion of any cylinder to be tested that day or 0.1 cc, whichever is larger.

I trust this information is helpful.  If you have further questions, please do not hesitate to contact this office.


Shane C. Kelley
Acting International Standards Coordinator
Standards and Rulemaking Division


Regulation Sections

Section Subject
180.205 General requirements for requalification of specification cylinders