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Interpretation Response #20-0057

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

Interpretation Response Details

Response Publish Date:

Company Name: R&D Engineer

Individual Name: Oliver Sánchez Muñoz

Location City: Sant Andreu de la Barca Country: ES

View the Interpretation Document

Response text:

October 13, 2020

Oliver Sánchez Muñoz
R&D Engineer
Johnson Controls
Josep Ros i ros, Naves 23. P.I. La Clota.
08740 Sant Andreu de la Barca, Spain

Reference No. 20-0057

Dear Mr. Muñoz:

This letter is in response to your August 4, 2020, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to service equipment for United Nations (UN) cylinders as it relates to certain ISO standards. You state you have a UN cylinder filled with a liquid extinguishing agent charged with a compressed gas, and the cylinder is equipped with pressure gauges and switches mounted to a quick release valve. Furthermore, you reference ISO 17871:2015, incorporated by reference in § 173.301b(c), and you indicate your understanding that section 4.2.6 of this standard provides additional requirements to those in ISO 10297:2014 as it relates to specification standards for service equipment under § 178.71(d). You also note that a recent update to ISO 17871 (2020) indicates that the valve burst test pressure is to be calculated at 1.5 times the valve test pressure, which is consistent with the same requirement for liquefied gases in ISO 10297:2014. Finally, you note your understanding that the instruction in section 4.2.6 of ISO 17871:2015 is that the valve test pressure must be at least the developed pressure of a full gas cylinder at 65 °C and will never exceed the test pressure of the pressure receptacle (i.e., the UN cylinder).

You ask whether pressure gauges and switches mounted to quick release valves covered under ISO 17871:2015 comply with the hydraulic burst pressure test requirement when successfully tested (e.g., no visible deformation or burst) at 1.5 times the developed pressure of a full gas cylinder at 65 °C regardless of the test pressure marked on the cylinder.

The answer to your question is no. The pressure gauge and switches mounted to the quick release valve must meet the burst test requirement of the cylinder that is being used. Furthermore, for purposes of performing the hydraulic burst pressure test in ISO 10297:2014, the formula you describe is used to determine the value of the burst test pressure. However, for purposes of § 178.71(d)(1), UN pressure receptacle equipment (e.g., a quick release valve) that is subjected to pressure must be designed and constructed to withstand at least 1.5 times the test pressure of the pressure receptacle. Therefore, if the calculated valve burst test pressure is less than 1.5 times the marked cylinder test pressure, the performance standard of § 178.71(d)(1) would not be achieved. Please also note that for purposes of ISO 10297:2014, section 6.3, valves designed to incorporate pressure gauges or pressure indicators must have the devices installed for testing, except for the hydraulic burst pressure test.

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

173.301b(c), 178.71(d)

Regulation Sections

Section Subject
173.301 General requirements for shipment of compressed gases and other hazardous materials in cylinders, UN pressure receptacles and spherical pressure vessels
178.71 Specifications for UN pressure receptacles