Introduction

This standard represents the minimum requirements for pressure relief devices (PRDs) considered to be appropriate and adequate for use on cylinders with a water capacity of 1000 lb (454 kg) of water or less. Refer also to Title 49 of the U.S. Code of Federal Regulations (49 CFR) or CSA B340, Selection and Use of Cylinders, Spheres, Tubes, and Other Containers for the Transportation of Dangerous Goods, Class 2 [1, 2].¹ This standard also applies to DOT-3AX, DOT-3AAX, and DOT-3T cylinders with a water capacity of over 1000 lb (454 kg) of water, and which comply with the design specifications and charging (filling) and maintenance regulations of the U.S. Department of Transportation (DOT) or the corresponding specifications and regulations of Transport Canada (TC) [1, 3].

This standard does not cover requirements for PRDs for CTC/DOT-4L and TC-4LM insulated cylinders containing cryogenic liquids (see CGA S-1.2, Pressure Relief Device Standards—Part 2—Portable Containers for Compressed Gases) [4]. This standard does not cover PRD requirements for multi-unit tank car tanks (DOT106A/TC106A and DOT110A-W/TC110A) (see 49 CFR 179.300-15 and CGSB 43.147, Construction, Modification, Qualification, Maintenance, and Selection and Use of Means of Containment for the Handling, Offering for Transport, or Transporting of Dangerous Goods by Rail, as appropriate) [1, 5].

This standard includes Tables 1 to 5, which provide information pertaining to PRDs. Table 1 contains information on the different types of PRDs. Table 2 contains the fire, toxicity, state of the gas, and corrosiveness (FTSC) code classification for gases. Table 3 provides a list of gases and their PRD assignments. Table 4 contains temperature correction factors. Table 5 includes values for basic orifice factors flange taps for flow in cubic feet per minute.

When cylinders that conform to the specification requirements of DOT or TC but are used in services beyond the jurisdiction of any of these authorities, it is recommended that the state, provincial/territorial, local, or other authorities having jurisdiction over these cylinders be guided by this standard in determining PRD requirements provided that the cylinders are charged and maintained in accordance with DOT or TC regulations.

It is further recognized that there can be cylinders that are used in services beyond the jurisdiction of DOT or TC that do not conform to the specification requirements of either authority. The authorities having jurisdiction over such cylinders should be guided by this standard in determining PRD requirements provided that such cylinders are considered by the authority as having a construction at least equal to the equivalent DOT or TC specification requirements and they are charged and maintained in accordance with DOT or TC requirements.

A number of states, provinces/territories, cities, and other local regulatory authorities have pressure vessel laws and regulations that include requirements for PRDs. This standard is prepared specifically for compressed gas cylinders, and the PRDs might not be acceptable unless special permission is obtained from the authority having jurisdiction. For cylinders that come within the jurisdiction of state, provincial/territorial, and local regulatory authorities, the user should check for compliance with all such regulations.

For newly constructed cylinders that come within the jurisdiction of DOT or TC, PRDs shall comply with requirements of this standard. The intent of this standard is to minimize the number and optimize the types of approved PRDs specified for each specific gas. This standard does not prohibit the continued use of previously approved and installed devices unless stated otherwise in Table 3, 49 CFR, and/or CSA B340 [1, 2]. However, if a PRD is replaced, the new device shall meet the requirements of this standard.

It is the filler's responsibility to ensure that the PRD is correct.

For PRD standards for bulk transport containers and stationary storage containers, see CGA S-1.2 and CGA S-1.3, Pressure Relief Device Standards—Part 3—Stationary Storage Containers for Compressed Gases [4, 6].

¹ References are shown by bracketed numbers and are listed in order of appearance in the reference section.

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