Requirements for local jurisdictions vary, so the AHJ should be consulted, but NFPA 2:2023, Hydrogen Technologies Code, Chapter 13 has requirements for installation of hydrogen generators up to 100 kg H2/h. Section 13.3.1 General says permitted water electrolysis systems are to be listed to ISO 22734:2019, Hydrogen Generators Using Water Electrolysis - Industrial, Commercial, and Residential…

It depends on the facility and risk assessment, but generally multiple pressure and temperatures to one vent stack is not the best practice unless all are similar in pressure and temperature, and the streams have compatible composition and flow rate. Care must also be taken to prevent reverse flow and misdirected flow between portions of the system. Additionally, one vent stack can become a…

The answers are in context of PEM and alkaline electrolysis operating at or below 30 bar and below 85 deg C°. A general suggestion: Ask component suppliers about material compatibility, but do an independent investigation to confirm. As a general resource,  safety data sheets (SDSs) sometimes provide material compatibility information. Specific recommendations follow. 

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The recognized and generally accepted good engineering practices (RAGAGEP) for employing a purge into a hydrogen vent stack is that inerting is not generally used. Best practice is that the vent stack should be designed for a fire and the overpressure caused by an internal deflagration. This is typically not an issue for smaller sizes (less than 4”) and when using typical materials for a vent…

The recognized and generally accepted good engineering practices (RAGAGEP) for employing a nitrogen purge into a hydrogen vent stack is that inerting is not generally used for nitrogen purge in a hydrogen vent stack because most inert gases freeze at liquid hydrogen temperatures. The vent stack should be designed for a fire and the internal overpressure caused by a deflagration. If inerting is…

NFPA 2 Annex G provides a summary of the conflicts with 29 CFR 1910.103. This is language that has been in NFPA 55 for several cycles as this conflict has existed for many years. The requirements in the Federal Regulations were established in the early 1970s. Since that time, OSHA has not had sufficient resources to update the applicable provisions.

The primary difference between OSHA…

Fuels like gasoline are exempt from OSHA process safety management (PSM) requirements. When asked about the applicability for hydrogen storage larger than 10,000 lb (4500 kg) being used as a fuel, OSHA responded with an interpretation that can be found at https://www.osha.gov/laws-regs/standardinterpretations/…

Equation 6.3.1.1 in CGA S1.3 is based on modeling to API methods described in: Heitner, T. Trautmauis, and M. Morrissey, “Relieving Requirements for Gas Filled Vessels Exposed to Fire,” 1983 Proceedings-Refining Department, Volume 62, American Petroleum Institute, Washington, D.C., pp. 112-122.

This method considers the transient nature of the vessel warming in combination with the…

API 520, Sizing, Selection, and Installation of Pressure-relieving Devices Part I - Sizing and Selection, was written for use in the process industries in gas and liquid service.

CGA S1.3, Pressure Relief Device Standards-Part 3-Stationary Storage Containers for Compressed Gases was written for fixed equipment in gas service.

Which standard to use depends on the choice by the owner…

Pressure relief systems may use reclosing devices like relief valves, non-reclosing devices like rupture discs, or a combination of both in parallel. Some systems may also be equipped with emergency blowdown systems that are operated by control systems. Selection of the proper devices is dependent on the system design and relative hazards. Variables that affect the selection include the type…