In the U.S., there is no specific national requirement for fuel cell test equipment to be certified. There may be requirements from the local authority having jurisdiction (AHJ). Local building codes will likely point to compliance with NFPA 2/55 for the hydrogen and other gas supply systems, ASME Boiler and Pressure Vessel Code for vessels, ASME B31 piping codes for piping, and National Electric Code for electrical. A conversation with the local authorities early in the planning process to determine what is required will be helpful. Consultation with a design firm for laboratories and factories may also be helpful. It may be possible to show that many test station components already certified to EU standards can meet U.S. requirements with some cross-reference work. Alternately, the AHJ may accept the CE Declaration of Conformity.

Even if a small experiment is being run inside a fume hood, the best practice is to use a dedicated vent line for hydrogen which vents hydrogen to a safe location outside.  This is especially recommended for planned venting.   This practice avoids situations where flammable mixtures could develop. Each system is unique and should be evaluated and approved for  use independently. For example, the relative flow rates could be considered to understand the concentration within the vent duct. Also, it is not recommended that safety relief devices be vented into a hood due to the high flow.
 

Assuming this question relates to the roof of the enclosure, there are no design criteria on this topic to the Panel’s knowledge. The key to the design would be ensure that the exhaust ventilation inlet is located at the highest point and that there are no pockets that can capture hydrogen (restrict flow to the exhaust inlet).

Information on Toyota’s repair garage approach is available at Toyota Mirai Hydrogen Fuel Cell EV- Repair Garage Design & Safety. CFD modelling could also be used to anticipate the flow of released hydrogen based on either natural or forced ventilation.

A best practice, even for small hydrogen vents, is to vent to a dedicated vent system outside the building where possible. Several international codes and standards can be used to provide guidance; the Panel recommends discussing the configuration with a local fire official to ensure their required standards are followed. In the U.S. NFPA 2, Hydrogen Technologies Code, has information in Section 13.3 (https://www.nfpa.org/product/nfpa-2-code/p0002code). Additional best practices can be found at Best Practice Overview: Use of an Electrolyzer.

Other considerations when venting the electrolyzer to the room in addition to making sure there is adequate ventilation include proximity of ignition sources near the exhaust release point of the electrolyzer, location of room air inlets and outlet exhaust, and shutdown of the electrolyzer if exhaust is lost. Increasing ventilation to dilute the venting hydrogen can be one method to resolve the situation, but other alternatives are to redirect the vent stream to a chemical exhaust system, a fume hood, or piped directly outdoors.

It is always recommended that the area in which this work would be done be adequately ventilated and in accordance with the Building Code, NFPA 2 and NFPA 45 if applicable. In the Panel’s opinion, it’s recommended that the weight measuring equipment as you’ve described it  be designed for Class 1, Group B, Division 2. Also consult with the local authority having jurisdiction as to the extent of the area classification.

While HSP members have limited experience with MFCs in experimental setups, the Panel does not consider them to be reliable to provide a positive flow shutoff. For safety, a shutoff valve in series is recommended. Projects will also need to consider hazardous electrical rating and location when flowing H2. Regarding Coriolis mass flow measuring devices, Coriolis flow meters measure mass rate changes by oscillating a flow tube and measuring tube distortion response. Measurement resolution is better with heavier, denser materials. Since hydrogen is the least dense gas, the response is much less than with denser materials. They are also expensive and very challenging to operate at low mass flow rates. 

The HSP is aware of a few used with electrolyzers for flow confirmation at the 500 slpm range but lacks feedback on how well these worked.  The project should consider working with the supplier regarding this application. There is a special MFC for vacuum application that has been observed to work well, the only difference is the valve on this is toward vacuum. On the other hand, MFCs made for pressures of atmospheric or above could be used in slight vacuum (up to 10 psia) and low flow rates (1-2 slpm) but are not very accurate due to the expansion of gas at the exhaust of the valve; it depends on the compressibility of that particular gas. 

The recalibration time recommended is 2 years. If there is a valve leak, check the inlet-outlet valve opening pressure ratings on the spec sheet. From a safety perspective, it is not recommended that an MFC be relied on to provide a leak-tight seal against hydrogen. Further, MFCs are not accurate if the gas has other constituents not originally included in the calibration. For instance, humidification of fuel cell supply gases would significantly change the accuracy.   Also, given the inherent risk in mixing H2 and O2 in a vacuum chamber, the HSP recommends a rigorous, multi-party, hazard analysis.  

It is difficult to provide trustworthy answers to these questions without understanding the design and configuration of the specific installation. It may be best to consult with a pressure systems expert to evaluate the specific installation and uses. The gas provider may also be a good resource for specifics on gas equipment use. Other beneficial resources include the HSP Best Practices online resource and the DOE Hydrogen Safety Training for Researchers, the AIChE Laboratory Safety Course.

NFPA 2, Hydrogen Technologies Code, and NFPA 45, Standard on Fire Protection for Laboratories Using Chemicals, may also be helpful in identifying requirements and best practices. In addition, the project designed should consult with the local authority having jurisdiction for safety guidance that is applicable to locally adopted codes.