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Hazards Analysis, System Design

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Hazards Analysis, System Design

Low-pressure vents at mostly low hydrogen purity are not as large safety risk as high-pressure pure hydrogen vents. These vents should still go to a vent stack, but it will probably be small in diameter and thus the tee vent at the top can be small.

If the purge requires high flow, if purging horizontally, the reaction forces of the flow exiting and the hydrogen cloud should be modeled…

Category: System Design

Delayed ignition is a significant hazard for hydrogen releases, either intended or unintended. The primary concern is the overpressure and energy release created from a vapor cloud which could contain a significant quantity of hydrogen. The H2Tools Incidents database contains a number of examples of delayed ignition. 

Liquid hydrogen will almost never accumulate in a vent system since vent systems are typically designed without insulation. The extremely cold liquid hydrogen temperature of -420 F.

Additionally, vent stacks on an LH2 tank are connected to the vapor phase of the tank. Only in a few rare instances will LH2 be entrained in the gas stream.

Accumulators are recommended at the bottom of…

Category: System Design

The deflagration pressure is dependent upon many variables.

However, some general concepts are:

  1. Deflagration pressure is proportional to operating pressure
  2. Deflagration pressure is inversely related to initial temperature
  3. Deflagration pressure is based on concentration and H2/O2 ratio
  4. In general, an internal deflagration is unlikely to exceed about a 10…
Category: System Design

Exhaust systems (sometimes referred to as ventilation systems) are used to exhaust hydrogen and air mixtures. Normally these are used to vent streams with less than flammable range hydrogen in air.

That is, hydrogen detectors trigger venting or the ventilation systems runs during all hydrogen operations. In these instances, low concentrations of hydrogen are expected, but deflagration is…

Category: System Design

Yes, there are differences due to the differences in the fluid properties. We’re not sure what is meant by blowdown. If this means that should the gases be vented to a vent stack, possibly, but for certain these need to be vented to a safe location.

Category: System Design
Keywords: Vent, Vent Stack

There is currently a published ASME BPV Code Case describing pressure design requirements for pressure design of electrolyzers. If the Code Case is adopted by the jurisdiction where a new electrolyzer will be installed, the new electrolyzer will have to meet the requirements in the Code Case. The responsible ASME committee is working to revise the Code Case and intends to incorporate the Code…

Category: System Design

Applicable EU Directives frequently include the following:

·        Low Voltage - 2014/35/EU

·        Machinery - 2006/42/EC

·        Electromagnetic Compatibility - 2014/30/EU, EMC

·        Pressure Equipment - 2014/67/EU

·        Restriction of Hazardous…

Category: System Design

When it is necessary or desirable to work on a part of a hydrogen system while another part of the system remains in operation or in standby condition. An example is a system with two compressors, where one is normally operating and the other acts as an installed spare. The two block valves are closed, and the bleed (vent) valve is open. This arrangement assures that any hydrogen leaking…

Category: System Design
Keywords: Valves, Double block

Water icing at the exit of a stack is certainly an issue in cold climates. Significant effort has been put into vent stack outlet design to minimize the probability. Documents such as CGA G5.5 have topworks that are recommended. Stacks that face upward have a higher probability of having water, ice, or snow enter the stack and freeze. 

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