Hydrogen Ventilation and Deflagration Venting Analysis
for Indoor Storage and Dispensing Facilities
By Bob Zalosh
Current and future anticipated use of hydrogen-fueled
vehicles entails using special facilities for storing hydrogen, compressing
it to the pressures needed for on-vehicle storage, and dispensing it during
refueling operations. Some of these facilities are unenclosed, so there
is no opportunity for accidentally released hydrogen to accumulate. Other
facilities are partially or completely enclosed such that hydrogen accumulation
and ignition of the accumulated gas layer are a significant concern.
Similar concerns exist for compressed natural
gas (CNG) vehicle refueling facilities. National Fire Protection Association
(NFPA) Standard 52, entitled Compressed Natural Gas Vehicular Fuel
Systems, provides guidance on the minimum ventilation rates to prevent/limit
methane accumulation and ignitions in indoor facilities. One way of approaching
the issue for hydrogen is to develop analogous guidelines to those for CNG.
This is the approach being followed by a committee currently in the throes
of drafting such a standard. One difficulty is the lack of any explanation
of the technical basis for the ventilation rates in NFPA 52.
The specific approach followed in this report
to suggest analogous ventilation rate guidelines is as follows:
Another guideline addressed in this report is
the deflagration venting requirements to prevent significant damage if a
flammable hydrogen-air mixture were ignited in a confined structure. Available
test data and existing NFPA guidelines on hydrogen deflagration venting
are reviewed following the discussion of ventilation.
- Develop a simple model of the steady-state ventilation rates needed
to achieve specified hydrogen and methane outflow concentrations for prescribed
- Use the model developed in Step 1, together with alternative premises
about equivalent release rates, to determine the ventilation rates for
hydrogen that would be equivalent to the recommended ventilation rate in
- Develop a simple model for the buoyant plume and ceiling layer associated
with methane releases and hydrogen releases under a confined ceiling. Use
this model to calculate hydrogen ceiling layer depths for specified ceiling
layer concentrations and ventilation rates.
[Note: Only the introduction to this paper is included
©1998. All Rights Reserved. A Publication of
the National Hydrogen Association.
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