Table Of ContentVladimir Molkov
Fundamentals of Hydrogen Safety
Engineering I
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Fundamentals of Hydrogen Safety Engineering I
© 2012 Vladimir Molkov & bookboon.com
ISBN 978-87-403-0226-4
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Fundamentals of Hydrogen Safety Engineering I Contents
Contents
1 Introduction 9
1.1. Why hydrogen? 9
1.2. Public perception of hydrogen technologies 9
1.3. The importance of hydrogen safety 10
1.4. Hazards, risk, safety 13
1.5. Hydrogen safety communication 15
1.6. The subject and scope of hydrogen safety engineering 16
1.7. The emerging profession of hydrogen safety engineering 17
1.8. Knowledge gaps and future progress 20
2 Hydrogen properties and hazards 22
2.1. Physical and chemical properties 23
2.2. Combustion properties 35
2.3. Comparison with other fuels 47
2.4. Health hazards 53
2.5. Concluding remark 55
3 R egulations, codes and standards and hydrogen safety engineering 56
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Fundamentals of Hydrogen Safety Engineering I Contents
4 H ydrogen safety engineering: framework and technical subsystems 63
4.1. Framework 63
4.2. Technical sub-systems 66
5 Unignited releases 67
5.1. Expanded and under-expanded jets 67
5.2. Under-expanded jet theories 70
5.3. The similarity law for concentration decay in momentum-dominated jets 76
5.4. Concentration decay in transitional and buoyancy-controlled jets 92
6 D ispersion of hydrogen in confined space 96
6.1. Dispersion of permeated hydrogen in a garage 97
6.2. The pressure peaking phenomenon 114
7 Ignition of hydrogen mixtures 125
7.1. Overview of hydrogen ignition mechanisms 125
7.2. Spontaneous ignition of sudden releases 131
8 Microflames 163
8.1. Quenching and blow-off limits 164
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Fundamentals of Hydrogen Safety Engineering I Contents
9 Jet fires 171
9.1. Introduction to hydrogen jet fires and safety issues 171
9.2. Chronological overview of hydrogen jet flame studies 174
9.3. The drawback of Froude-based correlations 187
9.4. The similitude analysis and a dimensional correlation 188
9.5. The jet flame blow-off phenomenon 193
9.6. The novel dimensionless flame length correlation 195
9.7. Flame tip location and equivalent unignited jet concentration 200
9.8. Separation distances from a hydrogen leak 202
9.9. Effect of nozzle shape on flame length 206
9.10. Effect of jet attachment of flame length 207
9.11. Pressure effects of hydrogen jet fires 208
9.12. Summary 214
10 Deflagrations Part II
10.1. General features of deflagrations and detonations Part II
10.2. Some observations of DDT in hydrogen-air mixtures Part II
10.3. Vented deflagrations Part II
10.4. Large eddy simulation (LES) of large-scale deflagrations Part II
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Fundamentals of Hydrogen Safety Engineering I Contents
11 Detonations Part II
11.1. Direct initiation of detonation Part II
11.2. LES of hydrogen-air detonations Part II
12 S afety strategies and mitigation techniques Part II
12.1. Inherently safer design of fuel cell systems Part II
12.2. Mitigation of release consequences Part II
12.3. Reduction of separation distances for high debit pipes Part II
12.4. Mitigation by barriers Part II
12.5. Mitigation of deflagration-to-detonation transition (DDT) Part II
12.6. Prevention of DDT within a fuel cell Part II
12.7. Detection and hydrogen sensors Part II
Concluding remarks Part II
Acknowledgements Part II
Appendix 1. Glossary Part II
References Part II
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Fundamentals of Hydrogen Safety Engineering I
Disclaimer. Author does not make any warranty or assumes any legal liability or responsibility for the
accuracy, completeness, or any third party’s use of any information, product, procedure, or process
disclosed, or represents that its use would not infringe privately owned rights. Any electronic website
link in this book is provided for user convenience and its publication does not constitute or imply its
endorsement, recommendation, or favouring by the author.
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Fundamentals of Hydrogen Safety Engineering I Introduction
1 Introduction
High priority research directions for the hydrogen economy include safety as a technological, a
psychological and sociological issue (US Department of Energy, 2004). This book provides the state-of-
the-art in hydrogen safety as a technological issue and introduces a reader to the subject of hydrogen
safety engineering. Hydrogen safety engineering is defined as application of scientific and engineering
principles to the protection of life, property and environment from adverse effects of incidents/accidents
involving hydrogen. The use of hydrogen as an energy carrier presents several unusual hazards. The
best investment in hydrogen safety is educated and trained personnel, informed public. This book
is a contribution to hydrogen safety knowledge transfer and education of all stakeholders including
technology developers and safety engineers, consultants and users, policy makers and investors, etc. It
can be used as a textbook for higher education programmes in hydrogen safety, e.g. MSc in Hydrogen
Safety Engineering course at the University of Ulster.
1.1. Why hydrogen?
The scarcity of fossil fuel reserves, geopolitical fears associated with fossil fuel depletion, and issues of
environment pollution and climate change as well as the need to ensure independence of energy supply
make the low-carbon economy with an essential hydrogen vector inevitable in the coming decades.
Today first series of hydrogen-fuelled buses and cars are already on the road and refuelling stations are
operating in different countries around the world. How safe are hydrogen technologies and fuel cell
products? This book will help to understand the state-of-the-art in hydrogen safety engineering and
assist to make this fast emerging market inherently safer. Global fuel cell demand will reach $8.5 billion
in 2016 (PennWell Corporation, 2007).
1.2. Public perception of hydrogen technologies
Public perception of hydrogen technologies is still affected by the 1937 Hindenburg disaster. The
catastrophe is often associated with hydrogen as a reason even there is an opinion that the difference in
electrical potential between the zeppelin “landing” rope and the ground during descending had generated
electrical current that ignited the dirigible canopy made of extremely combustible material. This was
followed by diffusive combustion of hydrogen in air without generation of a significant blast wave able
to injure people. Figure 1–1 shows a photo of burning Hindenburg dirigible fire demonstrating that there
was no “explosion” (Environmental graffiti alpha, 2010).
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Fundamentals of Hydrogen Safety Engineering I Introduction
Figure 1–1. Photo of the Hindenburg dirigible fire demonstrating that there was no “explosion” (Environmental graffiti alpha, 2010).
Contrary to popular misunderstanding hydrogen helped to save 62 lives in the Hindenburg disaster.
The NASA research has demonstrated (Bain and Van Vorst, 1999) that the disaster would have been
essentially unchanged even if the airship were lifted not by hydrogen but by non-combustible helium, and
that probably nobody aboard was killed by a hydrogen fire. The 35% who died were killed by jumping
out, or by the burning diesel oil, canopy, and debris (the cloth canopy was coated with what nowadays
would be called rocket fuel). The other 65% survived, riding the flaming dirigible to earth as the clear
hydrogen flames swirled harmlessly above them.
1.3. The importance of hydrogen safety
There is a clear understanding by all stakeholders of the role of hydrogen safety for emerging hydrogen
and fuel cell technologies, systems and infrastructure. This is supported by investment to safety of about
5–10% of the total funding of hydrogen and fuel cell programmes both in USA and in Europe. Hydrogen
safety studies were initiated decades ago as a result of accidents in the process industries, and were
supported by safety research for nuclear power plants and aerospace sector. For example, a study of the
Three Mile Island nuclear plant (USA) accident in 1979 (Henrie and Postma, 1983) demonstrated that
almost homogeneous 8% by volume of hydrogen in air mixture deflagrated. Fortunately, the deflagration
pressure increases to about 190 kPa only that was considerably below the strength of the large concrete
containment building.
Recent disasters involving hydrogen, i.e. the Challenger Space Shuttle explosion (1986) and the Fukushima
nuclear tragedy (2011), demonstrated that our knowledge and engineering skills to deal safely with
hydrogen even within these industries require more investment, from both intellectual and financial
perspective.
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