‘Safety challenges in view of the upcoming hydrogen economy: An overview’
Hans Pasman and William RogersMary Kay O’Connor Process Safety Center, Texas A&M University,
College Station, TX 7784
Contents
:
• Hydrogen economy and H2
‐properties as an energy carrier• Knowledge gaps regarding safety• Risk assessments• Conclusions
MKOPSC Symp Oct 27-28, 2009
The Hydrogen Economy Car driving and house heating (fuel cells)
• The quest for more sustainable energy has really started
•
Storage of electrical energy has its limitations; range of cars too
restrictive
• With air‐oxygen omnipresent: 142 MJ/kg H2
versus 45 MJ/kg gasoline
• H2
by nuclear hydrogen initiative, coal, natural gas, waste, directly solar
• 1974 IEA; 1977 HIA; 2004 Task 19 Hydrogen Safety
• 1993 Japan WE‐NET
• 2003 President Bush: Hydrogen Initiative
• 2003 Int’l Partnership for the H2
Economy: IPHE (17 partners)
•European Commission FP6 established HYdrogen PERmitting (HYPER) and
HySafe programs. (Latter revamped into Int’l Association HySafe Brussels)
•Current FP7 Joint Technology Initiative fuel cell and H2
application:
emphasis on PPPs.; hydrogen hi‐ways –
refueling stations.
• 2005, ‘07 and ’09: 3 Int’l Conferences on H2
Safety, ICHS
Hydrogen refuelling stations are spreading rapidly (ca. 400)
Hydrogen Hi-ways: California; Norway –Denmark, Hamburg; Amsterdam-Munich
Hydrogen fuel cells for household electricity and heating
Fuel cell
Elec-tronics
Vent
Storage tank
Risk informed Standards & Codes; ATEX requirements; skilled work
force; leak detection
Hydrogen properties
• NFPA 2 draft available for public review; NFPA 52 and 55 adaptation to H2
• Sandia Labs is doing supporting studies and risk assessments• EU HYPER Installation Permitting Guide completed• ASME, ISO, EIGA, SAE, EN etc.
• Storage: compressed up to 1000 bar, liquefied 20 K, as a hydride (research)• Liquefied currently most effective : but boil-off (e.g. in trunk BMW cars)• Flammable range ↑4% (↔7.2%; ↓9.5%) -75% (hydrocarbons roughly 2-10%) • Low MIE 0.02 mJ; self-ignition after pin hole jet leak possible• Low viscosity, high diffusivity, more prone to leakage, permeation•
In open space easily dispersion; in confined space filling from the top down with explosive mixture
• Minimum requirements of venting garage boxes• Codes, standards, best practices needed for use of H2
on large scale
In the US and elsewhere:
Knowledge gaps, research needs
Int’l Energy Agcy, IEA-HIA, Task 19, White Paper on Knowledge Gaps:1. Gaps in connection with Codes & Standards2. Gaps in existing risk assessment methods and tools3. Gaps in fundamental knowledge ( e.g. CFD modeling)
All IPHE countries made inventory. Hydrogen Research Advisory Council of Fire Protection Research Foundation of NFPA: 2008
document:27 items identified for NFPA 2 , 11 most pressing:
1.
Hydrogen explosion modeling refinement –
blast waves, flame speeds, etc2.
Development and evaluation of wide area hydrogen sensing technology3.
Hydrogen effects on materials, specifically fatigue loading4.
Hydrogen gas cabinets5.
Hydrogen deflagrations in partially enclosed areas6.
Pressure relief device reliability7.
Confined release mitigation strategies8.
Design, installation, testing, and maintenance of hydrogen detection systems9.
Ignition limits/criteria for large leak (dynamic) scenarios10.
Hydrogen safety study on infrastructure11.
Fire barrier effectiveness
Risk assessments: LaChance et al. rpt. SAND2009‐0874Hazards of hydrogen:
•Materials (metals) may embrittle: a long-term effect, and containment may fail.
•
When compressed in case of leak, jet of gas can self-ignite immediately, or after a short delay, and produce a jet flame, or in case it ignites at a source a certain distance from the leak (delayed ignition) in the open, a flash fire occurs and within a confinement a deflagration or even detonation.
•Liquefied H2
, the vessel may fail and liquid hydrogen spilled. It will immediately start to evaporate, in principle in a pool, which can be ignited. A cloud will disperse and can produce a vapor cloud explosion.
•Vessel containing liquid hydrogen may not be able to cope with the
boil-off due to heat influx, especially in case of fire, and the hydrogen may
BLEVE: Boiling Liquid Expanding Vapor Explosion producing blast, fragments, and
a fireball
•Finally hydrogen asphyxiates like nitrogen and other gases when a person suddenly enters a hydrogen filled space, while contact with cryogenic hydrogen direct or via metal results in cold burns or frost bite injuries.
Properties of H2
cannot be changed: Therefore appropriate measures/distances for
inherently safer system
LeakLeak
Ignition?Ignition?Yes
No
Immediate
Delayed
Conditions?Conditions?Congestion/confinement
Open
Cloud explosion
Flash fire / jet fireback to leak
Jet fire
Cloud disperses
Simplified H2 leak event tree
Risk assessment cont. (2): Leak frequencies (problem)
UK HSE offshore data: Spouge relationship pipes:
F(d) = f(D) dm
+ FrupF(d) = leak frequency of holes exceeding diameter d (minimum 1 mm) f(D) = specific leak frequency with size Ddm = pipe diameter influence (exponential law) on this frequencyFrup = (small) component rupture frequency
Cumulative probabilities for different leak sizes based on Bayesian analysis:
Prior distribution + few H2 data in Bayesian approach to posterior distribution:
Uj
= 134 m/s; Re = 2348
Risk assessment cont. (3): Hydrogen jets in the open: jet flames, flash fires
•
Schefer et al. concentration measurements jets: H2
jets penetrate in air
further than CH4
Risk assessment cont. (4): Models for cloud dispersion and explosion in confined space
•
ICHSs : Standard Benchmark Exercise Problems (6‐14 teams; SBEP Vs > 20)
checking CFD models:
• SBEP V1 : subsonic vertical release in vessel
• SBEP V3 : subsonic vertical release in garage
• SBEP V4 : horizontal under‐expanded jet
•
SBEP V5 : subsonic horizontal jet release in a multi‐compartment
room
•
NaturalHy (mixtures of H2 and CH4): Explosion tests by HSL and Shell in
UK in congestion rig3 x 3 x 2 m
Blockage 20%
50 mJ ignition spark
Tests by Shell and HSL in UK with methane and hydrogen
CH4
H2
2nd
frame after ignition
Risk assessment cont. (5): Liquid H2 pool and vapor dispersion
Experiments NASA 80s, BAM 90s, Juelich LAUV model of Verfondern and Dienhart, 2005
Predictive calculation with LAUV code of A310 Airbus simulated fuel spill in a crash
situation on the ground: Pool radius as function of time
Risk assessment cont. (6): Preventive and Protective measures; Harm distances, Risk criteria and guidelines
•
Improved engineering, suitable sensors, blocking valves, adequate ventilation,
catalytic recombiners
•
Flame barriers
against radiation, torch effect
•
Emergency response: scenario analysis, guideline drafting, SOPs
•
Hydrogen Executive’s Leadership (HELP) initiative: safest possible transition
•
Harm distances review heat radiation: borderline lethality 4.7 kW/m2
during 3
min
•
Overpressure: NL Purple Book 0.3 bar 100% lethality indoors
•
UK: 1 bar for 100% lethality, 0.05 bar for 1% lethality.
•
LaChance et al. most acceptance criteria ca. 10‐5
/yr as individual risk to be killed;
some go as low as 10‐6
/yr, e.g. the Netherlands.
•
(For comparison: Gasoline spill fatality risk in the US is 510
‐6/yr, while fires in
general is 1.210‐5
/yr)
Risk assessment cont. (7): Hypothetical case safety distances
•
Cryogenic tank rail car, 30,000 gallons, 90% filled = 100 m3
at 71 kg/m3
= 7000 kg
•
When stored it means the US RMP rule and EU Seveso threshold
quantity for
hydrogen has been exceeded, hence safety report
Safe distances according to various national systems
Country Criterion Prob. of Fatality
Over- pressure
bar
TNT eq. or MEM
distance
Distancem
US - 3500 kg 1 psi. 0.068 TNT eq.10% 18 401- 7000 kg 1 psi 0.068 TNT eq.10% 18 505- 3500 kg 1 psi 0.068 MEM 4 683
UK Dangerous dose 0.140 MEM 2.0 341IZ 80.10-6 1 0.4 68MZ 4.10-6 0.8 0.7 0.8 137OZ 0.4.10-6 0.08 0.12 2.2 175
France SELS Très grave 0.2 1.8 307SEL Grave 0.14 2 341SEI Irreversible 0.05 5 853Indirect Indirect 0.02 11 1877
Germany Distance 0.1 1.5 256If no details available 126
Netherlands Individual 1 outdoors 6 0.3 56Risk 10-6 /yr
new Bevi regulation
idem 1 outdoors 0.3 TNT eq.20% 6.4 143
1% lethality 0.01 indoors 0.1 TNT eq. 20% 5.0 853
Conclusions H2
‐safety•
Hydrogen
is
an
attractive
fuel
(energy
carrier),
producible
by
renewable
sources.
Mass
and
volume
storage
efficiency
+
safety
can
be
improved
by
absorption in a solid matrix (nanotechnology).
•
When
mixed
with
air
explosion
and
fire.
Knowledge
gaps
to
perform
risk
assessments, e.g. ignition probability, component failure rates.
•
To
enable
a
smooth
introduction
of
the
technology,
risk
studies
will
be
essential. Risk informed Codes and Standards has to be further developed.
•
Distribution
system
has
to
be
built
with
inherently
safer
features
to
cope
with hydrogen’s properties.
•
Further
international
coordination/cooperation
with
respect
to
risk
analysis and
acceptance
is highly desirable.
