1. Funded by FCH JU (Grant agreement No. 256823) 1 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE

2. Funded by FCH JU (Grant agreement No. 256823) 2 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Safety is often mistakenly called a “non-technical” barrier to the hydrogen economy. In fact, the hydrogen safety is a challenging area of science and engineering, technological development and innovation. Unresolved issues include the reduction of jet flame length from current 10-15 m from onboard storage to allow self-evacuation of passengers and their safeguarding by first responders.  Another unresolved safety issue to be addressed is the increase of fire resistance of onboard storage tanks from present 1-7 minutes for type 4 vessels to 1-2 hours to allow longer time for blow-down of tanks. This in turn would prevent destruction of civil structures like garages during accidental release, and exclude formation of large hydrogen-air clouds in tunnels able to make fatalities throughout the whole length of the tunnel. Higher fire resistance rating of storage tanks would permit safe evacuation from the accident scene, etc.

3. Funded by FCH JU (Grant agreement No. 256823) 3 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Range from micro-flames (10 -9 kg/s) to high debit flames (100 kg/s)  Laminar diffusion and turbulent non-premixed flames  Buoyancy-controlled and momentum-dominated jets  Subsonic, sonic and highly under-expanded supersonic jet fires  Fireballs during storage tank failure  Liquefied hydrogen (LH 2 ) fires (little knowledge) Combustion terminology is applied:  Laminar diffusion flame  Turbulent non-premixed flame

4. Funded by FCH JU (Grant agreement No. 256823) 4 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE The 1937 Hindenburg dirigible disaster No explosion

5. Funded by FCH JU (Grant agreement No. 256823) 5 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Fire was initiated on the instrumentation panel ashtrays. The PRD was actuated after 14 min 36 s (upward scenario). Upward release from PRD. Vehicle equipped with two 34 L capacity cylinders at 350 bar and “normal” PRD (5 mm). (Watanabe et al., 2007)  Do we accept 10-15 m flame from a car?  No harm separation distance is about 50 m (public perception!)  Flame jet of hydrocarbons longer in momentum controlled regime (methane 130%: propane 200%, Hestestad,1999) Car back viewCar side view

6. Funded by FCH JU (Grant agreement No. 256823) 6 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  The PRD was actuated after 16 min and 16 s ( downward scenario).  Blowdown less than 5 min (no tank failure, but…). (Watanabe et al., 2007) …what if car is indoor (public perception!)? Car side view Car back view

7. Funded by FCH JU (Grant agreement No. 256823) 7 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Type 4 (stand-along tank 72.4 L, 343 bar, 1.64 kg) : fireball diameter of 7.7 m (45 ms after tank rupture). Fireball is lifted in 1 s (Zalosh 2007).  Type 3 (tank under vehicle 88 L, 318 bar) : fireball diameter of 24 m. The simple correlation gives 9.4 m for 1.64 kg of hydrogen (Zalosh 2007).  Fireball duration is about 4.5 s. The correlation gives 0.6 s duration Heat flux (Type 3) at distance 15.2 m in peak spikes was 210-300 kW/m 2 (flux 35 kW/m 2 during 10 s -1% fatality).  Pressure: Type 4: 41 kPa-6.5 m (15% fatality); Type 3: 12 kPa-15 m (people knocked down). 0.07 s 0.17 s 0.045 s1 s Stand-alone Type 4 Type 3 (under vehicle)

8. Funded by FCH JU (Grant agreement No. 256823) 8 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Hydrogen tankCNG Tank  Catastrophic failure of stand alone storage tanks subjected to bonfire testing Stephenson (2005)

9. Funded by FCH JU (Grant agreement No. 256823) 9 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 16% of H 2 (1 car) damage 28.8% of H 2 (no car) damage NIST Hydrogen release and combustion measurements in a full scale garage (2010)

10. Funded by FCH JU (Grant agreement No. 256823) 10 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Froude number ( U - velocity, D – characteristic size, g – acceleration of gravity) is a ratio of inertial to gravity force (when multiplied by the product of density by area  A )  Reynolds number (U velocity, D – characteristic size,  – density,  – viscosity) is a ratio of inertial to viscous force  Mach number ( U - velocity, C – speed of sound) is a ratio of inertial force to inertial force at sonic flow The speed of sound in gas is

11. Funded by FCH JU (Grant agreement No. 256823) 11 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Hottel and Hawthorne, Proceedings of Combustion Institute, 4, 1949. Transition from laminar flame to non-premixed turbulent flame at Reynolds number Re≈2000. ?

12. Funded by FCH JU (Grant agreement No. 256823) 12 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Baev and Yasakov (1974) showed theoretically that depending on Froude number ( Fr) there will be a characteristic peak in the L F ( Re ) function or not. Confirmed experimentally by Shevyakov and Komov (1977). Expanded jets. ?

13. Funded by FCH JU (Grant agreement No. 256823) 13 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  m – mass flow rate, D – burner diameter.  Flame length increases with D ( m is fixed), and m ( D is fixed).  Data converges when a new group ( mD ) is used to correlate experiments. L f =f( m ) L f =f( m, D ) Kalghatgi (1984)

14. Funded by FCH JU (Grant agreement No. 256823) 14 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE +20% +50% Best fit (nomogram) Conservative

15. Funded by FCH JU (Grant agreement No. 256823) 15 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  The nomogram is based on the best fit curve of the dimensional correlation (conservative estimate 50% longer ).  Example: 3 mm orifice, storage 350 atm will produce 5 m flame (best fit).  Conservative estimate of flame length is 7.5 m. Thus, “no harm” separation distance (x3.5 of flame length – see later) is more than 26 m.  The nomogram incorporates “No flame area”: no stable flame was observed for D=0.1-0.2 mm as the flame blew off although the pressures were as high as 40 MPa. D =3 mm P =350 bar Flame L F =5 m No flame

16. Funded by FCH JU (Grant agreement No. 256823) 16 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  The blow-off means extinction as soon as the pilot burner is switched-off.  Left : blow-off area in “ P-D ” coordinates (<0.1 mm no flame up to 400 atm).  Right : blow-off as a function of P and D ( only 2 mm orifices have no blow-off). Mogi and Horiguchi, 2009

17. Funded by FCH JU (Grant agreement No. 256823) 17 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE The dimensionless correlationThe dimensionless correlation Buoyancy-controlled Momentum- Under-expanded Three jet fire regimes:  Buoyancy-controlled (only expanded)  Momentum-dominated (expanded jets)  Momentum-dominated (under-expanded jets) Validation:  P =0.1-90 MPa  D =0.4-51.7 mm  Flow: L/T; SS/S/SS

18. Funded by FCH JU (Grant agreement No. 256823) 18 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  (+) Hawthorn et al., 1949: Concentration fluctuations in turbulent flame or local “ unmixedness ” produce a statistical smearing of reaction zone and a consequent lengthening beyond the point where the mean composition of mixture is stoichiometric.  (-) Sunavala, Hulse, Thring, 1957: “Calculated flame length may be obtained by substitution the concentration corresponding to the stoichiometric mixture in equation of axial concentration decay for non-reacting jet ”.  (-) Bilger and Beck, 1975: flame length is defined “for convenience” as the length on the axis to the point having a mean composition which is stoichiometric (hydrogen concentration is twice that of oxygen).  (-) Bilger, 1976: the calculated flame length may be obtained by substitution the concentration corresponding to the stoichiometric mixture in the equation of axial concentration decay for a non-reacting jet. Contradictory statements: flame tip locationContradictory statements: flame tip location

19. Funded by FCH JU (Grant agreement No. 256823) 19 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Flame tip location: from 8% to 16% in unignited jet (average – 11%). Flame is longer than the distance to axial concentration 29.5% in unignited jet (stoichiometric hydrogen-air mixture) by 2.2 times (16%) to 4.7 times (8%)! 11% 8% 16%

20. Funded by FCH JU (Grant agreement No. 256823) 20 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  The nomogram developed originally for unignited releases, e.g. separation to 1%, 2%, 4%, etc.  Due to knowledge of flame tip location (8%-16%, average 11% in unignited release) it can be now applied to calculate flame length.

21. Funded by FCH JU (Grant agreement No. 256823) 21 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Pressure 205 bar, ignition delay 800 ms.  Attached jets – release 0.11 m above the ground (horizontal).  Free (unattached jets) – release 1.2 m above the ground (horizontal).  Explanation: change in entrainment (dilution by air), and momentum “killing”.  Conclusion: release along the ground, wall, ceiling or other surface can increase flame length (the same is valid for unignited releases). Jet flame elongation due to the attachmentJet flame elongation due to the attachment Orifice diameter, mm Flame length, m Attached jets Flame length, m Free jets Flame length increase, times 1.5 5.5 3 x1.83 3.2 9 6 x1.50 6.4 11 9 x1.22 9.5 13 11 x1.18

22. Funded by FCH JU (Grant agreement No. 256823) 22 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Outdoor hydrogen jet fire experiments by HSL:  Storage pressure: 205 bar (two 50 litre cylinders).  Stainless steel tubing ID=11.9 mm, a series of ball valves with internal bore of 9.5 mm, or restrictors of 2 mm length and diameter: 1.5, 3.2, 6.4 mm.  The release point is 1.2 m above the ground.  Ignition by a match head with small amount of pyrotechnic material.  Ignition 1.2 m above the ground.  Ignition point is located 2-10 m from the release point.  Pressure transducers pointed out upwards (except for wall mounted). Transducers are located at axial distance 2.8 m from the nozzle, 1.5 m (then +1.1 m and +1.1 m) perpendicular to the axis, at height 0.5 m.  260 ms to fully open the valve, 140 ms for hydrogen to reach 2 m, i.e. 400 ms is shortest ignition delay. Pressure effects of jet flames (1/5)Pressure effects of jet flames (1/5)

23. Funded by FCH JU (Grant agreement No. 256823) 23 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Free jet fire : 9.5 mm, 800 ms, visible ( 16.5 kPa ) Pressure effects of jet flames (2/5)Pressure effects of jet flames (2/5)

24. Funded by FCH JU (Grant agreement No. 256823) 24 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Free jet fire : 9.5 mm, 800 ms, infrared 4.1-5.3 microns ( 16.5 kPa ) Pressure effects of jet flames (3/5)Pressure effects of jet flames (3/5)

25. Funded by FCH JU (Grant agreement No. 256823) 25 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Effect of orifice diameter on overpressure  P Pressure effects of jet flames (4/5)Pressure effects of jet flames (4/5) Orifice diameter, mmIgnition delay, msMax overpressure, kPa 1.5800Not recordable 1.5400Not recordable 3.28003.5 3.24002.1 6.480015.2 6.44002.7-3.7 9.580016.5 9.54003.3-5.4 Conclusion: reduce the release orifice diameter ALARP (as low as reasonably practicable) to reduce overpressure following ignition of jet.

26. Funded by FCH JU (Grant agreement No. 256823) 26 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Effect of ignition location on overpressure  P (orifice D =6.4 mm, fixed ignition delay 800 ms. Pressure effects of jet flames (5/5)Pressure effects of jet flames (5/5) Ignition position, mMax overpressure, kPa 215.2 35.0 42.1 5 6Not recordable 8 10No ignition

27. Funded by FCH JU (Grant agreement No. 256823) 27 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Barrier 90 o : 9.5 mm, 800 ms ( 42 kPa ). Free jet  P=16.5 kPa. Pressure effects of jet flames: barriers (1/3)Pressure effects of jet flames: barriers (1/3)

28. Funded by FCH JU (Grant agreement No. 256823) 28 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Barrier 60 o : 9.5 mm, 800 ms ( 57 kPa ). Free jet  P=16.5 kPa. Pressure effects of jet flames: barriers (2/3)Pressure effects of jet flames: barriers (2/3)

29. Funded by FCH JU (Grant agreement No. 256823) 29 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Dynamics: release, ignition, deflagration, jet fire (free jet  P=16.5 kPa) Pressure effects of jet flames: barriers (3/3)Pressure effects of jet flames: barriers (3/3) 42 kPa 57 kPa

30. Funded by FCH JU (Grant agreement No. 256823) 30 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Hazards: a small leak burns undetected for a long period, damaging the containment system and providing an ignition source for a subsequent large release.  Left: hydrogen flowing downward into air (mass flow rate 3.9  g/s, power 0.46 W).  Right: hydrogen flowing downward into oxygen ( 2.1  g/s, 0.25 W).  The tube inside/outside diameters are 0.15/0.30 mm. The exposure time 30 s.  SAE J2600 permits hydrogen leak rates below 200 mL/hr (0.46  g/s) – no flame! Microflames: hazards and SAE J2600 limitMicroflames: hazards and SAE J2600 limit

31. Funded by FCH JU (Grant agreement No. 256823) 31 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Tube burner is used.  Quenching limits are nearly independent of diameter.  Hydrogen has the lowest quenching limit and the highest blow-off limit (here it is compared to methane CH 4, and propane C 3 H 8 ).  Quenching limit for tube burner is 3.9  g/s. Microflames: quenching and blow-offMicroflames: quenching and blow-off

32. Funded by FCH JU (Grant agreement No. 256823) 32 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Quenching diameter as a function of storage pressure for H 2, CH 4, C 3 H 8.  Upstream pressure required for 5.6  g/s hydrogen (a bit above the quenching limit) isentropic choked flow is shown.  For hydrogen at 690 bar, any hole larger than 0.4  m will support a stable flame. Microflames: quenching diameterMicroflames: quenching diameter

33. Funded by FCH JU (Grant agreement No. 256823) 33 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Quenching limits for a 6 mm compression fitting are shown.  Limits are independent of storage pressure.  Quenching limit for leaky fittings is 28  g/s – about 10 times larger than for tube burner ( 3.9  g/s ).  Hydrogen limit is the lowest compared to CH 4 and C 3 H 8 (order of magnitude). Microflames: leaky fittingsMicroflames: leaky fittings

34. Funded by FCH JU (Grant agreement No. 256823) 34 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE

35. Funded by FCH JU (Grant agreement No. 256823) 35 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Minimum quenching mass flow rate – H 2  Minimum quenching volumetric flow rate – C 3 H 8 Microflames: leaky fittings (quenching limits)Microflames: leaky fittings (quenching limits)

36. Funded by FCH JU (Grant agreement No. 256823) 36 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE There are three basic ways in which people exposed to hydrogen jet fires, may lead to incapacitation and death : hyperthermia, respiratory tract burns, and body surface burns (NFPA, 2002).  Hyperthermia (heat stroke) involves prolonged exposure (approximately 15 minutes or more) to heated environments at temperatures too low to cause burns.  Heat damage to the respiratory tract is more severe when the heated air contains steam and can cause damage deep down in the lung.  The time from the application of heat to the occurrence of body burns, of various degrees of severity, depends on the heat flux to which the skin is exposed. Three ways how fire can incapacitate peopleThree ways how fire can incapacitate people

37. Funded by FCH JU (Grant agreement No. 256823) 37 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE x =2. L F – “death” limit (309 o C, 20 s) x =3. L F – pain limit (115 o C, 5 min) x =3.5. L F – “no harm” limit (70 o C) Three separation distances for jet fireThree separation distances for jet fire

38. Funded by FCH JU (Grant agreement No. 256823) 38 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Radiant heat flux (kW/m 2 ) Effects on people 1.5Safe for stationery personnel and members of the public 2.5Tolerable over 5 minutes; severe pain above this threshold 3Tolerable in infrequent emergency situations for 30 minutes 5Tolerable for performing emergency operations 6Tolerable to escaping personnel (evacuation) 9.5Second degree burn after 20 seconds 12.5-15First degree burn after 10 seconds (1% fatality in 1 minute) 25Significant injury in 10 seconds (100% fatality in 1 minute) 35-37.51% fatality in 10 seconds Effects of radiant heat flux on people (Lees, 1996; BS, 2004).

39. Funded by FCH JU (Grant agreement No. 256823) 39 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Radiant heat flux (kW/m 2 ) Effects on structures and environment 5Significant windows breakage 8–12Domino effects 10Heating of structures; increase of T and P in liquid/gas storages 10–12Ignition of vegetation 16Failure of structures in prolonged exposure (except concrete) 20Concrete structures can withstand for several hours 30Non-piloted ignition of wood occurs 38Damages caused to process equipment and storage tanks 100Steel weakening 200Concrete structures to fail in several dozen of minutes

40. Funded by FCH JU (Grant agreement No. 256823) 40 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE

41. Funded by FCH JU (Grant agreement No. 256823) 41 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 400 bar titanium electrolyser (Japan) before and after the combustion in oxygen. http://www.nsc.go.jp/senmon/shidai/kasai/kasai004/ssiryo4-1.pdf

42. Funded by FCH JU (Grant agreement No. 256823) 42 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Titanium electrolyser materials (fluorine from the membrane) were dispersed into surroundings: car windshield before and after (few days) the accident. This is only one of the knowledge gaps relevant to hydrogen fires!