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

2. Funded by FCH JU (Grant agreement No. 256823) 2 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 2  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 3  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 (LH2) 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 4 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 5  Fire was initiated on the instrumentation panel ashtrays. The PRD was actuated 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).  Do we accept 10-15 m flame from a car?  No harm separation distance is about 50 m (public perception!) Car back viewCar side view

6. Funded by FCH JU (Grant agreement No. 256823) 6 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 6  The PRD was actuated 16 min and 16 s ( downward scenario).  Blowdown less than 5 min (no tank failure, but…). …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 7  Type 4 (stand-along tank 72.4 L, 343 bar, 1.64 kg) : fireball diameter of 7.7 m (45 ms after thank rupture). Fireball is lifted in 1 s.  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).  Fireball duration is about 4.5 s. The correlation gives 0.6 s duration (Zalosh).  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 8 16% of H2 (1 car) damage 28.8% of H2 (no car) damage

9. Funded by FCH JU (Grant agreement No. 256823) 9 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 9  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

10. Funded by FCH JU (Grant agreement No. 256823) 10 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 10 Hottel and Hawthorne, Proceedings of Combustion Institute, 4, 1949. Transition from laminar flame to non-premixed turbulent flame at Reynolds number Re≈2000. ?

11. Funded by FCH JU (Grant agreement No. 256823) 11 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 11 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. ?

12. Funded by FCH JU (Grant agreement No. 256823) 12 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 12  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)

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

14. Funded by FCH JU (Grant agreement No. 256823) 14 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 14  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

15. Funded by FCH JU (Grant agreement No. 256823) 15 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 15  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

16. Funded by FCH JU (Grant agreement No. 256823) 16 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 16 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

17. Funded by FCH JU (Grant agreement No. 256823) 17 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 17  (+) 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

18. Funded by FCH JU (Grant agreement No. 256823) 18 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 18 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%

19. Funded by FCH JU (Grant agreement No. 256823) 19 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 19  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.

20. Funded by FCH JU (Grant agreement No. 256823) 20 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 20  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

21. Funded by FCH JU (Grant agreement No. 256823) 21 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 21 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)

22. Funded by FCH JU (Grant agreement No. 256823) 22 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 22 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)

23. Funded by FCH JU (Grant agreement No. 256823) 23 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 23 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)

24. Funded by FCH JU (Grant agreement No. 256823) 24 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 24 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.

25. Funded by FCH JU (Grant agreement No. 256823) 25 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 25 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

26. Funded by FCH JU (Grant agreement No. 256823) 26 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 26 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)

27. Funded by FCH JU (Grant agreement No. 256823) 27 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 27 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)

28. Funded by FCH JU (Grant agreement No. 256823) 28 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 28 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

29. Funded by FCH JU (Grant agreement No. 256823) 29 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 29  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

30. Funded by FCH JU (Grant agreement No. 256823) 30 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 30  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 CH4, and propane C3H8).  Quenching limit for tube burner is 3.9  g/s. Microflames: quenching and blow-offMicroflames: quenching and blow-off

31. Funded by FCH JU (Grant agreement No. 256823) 31 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 31  Quenching diameter as a function of storage pressure for H2, CH4, C3H8.  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

32. Funded by FCH JU (Grant agreement No. 256823) 32 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 32  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 tomes larger than for tube burner ( 3.9  g/s ).  Hydrogen limit is the lowest compared to CH4 and C3H8 (order of magnitude). Microflames: leaky fittingsMicroflames: leaky fittings

33. Funded by FCH JU (Grant agreement No. 256823) 33 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 33

34. Funded by FCH JU (Grant agreement No. 256823) 34 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 34  Minimum quenching mass flow rate – H2  Minimum quenching volumetric flow rate – C3H8 Microflames: leaky fittings (quenching limits)Microflames: leaky fittings (quenching limits)

35. Funded by FCH JU (Grant agreement No. 256823) 35 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 35 There are three basic ways in which exposure of people 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 down to the deep lung.  The time from the application of heat to the occurrence of body burns of various degrees of severity, depends the heat flux to which the skin is exposed. Three ways how fire can incapacitate peopleThree ways how fire can incapacitate people

36. Funded by FCH JU (Grant agreement No. 256823) 36 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 36 x =2. L F – “death” limit (300 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

37. Funded by FCH JU (Grant agreement No. 256823) 37 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 37 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).

38. Funded by FCH JU (Grant agreement No. 256823) 38 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 38 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

39. Funded by FCH JU (Grant agreement No. 256823) 39 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 39 Heat flux from a jet fire (400 bar, 5 mm)Heat flux from a jet fire (400 bar, 5 mm) Safe for public (1.5 kW/m 2 ) Tolerable for performing emergency operations (5 kW/m 2 ) Significant injury in 10 s (100% fatality in 1 min) (25 W/m 2 )

40. Funded by FCH JU (Grant agreement No. 256823) 40 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 40 TypeAdvantagesDisadvantages UV / IRModerate speed. Moderate sensitivity. Low false alarm rate, not blinded by CO 2 fire protection discharges. Automatic self test. False alarms, for example combination of UV and IR sources. Blinded by thick smoke and vapours. Moderate cost. Triple IRVery high sensitivity. Very high speed. Moderate cost. IR/vis imaging Images the flame. Systems in use at NASA Stennis. Moderate cost.

41. Funded by FCH JU (Grant agreement No. 256823) 41 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 41 Direction of jet flow:  The flow shall be directed so that it will not reach equipment or people.  For instance, flanges (which are components where hydrogen leaks might occur) should be placed and directed in such a way that a possible leak would not cause any domino effect. Shielding:  The basic intent of the various methods of protection is to reduce the rate of heat transfer to the potential targets in the vicinity of a hydrogen jet fire. Flame shields are specifically intended to reduce the incident radiant heat flux by preventing direct flame impingement on equipment.  Flame shields (barriers) shall be properly designed (choice of the material, thickness, etc.). Jet fire mitigation: flow direction and shieldingJet fire mitigation: flow direction and shielding

42. Funded by FCH JU (Grant agreement No. 256823) 42 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 42 The basic intent of thermal insulation is to reduce the rate of heat transfer to the potential targets, e.g. hydrogen tanks, in the vicinity of a hydrogen jet fire. Thermal insulation is achieved by surrounding equipment with materials that preferably have the following main characteristics:  Relatively non-conductive heat materials  Non-combustibility and the added attribute of not producing smoke or toxic gases when subjected to elevated temperatures  Product reliability giving positive assurance of consistent uniform protection characteristics  Availability in a form that permits efficient and uniform application  Sufficient bond strength and durability  Resistance to weathering or erosion resulting from atmospheric conditions Fire protection coatings providing thermal insulation can be part of the fire protection strategy of compressed gaseous hydrogen vessels.

43. Funded by FCH JU (Grant agreement No. 256823) 43 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 43

44. Funded by FCH JU (Grant agreement No. 256823) 44 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 44 400 bar titanium electrolyser (Japan) before and after the combustion in oxygen. http://www.nsc.go.jp/senmon/shidai/kasai/kasai004/ssiryo4-1.pdf

45. Funded by FCH JU (Grant agreement No. 256823) 45 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 45 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 knowledge gaps relevant to hydrogen fires!