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

Funded by FCH JU (Grant agreement No ) 2 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Hydrogen is the most easy leaking gas (smallest molecule). Thus, more efforts are needed to exclude leaks (material choice!).  Leaks mostly arise from valves and connections rather than from pipe rupture. However, the full bore pipe rupture is credible worst-case scenario. Equipment/componentType of leak Pipe workPinholes, pipe split FlangesGasket failure, thermal movement, material creep Weld connectionWeld crack Solder connectionSolder crack, solder melt Union connectionThermal movement, leak Screw connectionLeak, sealant creep, material split Hose connectionSeal leak, material split, human error ValvesStem leak, seal leak, bonnet/housing split, opened by impact HosesPerforation split InstrumentsElement rupture RegulatorsDiaphragm rupture, seal leak, downstream rupture (overpressure) Solenoid valvesSeal leak PumpsPerforation, seal leak CylinderPerforation, rupture, permeation leak Reference: Check list of leaks sources and leak scenarios. European Industrial Gas Association (2007), Determination of safety distances. IGC Doc 75/07/E.

Funded by FCH JU (Grant agreement No ) 3 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Permeation (SAE J2578, 2009): diffusion through the walls or interstices of a container vessel, piping or interface material. Hydrogen permeation is atomic through metals and molecular through polymers.  The European Law (Commission Regulation, 2010) for type approval of hydrogen- powered vehicles) limits the permeation rate to maximum 6 Ncm 3 /hr/L (at 20 o C) per litre of the storage tank capacity. This will limit a permeation leak from 170 L tank by 25.3E-06 g/s.  Leak from a pipe, broken in an accident, to fuel cell of about 2000 L/min, i.e. (2000/22.4)*2/60= 3 g/s (about 150 kW fuel cell).  Release from Pressure Relief Device (PRD) at storage pressure 35 MPa and PRD diameter 5.08 mm has mass flow rate 390 g/s.  Existing industrial pipelines, e.g. under pressure of 2.5 MPa and diameter of 30 cm can produce at initial moment flow rates of the order of 1.0E+05 g/s.  We have to know how to deal with different releases in the range from to 10 5 g/s safely (both outdoors and indoors).

Funded by FCH JU (Grant agreement No ) 4 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  The permeability of hydrogen for a particular material can be calculated as where the pre-exponential factor P 0 (mol/s/m/MPa 1/2 ) and the activation energy E 0 (J/mol) are material dependent ; T is temperature, K; R universal gas constant ( J/mol/K). Non-metallic materials have a larger permeability than metallic.  The permeation rate through a single material’s membrane is calculated using the equation where p r is the reservoir pressure, MPa; and l is the reservoir wall thickness, m.  The permeation rate increases with an increase of storage pressure p r and a decrease of membrane thickness l. Equations are valid for metallic and non- metallic materials and applicable to a single membrane’s wall, but under limited range of pressure and temperature from 10 Pa to 50 MPa and ambient temperature less than 1273 K respectively.

Funded by FCH JU (Grant agreement No ) 5 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  CFD modelling and simulations of permeated hydrogen dispersion to prove its uniformity: volumetric release of hydrogen in a thin layer around the tank surface of 1.87 m 2. No artificial source with a mass fraction Y H2 =1 at “release orifice” (there is no layer Y H2 =1 on the tank’s surface!). Permeation rate 1.14 NmL/hr/L.  Typical garage L×W×H =5×3×2.2 m (V=33 m 3 ). Storage tank L =0.672 m, D =0.505 m, hemisphere at each end (V=0.2 m 3 ). Floor clearance is 0.5 m. T= 298 K.  Time to reach LFL of 4% in the closed garage with chosen tank and permeation rate will be 240 days.  Time for hydrogen diffusion through the height of the garage is H 2 / D H2 (at 298 K as D H2 =6.8E-05 m 2 /s). Thus, H 2 / D H2 =2.2 2 / =71177 s or 0.8 days (convection due to temperature non-uniformity of walls/floor/ceiling will mix hydrogen with air even faster).

Funded by FCH JU (Grant agreement No ) 6 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  CFD: negligible stratification.  No areas of 100% hydrogen!  Max concentration at 133 min: tank top - 8.2×10 -3 % by vol.; ceiling - 3.5×10 -3 % by vol.

Funded by FCH JU (Grant agreement No ) 7 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  The perfect mixing equation for concentration can be used to calculate the hydrogen leak rate Q g  The permeation rate is where: Q a – air flow, NmL/hr, V – water capacity of hydrogen storage, L; f a – aging factor, taken to be 2, for unknown aging effects; f t – test temperature factor (3.5 at test temperature 20 o C, 4.7 – 15 o C).

Funded by FCH JU (Grant agreement No ) 8 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  With homogeneously dispersed permeated hydrogen, at reasonable minimum natural ventilation rate of 0.03 ac/hr, at reasonable maximum prolonged material temperature of 55 0 C (test temperature factor 4.7 for 15 o C), with aging factor 2, the maximum hydrogen concentration will not be above 1% by volume, if the permeation rate for a new tank is below 6 NmL/hr/L (15 o C), or 8 NmL/hr/L (20 o C). For comparison:  Japan Automotive Research Institute: 5 NmL/hr/L (15 o C).  Society of Automotive Engineers J2579, end of life, 55 o C: 150 NmL/min/vehicle (HySafe equivalent figure would be 90 NmL/min/vehicle)  ISO/TS15869:2009 at end of life (20 o C): 75 NmL/min/container  With this level of permeation rate the hydrogen dispersion in typical garage is safe!

Funded by FCH JU (Grant agreement No ) 9 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Separation distance (horizontal) strongly depends on jet type (effect of buoyancy):  Fully buoyancy-controlled jet  Momentum jet transits to buoyant  Fully momentum-dominated jet

Funded by FCH JU (Grant agreement No ) 10 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Jets can be expanded (pressure at jet exit from equipment is atmospheric) and under-expanded (pressure is above atmospheric).  The jet is, at the source of the leak, composed of 100% of hydrogen. Downstream, as the air is entrained into the jet, the hydrogen concentration along the jet axis decreases.  Previously standards used the concentration 1% of hydrogen by volume as a limiting value. However, NFPA 2 uses 4% by volume (about 4 times shorter compared to 1% which is too conservative).  The original similarity law for expanded jets by Chen and Rodi (1980) was expanded at Ulster to under-expanded jets with only one unknown parameter, i.e. hydrogen density in the nozzle exit  N

Funded by FCH JU (Grant agreement No ) 11 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE The similarity law (line) is conservative to tests - effect of losses

Funded by FCH JU (Grant agreement No ) 12 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Distance to 4% v/v: (proportional to diameter!) (4% v/v) (1% v/v)

Funded by FCH JU (Grant agreement No ) 13 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Most of hydrogen releases will be momentum-dominated.  Momentum-dominated jet decays slower compared to buoyant jet/plume from the same source.  Separation distance for unignited jets, x, is proportional to (conclusion from the similarity law):  release diameter, D, and  square root from storage pressure (term density  N )  Key safety requirement: reduce diameter of piping (release diameter for a worst-case scenario) to the minimum that can be technologically affordable. The same is relevant to diameter of Pressure Relief Devices (PRD).

Funded by FCH JU (Grant agreement No ) 14 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Note : the similarity law is applicable to momentum- controlled jets only (this would be a conservative estimate for buoyant jets).

Funded by FCH JU (Grant agreement No ) 15 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Froude number Fr = U 2 / gD. Buoyant jet decays faster than momentum (smaller x/D ).

Funded by FCH JU (Grant agreement No ) 16 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Start from the Fr=U 2 /gD ( U and D are real or notional nozzle velocity and diameter). Buoyant part of jet Momentum part of jet

Funded by FCH JU (Grant agreement No ) 17 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Problem : Hydrogen-powered car is in a closed garage of 44 m 3 free volume. Release from an onboard storage through PRD of 5.08 mm diameter. Storage pressure is 350 bar. Mass flow rate 390 g/s (volumetric flow rate is 390/2*0.0224= 4.4 m 3 /s ). Consequences : Every second of non-reacting release pressure in the garage will increase by (44+4.4)/44=1.1 times, i.e. by 10 kPa. Civil building structures can withstand kPa… The closed garage would be destroyed in 1 s with currently used storage pressures and comparatively large PRD diameter (to decrease PRD diameter a fire resistance of storage tanks has to be increased).

Funded by FCH JU (Grant agreement No ) 18 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE Small vented garage 4.5x2.6x2.6 m (one brick vent). Mass flow rate 390 g/s. Pressure limit for structures to withstand H 2 only! Solution: smaller PRD diameter, increased fire resistance of storage.

Funded by FCH JU (Grant agreement No ) 19 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Pressure dynamics of unignited release of 5 kg of hydrogen in a 30 m 3 garage with ACH=0.18 (storage pressure 35 MPa):  Typical 5 mm PRD (dash)  “Safe” 0.55 mm PRD (solid)

Funded by FCH JU (Grant agreement No ) 20 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Nomogram for blowdown time of unignited release of 5 kg hydrogen in a garage of different volume and ACH (Air Change per Hour) from initial pressure 35 MPa down to different residual overpressures through “safe” diameter PRD (mitigates the pressure peaking phenomenon to about kPa).  This is an indication of fire resistance time for storage tank.  Example: garage V=45 m 3, ACH=0.18, residual pressure in tank 0.01 MPa. Time 4000/60= 67 min (D=0.7 mm). 67 min

Funded by FCH JU (Grant agreement No ) 21 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  The release of liquefied hydrogen (LH 2 ) can result in accumulation and formation of a liquid pool on the ground. The pool could expand, depending on the volume spilled and the release rate, radially away from the releasing point and will immediately start to vaporize.  At the boiling point, hydrogen in gaseous phase has a higher density ( kg/m 3 ) than air at ambient condition (David, 1994). When considering a LH 2 spill, this has to be taken into account (accumulate on the ground level hydrogen then warms up and starts rising).  In 1980, NASA carried a series of experiments with release of 5.7 m 3 of LH 2 downwards to the ground on sand in a time span of s. Thermocouples were deployed at 1, 2 and 3 m distance from the spill centre. Only the inner two were found to have gotten contact with the cold liquid, thus indicating a maximum pool radius not exceeding 3 m (see movie on the next slide).

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

Funded by FCH JU (Grant agreement No ) 23 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE When a release of hydrogen occurs in an enclosure with no opening, hydrogen builds up at the ceiling forming a descending layer. The gas mixture in this layer is re- entrained by the plume instead of fresh air. Consequently the concentration of the gas mixture continues to increase with time. U 0 : release velocity, m/sec Q 0 : release flow rate, m³/sec R 0 : radius of the releasing orifice, m ρ a : ambient density, kg/m³ ρ 0 : released gas density,kg/m³

Funded by FCH JU (Grant agreement No ) 24 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  The fuel cell (FC) 0.8x0.7x1.0 m is leaking in a passively ventilated room 2.8x3.2x2.8 m (1 vent at the ceiling and 2 at the floor level).  Release of hydrogen through “ruptured pipe” within fuel cell in its upper part close to ceiling/corner. The leak is directed upward through 1 mm with volumetric flow rate of 40 NL/min.  Iso-surfaces in the CFD movie on the next slide (release during 20 min):  0.5% of hydrogen by volume (light blue),  2.0% (dark blue),  4.0% (yellow).  Passive ventilation stabilises the height of hydrogen layer. It is not descending for sustained leak as in the case of closed enclosure (see previous slide).

Funded by FCH JU (Grant agreement No ) 25 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE CFD is a contemporary technique for hydrogen safety engineering.

Funded by FCH JU (Grant agreement No ) 26 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE White boxes : phenomena/events. Grey boxes : consequences to safety of life and property.

Funded by FCH JU (Grant agreement No ) 27 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  Well-mixed regime is usually observed in an enclosure with one opening. The opening should preferably be located in the upper part of a wall. Hydrogen rises and leaves the enclosure through upper vent part.  Displacement regime takes place usually when two openings are located on two different walls at different heights. Outside air enters by the low-level opening and displaces the buoyant gas mixture from the enclosure through the higher level opening.

Funded by FCH JU (Grant agreement No ) 28 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  100% of hydrogen concentration in an enclosure with one vent will be reached with time if the lower limit of mass flow rate is equal to (see equation).  Example: 3 g/s leak (line to fuel cell) will lead to 100% of H2 with time if the vent is 10x10 cm.  No dependence on enclosure volume!  Equation for “safe” mass flow rate for known vent area yet to be developed and validated.

Funded by FCH JU (Grant agreement No ) 29 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  The wind can be directed either to (two vents case):  a face with the lower opening (ventilation reinforcing wind ), or  a face with the upper opening (ventilation opposing wind ).  The best engineering solution: distribute vents at all sides (lower and upper locations). In this case any wind will decrease concentration of hydrogen in the enclosure.

Funded by FCH JU (Grant agreement No ) 30 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE  At some conditions H 2 can cool when it expands isenthalpically during throttling through porous plug (this is used in liquefaction). At some conditions the throttling could lead to some increase of hydrogen temperature. Hydrogen has the low Joule-Thomson inversion temperature (200 K, NASA 1997).  The temperature increase is not more than a few degrees Kelvin (5.6 K for expansion from 140 atm to 1 atm). It would not cause hydrogen to ignite unless the gas was already near the auto-ignition temperature and therefore it should not be considered as a hazard.  Change of temperature at expansion of gas during throttling is not relevant to comparatively large decrease of temperature during expansion of hydrogen flowing out of high pressure equipment to the atmosphere through an orifice.  The role of the Joule-Thomson effect in safety is often misinterpreted.