The Correlation for Non-Premixed Hydrogen Jet Flame Length in Still Air

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1 The Correltion for on-premixed Hydrogen Jet Flme Length in Still Air VLADIMIR MOLKOV, nd JEA-BERARD SAFFERS Hydrogen Sfety Engineering nd Reserch Centre (HySAFER) University of Ulster Shore Rod ewtownbbey, BT37 0QB, UK ABSTRACT The experimentl dt on the hydrogen flme length normlized by the nozzle dimeter re correlted with the dimensionless product of the density rtio (hydrogen density in the nozzle exit to the density of surrounding ir) nd the Mch number to the power of three. The current up-to-dte experimentl dt on hydrogen flme length re used to build the correltion tht covers lminr nd turbulent flows, buoyncynd momentum-dominted releses, subsonic, sonic nd highly under-expnded supersonic jets. The density nd velocity of hydrogen in the nozzle re tken either directly from experiments or clculted by the under-expnded jet theory published elsewhere. The correltion is vlidted in the rnge of hydrogen storge pressures from nerly tmospheric up to 90 MP nd nozzle dimeters from 0.4 to 51.7 mm. The predictive cpbility of this dimensionless correltion exceeds tht of previously published work bsed on the Froude number only. KEYWORDS: hydrogen jet fire, flme length, under-expnded jet. OMECLATURE LISTIG b hydrogen co-volume (m 3 /kg) T temperture (K) C speed of sound (m/s) U velocity (m/s) d dimeter (m) Greek Fr Froude number specific hets rtio g ccelertion of grvity (9.81 m/s 2 ) Pi (3.14) K Suth Sutherlnd constnt (K) density (kg/m 3 ) L F hydrogen flme length (m) dynmic viscosity (P. s) m mss flow rte (kg/s) subscripts M Mch number F flme M H2 hydrogen moleculr weight (kg/mol) nozzle Re Reynolds number S surroundings R H2 hydrogen gs constnt (J/kg K) ITRODUCTIO Emerging hydrogen nd fuel cell technologies nd infrstructures, including storge t up to 100 MP, pose new chllenges to fire sfety. One of them is the prediction of hydrogen flme length from highly underexpnded jets. Experimentl dt published decdes go re minly for subsonic releses of hydrogen or t pressures fr below 100 MP. Dimensionless flme length correltions suggested t tht time were bsed on the use of the Froude number (Fr) in one or nother form [1 3]. Recently Fr-bsed correltions [4,5] were expnded to high pressure hydrogen jet fires. The generl ide of this technique is to correlte experimentl dt with the modified Fr number tht is built on so-clled notionl or effective nozzle dimeter insted of the rel nozzle dimeter. However, the size of the notionl nozzle dimeter depends on the theory pplied to clculte it including number of simplifying ssumptions. For exmple, constnt flow velocity is ssumed t the notionl nozzle while in fct t high pressures there is strong supersonic flow on the periphery immeditely downstrem of the Mch disk nd prcticlly stgnnt flow in the middle of the jet. Besides, only limited number of their own experimentl dt were used by uthors to support their correltions. FIRE SAFETY SCIECE-PROCEEDIGS OF THE TETH ITERATIOAL SYMPOSIUM, pp COPYRIGHT 2011 ITERATIOAL ASSOCIATIO FOR FIRE SAFETY SCIECE / DOI: /IAFSS.FSS

2 In 2009 the dimensionl correltion for hydrogen jet flme length in still ir ws published [6]. The flme length of 95 hydrogen jet fires ws correlted with new similrity group tht includes the product of mss flow rte nd nozzle dimeter to exclude dependence on the model-dependent notionl nozzle prmeters. The originl under-expnded jet theory [7] ws used to clculte mss flow rte in the nozzle bsed on hydrogen storge pressure nd temperture. The correltion [6] ws updted in 2010 to include 123 experimentl hydrogen flme length dt points [8]. It demonstrtes better predictive cpbility in the momentum-controlled regime, which is the most pproprite for hydrogen leks from high pressure equipment, compred to the Fr-bsed pproch [4]. The im of this pper is to improve our understnding of underexpnded hydrogen jet fires nd develop correltion for the non-premixed flme length in dimensionless form. The correltion should cover the whole spectrum of hydrogen releses including lminr nd turbulent jets, buoynt nd momentum jets, nd expnded nd under-expnded jets. DIMESIOLESS CORRELATIO Dimensionless Groups Previous flme length correltions were bsed on Fr number nd vlidted minly ginst experimentl dt on subsonic buoynt jet fires with limited number of dt on momentum-dominted jets t moderte pressures t the source. However, experimentl dt indicte tht the flme length hs to be function of not only the Fr number but lso the Reynolds (Re) number nd the Mch (M) number. It is impossible to build universl correltion bsed on only one of these dimensionless numbers. Indeed, the simple ide tht n experimentl jet flme length cn only be correlted by the Fr number [1 4] does not work well in the momentum-controlled regime when more experiments hve been recently nlyzed [8]. The recent correltion [6] reproduces experimentl dt for momentum-dominted highly under-expnded jets within 20 % nd drops the predictive ccurcy to 50 % for subsonic jets. Thus, both types of correltions re not closing the problem for the whole rnge of jet conditions. There is need for dimensionless group tht would better predict hydrogen jet fire length for vrious conditions nd flow regimes. It follows from the dimensionl correltion L F = 76 ( m d ) [6] tht the dimensionless flme length L F /d is prcticlly independent of the physicl nozzle dimeter d nd depends on density nd velocity U of hydrogen in the nozzle. Thus, the following dimensionless group is suggested in this study to correlte with the dimensionless flme length L F /d 3 U, (1) S C where the speed of sound for non-idel gs ws corrected s function of temperture in the nozzle using Eq. 2, where is the hydrogen specific hets rtio (1.41), R H2 is the hydrogen gs constnt (4124 J/kg K) nd b the hydrogen co-volume ( m 3 /kg) C RH 2 T. (2) (1 b ) The form of dimensionless group given in Eq. 1 suggests for subsonic flows (M < 1) the dependence of the non-dimensionl flme length on the nozzle Mch number only. Indeed, the hydrogen density in the nozzle is constnt for subsonic flows (with the ssumption of constnt temperture). Hence, the rtio of hydrogen density in the nozzle exit to the density of surrounding ir / S is constnt too. For choked flows (M = 1) the dimensionless flme length depends only on the hydrogen density in the nozzle tht increses with the storge pressure. The dimensionless group given in Eq. 1 cn be rewritten in terms of Re nd Fr numbers s follows 934

3 S U C 3 g C S 3 Re Fr, (3) where Re nd Fr re determined through prmeters of hydrogen flow in the nozzle d U Re nd 2 U Fr, (4) d g nd the hydrogen dynmic viscosity (Sutherlnd constnt for hydrogen ws chosen s K Suth = 72 K nd the dynmic viscosity 293 = P. s) 3/ K Suth 293 T. (5) T KSuth 293 From Eq. 3 it follows tht t constnt temperture of hydrogen in the nozzle the dimensionless flme length depends on both Re nd Fr numbers not only the nozzle Fr number s in former correltions. Description nd Interprettion of Experiments Some of the experiments described in this section do not provide ll the necessry informtion for our clcultions. For instnce, only in few experiments ws the continer temperture history during blowdown provided [4,9]. In order to clculte flow prmeters in cses when experimentl temperture ws not provided, it ws ssumed tht the initil temperture in the continer ws 273 K. The temperture in the nozzle ws then clculted using the under-expnded jet theory [7] for under-expnded jets nd tken equl to storge temperture 273 K for subsonic releses. Clcultions using the under-expnded jet theory [7] showed tht decrese of hydrogen temperture in tnk by 50 K would increse the density in the nozzle by only 10 %. Hwthorne et l. [10] in 1949 reported results of two experiments with verticl subsonic hydrogen jet fires: one with 4.76 mm dimeter rounded nozzle gve L F /d = 134 (Re = 2,870; Fr = 92,000); nother with 4.62 mm dimeter shrp-edged nozzle hd L F /d = 147 (Re = 3,580; Fr = 158,000). The velocity t the nozzle ws clculted using the vlues given for Fr. The density t the nozzle ws ssumed to be kg/m 3 nd the temperture 273 K. In 1977 Shevykov nd Komov [2] published study on hydrogen subsonic flmes in tubulr burners of mm dimeter. The visul length of on-port flmes ws mesured in drkened room. The correltion L F /d (Fr) ws developed to cover both buoyncy- nd momentum-controlled regimes. For ech experimentl point, the dimeter, flme length nd flow velocity were provided. The hydrogen density of kg/m 3 nd the hydrogen temperture of 273 K were ssumed in the nozzle. In 1984 Klghtgi [11] published jet flme lengths for more thn 70 tests with subsonic nd sonic releses of hydrogen into still ir through nozzles with dimeter from 1.08 to 10.1 mm. Ech burner ws stright tube mounted t the end of settling chmber of internl dimeter 152 mm. The mss flow rte ws provided for ech mesurement nd exit flow prmeters (Mch number, velocity, temperture nd density) were clculted by Klghtgi using the Liepmn nd Roshko pproch [12]. In this study we ssumed tht hydrogen temperture in tnk ws 273 K nd tht the density in the nozzle ws kg/m 3 for subsonic flows. The flow velocity t the nozzle ws clculted from the experimentl mss flow rte provided using 2 the eqution U (4 m ) /( d ). For under-expnded jets n initil temperture in the continer ws ssumed to be 273 K nd the hydrogen density t the nozzle ws clculted using the under-expnded jet theory [7]. In 2005 Mogi et l. [13] published experimentl dt for horizontl hydrogen jet flmes from convergent nozzles of mm dimeter nd spouting pressures MP. The relese from four compressed 935

4 hydrogen storge tnks with internl volume of m 3 ech, ws done 1 m bove the floor nd 1 m wy from wll. For ech test, the hydrogen mss flow rte nd spouting pressure were provided. The temperture in the tnk ws ssumed to be 273 K. Then, hydrogen density nd flow velocity in the nozzle were clculted using the under-expnded jet theory [7]. Schefer et l. [4] published in 2006 study on sptil nd rditive properties of open verticl hydrogen jet flmes for subsonic nd high pressures releses up to 17.2 MP. They performed blow-down of two cylinders of m 3 ech with initil pressure 17.2 MP, through 7.6 m stright section stinless steel tubing of 7.94 mm dimeter. The blow-down time ws bout 100 s. There ws mm dimeter mnifold orifice ner the cylinder outlets. Shocked flow conditions were reched t the exit of the 7.94 mm dimeter tube erly in the blow-down. The tnk pressure hd dropped sufficiently to hve subsonic flow 40 s fter the strt of the relese. Two sets of dt were presented for the flme length: Releses performed using blow-down t n initil pressure of 17.2 MP through 7.94 mm dimeter tubing. Trnsients of dt during the blow-down t the tubing exit were provided for the 7.94 mm test: pressure, mss flow rte, nd jet velocity. The temperture in the continer ws ssumed to be 273 K. The under-expnded jet theory [7] ws then used to clculte hydrogen density nd temperture t the nozzle exit. For the subsonic relese t the end of the blow-down, the hydrogen density t the nozzle ws ssumed to be kg/m 3. For this prticulr set of dt, M 1 for under-expnded releses. This could be explined by n inccurcy in dt provided on the jet exit velocity nd/or by the ssumption of constnt temperture t 273 K in the tnk. In the sme pper, subsonic releses from 1.91 mm were presented nd the mss flow rte nd exit velocity were given long with the flme length. The density of the hydrogen t the nozzle ws ssumed to be kg/m 3. In 2007 Schefer et l. [14] mesured hydrogen jet flme lengths in tests t pressures up to 43.1 MP nd for nozzle dimeter of 5.08 mm. Their own notionl nozzle theory [14] ccounting for deprtures from the idel gs behvior ws pplied to ensure the pplicbility of lower-pressure engineering correltions bsed on the Fr number nd dimensionless flme length, when substituting flow prmeters nd dimeter in the nozzle by those t the notionl nozzle. The experimentl set-up ws composed of eight cylinders of volume m 3 ech nd filled t 43.1 MP. A stgntion chmber locted between cylinders nd exit ws used to mintin low exit flow Mch number. The experimentl dt provided, i.e. stgntion chmber pressure nd temperture history, exit mss flow rte, flow velocity t the nozzle, were used in this study to clculte the hydrogen density t the nozzle using the under-expnded jet theory [7]. In 2008 Immur et l. [15] conducted series of experiments to understnd the therml hzrds of hydrogen jet flmes nd more specificlly temperture field of hot currents in the downstrem region. They used hydrogen relese system composed of hydrogen cylinder, stop vlve, regultor, n ir-operted bll vlve nd nozzle locted 1 m bove ground. Experiments investigted the dependence of flme shpe on the spouting conditions: nozzle dimeters were 1, 2, 3 nd 4 mm nd spouting pressures 0.5, 1.0, 1.5, 2.0, 2.5 nd 3.0 MP. The hydrogen flme ws visulized by sprying Cl queous solution. Experimentl mesurements of jet flme length s function of dimeter were provided. The given spouting pressure ws mesured t the pressure trnsducer close to the nozzle. With the ssumption bout the temperture in the continer to be equl to 273 K, the underexpnded jet theory [7] ws pplied to clculte flow prmeters, i.e. velocity nd density, t the nozzle. In 2009 Studer et l. [16] published results of their experimentl study on hydrogen jet fires. Hydrogen ws stored in m 3 Type IV tnk t 10 MP nd relesed horizontlly through 5 m long flexible pipe with internl dimeter of 15 mm. The pipe ws mounted 1.5 m bove the ground nd the hydrogen ws ignited immeditely fter relese by n electric sprk. Pressure nd temperture were recorded in the pipe just prior to the nozzle but were not given in the publiction [16]. The uthors investigted releses through orifices of 4, 7 nd 10 mm. The experimentl dt on pressure history, jet flme length nd time of smpling were published elsewhere [17]. With ssumption of hydrogen temperture in the tnk of 273 K it ws possible to clculte the flow prmeters t the rel nozzle using the under-expnded jet theory [7]. In 2009 Proust et l. [9] used Type IV tnk with m 3 cpcity pressurized up to 90 MP to study hydrogen jet fires. Hydrogen ws relesed horizontlly 1.5 m bove ground vi 10 m long pipe with internl dimeter 10 mm, nd ignited by continuous propne-ir burner. The pressure ws mesured t the hed of the tnk, the temperture ws mesured inside the tnk using K-Type thermocouples nd the mss 936

5 flow rte ws deduced from mesurements of numericl weighting device where the tnk ws locted. The jet flme length ws mesured for orifice dimeter 1, 2 nd 3 mm. The experimentl set up ws similr to [16] nd there were some doubts bout the ccurcy of the mss flow rte provided. By this reson the experimentl dt on pressure nd temperture were used in this study to clculte the mss flow rte nd other flow prmeters t the nozzle by use of the under-expnded jet theory [7]. It ws found tht clculted mss flow rtes were in n excellent greement with the experimentl dt provided. The correltion in coordintes the dimensionless flme length, L F /d, nd the similrity group ( / S ). (U /C ) 3 is shown in Fig. 1. The summrized experimentl nd clculted dt re presented in Tble 1. Experimentl dt used to build Tble 1 include: continer or spouting pressure, when pplicble, rel nozzle dimeter, flme length, mss flow rte or velocity in nozzle. Other prmeters in Tble 1 were clculted bsed on the experimentl dt with use of the under-expnded jet theory [7], when pplicble, nd the described bove ssumptions Klghtgi, subsonic Klghtgi Mogi et l. Schefer et l., subsonic Schefer et l. Proust et l. Studer et l. Immur et l. Chevykov et l., subsonic Hwthorne, subsonic L F /d M=1 1E-009 1E-007 1E ( / S ). (U /C ) 3 Fig. 1. The dimensionless correltion for hydrogen jet flme length. 937

6 Tble 1. Experimentl nd clculted dt. Experiment P d, L F m (MP) (mm) d T U C (g/s) (kg/s) (K) (m/s) (m/s) (P s) Fr Re M Hwthorne, E E Hwthorne, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Shevykov, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E otes: - experimentl dt. 938

7 Tble 1 (continued). Experimentl nd clculted dt. Experiment P d, L F m (MP) (mm) d T U C (g/s) (kg/s) (K) (m/s) (m/s) (P s) Fr Re M Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Klghtgi, E E Mogi, b E E Mogi, b E E Mogi, b E E Mogi, b E E Mogi, b E E Mogi, b E E Mogi, b E E Mogi, b E E Mogi, b E E Mogi, b E E Mogi, b E E Mogi, b E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E Schefer, E E otes: - experimentl dt; b - spouting pressure. 939

8 Tble 1 (continued). Experimentl nd clculted dt. Experiment P d, L F m (MP) (mm) d T U C (g/s) (kg/s) (K) (m/s) (m/s) (P s) Fr Re M Immur, b E E Immur, b E E Immur, b E E Immur, b E E Immur, b E E Immur, b E E Immur, b E E Immur, b E E Immur, b E E Immur, b E E Immur, b E E Proust, E E Proust, E E Proust, E E Proust, E E Proust, E E Proust, E E Proust, E E Proust, E E Proust, E E Proust, E E Proust, E E Proust, E E Proust, E E Proust, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E Studer, E E otes: - experimentl dt; b - spouting pressure. DISCUSSIO There re three distinguished prts in the dimensionless correltion in Fig. 1 from the left to the right: trditionl buoyncy-controlled prt tht is represented by dt on subsonic releses of Shevykov et l. [2] nd Hwthorne et l. [10]; sturted momentum-dominted prt represented by subsonic relese tests by Klghtgi [11] nd Schefer et l. [4] where dimensionless flme length is essentilly constnt; nd finlly third prt tht stnds for choked nd under-expnded jet fires. 940

9 Log (Fr) nd Log (Re) Mch number It is cler tht there is no sturtion of dimensionless flme length t vlue L F /d = 230 observed in numerous previous studies with expnded jets. Currently reported experiments exhibit much higher vlues, e.g. L F /d = 3000 [9]. Anlysis of chnge in dimensionless groups (Re, Fr, M) vlue shows tht for underexpnded jets, the dimensionless flme growth depends prcticlly on Re number only s flow is choked nd thus nozzle Mch number M = 1 nd nozzle Fr number is constnt lso for fixed dimeter (Fig. 2) Froude number Reynolds number Mch number 7 6 Fr= Re= M=1 1E-009 1E-007 1E ( / S ). (U /C ) 3 0 Fig. 2. Dimensionless numbers Re, Fr, M s function of the new similrity group for experiments used for the correltion. There re three lines in Fig. 2. Line Re = 2000 seprtes lminr nd turbulent jets. Previling mjority of experiments used to vlidte the correltion were crried out for turbulent releses. Line Fr = 10 6 is indictive for trnsition from buoyncy- to momentum-dominted jets. Finlly, line M = 1 seprtes subsonic jets from choked in the nozzle flows. This explins the shpe of the correltion (Fig. 1). COCLUSIOS The dimensionless correltion for non-premixed hydrogen jet flme length in still ir in coordintes L F /d ginst ( / S ). (U /C ) 3 is developed. It is thoroughly vlidted by the experimentl dt on flme length for lminr nd turbulent hydrogen flmes, buoyncy- nd momentum-dominted flows, expnded nd highly under-expnded hydrogen jet fires. umerous experimentl dt obtined by different uthors collpsed into the sme curve. The correltion follows previously estblished pttern with trditionl buoyncy- nd momentum-controlled prts, nd incorportes power lw for dependence of the flme length on the Re number for under-expnded high momentum jets. The correltion cn be recommended for use 941

10 by fire sfety engineers nd requires knowledge of only hydrogen density nd velocity in the nozzle tht cn be clculted using the under-expnded jet theory published elsewhere. REFERECES [1] Bev, V.K. nd Yskov, V.A, (1974) Influence of buoynt forces on the length of diffuse flmes, Combustion, Explosion nd Shock Wves 10: , [2] Shevykov, G.G. nd Komov, V.F., (1977) Effect of non-combustible dmixtures on length of n xisymmetric on-port turbulent diffusion flme, Combustion, Explosion nd Shock Wves 13: , [3] Delichtsios, M., (1993) Trnsition from momentum to buoyncy-controlled turbulent jet diffusion flmes nd flme height reltionships, Combustion nd Flme 92: , [4] Schefer, R.W., Houf, W.G., Bourne, B. nd Colton, J., (2006) Sptil nd rditive properties of n open-flme hydrogen plume, Interntionl Journl of Hydrogen Energy 31: , [5] Mogi, T. nd Horiguchi, S., (2009) Experimentl study on the hzrds of high-pressure hydrogen jet diffusion flmes, Journl of Loss Prevention in the Process Industries 22:45 51, [6] Molkov, V.V., Hydrogen non-recting nd recting jets in stgnnt ir: overview nd stte-of-thert, Proceedings of the 10 th Interntionl Conference on Fluid Control, Mesurements, nd Visuliztion, August 2009, Moscow, Russi. [7] Molkov, V.V., Mkrov, D. nd Brgin, M.V., Physics nd modelling of under-expnded jets nd hydrogen dispersion in tmosphere, Proceedings of the 24 th Interntionl Conference on Interction of Intense Energy Fluxes with Mtter, 1-6 Mrch 2009, Elbrus, Russi. [8] Sffers, J-B. nd Molkov V.V., Towrds Hydrogen Sfety Engineering for Recting nd on- Recting Hydrogen Releses, Proceedings of the 8 th Interntionl Symposium on Hzrd, Prevention nd Mitigtion of Industril Explosions, 5-10 September 2010, Yokohm, Jpn. [9] Proust, C., Jmois, D. nd Studer, E., High pressure hydrogen fires, Proceedings of the 3 rd Interntionl Conference on Hydrogen Sfety, September 2009, Ajccio, Frnce. [10] Hwthorne, W.R., Weddell, D.S. nd Hottel, H.C., Mixing nd combustion in turbulent gs jets, Proceedings of the 3 rd Interntionl Symposium on Combustion, Flme nd Explosion Phenomen, 1949, pp [11] Klghtgi, G.T., (1984) Lift-off Heights nd Visible Lengths of Verticl Turbulent Jet Diffusion Flmes in Still Air, Combustion Science nd Technology 41: [12] Liepmn, H. nd Roshko, A., Elements of Gsdynmics, John Wiley nd Sons Inc. ed., [13] Mogi, T., ishid, H. nd Horiguchi, S., Flme chrcteristics of high-pressure hydrogen gs jet, Proceedings of the 1 st Interntionl Conference on Hydrogen Sfety, 8-10 September 2005, Pis, Itly. [14] Schefer, R.W., Houf, W.G., Willims, T.C., Bourne, B. nd Colton, J., (2007) Chrcteriztion of high-pressure, underexpnded hydrogen-jet flmes, Interntionl Journl of Hydrogen Energy 32: , [15] Immur, T., Hmd, S., Mogi, T., Wd, Y., Horiguchi, S., Miyke, A. nd Ogw, T., (2008) Experimentl investigtion on the therml properties of hydrogen jet flme nd hot currents in the downstrem region, Interntionl Journl of Hydrogen Energy 33: , 942

11 [16] Studer, E., Jmois, D., Jllis, S., Leroy, G., Hebrrd, J. nd Blnchetière, V., (2009) Properties of lrge-scle methne/hydrogen jet fires, Interntionl Journl of Hydrogen Energy 34: , [17] Hyper Project ( Instlltion Permitting Guidnce for Hydrogen nd Fuel Cells Sttionry Applictions. D4.3 Releses, Fires nd Explosions, WP4 Finl Report (2008). 943