1
EXPERIMENTAL STUDY ON HYDROGEN EXPLOSIONS IN A FULL-SCALEHYDROGEN FILLING STATION MODEL
Tanaka, T.1, Azuma, T.1, Evans, J.A.2, Cronin, P.M.2, Johnson,D.M.2 and Cleaver, R.P.2
1 Engineering Department, Osaka Gas Co., Ltd., 5-11-6,Torishima, Konohana-ku, Osaka, JAPAN 2 Advantica Ltd, Ashby Road,Loughborough, Leicestershire, LE11 3GR, UK
ABSTRACT
In order for fuel cell vehicles to develop a widespread role insociety, it is essential that hydrogen refueling stations becomeestablished. For this to happen, there is a need to demonstrate thesafety of the refueling stations. The work described in this paperwas carried out to provide experimental information on hydrogenoutflow, dispersion and explosion behaviour. In the first phase,homogeneous hydrogen-air-mixtures of a known concentration wereintroduced into an explosion chamber and the resulting flame speedand overpressures were measured. Hydrogen concentration was thedominant factor influencing the flame speed and overpressure.Secondly, high-pressure hydrogen releases were initiated in astorage room to study the accumulation of hydrogen. For a steadyrelease with a constant driving pressure, the hydrogenconcentration varied as the inlet airflow changed, depending on theventilation area of the room, the external wind conditions and alsothe buoyancy induced flows generated by the accumulating hydrogen.Having obtained this basic data, the realistic dispersion andexplosion experiments were executed at full-scale in the hydrogenstation model. High-pressure hydrogen was released from 0.8-8.0mmnozzle at the dispenser position and inside the storage room in thefull-scale model of the refueling station. Also the hydrogenreleases were ignited to study the overpressures that can begenerated by such releases. The results showed that overpressuresthat were generated following releases at the dispenser locationhad a clear correlation with the time of ignition, distance fromignition point.
INTRODUCTION
In order for the ‘hydrogen economy’ to become a reality, notonly is their a requirement to develop the fuel cell technology andassociated equipment and infrastructure in an economic manner, butalso it is necessary to demonstrate that all aspects of the supplyand use of hydrogen can be performed safely. Osaka Gas Co., Ltd.has been operating a hydrogen refuelling station [1] safely as ademonstration plant, in parallel with developing a compact hydrogenreformer [2], (see Figure 1). However, in 2003, Osaka Gas joinedthe Japanese National Project on Hydrogen, with the aim of carryingout further work to investigate the safety aspects of hydrogenrefuelling stations. One of the particular aims of this work was tohelp establish a suitable ‘safety zone’ around such a station.
Figure 1: Osaka Gas’s hydrogen station (left) and hydrogenproduction unit, HYSERVE (right)
2
The way in which an accidental release of hydrogen would behavewill be strongly affected by the layout and size of any hydrogenrefuelling station. As a result, a realistic scale model of arefuelling station was built for the purposes of these studies. Inthis way, the dispersion tests and explosion tests that werecarried out reproduced realistic conditions should such accidentpossibly happen. All of the experiments were planned by Osaka Gasworking together with Advantica Ltd. and were conducted byAdvantica at their Spadeadam test site.
As experimental data were already available demonstrating thebehaviour of hydrogen dispersion and explosion in an unobstructedenvironment, the main thrust of this work was to obtain a range ofdata to illustrate hydrogen behaviour in confined and/or congestedregions. The factors studied and the outcome from the experimentsare summarised in diagrammatic form in Figure 2.
Accidental ReleaseLeak diameter
Leak pressure
Amount of hydrogen that can leak
Release position/direction
Environmental FactorsOpen space/Confined volume/Congestedregion
Wind speed and direction
Hydrogen-Air CloudCloud volume
Hydrogen concentration
Ignition-ExplosionIgnition source/timing/positionFlowconditions
Environmental FactorsOpen space/Confined volume/Congestedregion
DamageOverpressure distributionThermal radiation variation withtime
Hazardous AreaExtent of flammable zone
Hazardous AreaAbove tolerable overpressure or radiationlevel
Figure 2: Aspects studied in the experiments
EXPERIMENTAL PROGRAMME
The experimental programme that was followed is shown in Figure3.
Idealised experiments studying dispersion/explosion in confinedvolumes
Dispersion Experiments Using Model Storage RoomHigh pressurehydrogen release
Determine hydrogen concentration distribution
Study effect of release parameters and natural ventilation
Explosion Experiments Using ChamberHomogeneous mixture ofhydrogen and air
Determine overpressure distribution
Study effect of gas concentration/position
Experiments at DispenserHigh pressure hydrogen release
Determine hydrogen concentration distribution and overpressureon ignition
Study effect of release parameters, wind conditions and ignitiontime and location
Experiments in Storage RoomHomogeneous mixture of hydrogen andair and high pressure releases
Determine concentration distribution and overpressuredistribution on ignition
Study effect of release parameters, ventilation conditions andgas concentration
Realistic experiments at hydrogen refuelling station modelIdealised experiments studying
dispersion/explosion in confined volumes
Dispersion Experiments Using Model Storage RoomHigh pressurehydrogen release
Determine hydrogen concentration distribution
Study effect of release parameters and natural ventilation
Explosion Experiments Using ChamberHomogeneous mixture ofhydrogen and air
Determine overpressure distribution
Study effect of gas concentration/position
Experiments at DispenserHigh pressure hydrogen release
Determine hydrogen concentration distribution and overpressureon ignition
Study effect of release parameters, wind conditions and ignitiontime and location
Experiments in Storage RoomHomogeneous mixture of hydrogen andair and high pressure releases
Determine concentration distribution and overpressuredistribution on ignition
Study effect of release parameters, ventilation conditions andgas concentration
Realistic experiments at hydrogen refuelling station model
Experiments at DispenserHigh pressure hydrogen release
Determine hydrogen concentration distribution and overpressureon ignition
Study effect of release parameters, wind conditions and ignitiontime and location
Experiments in Storage RoomHomogeneous mixture of hydrogen andair and high pressure releases
Determine concentration distribution and overpressuredistribution on ignition
Study effect of release parameters, ventilation conditions andgas concentration
Realistic experiments at hydrogen refuelling station model
Figure 3: Outline of experimental progamme
3
First of all, dispersion and explosions experiments were carriedout to acquire the basic data for hydrogen behaviour in confinedregion. Then, a realistic scale model of a hydrogen refuellingstation was constructed and experiments using high-pressurehydrogen were executed in the dispenser area and in the storageroom. The results that were obtained are outlined in the sectionsbelow.
DISPERSION AND EXPLOSION EXPERIMENTS IN A MODEL STORAGE ROOM
Dispersion experiments
A realistic scale model of a storage room was fabricated tostudy the distribution of hydrogen concentration produced withinthe room by a hydrogen leak. The hydrogen was released at highpressure through one of two different size of nozzle. The hydrogenvolume concentration distribution was monitored using 30 oxygensensors, located inside the room. In reality, a storage room wouldbe equipped with either mechanical ventilation or naturalventilation. Natural ventilation was used in this experimentalprogramme. A picture of the room is shown in Figure 4, along with aschematic demonstrating the different ventilation conditions thatwere studied. The roof was always fully closed, but naturalventilation openings were located along the top 1m of either two orall four of the sidewalls. These ventilation openings had aneffective open area of 50%.
Ventilation openings on 2 walls
Ventilation openings on 4 walls
4m or 8m6m
4m
1m
Ventilation openings on 2 wallsVentilation openings on 2walls
Ventilation openings on 4 walls
4m or 8m6m
4m
1m
Figure 4: Structure of storage room
See AlsoUniversità di Pisa - Valutazione della didattica e iscrizione agli esamiUniversità di Pisa - Valutazione della didattica e iscrizione agli esamiTable 1 lists the conditions studied in the experiments. In thisseries, the release pressure was maintained at a constant value of10Mpa, with nozzle diameters of 0.8mm or 1.6mm being used to studyhydrogen gas build-up from representative ‘pinhole’ leakages.
Table 1: Conditions used for the first series of dispersionexperiments
Gas Hydrogen Pressure 10 MPa Diameter 0.8mm or 1.6mm DirectionHorizontal
Vertically upwards or downwards
Release Parameters
Location Corner, Adjacent to sidewall Centre of enclosure
Dimensions Height 4m Depth 4m Width 8m or 4m
Enclosure
Size of Ventilation Opening (50% open)
Height 1m Present on 2 sidewalls or all 4 sidewalls
4
It was found that an approximate steady-state was recorded ateach sensor within about 3 minutes of the start of the release. Theaverage hydrogen concentration in the room was determined in thissteady-state from the individual sensor readings and the resultingvalues are shown in Table 2. The hydrogen mass flow rate changedlinearly with the nozzle area, because the flow speed is choked forboth size of nozzle diameters. It was found that the combination ofthe buoyancy-induced and wind-driven ventilation was sufficient tokeep the average concentration of hydrogen in the room to below17%, even in the cases when the ventilation was present only on towwalls, as in Experiment 1.
Table 2: Results of the first series of dispersionexperiments
Experiment number
Nozzle diameter, mm
Hydrogen flow rate, m3/h
Room width, m
Effective open area for ventilation, m2
Wind speed, m/s
Average hydrogen concentration in enclosure, %
1 1.6 600 4 4 1.5 16.8
2 1.6 600 4 10 5.0 5.0
3 0.8 150 4 4 4.9 5.1
4 1.6 600 8 8 3.7 3.7
5 1.6 600 8 14 4.2 3.3
6 0.8 150 8 8 4.3 4.3
Explosion experiments
A test chamber was used to study the overpressure distributionproduced by hydrogen explosions, such as might occur underunfavourable circumstances following the ignition of a hydrogen-airmixture that had accumulated in a storage room following a leak. Apicture of the chamber and a schematic showing the layout is givenin Figure 5.
3 m8.25 m
2.7 m
AB
C
3 m8.25 m
2.7 m
AB
C
8.25 m
2.7 m
AB
C
Figure 5: Chamber structure
The front face of the chamber was open in all of the experimentsand, in some cases, the upper half of the two long sidewalls werealso open. One third of the chamber inside was filled with a gasmixture and was ignited by a single electric spark at the center ofthe gas cloud. Overpressure measurements were made
5
inside and outside the chamber. The flame arrival time atvarious locations within the chamber was also measured. Theconditions are summarized in Table 3. Other than for the equipmentused to make the measurements, the chamber was empty.
Table 3: Conditions used in the explosion experiments in thechamber
Volume 22 m3 Hydrogen concentration 15%, 30%, 40% or 50%
Gas Cloud Parameters
Cloud position (see Figure 5) A, B or C Dimensions 2.7m high, 3mwide, 8.25m
long Enclosure Parameters
Vent openings Front face (all tests) Upper half of two long
sidewalls (some tests) Method Single electric spark IgnitionParameters Position Centre of gas cloud
The relationship between the peak overpressure measured outsidethe chamber and the distance from its open, front end is shown inFigure 6. The measurements shown in this figure are for experimentsthat had an opening on the front face only (i.e. the vents in thesidewall were not present).
-1
-0.5
0.5
1
1.5
0.6 0.8 1 1.2 1.4
Log(Distance(m ))
Log(Overpressure(kPa))
H2 conc. 50%
H2 conc. 30%
H2 conc. 15%
Figure 6: Correlation between overpressure and distance (resultsfor experiments without side vents)
The peak overpressure is seen to decrease almost inversely withdistance from the front face. The overpressure itself is biggerthan has been reported for explosions of a comparably sized,unconfined hydrogen cloud [3]. The effect of hydrogen concentrationon the overpressure is illustrated in Figure 7. The overpressurethat is generated is related to the flame speed and, as shown, thelargest flame speeds were measured for hydrogen concentrations of30-40%. (The average values as the flame progressed within theenclosure are shown in this figure). For such concentrations,pressures in excess of 9.8 kPa were measured outside of theenclosure. On the other hand, a hydrogen concentration of 15%generated only a small overpressure, being below 1 kPa for thewhole of the external area. An overpressure of up to about 9.8 kPais generally recognised as being tolerable for human beings. It canbe see therefore that any safety zone around such an enclosuredepends strongly on the hydrogen concentration and, as shown in thedispersion experiments, this in turn depends on the release andventilation conditions.
6
5
10
15
0 10 20 30 40 50 60Hydrogen Concentration（vol％）
Overpressure(kPa)
5
10
15
20
Flame speed(m/s)
O verpressure-5m (left axis)
O verpressure-10m (left axis)
Flam e speed(right axis)
Figure 7: Effect of hydrogen concentration (experiments withoutside ventilation, overpressure results shown for external locations5m/10m from front end)
DISPERSION AND EXPLOSION EXPERIMENTS USING A MODEL OF A HYDROGENSTATION
Although the previous experiments have provided basic data ondispersion and explosion in enclosures, such as a storage room, thesituation at a filling station would be somewhat different. Thehydrogen could be stored at a higher pressure and the high-pressurestorage cylinders in the storage room would act as obstacles thatcould promote flame acceleration in the event of an explosion.Also, because of the finite inventory of hydrogen that isavailable, any release that occurs would be transient in nature.This could be particularly important for a larger leak, as thedriving pressure will decrease rapidly. In order to investigatesuch factors, a realistic scale model of a filling station wasconstructed and a further series of dispersion and explosionexperiments was performed. First of all, a layout for a hydrogenrefuelling station was designed with help from Shimizu Corporation,as shown in Figure 8. The design was selected to achieve thecapacities noted in Table 4. Two of the sides of the station had a2m high perimeter wall and the other two sides were left open torepresent a filling station located near to a road junction. A partof these boundary walls was constructed from concrete with athickness of 150 mm and this was instrumented to measure itsdisplacement and strain.
Table 4: Specification of the hydrogen filling station
Hydrogen production capacity 300 Nm3/h Hydrogen compressor flow500 Nm3/h Hydrogen storage 3500Nm3 Number of hydrogen dispensers2
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Figure 8: Layout of hydrogen refueling station model (designedby cooperation with Shimizu Corporation)
Figure 9 shows the structure of storage room for the highpressure hydrogen. The room was 5m wide by 6m long with a height of4m. The walls of the room were constructed from reinforced concreteto a height of 3m, with the top 1m of the gap between the roof andthe walls was either open on all sides of had a mesh screen with50% open area to provide ventilation. The roof was made fromlightweight cladding.
Figure 9: Storage room for high pressure hydrogen (left) andcylinder models (right)
High pressure storage cylinders with a capacity of 250L aretypical of those that would be used at a hydrogen station in Japanand, as is also shown in Figure 9, an array of such ‘model’cylinders was positioned inside the storage room. In practice, theamount of hydrogen that would be released in the event of a leakwill depend on the location and size of the release and alsowhether the release is detected and action is taken to isolate theleaking sections of pipe work or vessels. The release of gas fromone storage cylinder was taken to be a representative ‘worst-case’to be studied in this programme. The initial pressure of thecylinders for the majority of the experiments was set at 40MPa. Inaddition, releases from a smaller inventory of 125L were alsoconsidered.
8
Dispersion experiments in the storage room
The dispersion experiments were carried out inside the storageroom, whilst the array of 35 cylinders was present. Theexperimental conditions that were studied are shown in Table 5.Three sizes of nozzle were employed and the ventilation openings atthe top of the sidewalls were either 100% or 50% open.
Table 5: Conditions for the dispersion experiments inside thestorage room
Gas Hydrogen Pressure 40 MPa Diameter 0.8mm ,1.6mm or 8mmDirection Horizontal
Release Parameters
Location Centre of enclosure Dimensions Height 4m
Depth 6m Width 5m
Enclosure
Size of Ventilation Opening
Height 1m Present on all 4 sidewalls 50% open or 100% open
Once the release was initiated the pressure in the cylindercontaining the hydrogen fell, as shown in Figure 10. In the case ofthe release through a nozzle of 8mm diameter, ca. 65Nm3 of hydrogenwas released during the first 10 seconds. Such a rapid decay wouldmake it very difficult to detect the leakage and shut any valves toisolate the supply before most of hydrogen is released. Also shownin Figure 10, are some predictions obtained using an outflow modelto predict the transient decay of pressure in the vessel. Thisshows that a simple model, based in this case on perfect gasbehaviour, is adequate to predict the observed trends.
5
10
15
20
25
30
35
40
0 20 40 60 80 100Time (s)
Leak
pre
ssur
e (M
Pa)
0.8mm Experiment0.8mm Prediction1.6mm Experiment1.6mmPrediction8mm Experiment8mm Prediction
Figure 10: Decay of pressure in the cylinder for the differentsize of nozzles
The average hydrogen concentration measured in the room forthese three experiments is shown in Figure 11. Figure 11a) showsthat a concentration of around 4% was measured for the releasethrough a nozzle with a diameter of 1.6 mm. This result suggeststhat even though the initial storage pressure is 40MPa, a flammablegas mixture is unlikely to be produced throughout the room forleaks with a diameter of below
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1.6mm. However, as Figure 11b) shows, the release through the8mm diameter nozzle reached an average concentration of 27%,presenting a potential explosion hazard, albeit for a short periodof time (less than a minute). The predictions of a simple gasaccumulation model, [4], are also shown in these figures. The modelis able to predict the concentration observed in the experimentsinvolving more slowly varying pressures very well, but tends toover-predict the concentration that was observed in the experimentcarried out with a nozzle with a diameter of 8mm. This may reflecta weakness in the model, which ignores the time taken for the gasto mix within the room (and so would overestimate a growingconcentration field, but underestimate a decaying one), or maypoint to the finite response time of the measuringinstrumentation.
1
2
3
4
5
6
0 20 40 60 80 100Time (s)
Ave
rage
hyd
roge
n co
ncen
trat
ion
(%)
0.8mm Experiment0.8mm Prediction1.6mm Experiment1.6mmPrediction
5
10
15
20
25
30
35
40
45
50
0 20 40 60 80 100Time (s)
Ave
rage
hyd
roge
n co
ncen
trat
ion
(%)
8mm Experiment8mm Prediction
Figure 11: Average hydrogen concentration observed for differentnozzle diameters
The later experiments in the programme provided evidence thatthe average hydrogen concentration in the room could be decreasedsignificantly by increasing the effective area in the ventilationopenings to 100% from 50% or by reducing the maximum gas inventorythat could be released. Figure 12 gives examples of this, includingdata from an experiment in which the inventory of the cylinders wasreduced to 125L. The predictions of the simple model are in similaragreement to that shown in Figure 11b) and so overestimate theobserved peak concentration, although to a slightly lesserextent.
5
10
15
20
25
30
0 20 40 60 80 100Time (s)
Ave
rage
hyd
roge
n co
ncen
trat
ion
(%)
250l vessel 50% vent Experiment
250l vessel 100% vent Experiment
125l vessel 100% vent Experiment
Figure 12: Average hydrogen concentration with smaller vesseland increased ventilation area
10
Explosion experiments in the storage room
Experiments were performed to investigate the explosionsproduced by the ignition of a homogeneous hydrogen air mixture inthe storage room. The hydrogen concentration was varied from 8% to26%. As with the explosion experiments carried out in the emptychamber, the hydrogen concentration was shown to have a significantaffect on the overpressure. Below a concentration of 15% hydrogen,there were no places that experienced overpressures that were abovethe tolerable limit. However, the explosion with a hydrogenconcentration of 26% generated high overpressures and the wholearea of the station experienced values in excess of the tolerablelimit. Indeed, the pressures were sufficiently large to cause anumber of cracks on the concrete wall of the storage room.
Table 6: Results from explosion experiments using homogeneousmixtures in the model storage room
Maximum Measured Overpressure, kPa Experiment DescriptionHydrogen Concentration in Room, % Inside Room At stationboundary
8 Minimal Not detected 15 0.4 –1.3 3.1 – 3.4
Homgeneous explosion 120m3 volume Central ignition with spark 26>100 28 – 111
Dispersion Experiment at the dispenser
A number of gas dispersion experiments were carried out in thestation model to study the concentration distribution produced by anumber of different releases of high pressure hydrogen from adispenser. Again, three different size of nozzle was employed andthe hydrogen was released from a storage vessel containing 250L at40MPa initially. The maximum extent of the resulting flammable gasregion produced for each test is shown in Figure 13a). The hydrogenwas directed horizontally and an approximately cylindricalflammable gas cloud was formed downstream of the release by thejet. In the case of the nozzles with diameters less than or equalto 1.6mm, the maximum extent of the flammable gas was 6m fromnozzle. On the other hand, the jet from the 8mm diameter nozzleformed a relatively large flammable cloud, extending along theboundary wall. A simple jet transient dispersion model, [5], wasused to predict the concentration on the centerline of the flow andthis is compared with the observations for the three experiments inFigure 13b). Again the model predicts the more slowly varyingexperiments with the 0.8mm and 1.6mm nozzle reasonably well, butoverpredicts the observed concentration in the near field for the8mm nozzle.
0.1
1
10
100
0 3 6 9 12Distance along trajectory (m)
Con
cent
ratio
n (%
)
8mm - Observation8mm - Prediction1.6mm - Observation1.6mm -Prediction0.8mm - Observation0.8mm - Prediction
0.1
1
10
100
0 3 6 9 12Distance along trajectory (m)
Con
cent
ratio
n (%
)
8mm - Observation8mm - Prediction1.6mm - Observation1.6mm -Prediction0.8mm - Observation0.8mm - Prediction
Figure 13: Hydrogen concentration
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Explosion experiments at the dispenser
Under the same condition as the dispersion experiments describedabove, the gas cloud that was formed by an 8mm diameter nozzle wasignited by electric spark at a location 4m point from nozzle. Ascan be seen from Figure 14, the ignition time from the start of therelease had a significant effect on the overpressure that wasproduced. The peak overpressure was increased as the time toignition was reduced. It appears that the log of overpressuredecreased linearly with the log of ignition time.
.1
10
1 10ignition time(s)
over
pres
sure
(kPa
)3.5m
7m
10.5m
Figure 14: Correlation between ignition time andOverpressure
The biggest overpressure was observed for an ignition delay of1.2 seconds and the overpressure distribution that was obtainedthere is illustrated in Figure 15. Overpressures exceeding thetolerable level were only measured in the immediate vicinity of therelease location. Compared to the confined explosions, the hazardsof explosion at dispenser are greatly reduced.
Figure 15: Overpressure distribution for explosion atdispenser
CONCLUSIONS
In order to help investigate the risks at hydrogen refuelingstation, dispersion and explosion experiments were carried out in afull scale model. The dispersion experiments in the storage roomrevealed that leak
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diameter, the volume of hydrogen released and the ventilationcharacteristics of the room significantly affected the hydrogenconcentration produced. Explosion experiments in confined enclosurealso revealed that the resulting overpressure varied significantlywith hydrogen concentration. The size of the resulting hazardousarea was negligible for the explosions in the storage room forhydrogen concentrations of up to 15%, but the whole of the fillingstation experiences overpressures exceeding the tolerable limit foran explosion with a hydrogen concentration of 30%. In contrast,explosions produced following releases from the dispenser showedthat there was only a small hazardous area around release nozzle.From a practical viewpoint, the work demonstrates that the greatbenefit to be obtained from being able to detect hydrogen leakageand isolate the supply before the hydrogen concentration in anenclosed space reaches 15%. Reducing the inventory in any one line(e.g. to below 125L) or designing a room to have sufficientventilation will also be effective in reducing the concentration orextent of any hydrogen accumulation. Finally, these experimentalresults are also of use in their own right in that they can beutilized for modeling study to broaden the application of currentassessment models.
ACKNOWLEDGEMENT
The authors wish to thank NEDO, The Institute of Applied Energyand Shimizu Corporation for support in performing this work.
REFERENCES
1. Report of Mission Achievements in 1992 of WE-NET Sub-Task7 2.http://www.osakagas.co.jp/rd/sheet/147e.htm 3. Report of MissionAchievement in 2002 of WE-NET Sub-Task2 4. R.P. Cleaver, M.R.Marshall and P.F. Linden, 1994, J. Haz. Materials, 36, 209-226 5.R.P. Cleaver and P.D. Edwards, 1990, J. Loss Prev. Process Ind., 3,91-96
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FAQs
What is the maximum pressure for hydrogen explosion? ›
They measured the pressure developed in various gas mixtures, the greatest pressure of 7.6 atm being developed for a stoichiometric mixture of hydrogen and oxygen. The flammability limits of hydrogen in air are very wide, from 4% to 75%, and the detonation limits narrower, from 18.3% to 59% at atmospheric pressure.
What is the detonation of hydrogen air mixture? ›Detonation is a coupled shock and flame front structure, which propagates with a supersonic velocity. The speed of detonation wave depends on the stoichiometry of hydrogen-air mixture and ranges from 1,600 to 2,000 m/s. The overpressures are also much higher: from 1,000 to 1,500 kPa.
Does hydrogen detonate or deflagrate? ›Combustion of hydrogen in air in a closed vessel generally results in a deflagration in which the hydrogen is oxidized at a subsonic velocity.
What is the explosive range of hydrogen? ›Hydrogen has a very broad flammability range—a 4 percent to 74 percent concentration in air and 4 percent to 94 percent in oxygen; therefore, keeping air or oxygen from mixing with hydrogen inside confined spaces is very important.
What makes hydrogen explosion so powerful? ›thermonuclear bomb, also called hydrogen bomb, or H-bomb, weapon whose enormous explosive power results from an uncontrolled self-sustaining chain reaction in which isotopes of hydrogen combine under extremely high temperatures to form helium in a process known as nuclear fusion.
What happens to hydrogen under extreme pressure? ›The squished hydrogen is a precursor to a state of matter first proposed in the 1930s, called atomic solid metallic hydrogen. When cooled to low enough temperatures, hydrogen (which on Earth is usually found as a gas) can become a solid; at high enough pressures, when the element solidifies, it turns into a metal.
What is the ratio of hydrogen to air for combustion? ›As these calculations show, the stoichiometric or chemically correct A/F ratio for the complete combustion of hydrogen in air is about 34:1 by mass. This means that for complete combustion, 34 pounds of air are required for every pound of hydrogen.
What air fuel ratio causes detonation? ›A compression ratio over 10.5:1 can create detonation even with 93 premium gasoline. The trick is to keep the compression ratio within a reasonable range for pump gas unless your engine is being built to operate on racing fuel.
What type of change is explosion of hydrogen gas in air? ›When hydrogen burns in air, the change is chemical.
Is hydrogen gas harmful to humans? ›For example, hydrogen is non-toxic. In addition, because hydrogen is much lighter than air, it dissipates rapidly when it is released, allowing for relatively rapid dispersal of the fuel in case of a leak. Some of hydrogen's properties require additional engineering controls to enable its safe use.
Can hydrogen self ignite? ›
When the hydrogen concentration of the layer is in the ignition range and the high temperature of air reaches the hydrogen self-ignition temperature, hydrogen ignites spontaneously according to the diffusion ignition theory of high-pressure hydrogen self-ignition.
Can hydrogen explode when ignited in air? ›Hydrogen possesses the NFPA 704's highest rating of 4 on the flammability scale because it is flammable when mixed even in small amounts with ordinary air; ignition can occur at a volumetric ratio of hydrogen to air as low as 4% due to the oxygen in the air and the simplicity and chemical properties of the reaction.
How explosive is hydrogen compared to TNT? ›Thus, the TNT equivalent of hydrogen is high: 28.65, that is, 28.65 g of TNT is energetic equivalent of 1 g of hydrogen.
How loud is hydrogen explosion? ›Further time waveform and spectral analysis was conducted to characterize hydrogen-oxygen balloons as impulsive noise sources. Pure hydrogen balloons produce low levels (less than 140 dB) and inconsistent reactions.
How many ppm of hydrogen is explosive? ›However, the lower explosive limit for hydrogen in air is 41,000 ppm, and 10% of this concentration is 4,100 ppm.
Why are hydrogen bombs worse than atomic bombs? ›Hydrogen bombs cause a bigger explosion, which means the shock waves, blast, heat and radiation all have larger reach than an atomic bomb, according to Page 3 Edward Morse, a professor of nuclear engineering at University of California, Berkeley.
Which bomb is more powerful than hydrogen? ›The thermonuclear Tsar Bomba was the most powerful bomb ever tested.
Do hydrogen bombs give off radiation? ›A fission bomb, called the primary, produces a flood of radiation including a large number of neutrons. This radiation impinges on the thermonuclear portion of the bomb, known as the secondary. The secondary consists largely of lithium deuteride.
What is the most powerful fuel in the world? ›TRISO Particles: The Most Robust Nuclear Fuel on Earth.
At what pressure temperature does hydrogen become a liquid? ›Liquefaction. Gaseous hydrogen is liquefied by cooling it to below −253°C (−423°F).
At what pressure does hydrogen become supercritical? ›
Supercritical region observed starting at approximately 8 bar pressure between 34-36 K isotherms. Critical pressure of ionization or decomposition for H2 molecules was found as 1800 bar.
How much oxygen is required to burn hydrogen? ›An explosion cannot occur in a tank or any contained location that contains only hydrogen. An oxidizer, such as oxygen must be present in a concentration of at least 10% pure oxygen or 41% air.
What is the best air fuel ratio for power? ›For optimum fuel economy 16-17:1 is usually best, leaner than that and the car will begin to misfire. Maximum power is usually found between 12-14:1, but this may be too lean for safety on many engines. For maximum reliability at full power, air fuel ratios from 10.5-12.5:1 are considered best, depending on the engine.
How do you know if your car is detonating? ›What Are the Symptoms of Detonation? Detonation—sometimes called knock or pre-ignition—is a pinging sound that can sometimes be heard during acceleration and throttle tip-in. Unlike normal exhaust noise, detonation is a higher-pitched, raspy note that emanates from the engine compartment.
Can old spark plugs cause detonation? ›Another issue with your engine's detonation can lie with the spark plugs. If they are worn and not firing correctly, the timing inside each cylinder will be off. Consequently, you may end up with more than one detonation in each cylinder that causes an engine knock.
How do you get rid of detonation? ›If you get the idea that detonation and pre-ignition are bad, thats good. Of all the things that can kill an engine, detonation should be right at the top of the hot rodders Public Enemy Number One list. The quickest and easiest way to cure detonation is to use a high-quality, higher-octane gasoline.
Can hydrogen explode without oxygen? ›Combustion can't occur in a tank that contains only hydrogen. Oxygen (or air) and an ignition source are required for combustion to occur. Hydrogen burns with a pale blue flame that is nearly invisible in daylight.
What reacts with hydrogen to explode? ›The hydrogen mixes with oxygen in the air forming an explosive mixture. Because the hydrogen and oxygen must mix before an explosion can occur, the explosion is relatively slow and diffuse.
What happens if you mix hydrogen gas and oxygen gas? ›When molecular hydrogen (H2) and oxygen (O2) are combined and allowed to react together, energy is released and the molecules of hydrogen and oxygen can combine to form either water or hydrogen peroxide.
Why hydrogen Cannot be used as a fuel? ›But it is not used as domestic fuel, due to several reasons : Hydrogen is not easily available and cost of production is high Unlike other gases, hydrogen is not readily available in the atmosphere. It requires processes like electrolysis of water for its production. This is a very costly process and time consuming.
Why do we not use hydrogen as a fuel? ›
Currently, most hydrogen is produced using coal or natural gas as feedstocks. Both emit harmful by-products into the atmosphere, including carbon dioxide. So, while hydrogen itself is eco-friendly the processes used to isolate the chemical element have a significant environmental footprint.
Is hydrogen gas a carcinogen? ›Hydrogen is a colorless gas with no odor. It is not toxic; the immediate health hazard is that it may cause thermal burns. It is flammable and may form mixtures with air that are flammable or explosive.
At what temperature does hydrogen spontaneously combust? ›it has quite a high spontaneous ignition temperature (SIT) of 650oC – it needs a spark to ignite; it has very wide flammability limits (3–70% H2 in air mixture) – it is easier to maintain a flame; it burns to water vapour, thus eliminating CO2 emissions; and.
Can hydrogen explode without a spark? ›Hydrogen Combustion
The auto-ignition temperature of a substance is the lowest temperature at which it will spontaneously ignite without the presence of a flame or spark. The auto-ignition temperatures of hydrogen and natural gas are very similar.
Any laboratory containing hydrogen has an explosion hazard and should rely on a combination of hydrogen containment, purging operations to isolate hydrogen from air or other oxidizers, ventilation, and ignition source control to prevent an explosion.
Can hydrogen explode in a car? ›For example, hydrogen is very highly flammable, however, because of the way it is stored for use in a vehicle the likelihood of an accident is at least as low as with any other fuel.
Can a electric spark ignite hydrogen? ›There are number of potential ignition sources for flammable mixtures of hydrogen with an oxidant, which include flames, electrical sparks, fused wires, incendiaries, hot surfaces, heating, rapid adiabatic compression, shock waves and catalytic materials.
What happens if you ignite hydrogen gas? ›The most important benefit of using hydrogen as a fuel is that when you burn it, the byproduct is just water. Hydrogen can also be used as a way to store energy, and this use has the potential to have a large impact on our future.
What explosive is stronger than TNT? ›As an explosive, RDX is one and a half times more powerful than TNT and is easily initiated with mercury fulminate (Lewis 2007).
Which is more explosive propane or hydrogen? ›The hydrogen/air cloud explosion has higher peak overpressure and the overpressure rises locally at the nearby region of the cloud boundary. The explosion overpressures of both methane/air and propane/air are lower, compared with the hydrogen/air, and decreases with distance.
How much hydrogen is equivalent to TNT? ›
1. The TNT equivalent mass was calculated based on the value of energy/mass of hydrogen (119.628 MJ/kg) [5] and TNT (4.533 MJ/kg) [6], as shown in Table 1.
What is the loudest man made explosion? ›Mines on the first day of the Somme
On the morning of 1 July 1916, a series of 19 mines of varying sizes was blown to start the Battle of the Somme. The explosions constituted what was then the loudest human-made sound in history, and could be heard in London.
Inhalation of 2.4% hydrogen gas does not appear to cause clinically significant adverse effects in healthy adults.
How many ppm is 1% LEL? ›This one is important: 1% = 10,000 ppm.
Why is hydrogen most explosive? ›Hydrogen has a very broad flammability range—a 4 percent to 74 percent concentration in air and 4 percent to 94 percent in oxygen; therefore, keeping air or oxygen from mixing with hydrogen inside confined spaces is very important.
At what pressure does hydrogen explode? ›They measured the pressure developed in various gas mixtures, the greatest pressure of 7.6 atm being developed for a stoichiometric mixture of hydrogen and oxygen. The flammability limits of hydrogen in air are very wide, from 4% to 75%, and the detonation limits narrower, from 18.3% to 59% at atmospheric pressure.
What is the maximum explosion pressure? ›Maximum explosion pressure (pmax, MPa) is the maximum pressure, incipient by explosion of airborne powder in a closed vessel with initial pressure 101.325 kPa. These data are necessary for strength design of the equipment.
Can hydrogen combust under pressure? ›It is well-known that sudden hydrogen release from high-pressure vessel into air can be spontaneously ignited without any apparent ignition sources present, such as spark, hot surface, fire, etc.
What is hydrogen safe pressure? ›Hydrogen is compressed to a high pressure, typically 350 Bar (~5,000 PSI) and 700 Bar (~10,000 PSI), to help increase the amount of hydrogen that can be stored on site. Highly reliable pressure sensors are required to safely monitor these tanks and other high pressure hydrogen applications.