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

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Presentation on theme: "Funded by FCH JU (Grant agreement No. 256823) 1 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 1."— Presentation transcript:

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

2 Funded by FCH JU (Grant agreement No ) 2 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 2  Hydrogen is not more dangerous or safer compared to other fuels (energy carriers).  Hydrogen safety fully depends on how professionally it is handled at the design stage and afterwards.  Hydrogen leak is difficult to detect: colourless, odourless and tasteless gas, dimmest flame of any fuel in air  High pressures (potential hazards to humans, equipment, structures): hydrogen systems are used at pressures up to 100 MPa = 1000 bar  Low temperatures (cold burns, etc.): down to -253 o C = 20 K (liquefied hydrogen = LH2)  Hydrogen is mostly found in combination with other elements in form of e.g. water, methane, biomass, etc.

3 Funded by FCH JU (Grant agreement No ) 3 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 3  Atomic hydrogen (H, mass g/mol) is formed by a nucleus with one unit of positive charge (proton) and one electron (negatively charged “probability cloud” surrounding the nucleus like a fuzzy, spherical shell). H atom is electrically neutral.  Atom is highly reactive (embrittlement: atomic H solution in metals).  The proton is more than 1800 times more massive than the electron. Neutron can be present in the nucleus. Neutron has the same mass as proton and does not carry a charge.  The radius of the electron’s orbit (the size of the atom), is 100,000 times as large as the radius of the nucleus: m (1 angstrom).  Three isotopes: protium (99,985% in nature) - proton in the nucleus; deuterium (0.015%) - proton and a neutron; tritium - proton and two neutrons (generates β rays). Atomic mass 1, 2 and 3 respectively. H

4 Funded by FCH JU (Grant agreement No ) 4 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 4  In normal conditions hydrogen is a gas formed by diatomic molecules, H g/mol), in which two hydrogen atoms have formed a covalent bond. Molar volume of any ideal gas (1 atm, 0 o C): 22.4 L/mol. Leak 2000 L/min = 2000/22.4*2 /60 = 2.98 g/s.  Molecular hydrogen is a stable form compared to atomic hydrogen because the atomic arrangement of a single electron orbiting a nucleus is highly reactive. For this reason, hydrogen atoms naturally combine into pairs.  Hydrogen is colourless, odourless and insipid (tasteless). That is why its leak is difficult to detect. Compounds such as mercaptans, which are used to scent natural gas, cannot be added to hydrogen for use in PEM (proton exchange membrane) fuel cells as they contain sulphur that would poison the fuel cell’s catalyst (platinum). HH

5 Funded by FCH JU (Grant agreement No ) 5 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 5  Two forms of molecular hydrogen are ortho-, and para-hydrogen. They are distinguished by the relative nuclear spin-rotation of the individual atoms.  These molecules have slightly different physical properties but are chemically equivalent.  The equilibrium mixture of ortho- and para-hydrogen at any temperature is referred to as equilibrium hydrogen.  Normal hydrogen: the equilibrium ortho-para-hydrogen mixture 75%:25% at room temperature.

6 Funded by FCH JU (Grant agreement No ) 6 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 6  Boil-off is the vaporization of LH2 due to heat transfer from surroundings to a storage tank. Hydrogen has to be released not to exceed working pressure of the LH2 tank. Cause of H2 release!  At lower temperatures, equilibrium favours the existence of the less energetic para-hydrogen (LH2 at 20 K is 99,8% of para-H2).  The para-ortho-hydrogen conversion is accompanied by a consumption of heat, 703 kJ/kg at 20 K. No pressure growth!  Cryo-compressed hydrogen (CCH2) storage is favourable compared to LH2 due to exclusion of the boil-off at day-to-day driving (weekly?).  Due to conversion of para- to ortho-hydrogen during “consumption” of external heat the release of hydrogen from the storage tank as a result of boil-off is practically excluded for CCH2 storage with clear safety improvement.

7 Funded by FCH JU (Grant agreement No ) 7 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 7  Hydrogen is used as gas, liquid, or slush. Slush hydrogen is a mixture of solid and liquid hydrogen at the triple point temperature (13.8 K).  Three curves: boiling (condensation=liquefaction), melting (freezing), sublimation (gas to solid).  The triple point: all three phases can coexist (13.8 K, 7.2 kPa). The vapour pressure of slush hydrogen is low. Safety measures must be taken during operations to prevent air leakage into the system that could create flammable mixture.

8 Funded by FCH JU (Grant agreement No ) 8 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 8  The highest temperature, at which a hydrogen vapour can be liquefied, is the critical temperature of K (“ critical point ”). The corresponding critical pressure is 1.3 MPa (density is kg/m 3 ).  Above the critical temperature it is impossible to condense hydrogen into liquid just by increasing the pressure. All you get is cryo- compressed gas.  The normal boiling and melting points (pressure 101,325 kPa = 1 atm) are: NBP = 20.3 K ; NMP = 14.1 K

9 Funded by FCH JU (Grant agreement No ) 9 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 9  Liquid hydrogen (LH2) at NBP has a density of kg/m 3. The specific gravity is (the reference substance is water with specific gravity of 1). Thus, LH2 is 14 times less dense than water.  Ironically, every cubic meter of water (made up of hydrogen and oxygen) contains 111 kg of hydrogen whereas a cubic meter of LH2 contains only kg of hydrogen. Thus, water packs more mass of hydrogen per unit volume, because of its tight molecular structure, than hydrogen. This is true of most liquid hydrocarbons “H2 carriers”.  The higher density of the saturated hydrogen vapour at low temperatures may cause the cloud to flow horizontally or downward immediately upon release if liquid hydrogen leak occurs. These facts have to be accounted for by first responders during intervention at an accident scene.

10 Funded by FCH JU (Grant agreement No ) 10 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 10  Safety concern of LH2: low temperature (NBP=20 K) (exception of Helium NBT=4.2 K, NMT=0.95 K): gases will condense or solidify (Nitrogen: NBP=77.36 K, NMP=63.15 K; Oxygen: NBP=90.2 K - liquid O2, NMP=54.36 K – solid O2).  Leaks of air or other gases into direct exposure with liquid hydrogen can lead to several hazards :  The solidified “other” gases can plug pipes and orifices and jam valves.  In a process known as cryo-pumping the reduction in volume of the condensing gases may create a vacuum that can draw in “other” gases, e.g. air (oxidiser).  Large quantities of “other” material can accumulate due to “draw in” and displace LH2 if the leak in persists for long periods. At some point, should the system be warmed for maintenance, these frozen “other” materials will re-gasify possibly resulting in high pressures or explosive mixtures. These other gases might also carry heat into LH2 and cause enhanced evaporation losses or “unexpected” pressure rise.

11 Funded by FCH JU (Grant agreement No ) 11 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 11  Oxygen (O2) enrichment can increase the flammability and even lead to the formation of shock-sensitive compounds.  Oxygen particulate in cryogenic hydrogen gas may even detonate.  Vessels with LH2 have to be periodically warmed and purged to keep the accumulated O2 content to less than 2%.  Caution should be exercised if carbon dioxide (CO2) is used as a purge gas. It may be difficult to remove all CO2 (mass 44 g/mol) from the system low points where the gas can accumulate.  Usually the condensation of atmospheric humidity during release to atmosphere (spill of 5.11 m 3 =361.8 kg of LH2 in 38 s) will add water to the mixture cloud, firstly making it visible (visible cloud shape is close to flammable cloud ), and secondly increasing the molecular mass of the mixture.release to atmosphere

12 Funded by FCH JU (Grant agreement No ) 12 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 12  The volume of LH2 expands with the addition of heat significantly more than can be expected based on our experience with water. The coefficient of thermal expansion at NBP is 23 times that of water at ambient conditions.  The significance for safety arises when cryogenic storage vessels have insufficient ullage space to accommodate expansion of the liquid. This can lead to an over pressurisation of the vessel or penetration of LH2 into transfer and vent lines.  The phase change of LH2 to gaseous hydrogen (GH2), and yet another volume increase for GH2 to warm from the NBP (20 K) to K gives the expansion ratio of 847. This results in a final pressure of 177 MPa (initial MPa) if LH2 is in a closed vessel. Pressure relief devices (PRD) should be installed as a safety measure.

13 Funded by FCH JU (Grant agreement No ) 13 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 13 Hydrogen: kg/m³; Methane: kg/m³; Propane: kg/m³; Gasoline vapours: 4.25 kg/m³.

14 Funded by FCH JU (Grant agreement No ) 14 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 14  The main hydrogen safety asset, i.e. its highest on The Earth buoyancy, confers the ability to rapidly flow out of an incident scene, and mix with the ambient air to a safe level below the flammability limit.  Indeed, hydrogen density is kg/m 3 (at normal temperature and pressure (NTP) defined by IUPAC (International Union of Pure and Applied Chemistry): 20 C and 10 5 Pa (previous definition with 1 atm is discontinued – difference between two definitions is negligible for safety engineering applications) which is far below air density kg/m 3.  Contrary, heavier hydrocarbons are able to form a huge combustible cloud, as in cases of disastrous Flixborough (1974) and Buncefield (2005) explosions. In many practical situations, hydrocarbons may pose stronger fire and explosion hazards than hydrogen. Hydrogen high buoyancy affects its dispersion more than its high diffusivity.

15 Funded by FCH JU (Grant agreement No ) 15 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 15  Pure hydrogen is positively buoyant above a temperature of 22 K, i.e. over almost the whole temperature range of its gaseous state.  Outdoors only small fraction of released hydrogen would be able to deflagrate. Indeed, a hydrogen-air cloud evolving from the release upon the failure of a storage tank or pipeline liberates only a small fraction of its thermal energy in case of a deflagration, which is in the range % and in most cases below 1% of the total energy of released hydrogen (Lind, 1975). This makes safety considerations of hydrogen accident with large inventory at the open quite different from that of other flammable gases with less or no consequences at all.  Caution should be taken in applying GH2 buoyancy observations to releases of hydrogen vapours at cryogenic temperatures. LH2 release vapours at low temperature can be denser than air (plus H2O!).

16 Funded by FCH JU (Grant agreement No ) 16 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 16  Diffusivity of hydrogen is higher compared to other gases due to small size of the molecule: diffusion coefficient of hydrogen in air is 6.8 cm 2 /s (methane cm 2 /s; propane cm 2 /s).  Hydrogen effective diffusion coefficient through gypsum panels is found to be 1.45 cm 2 /s at 22 C. The interior of most garages in the U.S. have large surface areas covered with gypsum panels. The diffusion process should not be overlooked in the hazard assessment of release of hydrogen in garages or enclosures lined with gypsum panels.  The low viscosity of hydrogen and the small size of the molecule cause a comparatively high flow rate if the gas leaks through fittings, seals, porous materials, etc. This negative effect is to a certain extent offset by the low energy density (volumetric) of hydrogen in comparison with e.g. methane or other hydrocarbon gases.

17 Funded by FCH JU (Grant agreement No ) 17 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 17  Many safety problems related to interaction of hydrogen with materials involve welds or the use of an improper material.  Hydrogen is non-corrosive yet a reason for hydrogen embrittlement - the process by which various metals, most importantly high-strength steel, become brittle and fracture following exposure to hydrogen.  Embrittlement involves a large number of variables: temperature and pressure; purity, concentration, exposure time; stress state, physical/ mechanical properties, microstructure, surface conditions, nature of the crack front, etc. The material must have certain minimum values of these properties over the entire range of operation, with appropriate consideration for non-operational conditions such as a fire.  There is an atomic solution of hydrogen in metals. Permeated H atoms recombine to molecule on the surface to diffuse into surrounding gas.

18 Funded by FCH JU (Grant agreement No ) 18 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 18  Compressed gaseous hydrogen (CGH2) behaves non-ideally. The Abel- Noble equation of state is applied instead of the ideal gas state equation. The density then can be calculated from the equation b = m 3 /kg is the co-volume constant, R H2 is the gas constant.  The ideal gas equation overestimate the density by: 1% (1.57 MPa), 10% (15.7 MPa), 30% (48 MPa), 40% (64 MPa), 50% (78.6 MPa). Implication for separation distances.

19 Funded by FCH JU (Grant agreement No ) 19 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 19  Speed of sound in gaseous hydrogen is 1294 m/s at 20 o C and 355 m/s at NBP (20.3 K at pressure 101,325 Pa).  The specific heat at constant pressure of liquid para-hydrogen is c p =9.688 kJ/kg/K. This is more than double that of water and greater than 5 times that of liquid oxygen at its NBP.  Gas constant of hydrogen is kJ/kg/K (this is the universal gas constant divided by the molecular mass).  The specific heats ratio of hydrogen at 20 o C and 1 atm is  =1.39 and at 0 o C and 1 atm is  =  Thermal conductivity of hydrogen is significantly higher than that of other gases. GH2 (W/m/K): (NTP), (NBP). LH2 (W/m/K): (NBP). Use in superconductivity applications.  Hydrogen is non-carcinogenic, non-corrosive (yet embrittlement!).

20 Funded by FCH JU (Grant agreement No ) 20 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 20  At normal temperature hydrogen is a not very reactive, unless it has been activated somehow, e.g. by an appropriate catalyser. Hydrogen reacts with oxygen to form water at ambient temperature extraordinarily slow. However, if the reaction is accelerated by a catalyser or a spark, it proceeds with high rate and “explosive” violence.  Hydrogen burns in a clean atmosphere with an invisible flame. It has a somewhat higher adiabatic premixed flame temperature for a stoichiometric mixture in air of 2403 K compared to other fuels.  This temperature can be a reason for serious injure, especially at clean laboratory environment.  Combustion and hot currents will cause changes in the surroundings that can be used to detect the flame. These changes are called the signature of the fire.

21 Funded by FCH JU (Grant agreement No ) 21 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 21  Stoichiometric mixture is a mixture in which both fuel and oxidiser are fully consumed (complete combustion) to form combustion products.  The stoichiometric composition of hydrogen-oxygen mixture is 66.66% by volume of H2 and 33.33% of O2. The reaction equation H2 + ½ O2 → H2O  The stoichiometric composition of hydrogen-air mixture is 29.6% by volume of H2 and 70.4% of air. The reaction equation is H2 + ½ (O N2) → H2O +1.88N2 or H air → H2O N2  Lean mixtures – concentration of hydrogen in mixture with oxidiser is below stoichiometric.  Rich mixtures – concentration of hydrogen in mixture with oxidiser is above stoichiometric.

22 Funded by FCH JU (Grant agreement No ) 22 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 22 The lower heating value (lower heat of combustion) of hydrogen is kJ/mol and the higher heating value is kJ/mol. The difference of about 16% is due to the heat of condensation of water vapour, and this value is larger compared to other gases. Blue – lower heating value Blue+Red – higher heating value  H c, kJ/g

23 Funded by FCH JU (Grant agreement No ) 23 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 23  Hydrogen flame is not visible in clean atmosphere.  Real jet flame can be seen due to combustion of entrained particulates (dust, etc.).  Radiation emitted from a hydrogen flame is very low (emissivity ε < 0.1) unlike hydrocarbon flames (ε ~ 1) (ADL, 1960).  Recent large-scale studies performed by Sandia National Laboratory (USA) indicate that emissivity could be higher yet at the level below 0.3.

24 Funded by FCH JU (Grant agreement No ) 24 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 24  Flammability range is the range of concentrations between the lower and the upper flammability limits.  The lower flammability limit (LFL) is the lowest concentration of a combustible substance in a gaseous oxidizer that will propagate a flame (… flammable envelope).  The upper flammability limit (UFL) is the highest concentration of a combustible substance in a gaseous oxidizer that will propagate a flame (…air to compressor).  The flammability range of H2 in air (4%-75% by volume ) is wider compared to most hydrocarbons : - methane ( ); - propane ( ); - gasoline ( ); - methanol (6-36.5).

25 Funded by FCH JU (Grant agreement No ) 25 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 25 Table shows the scattering of the flammability limits (% by volume) determined by different standard apparatuses and procedures applied (Schröder and Holtappels, 2005). Note: (T) – tube; (B) – constant volume bomb. LimitDIN 51649EN 1839 (T)EN 1839 (B)ASTM E 681 LFL3.8%3.6%4.2%3.75% UFL75.8%76.6%77.0%75.1%

26 Funded by FCH JU (Grant agreement No ) 26 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 26  Flammability range depends on a flame propagation direction.  In quiescent mixture a conservative value of LFL changes: from 3.9% by volume for upward propagation (flame balls), through 6% for horizontal, to 8.5% for downward propagation. Upward propagationHorizontal propagationDownward propagation LFLUFLLFLUFLLFLUFL % % % % % %

27 Funded by FCH JU (Grant agreement No ) 27 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 27  Quiescent mixtures <8% - no overpressure!  Turbulent mixture can generate in closed vessel p=2.5 bar. 3.9% upward propagation 6.0% horizontal propagation 8.5% downward Red dashed lines: upward, horizontal, and downward flame propagation

28 Funded by FCH JU (Grant agreement No ) 28 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 28  Upward and downward flammability limits.  The flammability range expands practically linearly with temperature.  For example: LFL decreases from 4% to 1.5% by volume with temperature increase from 20 o C to 400 o C.

29 Funded by FCH JU (Grant agreement No ) 29 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 29 Hydrogen- air mixture

30 Funded by FCH JU (Grant agreement No ) 30 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 30 Hydrogen- oxygen mixture (20 o C and 80 o C)

31 Funded by FCH JU (Grant agreement No ) 31 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 31  Mixture: 45% of hydrogen, 30% of air and 25% of diluent.  Diluents: CO2, He, or N2. The mixture is flammable.  Diluent: H2O. The mixture is inflammable.

32 Funded by FCH JU (Grant agreement No ) 32 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 32  The minimum ignition energy of hydrogen is smaller than for other fuels:  Hydrogen0.017 mJ  Methane0.28 mJ  Propane0.25 mJ  Gasoline mJ  Methanol0.14 mJ  A weak spark caused by the discharge of static electricity from a human body may ignite these fuels in air.  The ignition energy is a function of the mixture concentration.

33 Funded by FCH JU (Grant agreement No ) 33 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 33  Flashpoint is the lowest temperature at which the fuel produces enough vapours to form a flammable mixture with air at its surface.  Auto-ignition temperature (AIT) is the minimum temperature required to initiate combustion reaction of fuel-oxidiser mixture in the absence of an external source of ignition. Over catalytic surfaces like platinum, the AIT of hydrogen can be drastically reduced down to 70°C. Other hydrogen catalysts include but not limited to carbon nanomaterials, nickel, etc.  Minimum ignition energy (MIE) is the minimum value of the electric energy, which (upon discharge across a spark gap) just ignites the quiescent mixture in the most ignitable composition.  Maximum experimental safe gap (MESG) of flammable gases and vapours is the lowest value of the safe gap measured according to IEC (2002) by varying the composition of the mixture. The safe gap is the gap width (determined with a gap length of 25 mm) at which in the case of a given mixture composition, a flashback just fails to occur. FuelFlashpoint, ºCAIT, ºCMIE, mJMESG, mm Hydrogen< Methane Propane Gasoline-(11-45) Diesel Methanol

34 Funded by FCH JU (Grant agreement No ) 34 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 34  Laminar burning velocity of stoichiometric hydrogen-air mixture of about 2 m/s is far greater compared to most of hydrocarbons of m/s. Maximum burning velocity is at rich mixture of 40.1% by volume.  Maximum expansion coefficient at stoichiometric mixture of 29.5% by volume.

35 Funded by FCH JU (Grant agreement No ) 35 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 35  Detonation is the worst case scenario.  The detonability range mentioned in ISO/TR 15916:2004 ( 18-59% of hydrogen in air) is narrowed.  The detonation range 13-70% is reported for hydrogen-air in a 43 cm diameter tube.  A lower detonability limit of 12.5% was observed in the RUT facility (Russia).  The widest detonability range of hydrogen in air 11-59% by volume is recommended by Alcock et al. (2001).  A conservative generalisation of available data gives the detonability range 11-70%. This is narrower and as expected within the flammability range of 4-75%.  Inherently safer range of concentrations: 4-11%, or above 70%.

36 Funded by FCH JU (Grant agreement No ) 36 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 36 The detonability limits are not fundamental characteristics. They strongly depend on the size of the experimental set up. A diameter of the tube, where detonation can propagate, should be of the order of a detonation cell size. A detonation cell size increases with approaching the detonability limits. Thus, the larger is the scale of an experimental apparatus the smaller is the lower detonability limit (the larger is the upper detonability limit). Photo of cells:

37 Funded by FCH JU (Grant agreement No ) 37 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 37  Odorants are artificially added to propane and methane, while gasoline has naturally a strong odour.  No odorant can be added to hydrogen for use in PEM fuel cells due to poisoning of the membrane.  Odorant for hydrogen is absent. It would require specific physical properties not to be harmful to fuel cells. FuelToxicOdorant added HydrogenNo GasolineYesNatural odour PropaneNoYes MethaneNoYes

38 Funded by FCH JU (Grant agreement No ) 38 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 38  Hydrogen is not expected to cause mutagenicity, embryotoxicity or reproductive toxicity.  There is no evidence of adverse effects if skin or eyes, it cannot be ingested (unlikely route). However, inhaled hydrogen can result in a flammable mixture within the body.  Hydrogen is classified as a simple asphyxiant, has no threshold limit value (TLV), non-carcinogen. High concentrations in air can cause an oxygen-deficient environment. Individuals may experience symptoms which include: headaches, dizziness, drowsiness, unconsciousness, nausea, vomiting, depression of all the senses, etc.  A victim of asphyxiation may have a blue colour skin, and under some circumstances, death may occur.  Inhaling vapour or cold hydrogen produces respiratory discomfort and can result in asphyxiation.

39 Funded by FCH JU (Grant agreement No ) 39 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 39 H 2, % volO 2, % volPhysiological response No particular symptom Decreased ability to perform tasks; may induce early symptoms in persons with heart, lung, or circulatory problems, night vision impairment Deeper respiration, faster pulse, poor coordination Poor judgment, slightly blue lips, dizziness, headache and early fatigue with a tolerance time of 30 minutes Nausea, vomiting, unconsciousness, ashen face, fainting, mental failure, with a tolerance time of 5 minutes Unconsciousness occurs after about 3 minutes and death in 8 min. 50 percent death and 50 percent recovery with treatment in 6 min, 100 percent recovery with treatment in 4 to 5 min Coma occurs in 40 s, convulsions, respiration ceases then death Death within 45 s.

40 Funded by FCH JU (Grant agreement No ) 40 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 40  If hydrogen is inhaled and above symptoms observed then remove a person to fresh air, give oxygen if breathing is difficult, or apply artificial respiration if not breathing.  The system design shall prevent any possibility of asphyxiation in adjacent areas. It is recommended to check oxygen content before entering an incident area.  Contact with LH2 or its splashes on the skin or in the eyes can cause serious burns by frostbite or hypothermia.  Direct physical contact with LH2, cold vapour, or cold equipment can cause serious tissue damage. Short contact with a small amount of LH2 may not pose as great a danger because a protective film may form.  The kinetic energy of high pressure hydrogen jet represents a hazard due the possibility of high pressure injection injuries. It takes a minimum pressure of 7 bar for liquid, vapour or gas to breach intact human skin.

41 Funded by FCH JU (Grant agreement No ) 41 © HyFacts Project 2012/13 CONFIDENTIAL – NOT FOR PUBLIC USE 41 It can be concluded that hydrogen is not more dangerous or safer compared to other fuels. Hydrogen is different and has to be professionally handled with knowledge of underpinning science and engineering to provide public safety as well as competitiveness of hydrogen and fuel cell products and infrastructure.


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