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Lecture 18. Hydrogen Safety

Lecture 18. Hydrogen Safety. Properties of Hydrogen Hydrogen Hazards & Prevention Hydrogen Facility Related Safety . Hindenburg Disaster. The infamous Hindenburg disaster (May 6, 1937). H 2 is a very unique gaseous element H 2 leaks fast through small orifices

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Lecture 18. Hydrogen Safety

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  1. Lecture 18. Hydrogen Safety • Properties of Hydrogen • Hydrogen Hazards & Prevention • Hydrogen Facility Related Safety

  2. Hindenburg Disaster The infamous Hindenburg disaster (May 6, 1937) • H2 is a very unique gaseous element • H2 leaks fast through small orifices • It is highly volatile and flammable • It is labeled as dangerous substance • Hindenburge disaster ended its • application in transportation • 37 Casualties, 2/3 on board survived • The fire did not start with H2, but • with the flammable skin of the airship • It was the propulsion fuel (diesel fuel), • not H2, made the most damage

  3. HYDROGEN HAZARDS? • A Hazard: Event or Condition that Can Result in Exposure to Harm or Loss. • The Primary Issues For Hydrogen Are: • Combustion Hazards • Pressure Hazards • Low Temperature Hazards • Hydrogen Embrittlement Hazards • Health Hazards

  4. HYDROGEN PROPERTIES • General Properties • GH2: Flammable, Nontoxic, Noncorrosive • Asphyxiant, Colorless, Odorless, Tasteless • Lightest Gas (15x less dense than air) • LH2: Noncorrosive, Colorless Liquid • Physical Properties • Several Isotopes and Molecular Forms • Physical Forms Considered for Storage: Gas, Liquid, and Slush • Cryogenic Properties • NBP 20.3 K • LH2: Condenses/Freezes all Gases Except He • Liquid Density: 14x less dense than water • Liquid Thermal Expansion: 23.4x that of water • Gas Above Critical Temperature (33 K)

  5. SAFETY RELATED PROPERTIES • Equivalent Gas Volume Factor 845.1 times (@ NTP for NBP Liquid) • Pressure (Liquid expansion in a fixed volume)172 MPa • Small Molecular Size 1.8 angstroms • Passes Through Openings too Small for Helium • Low Viscosity • Through Porous Materials • Penetrates Softgoods • Penetrates Intermolecular Spaces and Grain Boundaries in Metals • High Diffusivity [Diffusion Coefficient - 0.061 cm2/s in NPT air] • High Buoyancy [up to 9 m/s]/Promotes Forced Convection • Flame is Invisible in Ambient Light/Produces Little IR • Unless Impurities are Present [Carbon, Sodium give Color]

  6. HOW TO ADDRESS HAZARDSGENERAL STRATEGIES • Work to Minimize Severity • Minimize Quantities to Only What’s Needed • Apply Area Control, PPE, & Good Housekeeping • Use Detectors, Warning Devices • Follow Operational Requirements • Use Safe, Proven, Principles & Practices • Prevent Fuel-air Mixtures, Remove sources of ignition • Use Defensive Practice • Use Situational Awareness • Control Through Organizational Policies & Procedures • Use Approved Procedures & Checklists • Review (Design, Safety, Hazards, Operations) • Follow Approved Maintenance & Quality Control Programs

  7. HOW TO ADDRESS HAZARDS Detailed Hydrogen Hazards Analysis Process

  8. Combustion Hazards • Combustion: Fire, Deflagration, Detonation • Requires Mixing with an Oxidizer • Basic Combustion Properties • Flammability Limits In NTP Air 3.9 - 75.0 vol % • Flammability Limits In NTP Oxygen 3.9 - 95.8 vol % • Detonability Limits In NTP Air 18.3 - 59.0 vol % • Detonability Limits In NTP Oxygen 15 - 90 vol % • Minimum Ignition Energy in Air 0.017 mJ • Autoignition Temperature 858 K (1085°F) • Quenching Gap In NTP Air 0.064 cm • Flame Velocity 2.70 m/s (8.9 ft/s) • Flame Emissivity 0.10

  9. Combustion Hazards Flammable Region Methane Propane Hydrogen 0 10 20 30 40 50 60 80 90 100 70 % Volume Fuel in Air

  10. Combustion Hazards Comparison of Properties Commonly Used Fuel Gases Conclusion: All things considered, H2 is no more dangerous, and in some respects it is rather less dangerous than other commonly used fuels. H2 has a wide range for detonation, its flame is invisible, but its lowest density makes it dissipate very fast.

  11. I G N I T I O N F U E L Fire Triangle O X I D I Z E R BASIC COMBUSTION PRACTICE Hydrogen Electric Spark Electric Arc Heat Oxygen Air

  12. Combustion Hazards Prevent formation of a combustible mixture • Prevent leaks and spills of H2 from a H2 system • Keep external air from entering a H2 system • Prevent H2 or air from leaking from one part of a system into another part • Prevent contamination from entering a H2 system with - the H2 - a pressurization gas

  13. Combustion Hazards Prevent formation of a combustible mixture • Avoid contaminating a H2 system by - an insufficient purge process - a contaminated purge gas • Purge air from a H2 system prior to introducing H2 into the system • Purge H2 from a H2 system prior to introducing air into the system • Maintain adequate ventilation • Use proper materials

  14. Combustion Hazards Eliminate ignition sources • Electrical (e.g. static, sparks, lightning) • Mechanical (e.g. friction, galling, fracture) • Thermal (e.g. match, cigarette, welding) • Chemical (e.g. catalysts, reactants)

  15. Pressure Hazards Potential exists for creation of extremely high pressure in a closed volume • Equivalent volume gas @ NTP/volume liquid @ NBP = 845 • Pressure to maintain NBP liquid density in NTP gas = 172 MPa (24,946 psi) • Heat of vaporization = 445.6 J/g (small heat input will vaporize LH2)

  16. Pressure Hazards • Pressure relief devices must be used in any volume in which LH2 or cold H2 gas can be trapped • Cryopumping can create subatmospheric pressure

  17. Pressure Hazards • Pressure Hazards Arise from the Need to Concentrate Hydrogen • Significant Stored Energy (Cryogenic or High Pressure) • Overpressure, Shockwaves, and Shrapnel, when Suddenly Released • Possible Causes • Liquid to Gas Phase Change • Overfilling • Pressurization System Failure, Relief System Failure, or Inadequate Venting • Fire or Overheating from an External Source

  18. Low Temperature Hazards LH2 will solidify any gas except He(NBP H2 = 20.3 K; NBP He = 4.2 K) • Contaminant solidification • Liquid air can form on uninsulated surfaces (oxygen enriched to ~50%) • Liquid air can be trapped in foam insulation (within gaps and within foam cells)

  19. Low Temperature Hazards • Low temperature embrittlement of containment materials and nearby materials • Use appropriate materials • Contact with a cold surfaces can result in cryogenic burn (frostbite) • Insulate cold surfaces • Use appropriate personal protective equipment

  20. Low Temperature Hazards • Dimensional changes because of contraction • For temperature change from 300 K to 20 K: • Stainless steel will contract ~ 0.3% • PTFE will contract ~ 2.1% • Many plastics become extremely brittle, even cracking when cooled to 20 K • Such materials cannot be used for seals, valve seats, etc.

  21. Embrittlement Hazards • H2 Dissociates and Atomic Hydrogen Penetrates Metals Causing a Decrease in Material Strength • Mechanical properties can be significantly reduced • Tensile strength • Ductility • Fracture toughness • Crack behavior • Failures have occurred unexpectedly

  22. Embrittlement Hazards H2 embrittlement commonly addressed by: • Material selection • Conservative design stress (avoid yielding) • Increased material thickness • Welding technique • Surface finish

  23. Embrittlement Hazards Examples of material susceptibility: • Extremely embrittled • 410 SS, 1042 steel, 17-7 PH SS, 4140, 440C • Severely embrittled • AISI 1020, 430F, Ti-6Al-4V • Slightly embrittled • 304 ELC SS, 305 SS, Be-Cu alloy 25, Titanium • Negligible embrittled • 310 SS, 316 SS, 1100 Al, 6061-T6 Al, OFHC copper

  24. Health Hazards • Fire burn • Direct contact with flame • Thermal energy radiated from flame • UV exposure • Cryogenic burn (frostbite) • Asphyxiation • Hydrogen • Purge gas (He, N2) • Hypothermia

  25. Health Hazards • Exposure to Flame • Direct Contact with Flame (2nd Degree Thermal Burns ) • Thermal Energy Radiated from Flame (Flash burn) • UV Exposure • Cryogenic Burn (Frostbite) (3rd Degree Cryogenic Burns ) • Hypothermia • Asphyxiation • Hydrogen • Purge Gas (N2, He) • Overpressure  Maximum Overpressure Effect On Personnel (kPa) (psi) 7 1 Knock Personnel Down 35 5 Eardrum Damage 100 15 Lung Damage 240 35 Threshold For Fatalities 345 50 50% Fatalities 450 65 99% Fatalities

  26. H2 COMBUSTION ANALYSIS LEMENTS • Anticipate Failures that Result in Hydrogen Release • Know What Mixtures can Form and Under What Conditions • Be Aware of the Effects of Confinement • Identify Potential Ignition Sources • Understand Combustion Modes: Fire, Deflagration, & Detonation

  27. H2 COMPONENTS ---- GENERAL • Joints, Connections, Valves, Pressure Relief Devices, Filters, Thermal Insulation, Vacuum Subsystems, Detectors, etc... • Components, including softgoods, must be compatible with the operating conditions • Materials of Construction Must be Compatible with Hydrogen • Dimensional Changes Must Be Accounted for Where Large Temperature Gradients Occur • Where Appropriate, Energized Components Must be Compatible with Flammable Atmospheres • Volumes that Contain Hydrogen Shall have Adequate Instrumentation and Controls to Ensure that Operation is within Acceptable Limits

  28. HYDROGEN COMPONENTS • Joints and Connections • Welding Recommended, Soft-Solder Not Permitted • Threaded with Sealant Ok for GH2, not LH2 • Bayonet Connections used with LH2 • Under 2” OD Flared, Flareless, and Compression Joints Ok • Use Demountable Joints Only When Necessary • Valves should have provisions to prevent trapping LH2 • Relief Devices • Required for Cryogenic Systems • Redundancy & Redundancy in Types Commonly Required • Limit Pressures to MAWP and Size for Adequate Flow Capacity • Output Should not Impinge on Adjacent Components or Personnel and Should not be Restricted or Impeded • Are Required on Lower Pressure Regions and Vacuum Volumes

  29. FACILITY SUBSYSTEMS CONSIDERATIONS • Storage Systems - Sited per 29CFR, Designed ASME BCPV or DOT regulations • Piping - Designed, Fabricated, & Tested per ASME B31.3 • Venting, Flaring, and Dispersion: CGA G-5.5 • Air and Precipitation Shall be Prevented from Entering a Vent System • Vents Should be Located to Prevent Hydrogen from Impinging on Ventilation Ducts or Other Equipment • Flaring Typically Used for Quantities > 0.5 lb/sec • Disposal Factors Include: Quantity & Extent of Combustible Cloud, Thermal Radiation Hazards, Surrounding Site Conditions

  30. FACILITY SUBSYSTEMS CONSIDERATIONS • Buildings - Designed to Minimize Injury & Damage in Event of a Fire or Explosion (See 29CFR 1910.103) • Avoid Collection Points, Maintain Adequate Ventilation • Provide Explosion Venting, 2 Hour Fire Resistance Rating • Inert Gas Subsystems - Consider Positive Means of Shutoff

  31. FACILITY SUBSYSTEMS CONSIDERATIONS • Fire Protection Subsystems: Include Automatic Shutdown, Sprinklers, Deluge systems, Water Spray Systems

  32. FACILITY SUBSYSTEMS CONSIDERATIONS • Electrical Support Equipment Considerations • Explosion Proof or Purged Equipment • Bonded and Grounded • Lightening Protection • Provide Adequate Illumination • Transportation - per 49CFR

  33. LH2 Transfer Operations • Transfer via • Pump • Pressure differential • Maintain flow rate within minimum and maximum limits • Cooldown process must be controlled • Prevent over-stressing • Eliminate pipeline bowing

  34. HYDROGEN SAFETY SUMMARY • Hydrogen Use is Important, but There are Hazards/Risks • A Core Body of Knowledge Exists and Hydrogen can be Used Successfully • Hydrogen can be Used Safely by Thinking, Planning, Training, and Being Prepared • Use Conservative Approach • Recognize Hazards and Limitations • Search for Hazards • Don’t take chances or shortcuts

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