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Properties of Hydrogen

• H₂ is a unique gaseous element that leaks quickly through small spaces.
• It is highly volatile and flammable, considered a dangerous substance.

The Hindenburg Disaster

• The Hindenburg disaster occurred on May 6, 1937, ending hydrogen's use in transportation.
• The crash resulted in 37 casualties.
• Most of aboard survived.
• The fire started with the airship's flammable skin, not with H₂.
• The propulsion fuel, diesel, caused the most damage.

Hydrogen Hazards

• Hazards are events or conditions that can cause harm or loss.
• Primary issues include combustion, pressure, low temperature, hydrogen embrittlement, and health hazards.

Hydrogen Properties

• GH2 is flammable, nontoxic, and noncorrosive, but it can cause asphyxiation, and is colorless, odorless, and tasteless.
• As a gas it is 15 times less dense than air.
• LH2 is noncorrosive and colorless.
• Hydrogen has several isotopes and molecular forms.
• It can be stored as gas, liquid, or slush.
• Has a NBP of 20.3 K.
• LH2 condenses/freezes all gases except Helium.
• Hydrogen's liquid density is 14 times less than water, and its liquid thermal expansion is 23.4 times more than water.
• Gas exists above a critical temperature of 33 K.

Safety Related Properties

• Equivalent Gas Volume Factor is 845.1x (@ NTP for NBP Liquid).
• Pressure from liquid expansion is 172 MPa.
• Its small molecular size (1.8 angstroms) allows it to pass through openings too small for helium and allows to penetrate soft goods.
• Low viscosity allows it to pass through porous materials and penetrate intermolecular spaces and grain boundaries in metals.
• High Diffusivity accounts for .061 cm²/s in NPT air.
• High Buoyancy promotes forced convection up to 9 m/s.
• A flame is invisible in ambient light and produces little Infra-red unless impurities are present.

Addressing Hazards

• Work to minimize the severity of hazards.
• Minimize quantities to only what is needed.
• Apply area safe-controls, use PPE, & good housekeeping.
• Use detectors and warning devices.
• Follow operational requirements.
• Use safe, proven principles & practices.
• Prevent fuel-air mixtures and remove sources of ignition.
• Use defensive practices and situational awareness.
• Control through organizational policies & procedures, use approved procedures & checklists.
• Review design, safety, hazards, and operations.
• Follow approved maintenance & quality control programs.

Hydrogen Hazards Analysis Process

• This process includes defining scope analysis, selecting hazards team members, compiling component/system information, and component analysis strategy.
• Next, determine component hazards scenarios, consider assesing possible combustable mixture formation while performing team analysis.
• Assesses possible ignition and combustion mechanisms analyze possible secondary effects, assess reaction effects, and complete the report.

Combustion Hazards

• Combustion includes fire, deflagration, and detonation, requiring mixing with an oxidizer.
• Flammability limits in NTP air are 3.9 - 75.0 vol %.
• Flammability limits in NTP oxygen are 3.9 - 95.8 vol %.
• Detonability limits in NTP air are 18.3 - 59.0 vol %.
• Detonability limits in NTP oxygen are 15 - 90 vol %.
• Minimum ignition energy in air is 0.017 mJ.
• Autoignition temperature is 858 K (1085°F).
• Quenching gap in NTP air is 0.064 cm.
• Flame velocity is 2.70 m/s (8.9 ft/s).
• Flame emissivity is 0.10.

Combustion Hazard Management

• Prevent leaks and spills of H₂ from H₂ systems.
• Keep external air from entering H₂ systems.
• Prevent H₂ or air from leaking between system parts.
• Avoid contaminating systems by ensuring purge systems and gases are sufficient and uncontaminated.
• Purge air from H₂ systems before introducing H₂ and vice versa.
• Maintain adequate ventilation and use proper materials.
• Eliminate electrical(eg. static, sparks, lightning), mechanical (friction, galling, fracture), Thermal (Match, cigarette, welding), and chemical (catalysts, reactants) ignition sources.

Pressure Hazards

• High pressures can be created in closed volumes because the equivalent volume gas at NTP/volume liquid at NBP = 845.
• Pressure to maintain NBP liquid density in NTP gas equals 172 MPa (24,946 psi).
• the heat of vaporization = 445.6 J/g, meaning a small heat input will vaporize LH₂.
• Pressure relief devices must be used in any volume in which LH2 or cold H₂ gas can be trapped.
• Cryopumping can create subatmospheric pressure.
• Hazards also arise from the need to concentrate hydrogen, leading to significant stored energy and potential for overpressure.
• Potential causes- liquid to gas phase change, overfilling, pressurization system failure, relief system failure, or inadequate venting, fire or overheating from an external source.

Low Temperature Hazards

• LH₂ will solidify any gas except Helium; NBP H₂ = 20.3 K; NBP He = 4.2 K.
• Risk factors :Contaminant solidification, liquid air forming on uninsulated surfaces, oxygen enriched to ~50%, liquid air trapped in foam insulation.
• Poses risk low temperature embrittlement of containment materials and nearby structures.Appropriate materials should be used.
• Contact may result in cryogenic burn, requiring insulated surfaces and PPE.
• Dimensional changes occur causing contraction-300K to 20K-Stainless steel contracts .3%- PTFE will contract ~ 2.1%.
• Many plastics become extremely brittle when colled to 20K cannot be used for valve seats, etc.

Embrittlement Hazards

• H₂ dissociates and atomic hydrogen penetrates metals, reducing material strength which effects tensile strength, ductility, fracture toughness, and cracking.
• Embrittlement is commonly addressed by material selection, conservative design stress (avoiding yielding), increased material thickness, welding technique, and surface finish.
• Examples of material susceptibility varies. Materials like 410 SS, 1042 steel, 17-7 PH SS, 4140, and 440C are extremely embrittled.
• AISI 1020, 430F, and Ti-6Al-4V are severely embrittled.
• 304 ELC SS, 305 SS, Be-Cu alloy 25, and Titanium are slightly embrittled.
• Materials like 310 SS, 316 SS, 1100 Al, 6061-T6 Al, and OFHC copper are negligibly embrittled.

Health Hazards

• Fire burns can arise from direct contact, thermal energy radiated from the flame, and UV exposure- Direct contact with flame (2nd Degree Thermal Burns ->Direct Contact with Flame (2nd Degree Thermal

• Cryogenic burns (frostbite) can occur.

• Asphyxiation results from hydrogen or purge gases, (He and N₂).

• Hypothermia is also a potential hazard.

• Overpressure can effect all personnel.

• 7 kPa/1 (psi) might knock someone down.

• 35 kPa/5 (psi) can damage eardrums.

• 100 kPa/15 (psi) may damage lungs.

• 240 kPa/35 (psi) is threshold for fatalities. -345 kPa/50 (psi) causes 50% fatalities. -450 kPa/65 (psi) is almost certain death/ 99% fatalities.

H2 Combustion Analysis

• Anticipate failures that may releases Hydrogen.Know what mixtures can form and conditions that may apply.
• Be aware of possible effects of possible confinement and identify potential ignition sources.
• Be aware of and understand all modes of Combustion which include : fire, deflagration, and detonation are all possible.

H2 Components

• Including Joints, Connections, Valves, Pressure Relief Devices, Filters, Thermal Insulation, Vacuum Subsystems and Detectors. 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.

Hydrogen Components specifics

• For joints/connections-Welding is Recommended, Soft-Solder is Not Permitted.
• Threaded with Sealant is Ok for GH2, not LH2.
• Bayonet Connections used with LH2
• Under 2" OD Flared, Flareless, and Compression Joints are OK.
• Use Demountable Joints Only When Necessary.
• Valves should have provisions to prevent trapping LH2 Relief Devices are -Required for Cryogenic Systems Redundancy and Redundancy in Types Commonly.
• Required-Limit Pressures to MAWP and Size for Adequate 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.

Facility Subsystems Considerations

• Storage Systems - Sited per 29CFR, Designed ASME BCPV or DOT regulations.
• Piping which is - Designed, Fabricated, & Tested per ASME B31.3.
• Venting, Flaring, and Dispersion CGA G-5.5Air and Precipitation Shall be Prevented from Entering Vent System
• Vents Should be Located to Prevent Hydrogen from Impinging on Ventilation Ducts or Other Equipment Flaring is Typically Used for Quantities above 0.5 lb/sec
• Considerations must factor inQuantity and Extent of Combustible Cloud, Thermal Radiation Hazards, Surrounding Site Conditions.
• Buildings must - Designed to Minimize Injury and Damage in Event of a Fire or Explosion (See 29CFR 1910.103)Avoid Collection Points, Maintain Adequate Ventilation Provide Explosion Vent with a 2 Hour Fire Resistance Rating.
• Inert Gas Subsystems - Consider Positive Means of Shutoff.

Facility Subsystems

• Also requires - Fire Protection Subsystems that Include Automatic Shutdown, Sprinklers, Deluge systems, Water Spray Systems.
• Electrical Support Equipment considerations should include: Explosion Proof or Purged Equipment, Bonding and Grounding, Lightening Protection, and Adequate Illumination Transportation - per 49CFR.

LH₂ Transfer Operations

• Transfer should be conducted via pumps or pressure differentials.
• Maintain flow rate within minimum and maximum limits, along monitored with a controlled cool-down process.
• Prevent over-stressing or causing pipeline bowing during Hydrogen transfer.

Hydrogen Safety Summary

• Includes use with appropriate knowledge is vital.
• Thinking, Planning, Traning, and Being Prepared is essential.
• Apply a conservative approach, recognize hazards, and search for potential hazards that may exist.
• Do not take chances or shortcut established safety measures.