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Overview of Hydrogen Hazards

Hydrogen hazards can be broadly categorized into three main types:

• Physiological Hazards

• Physical Hazards

• Chemical Hazards

Physiological Hazards

• Injury from Explosions: Presence at hydrogen leaks, fires, or explosions can cause severe injuries due to ignition of air and hydrogen mixtures.

• Asphyxiation Risk: Hydrogen leaks can displace oxygen in confined spaces, leading to asphyxiation if oxygen levels drop below 19.5%.

• Blast Wave Injuries: Explosions create blast waves that can cause various injuries or organ failures based on exposure duration.

• Thermal Burns: Heat from hydrogen accidents can lead to burns dependent on exposure time, burn rate, temperature, and surface area.

• Cryogenic Burns: Contact with cryogenic fluids can cause severe cold injuries.

Physical Hazards

• Embrittlement: Mechanical property changes in materials owing to exposure to hydrogen may cause failure, rupture, or leakage.

  • Types of Embrittlement:

    • Environmental Hydrogen Embrittlement: Crack propagation starts from the outer surface.

    • Internal Hydrogen Embrittlement: Cracks propagate from the inner surface.

    • Hydrogen Reaction Embrittlement: Hydrogen reacts with metal, leading to hydride formation.

Chemical Hazards

• Reactions with Materials: Oxidation/combustion of hydrogen-air mixtures can lead to fires, tank ruptures, or vapor cloud explosions.

Key Terms Related to Hazards

• Explosion: Loss of confinement due to pressure rise and subsequent release of fuel.

• Deflagration: Flame front moves through mixture at subsonic speed.

• Detonation: Flame front coupled with shock wave at supersonic speed, causing more devastation.

• BLEVE: Boiling liquid expanding vapor explosion leading to fireballs or flash fires based on the ignition of hydrogen clouds.

Hazard Evaluation Techniques

• Hazards can be assessed through:

  • Experimental Techniques: Insightful but costly and impractical for large-scale incidents.

  • CFD Techniques: Used as predictive tools for understanding the hazards and risk components.

Materials-Related Hazards

• Hydrogen Embrittlement: Decreases ductility of metals, influenced by numerous factors such as exposure time, concentration, and material properties.

• Hydrogen Permeation: Small hydrogen molecules migrate through materials leading to embrittlement; influenced by temperature and pressure.

• Low-Temperature Effects: Changes in material properties when exposed to cryogenic temperatures can lead to failures.

• Liner Blistering: Occurs in type-4 vessels when depressurization exceeds diffusion rates, often leading to catastrophic failures.

• Carbon Fiber Damage: Damage to material structures can compromise safety.

Handling-Related Hazards

• Gaseous Hydrogen Leakage: The release of hydrogen can cause immediate ignition (jet fires) or delayed ignition (explosions).

• Thermal Radiation: Increased temperature can result in failures of hydrogen containment vessels.

• Temperature Variations: Rapid pressure changes during filling or releasing can lead to catastrophic events.

• Release of Liquid Hydrogen: Can cause vapor clouds and compete between condensation and buoyancy effects.

• Boiling Liquid Expanding Vapor Explosion: Results from rapid release of heated hydrogen leading to vessel ruptures.

• Vapor Cloud Explosions: More hazardous than jet fires or flash fires.