Liquid Hydrogen Properties and Behaviors
Some basic properties and behaviors of cryogenic liquid hydrogen (LH2) are highlighted on this page.
- At atmospheric pressure, hydrogen exists as a liquid at -253°C (-423°F). Contact with materials at this low temperature can cause frostbite and cryogenic burns. Inhalation of gas from vaporizing liquid hydrogen is also extremely cold and can cause lung damage, so personal protective equipment (PPE) to protect against accidental exposure is needed.
- Liquid hydrogen is approximately 14x less dense than water.
- Liquid hydrogen is non-corrosive and has a light-blue tint.
- Hydrogen undergoes a rapid phase change from liquid to gas when exposed to higher temperatures, so ventilation and pressure relief devices are built into cryogenic hydrogen systems to ensure safety.
- The volume ratio of liquid to gas is 1:848. If you picture a gallon of liquid hydrogen, that same amount of hydrogen, existing as a gas, would occupy 848 gallon containers without compression.
- All gases except helium are solid at LH2 temperatures and if present in the LH2 may cause system malfunction due to particles of solid ice.
- Condensed air (oxygen and nitrogen) will form on the outside surface of uninsulated LH2 piping and could result in oxygen enrichment and explosive conditions.
- Air leakage into a liquid hydrogen storage vessel will result in condensation and freezing of the air and any contained moisture.
- The LH2 exposed to air at ambient pressure will continually draw in air due to a process called cryo-pumping; the resulting solid nitrogen, oxygen, and frozen water can cause obstructions in piping or instrument causing malfunction and present a possible mechanical, fire, or explosion hazard. Therefore LH2 must be stored, transported, and evaporated under pressure.
- The continuing evaporation of liquid hydrogen increases the pressure in a closed containment and may result in a pressure failure (bursting) of the component if not properly vented.