Hydrogen Leaks

Because gaseous hydrogen consists of such a small molecule, very small leaks are common. In properly designed systems these very small leaks do not present a problem as the tiny amount of hydrogen released will not be enough to cause a flammable mixture in air. Only when hydrogen gas can accumulate over time in a confined area will a risk of a flammable mixture or asphyxiation arise.

  • Small gaseous hydrogen leaks are difficult to detect by human senses since hydrogen is colorless, odorless, and tasteless.
  • If hydrogen accumulates in a confined space in sufficient concentrations it, like all other gasses except oxygen, is an asphyxiant.
  • Leaking hydrogen will rise and diffuse quickly in air because its low density results in high buoyancy (14 times less dense than air).
  • Hydrogen mixes readily with air, creating an ignitable mixture (3x greater diffusivity than nitrogen in air). This hazard is especially important where hydrogen can accumulate in a confined area.
  • Hydrogen leak detection methods include:
    • Listening for high-pressure gas leaking (loud hissing sound).
    • Using portable hydrogen detectors.
    • Using permanently installed hydrogen detectors linked to local or facility-wide audible or visible alarms.
  • Because liquid hydrogen (LH2) is a cryogenic liquid, leaks of LH2 behave differently than gaseous hydrogen leaks and may be easier to detect.
  • Even in dry climates, a liquid hydrogen leak will create a white cloud of condensed water vapor due to the cryogenic temperature affecting condensing the humidity in the surrounding air. This low-temperature water vapor is heavier than air, so the cloud will remain localized and may move horizontally. As the hydrogen warms, it will dissipate and quickly rise.


  • Leaks can create combustible mixtures of hydrogen and air, resulting in