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Engineering | Safe Engineering

I've worked with flammable materials before. What makes hydrogen special?

Hydrogen gas (CAS# 1333-74-0) has a low LEL and a broad flammability range. The LEL, or lower explosive/flammable limit, is the lowest volume percent in air at which the gas can flash or catch fire in the presence of heat or sparks. The LEL for hydrogen is 4%, and it remains quite flammable all the way up to 77% in air (77% is the UEL, or upper explosive/flammable limit).

Hydrogen is much lighter than air and can become trapped near the ceiling above a leak.

Hydrogen is also a very small molecule. Not only can it leak out of fittings and joints in the gas system that larger-molecule gases might not leak through, but it is small enough to pass into and through the crystal lattice of metals. This includes stainless steel tubing, fittings, and other compressed gas system hardware. Hydrogen gas infiltration of metals can cause hydrogen embrittlement, resulting in the expansion of cracks along points of mechanical stress in the metal.

Required Documents

Hydrogen Standard Operating Procedure template

Hydrogen Safety Plan template (coming soon)

Gas Schematic template