Hydrogen

Hydrogen (H₂₁, LH₂)

Hydrogen is the lightest gas known. It is a colorless, odorless, tasteless and nontoxic gas at atmospheric temperatures and pressures, but can be an asphyxiant. Hydrogen burns in air with a pale blue, almost invisible flame. Its ignition temperature will not vary greatly from 1050° F in mixtures with air or oxygen at atmospheric pressure. The flammable limits are four to 94 percent hydrogen by volume.

Used as a fuel, the oxy-hydrogen flame has a 4000° F (2200° C) temperature, good for low-temperature brazing and welding of aluminum, magnesium and lead, and for underwater cutting at pressures that would liquefy other fuels.

The most common metalworking use for hydrogen is as an “oxygen getter”, as in some shielding-gas mixtures. In these cases, it combines readily with the oxygen in metal oxides to form water, leaving reduced metal behind.

Many metals are sensitive to hydrogen embrittlement, and caution must be exercised in its use and in the piping equipment handling it.

The Compressed Gas Association (CGA) specification G-5.3 is the industry standard Type II, Grade A (99.995 percent pure) is considered “commercial” liquid hydrogen and Type I, Grade B (99.95 percent pure) is considered “commercial” gaseous hydrogen.

Safety

The most common hazards associated with liquid hydrogen are explosion, fire, and exposure to the product’s extremely cold temperatures. Users should eliminate any sources of ignition such as an open flame, static spark, electric spark, or any source of high heat which might cause ignition of hydrogen. Hydrogen is extremely light and will collect in high areas such as under the peak of a roof. Care must be taken to prevent accumulation of an explosive mixture in pockets. Venting of hydrogen through a stack should be done while mixing nitrogen or other inert gas into the ventline to prevent ignition of the hydrogen emerging from the vent stack.

Hydrogen is nontoxic. It can be an asphyxiant, but the precautions taken to prevent explosive mixtures will normally prevent asphyxiating atmospheres as well.

The danger of burns caused by extremely cold temperatures can be minimized by using protective clothing, goggles and gloves. The eyes and lungs are especially sensitive to the cold vapors.