At atmospheric pressures and temperatures, hydrogen is a highly flammable, colorless, odorless, tasteless, nonirritating, and nontoxic gas. Its wide flammability range (4%–75% in air) and the small amount of energy needed for ignition necessitate special handling to prevent fires or explosions that can result when hydrogen mixes with air. Hydrogen can also act as an asphyxiant by displacing the oxygen in air. Hydrogen is commonly stored and transported as a cryogenic liquid, with a temperature of –423°F at atmospheric pressure. Contact with skin will cause severe burns. Upon heating, liquid hydrogen expands to 850 times its original volume, which if confined can rapidly over-pressurize equipment and piping. This article explains the hazards of hydrogen and outlines precautions for using hydrogen safely.