Let's travel back in time to the year 1520. In Switzerland, an alchemist named Philippus Aureolus Paracelsus has put a piece of iron in a solution of sulfuric acid. The acid begins to bubble in "an air which bursts forth like the wind." Although Paracelsus didn't know it then, that bubble-making wind turned out to be hydrogen. The No. 1 element was officially named in the late 18th century by Antoine-Laurent Lavoisier, a French aristocrat who dabbled in science and eventually lost his head during the French Revolution [sources: ASME, Chemical Heritage].
Scientists and inventors soon found that Lavoisier's hydrogen was the lightest element in the universe. While that might prove wonderful for filling up balloons, it wasn't so awesome when it came to interactions between hydrogen and metal. In fact, hydrogen atoms have the uncanny ability to seep through various metals, turning them brittle, eventually cracking, rupturing and breaking them [source: Science Daily].
Although scientists have been studying the phenomena since 1875, they don't understand fully the physics of the problem. What they do know is that hydrogen atoms easily diffuse, or spread, through metals, especially at high temperatures. The atoms recombine with one another to form hydrogen molecules. These molecules find a home in the microscopic nooks and crannies of the metal, creating a huge amount of pressure. That pressure reduces the metal's tensile strength. Crack! The metal breaks [source: McGill University].
Researchers can't predict where hydrogen embrittlement will occur. All they know is that the tiny hydrogen atom loves to permeate and gobble up most high-strength alloys, including steel and those that are nickel-based. They can even watch it happen during computer simulations [source: McGill University]. The severity of embrittlement varies with the type of alloy and with temperature [source: Gray].
Hydrogen embrittlement has become the bane of such things as aircraft carriers, battleships, airplanes, spaceships and nuclear reactors. Occasionally, the consequences have been deadly. In 1985, a soldier died in Great Britain when the bolts on an American-made 155 mm howitzer self-propelled gun failed. The bolts were holding down the manifold that raised and lowered the gun. The bolts snapped, pinning the soldier under the manifold. Investigators blamed hydrogen embrittlement. The gas made the bolts so fragile that they couldn't withstand the heavy jolts produced by the firing gun. In 1984, the bolts (also for the gun mounts) on an M1 Abrams tank snapped, too [source: Anderson].