Most baby boomers have heard the radio announcer's wail: "Oh the humanity! The humanity!" Some have even seen the film footage of the Hindenburg's crash, which occurred in Lakehurst, New Jersey, on May 6, 1937. Those records of the catastrophe sealed the fate of these airships, even though the Hindenburg fire was an anomaly; hydrogen-lift ships rarely ignited.
Even so, Germany had long been cognizant of the gas' potential for combustion, and began negotiating with the US in the 1920s to import helium, which is 7 percent heavier than hydrogen but has the distinct advantage of not blowing up. (At the time, the US controlled the entire world supply of helium.) By 1937, political tensions in Europe prompted the US to hoard the gas, forcing the Germans to fill the Hindenburg with hydrogen.
Emphasis mine.