Why did balloons and dirigibles stop using hydrogen as a lifting gas?

Balloons and dirigibles largely stopped using hydrogen as a lifting gas primarily due to its extreme flammability, which posed a severe safety risk. While hydrogen is the lightest known gas and provides excellent buoyancy, its use led to numerous fatal disasters.12

The most prominent example of this danger was the 1937 explosion of the Hindenburg, a disaster that was captured on film and significantly contributed to the decline of commercial airship travel. Although the Hindenburg was originally designed to use helium, it was filled with hydrogen because of United States export restrictions against Nazi Germany at the time.13

Following these events, helium became the preferred lifting gas for airships because it is nonflammable and far safer, despite being less buoyant than hydrogen. By the late 1930s, the combination of these safety concerns, the high costs of operation, and the rapid advancement of heavier-than-air aircraft rendered dirigibles commercially obsolete for most applications.12