Since hydrogen is so light though, it escapes into the atmosphere before collecting enough to explode in a car. BMW claimed this way back in the 90s when it was experimenting with the gas.

There’s probably more of a danger of the tank and in hydrogen cars bursting, since the hydrogen is stored at relatively high pressures. But the gas could easily escape without igniting.

Obviously anything is possible when you are storing energy as densely as possible. And one of the highest density energies we store is still hydrocarbons.