At NASA, when looking for the leak in a tank of hydrogen fuel, since a burning jet of hydrogen is more-or-less invisible, they would (perhaps still do) have to slowly walk around the tank holding a piece of cardboard in front of them. The idea was that they would (hopefully) see the cardboard char before they walked into the jet.
I don't actually think that using hydrogen, even highly compressed hydrogen, to power a car is all that dangerous. As I understand it, the tanks are wrapped in a carbon fiber bag which is supposed to catch any fragments if the tank explodes.
However, highly compressed hydrogen can be very dangerous under the wrong circumstances, especially if ignited by a spark or static electricity. It's rather mind-boggling to see fool cell fanboys try to promote fool cell cars as being less of a fire hazard than battery-electric vehicles!
But then, I guess when you're a fool cell fanboy, you have to grasp at even the most feeble of arguments, because you don't have
any good ones!