"Mr. cod"'s arguments, while in themselves factually correct, actually are strawmen. The hydrogen economy is NOT talking about liquid hydrogen. Transmission and storage will be as compressed gases, not liquid. Sure, hydrogen-air mixtures become flammable at 4%--but we already know how to work with hydrogen--thousands of laboratories do it every day (running gas chromatographs with flame ionization detectors)--working with hydrogen is actually LESS dangerous than filling your automobile up with gasoline. The "invisible flame" problem is fixed in a manner analogous the the current use of natural gas (natural gas is odorless--so we ADD a chemical which has an odor--for hydrogen we ADD a trace chemical which emits light in the visible spectrum if there is a flame--a few ppm of benzene vapor will probably do the trick). Using hydrogen safely is NOT rocket science--despite Snope's assertions to the contrary.
Disastrous, as my post 38 says. Compressed H2 is much less dense than the liquid, which itself is 11 times less dense than gas.
If you try to use compressed H2 for transportation, you get gigantic, enormously heavy tanks, and even more limited range.
Even worse, compressed gas tanks are more dangerous than liquid dewars because they can (and will) explode. Common metals cannot be used for compressed hydrogen because of a phenomenon called 'hydrogen embrittlement', which forces the tanks to become gigantic, heavy, and costly, which I guess is a home run for the environmentalists and luddites...such as you.
--Boris