Does hydrogen have a lower flashpoint or some other quality which makes it more dangerous?
Limits for hydrogen leaks that can support stable flames, International Journal of Hydrogen Energy Volume 34, Issue 12, June 2009, Pages 5174–5182
Hydrogen is an unusual fuel. It has a high leak propensity and wide flammability limits, 4–75% by volume. Among all fuels, hydrogen has the lowest molecular weight, the lowest quenching distance (0.51 mm), the smallest ignition energy in air (28 mJ), the lowest auto-ignition temperature by
a heated air jet (640C), the highest laminar burning velocity in air (2.91 m/s), and the highest heat of combustion (119.9 kJ/g). Hydrogen flames are the dimmest of any fuel. Hydrogen embrittles and attacks metals more than any other fuel.
Mind you, this is from researchers generally inclined towards the use of hydrogen.