Some recent minor leaks in US:
At US Boston University: http://www.dailyfreepress.com/second-hydrogen-alarm-sounds-in-a-week-1.1945071.
At US Washington refuelling station: http://www.wavy.com/dpp/news/virginia/va_ap_leak_closes_dc_hydrogen_fuel_station_20091006
For your entertainment, this is what may happen with hydrogen researchers: http://www.thestar.com/news/gta/article/707234–why-a-towed-away-van-led-to-scarborough-evacuation