On 6th of April 9 am at the GE aviation site in Hooksett N.H. USA a quarter of a hydrogen tank (135 pounds) was incidentially released. The valve was opened during the installation. The staff in the vicinity was evacuated and the fire brigade managed to close the valve. That’s it.
For details see e.g. http://www.wmur.com/newsarchive/23066379/detail.html.