Because of the near invisibility of a hydrogen flame in daylight and hydrogen's extremely low ignition coefficient, if a known leak is present (e.g., an audible hissing), ignition should always be presumed. The primary cause of this incident derives from the technician improperly performing hot work in the vicinity of a charged flammable gas line. Given the location of the flammable gas line, an alternative to performing hot work or relocating the hot work should have been considered. If such work was necessary at this location, it should have been performed only after the gas supply was verified closed (along with a lock and tag). Also, if this latter option was chosen, then the system should be checked for leaks prior to turning the gas back on.