I worked for a power line company one summer in college and I was amazed to find out how far high voltage current could jump, when offered a ground.Scary stuff... Back when I had a tall stick (55' clearance) HV lines always scared me. Chart says clearance is 25' above the stick, but looking up it always seemed about 2'.
Another real point to keep in mind is the very real possibility of "flash over"... You don't have to touch the line, just get close enough. 10' minimum clearance on lines of up to 345 kV and 16' at voltages over that... Visual rule of thumb, clearance should be (at least) twice the length of the insulators on the tower. Under all circumstances stay well clear of the mast(s) and standing rigging while transiting under HV lines.
Interesting to note (@34sec in the vid) the initial arc seems to have jumped from the lower spreader on the foremast to the bridge rail.... Flashover