I'm not interested in assigning blame but wish to introduce two elements into this discussion.
Firstly; Canuck Guy quite rightly makes the point that the pilot has the final say on the choice of the landing site; whilst that is correct, there are constraints in Europe with respect to the size. The regulations state that the HEMS Operating Site must be big enough to provide adequate clearance from all obstructions and then in guidance - because it cannot be a requirement - states that the minimum dimension should be 2D. Clearly this site is not 2D wide.
Secondly, the manoeuvre contributed to the incident.
In general, spot turns can be placed into one of three types:
the standard one that is centred upon the rotor axis (this is the one taught to student pilots and is the easiest to perform because it requires only the application of pedal and the maintenance of stability) - this requires an area of 1.2D in which to contain the helicopter;
the one that is centred on the midpoint of the helicopter - this is the most difficult to perform and usually requires markings to follow (the 'touchdown and positioning marking' is specified in heliport/helideck requirements and has an inner dimension of 0.5D of the helicopter) - this requires an area of 1D in which to contain the helicopter;
the last is the one centred upon the pilot - this was the one used by the pilot in the incident, in some sense it is the most accurate because the pilot can pick and maintain a spot around which to turn - unfortunately it requires an area of 1.5D in which to contain the helicopter.
The landing site in the video is just over
one rotor diameter wide (about 0.83D) - more importantly the obstacles on the starboard side are just over a rotor radius from the centreline of the site. As the pilot performs the spot turn, the tail rotor is inevitably placed under wires (this would probably have been the case with any of the spot turns described above).
As has been mentioned in another post, it was lucky that the main rotor disc cut the wire, a tail rotor strike would have led to far more serious consequences.
Jim