The block 4 doesn't possess local underground nor proper battery
of filters and its access gets used directly to the level of the
main gallery by a very long passageway (more than 200 m) then
a staircase in staples of about twenty meters clearing directly
in the room of the observers, that is the lower floor of the block,
and above to the superior floor from where one has access directly
either to the gap or ito the VDP "cloche". This block
is extremely tiny, each of the levels having a surface of about
2 m by 2.50 m. It is more an integrated observatory in the "ouvrage"
than an actual block.
The FM allowed to beat the whole glaze of the tray, among the
top of the South flanking block, of the block turret and the surroundings
of the chimney.