The "plank breaking'' rule is implemented here in its door_to routine. Note that this returns 'true' after killing the player.

Object -> PlankBridge "plank bridge"
  with description "Extremely fragile and precarious.",
       name "precarious" "fragile" "wooden" "plank" "bridge",
       when_open
           "A precarious plank bridge spans the chasm.",
       door_to
       [;  if (children(player)~=0)
           {   deadflag=1;
              "You step gingerly across the plank, which bows under
               your weight. But your meagre possessions are the straw
               which breaks the camel's back! There is a horrid crack...";
           }
           print "You step gingerly across the plank, grateful that
                  you're not burdened.^";
           if (location==NearSide) return FarSide; return NearSide;
       ],
       door_dir
       [;  if (location==NearSide) return s_to; return n_to;
       ],
       found_in NearSide FarSide,
  has  static door open;