Men wearing orange safety vest are filling blue bags.
They are putting things in the bag.
Men indicates several men, which can be referred to as they.  If they are putting things in a bag, then they are filling that bag.
exists e1 e2 s1 x1 x2 x3 x4 x5 x6.(Theme(e2,x6) & Actor(e2,x1) & v_fill(e2) & n_bag(x6) & a_blue(s1) & Theme(s1,x6) & Theme(e1,x3) & Actor(e1,x2) & v_wear(e1) & n_vest(x3) & of(x3,x5) & n_safety(x5) & of(x3,x4) & n_orange(x4) & (x1 = x2) & n_man(x1))
exists e1 x1 x2 x3.(n_bag(x3) & n_thing(x1) & in(e1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_put(e1) & n_thing(x2))