Disentangling the Black Hole Vacuum
  We study the question whether disentanglement of Hawking radiation can be achieved with any local operation. We assume that the operation we look for is unitary and can be described by a Bogoliubov transformation. This allows to formulate requirements on the operation of disentanglement. We then show that these requirements can be fulfilled by a timelike boundary condition in the near-horizon area and that the local observer does not notice the presence of the boundary and does not encounter a firewall. 
S. Hossenfelder
hep-th gr-qc