Singularity Resolution + Unitary Evolution + Horizon = Firewall ?
  We assume that a quantum gravity theory exists where evolutions are unitary, no information is lost, singularities are resolved, and horizons form. Thus a massive star will collapse to a black hole having a horizon and an interior singularity--resolved region. Based on unitarity and on a postulated relation, we obtain an evolution equation for the size of this region. As the black hole evolves by evaporation and accretions, this region grows, meets the horizon, and becomes accessible to an outside observer. The required time is typically of the order of black hole evaporation time. If the boundary of the singularity--resolved region can be considered as the firewall of Almheiri et al then this marks the appearance of a firewall. 
S. Kalyana Rama
hep-th gr-qc