  Let $G$ be any connected graph on $n$ vertices, $n \ge 2.$ Let $k$ be any
positive integer. Suppose that a fire breaks out on some vertex of $G.$ Then in
each turn $k$ firefighters can protect vertices of $G$ --- each can protect one
vertex not yet on fire; Next a fire spreads to all unprotected neighbours.
  The \emph{$k$-surviving} rate of G, denoted by $\rho_k(G),$ is the expected
fraction of vertices that can be saved from the fire by $k$ firefighters,
provided that the starting vertex is chosen uniformly at random. In this paper,
it is shown that for any planar graph $G$ we have $\rho_3(G) \ge \frac{2}{21}.$
Moreover, 3 firefighters are needed for the first step only; after that it is
enough to have 2 firefighters per each round. This result significantly
improves known solutions to a problem of Cai and Wang (there was no positive
bound known for surviving rate of general planar graph with only 3
firefighters). The proof is done using the separator theorem for planar graphs.
