Abstract
We study, using the damage spreading method and within the heat bath dynamics, the dynamical behaviour of the square lattice three-state Potts ferromagnet subjected to an external field. In the zero field case, we verify that this very simple model presents, besides the transition consistent with the equilibrium one, a new dynamical chaotic phase with unusual features. Although the unexpected transition occurs, within the error bars, at the static Ising critical temperature, it is in the directed percolation universality class. We observe that the application of a uniform magnetic field does not destroy any of the two transitions, while the unexpected one is annihilated by a new kind of field which plays the role of a conjugate field to the Hamming distance.