  Rigorous implementation of the effects of collisions in modeling the
formation of the polarized solar lines is of utmost importance in order to
realistically analyze the available, highly sensitive solar spectropolarimetric
observations. Indeed, even when an observation seems to fit well with theory,
one can misinterpret results if important effects due to collisions are not
correctly implemented in the modeling process. We point out inconsistencies in
the models adopted to implement the Paschen Back effect together with
collisional effects on the solar linear polarization formed by scattering of
anisotropic radiation. Because the significance of these inconsistencies
increases as polarization becomes increasingly responsive to collisions, we
investigate the range of hydrogen densities $n_\text{H}$ to which the
polarization is sensitive. We used the density matrix formalism in the
tensorial irreducible basis, which was developed within the theory of
atom-radiation interaction and of atomic collisions. We solved the statistical
equilibrium equations for multi-level atoms with hyperfine structure (HFS) in
order to evaluate the collisional depolarization of levels of the D1-D2 lines
of the K I atom. We find that collisions play a prominent role, particularly at
hydrogen densities of between 10$^{13}$ and 10$^{16}$ cm$^{-3}$. So far,
analyses of polarized lines formed in the presence of solar magnetic field have
incorporated, if at all, collisional rates calculated assuming zero magnetic
field. This could be a good approximation in the Hanle regime but not in the
Paschen Back regime. For typical quiet Sun magnetic fields, the latter regime
could be reached, and level-crossing takes place in several atomic systems.
Therefore, one must be careful when using collisional rates calculated in the
zero-field case to interpret linear polarization formed in magnetized media.
