Very short and intense x-ray pulses can be used for diffraction imaging of single biological molecules. Inevitably, x-ray absorption initiates damage that degrades the molecule's image. This paper presents a continuum model of the physics that leads to damage when a small particle absorbs a large x-ray dose. The main processes are found to be ionization and Coulomb-force driven atomic motion. Trapping of electrons, Debye shielding, and nonuniform collisional ionization all have a significant effect on the overall damage kinetics.