Abstract
Studies a two-state version of the sandpile model of self-organized criticality. Instead of a critical height of stability as in the sandpile model, the author introduces a hard core repulsion among different particles at the same position. In the case of a collision particles hop randomly to the nearest neighbours. Critical exponents obtained by numerical simulation show strong disagreement with the values theoretically predicted for the sandpile model but they are close to the numerical values of other models.