A model is proposed for calculating magnetic field effects formed in a radical triad composed of a biradical and a paramagnetic particle. To describe the influence of the “third” spin on the spin evolution in a biradical, the electron spin exchange interaction of the added spin with one of the paramagnetic centers of the biradical has been considered. Calculating the field dependence of the recombination probability of the biradical-oxygen complex revealed both an increase in recombination probability earlier attributed to spin catalysis and the influence of the values and signs of the exchange interaction in the complex on the shape of the magnetic-field effect dependence. Calculation results are in agreement with the experimental data on the photolysis of 7,7’-dimethyl-silanorbornadiene in aerated and deaerated solution.