To investigate the clogging of high-efficiency particulate air (HEPA) filters by soot during fire events, the Carman-Kozeny relation, which is an equation of pressure drop for fluid passing through a particle packed layer, has been applied to the pressure drop evaluation of fluid through the soot deposition layer on a HEPA filter. Particular attention has been paid to the characteristics of the soot and the compressibility of the soot deposition layer on the HEPA filter. It has been shown that the pressure drop of fluid through the soot deposition layer depends on the specific resistance and compression coefficient of the soot deposition layer as well as on the amount of soot deposited per unit area of HEPA filter and the filtration air flow velocity.