A simple approximate analytical theory is developed to predict the rate of decay of a planar shock wave travelling through the gaseous medium blocked by barriers and screens. It involves the following assumptions: (1) the flow is uni‐dimensional; (2) The gas obeys the perfect gas law; (3) heat transfer to confinements is neglected; (4) shock wave velocity is independent of conditions behind it (this is known as Whitham’s approach) and depends only on confinement geometry, distance travelled by the shock wave through the blocked space and its initial Mach number. Experimental data on shock wave attenuation in beds of granular solid material, gas‐solid suspensions, gauzes, porous packings, rough tubes, diaphragms, etc. have been used to varify the theory. It is found the proposed approximate theory gives satisfactory prediction for quenching efficiency in all cases considered, thus allowing to use it for comparative study of various safety measures.