Abstract: A bridge of particulate and ground food, feed and inorganic substances, such as soybean meal, corn meal, flour, cement and the like in a storage vessel is broken by reducing the internal pressure of the vessel and introducing inert gas under pressure of from atmosphere to up to 10 kg/cm.sup.2 to impart impact for breaking the bridge of the particulate and ground substances. After discharge of the particulate and ground substances from the storage vessel, the matter sticking to the internal walls of the vessel can be removed by again reducing pressure and giving impact of introduced atmosphere or pressurized gas. Further, the internal pressure of the closed storage vessel is reduced prior to injecting fumigant gas and thereafter by introducing inert gas the internal pressure is brought to normal pressure to improve fumigation of the substances.