Fires are dangerous in the aftermath. Temperatures created by fire, even short-lived, they have a destructive effect on mortars and many natural stones, especially on limestone, dolomite, granite and sandstones. Because mineral materials are characterized by different resistance and fire resistance, under the action of fire, additional stresses and intermolecular deformations develop in the structure of the elements due to their uneven expansion and volume changes. These phenomena lead to the formation of cracks on the surface of masonry materials, separation of layers, peeling and crushing, and in consequence - loss and weakening of the cross-section.
Further physical and chemical changes occur in the mass of masonry materials with longer heating, and, above all, dehydration of binders, increase in porosity and decrease in mechanical strength. From laboratory experiments it follows, that even at a temperature of 200 ° C, the strength of masonry materials drops by 12-30%, and at a temperature of 500 ° C - almost by 50%. As a result, as a result of these and other accompanying phenomena, in most cases, a fire is followed by irreversible displacements and deformations in the arrangement and structure of individual links of the superstructure, which become especially dangerous, when the regimes are under sustained heavy loads.
High temperatures can be caused not only by fires, but also lightning strikes, explosions of explosives, etc.. In these cases, the destruction of the structure, violation of technological threads and decor, they increase the accompanying shocks and, to a large extent, the use of water in rescue operations.