Abstract: A blast-proof building having one or more stories, each story comprising one or more rows of internal supports and having walls and a ceiling comprises of: (a) one or more intermediate "L" shaped components defining a wall portion and a ceiling portion, each corner of the free end of the-ceiling portion being carried by a support; (b) four or more corner components defining two wall portions and a co-joining ceiling portion, the free corner of the ceiling portion being carried by a support; and (c) one or more ceiling components for placement between each row of supports where there are a plurality of rows of supports; each component being secured to a neighboring component. The building meets the criteria of blast-proof protection, speed of erection, flexibility of size and demountability.