Wards in an hospital are sterilized by the following method:

Formaldehyde gas is used for sterilizing instruments and heat sensitive catheters and for fumigating wards, sick rooms and laboratories. Under properly controlled conditions, clothing, bedding, furniture, and books can be satisfactorily disinfected. In aqueous solutions, it is markedly bactericidal and sporicidal and also lethal effect on viruses. Ref: Textbook of Microbiology By Ananthanarayan, 6th edition, Page 29.