Abstract: A novel apparatus and method for sterilizing microbially contaminated materials, e.g., hospital linens, packaged goods, etc., by contact with a flammable chemical sterilant gas such as ethylene oxide, employs a bulk supply vessel for the sterilant gas and a small unit dosage vessel which receives a unit dosage of sterilant gas from the bulk supply vessel. The unit dosage vessel delivers a charge of sterilant gas to a separately enclosed sterilizing chamber in which the materials to be sterilized are placed. Water flooding means in a supply cabinet in which the bulk supply vessel is positioned, protects against possible deflagration of the sterilizing gas in the event of leakage or rupture of the gas supply means.