A recirculating fumigation system for facilities that store agricultural products employs a blower which is chemically inert to the gaseous fumigant, driven by a variable speed pneumatic motor which provides the system with adjustable capacity over a range of recirculation blower speeds and the capability of high speed operation for degasation. In ship holds the system may be mounted in the manway of the hatch of the cargo hold. The system is entirely nonelectrical and isolated from the gaseous fumigant as the pneumatic motor is driven by a separate air supply.
