Sterilisation by gaseous biocides

Several biocides which were formerly used to sterilise freeze-driers for pharmaceutical processing have been prohibited for use because of their toxicity. Such prohibitions may be reconsidered when these biocides are used for decontaminating a freeze-drier for processing pathogens or toxins 

The outstanding advantage of gaseous biocides is their ability to permeate all parts of the freeze-drier which are inaccessible for topical cleaning. 

The interior of the freeze-drier can be decontaminated with gaseous biocides by two methods  

Stoppered vials can be left in the chamber and exposed to a sterilising vapour in order to decontaminate the outside of the vials before their removal from the freeze-drier. In this laboratory we have been able to demonstrate that formaldehyde vapour will not permeate stoppered vials which contain freeze-dried samples. 

Disadvantages of gaseous biocides are that they may be corrosive, flammable or explosive, are invariably toxic and require a critical balance of temperature/relative humidity/biocidal concentration for effectiveness. 

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