Freeze drier decontamination

Unloading freeze driers contaminates the immediate environment. Therefore, for single-ended freeze driers, the clean room should be decontaminated before a further manufacturing batch is introduced into the area, unless this contains the same organisms, and double door freeze driers should be sterilized after each cycle unless opened in a dean area. 

Laboratory freeze-driers can be decontaminated in the filling area using... 

Modifications and adaptations in design are obviously influenced by the scale of operation. For example, in this laboratory, safe processing of small batches of pathogens can be achieved using a modified laboratory freeze-drier which can be sited, operated and decontaminated in a contained area. Clearly when processing several thousand vials it is not possible to move larger industrial machines. 

Irrespective of whether the freeze-drier has been fitted with filters, incinerators or other features designed to reduce internal contamination, freeze-driers used to process biohazardous materials must be capable of decontamination at the end of the cycle. As well as protecting personnel and environment from the processed agent, decontamination will prevent cross-contamination from materials previously processed within the freeze-drier. 

In one respect, decontamination following freeze-drying of a known pathogen is a more simple procedure than general decontamination of a freeze-drier for pharmaceutical processing since the nature of the pathogen or toxin will be known and its sensitivity to a particular biocide can be experimentally validated. 

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

By opening the freeze-drier door and decontaminating the chamber interior as an extension of the dispensing area. This method can also be used for decontaminating the exterior of laboratory freeze-driers operated within a contained area. 

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. 

Method of use. The chamber is evacuated and then warmed to 40 °C with hot air or steam to give an RH of 25-50%. Ethylene oxide is then injected into the chamber to a concentration of 400-1000 mg per litre and sterilising conditions maintained for 4—8 hours. The freeze-drier is then returned to atmospheric pressure and the ethylene oxide vented from the drier. An explosion-proof mixture of 60% ethylene oxide and 40% methyl bromide has been used for decontamination. Ethylene oxide has been more widely used in the USA than in the UK for sterilising freeze-driers. 

Temperatures above 100 °C cannot be attained unless the steam is pressurised. Because bacterial spores are only destroyed at temperatures above 110 °C, live steam is therefore not an effective sterilant and consequently is only used to decontaminate freeze-driers when combined with a gaseous biocide such as formaldehyde. 

Of the methods discussed for decontaminating a freeze-drier, in the absolute sense only pressurised steam can be regarded as a sterilant. Since 1970, the use of pressurised steam for sterilising pharmaceutical freeze-driers has become standard and freeze-drying manufacturers are conversant with the problems associated with the fabrication of steam-sterilisable machines. Exhaustive literature exists detailing the temper-ature/pressure relationship required to destroy individual micro-organism species and these conditions can be readily achieved within the freeze-drier. 

The use of pressurised steam for decontaminating a freeze-drier The advantages of using pressurised steam as outlined above strictly apply only when sterilising freeze-driers prior to processing parenteral products. When it is intended to use pressurised steam to decontaminate a freeze-drier which has been used to dry hazardous materials, a potentially serious disadvantage should be considered related to the need to raise the... 

As part of a planned, preventative maintenance (PPM) schedule, pump oil should be drained and sterilised before discarding together with decontaminated filters, used gaskets, seals and components which have been changed during maintenance. After the PPM schedule, the freeze-drier should be validated to confirm the correct functioning of the drier and components including specialist items added to ensure safe operation. 

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