Safe change filtration

Safe change filtration was initially developed for the nuclear market to handle potential radioactive airflows. In more recent times this technology has been extended and applied to the pharmaceutical and microbiological industries to handle raw product and viruses which may need containment. In short, safe change filtration is a process of changing a hepa/ultra filter without exposure by the operative to the filter or inside of the filter housing. Also to fully contain any high risk contaminant within the housing. There are three essential features synonymous with safe change:

Construction To guarantee the total security essential with these systems the filter housing must be a totally welded construction. The industry standard for tightness is to factory test to DIN 25496 which has an allowable leakage rate of < 3 x 10 - 5 of nominal air flow at Dp = 2000pa. To comply with the ever increasing corrosive properties of disinfection and fumigation agents used, stainless steel is strongly recommended and is rapidly becoming a standard requirement – this is particularly relevant in the pharmaceutical industry. A further advantage is the resistance to site damage during handling and installation when compared to alternative paint finishes. Such paint finishes (usually epoxy-coated ) cannot be site repaired which can have severe implications to overall costs and programme.

Security of filter seal The phrase "any filter is only as good as its seal" could not be more relevant in these critical systems any airflow under pressure will always find the easiest path. It is therefore vital in such critical applications requiring safe change that the filter is

• Fully sealed to the filter housing
• Have a system of verifying this
• Ensure the filter remains fully sealed throughout it's life (often a number of years)

• Provides a surface within the housing to ensure the filter cell gasket is fully sealed on all four sides without any bypass.
• Allows a site verification test of the seal by pressurisation followed by measurement of the allowable leakage.

Security of bagging system Over the years many types of housing collars (sometimes known as service boards) have been developed to find a solution to the problem of the bag and ring becoming detached during the filter change. To off set this problem it has resulted in operatives requiring being fully suited with air supply – a costly and cumbersome safeguard. Developments by The Nuclear Research Centre in Karlsruhe have resulted in a new collar design incorporating an undercut double groove. This type of groove allows the securing rubber band to be totally secure during the changing procedure and therefore allows unprotected operatives to perform the filter change. Safe change filtration by its very name should always be looking to improve safety and be updated with current Health & Safety at Work regulations. Most safe change filtration is on extract systems and once again emissions to the atmosphere are controlled and public safety should always be a prime consideration. Developments in the pharmaceutical and microbiological industries with regard to handling of viruses and other harmful substances are on the increase and commercial considerations should not outweigh the critical technical and safety issues discussed. To ensure all operating and environmental issues are fully considered the above comments will I trust prove helpful to both users and specifiers.

Stewart Horne UK Filter Sales Manager, Krantz Systems