Taking meticulous care, an operator guides an instrument with a measuring funnel under the sterilising tunnel filter. The entire surface of the filter has to be scanned. The test results are printed onto heat-sensitive paper using a small external printer. The printouts, which resemble sales receipts, then have to be glued onto the test report by the operator. The purpose of the filter integrity test for hot-air sterilisation tunnels is to make sure that the filters are not leaking, that they are properly fitted and that no ingress of unfiltered air takes place. Considering the high degree of automation in the pharmaceutical sector, this might seem too laborious a way of going about the task. “Actually, this is best practice today”, explains Thomas Seiffer, Head of Research and Technology at filling and packaging machine manufacturer Bausch+Ströbel.
Seiffer and his team refused to accept this as given, especially as stationary particle counters are already integrated in B+S filling machines. B+S’s developers had been searching for a better test method for a while. It had to be much more user-friendly and, most importantly, it had to deliver reliable and reproducible results. The breakthrough came at a trade show in 2017, when Daniel Engel, a Bausch+Ströbel particle testing expert, discovered a system by the Infrasolution Group. This system utilised robotics for automatic testing of filters in cleanrooms. “Of course, the conditions inside a sterilising tunnel are different, mainly due to the difficulty of access here, but we thought that this system could be adapted to suit our application”, Engel explains.
Infrasolution was amenable to the plant constructor’s offer of a development partnership. “We liked the idea from the very beginning and saw right away that it had potential”, says Christian Dorfner, Head of Research & Development at Infrasolution. Infrasolution has many years of experience in cleanroom test systems, having started out as a service provider before branching out several years ago into the development of related test instruments.
The result of this collaboration is a small and compactly designed instrument named Lineartwinscan. It has twin particle measuring funnels and is guided through the sterilising tunnel on the tunnel conveyor belt in a precisely predetermined way. “For this purpose, of course, the measuring instrument has to be integrated into the controller of our sterilising tunnel”, Engel adds. The operator makes all the necessary settings at the tunnel’s operating panel, where they can also track the progress of the test while it is running and call up the test results. Unlike with the old method, these results are instantly available in a digital form. They can be saved and processed as required and therefore meet the relevant statutory requirements
(21 CFR Part 1/GMP Annex 11).
Lineartwinscan effectively combines two tests: an ISO classification test (under development) and a filter integrity test (or “DEHS test”, as it is also known). The DIN EN ISO 14644 standard applies to both tests. The first involves taking particle measurements at predefined measuring points. The second entails admitting a defined number of particles into the sterilising tunnel on the non-sterile side above the filter. A particle count is then taken above and below the filter on the sterile side to determine the filter’s separation efficiency. The entire surface of the filter must be scanned. “These measurements are necessary several times a year”, Engel continues. B+S’s service technicians already carry out the tests at the request of customers. “By launching Lineartwinscan, we aim to take this service to the next level”, Seiffer comments. The benefit for customers is not only exact test results – the B+S service technician can also perform any necessary maintenance work, such as filter replacement, without delay. Sterilising tunnels can be retrofitted for use with Lineartwinscan by the customer’s own qualification personnel.
The advantages of the new system are obvious: measuring accuracy is no longer dependent on the meticulousness and experience of the operator. The test results are consequently more reliable, exact and reproducible. What’s more, all data is available in a digital form. A graphical display allows users to track the progress of the test at any time.