Automatic filter integrity test

With metic­u­lous care, an oper­a­tor guides an instru­ment with a mea­sur­ing fun­nel under the ster­il­iz­ing 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 small sales receipts, then have to be glued onto the test report by the oper­a­tor. The pur­pose of the fil­ter integri­ty test for hot-air ster­il­iza­tion tun­nels is to make sure that fil­ters are not leak­ing and 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 this 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, for a while, been search­ing for a bet­ter test method. 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+Stroebel par­ti­cle test­ing expert, dis­cov­ered a sys­tem by the Infra­So­lu­tion Group. This sys­tem uti­lized robot­ics for auto­mat­ic test­ing of fil­ters in clean rooms. “Of course, the con­di­tions inside a ster­il­iz­ing tun­nel are dif­fer­ent, main­ly due to the dif­fi­cul­ty of access here, but we thought that this sys­tem could be adapt­ed to suit our appli­ca­tion,” explains Engel.

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 clean-room 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 ster­il­iz­ing 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 ster­il­iz­ing tun­nel,” explains Daniel Engel. The oper­a­tor makes all the nec­es­sary set­tings at the tun­nel oper­at­ing pan­el, where he 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 involves admit­ting a defined num­ber of par­ti­cles into the ster­il­iz­ing 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 sep­a­ra­tion effi­cien­cy of the fil­ter. The entire sur­face of the fil­ter has to be scanned.“These mea­sure­ments have to be tak­en sev­er­al times a year,” explains Daniel Engel. B+S’s ser­vice tech­ni­cians already car­ry out these tests at the request of cus­tomers. “By launch­ing Lin­earTwin­Scan, we aim to take this ser­vice to the next lev­el,” says Thomas Seif­fer. The ben­e­fit for the cus­tomer is not only exact test results – the B+S ser­vice tech­ni­cian can also car­ry out any nec­es­sary main­te­nance work, such as fil­ter replace­ment, with­out delay. Ster­il­iz­ing tun­nels can be retro­fit­ted for use of 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. Test results are, there­fore, more reli­able, exact and repro­ducible. What’s more, all data are avail­able in a dig­i­tal form. A graph­i­cal dis­play allows the user to track the progress of the test at any time.