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How often do HEPA Filters have tobe changed?
Inthe pharmaceutical industry, HEPA filters are used as terminal filters for theprocessing or filtration of air in production spaces. They are mandatory insterile production, although they are sometimes also used in the manufacture ofsolid or semisolid dosage forms. Amongst the HEPA or high-efficiencyparticulate air filters are Filter Classes H13 to H14 (DIN 1822), the latterwith a retention rate of 99.995%. But how often do they need to be changed?
Onecan frequently find internal company guidelines according to which the filtersshould be changed annually, regardless of monitoring results. Is that sensible?An exact number, meaning the maximum duration of use for HEPA filters inmonths, cannot be found in the relevant GMP guidelines. According to GMP, thefilter has to be free of leaks. This is verified by qualification and regularlyperformed leak tests as per ISO 14644-3, which are mandatoryfor sterile facilities. According to the technical interpretation of the Annex1 (PIC/SPI 032-2), leak tests are to be performed every six monthsin A/B zones and every twelve months in C/D zones. The FDA Aseptic Guidedemands a regular inspection. The requirements of Annex 1 can be applied hereas well. Leaks may be repaired; those repaired areas may only take up 0.5% ofthe filter surface per filter.
大家经常会看到在企业内部文件中,要求每年更换过滤器,而不管监测结果如何。这合理么?在相关的GMP指南中其实并没有高效过滤器可以使用时长的具体数字。根据GMP的要求,过滤器必须无泄漏,通过确认和定期实行ISO14644-3泄漏测试就能进行核对,无菌车间来说这是必须的。根据附录1(PIC/S PI032-2)的技术诠释,A/B区每6全月要进行泄漏测试,C/D级区则为12个月。FDA无菌指南要求进行定期检查。附录1的要求在这里也可以应用。泄漏是可以修补的,但修补的面积不能超过单个过滤器面积的0.5%。
However,not only the integrity of the HEPA filter is relevant. The load of the filter(layer) and thus the pressure drop at the filter is also important. If thepressure drop at the filter rises, the energy demand of the ventilation systemincreases to maintain the necessary air change rates. This pressure drop at thefilter can increase to the performance limits of the ventilation system. Toprotect the HEPA filters, preliminary filters are used - usually fineparticulate air filters like F7 und F9 filters (EN779). Those have to bereplaced regularly and protect the HEPA filters from clogging.
Froma practical viewpoint, one could say that the maximum duration of use dependsdirectly on the pressure drop. Changing the filters only makes sense if thepressure drop gets too high for the performance of the ventilation system or ifthe cost of energy demand lies above the cost of a filter change. The filtersdo have to pass the leak tests (see above), of course. In practice,several companies do not use a filter for more than eight years. As mentionedbefore, though, this is not a legally binding value, but merely based onexperience.








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