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What is the Acceptance Criteria of HEPA?



The approach most test standards take regarding acceptance criteria isthat the acceptable leak size limitsare ultimately determined by the customerand supplier. However, a scan test leak size limit of greater than or equal to0.01% has generally been adopted for many applications utilizing HEPA flters orclean areas of varying classifcations. Although the 0.01% leak size has beenused historically and has its origins linked to early generation analog photometertest equipment, establishing a leak size limit of 0.01% as an acceptancecriteria without performing a science and risk-based assessment can result inissues relating to leak testing and can contribute to signifcant operationalcosts if an out of tolerance or failed condition is identifed in a low riskarea. As previouslynoted in Section 6.5, flters are not 100% efcient and areexpected to have some natural or integral penetration of particles near theMPPS. Test acceptance limits become more controversial or problematic whenutilizing lower-rated HEPA flters where the acceptable factory penetration ator near MPPS can be comparable to or larger than the feldtest leak sizeacceptance criteria. This is especially true where the bleed through e?ectcan occur (see Section 6.9).When purchasing a flter, it is thereforeimportant to consider a flter’s rating as well as how it will be tested after installationin order to avoid unnecessary feld test failures.



ISO 14644-3 [33] gives guidance on how alternative leak acceptancecriteria can be implemented. In a risk-based approach, it may be ideal to haveacceptance criteria that trends with the eficiency of the flters being used orthecleanliness of the room being tested. ISO 14644-3 uses the factory flter efciency rating as the basis of acceptancecriteria negotiation. The leak acceptancecriteria for a photometer leak test and a particle counter based leaktestshould be the same, as the theory and methodology behind leak sizing isidentical for both methods. If performedproperly, a leak test with a photometerand a particle counter will result in the same leak size (Meek, et al., 2011[121]).

ISO 14644-3 [33]提供了有关如何实施泄漏替代标准的指南。 在基于风险的方法中,理想的接受标准是,该接受标准可以反映所使用过滤器的效率或所测试房间的洁净度。 ISO 14644-3使用工厂过滤效率等级作为接受标准协商的基础。光度计泄漏测试和基于粒子计数器的泄漏测试的泄漏接受标准应该相同,因为两种方法背后的理论和方法是相同的。如果执行得当,使用光度计和粒子计数器进行的泄漏测试将得到相同的泄漏率结果(Meek等,2011 [121])。

A leak detected in excess of 0,01 % of the upstream massconcentration is deemed to exceed themaximum allowable penetration. However,for filter systems of an integral efficiency at MPPS ≥ 99,95 %and less than99,995 %, the acceptance criterion is 0,1 %.



If filter systems of an integral efficiency lower than 99,95 %at MPPS are to be tested, a different acceptance criterion are necessary, basedon agreement between customer and supplier.

如果要测试 MPPS 整体效率低于 99.95% 的过滤系统,则根据客户和供应商之间的协议,需要不一样的接受标准。

The flters for depyrogenation tunnel


The flters ftted to a depyrogenation tunnel are subject toprolonged periods of high temperature operation, so standard flters are notsuitable. Special flters rated to 350°C are available with a manufacturerguaranteed efciency of 99.99% for 0.3 μm particles (note that the FDA defnitionof a HEPA is > 99.97% at 0.3 μm) at a temperature of 350°C) with a ceramicmaterial used for the media to frame seal. Recently there have been advances inthe materials available and ?exible sealants are being introduced that canreduce the heat up time and reduce the risk of sealant cracking. Traditionalflters need to have a controlled heat up and cool down time (typically not toexceed 1°C per minute; the rate should be confrmed with the flter supplier) toprevent heat stress damage to the seals. Often the systems are maintained hotduring periods of non-use to reduce the heat cycling on the flter.

安装到去热原隧道中的过滤器需要经受长时间的高温操作,因此不适用标准过滤器。厂家使用陶瓷材料用于滤材与边框的密封可提供耐受350℃的对0.3 μm颗粒的效率为99.99%的特殊过滤器(注,FDA对HEPA的定义为> 99.97%@0.3 μm)。最近,可用的材料有了进步,并且引入了柔性密封剂,可以减少加热时间并降低密封剂开裂的风险。传统的过滤器需要具有受控的加热和冷却速度(通常不超过1℃/分钟;应与过滤器供应商确认该速率),以防止热应力损坏密封件。通常,在不使用期间,系统会保持高温,以减少过滤器的加热循环。


Filters used for depyrogenation tunnel are generally H14. Theseflters can be full face scan leak tested on installation, but after the initialheating cycle (burning in the flter, which usually results in the flter gradebecoming equivalent to H13) traditional testing is not recommended. The oilaerosol (if it is Polyalphaolefn (PAO)) will load onto the flter and burn o?,giving o?unhealthy fumes, and may load the flter media; this is usually more fragileafter burn in as the binder holding the media together has o?-gassed.DEHS (Diethylhexyl Sebacate) is an alternative oil that may evaporatefaster.