The number of requests we get for replacemnt "2x4" clean room filters is astounding and it seems that this very common request would be easy to answer - but clean room HEPA filters are not quite that easy. Some additional information is key to be able to ensure you get what you're looking for - even a small mistake or oversight can result in worthless product being made and shipped to you. Here are the most common things to know when trying to specify or purchase clean room HEPA filters:
1) Size - Nominal vs Actual The biggest issue with HEPA panels for clean rooms or operating rooms is that they are most commonly nominally sized as 2x4 or 2x2 to fit nicely in a ceiling grid system, however the actual size of the filter that sits in that module can vary from manufacturer to manufacturer and model year to model year. There are hundreds of variations of the actual sizing for a 2x4 panel, so knowing the actual size is a must. Actual sizes are usually included in decimal form in the product code or description, other times a manufacturer may include their own jargon to denote the actual size of the panel to make it harder for you to source the correct size from a different company.
2) Options Most commonly in the United States, Gel Seal is the preferred "gasketing" as they are less prone to leakage and make the replacement process easier. However most everywhere else in the world still use gasket seal so it does pop up on occasion in the US. Cross bars/supports and filter screening are other common options. Filter screens are nice for installers as they lessen the chance of damage during installs, but they do change how the air goes through the filter as the screen sits directly on the media - shortening the life of the filter.
3) Efficiency - HEPA/ULPA Again, the most common effeicney seen throughout ORs is 99.99% @ 0.3 micron HEPA filter, but efficiencies up to 99.999995 @ MPPS are used in clean room filters. Although air changes in a room tend to have a larger impact on particle counts in a room rather than the efficiency of the filter, in critical environments these ULPA filters are needed. When specifiying filter efficiency it is also common to refer to them as "Four Nines" or "Five Nines" - this is a risky shortcut to take as some companies view this as the total number of figures and others assume it is the count after the decimal. Depending on how the manufacturer understands it a "Four Nines" panel could either be 99.99% or 99.9999% - a significant difference, so be careful and verify you're speaking in the same terms.
4) ePTFE or Membrane Clean Room Filters Growing in popularity is the use of ePTFE or Membrane filter media in the ULPA filters. It offers much lower static pressure/airflow restriction than traditional medias and is significantly more durable. This durability is important when installing as it can all but eliminate failures during room certification due to rough or imporper handling. Orignally developed for use in the Microelectronics market due to the absence of Boron (which makes up about 13% of traditional filter media), their use has rapidly expanded in the Life Sciences/Pharmaceutical Manufacturing industry. An important note here, is Pharma is required to have a minimum efficiency of H14 and many ePTFE panels are limited to only H13 efficenicy. There are some other concerns as they need to be tested with specific challange aerosols and there are cases where ePTFE media tesetd with the commonly used PAO has caused the efficiency of the filter to degrade.
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