The Institute of Environmental Science and Technology (IEST) has identified six classes of HEPA filters based on their performance: A, B, C, D, E, and F. Each one has its own unique characteristics, as illustrated in Graph 1.The high-quality HEPA filter of the second phase is designed to capture the finer particles that escape the prefilter. The concept of the HEPA filter was first developed for use in gas masks worn by soldiers during World War II. For a vacuum's HEPA filter to be effective, it must be designed so that all air entering the machine is expelled through the filter, without any air passing through it.
This is why modern air purifiers come with a detector that indicates when HEPA filters need to be changed. At its most basic level, a HEPA filter is a very fine filter made up of perfectly intertwined fiberglass fibers. If a HEPA filter is not changed in time, it can cause stress on the machine or system and will not be able to properly remove particulates from the air. Ideally, all HEPA filters should be intact when installed and should not allow air to pass through their joints. They should work perfectly until they need to be changed, which is usually done every 6 to 12 months (or as appropriate depending on use, prefilters, etc).
By definition, HEPA filters are capable of removing more than 99.97% of all airborne particles larger than 0.3 microns in diameter. The zigzag motion of the fibers makes it much more likely that small particles will be trapped in the fibrous labyrinth of the HEPA filter. When a new replacement HEPA filter is installed, it will once again be able to capture small particles through the intercept mechanism. To ensure that factory-tested HEPA filters do not leak through small holes and that gaskets and frames do not leak, on-site testing with heterogeneous dioctyl phthalate (DOP) (cod) or a suitable substitute is strongly recommended.
HEPA filtersare essential for preventing the spread of bacterial and viral organisms in the air and thus reducing infections. Larger particles (more than 1 micron in diameter) will inevitably collide with the fiberglass fibers of the HEPA filter. The Institute of Environmental Science and Technology (IEST) has identified three main classes of HEPA filters: Class A, Class B, and Class C.
Each one has its own unique characteristics and performance levels.
Class A HEPA FiltersClass A HEPA filters are designed to capture particles larger than 0.3 microns in size with an efficiency rate of 99.97%. This type of filter is typically used in medical facilities and other areas where air quality is critical.
Class B HEPA FiltersClass B HEPA filters, also known as “ultra-low penetration air” (ULPA) filters, are designed to capture particles larger than 0.12 microns in size with an efficiency rate of 99.999%. This type of filter is typically used in cleanrooms and other areas where extremely high levels of air quality are required.
Class C HEPA FiltersClass C HEPA filters, also known as “high-efficiency particulate air” (HEPA) filters, are designed to capture particles larger than 0.3 microns in size with an efficiency rate of 99.97%. This type of filter is typically used in residential homes and other areas where air quality needs to be improved.
It's important to note that all three classes of HEPA filters, regardless of their efficiency rating, must meet certain standards set by IEST in order to be considered true HEPA filters. When choosing a HEPA filter, it's important to consider your specific needs and environment before making a decision. Knowing which class of HEPA filter you need can help you make an informed decision about which one will best suit your needs.