HEPA stands for High Efficiency Particulate Air (filter). HEPA filters are used widely throughout the pharmaceutical industry, offering a minimum efficiency of 99.95% (for particles of 0.3µm or above).
This makes HEPA filters a common choice as they ensure potentially dangerous materials in an airstream are captured and can be removed safely in combination with a safe-change bag.
The high efficiency of HEPAs also means they are likely to block relatively quickly, requiring potentially costly changes and downtime. Using a Hanningfield Powder Recovery Cyclone can help to eliminate some of these problems (application dependent).