Different filters are recommended for a specific farm based on it’s operations. HEPA filters are often recommended due to their 99.97%+ efficiency and ability to catch up to 0.3 micron particle size. The efficiency percentage increases for larger particles and decreases for smaller particles, but as the particle size becomes extremely small, the efficiency actually increases again.
For isolation rooms in hospitals, the main goal is to keep airborne infectious diseases such as tuberculosis from entering the atmosphere. To accomplish that, the air from hospital isolation rooms is filtered on the exhaust side as well as on the incoming side, using a sophisticated exhaust fan system on the ceiling where the air has to go through a minimum of two stages: a pre-filter stage and a high efficiency particulate air (HEPA) stage.