Andy Stillo, HPP Research & Development Manager, Camfil USA:
Most manufacturers change their HEPA filters based on pressure drop. Some users set a time frame on change frequency, especially in the most critical space (Grade A). A period of three to five years is not uncommon. There have been limited long-term studies on the HEPA lifetime, many factors influence life, inadequate pre-filtration, outside air, velocity/airflow (too high) cleanroom conditions & good housekeeping (or not) excessive loading of PAO has been quoted as reducing filter life with no real hard data. A Lawrence Livermore Labs study quoted 10 years as a fair estimation of the life for a HEPA filter.

In reality it can take years, in theory decades for HEPA filters to reach their final pressure drop (twice the initial is the historic rule of thumb assuming “normal” design airflow). Don’t forget, we are generally recirculating clean air. There are full fresh air applications and they will obviously load sooner if the HEPA’s do not have good pre-filter protection, (i.e. MERV 14/F8 glass fiber pre-filters), then HEPA life is significantly increased. Cleaning, decon or wash-down during routine maintenance can cause more damage to a HEPA filters life than actual loading over a long period.