A modern cabin air filter removes particles by utilizing three primary mechanisms. These are:

Tests by an independent laboratory¹ show that Pall HEPA Cabin Air Filters have a microbial removal efficiency of greater than 99.999% with bacteria and viruses. This can be equated to an H13-level classification.

In standard tests, the filters are tested with maximum penetrating sizes. The graph illustrates that particles smaller and larger than the tested size will be removed more efficiently. (Right). The ASHRAE Standard 161-2007 states that HEPA filters should provide a minimum of 99.97% collection efficiency for 0.3 micron particles.

[1] Centre for Applied Microbiology and Research (CAMR), now known as Public Health England.

Processes include pleating of the glass fiber HEPA filter media, forming the hardware from sheet aluminum, assembly of the odor and HEPA stages, assembly and sealing into the hardware and efficiency testing every batch.

In HEPA media production, fibers suspended in a liquid are poured over a screen so that the liquid can drain away from the fibers. Quality control checks that the distribution of pore sizes within the fibrous structure is within defined limits. The efficiency of the medium, particularly with smaller particles, is related to the thickness of the fibrous medium, the density of fibers, and the thickness of the individual fibers. Optimizing these three parameters contributes significantly to particle removal via diffusional interception.

Aircraft manufacturers specify recommended filter element change-out intervals. The time interval varies between aircraft types and between aircraft systems. Pall also works with airlines and aircraft manufacturers to determine the optimum service interval for specific operating environments.

We recommend following the aircraft/system integrator guidance and any local airworthiness/regulatory guidance. However, the efficiency of a HEPA filter improves with usage. Filters needn't be changed after exposure to contamination until the maximum flight hours or differential pressure is met.

We recommend following the official WHO and local government guidelines. The above applies to all Pall Aerospace cabin air filters, OEM or IPC-listed filters and any Pall PMA-approved parts.

*World Health Organization, Naming the coronavirus disease (COVID-19) and the virus that causes it (accessed March 2020).

Replacement of used HEPA or A-CAF filters carries no greater risk than undertaking general maintenance on any in-service aircraft part. Maintenance staff concerned about the general accumulation of dust or debris on cabin air filters should wear the same personal protective equipment used for similar aircraft maintenance tasks. Contact airline safety and health personnel to advise if specific PPE is required.

Pall Aerospace have extensively tested and examined numerous new and returned filters. These tests have looked at microbial growth, remaining filter life and also potential Volatile Organic Compound contaminants that may have accumulated due to a fume or odour event. Filters can be returned directly to Pall Aerospace Scientific Laboratories in Portsmouth, UK for further analysis and in an effort to greater support our customers in service.