HEPA stands for High Efficiency Particulate Air. The Institute of Environmental Sciences and Technology dictates that a HEPA filter must trap 99.97% of particulates 0.3 microns or larger.
HEPA filters trap air contaminants in a complex web of fibres. Depending on the size of the particle, this can happen in four different ways: Inertial Impaction, Diffusion, Interception, or Sieving.
Larger contaminants are trapped via inertial impaction and sieving. The particles either collide with the fibres and become trapped or are trapped while attempting to travel through the fibres. Medium sized particles, as they move through the filter, are grabbed by the fibres via interception. Smaller particles are dissipated as they travel through the filter and eventually collide with a fibre and are trapped.
The standard lifespan of a HEPA filter varies between 3 and 5 years in a standard cleanroom environment. This is dependent on the degree of contamination in the environment and maintenance of the pre-filters. The capacity of the fan filter unit (HEPA or ULPA filter) decreases over time as the filter becomes saturated.
An advantage of the HEPA Filter is that as they become saturated with contaminant, airflow capacity decreases and static pressure increases, as a result the filters become more efficient as the filter loads.
As soon as the recommended speed of 0.45 m/s at the filter surface can no longer be met, a replacement of the filter is required. This process is monitored by a differential pressure gauge and information made available via the cleanroom’s touchscreen control interface, Visionaire®.
For more information please call Monmouth Scientific on 01278 458090 and discuss your requirements with one of our experienced Technical Sales Representatives.