Electrostatic charges – Good or Bad?

Understanding EN779-2012

Why was EN779 revised? Because there were too many examples both in the field and in the laboratory where electrostatic charges (naturally occurring or induced by the suppler) dissipated allowing the efficiency to reduce below levels expected by end users. Years of discussions arguing the “positives and negatives” of the electrostatic enhancement of filters took place between filter manufacturers. The labs of course were all too pleased to help re-create conditions that would prove the loss of efficiency.

ASHRAE 52.2/EN779 - both testing protocols were amended to provide a controllable method to remove static charges. In the ASHRAE test a KCL aerosol was used to measure a discharged efficiency. But again, actual ambient conditions still allowed additional static discharge to take place.

The original EN779-2012 dissipation protocol promoted “dipping” sample media into a bath of isopropyl alcohol (IPA).. This method definitely removed charges, but also damaged fibers impacting subsequent efficiency testing. Later, an “IPA Fume” was proven effective without noticeable damage to fibers or filter.

The bottom line of the controversy is there is no question that electrostatic charges can provide significantly improved initial efficiency with the capture of sub micron dust particles. But it is probable that the charge will diminish over time. When tested according to EN779-2012 and using the IPA Fume method (ISO 16890) a user can expect a “minimum” efficiency level that is verifiable in the lab.

Having said all of the above and all testing not being equal, consider that dissipation may or may not occur with any severity during the early stages of filters life. A static charge is neither good or bad when making a filter decision. But it is worth considering comparing the higher the initial efficiency before testing and the difference after static discharge. This will most likely provide you the best over all view “initial filter efficiency” and filter performance.