The efficiency of the pre filter is directly related to the life of the HEPA in that the more particulates captured in it, the less can pass through and prematurely block the HEPA. Most pre filters have an efficiency grading of F5 - F7. When plastics are being lasered, the particulate size generated is typically 0.2microns. At this level of filtration the media has an efficiency of 35% in F5 to 65% in F7. When metals are being lasered the particulate size being generated is typically below 1micron. This equates to an efficiency of 65% in F5 to 80% in F7.
The BOFA Advantage range of laser fume purification systems has an F8 grade media which gives an efficiency of 80% at 0.2 microns and 95% at 1micron.