// HEPA MICRO FILTERS
This is essentially the most important filter in any system. HEPA's or High Efficiency Particle Arrestor's were designed in the 1940's to originally contain the spread of radioactive contaminants. Nowadays the HEPA filter rating is applicable to any highly efficient air filter that can attain the same filter efficiency performance standards as required by COSHH regulations. The typical figures quoted show HEPA to remove 99.97% of all particles down to a size of 0.3 Microns and 95% of all particles down to 0.1 Microns. These particles are considered to have the most penetrating particle size (mmps).
A HEPA air filter can reduce the amount of airbourne particles in the fumes generated by the laser.
The common assumption that a HEPA filter acts like a sieve where particles smaller than the largest opening can pass through is incorrect. In the case of pre filters this is correct, however HEPA filters are designed to target much smaller pollutants and particles are trapped (they stick) to the fibres using one of 3 methods Interception, impaction and diffusion.
These particles have been trapped through impaction, which is common in high flow rates as used in laser fume extraction devices.
Notice the relative gaps between fibres in comparison to particle size in the image on the left. These particles have been trapped through impaction, which is common in high flow rates as used in laser fume extraction devices.
