Replacement HEPA Filter / Model 688 HEPA stands for High Efficiency Particulate Air, and a true HEPA filter is widely regarded as the ultimate filter. In World War II the Atomic Energy Commission needed a filter to protect researches from radioactive dust particles that might present a health hazard to them. The HEPA filter was born. It traps particles as tiny as .3 microns with an efficiency rating of 99.97%. To give you an idea of the size of a micron, it takes 24,500 microns to equal 1 inch (2.54 cm). Conversely, 4/10,000ths of an inch equals one micron. In metric terms, a single micron is 1 millionth of a meter. A particle of 10 microns is invisible to the naked eye. Pollen ranges between 5-100 microns. Human hair between 70-100 microns. A HEPA filter is so efficient that for every 10,000 particles that enter the filter within its filtering range, only 3 particles will get through. For this reason HEPA filters are used in environments that rely on high clean-air standards. Surgical facilities, tuberculosis wards, NASA clean rooms, and laboratories are a few examples of environments that utilize HEPA filters. HEPA filters are particularly useful for allergy sufferers.

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