Bulletin 83

Air Purification with Hepa Filters and UV Germicidal Lamps

Bulletin 83

Air Purification with Hepa Filters and UV Germicidal Lamps

 The public's insistence for a cleaner environment has placed a heavy responsibility on the scientific and industrial community to develop and manufacture efficient and effective products.  This short treatise on the fundamentals of air purification is part of our overall presentation.  The topic of this discussion is the Hepa/UV system, its function, capability and maintenance.  This dissertation is designed to acquaint you with basic theories and terminology, and it will provide you with the knowledge and confidence regarding Hepa/UV filtration devices.

  The terrible holocausts of both World War I and II which resulted in tragedies, death and destruction, also produced some exciting benefits which are used extensively even today.  The heart of the Fuller Hepa System success is the Hepa filter.  The composition of the system components utilize the spin off benefits of the technology developed during World War I and World War II and in addition incorporates space age State of the Art to totally ensure the most effective air filtration system ever developed.

   The poison gas attacks during World War I prompted development of activated carbon filters for use in gas masks.  Today, activated carbon is frequently used to filter gases and odors.  All Fuller purification devices can contain activated carbon and potassium permaganate.

   World War II gave us the atomic bomb and subsequently the H bomb.  We have learned to harness atomic power and now all we have to do is harness man in his quest for greed.  In any respect, the birth of the atomic bomb prompted the development of an air filtration device which even today has no parallel in efficiency and effectiveness.  During the development of the bomb, it became necessary to devise a method to safely handle highly radioactive materials.  The radioactive materials emitted many rays, which contaminated even the smallest or microscopic dust particles.  The problem of ventilating the rooms that contained radioactive materials resulted in the creation of the Hepa filter.  Hepa stands for High Efficiency Particulate Air.  The Hepa filter was invented by Mr.Willis Whitfield, an employee of the Sandig Corporation while he was at Atomic energy facility at Albuquerque, New Mexico.  It was patented by the United States Government and consequently is part of the public domain.  The first Hepa filter had a material that felt like paper.  Actually, it was a combination of asbestos and cellulose fibers.  The fibers were matted or felted, then folded and placed into a wood frame.  The result was a Hepa filter with extremely high efficiency and extremely fine particle removal.

   One of the first uses of the Hepa filter occurred in the 1960's when the electronic industry became involved in miniature circuitry involving transistors and printed circuit boards.  The miniaturization requirements dictated the need to control airborne contaminants.  An attempt was made to create a "clean room".  Many types of devices were used, however, the so called "clean room" weren't very effective and they soon became known as "gray rooms" or "white rooms" because of the amounts of duct that was present.  The Hepa filter was finally used and the "clean room" actually came into existence.  In addition to electronic, aerospace, communication, space technology, computer and data processing situations, the medical field has found "significant demand for "clean rooms" for surgical purposes for orthopedic surgery and other types of operations.

   A Hepa filter efficiency is as good as 99.999% for particulates .3 microns in size and larger.  To understand what this means, one micron is about 1/25000 of an inch in size, which is really beyond our ordinary comprehension.  The following depiction graphically describes the size of a micron.

A.     A human hair is about 90 microns.  Let the following represent a 90 micron size.

B.     The human eye can see a 10 micron size particle.  Suppose for practical purposes, this 10 micron size particle was this size.

C.     A .3 micron particle then is this size in relation to the above size.

  Obviously, the Hepa filter is quite unique.  Its ability to stop particulates .3 microns in size and larger makes it a perfect filtering agent.  It will stop many viruses, and all bacteria, fungi, mold spores, yeast cells, pollen, all organic and inorganic particles and dust and it does so with remarkable efficiency.  A close inspection of the Hepa filter shows that it feels like paper.  Actually, it is now made of glass and cellulose fibers.

  There are various grades of Hepa filters; 65% efficiency, up to 95% and as high as 99.999% percent efficiency.  The ideal Hepa blower has a large volume at slow speeds with not too much pressure or noise.  If the blower has too much pressure, it could damage the Hepa or even blow the media out of its frame.  Hepa efficiency is actually governed by the blower pressure.  Too little pressure and the particulates will actually wander through the Hepa filter opening.  On the other hand, if there is too much pressure, the particulates will be forced through.  With the proper air pressure, the particulates vibrate and shake and this action causes the particulates against the Hepa material where they get stuck.

   There are two terms you might want to add to your repertoire; namely the Brownian Movement and Agglomeration. These terms are described below.

  Brownian Movement:  The vibration or shaking of particles.

  Agglomeration: Basically, this means that small particles have a static charge and when two particles collide, they often stick together.  The particles build up on the Hepa media by sticking together causing a "caking".  This cake actually becomes more filter.  This fact actually makes the Hepa filter improve in efficiency until finally no more air can pass through the cake.  At this point, the Hepa filter must be replaced.

  In most instances, Hepa filters can last a long time.   Even in the worst of conditions, Hepa filters will last at least six months.  There is actually no maintenance for a Hepa.  You shouldn't touch the glass and cellulose fibers since they are quite brittle and can crack.  We recommend that Ultimate-Aire units be operated continuously.  Starting and stopping of the device will eventually crack the Hepa media.  The secret to Hepa filter life is in keeping the primary filter clean and changing the filter regularly.  Even though primary filters have a comparatively low efficiency rating, they do trap larger particles, aerosols, lacquer and greasy particles, which could clog the Hepa filter.  The primary filter should be changed regularly and the frequency will depend on the ambient condition of the area where the purifier is installed.  A visual inspection will indicate if weekly, bi weekly or monthly changes are required.  Obviously, when the primary filter is dirty, it's time to change.

  Hepa filtration answers the need for clean air.  The use of ultraviolet germicidal lamps with a Hepa filter is the best of both worlds.  Their synergistic reactions provide outstanding protection from contaminated air.

  Ultraviolet germicidal lamps produce energy which is emitted at 253.7 nanometers and this energy is lethal to micro-organisms if applied in sufficient quantity and exposure time.  All Fuller devices which contain the ultraviolet germicidal lamp cartridge, have been carefully designed and constructed to ensure the best micro-organism destruction ratio possible.  The ultraviolet chamber has been designed to hold, reflect and concentrate ultraviolet light and as the contaminated air passes through the chamber, the micro-organisms are actually destroyed.  The continuous cycling of ambient room air ensures a nearly bacteria free room air.

 For further information on ultraviolet germicidal light energy, we suggest reviewing Fuller Bulletins 66 and 82.   

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