Selecting Filters

Selecting the proper filter for your application.

Airfiltronix fume hoods and fume/particle extraction devices are designed to accept a series of filters including aluminum or dacron prefilters, HEPA particulate filters, activated carbon or specially treated carbon for organics, ammonia, acid gases, formaldehyde, radioactive iodine and mercury.

Proper filtration is a combination of two factors. The first is matching the filter medium to the pollutant. This is accomplished through the use of material safety data sheets and any other means available for identifying the precise nature of the pollutant. The second involves determining the capacity of the filter as it relates to the amount of pollutant it will be exposed to. This is more complicated. However, with proper information this can be done with reasonable accuracy. Ideally, we would expect filters to function for about two months or more to consider an application feasible. The range could be from one month to one year depending on conditions and frequency of use. HEPA filters, when properly applied, typically last from six to twelve months. They are generally used in conjunction with a pre-filter to extend the life of the HEPA filter. The average life expectancy for carbon filters is four to six months. This is based solely on our statistical average and is never implied as a guarantee. Each situation should be evaluated and our application engineers will offer an "expected range" of filter life. Customers should implement a regular monitoring program to test the system's effectiveness.

Activated Carbon: Steam activated charcoal or coconut shell carbon is effective in adsorbing most commonly found organic vapors and odors. It can adsorb up to 50% of its own weight in some cases with the average being 33 1/3%. Standard activated carbon does not have much capacity for some reactive gases. Where gases are chemically reactive, specially impregnated carbon can be recommended.

Specialty Carbon: These are treated carbons that combine a chemical reaction with carbon's adsorption capacity. Compounds are broken down into their various elements for easy adsorption. Common types are treated to adsorb ammonia, formaldehyde, radioactive iodine, etc.. If you have a special application, please call us to discuss your particular needs.

HEPA Filters: High Efficiency Particulate Arrester filters were originally developed by the military for nuclear particle filtration. HEPA filters will capture particles at 99.99% efficiency - down to 0.3 microns or greater. HEPA filters are an effective way to capture particulates of smoke, dust, asbestos, actinolite, bacteria and other pathogens, radioactive dust and mold spores. Each filter is individually tested for efficiency.

ULPA Filters: Available upon request. They achieve higher filtration levels than a HEPA at smaller particle sizes.

Prefilters: Two types of prefilters are used when pollutants will be present in large enough quantities to rapidly clog HEPA or carbon filters on any fume hood.
1. Dacron Filters are 4 ply with decreasing pore sizes for each ply. They are rated at 60% efficient for particles of 5 microns or larger. As such, they will remove most gross particulates, saving the HEPA for only the smallest particles. They are also used with carbon when the environment is dusty enough to reduce carbon filter effectiveness or as an after filter to contain possible carbon particle emission.
2. Aluminum Prefilters will remain cool in moving air and their large surface area makes them ideal condensation media for airborne greases and mists, such as solder flux. These filters will also extend the life of more expensive carbon and HEPA filters by removing gross contaminants before they can reach sensitive filter surfaces.

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