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Air Filters In Hospital Critical Care Areas

Hospitals have a variety of air filter needs depending on the purpose of any one area or room.  Areas of special concern are critical care areas where various pollutants and contaminants must be controlled or eliminated as much as possible from the airflow.  These areas include the areas where surgery is performed, where babies are delivered and care for, where patients recover, etc.  It is critical that pollutants and contaminants be removed for the well-being and health of patients.

In these critical care areas, air filters should be located on both sides of the air conditioning equipment, in other words, upstream and downstream of the air conditioning equipment.  The air filters upstream of the equipment must have an average efficiency of 30% or better.  On the other hand, the air filters downstream of the supply blower must have an efficiency of 90% or better.  One type of air filter recommended for this purpose is a high efficiency synthetic and glass micro fiber rigid extended surface air filter.

Some of the pollutants and contaminants to be filtered are; Bacteria, Fungi, Pollen, and of course dust.  Along with those already mentioned, there are many more pollutants and contaminants that must be removed from the airflow in order to have a safe, healthy environment for patients.

Once high efficiency air filters are in place, they must be inspected on a regular basis.  A visual inspection should be made to make sure that the filtering media is not torn, and the integrity of the air filter frame is intact.  This evaluation should be performed with the blower running, as well as with the blower idle.  

To keep the filtration at optimum efficiency, the air filters must be replaced and/or cleaned periodically, as per manufacturer specifications.  Records should be maintained of inspections, replacements, pressure drop, and the types of air filters installed.

Finally, depending on the use of the critical care area, it may be desirable to remove VOC’s (volatile organic compounds) from the area.  VOC’s are gases that are released from certain liquids and solids found throughout hospital buildings, such as, building materials, plastics, solvents, etc.   The list of solids and liquids that emit VOC’s is nearly limitless.

A HEPA (high efficiency particulate arresting) air filter will not remove VOC’s.    For this job, a high capacity gas phase absorber air filter is needed.  These are air filters that incorporate charcoal and/or potassium permanganate as the filtering media.  These air filters are very effective in absorbing hundreds, if not thousands of gases.  When the air filter becomes saturated, it is removed and replaced with a new air filter.

See table below:


Some contaminants listed in the table use specific chemical compounds, some represent classes of components, and others are mixtures of variable composition.  Activated charcoal's capacity for odors varies somewhat with the concentration of air, humidity, temperature, and with the actual velocity used through the filters.  The numbers given represent typical or average conditions and might vary in specific instances.  The values in the table have been assembled from many sources including laboratory tests and field experience.  In cases where numerical values were not available, the author has listed his opinion of the probable capacity based on general experience.  This table should be used as a general rule only.  The capacity index has the following meaning:

4. High capacity for all materials in this category.  One pound takes up about 20% to 50% of it's own weight-average about 1/3 (33 1/3%).  This category includes most of the odor causing substances.
3. Satisfactory capacity for all items in this category.  These constitute good applications but the capacity is not as high as for category four.  Absorbs about 10% to 25% of it's weight-average about 16.7%.
2. Includes substances which are not highly absorbed but which might be taken up sufficiently to give good service under the particular conditions of operation.  These require individual checking.
Absorption capacity is low for these materials.  Activated charcoal cannot be satisfactorily used to remove them under ordinary circumstances.

  Acetaldehyde 2
  Acetic Acid 4
  Acetic Anhydride 4
  Acetone 4
* Acetylene 1
* Acrolein 3
  Acrylic Acid 4
  Acrylonitrile 4
  Adhesives 4
  Air-wick 4
  Alcoholic Beverages 4
* Alines 2
* Amonia 2
  Amyl acetate 4
  Amyl alcohol 4
  Amyl ether 4
  Animal odors 3
  Anesthetics 3
  Aniline 4
  Antiseptics 4
  Asphalt fumes 4
  Automobile exhaust 3
  Bathroom smells 4
  Benzene 4
* Bleaching solutions 3
  Body odors 4
  Borane 3
  Bromine 4
  Burned flesh 4
  Burned food 4
  Burning fats 4
  Butadiene 3
  Butane 2
  Butanone 4
  Butyl acetate 4
  Butyl alcohol 4
  Butyl cellosole 4