Pollen
Plants release pollen grains as part of the plant reproductive process. Although pollen is not truly pathogenic, it can cause allergic reactions such as eye irritation, sinus inflammation, and asthma. Pollen grains are one
of the reproductive cells of plants. Because most pollen grains exceed
15 micrometers in size, it is quite easy to remove pollen from the air
with the right filtration media.
Dusts
Normally
dust is not considered a pathogen at moderate levels. It is comprised
of soil particles, soot and organic debris. However, dust particles can
serve as carriers and sources of nutrition for microorganisms.
Fungal Spores
Fungi
are a serious air pollution concern because they produce airborne
spores as part of the reproduction process. There are many hundreds of
organisms that are considered fungi and almost all of them are
considered allergens. A few fungi can cause serious infection or even death. Fungal spores can be broken down into two categories:
- Yeasts - Yeasts remain spherical during reproduction and form colonies of round cells.
- Molds - Molds reproduce by means of a "mycelium". The gray fuzzy clumps seen on decaying food are an example of mycelium.
Viruses
Viruses are so small (less than 0.1 micrometer) that filters do not reliably remove them from the air. The best filters for viral capture are HEPA filters but even they are not totally reliable.
Specific areas of the hospital and their respective filtration requirements as detailed in the Uniform Mechanical Code for hospitals:
-
Area 1 - Sensitive Health Care Rooms,
e.g., Operating rooms, nurseries, isolation rooms, delivery rooms,
intensive care rooms, recovery rooms, laboratory media preparation
rooms and recirculated central air systems serving other hospital areas.
Filtration Requirements:
Such
rooms are generally equipped with a minimum of 2 filter banks. Filter
bank #1 is located upstream of the conditioning equipment and should
have an average efficiency rating of at least 25%. The 2nd filter bank is located downstream of the supply fan and all cooling and humidification equipment and should have an average efficiency rating of at least 90%.
-
Area 2 - Central Air Conditioning Systems (any unit requiring ductwork on the supply or inlet side and serving more than one room).
Filtration Requirements:
Central
systems using 100% outdoor air and serving other than sensitive areas
shall be provided with after filters with an average efficiency of at
least 80% (Bank #2 downstream. Bank #1 shall be 25%).
-
Area 3: Laboratory Hoods
Filtration Requirements: Exhausts
from all laboratory hoods in which infectious or radioactive materials
are processed. Filters with 99% efficiency rating should be used to
capture 0.3 micrometer particle based upon the DOP (Dioctyl Phthalate)
test method. Frames should be dimensioned accurately and an airtight
seal is essential.
-
Area 4: Media transfer rooms Filtration Requirements:
Filters with 90% efficiency should be installed in air supply system at
the entrance to the media transfer room.
-
Area 5: Kitchen and Dining Rooms
Filtration Requirements:
Air
from the dining areas may be used to ventilate the food preparation
areas only after it has passed through a filter with 80% efficiency.
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