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The biological contaminants

 

The biological contaminants, also called aerobiocontaminants, are micro-organisms, viruses and the organic substances, like pollens and enzymes, that can have allergenic properties

 

Micro-organisms can be divided in 3 families:

 

Family

Smallest size

 

Bacteria

0.5 µm

 

Fungi

 

4µm

Yeasts

4µm

 

Micro-organisms suspended in the air, called “airborne” micro-organisms”,  are mainly adsorbed on or in a solid particles but can also be entrapped in fine water droplets, called water aerosols.

 

The first action to abate airborne micro-organisms is to separate the particles that can act as carrier for them. These “carrier” particles have a diameter larger than 0.5µm. It is the reason why clean rooms are classified according to the concentration of those particles:

 

Clean Room

 

ISO class

 Old classification

(particles > 0.5 μm / ft3)

 

New classification

(particles > 0.5 μm / m3)

 

5

100

3,520

 

6

 

1000

 

35,200

 

7

 

10,000

 

352,000

 

8

 

100,000

 

3,520,000

 

The second action is to abate the micro-organisms entrapped in aerosols, either
  • by physically separating them via a mechanical action, for instance via ahigh centrifugal force, or
  • by killing them with oxidizing agents

Water peroxide, ozone and free radicals are efficient but cannot be released in the room. The only process efficient but non dangerous, and even healthy for the man is to use a high concentration of negative air ions and a micro-concentration ozone, which is the natural air purification process of the earth, generated by flashes of lightning (see Air Purification).

 

Viruses and allergens like pollen and enzyme powders have a submicronic size. The most efficient way to abate those submicronic substances is to ionize the air, in order to promote their adsorption on larger carriers that can be easier separated.

 

Impact on the Air Purification or Conditioning Concept

 

Classical Air Purification & Conditioning Systems integrate as prefilters a couple of mechanical filters (1) that can easily entrap the micro-organism carriers. Those micro-organisms are going to growth in those filters, to pass through them and to contaminate the whole system and the whole air duct network on its downstream side. This problem is more critical in Air Conditioning Systems because the micro-organisms start growing in the cooling battery where water condensates, If the end of the duct is not protected by an absolute filter (HEPA filter) those micro-organisms are released in the room, consequently quickly spreading infections and diseases. This problem becomes even more critical in presence of high air humidity.
 
 

Another problem is that, once dead, the micro-organisms may release dangerous endotoxins.  This situation can have some dramatic consequences on human health, particularly in hospitals, a phenomenon called nosocomial infection.

 

In order to prevent this problem in any air purification or conditioning system, it is essential that this system:

 

 

Appropriate

Technology

 

=> efficiently separates particles down to 0.5µm, without mechanical filters and, if possible, without pressure drop increase

 
Electrofiltration,

Cyclonic heat exchanger

 

=> integrates an oxidizing process in order to kill the free micro-organisms and to prevent any development in the purification process and in the downstream ducts

Generators of negative air ions
& a micro-concentration ozone

 

 

© 2008 Air Quality Concept