1. WHY FILTER THE AIR

Interior and exterior air are polluted by particles, molecules and bio-contaminants. These pollutions can be of natural, industrial or human origin.

2. FILTRATION MECHANISMS

Filtration on filter media is the result of four effects:

Sieve effect
Inertia effect
Interception effect
Diffusion effect

3. CATEGORIES OF FILTERS

There are four main categories of filters:

Medium efficiency filters:
Large filters for particles < 5µ

High efficiency filters:
Fine filters effective for atmospheric aerosols

Very high efficiency filters:
“Absolute” HEPA and ULPA filters, for the most demanding applications in terms of air clarity (clean rooms)

Molecular filters:
Filters for the elimination of gases

4. FILTERS CLASSIFICATION

Medium efficiency filters
Class Average Gravimetric Efficiency (Am) %.
G1 50 ≤ Am ≤ 65
G2 65 ≤ Am ≤ 80
G3 80 ≤ Am ≤ 90
G4 90 ≤ Am

High efficiency filters
Class Average efficiency.
F5 40 ≤ Em ≤ 60
F6 60 ≤ Em ≤ 80
F7 80 ≤ Em ≤ 90
F8 90 ≤ Em ≤ 95
F9 95 ≤ Em

Very high efficiency filters
Class Global value Local value:
Penetration Efficiency
H10 85 15 —
H11 95 5 —
H12 99,5 0,5 —
H13 99,95 0,05 99,75 0,25
H14 99,995 0,005 99,975 0,025
U15 99,999 5 0,000 5 99,997 5 0,002 5
U16 99,999 95 0,000 05 99,999 75 0,000 25
U17 99,999 995 0,000 005 99,999 9 0,000 1