EN 779 classified filters by average arrestance against a synthetic dust, producing the familiar G4, F7, F9 designations. The problem was that two filters with identical F-class ratings could perform very differently against the particle sizes that matter to human health and to process equipment.
What ISO 16890 measures
The current standard reports efficiency against three real particulate fractions — ePM1, ePM2.5 and ePM10 — corresponding to the particle size groupings used in air quality regulation worldwide.
A filter is classified in a group only if it achieves at least 50% efficiency for that fraction, and the reported value is rounded down in 5% steps. The result is a specification that says something concrete: ePM1 70% means the filter removes 70% of particles below 1 µm.
Why this changes purchasing
Under the old standard, a filter could achieve F7 through good performance on large particles while performing poorly on the sub-micron fraction that reaches deep into lungs and coats turbine blades.
Under ISO 16890, that filter reports a low ePM1 value and the deficiency is visible on the datasheet. For any application where fine particulate is the concern — turbine intakes, cleanroom pre-filtration, occupied-space HVAC — ePM1 is the number to specify against.
Practical specification guidance
A reasonable starting point for common applications:
- General HVAC pre-filtration: ISO Coarse 60% or ePM10 50%
- Occupied commercial space final filtration: ePM1 60% to 70%
- Gas turbine intake final stage: ePM1 80% or higher, or EPA class E10 to E12
- Cleanroom pre-filtration ahead of HEPA: ePM1 70% to 80%
- Pharmaceutical and food process air: ePM1 80% plus terminal HEPA H13 or H14