DOP-Test© Karl Bleymehl GmbH, Inden-Pier

The standard for determining the retention efficiency of HEPA filters.

The filter is challenged with a DOP aerosol of a defined particle size of 0,3 µm. A comparison is made of the number of particles counted in front of and behind the filter. In order to obtain reliable results, the filter must be challenged with a defined and sufficiently large number of particles!


Testing of HEPA filters mounted in equipment. Determination of the retention efficiency and the intergity of the filter, the air-tight seating of the filter and detection of leaks. This is also required by the American Health Department FDA.
The method is in accordance with

  • the GMP and PIC guidelines
  • DIN EN 12 469, Annex D
  • the FDA requirements for the DOP test
  • suitable for large aeration units up to 100.000 m³/h.



Laminar-Flow equipment usually is used in an environment with low particulate background contamination of 10,000 - 100,000 particles / 28 litres of air (Cl. 10,000 - 100,000 of the US-Fed. Standard 209e). The HEPA filters Class H 14 (earlier class S) have a retention efficiency of 99.999 % with regard to particles of Ø 0,3 µm. With class 100 of the US Federal Standard 209e, no more than 100 Particles of Ø 0,5 mm in 28 liters of air may pass the filter.

For example:

Qualification of LF Equipment

With the help of this test it is possible to determine the correct function of Laminar-Flow equipment.

  • to determine the retention efficiency of the filter
  • to test the integrity of the filter
  • to check the tightness of filter seating and leak-free construction

For this test, an aerosol generator and a suitable measurement system with a measurement range covering 5 - 6 log units are needed.
Photometers or a combination of particle counters with diluters are suitable. The combination of particle counters and diluters is more laborious to use than a photometer, but allows measurements to be made on Laminar-Flow equipment with air flow rates of up to 100.000 m³/h.
With Laminar-Flow equipment functioning with a high proportion of recirculated air, its only possible to assess the condition of the equipment with this method.

DOP = DiOctylPhthalate pfeilgruen comparable results are also obtainable with paraffin oil, DAB quality

Cl. 100.000 in the 
surrounding air.
Measured value:
99.999 %
Particles in front of the filter
Particles behind the filter
It is impossible to determine the retention
efficiency of the HEPA with such a low number
of particles.