Tecomak is a specialist supplier of HEPA and ULPA filters used in ventilation systems. We offer the following main services:

  • On site DOP testing and Validation of HEPA filters
  • Preparing design specifications for new filter systems
  • Supply and installation of new HEPA filters
  • Removal and disposal of contaminated HEPA filters
  • Filter management services (storage and routine replacement)

HEPA (High Efficiency Particulate Air) filters are devices which remove solid particles such as dust, pollen, mold, and bacteria from the air. They are used to remove ultrafine dust, aerosols and viable organisms. Applications are commonly found within hospitals (operating theatres, patient isolation rooms), cleanrooms and laboratories but also for micro-electronic, optical and pharmaceutical production.

EN 1822 Filter Classification Standard

The European standard EN 1822: 2009 has been published as a British Standard for the UK as BS EN 1822-1: 2009. This standard describes the factory testing of filtration properties based on the retention efficiency at the most penetrative particle size (MPPS) as shown in the table below:

Leaks are specified as maximum allowable local penetration at the MPPS and must not exceed 5 x the overall penetration. U17 is an exception to the rule; in this case local penetration must not exceed 20 x the overall penetration value.



Efficiency (%) at the MPPS


Common Uses

retention (total)

retention (local)

EPA Filters

(Efficiency Particulate Air Filters)

These filters do not require verification of local penetration


> 85%

EPA Filters

(Efficiency Particulate Air Filters)

These filters do not require verification of local penetration

Removal of airborne pollutants in critical ventilation systems.

Lowest grade filter that can be fitted to Ultra-Clean Operating Theatres


> 95%

Domestic vacuum cleaners outlet filters


> 99.5%

Air intakes to vehicle engines

HEPA Filters

(High Efficiency Particulate Air Filters)


> 99.95%

> 99.75%

HEPA Filters

(High Efficiency Particulate Air Filters)

Final filter for dust extract systems


> 99.995%

> 99.975%

GMP cleanroom supply systems

Any system that requires on site DOP testing with a maximum penetration of 0.01%

ULPA Filters

(Ultra Low Penetration Air Filters)


> 99.9995%

> 99.9975%

ULPA Filters

(Ultra Low Penetration Air Filters)

Final filter for GMP Grade A cleanroom zones


> 99.99995%

> 99.99975%

Air supply systems in the Microelectronic cleanroom production facilities


> 99.999995%

> 99.9999%

Filter Maintenance & Testing

An integral part of your specialist ventilation system, high efficiency particulate air (HEPA) filters require regular maintenance and validation, and DOP testing plays an essential role in this. HEPA filter testing forms a part of the regulatory requirements for operations relying on specialist ventilation, and needs to be carried out in a consistent way by experts to ensure reliability.

Tecomak carry out DOP (dispersed oil particulate) filter testing to industry standards to ensure clean rooms and other specialist or critical environments are operating to the highest standards.

DOP Filter Testing – Tecomak provides DOP filter testing for all types of specialist ventilation systems.

What is DOP Filter Testing?

Within your specialist ventilation system, your high efficiency particulate air (HEPA) filter works to remove fine powder and dust from the environment, providing particulate free, clean air in its place. A DOP HEPA test is used to determine whether these filters are performing to the standards deemed acceptable by your regulatory bodies, keeping your operations running smoothly.

Using a cloud of dispersed oil particulate as an aerosol, DOP testing involves releasing a high concentration of the aerosol into the airstream, upstream of the filter. Measurements will then be taken to ensure that no seepage has occurred, either through the filter itself, or through its casing.

Filter integrity testing provides assurances for all parts of the filter, including the seals, the housing of the filter, and the joints onto the duct work itself. During the test, a check is also made to ensure that all of the air within the clean room is passing successfully through the filter, ensuring there are no dead spots where contamination can build up.

Involving highly specific and technical guidelines to ensure consistent testing, as well as being a part of your regulatory obligations, the HEPA filter testing for your specialist ventilation system should be carried out by professionally qualified engineers to avoid costly mistakes.

As well as having the correct equipment, and the training to use it, to carry out the task effectively your DOP filter tester will require a full understanding of BS EN ISO 14644-3 (B.6), PD6609:2007, current Good Manufacturing Practice (GMP) and a sufficient level of experience to be able to problem solve any leakages identified.

How is DOP Testing Carried Out?

DOP HEPA testing is carried out following a predetermined and compliant procedure.

After inspecting the air supply system a smoke injection point will be located and a safe means of injection ascertained. If pre and secondary filters need to be removed, power to the AHU will be isolated before the filter removal. If the DOP is to be injected downstream of the fan unit or in a positive pressure section of ductwork a blower pump will be set up adjacent to the injection point.

Following this we will position the aerosol generator adjacent to the blower pump and power up the generator to warm up. If extension leads are required, we will ensure any trailing cables are secured and do not present tripping hazards.

The aerosol photometer will be set up in accordance with the filter manufacturer’s instructions and attached to sample points, fitted upstream of each HEPA filter under test.

Normally working in pairs the lead engineer operating the photometer will maintain regular communication with the support engineer controlling the smoke generator by means of site radio or mobile phones.

Using a photometer, the lead engineer will measure upstream concentration of aerosol, calibrating as required. The DOP may need to be increased or decreased.

Downstream penetration of aerosol will then be measured using a photometer, scanning the filter face with overlapping strokes at a speed no greater than 5cm/s. The ISO 14644 Part 3 standard permits a maximum downstream limit of 0.01% penetration.

Filter differential pressures and airflow volume will be measured using a micro manometer and an anemometer or balometer at suitable points.

All DOP test results for HEPA filters are recorded on raw data sheets which are included with test reports for traceability.

The DOP Filter Testing Service From Tecomak

At Tecomak we have a wealth of experience testing all grades of cleanroom facility. For GMP facilities, this includes Grade A areas for high risk operations, such as the filling zone, stopper bowls, open ampoules and vials, making aseptic connections, those carrying out aseptic preparation and filling.

Carried out either as a part of your routine clean room validation or ad hoc when you need it, we carry most types of air filters and spares for them in case of a DOP test failure. When working with you under contract we keep detailed records of all of your assets and carry a full set of replacement HEPA filters ensuring fast replacement and restoration of your operations, even in event of a failure.

And ensuring your down time is kept to its absolute minimum, our test reports can be written, quality checked and printed for approval, all before leaving your site.

DOP Filter Testing – Tecomak are professional engineers qualified for all of your DOP filter testing requirements.