DOP & PAO Filter Integrity Testing

DOP originally referred to dioctyl phthalate, the aerosol substance historically used for filter testing.

The term “DOP test” remains common within industry, although modern integrity testing frequently uses PAO, Ondina or another suitable challenge aerosol instead.

PAO stands for polyalphaolefin.

PAO can be generated as an aerosol upstream of an installed filter so that a photometer can detect any penetration or leakage downstream.

COSHH Regulation 9 requires engineering controls used to control exposure to hazardous substances to be maintained and thoroughly examined and tested at suitable intervals.

Where a HEPA or ULPA filter is critical to the performance of that control, an integrity test may form part of the evidence needed to confirm that the system remains effective. The exact test method and frequency depend on the equipment, risk assessment, applicable standards and industry requirements.

They describe the same general type of aerosol-based filter integrity test, but DOP and PAO are not the same substance.

“DOP testing” is often used as the generic industry name for the method, while PAO is one of the aerosols commonly used during modern testing.

A DOP test is used to identify unacceptable leakage in an installed HEPA or ULPA filter system.

It can detect defects within the filter media and leakage around seals, gaskets, frames and housings that may allow contaminated air to bypass the filter.

A PAO filter integrity test introduces a controlled polyalphaolefin aerosol upstream of the filter and measures penetration downstream using a calibrated photometer.

The purpose is to confirm that the installed filtration system remains leak-tight and suitable for its intended application.

Filter integrity testing checks an installed filter system for localised leaks through the media, seals, gasket, frame or housing.

Filter efficiency testing determines the overall filtration performance or classification of a filter under a defined test method. An in-situ DOP or PAO test should not automatically be treated as a complete factory efficiency-classification test.

Velocity Safety tests installed HEPA and ULPA filters used in cleanrooms, LEV systems, negative pressure units, air scrubbers, spray booths, fume cupboards and suitable portable dust extraction equipment.

Testing feasibility depends on having an appropriate aerosol injection point, airflow conditions and safe downstream access.

Yes. We provide in-situ HEPA and ULPA filter integrity testing for cleanrooms and associated controlled environments.

The test method and acceptance criteria are agreed according to the facility, validation requirements and applicable standards, including BS EN ISO 14644-3 where relevant.

Yes. We test suitable H-Class vacuums, portable dust extractors, air scrubbers, negative pressure units and other mobile HEPA-filtered equipment.

The equipment must provide safe access for aerosol introduction and downstream measurement.

The required interval depends on the filter application, level of risk, manufacturer instructions, equipment history and applicable examination or validation programme.

Testing should also be considered after initial installation, filter replacement, repairs, relocation, suspected damage or an unexplained change in system performance.

The system normally needs to operate under controlled test conditions so that the challenge aerosol can pass through the filter and be measured downstream.

Parts of the process or surrounding work area may need to be isolated for safety, but the exact arrangement depends on the equipment and testing procedure.

The location and level of leakage will be recorded, and the affected system should not be assumed to provide its intended containment until the issue has been resolved.

Corrective work may involve reseating the filter, repairing or replacing seals, addressing housing leakage or replacing the filter. The system should then be re-tested before being returned to normal use.

The report may include the equipment and filter identification, test location, aerosol used, instrument details, upstream challenge concentration, downstream readings, leakage locations, acceptance criteria and overall result.

Any failures or remedial recommendations will also be clearly recorded.

Yes. Velocity Safety provides mobile DOP, PAO and HEPA filter integrity testing throughout the North West and across the wider UK.

We support cleanrooms, laboratories, healthcare sites, workshops, spray booths, construction projects and organisations managing filtered equipment across multiple locations.

Yes. Where the filter forms part of a local exhaust ventilation system, integrity testing can often be coordinated with the system’s LEV thorough examination and test.

Combining the work can reduce repeat site access and provide a clearer assessment of the extraction system and its filtration performance.