DOP Testing: HEPA Filter Integrity

What is DOP Testing?

A DOP test is the procedure used to test the effectiveness of a HEPA (High Efficiency Particulate Air) filter. A HEPA filter is the device used to remove solid particle such as dust, mold, pollen from the air. HEPA filters are used in hospitals, cleanrooms., laboratories, optical and pharmaceutical production.

DOP: Let's go in Depth

DOP (Dispersed Oil Particulate) or Dioctyl Phthalate is a liquid chemical which produces mono or poly dispersed test aerosol of submicron particles.

In DOP testing, an aerosol generator is used to convert DOP oil into aerosol with particle sized down to 0.3 micron and released into in the upstream flow of the filter media. The downstream flow is measured using a photometer that will detect particles down to 0.3 microns in diameter. These measurements are taken to ensure that no leakage has occurred, either through the filter, gasket or through its casing.

DOP Testing Regulations and Guidelines

According to Alberta Asbestos Abatement Manual, employers must assess the effectiveness of HEPA filters by DOP testing or similar means. HEPA filters must be tested at least every 30 days, or more frequently when in operation and at least annually when not in operation. Moreover, the test must be performed when a filter is replaced in a HEPA filter vacuum cleaner or ventilation unit, or on site prior to the start of work before a negative air ventilation system begins to filter the contaminated air.

Along with DOP testing, the equipment must be visually inspected for any major deficiencies such as; cracked frame, holes from screws or rivets, damage to controls, etc. It is also crucial to make sure the equipment is operating correctly.

DOP Documentation

The equipment passing the DOP test should be labeled correctly. As well, the documentation for a DOP test should include the certificate of testing (the paper copy documentation) and certificate label (the sticker that is attached to tested equipment).

A DOP certificate should include all information such as testing company name and contact information, certificate or test number, date of testing, technician name and signature, equipment owner company and contact information, equipment make/model/serial number and if there is any damage to the equipment.

The certificate should include the test efficiency rating (e.g. 99.97%) and test result (pass or fail).

What Happens if the Test Fails?

If the equipment fails the DOP testing then no labeling is required, and the supervisor should be reported to regarding all the deficiencies. These deficiencies may be fixed on-site, and the unit can be re-tested. The unit may be fixed, but no direct repair to the filter should be done. Instead, a new filter may be installed.

DOP testing of negative air units, vacuums and any other HEPA filtered equipment used on abatement projects shall be completed in accordance with the Alberta Asbestos Abatement Manual “DOP/PAO Testing Guideline”, 2019 or a similar standard.


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