HEPA Filters

An integral part of any specialist ventilation system in an environment requiring dust and particle free air are the High Efficiency Particulate filters (HEPA). These filters require regular maintenance and validation to ensure that they operate as required as any blockage, leakage or air bypass could significantly compromise the effectiveness of the filtration system.

Dispersed Oil Particulate (DOP) testing is a crucial part of the validation of the HEPA filters to ensure that they are operating to the standards required. DOP testing involves releasing a high concentration of the aerosol into the airstream, upstream of the filter. Measurements are then taken to ensure that no leakage 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.

Our specialised and trained technicians follow highly specific and technical guidelines to ensure consistent and repeatable testing. HEPA filter testing should only be carried out by qualified technicians to avoid costly mistakes.

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 required pre and secondary filters will be removed. An 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. Using a photometer, upstream measurements of the aerosol concentration will be taken, 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 at suitable points.