This article looks at HEPA filters, the DOP testing procedures which are used to check them, and why the methodology has to be so stringent and precise.
This article is a three-minute read.
If you have ever been in an operating theatre or a research laboratory, then the chances are it was fitted with a ventilation system containing HEPA filters. These filters will usually be tested using a DOP procedure. Here we explain the two abbreviations and why it’s so important for the filter tests to be so rigorous.
DOP Tests for HEPA Filters from Tecomak Environmental Services
At Tecomak, we can offer DOP testing on an ad hoc basis or as part of a scheduled maintenance contract. We are equally experienced in carrying out the tests in cleanrooms, production facilities, operating theatres, isolation units or any laboratories where air quality is a prime consideration.
What is a DOP Test?
A Dispersed Oil Particulate (DOP) test uses a cloud of oil particles as an aerosol. A high concentration of this aerosol is released 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.
What is a HEPA Filter?
A High Efficiency Particulate Air (HEPA) device should remove solid particles such as dust, pollen, mould, and bacteria from the air in high-risk environments such as operating theatres, patient isolation units, cleanrooms and some pharmaceutical production facilities.
HEPA filters are superior to EPA (Efficient Particulate Air) filters because they capture a significantly higher percentage of airborne particles, including microscopic allergens, bacteria, and virus-carrying particles.
However, sometimes the HEPA filters can malfunction because of their age, their poor installation, or an inherent defect. Any failure on their part can put patients and staff at risk so it is essential that they are tested regularly and to a high standard. A DOP test is usually considered to be the most stringent and accurate safety process for the reasons outlined below.
It Targets Particular Particles
DOP tests are so accurate because they can detect the Most Penetrating Particle Size (MPPS) – the particle size that is most difficult for a filter to capture. For HEPA filters, this is typically around 0.3 microns, where a micron is equivalent to a thousandth of a millimetre.
Particles which are of a MPPS are small enough to follow airflow streams through the filter without being intercepted, but large enough to avoid the random motion (diffusion) that helps to capture even smaller particles.
It Measures the Whole System
DOP tests don’t just measure specific areas upstream of the filter – they can check other parts of the system as well. So if there are any leaks in the filter media, the seals, the gaskets or the housing frame, these should all show up on the test, which is carried out ‘in situ’.
It Uses Sensitive Technology
DOP tests use calibrated aerosol photometers to scan downstream of the filter. These instruments can detect incredibly small concentrations of particles, allowing them to pinpoint microscopic leaks.
The test requires a uniform, high-concentration aerosol spray on the upstream side (roughly 10–20 micrograms per litre), ensuring that every part of the filter face is challenged equally.
It Records Results Precisely
The testing procedures must adhere to strict protocols which define how to measure and interpret results to ensure consistency.
The test also provides a precise, numerical measurement of the penetration percentage, ensuring that if a filter fails (for instance, if it identifies 0.01% penetration), it is identified exactly.
DOP Testing from Tecomak Environmental Services
At Tecomark, we can carry out DOP testing on HEPA filters which are already in place or we can design and install a new filter system ourselves. If your system fails its test, then we will look to carry out any remedial action on the spot rather than come back for a second visit, potentially saving you time and money. We can also remove and dispose of any contaminated filters.
For more information about our DOP tests for HEPA filters, follow this link. You can also call us on 01732 852250 or complete the online form on the page above.
FAQs
Q: What regulations apply to DOP testing?
A: Key standards include ISO 14644-3:2005 (covering cleanroom testing), and BS EN 1822 (filter efficiency). If your HEPA filters fail their DOP test, then they will need to be replaced before the standards are met.
Other frameworks are provided by the Control of Substances Hazardous to Health (COSHH) regulations of 2002 (which protects employees at work) and Good Manufacturing Practice (where the testing is carried out in a production facility, usually for the pharmaceutical industry).
Q: How often should DOP tests on HEPA filters take place?
A: Testing should generally be carried out every six months to a year. Fixed, non-critical systems in cleanrooms typically require testing every six months to two years. Testing is mandatory upon initial installation, following filter replacement, or after any repairs.
Q: What other cleanroom services do Tecomak offer?
A: Apart from DOP testing, we can also design, install, maintain and validate cleanrooms, whether they are in a research lab, production facility or healthcare location. For more information click here.
