What is a HEPA filter?
‘What is a HEPA filter’ is a commonly asked question.
A HEPA (High-Efficiency Particulate Air) filter is a specialised air filter designed to remove at least 99.97% of airborne particles as small as 0.3 microns. These filters are essential in environments where clean, particle-free air is critical, including healthcare, laboratories, cleanrooms, homes, transport, and highly controlled industrial spaces.
HEPA filters are made from a dense mat of randomly arranged fibres (often fibreglass) and trap contaminants such as dust, allergens, bacteria, and even some viruses. To be classified as a true HEPA filter, it must meet strict industry efficiency standards (e.g., EN1822 or ISO 29463).
How Do HEPA Filters Work?
HEPA filters use a combination of three mechanisms to capture particles:
- Diffusion: Tiny particles collide with gas molecules and are effectively slowed down, increasing the chances of being caught by the fibres.
- Interception: Particles that follow a streamline in the air flow come within one radius of a fibre and stick to it.
- Inertial Impaction: Larger particles cannot follow the curved contours of the air stream and are forced to embed in one of the fibres directly.
Why 0.3 Microns?
The 0.3-micron particle size is known as the Most Penetrating Particle Size (MPPS) — the hardest size for filters to capture.
If a filter can remove 99.97% of 0.3-micron particles, it will be even more effective at capturing both larger and smaller particles via the three mechanisms above.
Where are HEPA Filters Used?
To help answer the question of what is a HEPA filter, it is important to understand where the HEPA filters are used. HEPA filters are used in a variety of settings where clean air is critical. Here are some examples:
- Healthcare Facilities: Hospitals and clinical areas use HEPA filters to maintain clean air in operating rooms, isolation rooms, and laboratories, reducing the risk of airborne infections.
- Residential Use: Many home air purifiers and HVAC systems are equipped with HEPA filters to improve indoor air quality by trapping allergens, dust, pet dander, and other contaminants.
- Industrial Settings: Industries such as pharmaceuticals, biotechnology, and food processing use HEPA filters in clean rooms to ensure a contaminant-free environment for production processes.
- Aerospace and Transportation: HEPA filters are used in aircraft cabins to maintain air quality and reduce the spread of airborne pathogens among passengers.
- Laboratories: Research labs, especially those dealing with hazardous materials or requiring a sterile environment, rely on HEPA filters in laminar flow cabinets and fume hoods.
- Vacuum Cleaners: High-end vacuum cleaners use HEPA filters to capture fine dust and allergens, preventing them from being recirculated into the air.
- Data Centres: To protect sensitive electronic equipment from dust and other particulate matter, HEPA filters are often used in the HVAC systems of data centres.
- Research & Medical Laboratories – Laminar flow cabinets, biosafety cabinets, and fume hoods rely on HEPA filtration to maintain sterility and operator safety.
How Often Should HEPA Filters Be Replaced?
The replacement interval for HEPA filters depends on several factors, including:
- The operating environment (cleanroom vs. office vs. healthcare)
- Airflow volume and duty cycle
- Particle or contamination load
- Manufacturer recommendations
Typical practice is 6–12 months for high-demand or critical environments, and 1–3 years where contamination risk is low and performance remains stable. However, filters should be replaced early if:
- Differential pressure exceeds design limits
- Physical damage or seal leakage is detected
- Microbial growth or moisture contamination occurs
- Certification scan testing fails (e.g. PAO/DOP test)
Ultimately, a regular HEPA Filter Integrity Test remains the most reliable way to confirm whether a filter is still performing as intended and safe to remain in service.
What Is HEPA Filter Integrity Testing?
- HEPA integrity testing verifies that:
- The filter is installed correctly
- No leaks are present
- Efficiency meets the required standard
- The system maintains cleanroom-class air quality
RJ Urmson Commissioning Engineers Ltd provides full HEPA filter integrity testing, including DOP/PAO testing in accordance with ISO and EN standards.
HEPA Filter FAQ and Summary
HEPA filters are essential in various applications where high air quality is paramount.
From healthcare to homes, these filters play a critical role in trapping potentially harmful particles, thereby protecting health and ensuring safe, clean environments.
At RJ Urmson Commissioning Engineers Ltd we offer a full range of HEPA filters suitable for air filtration in a wide range of applications including clean rooms, research and medical laboratories, pharmaceutical establishments, electro technology and micro technology sites.
What is a HEPA filter?
A HEPA filter is a high-efficiency air filter that captures 99.97% of particles down to 0.3 microns.
Are HEPA filters better than standard filters?
Yes, they are far more effective, particularly in medical, laboratory, and controlled environments.
Do HEPA filters remove viruses?
Yes, many viruses attach to larger particles, and HEPA mechanisms can capture them.
How often should HEPA filters be replaced?
Typically every 6–12 months in critical environments, depending on contamination levels.
What is HEPA integrity testing?
A certified testing process ensuring the filter is leak-free and performing to required standards.
Find out more about HEPA Filters
For more information on how we can help with HEPA filter replacements, visit our HEPA Filter Integrity Testing Page or get in touch with the team directly by completing our contact form or calling on 01257 262683.
