This article takes an in depth look at HEPA filters and their use.
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HEPA filters are advanced air filtration devices engineered to capture extremely fine particles, down to one micron (µ), or one-millionth of a meter. These filters are vital components of air purifiers as they meet stringent standards for removing pollutants. The term HEPA translates to High Efficiency Particulate Air, identifying a benchmark for air filtration systems that successfully remove even the tiniest of particles.
For a filter to be considered a HEPA filter, it must successfully capture at least 99.9% of airborne particles, including those as small as 0.3 micrometers. These filters are adept at removing various types of contaminants such as dust mites, pet dander, pollen, smoke, mold spores, and numerous other microscopic pollutants invisible to the naked eye.
A HEPA filter system channels air through a tightly woven mesh of fine fibers, which trap harmful particles. This intricate mesh, consisting of thousands of delicate fibers, effectively captures even the smallest pollutants. Although all HEPA filters adhere to a specific standard, multiple classifications exist to signify different degrees of filtration efficiency.
When talking about HEPA filters, it's crucial to differentiate between “True HEPA� filters and those labeled as “HEPA Like,� “HEPA Type,� or “HEPA Style.� A filter must remove 99.97% of airborne particles as small as 0.3 microns to be considered a True HEPA filter. This rigorous standard for air filtration, set by the Environmental Protection Agency (EPA) and adopted by other governing bodies, ensures the highest level of air purification typically used in medical, laboratory, cleanroom, and residential applications. The EPA utilizes a grading scale ranging from “A� (least effective) to “E� (most effective), based on military and industrial filtration standards.
HEPA filters act as advanced air filtration media, functioning similarly to strainers or sieves but with a much more complex design that effectively captures and retains extremely small airborne particulates and pollutants, including allergens, dust mites, mold spores, fine dust, pet dander, smoke particles, and certain bacteria and viruses commonly found in indoor air.
True HEPA filtration works through four key mechanisms—impaction, interception, diffusion, and electrostatic attraction—ensuring particle removal across a range of sizes. Larger particles are initially filtered out, while finer and ultrafine particles are progressively trapped as air passes through the filter’s multi-layered fibers. This sophisticated process is crucial for maintaining indoor air quality (IAQ), reducing exposure to harmful airborne contaminants, and promoting respiratory health. The overall efficiency of the HEPA filter can be illustrated with the diagram provided below.
When particles with a diameter of 1.0 ÎĽm or greater (such as pollen, dust, and some mold spores) enter a HEPA filter, they collide with the filter's dense matrix of fibers and are too large to pass through. This mechanism, known as inertial impaction, efficiently captures most large airborne contaminants and particulate matter.
To extend the service life of a HEPA filter and improve overall system performance, most quality air purifiers and ventilation units include a prefilter to intercept these larger particles before the air reaches the HEPA media. While 1.0 ÎĽm particles are considered large in the context of HEPA filtration, they are still incredibly tiny compared to visible objects like human hair or grains of sand. The visual below helps contextualize particle sizes and the comparative effectiveness of HEPA filters in removing microscopic pollutants:
Following inertial impaction, particles sized between 0.3 ÎĽm and 1 ÎĽm (such as fine dust, some bacteria, and certain smoke particles) encounter the interception stage of the filter. As these minute particulates travel through the filter along with the airstream, they attempt to navigate the maze of fibers but are unable to bypass them due to their physical size and inertia, becoming trapped by direct contact with the filter media.
During this critical interception phase, particles as small as 0.1 μm adhere to the filter’s fibers and are retained, contributing to the filter’s high efficiency in capturing hazardous airborne material. This property makes HEPA filters highly valuable in environments requiring precise contamination control, such as hospitals, cleanroom facilities, schools, and even HVAC systems in modern homes.
As filter loading increases and more contaminants are trapped, the HEPA filter’s airflow resistance will also rise, necessitating regular filter replacement or maintenance schedules. Unlike the inertial impaction stage, which is protected by a pre-filter, the interception stage relies solely on the main filter media for particle capture.
At this phase of the HEPA filtration process, particles become so minuscule—typically under 0.1 μm—that they have negligible mass and move erratically in a zigzag, random pattern. This phenomenon, known as Brownian motion, results from constant collisions of these microscopic particles with gas molecules in the air.
Despite their tiny size, HEPA filters are meticulously engineered to address Brownian motion, ensuring that ultrafine particulate matter such as smoke, viruses, volatile organic compounds (VOCs), and combustion byproducts are controlled. Advanced modeling and rigorous testing confirm that HEPA air filters remain effective at removing even the smallest airborne pathogens and contaminants using a combination of both mechanical and electrostatic forces.
These submicron and nanoparticles (as small as 0.1 μm) enter the diffusion section of the HEPA filter, where fibers are arranged in a non-linear, random orientation. As these ultrafine particles experience Brownian motion and collide repeatedly with each other, they lose kinetic energy and are more likely to contact and bind to the filter fibers—a phenomenon sometimes called diffusive deposition.
Very small particles—such as smoke, odors, chemical fumes, and industrial pollutants—often carry an electrostatic charge. The fine glass or synthetic fibers used in modern HEPA filter media also maintain an electrostatic charge. This creates an attractive force between opposite charges, which enhances the filter’s ability to trap and retain the most elusive airborne particles.
The synergy of these five mechanisms enables True HEPA filters to provide superior particulate removal that meets strict industry and regulatory standards for indoor air purification. The following diagram summarizes the main stages of the HEPA filtration process.
A HEPA filtration system inevitably causes a pressure drop in airflow because the dense network of filter fibers restricts movement of air while maximizing particle capture. The magnitude of this pressure drop depends on variables including HEPA filter grade, filter media composition, thickness, system design, pre-filter integration, and air handler (fan) power. Typical industrial and commercial HEPA filters are engineered to maintain efficient airflow—up to 250 feet per minute (FPM) or more—while minimizing energy loss and mechanical wear over time.
Performance and longevity are linked: as a HEPA filter captures increasing quantities of particulate pollutants, its resistance to airflow increases, causing a more significant pressure drop. If this is allowed to continue unchecked, energy costs rise, overall air quality drops, and strain on HVAC or air purification equipment increases. For optimal system performance and maximum indoor air quality, HEPA filters must be inspected routinely and replaced according to manufacturer guidelines based on airflow measurements, filter condition, and usage environment.
If you are choosing between HEPA filter models or air cleaners, consider pressure drop ratings, filter lifespan, certified removal efficiency, and the specific indoor air quality requirements of your space. Seeking expert consultation from reputable HEPA filter suppliers or HVAC professionals can ensure your selection meets both health and regulatory standards.
HEPA filters are used extensively in diverse settings to enhance air purity. In residential environments, they provide relief for allergy and asthma sufferers by removing airborne allergens and dust. In healthcare facilities, they are integral to infection control, eliminating bacteria and virus-laden particulates from the air. Industrial cleanrooms and laboratories use HEPA filtration to maintain contamination-free workspaces essential for pharmaceutical production, electronics manufacturing, and biotechnology. Educational facilities, commercial offices, and hospitality venues leverage HEPA-equipped HVAC systems and air purifiers to protect occupants from harmful pollutants and improve overall indoor air quality (IAQ).
Choosing the right HEPA filtration system depends on understanding the removal efficiency required, the types of contamination present, and the unique airflow demands of your application. Always confirm that products are independently certified to meet or exceed standards for particulate filtration.
Whether you are looking to install a HEPA filter in your home, upgrade your facility's cleanroom air handling system, or source high-performance air purification products, working with reputable manufacturers and suppliers ensures long-term value, compliance, and peace of mind.
HEPA, or High Efficiency Particulate Air, refers to an advanced air filtration technology capable of removing at least 99.97% to 99.99% of microscopic airborne particles, including dust, pollen, mold spores, bacteria, and smoke. Endorsed by regulatory agencies like the EPA (Environmental Protection Agency), EN (European Norms), and IEST (Institute of Environmental Sciences and Technology), the HEPA standard encompasses several levels of air filter efficiency and particulate retention. These standards are crucial for ensuring indoor air quality and compliance in both commercial and industrial environments.
Over the past two decades, HEPA filters have become indispensable not only in residential HVAC systems but also in specialized industrial settings such as cleanrooms, hospitals, pharmaceutical manufacturing, laboratory environments, and electronics fabrication. Governing bodies and international organizations have developed air filter rating and classification systems to help manufacturers, HVAC engineers, and end users evaluate and select the best air filter for their needs. Chief among these is the Minimum Efficiency Reporting Value (MERV) system, which categorizes HEPA filters in the highest efficiency tiers (MERV 17-20), indicating their suitability for critical applications requiring true particle filtration and superior air purification.
The MERV scale is the industry-standard method for rating air filter efficiency based on the filter’s ability to capture varying sizes of particulate contaminants. MERV ratings range from 1 to 20, with HEPA filters occupying the highest grades—MERV 17 to 20. This indicates that HEPA filters excel at trapping the smallest and most hazardous airborne particles, including viruses, carbon dust, sea salt, tobacco smoke, and bacteria. By specifying filter performance at different particle size ranges, the MERV scale ensures air filtration systems can be matched to the required level of contaminant removal.
HEPA filters with a MERV 17-20 rating are recommended for environments that demand the purest air quality, such as hospital surgery suites, critical cleanrooms, pharmaceutical production plants, semiconductors facilities, and any area where hazardous biological materials or radioactive contaminants are present. A filter’s ability to capture 99.97% or greater of particles at 0.3 microns—the most penetrating particle size (MPPS)—confirms its compliance with true HEPA standards and provides assurance for applications requiring stringent particulate removal. These filters surpass the minimum efficiency levels outlined by the MERV system and are often preferred for advanced contaminant control.
| Minimum Efficiency Reporting Value (MERV) Scale | |||||
|---|---|---|---|---|---|
| MERV Std 52.2 Spot Efficiency | Intended Dust Spot Efficiency Std 52. (2) | Average Arrestance | Particle Size Ranges | Typical Size Applications | Typical Filter Type |
| 1-4 | <20% | 60 To 80% | >10.0 ÎĽm | Residential/Minimum Light Commercial/Minimum Minimum Equipment Protection |
Permanent/Self Charging(Passive) Washable/Metal,Foam Synthetics Disposable Panel Fiberglass/Syntheics |
| 5-8 | <20% To 60% | <80% To 95% | >3.0-10.0ÎĽłľ | Industrial VVorkplaces Commercial Better/Residential Paint Booth/Finishing | Pleated Filter Extended Surface Filters Media Panel Filters |
| 9-12 | 40% To 85% | >90% To 98% | 1.0-3.0ÎĽłľ | Superior/Residential Better/lndustrial Workplaces Better/Commercial Buildings Care Superior/Commercial Buildings | Non-Supported/Pocket Filter/Rigid Box Rigid Cell/Cartridge V-Cells |
| 13-16 | 70% To 98% | >95% To 99% | Smoke Removal General Surgery Hospitals & Health | Rigid Cell/Cartridge Rigid Box Non-Supported/Pocket Filter V-Cells | |
| MERV Std 52.2 | Efficiency | Typical Applications | Typical Filter Type | ||
| 17-20 | 99.97%-99.9999% | Hospital Surgery Suites Cleanrooms Hazardous Biological Contaminants Nuclear Material |
HEPA ULPA |
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In 1998, the European Standards (EN for Europäische Norm) introduced comprehensive, harmonized test methods for HEPA and ULPA filter classification with the implementation of EN 1822. A significant innovation of this standard was the Most Penetrating Particle Size (MPPS) test, which identifies the particle size (typically around 0.1�0.3 μm) that is most likely to penetrate filter media. MPPS testing enables more precise classification and quality assurance compared to general efficiency ratings. Understanding MPPS is critical for industries where the highest standard of air cleanliness is needed, such as semiconductor manufacturing, hospital isolation rooms, pharmaceutical cleanrooms, and biotechnology labs. The MPPS concept is now widely referenced in both HEPA and ULPA filter performance specifications.
Like the MERV system, the EN 1822 standard uses performance metrics to rate filters for efficiency and particulate penetration. EN classifications range from EPA (Efficient Particulate Air) filters—which offer above-average filtration but are not true HEPA—up through H13, H14, and finally ULPA (Ultra-Low Particulate Air) filters, with efficiency ratings exceeding 99.999%. Despite EN's intent to standardize filter evaluation and selection, various rating systems still exist globally, with notable standards also set by the United States, the International Organization for Standardization (ISO), and IEST. When evaluating a filter for your application, ensure it meets the relevant certification and efficiency standards for optimal air quality and compliance.
| EN 1822 Classification of Filters | ||||
|---|---|---|---|---|
| Overall Value | Local Value | |||
| Filter Classes According EN 1822 | Efficiency | Penetration | Efficiency | Penetration |
| E10 | ≥85% | <15% | - | - |
| E11 | ≥95% | ≤5% | - | - |
| ≥99% | ≤1% | - | - | |
| E12 | ≥99.5% | ≤0.5% | - | - |
| ≥99.90% | ≤0.1% | - | - | |
| H13 | ≥99.95% | ≤0.05% | ≥99.75% | ≤0.25% |
| ≥99.99% | ≤0.01% | ≥99.95% | ≤0.05% | |
| H14 | ≥99.995% | ≤0.005% | ≥99.975% | ≤0.025% |
| ≥99.999% | ≤0.001% | ≥99.995% | ≤0.005% | |
| U15 | ≥99.9995% | ≤0.0005% | ≥99.9975% | ≤0.0025% |
| ≥99.9999% | ≤0.0001% | ≥99.9995% | ≤0.0005% | |
| U16 | ≥99.99995% | ≤0.00005% | ≥99.99975% | ≤0.00025% |
| ≥99.99999% | ≤0.00001% | ≥99.99995% | ≤0.00005% | |
| U17 | ≥99.999995 | ≤0.000005% | ≥99.9999% | ≤0.0001% |
The Institute of Environmental Science and Technology (IEST) provides industry-specific HEPA filter classifications following rigorous military and scientific protocols, specifically those established by Military Standard (MIL-STD) 282. Developed initially during World War II to safeguard personnel from radioactive airborne particles, these standards now underpin modern HEPA filter testing for leak detection and performance validation across research, healthcare, and high-precision manufacturing applications.
IEST's filter types range from Type A (basic HEPA filters suitable for general-purpose home air purification and commercial building HVAC systems) to Type E, F, and ULPA variants, engineered for contamination control in semiconductor cleanrooms, the biopharmaceutical industry, and controlled production areas demanding the highest particle retention rates. When selecting a filter, understanding the type is key to ensuring the air cleaning solution matches both regulatory and application-specific requirements, whether the goal is allergen protection, infection control, or sterile process support.
| IEST HEPA Filter Types | ||||||
|---|---|---|---|---|---|---|
| Filter Type | Penetration Test | Scan Test (See Notes) | Comments | Minimum Efficiency Rating | ||
| Method | Aerosol | Method | Aerosol | |||
| A | MIL-STD 282 | Thermal DOP | None | None | 99.97 % * At 0.3 ÎĽm | |
| B | MIL-STD 282 | Thermal DOP | None | None | Two Flow Leak Test | 99.97 % * At 0.3 ÎĽm |
| C | MIL-STD 282 | Thermal DOP | Photometer | Polydisperse DOP | 99.99% At 0.3 ÎĽm | |
| D | MIL-STD 282 | Thermal DOP | Photometer | Polydisperse DOP | 99.999% At 0.3 ÎĽm | |
| E | MIL-STD 51477 or MIL-STD F51068 | Thermal DOP | Photometer | Polydisperse DOP | Two Flow Leak Test | 99.97 % At 0.3 ÎĽm |
| F | IES-RP CC007 | Open | Photometer | Open | 99.999% At 0.1 To 0.2 ÎĽm | |
ISO 29463 is the globally accepted benchmark for HEPA and ULPA filter classification, aligning closely with EN 1822 for test methodologies and performance validation. Divided into five parts addressing everything from test methods to specialized materials, ISO 29463 provides a comprehensive framework that assures cross-border consistency for the selection, manufacturing, and certification of air filters for cleanrooms, high-purity manufacturing, and sterile environments. ISO classes span from ISO 15 E (non-HEPA) through to ISO 75 U (ULPA class), allowing consumers and specifiers to choose the exact filter type to meet regulations and target particle removal goals for their application.
Under ISO standards, true HEPA filters typically start at ISO 35 H and up, where efficiency rates exceed 99.95% for 0.3-micron particles—a crucial criterion for critical process control and indoor environmental safety. Those adhering to EPA requirements usually begin at ISO 30 E, representing a mid-range standard above conventional particulate air filters but below true HEPA or ULPA capabilities. When evaluating ISO-rated filters, industries should consider not only the efficiency rating but also local (leak) standards, which ensure uniform protection across the entire surface of the filter element.
| ISO Filter Standards | ||
|---|---|---|
| Filter Class | Overall Efficiency (%) | Local Or Leak |
| Penetration (%) | ||
| ISO 15 E | ≥95 | NA |
| ISO 20 E | ≥99 | NA |
| ISO 25 E | ≥99.5 | NA |
| ISO 30 E | ≥99.90 | |
| ISO 35 H⁴ | ≥99.95 | ≤0.25 |
| ISO 40 H⁴ | ≥99.99 | ≤0.05 |
| ISO 45 H⁴ | ≥99.995 | ≤0.025 |
| ISO 50 U | ≥99.999 | ≤0.005 |
| ISO 55 U | ≥99.9995 | ≤0.0025 |
| ISO 60 U | ≥99.9999 | ≤0.0005 |
| ISO 65 U | ≥99.99995 | ≤0.00025 |
| ISO 70 U | ≥99.99999 | ≤0.0001 |
| ISO 75 U | ≥99.999995 | ≤0.0001 |
| Table 1 - ISO FIlter Classes | ||
While the International Organization for Standardization (ISO) is typically the leading authority on manufacturing and industrial standards, HEPA filters have various classification systems developed by different countries and professional organizations. These widely recognized standards—including MERV, EN 1822, IEST, and ISO 29463—offer multiple frameworks for measuring particulate retention, air filtration efficiency, and application suitability. Understanding these systems will help you select the best HEPA filter for your specific HVAC, cleanroom, or process air requirements, whether you are seeking allergen control for homes, contamination control for sensitive production, or advanced airborne microorganism filtration for research labs and hospitals.
Originally designed to protect personnel from toxic and radioactive dust particles, HEPA filtration technology has advanced alongside the demands of modern industries and public health needs. Today, true HEPA and ULPA filters are essential across fields ranging from healthcare (protection against airborne disease transmission and allergens), to microelectronics (dust-free environments), pharmaceutical production, food processing, and critical infrastructure, delivering reliable protection, improved air quality, and regulatory compliance.
ULPA filters represent an even higher level of air purification than standard HEPA filters. Ultra-Low Particulate Air (ULPA) filters capture at least 99.999% of airborne contaminants with diameters of 0.12 µm or larger, making them ideal for critical cleanroom environments, pharmaceutical manufacturing, and applications where molecular contamination must be minimized. With a denser and more randomly arranged fiber structure than HEPA media, ULPA filters can remove a broader spectrum of submicron particles, including fine dust, smoke, bacteria, and certain viruses. The only exception is some ultra-tiny viral particles, which may fall below ULPA’s removal range. ULPA filters are typically used in semiconductor production, biotechnology labs, and high-precision assembly zones where ultra-clean air is a process or health requirement.
Ducted and fan-powered HEPA filter units play a vital role in cleanrooms, laboratories, hospitals, and pharmaceutical environments where controlling airborne particle concentration and maintaining sterility is critical. These self-contained filtration devices are engineered to process re-circulated air within both turbulent and unidirectional (laminar) airflow cleanrooms. By generating and sustaining positive air pressure inside the controlled zone, they not only filter out harmful contaminants but also help prevent cross-contamination from adjacent spaces, such as ceiling bypasses or entry ports.
For best results in air quality and contamination prevention, select HEPA filter units with validated test certifications (such as EN 1822 or ISO 29463) and ensure proper installation and regular maintenance. These units provide versatile and effective solutions for controlling particulate levels, minimizing dust, allergen, and microbe spread, and supporting compliance with GMP (Good Manufacturing Practice) and other regulatory standards in high-stakes environments.
At first glance, a HEPA filter appears similar to other filters, featuring interwoven fibers and pleated structures. However, the true effectiveness of a HEPA filter lies in its fiber composition, typically consisting of randomly arranged fiberglass fibers.
The effectiveness of a HEPA filter stems from the random arrangement of these fibers. This design leverages Brownian Motion, ensuring that even the tiniest particles are trapped within the intricate mesh of fibers and cannot escape.
HEPA filters are made from polyester, polypropylene, or fiberglass fibers that are tightly interlaced with diameters of less than one micron. The fibers are twisted, turned, scattered, and randomly placed in different directions to create a mesh maze without a straight true path.
The spaces between the fibers in a HEPA filter are smaller than half a micron, allowing the filter to capture particles smaller than 0.3 microns. The image below, taken from a microscopic view of HEPA filter fibers, clearly shows the irregular and non-uniform arrangement of the fibers.
The frame of a HEPA filter can be made from a variety of materials. For ones being used for industrial and manufacturing operations, the frames are normally made of tough, resilient, and durable materials such as carbon steel, aluminum, stainless steel, or galvanized steel. The size of the frame has to be carefully planned since its resistance to the airstream can increase the pressure drop.
Choosing the right adhesive for HEPA filter construction is crucial to ensure it does not impact the filter's performance. The adhesive must stay in place without migrating into the fiber material. Common adhesives for HEPA filters include polyurethane, silicone, and ceramic.
Polyurethane is often used in HEPA filters due to its suitability for the filtering process. It securely bonds the fiber material within metal frames and cures either at room temperature or through accelerated heat curing.
Silicone adhesives offer flexibility, temperature resistance, and come in various hardness levels, transparencies, and viscosities. They withstand shock, vibrations, heat, and corrosion and can also provide electrical insulation.
Ceramic adhesives form a strong bond between filter materials and metal frames, such as stainless steel or aluminum. They are ideal for HEPA filters and can secure various internal components.
Gaskets play a critical role in the performance of a HEPA filter and can be made from die cut urethane rubber and closed cell sponge rubber. The choice of rubber as a gasketing material is more economical and easier to install than liquid silicone systems.
To prevent mold release, the material is processed by splitting or skiving the top layer. Gaskets are then precisely cut from sheets or rolls to ensure they fit the required shape.
Common gasket shapes include strip, one-piece, and interlocking designs, with interlocking being the most cost-effective and easiest to install. Gaskets are affixed to the frame using solvent-activated or pressure-sensitive adhesives. The joints are sealed with RTV materials compatible with closed-cell rubbers.
The most commonly used gasket type is die-cut, which is attached to the outer edge of the frame and pressed against a flat surface. All HEPA filter gaskets are resistant to oil and ozone.
In HEPA filters, separators are positioned between the pleats or folds of the filter material. These separators, made from aluminum, glass fiber strings, or hotmelt, keep the pleats open. This design enhances particulate matter capture and reduces airflow resistance.
The description provided outlines the basic elements of HEPA filter design. However, each manufacturer may use proprietary methods and variations in their production processes, which can differ from this general overview.
With rapid technological advancements, air filtration systems have become crucial for building management and industrial operations. In technical and craft industries where air quality is vital for worker safety, HEPA filters are essential for removing contaminants and maintaining air purity.
HEPA filters are particularly critical in clean room environments, where even minor contaminants can disrupt processes. Clean rooms are classified based on the particle count and size per volume of air, with particles as small as 0.1 ÎĽm being measured. HEPA filters must meet and often exceed these stringent requirements to ensure clean room standards are maintained.
Biosafety cabinets are designed to protect workers handling hazardous materials by using vertical laminar airflow to create a barrier against airborne particles and microorganisms. HEPA filters are employed to clean the air as it is recirculated back into the workspace and released into the environment.
Biosafety cabinets are categorized into three classes: I, II, and III. Classes II and III provide comprehensive protection for workers, the environment, and products, while Class I cabinets offer basic protection primarily for the environment and personnel. When used correctly, biosafety cabinets significantly reduce the risk of contamination, disease, and the spread of hazardous materials.
The working conditions that require the most enhanced methods of contamination removal are cleanrooms, which work with a wide variety of substances, products, and materials that can be potentially damaged by unfiltered and unclean air. The term clean room covers a wide array of work areas constructed and designed to create a perfect and ideal set of working conditions.
The clean room industry consists of specialized engineers and designers who excel in creating environments that are sealed and meticulously cleansed to capture and remove even the tiniest particles instantly.
Cleanroom classifications are based on the quantity and size of particulate matter present in the room. The fewer particles present per cubic foot, the higher the cleanroom's classification. The filtration system, which includes HEPA filters installed in ceilings, walls, or cabinets, plays a crucial role in maintaining these stringent conditions.
The image below illustrates how every component of a cleanroom is thoroughly inspected to ensure that the environment is maintained at the highest level of cleanliness and particle-free conditions.
HEPA filters are crucial in hospitals to prevent cross-contamination and the spread of infectious diseases. In the context of COVID-19, these filters are essential for safeguarding both patients and healthcare workers.
In operating rooms, maintaining clean and clear air is critical. HEPA filters are employed to eliminate airborne contaminants that could pose risks during surgical procedures when patients' organs are exposed.
Newborns, with their vulnerable immune systems, are at risk from airborne diseases. HEPA filters in incubators, especially in neonatal intensive care units, remove bacteria, viruses, and other infectious agents to ensure a sterile environment.
Warming beds in forced air systems help regulate patient temperature. HEPA filters in these systems capture dangerous particulate matter, ensuring it does not come into contact with the patient.
Laboratories, similar to clean rooms, handle hazardous pathogens and require HEPA filters to meet legal standards. These filters are essential for removing microbes and contaminants, preventing their spread beyond the testing environment.
Typically, warehouses are used for short-term storage before items are shipped. However, some goods may remain in a warehouse for extended periods. Despite the large space, prolonged storage can lead to stagnant air filled with harmful particles, dust, and dirty surfaces.
In such conditions, HEPA filters are highly effective. They help remove harmful particles and improve air quality by cleaning and refreshing the air in warehouses.
Weather conditions can lead to mold buildup, which, although invisible, is highly dangerous and harmful. Using air scrubbers along with HEPA filters helps remove mold from the air, protecting public health from mold contamination.
In severe weather, water and moisture can infiltrate buildings, homes, and manufacturing facilities, fostering mold growth. While drying out these areas is essential, it is not enough to address airborne mold. HEPA filtration systems are necessary to capture and remove mold spores from the air effectively.
COVID-19 particles can remain airborne for hours following exposure. Agencies such as the EPA and the CDC recommend using air purifiers equipped with HEPA filters to remove contaminants, including COVID-19, from the air. When choosing an air purifier, it is important to consider the size of the area it will serve and ensure it is capable of handling the required airflow.
The pharmaceutical industry shares similar requirements with hospitals for controlling contaminants and hazardous substances. Quality assurance in drug production is closely regulated by the Food and Drug Administration (FDA), which mandates the use of HEPA filters with efficiency ratings of H13, H14, or U15 due to the sensitive nature of the materials handled.
Moreover, to comply with FDA standards, all HEPA filter installations must be tested for leaks, efficiency, and reliability. The industry’s stringent demands necessitate regular inspections and approvals of air processing equipment to ensure safety and efficacy.
The applications of HEPA filters outlined above are among the most critical, but they represent only a portion of their uses. HEPA filters are also employed in industries such as aerospace manufacturing, electronics production, fertilizer blending, cement production, and other sectors where dust, chemicals, and hazardous materials are present.
In the past two decades, HEPA filters have significantly evolved to meet the increasing demand for cleaner air, and this trend is expected to continue well into the future.
Manufacturers of HEPA filters rigorously test their products for efficiency, integrity, and performance as part of the production process to ensure high quality. However, HEPA filters must also undergo a secondary round of testing after installation to confirm their effectiveness in the operational environment.
Before assessing a HEPA filter, it is crucial to evaluate the flow rate through it. The ISO provides standards for on-site testing of HEPA filters to check for leaks and verify airflow volume. These standards are detailed but offer some flexibility between vendors and customers.
To test HEPA filters in clean rooms, cold and hot generated aerosols, including microspheres, are used. These test aerosols are produced from oil-based liquids. The concentration of test aerosols is set upstream of the filter at levels of 10µg/l and 100µg/l, with lower concentrations recommended to avoid blockage or bleed-through.
Leak detection is performed using a probe, with smaller probes generally offering better accuracy than larger ones. The speed of scanning also impacts the effectiveness of leak detection.
HEPA filters are designed with a gap between the filter and its housing, with the gasket positioned at the rear. To detect leaks between the frame and housing, a probe scans the area. If there is a gasket leak, particles will spread and fill the surrounding space, causing the scanner to detect a higher concentration of particles away from the actual leak.
The image below illustrates a gasket leak.
To scan the entire face of a HEPA filter for leaks, a probe is used to make overlapping strokes across the filter at a controlled, consistent speed. This process may require multiple passes to accurately locate any leaks. For increased precision, a baffle plate can be placed over the filter face to distinguish between gasket and face leaks. The probe operates at a fraction of an inch from the filter surface to ensure all potential leaks are detected.
Manufacturers and the IEST provide several procedures for repairing leaks in HEPA filters. The IEST offers guidelines to prevent creating blockages or restrictions during the repair process. After any repair is made, the system must be retested to verify that the leak has been properly patched and that airflow remains unobstructed.
Ensuring the proper performance of a HEPA filter system is crucial, and thorough testing and examination are integral to this process. These steps are essential for confirming the effectiveness and reliability of the HEPA filter system as part of the installation and maintenance procedures.
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