In a cleanroom environment, the operational stability of high-efficiency filters (HEPA) is the core for maintaining cleanliness levels and ensuring production/experimental safety. The guarantee of its stability needs to run through the entire life cycle of selection, installation, operation, monitoring, and maintenance management, and be achieved through multi-dimensional technical measures and management norms. The following are the specific guarantee strategies:
I. Pre-installation Assurance: Scientific selection and compliant installation
Selection and installation are the “fundamental engineering” for the stable operation of filters, directly determining their compatibility and initial performance.
1. Precise selection: Match the core requirements of the cleanroom
The selection of filters should be based on core parameters such as the cleanliness level of the cleanroom (such as ISO 5-8), the air volume to be treated, the characteristics of contaminants (particle size, concentration), temperature and humidity/corrosive environment, etc., to avoid the decline in stability caused by “overload operation” or “performance redundancy”.
Air volume matching: The rated air volume of the filter needs to be precisely matched with the supply air volume of the clean room (generally leaving a margin of 10% to 15%). If the actual air volume far exceeds the rated value, it will cause the air velocity of the filter material to be too high, the resistance to increase sharply, and accelerate the aging and damage of the filter material. If the air volume is insufficient, the clean pressure difference cannot be maintained, and the filtration efficiency will be reduced in a disguised way.
Performance compatibility: For clean rooms containing oil mists (such as semiconductor lithography) and corrosive gases (such as chemical and pharmaceutical synthesis), special filter materials with anti-static and chemical corrosion resistance (such as PTFE-coated filter materials) should be selected. Ordinary glass fiber filter materials are prone to corrosion and failure.
Structural selection: In high-humidity environments (such as biological cleanrooms), waterproof frames (such as stainless steel) should be chosen to prevent wooden or ordinary carbon steel frames from deforming due to moisture, which could lead to the failure of the filter seal.

2. Compliant installation: Eliminate “initial leakage” and structural hazards
The “installation sealing performance” of high-efficiency filters directly affects operational stability – even if the filter material itself meets the efficiency standards, if there is leakage in the installation gap, unfiltered air will directly enter the clean room, leading to the failure of cleanliness. Installation must comply with the following specifications:
Pre-installation inspection: Before installation, the filter must undergo integrity testing (such as the sodium flame method, the PAO method), and filter materials that may be damaged during transportation must be removed. At the same time, clean the installation frame (such as the static pressure box and air outlet) to prevent dust and debris from adhering to the surface of the filter material.
Sealing measures: Adopt “liquid tank sealing” or “double-sealing rubber strip” technology
Liquid tank sealing: Insert the filter frame into the liquid tank filled with sealing liquid (such as special silica gel liquid) to form a gap-free seal, which is suitable for high cleanliness levels (such as ISO 5 and above).
Rubber strip sealing: Select EPDM rubber strips with excellent elasticity. During installation, ensure that the rubber strips have no uneven compression or breakage. If necessary, apply sealant to assist in sealing.
Uniform force application during installation: When fixed by bolts or pressure strips, force should be applied evenly along the frame (with consistent torque) to prevent excessive local force from causing deformation of the filter material or warping of the frame.
Ii. Operational Assurance: Dynamic Monitoring and Environmental Control
During the operation of a cleanroom, real-time monitoring and environmental regulation are necessary to prevent external factors from causing “extra load” or “damage” to the filters.
Establish a “three-stage filtration” pre-protection system.
The filter material of high-efficiency filters (such as glass fiber) is fragile and cannot be cleaned. If it is directly used to handle air with high dust content, it will quickly clog, increase resistance, shorten the service life, and reduce stability. “Gradient interception” must be achieved through a three-level filtration system of “primary efficiency + medium efficiency + high efficiency” :
Primary filter (G1-G4 grades) : Intercepts large particles such as dust and hair with a diameter of ≥5μm, protecting the medium-efficiency filter.
Medium-efficiency filters (F5-F9 grades) : They intercept suspended particles with a diameter of ≥1μm, reducing the dust content of the air entering the high-efficiency filter to an extremely low level (generally ≤0.1mg/m³).
Through the “load reduction” of the pre-filter, the resistance rise rate of the high-efficiency filter can be reduced by more than 50%, making its operation more stable.
2. Real-time monitoring of core operating parameters
The operating status of the filter is monitored 24 hours a day through an automated system to promptly detect and intervene in any abnormalities.
Resistance monitoring: Install differential pressure gauges on the “intake side” and “exhaust side” of the high-efficiency filter to monitor the operating resistance in real time. Each filter needs to preset “initial resistance”, “design resistance”, and “final resistance” (generally 2 to 3 times the initial resistance) :
When the resistance is lower than the initial value, it may be due to filter material damage or installation leakage.
When the resistance approaches the final resistance, it indicates that the filter material is clogged and needs to be replaced in time to prevent the fan from being overloaded or the air volume from decreasing.
Air volume/wind speed monitoring: Monitor the supply air volume through the air outlet anemometer or air duct air volume sensor. If the wind speed drops sharply, it may be due to filter blockage or fan failure, and immediate investigation is required.
Cleanliness linkage monitoring: Link the filter status with the online particle counter in the clean room. If the particle concentration in a certain area suddenly exceeds the standard, prioritize the inspection of the sealing performance or filter material integrity of the high-efficiency filter corresponding to the air outlet.
3. Strictly control the parameters of the operating environment
Environmental factors such as temperature, humidity, pressure difference, and corrosive gases in a cleanroom will directly affect the lifespan and stability of filters.
Temperature and humidity control: There are upper limits to the temperature resistance of the filter material (for example, the temperature resistance of ordinary HEPA is ≤80℃) and the bonding strength of the adhesive (which is prone to aging at high temperatures and delamination at high humidity). The ambient temperature should be controlled between 10 and 30℃, and the relative humidity should be controlled between 40% and 65% (special environments such as biosafety laboratories require separate adaptation).
Pressure difference control: Maintain a “positive pressure difference” (generally 5-10Pa) between the clean room and adjacent areas to prevent contaminated air from the outside from flowing back and impacting the filters. At the same time, ensure that the pressure in the static pressure box on the air intake side of the high-efficiency filter is stable to avoid vibration and damage to the filter material caused by pressure fluctuations.
Corrosion control: For cleanrooms containing acids, alkalis, and organic solvents, chemical filters (such as activated carbon filters) should be added to the pre-system to remove corrosive gases and prevent the filter materials and frames from being corroded and failing.
Iii. Maintenance and Assurance: Standardized Management and Regular Verification
Regular maintenance and calibration are the keys to extending the service life of filters and maintaining their stability. It is necessary to establish a standardized management process.
Formulate a periodic maintenance plan.
Pre-filter replacement: The primary filter should be replaced every 1 to 3 months, and the medium-efficiency filter every 3 to 6 months (specifically adjusted according to the pressure difference changes) to prevent the high-efficiency filter from being “prematurely scrapped” due to the failure of the pre-filter.
High-efficiency filter replacement: When the operating resistance reaches the final resistance or the integrity test fails, it must be replaced immediately. Even if the resistance does not meet the standard, the service life of a common HEPA is still recommended not to exceed two years (for special environments such as pharmaceutical clean rooms, the cycle should be shortened in accordance with GMP standards).
Post-replacement verification: After each replacement of the high-efficiency filter, it must undergo integrity testing (the PAO method is an internationally recognized standard), and the leakage rate should be detected (≤0.01%). Only after passing the test can it be put into operation.
2. Strengthen the standardization of maintenance operations
Replacement operation: When replacing the filter, it should be carried out during the “non-production period” of the clean room. The operator must wear clean suits and gloves to avoid direct contact of hands with the filter material. During the replacement process, the opening of the static pressure box should be covered to prevent dust from falling in.
Compliance for scrapping and disposal: For cleanrooms containing pathogenic bacteria and toxic pollutants (such as biosafety laboratories and pharmaceutical fermentation workshops), the replaced waste filters must first undergo sterilization/sealing treatment and then be disposed of in accordance with hazardous waste standards to prevent secondary pollution.
3. Establish a full life cycle file
Establish an “identity file” for each high-efficiency filter, recording its model, rated parameters, installation date, initial resistance, pressure difference data for each maintenance, integrity test report, replacement date and other information. Through data traceability and analysis of the operation patterns of the filters, optimize the maintenance cycle (for example, if the resistance of a filter in a certain area rises too fast) It can be checked whether the pre-filter is insufficient or the environmental dust content exceeds the standard.
Iv. Enhanced Protection for Special Scenarios
For high-demand cleanrooms (such as semiconductor wafer manufacturing and biosafety level 3 laboratories), additional strengthening measures need to be taken:
Redundant design: The key areas adopt a “one in use and one on standby” dual high-efficiency filter system. When the main filter fails, the standby filter can automatically switch to ensure that the cleanliness is not interrupted.
Online monitoring upgrade: Adopting “laser particle counter + remote alarm system”, when the filter leaks and causes the particle concentration to exceed the standard, it will immediately trigger an audible and visual alarm and notify the operation and maintenance personnel.
Special treatment of filter material: The filters in the biological clean room are subjected to “antibacterial film coating treatment” to inhibit the growth of microorganisms on the surface of the filter material and prevent abnormal resistance increase caused by biological adhesion of the filter material.
Summary
The operational stability of high-efficiency filters is the result of the combined effects of “precise selection, airtight installation, real-time operation monitoring, and standardized maintenance”. The core logic is: to reduce the load on the filter through pre-protection, to detect abnormalities in a timely manner through real-time monitoring, to extend the effective service life through standardized maintenance, and ultimately to achieve long-term stable compliance of the clean room. This process requires the formulation of personalized plans in combination with the specific application scenarios of the cleanroom (such as medicine, electronics, and food), and strictly follows industry standards such as GMP and ISO 14644.