When to Replace the HEPA Filter?
Four major indicators determine whether HEPA filter replacement is required:
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Failure to reach the rated airflow velocity even at maximum fan speed The average airflow velocity in the working zone of a horizontal clean bench shall be maintained at 0.3–0.5 m/s. If the velocity cannot recover after the pre-filter is cleaned or replaced even at the highest gear, the HEPA filter has excessive resistance and needs replacement.
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Significant rise in pressure drop Replacement is required when the final resistance reaches 1.5–2 times the initial resistance, or exceeds 450 Pa. Excessive resistance reduces air supply and increases the load on the fan, which may shorten the fan service life over long-term operation.
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Failed leak test Leak tests shall be performed after HEPA filter installation or replacement, commonly using PAO/DOP aerosol scanning or particle counter scanning. If the leakage rate exceeds 0.01% and cannot be fixed by tightening or sealing caulking, the filter must be replaced.
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Persistently unsatisfactory cleanliness If continuous abnormal results of airborne particles and settle plates are detected in the working zone, and human operation disturbance, ambient interference and pre-filter blockage have been excluded, inspect the HEPA filter for media damage, seal failure or filter penetration.
In addition, early evaluation and replacement are required if the filter gets damp, mildewed, deformed, or the frame seal ages, or if incidents such as chemical vapor emission, water accumulation and mildew, or dust leakage occur on site.
Reference Cycle for Different Operating Environments
There is no fixed service life for HEPA filters due to varied on-site working conditions:
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Low-dust laboratories, low-frequency use: Approximately 18–30 months
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Shared by multiple users, non-stop operation at production stations: Approximately 12 months
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High humidity, high dust, high temperature or stringent cleanliness requirements: 6–12 months
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GMP-compliant scenarios including pharmaceutical, medical device and food cleanrooms: The cycle shall be defined based on pressure difference monitoring, leak tests, environmental monitoring and change control; shorten the cycle when necessary.
Pre-Replacement Precautions
Power off and shut down the equipment before replacement. Clean the internal and external surfaces of the bench to prevent dust from falling into the plenum chamber during disassembly. Handle and unpack the new filter gently; never touch the filter media directly to avoid damage. Inspect the new filter against light before installation to check for transit damage, and verify the model, dimension and sealing structure match the equipment. For horizontal clean bench installation, align the airflow arrow mark of the filter with the airflow direction, and keep the frame gasket flat without distortion. Tighten compression bolts or clamps evenly to avoid frame leakage caused by uneven stress. After replacement, re-test airflow velocity and cleanliness, and complete leak inspection on the filter media and frame. The equipment can be put back into service only after passing the test.
Core Measures to Extend HEPA Filter Service Life
The service life of the HEPA filter largely depends on upstream filtration and daily management. Pre-filters shall be cleaned or replaced every 3–6 months; replace the pre-filter after 2–3 cleaning cycles. Avoid direct air blast from doors, windows or air conditioning vents, and frequent personnel movement around the bench to reduce external dust ingress. When the equipment is idle for a long time, clean the work surface, power off the unit and cover it with a dust cover. Run the equipment periodically to prevent internal moisture accumulation. Keep complete replacement records, including replacement date, filter model, airflow data, leak test results and operating environment information. This ensures stable cleanliness and facilitates subsequent maintenance and compliance audit.
