To determine whether a high-efficiency filter needs to be replaced, it is necessary to combine core indicators such as resistance changes, filtration efficiency decline, and physical condition checks, rather than relying solely on usage time. The following are the specific methods and criteria for judgment:

I. Core judgment Index: Resistance (pressure difference) reaches the upper limit
The resistance of high-efficiency filters will increase with the increase in usage time (as the filter material gradually clogs due to the adsorption of pollutants). When the resistance reaches the following thresholds, it must be replaced:
Standard threshold: The operating resistance reaches twice the initial resistance (industry-wide standard).
For example, the initial resistance of the new filter is 150Pa. When the resistance rises to 300Pa during operation, it needs to be replaced.
Manufacturer threshold: For some special filters (such as ULPA ultra-high efficiency filters), manufacturers will indicate the upper limit of resistance (such as 400Pa), which should be followed first.
Principle: Excessive resistance will lead to a decrease in air volume (affecting the air change rate in the clean room), a sharp increase in energy consumption (increasing the load on the fan), and the filter material is approaching the clogging limit. Continuing to use it may cause the filter to fail due to the airflow “penetrating” the gaps in the filter material.
Ii. Key Verification: Filtration efficiency decline or leakage
Even if the resistance has not reached the upper limit, if the filtration efficiency decreases or leakage occurs, it must be replaced
The leak detection test failed
Tested by the DOP/PAO leak detection method (industry standard) :
High-efficiency filter (HEPA): Leakage rate exceeds 0.01% (for particles ≥0.3μm).
Ultra-high Efficiency Filter (ULPA): Leakage rate exceeds 0.001% (for particles ≥0.12μm).
Leakage may be caused by damaged filter materials, poor sealing of the frame (such as aging of the rubber strip), or misalignment during installation, which directly affects the compliance of the clean environment.
The efficiency test fails to meet the standard.
Regular (such as once a year) third-party testing should be conducted. If the filtration efficiency drops below 80% of the designed value (for example, from 99.97% to below 90%), it indicates that the filter material structure has been damaged (such as fiber breakage, enlarged pore size), and replacement is required.
Iii. Abnormal physical state: Directly trigger replacement
When the following visible damages occur, replace them directly without inspection:
The filter material is damaged (such as with holes, tears, or severe wrinkles on the surface).
The frame is deformed, and the sealing rubber strip is aged and has fallen off (resulting in air leakage at the edge).
The filter material is damp, moldy, or contaminated by oil or chemicals (the efficiency of non-moisture-proof filters will drop sharply when exposed to water).
In the event of sudden pollution incidents (such as dust explosions in workshops or chemical leaks), pollutants may penetrate deep into the filter materials and cannot be removed.
Iv. Auxiliary References: Usage Time and Environment
Although time is not the only criterion, it can serve as an auxiliary judgment:
High-pollution environments (such as foundry workshops and cement plants): If the pre-filter is well maintained, it usually needs to be inspected and replaced every 6 to 12 months.
In general, clean environments (such as food workshops and general laboratories), resistance, and efficiency should be closely monitored every 1-2 years.
High-cleanliness environments (such as operating rooms and electronic clean rooms): 2 to 3 years should be determined based on the test results, but it is not recommended to exceed 3 years at the longest (filter materials will naturally age).
Summary: The “3 Musts” for Replacement
When the resistance reaches twice the initial resistance or the manufacturer’s upper limit, it must be replaced.
Leak detection/efficiency test fails → Must be replaced;
The filter material is damaged, damp, or contaminated → must be replaced.
The replacement of high-efficiency filters should be based on performance data as the core basis rather than “delaying based on experience”, otherwise it may lead to an over-standard clean environment, increasing the risk of product scrapping, experimental failure, or medical infection.