Several situations where it is necessary to replace the high-efficiency air filter in a biosafety cabinet in a timely manner

The timely replacement of high-efficiency air filters (HEPA/ULPA) is an iron rule to ensure the core protective function of biosafety cabinets. The following are several clear situations where the safety cabinet must be immediately stopped and replaced, divided into two categories: mandatory replacement and strongly recommended replacement.
Category 1: Cases of mandatory immediate replacement (safety red line, non-negotiable)
Any of the following situations indicates that the protective barrier has failed or is on the verge of failure, and immediate action must be taken.

Situation description: During the "in-situ scanning leak detection test" conducted by professionals, an aerosol photometer was used to scan any point of the filter, and the leakage rate exceeded 0.01%.
Risk: This indicates that the filter has invisible damage or seal failure, and pollutants can escape directly through the leakage point. This is the most direct and scientific basis for replacement.
Action: Immediately stop using, replace the filter, and conduct a leak test again after replacement. Only after passing the test can it be put into use.

Situation description: The safety cabinet continues to issue "filter blockage" or "low wind speed" alarms, and the problem persists after the following troubleshooting:
Confirmed that there are no objects obstructing the front window intake grille and rear exhaust grille.
The clogged pre filter has been checked and replaced.
The fan speed has been adjusted to the maximum allowable value, but the front window wind speed is still below the minimum standard of 0.3 m/s.
Risk: Indicates that the main HEPA filter is severely clogged and the dust holding capacity is saturated. The fan can no longer maintain safe airflow, the personnel protection barrier has failed, and the fan is prone to damage due to long-term overload operation.
Action: Stop immediately and arrange for replacement of the main filter.

Situation description:
The filter material shows tearing, holes, and burn marks (usually caused by improper use of open flames).
The filter may experience widespread moisture, mold growth, or structural collapse due to liquid splashing, backflow, or condensation.
Severe deformation of the border, cracking or detachment of the sealant.
Risk: Physical damage directly destroys the filtering structure; Moisture can lead to a decrease in the strength of filter fibers, the growth of microorganisms, and the possibility of penetrating the filter, completely losing its protective effect.
Action: Immediately discontinue and replace. Simultaneously investigate the cause (such as disabling open flames and checking drainage pipelines) to prevent the problem from recurring.
Category 2: strongly recommended replacement situations (based on performance and preventive principles)
Although the following situations did not immediately trigger an alarm, based on performance data and risk prevention, testing and replacement should be arranged as soon as possible.

Situation description: Through differential pressure monitoring or maintenance records, it has been found that the operating resistance of the filter has increased to twice its "initial resistance" at the rated air volume.
Principle: This is a commonly used standard in engineering to determine the end of filter life. Doubling the resistance means that the filtering channel has been largely occupied by particulate matter and may be completely blocked at any time.
Action: Professional personnel should be contacted immediately for testing and preparation for replacement.

Situation description: Under strict and standardized operation, sterile experiments (such as cell culture) conducted in the cabinet are frequently contaminated, and other sources of contamination such as operators, reagents, and vessels have been ruled out.
Risk: This strongly suggests that the air supply filter may fail, as unfiltered air contains fungal spores or bacteria, directly contaminating the work area.
Action: The safety cabinet, especially the air supply filter, should be immediately subjected to complete performance testing and leak detection, and replacement should be decided based on the results.

Situation description: The filter has been continuously used for a period of time that has reached or exceeded the "recommended maximum service life" stated by the manufacturer in the manual (e.g. 3 years, 5 years, or cumulative operating hours).
Principle: Even if there is no obvious blockage, the sealing material (glue, gasket) of the filter will naturally age over time, posing a potential risk of sealing failure.
Action: As part of the preventive maintenance plan, strict integrity leak testing should be arranged upon reaching the deadline, and replacement should be decided based on the leak testing results and risk assessment.

Summary: Decision and Action Process
Once the above situation occurs, please follow the following process:
Immediately stop use: Hang a warning sign in the corresponding position that reads' Equipment malfunction, prohibited from use '.
Safety disinfection: Thoroughly disinfect the working area of the safety cabinet.
Contact professionals: Notify laboratory equipment administrators or qualified biosafety cabinet service providers.
Professional diagnosis and replacement: Professional personnel are present to diagnose, replace filters, and perform mandatory in-situ scanning leak testing after replacement.
Re certification: Only when the leak test is fully qualified after replacement and other performance parameters (wind speed, airflow mode) meet the standards, can the safety cabinet be put back into use.
Record archiving: Complete archiving of events, test reports, and replacement records as key evidence of laboratory quality and safety systems.
Remember: High efficiency air filters are the "lungs" of biosafety cabinets, and their integrity is directly related to life safety. In the issue of replacement, "preventive" and "evidence-based" decision-making far outweigh "passive response" and "luck mentality".