The replacement cycle and method of the high-efficiency air filter (HEPA filter) in the clean bench

I. Replacement Cycle of HEPA Filters
The replacement cycle of HEPA filters is influenced by factors such as usage frequency, environmental cleanliness, and type of experiment. It is necessary to make a comprehensive judgment based on the following indicators:
Replacement standard based on resistance (pressure difference)
Monitoring method: Some clean benches are equipped with resistance indicators (differential pressure gauges), which display the pressure difference before and after the filter in real time.
Replacement threshold: When the measured resistance reaches 1.5 to 2 times the initial resistance (for example, when the initial resistance is 200Pa and it reaches 300 to 400Pa), it indicates that the filter has increased the airflow resistance due to dust accumulation and needs to be replaced promptly.
2. Regular replacement based on usage time
General recommendation: In a regular laboratory environment (non-highly polluted scenarios), even if the resistance does not reach the threshold, it is recommended to replace it every 1-2 years.
High-frequency usage scenarios: If it is used for more than 8 hours per day or in high-risk scenarios such as microbiological experiments and cell culture, it is recommended to replace it every year.
3. Other abnormal situations trigger the replacement
Abnormal appearance: The surface of the filter shows obvious damage, holes, or severe dust accumulation (such as a large amount of visible particles adhering to the naked eye).
Abnormal airflow: The wind speed on the workbench surface is lower than the standard value (0.3-0.6m/s), and cannot be restored by adjusting the fan (measured with an anemometer).
Contamination incident: If microbial contamination (such as mold growth) occurs inside the workbench and there is still a risk after disinfection, the filter needs to be replaced.
Ii. Replacement Methods for HEPA Filters
The replacement of HEPA filters must follow strict aseptic and safety regulations. The following is the standard operating procedure (taking a conventional vertical flow laminar flow hood as an example) :
Preparations before replacement
Tools and materials: Screwdrivers, wrenches, and other disassembly tools, new HEPA filters (confirm that the model and size match, such as 320×320×50mm, etc.), sealing strips, 75% ethanol, dust-proof cloth.
Environmental preparation: Turn off the power of the workbench, remove all items on the tabletop, and wipe the inner tabletop, four walls, and the filter installation area with 75% ethanol to reduce dust and contaminants.
Personnel protection: Wear disposable gloves and masks. If the filter may carry contaminants, a lab coat or protective suit must be worn.
2. Remove the old filter
Locate the installation position: HEPA filters are usually installed in the static pressure box at the top of the workbench. For some equipment, the control panel or top cover plate needs to be removed first (follow the instructions in the manual).
Power-off and pressure relief: After ensuring the equipment is powered off, unscrew the screws (usually 4 to 6) that fix the filter, and slowly open the cover plate of the static pressure box to prevent dust from falling.
Carefully remove the old filter: Grasp the edge of the filter (avoid touching the surface of the filter material), and take out the old filter horizontally. If the filter material is found to be damaged, wrap it with a dust-proof cloth and carefully discard it to prevent the spread of dust.
3. Install the new filter
Clean the installation surface: Wipe the filter installation frame with ethanol to remove dust and residual old sealant, ensuring the surface is flat and dry.
Check the new filter: Before opening the new HEPA filter, check if the packaging is intact and if the filter material is damaged. After confirming that the model and size are correct, gently place it into the installation frame to ensure that the edges fit tightly against the frame.
Fixation and sealing: Fix the filter with screws. Make sure to tighten them evenly diagonally to avoid deformation caused by uneven force. If the original sealing rubber strip ages, a new one (usually made of sponge or silicone) should be replaced to ensure there is no gap between the filter and the frame (which can be inspected visually or by touch).
4. Sealing and Testing
Sealant treatment: If there are tiny gaps in the installation frame, a small amount of food-grade sealant (such as silicone sealant) can be applied to the edge of the filter. After the sealant has cured, the equipment can be activated.
Preliminary leak detection: After installation is completed, turn on the fan and run it for 10 minutes. Place your hand close to the edge of the filter to feel if there is any air leakage, or bring a smoke test agent (such as aerosol) close to the edge to observe if the smoke is sucked into the gap (no smoke leakage indicates good sealing).
5. Verification after replacement
Wind speed detection: Use an anemometer to evenly select 5 to 9 points above the workbench surface (such as diagonal or grid points). The measured wind speed should be within the range of 0.3 to 0.6m/s, and the deviation of wind speed at each point should not exceed 20%.
Resistance test: Check the resistance indicator. The initial resistance of the new filter should be consistent with the value marked in the manual (e.g., 200±20Pa).
Sterility test: If it is used for high-level sterility experiments, a sedimentation bacteria test (incubate after placing the petri dish for 30 minutes) is required to confirm that the number of colonies in the workbench is ≤5CFU per dish.
6. Waste disposal and record-keeping
Disposal of old filters: If the old filters are not contaminated, they can be discarded as ordinary solid waste. If exposed to microorganisms or harmful substances, it should be treated as biohazardous waste in a sealed manner (such as wrapped in double-layer plastic bags and then sterilized under high pressure).
Maintenance records: Record the replacement time, filter model, initial resistance, operator, and other information in the ledger to facilitate subsequent traceability.
Iii. Precautions
Do not touch the filter material with bare hands: The filter material of HEPA filters is made of superfine fibers. Touching it with bare hands may cause the fibers to fall off or the filter material to be damaged, affecting the filtration efficiency.
The professional operation takes priority: If it is the first time replacement or the equipment model is special, it is recommended to contact the manufacturer's technical personnel for on-site guidance to avoid air leakage or efficiency decline due to improper installation.
Avoid secondary pollution: During the replacement process, keep the workbench clean. After the operation, wipe the interior again with ethanol. If necessary, turn on the ultraviolet lamp to irradiate for 30 minutes.
Filter storage requirements: Unopened HEPA filters should be stored in a dry and dust-free environment, avoiding heavy pressure or tilting to prevent deformation of the filter material.
Through scientific assessment of the replacement cycle and standardized operation, it can be ensured that the HEPA filter continuously and effectively blocks particles ≥0.3μm (filtration efficiency ≥99.97%), maintaining the sterile environment of the laminar flow hood. If abnormal wind speed or air leakage still occurs after replacement, the machine should be stopped immediately to check the installation quality or contact professional maintenance personnel.