In the purification system of hospital operating rooms, the HEPA Filter (High-Efficiency Particulate Air Filter) plays an essential role in achieving air cleanliness and controlling microbial contamination. The filter directly affects the aseptic level of the surgical environment and the patient’s risk of postoperative infection. Its application focuses on three main goals: efficiently capturing particles, ensuring clean airflow, and adapting to the design of purification systems. These goals are reflected in several areas: application principles, key features, installation scenarios, selection criteria, and maintenance requirements.
The following section outlines the application principle for these filters, focusing on how they efficiently intercept particles and block the transmission path of microorganisms.
Particles in the air of the operating room—such as dust, dander, bacterial spores, and virus droplet nuclei—are key triggers for surgical site infections (SSI). The main function of the non-woven high-efficiency filter is to retain particles in the airflow. It does so using four mechanisms: mechanical interception, inertial collision, diffusion deposition, and electrostatic adsorption.
Mechanical interception: For larger particles with a diameter greater than 0.5μm, they are directly blocked by the fiber mesh of the filter.
Inertial impact: Particles in high-speed airflow deviate from the streamline due to inertia and collide with the surface of fibers, thus being captured.
Diffusion deposition: For tiny particles with a diameter of less than 0.1μm, they are adsorbed due to random collisions with fibers caused by Brownian motion.
Electrostatic adsorption: The fibers of some filters have undergone electrostatic treatment, which adsorbs charged particles through electrostatic force (even if the particles are not charged, they may still be captured due to induced charging).
According to the national standard “High-Efficiency Air Filters” (GB/T 13554-2020), the non-woven high-efficiency filter has a capture efficiency of ≥99.97% for standard particles of 0.3μm, and can effectively retain the vast majority of pathogenic microorganisms in the operating room (such as bacteria with diameters mostly ranging from 0.5 to 5μm, and virus droplet nuclei mostly ranging from 0.3 to 1μm). Cut off the airborne transmission route from the source.
Ii. Core Features: Key advantages Compatible with operating room purification systems
Compared with traditional high-efficiency filters with separators (using glass fiber as the separator to separate the filter material), high-efficiency filters without separators have become the preferred choice for operating room purification systems due to the following characteristics:
| Characteristic dimension | Advantages of high-efficiency filters without separators | The core value of the operating room |
| Structural compactness | Using hot melt adhesive or silk thread instead of fiberglass partitions, the thickness is only 1/3 to 1/2 of that with partitions (usually 40-80mm), and the volume is smaller. | Save installation space in the ceiling and adapt to the compact purification system layout of the operating room (especially suitable for the supply air static pressure box in laminar flow operating rooms). |
| Airflow uniformity | The unfolded area of the filter material is larger, the air flow velocity through the filter material is lower (usually < 0.5m/s), and the air flow distribution at the outlet is more uniform. | Avoid local airflow disorder, ensure the stability of the airflow in the surgical area (especially in the “Class 100 clean area”), and prevent the secondary flying of particles. |
| Lightweight | The filter material is glass fiber or PTFE (polytetrafluoroethylene), without heavy partitions. The weight of a single unit is only 1/5 to 1/3 of that with partitions. | Reduce the load-bearing pressure on the ceiling, decrease the operational difficulty during installation and replacement, and enhance maintenance safety. |
| Better sealing performance | The use of one-piece formed sealant (such as polyurethane sealant) ensures a tight bond with the frame, reducing the risk of “bypass leakage”. | Prevent unfiltered contaminated air from seeping into the clean area through the gap between the filter and the frame to ensure the purification effect. |
| It has strong moisture resistance |
Some models can withstand temperatures below 80℃ and relative humidity above 60%, making them suitable for the environment after disinfection in operating rooms (such as formaldehyde fumigation). |
To meet the regular disinfection requirements of the operating room and prevent the filter from deforming due to moisture or losing efficiency. |
Iii. Installation Scenario: Covering the core airflow path of the operating room purification system
The installation position of the non-partitioned high-efficiency filter directly determines the performance of the purification system. In operating rooms, it is mainly applied at the end of the supply air system and the front end of the exhaust air system. The specific scenarios are as follows:
1. “Supply air terminal” of laminar flow operating room: Achieve local 100-level cleanliness
Laminar flow operating rooms (such as vertical laminar flow and horizontal laminar flow) are the surgical environments with the highest cleanliness requirements (the core area needs to meet the “Class 100” standard in “Technical Specifications for Clean Operating Rooms in Hospitals” GB 50333-2013), and the non-partited high-efficiency filter is the core to achieve this standard:
Vertical laminar flow operating room: The filter is installed at the bottom of the “supply air static pressure box” in the ceiling, forming a “top supply and bottom return” air flow organization – clean air is evenly conveyed downward through the filter, covering core areas such as the operating table and the doctor’s operation area, while contaminated air is pushed to the ground and discharged from the return air outlet, preventing contaminants from spreading to the operating area.
Horizontal laminar flow operating room: The filter is installed in the supply air static pressure box on the side wall, and the clean air flows horizontally to the return air outlet on the opposite side. It is suitable for small-scale surgeries or special surgeries (such as neurosurgery and ophthalmology), ensuring the cleanliness of the surgical area along the airflow direction.
2. “End of the supply air main pipe” in non-laminar flow clean operating rooms
For operating rooms with slightly lower cleanliness requirements (such as Class 10,000 and Class 100,000), high-efficiency filters without separators are installed at the end of the supply air main pipe. Clean air is sent into the room through diffusers and, in combination with the primary/medium efficiency filters at the return air outlets, forms a “turbulent clean” environment to meet the aseptic requirements of general surgical operations.
3. “Front-end pretreatment” of the exhaust system: Preventing pollution leakage
In the exhaust system of the operating room, the non-woven high-efficiency filter is installed at the front end of the exhaust unit, which is used to intercept microorganisms and harmful particles (such as aerosols and drug dust generated during surgery) in the indoor exhaust air, preventing contaminated air from being directly discharged outdoors or causing pollution to the machine room. It is particularly suitable for exhaust treatment in infectious disease operating rooms and negative pressure operating rooms.
4. Auxiliary area: Ensure the integrity of the clean chain
In addition to the operating room itself, high-efficiency filters without separators should also be installed in the supply air systems of the clean auxiliary areas (such as the sterile item storage room, hand-washing room, and pre-anesthesia room) to ensure that the “clean chain” of the entire operating department has no breaks.
Iv. Selection and Acceptance: Core standards for matching the cleanliness level of the operating room
The selection of high-efficiency filters without separators must be strictly based on the cleanliness level, air flow organization form and usage scenarios of the operating room. The core selection indicators are as follows:
The installation position of the non-partitioned high-efficiency filter directly determines the performance of the purification system. In operating rooms, it is mainly applied at the end of the supply air system and the front end of the exhaust air system. The specific scenarios are as follows:
1. “Supply air terminal” of laminar flow operating room: Achieve local 100-level cleanliness
Laminar flow operating rooms (such as vertical laminar flow and horizontal laminar flow) are the surgical environments with the highest cleanliness requirements (the core area needs to meet the “Class 100” standard in “Technical Specifications for Clean Operating Rooms in Hospitals” GB 50333-2013), and the non-partited high-efficiency filter is the core to achieve this standard:
Vertical laminar flow operating room: The filter is installed at the bottom of the “supply air static pressure box” in the ceiling, forming a “top supply and bottom return” air flow organization – clean air is evenly conveyed downward through the filter, covering core areas such as the operating table and the doctor’s operation area, while contaminated air is pushed to the ground and discharged from the return air outlet, preventing contaminants from spreading to the operating area.
Horizontal laminar flow operating room: The filter is installed in the supply air static pressure box on the side wall, and the clean air flows horizontally to the return air outlet on the opposite side. It is suitable for small-scale surgeries or special surgeries (such as neurosurgery and ophthalmology), ensuring the cleanliness of the surgical area along the airflow direction.
2. “End of the supply air main pipe” in non-laminar flow clean operating rooms
For operating rooms with slightly lower cleanliness requirements (such as Class 10,000 and Class 100,000), high-efficiency filters without separators are installed at the end of the supply air main pipe. Clean air is sent into the room through diffusers and, in combination with the primary/medium efficiency filters at the return air outlets, forms a “turbulent clean” environment to meet the aseptic requirements of general surgical operations.
3. “Front-end pretreatment” of the exhaust system: Preventing pollution leakage
In the exhaust system of the operating room, the non-woven high-efficiency filter is installed at the front end of the exhaust unit, which is used to intercept microorganisms and harmful particles (such as aerosols and drug dust generated during surgery) in the indoor exhaust air, preventing contaminated air from being directly discharged outdoors or causing pollution to the machine room. It is particularly suitable for exhaust treatment in infectious disease operating rooms and negative pressure operating rooms.
4. Auxiliary area: Ensure the integrity of the clean chain
In addition to the operating room itself, high-efficiency filters without separators should also be installed in the supply air systems of the clean auxiliary areas (such as the sterile item storage room, hand-washing room, and pre-anesthesia room) to ensure that the “clean chain” of the entire operating department has no breaks.
Iv. Selection and Acceptance: Core standards for matching the cleanliness level of the operating room
The selection of high-efficiency filters without separators must be strictly based on the cleanliness level, air flow organization form and usage scenarios of the operating room. The core selection indicators are as follows:
| Selection index | Basis for requirements | Example (Class 100 Vertical Laminar Flow Operating Room) |
| Efficacité de la filtration | For a Class 100 operating room, “High-efficiency Grade 13” (with an efficiency of ≥99.97% for 0.3μm particles) should be selected. For levels 10,000 and below, “High Efficiency Level 12” can be selected. | Select H13 grade non-partitioned high-efficiency filters (conforming to GB/T 13554-2020 standard). |
| Rated air volume | The area of the operating room and the air flow velocity should be matched (the wind speed in the core area of the vertical laminar flow should be ≥0.25m/s) to avoid insufficient air volume or overload. | For a 40㎡ operating room, 2 to 3 filters with a single rated air volume of 1500m³/h should be selected. |
| Matériau du cadre | Aluminum alloy or stainless steel frames are preferred as they are corrosion-resistant, non-volatile and can prevent secondary pollution. | The anodized aluminum alloy frame is selected, with a thickness of ≥1.5mm. |
| Sealing form |
It adopts “liquid trough seal” or “double rubber seal”. The liquid trough seal is suitable for Class 100 operating rooms (with better sealing performance). |
Polyurethane liquid tank sealing is adopted, combined with silicone sealing strips, to ensure no bypass leakage. |
| Temperature and humidity resistance | It needs to withstand the disinfection temperature of the operating room (such as formaldehyde fumigation temperature ≤60℃) and relative humidity (≤80%). | Select filter materials and sealants with a temperature resistance of 70℃ and a moisture resistance of 85%. |
Acceptance criteria: After installation, it is necessary to pass the “scanning leak detection test” (in accordance with the requirements of GB 50333-2013) – use an aerosol photometer to scan the frame, sealing area and surface of the filter material of the filter. The leakage rate should be ≤0.01% to ensure that no polluted air seeps in.
V. Maintenance and Replacement: The Key to Ensuring long-term Stable Operation
The performance of the high-efficiency filter without separators will decline over time (such as filter material clogging and seal aging), and a strict maintenance system needs to be established
Regular monitoring
Monitor the “resistance change” of the filter every month (through the differential pressure gauge on the static pressure box). When the resistance reaches twice the initial resistance, it needs to be replaced in time.
Every quarter, the capture efficiency of the filter is verified through “cleanliness testing” (such as particle counters) to ensure that the cleanliness level of the operating room is not lower than the design standard.
Replacement requirements
When replacing, the operation should be carried out in a clean environment (such as wearing sterile clothing and using dust-free tools) to prevent the filter material from being contaminated.
Before installing a new filter, it is necessary to check the sealing of the frame and the integrity of the filter material. After installation, a re-scan for leak detection should be conducted.
The replaced waste filters should be sealed and packaged and treated as “medical waste” (to prevent the spread of retained microorganisms).
Daily protection
The front end of the filter needs to be equipped with a “primary filter” (G4 grade) and a “medium filter” (F8 grade) to intercept large particle pollutants and extend the service life of the high-efficiency filter (usually 1-2 years, depending on the frequency of use in the operating room).
When disinfecting the operating room, the air supply system should be turned off to prevent the disinfectant from corroding the filter materials.
Vi. Summary: The “Last Line of Defense” for Operating Room Purification
The non-woven high-efficiency filter, with its highly efficient particle retention capacity, compact structural design and stable operational performance, has become an irreplaceable core device in the purification system of hospital operating rooms. Its application not only directly determines the cleanliness of the surgical environment, but also is the key to reducing the risk of postoperative infection for patients and ensuring surgical safety. In practical applications, it is necessary to combine “scientific selection, standardized installation and regular maintenance” to fully exert its efficiency and provide a continuous and stable sterile air environment for the operating room.
V. Maintenance and Replacement: The Key to Ensuring long-term Stable Operation
The performance of the high-efficiency filter without separators will decline over time (such as filter material clogging and seal aging), and a strict maintenance system needs to be established
Regular monitoring
Monitor the “resistance change” of the filter every month (through the differential pressure gauge on the static pressure box). When the resistance reaches twice the initial resistance, it needs to be replaced in time.
Every quarter, the capture efficiency of the filter is verified through “cleanliness testing” (such as particle counters) to ensure that the cleanliness level of the operating room is not lower than the design standard.
Replacement requirements
When replacing, the operation should be carried out in a clean environment (such as wearing sterile clothing and using dust-free tools) to prevent the filter material from being contaminated.
Before installing a new filter, it is necessary to check the sealing of the frame and the integrity of the filter material. After installation, a re-scan for leak detection should be conducted.
The replaced waste filters should be sealed and packaged and treated as “medical waste” (to prevent the spread of retained microorganisms).
Daily protection
The front end of the filter needs to be equipped with a “primary filter” (G4 grade) and a “medium filter” (F8 grade) to intercept large particle pollutants and extend the service life of the high-efficiency filter (usually 1-2 years, depending on the frequency of use in the operating room).
When disinfecting the operating room, the air supply system should be turned off to prevent the disinfectant from corroding the filter materials.
Vi. Summary: The “Last Line of Defense” for Operating Room Purification
The non-woven high-efficiency filter, with its highly efficient particle retention capacity, compact structural design and stable operational performance, has become an irreplaceable core device in the purification system of hospital operating rooms. Its application not only directly determines the cleanliness of the surgical environment, but also is the key to reducing the risk of postoperative infection for patients and ensuring surgical safety. In practical applications, it is necessary to combine “scientific selection, standardized installation and regular maintenance” to fully exert its efficiency and provide a continuous and stable sterile air environment for the operating room.
