In the hallowed halls of modern medicine, clean operating rooms are the last physical barrier protecting patients' lives. While we marvel at the advanced surgical techniques, we often overlook the air purification system that works tirelessly day and night overhead. This system is like the "respiratory system" of the operating room, and its core component---the air filter---is the "invisible defense" against bacteria and dust.
Primary filter: The vanguard in the battle.
The primary filter (pre-filter) is the first line of defense in an air purification system, typically installed at the fresh air inlet or mixing section of an air handling unit (AHU). Its role is like that of a strong and capable "vanguard," responsible for intercepting those visible "large" enemies in the air.
These filters are primarily made of non-woven fabric (synthetic fiber), metal mesh (stainless steel mesh), or nylon mesh, and have a relatively coarse structure. Their main task is to capture particles larger than 5 micrometers in diameter, such as airborne hair, lint, pollen, and large dust particles. Without the effective interception of the primary filter, these impurities will quickly clog subsequent, more sophisticated filtration devices. Therefore, primary filters require the most frequent maintenance, typically needing to be replaced every 1 to 2 months, or cleaned promptly when dust accumulation is severe to ensure sufficient fresh airflow.
Medium-efficiency filter: the "backbone" bridging the gap between upstream and downstream applications.
Although the air that has passed through the primary filter removes large particles, it still contains many fine dust particles and microorganisms. This is where the medium-efficiency filter (medium filter) comes in. Located after the primary filter and before the high-efficiency filter, it plays a crucial role in bridging the gap between the two.
Medium-efficiency filters typically employ a bag-type structure (pocket filter), filled internally with glass fiber or synthetic fiber, with a denser fiber arrangement. They effectively capture particles with diameters between 1 and 5 micrometers, such as fine dust, smoke, and some bacterial carriers. As the "backbone" of the system, medium-efficiency filters not only further purify the air, but more importantly, they protect the expensive high-efficiency filters at the end, preventing premature clogging. Generally, medium-efficiency filters should be replaced every 3 to 6 months, making them a crucial element in maintaining stable system operation.
High-efficiency air filters (HEPA) filters: the ultimate gatekeeper for victory.
If the first two stages of filtration are the foundation, then the high-efficiency air filters (HEPA ) is the "ultimate arbiter" of air quality in a clean operating room. It is usually installed at the air supply terminal in the ceiling of the operating room (ceiling HEPA) and is the last barrier before the air enters the surgical area.
HEPA filters are made of countless extremely fine glass fibers folded together, forming intricate nanoscale channels. They boast a filtration efficiency of over 99.97% for particles with a diameter of 0.3 micrometers or larger (including the vast majority of bacteria, viruses, and dust). This barrier ensures that the air delivered to the operating table is nearly sterile, significantly reducing the risk of postoperative infection. HEPA filters have a long lifespan, typically lasting more than 3 years, but require regular resistance testing (pressure drop test). Once the resistance exceeds 160% of the initial resistance, the filter must be replaced immediately.
Sub-HEPA filters: "Elite guardians" for specific scenarios.
In areas where cleanliness requirements are slightly lower than Class 100 or Class 1000 operating rooms, or as a pre-filter for HEPA systems, Sub-HEPA filters (Sub high efficiency air filter) play a unique role. Their filtration efficiency falls between medium and high efficiency, primarily targeting particles larger than 0.5 micrometers in diameter, with filtration efficiencies ranging from 95% to 99.9%.
Sub-HEPA filters are compact in structure and have moderate resistance, and are commonly used in Class III and IV clean operating rooms or clean auxiliary rooms. Like an "elite guardian," while not as stringent as HEPA filters, they are sufficient to meet the aseptic requirements of general surgeries. They are also often used as pre-filters in HEPA systems to further extend the lifespan of the final filter.
From the coarse primary filter to the precise HEPA filter, these four stages of filters work in tandem to construct a comprehensive air purification network. Though hidden in ceilings and machine rooms, working silently, they are an indispensable cornerstone of the modern medical safety system. Regular maintenance and scientific management of these "invisible defenses" safeguard the life and health of every patient.
High-efficiency air outlets are ideal terminal filtration devices, widely used in medicine, health, electronics, chemicals and other industries. In order to verify whether the clean room can meet the cleanliness requirements, it is necessary to test the clean room and high-efficiency air outlets, so its detection is very important.
How to measure the air volume of high-efficiency air outlets:
1. You can use the air volume hood to directly aim at the nozzle for one-time measurement, direct measurement. Since your nozzle has many small holes (to make the air volume uniform) and there is a grille, then your anemometer can be kept 3-5 cm away from the nozzle. If you have a thermal anemometer, try to face the gap instead of the grille, and measure the average value by the grid method. The same cross-section can be measured.
2. You can measure at multiple points at a distance of 2 times the width of the diffuser from the air outlet. The measuring points should be like a grid and then the wind speed is averaged. The sizes of these vents are similar. Use tinplate or even plastic board to make a barrel that is slightly larger than the cross-section of the air outlet. When measuring, cover the barrel on the air outlet and use the anemometer to measure the nozzle of the barrel at multiple points and then calculate the average value.
3. Through the clean air conditioning circulation fan, through the high-efficiency air filter, medium-efficiency filter, and primary air filter, clean air can be obtained. The cleanliness is different and the wind flow direction is different. Of course, it is also necessary to supplement some fresh air through the fresh air outlet, otherwise people will feel stuffy inside.
Air volume measurement of high-efficiency air outlet:
1. The detection method of high-efficiency air outlet uses active sampling and passive sampling. Active sampling uses filtering method and impact method. Filtration method allows a certain amount of air to pass through an analytical filter.
2. The impact method can use Anderson sampler, Lute centrifugal sampler, and slit sampler. Passive sampling uses the landing method. Use the principle of diffusion of the open agar plate of suspended particles.
3. Of course, with the development of science and technology today, some more sophisticated detection instruments can also be used to quickly detect it.
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