I. Indoor air pollution sources and their transmission routes
1. Indoor staff
Personnel dust is the most important source of dust-free indoor air pollution, accounting for 80% to 90%. The amount of dust generated when a person moves is quite complicated, and the amount of dust generated when a person is stationary (or substantially stationary) and the amount of dust generated during intense activity are approximately 10 times different. It is impossible for a person to be active during indoor activities. If the average of these actions is taken, it can be considered that the amount of dust generated by a person during indoor activities is 5 times that of his or her resting (or substantially still), namely: 5× 105 tablets / (min • person).
According to the nature of the process, the number of people's movements and the strength and weakness, the multiples are different and can be divided into lower (labor intensity is very low or sitting operation, almost rarely active) and higher (labor intensity than normal level) High or active (two), respectively, 3 times and 7 times the amount of static dust, corresponding to 3 × 105 / (min • person) and 7 × 105 / (min • person). Of course, the amount of dust generated by the human body also has a great relationship with the clothing, and it also has a great relationship with the washing and drying of the clothes. According to the actual use and experimental measurement, the nylon silk clean clothes have the least amount of dust, and the cotton cleansing work clothes are more dusty than the nylon silk. If a cotton overall workwear is added to the nylon silk garment, the amount of dust generated by the nylon silk overalls can be further reduced. In addition, clean overalls should not be washed, and should be dried in a clean environment after washing.
2, equipment and process dust
The dust generated by the equipment is particularly prominent in rotating equipment. Motors (especially motors with carbon brushes), gear rotating parts, servo mechanical parts, hydraulic and pneumatic starter switches or manually operated equipment are all due to moving (rotating) surfaces. Particles are generated by friction between them. Western industrial countries have carried out corresponding experimental research on the different operation modes of clean rooms, the different speeds, the typical actions of mechanical equipment of different materials and the dust production of some electrical appliances. The reference value of some dust particle emission is given to the mechanical and electrical pollution sources of the clean room, which provides a calculation basis for the clean room ventilation design.
3. Contaminated areas adjacent to the clean room
In areas with low cleanliness or non-clean areas adjacent to or in close proximity to the clean room, contaminated air carried by personnel or materials, or contaminants deposited on people and materials are brought into the room. Another important source of pollution for cleanliness. A reasonable positive pressure difference is an important measure to reduce the intrusion of polluted air through the gaps of the envelope structure and the transmission windows, doors, and conveyor belt openings. The air lock chamber, the buffer chamber and the air shower chamber located at the door also have a certain effect. However, it is also difficult to completely avoid the interference and influence of the surrounding pollution area on the clean room environment, especially the clean room is in the vicinity of the outer door. Therefore, the key process areas should be kept away from the outer door.
4, unfiltered air supply
Under normal circumstances, after the new or rebuilt clean room or the final filter is replaced, the strict acceptance test is carried out according to the specifications. If the high-efficiency filter itself, the contact surface of the high-efficiency air filter and the support frame leaks, All should be detected and dealt with. At this time, the air supply system does not have air that has entered the clean room without being filtered. It is worth noting and paying attention to the fact that during the production process, the fragile high-efficiency filter paper core is not inadvertently touched according to the operating regulations, or the high-efficiency filter support frame is caused by vibration or aging and deterioration of the sealing pad, resulting in a high-efficiency filter and Cracks in the gasket or strip of the contact surface of the frame, which leak unfiltered air and contaminate the clean room, are also the focus of daily monitoring work.
5, raw materials, packaging, etc.
Pre-cleaning, unpacking locations and methods for equipment, materials, containers, packaging, etc. entering the clean room, as well as procedures for entering the clean room, shall be performed in accordance with the relevant regulations for clean room operation management. However, even if it is strictly in accordance with relevant regulations and procedures, it is still difficult to completely prevent contaminants adhering to raw materials, containers, packaging, and especially small components of products that are difficult to thoroughly clean, from being carried into the clean room. They constitute another important source of pollution in the production process and are often overlooked at this point. When a problem arises, it is usually focused on finding defects in the air conditioning purification system.
Second, the control method for pollution sources
1. Pollution emitted by control personnel
People's nose, mouth, skin, hair and body clothing emit pollutants. The pollution emitted by the control personnel is first controlled by the number of people entering the clean room. Those who are not directly related to production and scientific research, and who are not trained in the code of the clean room staff, shall not enter the clean room. The entering personnel should follow the clean room code of practice, neatly wear clean overalls, wear work gloves, masks, headgear, clean shoes, and enter through clean passages. Strict management is required for personnel entering and leaving the clean room. For example, cosmetics are not allowed to enter the clean room, bathing regularly, watches and jewelry are not allowed in the clean room, smoking is not allowed within a few hours before entering the clean room. Personal belongings enter the clean room and so on. In addition to minimizing the pollutants emitted by the personnel, the airflow of the air-conditioning purifying air is also an important means to effectively dilute, channel and discharge the pollutants emitted by the personnel. For example, the passage of personnel walking is the main location for emitting pollutants, where the return and exhaust vents are placed in the indoor downwind direction to minimize the spread of pollutants emitted by personnel to other areas of the clean room. Another example is that the key process parts are placed in the clean room where non-operators are not easily accessible to reduce additional personnel pollution.
2. Control the dust production of process equipment and processes
The process equipment in the clean room should be well-selected, smooth and wear-resistant. Those rotating and sliding parts are especially important, and the wear and dust should be reduced as much as possible. For those dust-producing processes, they should be closed or fenced as much as possible, and supplemented with exhaust air to form a partial pressure relative to the clean room to limit the diffusion of pollutants to other areas of the clean room. Regular cleaning and wiping of indoor machinery and equipment is a necessary system and an effective measure to reduce the secondary flight of dust.
3, the pressure difference between adjacent clean rooms of different levels
The main method to prevent the spread of pollution from the adjacent cleanliness area to the clean room is to maintain a high cleanliness area relative to the low cleanliness area, the low cleanliness area relative to the service area, and the service area relative to the outside. Positive pressure value. According to different situations, the positive pressure values ​​of adjacent rooms of different levels are about 5Pa-10Pa. The pressure difference of the ladders at different levels of cleanliness is maintained. When the door of the room is closed, the flow of air through the gap flows from the high-grade clean room to the low-level clean room and from the low-grade clean room. The corridor and service area flow to the outside. This can reduce the floating pollutants in the air from the outdoor to the service area, the service area to the low-grade clean room, and the low-grade clean room to the high-grade clean room. The positive pressure value is not as large as possible. Many theoretical studies and practices have proved that even when the personnel and materials pass through the door, even if the pressure difference between the two sides of the door is as high as 50Pa~60Pa, it is difficult to absolutely avoid the carrying air flow when the personnel and materials move inward. Bring pollution into the room. Especially when there is a temperature difference on both sides of the door, after the door is opened, even if there is no movement, there is a reverse flow in the area of ​​the opening section, and the air is polluted. In addition, too high positive pressure difference will make the door of the clean room difficult to open and difficult to close, the squeak noise caused by the door airflow, and the increase of air volume due to excessive airflow overflow, waste energy and increase the filter of each level. burden.
4, clean room air supply filtration
The end device of the clean room air conditioning air supply system--high efficiency air filter or ultra-high efficiency air filter can effectively filter the particulate pollutants in the fresh air and return air treated by the air conditioning unit under normal conditions. The clean air treated by the high-efficiency and ultra-efficient air filter is sent into the room, which can effectively replace and dilute indoor pollutants to maintain indoor cleanliness. However, if the final filter is damaged or the seal between the filter and the support frame is cracked and the airtightness is invalid, the air filtered by the high-efficiency air filter may carry a large amount of polluted particles into the room and diffuse with the airflow, and the harmful influence The scope is large. Therefore, it is very important to check, leak or replace the final filter before the clean room is put into use. It is also important to protect against damage to the final filter during operation.
5. Cleaning of materials and components entering the clean room
Cleanroom products and raw materials, product containers and packaging materials must be made of non-contaminating materials. The manufacture of these materials is also carried out in an environment where the product contamination is relatively small. For example, injection molding workshops for large infusion plastic bottles should maintain a certain level of cleanliness to reduce the pollution load of the large infusion potting process environment. The various components entering the clean room should be clean and packaged to meet the requirements. When unpacking in a dust-free room, ensure that these parts are not contaminated. Parts that do not meet the requirements for clean room use should be cleaned before entering the clean room. I. Indoor air pollution sources and their transmission routes
1. Indoor staff
Personnel dust is the most important source of dust-free indoor air pollution, accounting for 80% to 90%. The amount of dust generated when a person moves is quite complicated, and the amount of dust generated when a person is stationary (or substantially stationary) and the amount of dust generated during intense activity are approximately 10 times different. It is impossible for a person to be active during indoor activities. If the average of these actions is taken, it can be considered that the amount of dust generated by a person during indoor activities is 5 times that of his or her resting (or substantially still), namely: 5× 105 tablets / (min • person).
According to the nature of the process, the number of people's movements and the strength and weakness, the multiples are different and can be divided into lower (labor intensity is very low or sitting operation, almost rarely active) and higher (labor intensity than normal level) High or active (two), respectively, 3 times and 7 times the amount of static dust, corresponding to 3 × 105 / (min • person) and 7 × 105 / (min • person). Of course, the amount of dust generated by the human body also has a great relationship with the clothing, and it also has a great relationship with the washing and drying of the clothes. According to the actual use and experimental measurement, the nylon silk clean clothes have the least amount of dust, and the cotton cleansing work clothes are more dusty than the nylon silk. If a cotton overall workwear is added to the nylon silk garment, the amount of dust generated by the nylon silk overalls can be further reduced. In addition, clean overalls should not be washed, and should be dried in a clean environment after washing.
2, equipment and process dust
The dust generated by the equipment is particularly prominent in rotating equipment. Motors (especially motors with carbon brushes), gear rotating parts, servo mechanical parts, hydraulic and pneumatic starter switches or manually operated equipment are all due to moving (rotating) surfaces. Particles are generated by friction between them. Western industrial countries have carried out corresponding experimental research on the different operation modes of clean rooms, the different speeds, the typical actions of mechanical equipment of different materials and the dust production of some electrical appliances. The reference value of some dust particle emission is given to the mechanical and electrical pollution sources of the clean room, which provides a calculation basis for the clean room ventilation design.
3. Contaminated areas adjacent to the clean room
In areas with low cleanliness or non-clean areas adjacent to or in close proximity to the clean room, contaminated air carried by personnel or materials, or contaminants deposited on people and materials are brought into the room. Another important source of pollution for cleanliness. A reasonable positive pressure difference is an important measure to reduce the intrusion of polluted air through the gaps of the envelope structure and the transmission windows, doors, and conveyor belt openings. The air lock chamber, the buffer chamber and the air shower chamber located at the door also have a certain effect. However, it is also difficult to completely avoid the interference and influence of the surrounding pollution area on the clean room environment, especially the clean room is in the vicinity of the outer door. Therefore, the key process areas should be kept away from the outer door.
4, unfiltered air supply
Under normal circumstances, after the new or rebuilt clean room or the final filter is replaced, the strict acceptance test is carried out according to the specifications. If the high-efficiency filter itself, the contact surface of the high-efficiency air filter and the support frame leaks, All should be detected and dealt with. At this time, the air supply system does not have air that has entered the clean room without being filtered. It is worth noting and paying attention to the fact that during the production process, the fragile high-efficiency filter paper core is not inadvertently touched according to the operating regulations, or the high-efficiency filter support frame is caused by vibration or aging and deterioration of the sealing pad, resulting in a high-efficiency filter and Cracks in the gasket or strip of the contact surface of the frame, which leak unfiltered air and contaminate the clean room, are also the focus of daily monitoring work.
5, raw materials, packaging, etc.
Pre-cleaning, unpacking locations and methods for equipment, materials, containers, packaging, etc. entering the clean room, as well as procedures for entering the clean room, shall be performed in accordance with the relevant regulations for clean room operation management. However, even if it is strictly in accordance with relevant regulations and procedures, it is still difficult to completely prevent contaminants adhering to raw materials, containers, packaging, and especially small components of products that are difficult to thoroughly clean, from being carried into the clean room. They constitute another important source of pollution in the production process and are often overlooked at this point. When a problem arises, it is usually focused on finding defects in the air conditioning purification system.
Second, the control method for pollution sources
1. Pollution emitted by control personnel
People's nose, mouth, skin, hair and body clothing emit pollutants. The pollution emitted by the control personnel is first controlled by the number of people entering the clean room. Those who are not directly related to production and scientific research, and who are not trained in the code of the clean room staff, shall not enter the clean room. The entering personnel should follow the clean room code of practice, neatly wear clean overalls, wear work gloves, masks, headgear, clean shoes, and enter through clean passages. Strict management is required for personnel entering and leaving the clean room. For example, cosmetics are not allowed to enter the clean room, bathing regularly, watches and jewelry are not allowed in the clean room, smoking is not allowed within a few hours before entering the clean room. Personal belongings enter the clean room and so on. In addition to minimizing the pollutants emitted by the personnel, the airflow of the air-conditioning purifying air is also an important means to effectively dilute, channel and discharge the pollutants emitted by the personnel. For example, the passage of personnel walking is the main location for emitting pollutants, where the return and exhaust vents are placed in the indoor downwind direction to minimize the spread of pollutants emitted by personnel to other areas of the clean room. Another example is that the key process parts are placed in the clean room where non-operators are not easily accessible to reduce additional personnel pollution.
2. Control the dust production of process equipment and processes
The process equipment in the clean room should be well-selected, smooth and wear-resistant. Those rotating and sliding parts are especially important, and the wear and dust should be reduced as much as possible. For those dust-producing processes, they should be closed or fenced as much as possible, and supplemented with exhaust air to form a partial pressure relative to the clean room to limit the diffusion of pollutants to other areas of the clean room. Regular cleaning and wiping of indoor machinery and equipment is a necessary system and an effective measure to reduce the secondary flight of dust.
3, the pressure difference between adjacent clean rooms of different levels
The main method to prevent the spread of pollution from the adjacent cleanliness area to the clean room is to maintain a high cleanliness area relative to the low cleanliness area, the low cleanliness area relative to the service area, and the service area relative to the outside. Positive pressure value. According to different situations, the positive pressure values ​​of adjacent rooms of different levels are about 5Pa-10Pa. The pressure difference of the ladders at different levels of cleanliness is maintained. When the door of the room is closed, the flow of air through the gap flows from the high-grade clean room to the low-level clean room and from the low-grade clean room. The corridor and service area flow to the outside. This can reduce the floating pollutants in the air from the outdoor to the service area, the service area to the low-grade clean room, and the low-grade clean room to the high-grade clean room. The positive pressure value is not as large as possible. Many theoretical studies and practices have proved that even when the personnel and materials pass through the door, even if the pressure difference between the two sides of the door is as high as 50Pa~60Pa, it is difficult to absolutely avoid the carrying air flow when the personnel and materials move inward. Bring pollution into the room. Especially when there is a temperature difference on both sides of the door, after the door is opened, even if there is no movement, there is a reverse flow in the area of ​​the opening section, and the air is polluted. In addition, too high positive pressure difference will make the door of the clean room difficult to open and difficult to close, the squeak noise caused by the door airflow, and the increase of air volume due to excessive airflow overflow, waste energy and increase the filter of each level. burden.
4, clean room air supply filtration
The end device of the clean room air conditioning air supply system--high efficiency air filter or ultra-high efficiency air filter can effectively filter the particulate pollutants in the fresh air and return air treated by the air conditioning unit under normal conditions. The clean air treated by the high-efficiency and ultra-efficient air filter is sent into the room, which can effectively replace and dilute indoor pollutants to maintain indoor cleanliness. However, if the final filter is damaged or the seal between the filter and the support frame is cracked and the airtightness is invalid, the air filtered by the high-efficiency air filter may carry a large amount of polluted particles into the room and diffuse with the airflow, and the harmful influence The scope is large. Therefore, it is very important to check, leak or replace the final filter before the clean room is put into use. It is also important to protect against damage to the final filter during operation.
5. Cleaning of materials and components entering the clean room
Cleanroom products and raw materials, product containers and packaging materials must be made of non-contaminating materials. The manufacture of these materials is also carried out in an environment where the product contamination is relatively small. For example, injection molding workshops for large infusion plastic bottles should maintain a certain level of cleanliness to reduce the pollution load of the large infusion potting process environment. The various components entering the clean room should be clean and packaged to meet the requirements. When unpacking in a dust-free room, ensure that these parts are not contaminated. Parts that do not meet the requirements for clean room use should be cleaned before entering the clean room.
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