Misunderstanding of Clean Room Cleanliness and HEPA Filter Selection

1     A misconception

As we all know, the highest filtration efficiency level of high-efficiency filters can reach 99.999995 or more for different particle sizes of pollution. In the past, there are always people who correspond the level of clean room with the efficiency level of high efficiency filter, and always think that the more 9 high efficiency filters are used, the cleaner the clean room can reach the cleanliness of 100 or even 10 levels.

In fact, this concept is wrong, although the high efficiency filter is the core component of the clean room, but the clean room want to achieve 100 or even 10 levels of cleanliness, high efficiency filter is not the only condition.

2 Influence factors of clean room cleanliness level

There are many factors affecting the cleanliness level of clean room, such as the number of air changes, door and window sealing, and personnel entering and leaving the air shower room.

2.1 Number of air changes

First of all, the number of air changes is one of the important factors that affect the cleanliness level of clean room. The number of air changes refers to the number of air exchanges inside and outside the clean room per unit of time. The clean room filters the dust and microorganisms in the air through high efficiency filters, while the air exchange can discharge the indoor pollutants in time and keep the cleanliness of indoor air. The higher the number of air exchange, the lower the concentration of pollutants in the clean room, and the higher the cleanliness level.

2.2 Door and window sealing

Secondly, the sealing degree of windows and doors is another important factor that affects the cleanliness level of clean rooms. The door and window sealing degree of clean room directly affects the degree of indoor and outdoor air exchange. If the doors and windows are not sealed tightly, the pollutants from outside can easily enter the clean room and affect the cleanliness of indoor air. Therefore, to improve the sealing performance of clean room doors and windows can effectively improve the cleanliness level.

2.3 Personnel entering and leaving

In addition, personnel access is also one of the key factors affecting the cleanliness level of clean rooms. When people enter and leave a clean room, they bring in outside contaminants such as dust, bacteria and viruses, which affects the cleanliness of indoor air. In order to reduce the impact of personnel access to clean room cleanliness, a series of measures can be taken, such as personnel dressing, clean room pressure settings, etc., to minimize the opportunity for outside contaminants to enter the clean room.

In summary, the cleanliness level of clean room is affected by the number of air changes, door and window sealing degree and personnel access and other factors. Reasonable control of the number of air changes, improved door and window sealing performance, and effective personnel access management measures can improve the cleanliness level of the clean room and ensure the quality of indoor air and the degree of hygiene. In future cleanroom design and operation, more attention needs to be paid to the consideration of these key factors in order to improve the cleanliness level and usage effect of cleanrooms.

3 Clean room Cleanliness levels and filter selection

Due to the different characteristics of the clean room, the choice of high-efficiency filters should first be determined according to the level of the clean room, the degree of sterility, temperature and humidity, the degree of fire resistance, anti-corrosion and other different requirements.

Such as the following 100 levels to choose Class A or B, more than 100 levels need to choose Class C filters; high temperature and high humidity conditions should be used metal dividers and metal frame filters; anti-corrosion requirements should be used plastic dividers and plastic frame filters; fire requirements, all the materials of the filter should be non-combustible and so on.

In practice, conventional filters refer to the high-efficiency air filter standard A and B, they are the most commonly used high-efficiency filters in the design of clean plants, generally less than or equal to 100,000 can choose A class; 10,000 ~ 100 can choose B class. Where the conventional high-efficiency filter, for ≥ 0.5μm particles can be calculated in accordance with the efficiency of 5 "9" that is 0.9999.

High efficiency filter is mainly used to filter air suspended particles below 0.3um, as a variety of filtration system end filtration; as for 300,000 level, 10,000 level, 1,000 level, and 100 level clean room clean area air filter selection configuration, generally speaking, the choice of filter is based on the clean room level requirements selected.

4 The general recommendation of HEPA filter configuration requirements

Class100: panel filter G4 (F5) + bag filter F7 (F8) + bag filter F9 + panel filter H13 + (air duct end FFU filter unit).

Class 1000: panel filter G4 (F5)+ bag filter F7 (F8)+ bag filter F9+ panel filter H11+(air duct end FFU filter unit).

Class10000: panel filter G4 (F5) + bag filter F7 (F8) + bag filter F9 + panel filter H11.

Class 100000: panel filter type G3 (G4) to F5 + bag filter F7 (F8) + bag filter F9.

Class 300000: panel filter G3～F5+ bag filter F6～F8.