Why can’t the sampling point be located just below the air supply outlet?

In the clean area test, the place under the air supply outlet is the cleanest place for air flow. The air just processed by the filter is sent out here, and the particle concentration is usually lower than other areas. If the sampling points are concentrated here, the test data is often ideal, but the representativeness of the data is problematic.

The selection of sampling point locations should answer the question 'What is to be evaluated?' If the evaluation is for the entire room or key workstations, the area under the air supply outlet is only one of the locations and cannot represent the entire area.

Sampling locations should serve the evaluation task

The location of the sampling point is directly related to the detection task. Common detection tasks include:

• Clean area classification test: Distribute sampling points in the area according to standard requirements;

• Leak detection during filter installation: Detect on the filter outlet surface and sealing area;

• Monitoring of key workstations: sampling near product exposure locations;

• Pollution source investigation: Take samples near the suspected dust-producing location.

Different tasks correspond to different sampling locations. The bottom of the air supply outlet is suitable for evaluating the air outlet status of the filter, but it cannot replace the evaluation of area classification or workstation protection. To determine the evaluation area and test status, please refer to What preparations need to be completed before clean room acceptance?。

The bottom of the air supply outlet mainly reflects the fresh filtered air flow

The particle concentration measured below the air supply outlet mainly reflects the cleanliness of the air outlet from the filter. The airflow here is freshly filtered, has generally lower particle concentrations, and is less affected by external contamination.

The data at this location can be used to determine whether the filter is working properly, but if it is used to represent the entire room or workstation, it will overestimate the actual cleanliness level. Local pollution caused by personnel activities, equipment dust and boundary interference will not be significantly reflected in this location.

Key workstations are the ones that need protection

The protection object of the clean area is the product or process, and the actual exposed location of the product is the area that needs to be monitored. These locations may be far away from the air supply vent, and the airflow reaches them after traveling a certain distance, and the boundary conditions are more complex.

Sampling points should cover:

• The actual location where the product is exposed;

• Personnel operating position;

• Material entry and exit locations;

• Where airflow may become trapped or deflected.

For the relationship between key workstation protection and sampling locations, please refer to What are the prerequisites for purifying only key workstations? , first confirm the boundaries of sensitive links.

Contamination weak points are easily missed by air outlet sampling

In actual operation, particle pollution often appears in specific locations:

• the back and underside of the device;

• Room corners and near columns;

• The position where the return air outlet is blocked;

• Opening doors and passing positions;

• Areas with frequent human activities.

These locations are usually not under the air supply vents. If the sampling point is only selected below the air supply outlet, these weak points may be missed. For troubleshooting methods for reflow areas, airflow short circuits and eddy currents, please refer to Why is it easy for contamination to accumulate in the return flow area? and What particle problems can airflow short circuits cause?。

The sampling height should correspond to the actual working surface

The sampling location must consider not only the plane distribution, but also the height. Different heights correspond to different airflow and particle conditions. The sampling height below the air supply vent is usually close to the air outlet surface, while the product exposure location may be on the countertop or at a specific height.

If sampling is done only at the height of the air outlet, it cannot represent the particle level at the product location. The sampling height should be determined based on the actual exposure location of the product. For the impact of changes in working height on the detection position, please refer to How does a change in working height affect the detection position?。

Static and dynamic sampling locations may differ

During static testing, personnel and equipment are not running, and there are fewer sources of pollution. During dynamic testing, personnel activities, equipment dust generation and material entry and exit will change the local particle distribution. In the two states, the locations that need attention may be different.

During dynamic evaluation, the sampling points should cover the weak locations under actual operating conditions. If you only arrange points according to static conditions, you may miss the sources of pollution under dynamic conditions. To determine the operating status of the equipment during acceptance, please refer to Which equipment should be in operation during acceptance?。

Standard positions and supplementary positions should be arranged separately

The positions specified in the standard are used for clean area classification and should be distributed within the area according to the standard requirements. The supplementary position is used for risk monitoring and can be set according to process characteristics.

The two types of locations should be recorded separately:

• Number, location and results of standard positions;

• The number, location and purpose of supplementary locations;

• The results of the two correspond to their respective evaluation ranges.

Supplementary positions cannot replace standard positions, and standard positions cannot cover all risk points. For the method of determining the number of sampling points, please refer to How to determine the number of cleanliness sampling points?。

Equipment selection and terminal matching

For the equipment and filtering configuration involved in sampling, please refer to FFU clean air supply products and EFU equipment side fan filter unit . Filter installation, sealing and leak detection requirements can be learned HEPA and ULPA filters . If you are still unclear about the difference between space rating and filter efficiency, you can read What is the difference between cleanliness level and filtration efficiency?。

Project judgment example

During the acceptance of a certain project, the sampling points were concentrated under the air supply outlet, and the data was qualified. However, the particles at the workstation are occasionally high during production. The investigation found that personnel operating positions and material entry and exit locations were not included in the sampling scope. Adjustment method: Re-distribute points according to actual work stations and weak points to confirm the actual protection effect.

Another project added a supplementary sampling point on the back of the device and found that particles continued to be high at this location. Adjustment method: Adjust the spacing between equipment and the return air path to improve local circulation. After adjustment, the particles at this position decreased.

These two situations illustrate that the location of the sampling point must serve the evaluation task and cover key work positions and weak points. You cannot just select the cleanest location.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

The choice of sampling point location is related to whether the detection results can reflect the actual protection effect. Aili Industrial has collaborative capabilities in fans, motors, filters, control systems and complete machine assembly. It can cooperate to check the air supply distribution, key station airflow and weak position status during the equipment debugging and operation stages, helping the project arrange sampling locations according to actual protection needs, rather than just looking at the cleanest locations. Specific models can be viewed FFU clean air supply products , supporting equipment can be viewed EFU equipment end fan filter unit , please refer to the filter package. HEPA and ULPA filters。