How to locate the cause of increased particle number after personnel enter?

Personnel entry is one of the most common triggering events for particle fluctuations in clean areas. However, when the number of particles increases after personnel enter, it is not necessarily just a problem of the personnel themselves. The dressing process, channel design, door opening pressure difference, action path and system carrying capacity may all be involved.

To locate the cause, it is necessary to observe the 'entry' and 'operation' stages separately, and investigate them one by one based on the passage, pressure difference and personnel conditions.

Observe the entry and operation stages separately

The particle changes after people enter can be recorded in stages:

• Before opening the door: record the baseline concentration;

• The moment the door is opened: observe the particle peak value and airflow direction;

• Personnel passing through the passage: observe the status of the passage and air shower equipment;

• When personnel arrive at the work station: observe changes in particles at the work station;

• The person starts the operation: observe the correlation between the action and the particles.

If the peak value mainly occurs at the moment of opening the door, focus on checking the pressure difference and interlocking; if the particles continue to rise after personnel arrive at the work station, attention should be paid to personnel movements and materials.

The dressing process is the first inspection step

The dressing process directly affects the amount of particles brought in by personnel. During inspection, you should confirm:

• Whether the changing order complies with the regulations;

• Whether the clean clothes are worn and changed according to regulations;

• Do gloves, masks and shoe covers match?

• Whether the pressure difference and cleanliness of the dressing area are normal;

• Is there enough buffer space in the dressing area?

If the dressing process is incomplete, personnel's clothing may carry more particles into the clean area. The airflow organization of the dressing area itself will also affect the amount brought in.

Air shower and tunnel equipment status

The air shower room and transfer channel are key links for personnel to enter. During inspection you should pay attention to:

• Whether the air shower room starts and blows normally;

• Whether the nozzle is clogged or angled;

• Whether the air shower time meets the setting;

• Whether the access door is interlocked normally;

• Whether there is dust or obstruction in the passage.

When the air shower equipment is in abnormal condition, particles on the surface of personnel cannot be effectively removed. For daily inspection items of air shower room, please refer to What air equipment should be covered in daily inspections of clean areas? , understand the scope of air equipment inspection.

Door opening and pressure differential changes

Opening the door breaks the pressure differential in the room and changes the direction of airflow. If the particle peak is obvious when the door is opened, check:

• Is the room pressure difference stable?

• Whether the door interlocking is normal;

• Whether the door opening time is too long;

• Is there a buffer room at the entrance?

When the pressure difference is insufficient or the interlock fails, outside air may enter the moment the door is opened. For troubleshooting methods of inlet pressure difference, please refer to How to identify lateral interference in unidirectional flow areas? , to understand the impact of doors and openings on airflow.

Number of personnel and action paths

The number of people and the intensity of the action will affect the particle concentration. During inspection, you should confirm:

• Whether the actual number of people entering exceeds the verification range;

• Personnel activity range and action paths;

• Whether you move around frequently near sensitive workstations;

• Are there quick turns or leaping movements?

When the number of people exceeds the number of verifications, the original test results may no longer be applicable. For the impact of personnel activities on airflow, please refer to How will operating the arm interfere with the air supply to the workbench? , to understand the interference of movements on local airflow.

Air system carrying capacity

The increase in particles after personnel enter may also reflect insufficient carrying capacity of the system. During inspection you should pay attention to:

• Is the air supply volume sufficient to cope with dynamic loads?

• Whether the return air channel is clear;

• Whether the system recovery time is significantly extended;

• Is the filter status normal?

If the system is slow to recover after personnel entry, it may be necessary to check the air volume, return air, and filtration status. To judge the system recovery capability, please refer to What particle problems can airflow short circuits cause? , learn about common causes of slow recovery.

Narrow down the scope with controlled testing

When troubleshooting, you can use control testing to narrow the scope:

• Empty baseline vs after personnel enter;

• Open state vs closed state;

• Single person entry vs multiple person entry;

• Normal dressing vs abnormal dressing process;

• Air shower on vs air shower off.

Changing only one variable at a time and comparing the particle changes can help determine the main factors. Subtesting makes it easier to establish cause and effect than adjusting for multiple conditions simultaneously.

Record and correlate data

Investigation records should include:

• Time and number of personnel entering;

• Door opening time and duration;

• Channel and air shower equipment status;

• Particle concentration change curve;

• Personnel movements and paths;

• System operating parameters.

By correlating this information with granular data, we can determine at which stage the anomaly occurs. To determine the personnel conditions during acceptance, please refer to Which equipment should be in operation during acceptance?。

Equipment selection and terminal matching

The troubleshooting involves equipment and filtering configuration, 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

After a certain project personnel entered, the particle peak was obvious. The investigation found that the pressure difference fluctuated when the door was opened and outside air entered. Adjustment method: adjust pressure difference setting, repair door interlocking, and increase buffer time. The peak value dropped after adjustment.

After another project worker entered the workstation, the particles continued to be high. The investigation found that the movement path of personnel passed upstream of sensitive workstations, and particles brought up by movement were brought into the protected area. Adjustment method: Adjust personnel movement lines and tool positions to reduce crossing movements. The particles dropped after adjustment.

These two situations show that the increase in particles after people enter requires separate stages and item-by-item investigation, and cannot be attributed solely to personal cleanliness.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

The increase in particles after personnel enter involves multiple links such as passages, pressure differences, changing clothes, and system loading. Aili Industrial has collaborative capabilities in fans, motors, filters, control systems and complete machine assembly. It can cooperate to check the air supply volume, pressure difference status, filter sealing and system recovery capabilities during operation inspections, helping to determine whether the abnormality comes from the inlet air flow, personnel introduction or insufficient system load. 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。