How to distinguish external and internal contamination when particles exceed the standard?

When the particles in the clean area exceed the standard, the investigation direction often determines the processing efficiency. External pollution comes from outside the area, entering through doors, windows, materials, personnel, or supplementary air; internal pollution is generated within the area, from equipment, personnel, materials, or process actions. The processing methods of the two are different. If you judge the wrong direction, you may waste troubleshooting time.

A single high reading cannot directly pinpoint the source. Distinguishing between external and internal requires comprehensive judgment based on abnormal location, time correlation, air flow path and upstream and downstream sampling.

First, let’s clarify the common paths of the two types of pollution.

Common entry routes for external contamination:

• The opening of doors and windows and the entry and exit of people;

• Bringing in materials and packaging;

• Make-up air and fresh air systems;

• Transfer windows and material channels;

• Gaps in the building envelope.

Common sources of internal contamination:

• Equipment mechanism wear and movement;

• Personnel clothing and movement;

• Material unpacking and turnover;

• Tool friction and fixture action;

• Process and exhaust switching.

The two types of pollution may exist at the same time or may transform into each other. For example, foreign particles enter and settle, and are then lifted up by human actions, forming internal resuspension.

Narrow down scope with running events

When troubleshooting, particle abnormalities should be compared with operating events:

• The time for door opening and entry and exit;

• Material entry and exit and unpacking time;

• Start and stop air conditioning and exhaust equipment;

• Operational stages of process equipment;

• Cleaning and maintenance operation times.

If the abnormality is synchronized with the opening of the door, external contamination is more likely; if the abnormality is synchronized with the equipment action, internal contamination is more likely. Please refer to the troubleshooting method for particles rising after people enter. How to locate the cause of increased particle number after personnel enter?。

Determine the path based on upstream and downstream sampling

Taking samples both upstream and downstream of the suspected source can determine whether particles are entering or originating. If the upstream concentration is high and the downstream concentration is low, it means that the particles may be generated at the source and then spread; if the downstream concentration is high and the upstream concentration is low, it means that the particles may enter from other routes.

Sampling points should be arranged to cover suspected sources and airflow paths. For representative questions about sampling locations, please refer to Why can’t the sampling point be located just below the air supply outlet?。

Observe the airflow path to confirm the input direction

Airflow visualization can help determine the direction of particle entry. Visualization can show airflow paths if particles enter through doorways or openings, and localized dust generation if particles are generated near equipment.

The airflow path judgment needs to combine the return air and exhaust air conditions. For the impact of reflow area and airflow short circuit, 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?。

Characteristics of external pollution

External pollution usually has the following characteristics:

• Relevant to the time of door opening, personnel entry and exit, or material entry and exit;

• Concentrations are higher near entrances or openings;

• The range of influence is related to the airflow path;

• After turning off the external input, the particle concentration may decrease;

• May appear in different areas at the same time.

The treatment direction of external pollution usually includes improving inlet isolation, adjusting pressure difference, strengthening material cleaning and optimizing personnel flow.

Characteristics of internal contamination

Internal contamination usually has the following characteristics:

• Synchronized with equipment actions, personnel operations or process processes;

• The concentration is higher near the dust generation location;

• The range of influence is related to local airflow;

• After stopping dust production, the concentration may gradually decrease;

• May focus on specific workstations or equipment.

The treatment direction of internal pollution usually includes source isolation, local exhaust, adjusting air flow paths and optimizing operating procedures. For the impact after startup of process equipment, please refer to What should I do if the cleanliness of the process equipment drops after it is started?。

A single high reading cannot directly pinpoint the source

Sometimes a single high reading occurs during a walkthrough. A single high reading may result from instantaneous dust production, sampling interference or instrument fluctuation, and cannot be directly used as a basis for source determination.

The judgment should be made in conjunction with:

• Is there repeatability?

• Whether it is synchronized with a specific event;

• Whether the upstream and downstream data are consistent;

• Whether the airflow path supports the source.

If abnormalities occur in multiple locations at the same time, priority should be given to systemic sources; if only local locations are abnormal, attention should be paid to local dust generation or input.

Troubleshooting suggestions and records

To check for external and internal contamination, it is recommended to follow the following steps:

• Record abnormal time, location and concentration;

• Correlate door opening, personnel, material and equipment events;

• Sampling upstream and downstream respectively;

• Observe the airflow path and entry direction;

• Itemized exclusion to avoid changing multiple variables at the same time;

• Record the conditions and results of each investigation.

Itemization helps establish cause and effect relationships rather than making intuitive judgments. If it involves equipment sealing and filtration status, please refer to What should be checked when cleaning equipment is accepted?。

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

The particle anomalies in a certain project were synchronized with the door opening time, and the concentration near the entrance was high. The investigation confirmed that external contamination entered through the door. Adjustment method: improve inlet isolation, adjust pressure difference, and increase buffering. After adjustment, the particle peak value when opening the door is reduced.

In another project, particle anomalies were synchronized with the movements of the manipulator, and the concentration near the equipment was high. Check to confirm internal dust production. Adjustment method: Isolate the dust-producing mechanism, adjust local airflow, and increase exhaust air. The particles dropped after adjustment.

These two situations illustrate that distinguishing external and internal pollution requires comprehensive judgment based on time, location, airflow path and upstream and downstream data, and cannot rely solely on a single reading.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

Distinguishing external and internal contamination requires comprehensive judgment based on equipment operation, air flow paths and operation records. Aili Industrial has collaborative capabilities in fans, motors, filters, control systems and complete machine assembly. It can cooperate to check filter seals, air supply status, return air paths and operation settings during the investigation process, helping the project narrow down the source of pollution rather than judging based on a single reading. 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。