How to distinguish between dust accumulation on the surface of equipment and excessive air particles?

Dust accumulation on the surface of equipment and excessive air particles are common problems in clean management. However, the two reflect different objects: dust accumulation on the surface reflects the settlement, entrainment or cleaning state over a period of time, and excessive air particles reflect the air concentration under specified sampling conditions. The two are related, but cannot replace each other.

When the air test is qualified, dust may still accumulate on the surface due to long-term sedimentation or direct contact; when dust accumulation on the surface is obvious, the air concentration may also be within the qualified range. To determine the source of the problem and the direction of treatment, two indicators need to be distinguished first.

The objects measured by the two are different

Air particle testing measures the concentration of suspended particles in the air. The sampling point collects air at a specified location and in a specified volume, and records the number of particles of different sizes.

Surface evaluation measures particle deposition or residue on the surface. Methods may include swabbing, sticking or optical inspection, reflecting the results of settling or contact over time.

The units, sampling methods and evaluation purposes of the two indicators are different and cannot be directly compared. The qualified air concentration does not mean that the surface must be clean, and the obvious dust accumulation on the surface does not mean that the air concentration must exceed the standard.

different time scales

Air particle detection usually reflects the state of the air within a short period of time during sampling. If there is no significant dust production during the sampling period, the results may be acceptable.

Surface dust accumulation reflects accumulation. Even if air concentrations are acceptable for a short period of time, particles may still settle slowly, forming visible or detectable deposits over a longer period of time.

Therefore, the time scales for air detection and surface evaluation are different. When judging the cleanliness of a surface, consider the time since it was last cleaned. For the phenomenon of increased particle readings after floor cleaning, please refer to Is it normal for particle readings to increase after floor cleaning? , understand the different effects of cleaning operations on air and surfaces.

Contamination pathways may differ

The sources of excessive air particles are usually related to air flow, filtration, personnel and process dust. Sources of surface deposits may also be:

• Direct contact: tools, gloves, container contact surfaces;

• Materials brought in: particles carried by packaging and parts fall on the surface;

• Sedimentation: The settling of airborne particles on a surface;

• Cleaning residue: Residue left behind by cleaning tools or materials.

Surface deposition is not necessarily caused by chronically high air concentrations. For example, wiping the material itself may produce fibers, and tool contact may leave behind particles. Contamination paths should be distinguished when making judgments.

Air testing is not a substitute for surface evaluation

A passing air test does not prove that all surfaces are clean. Settlement is a slow process. When the air is qualified for a short period of time, a certain amount of sediment may have accumulated on the surface.

If the product requires surface cleaning, surface evaluation should be arranged separately rather than relying solely on air testing data. For analysis of the sources of dust and air particles on the surface of the equipment, please refer to The FFU is running normally, why is dust falling at the workstation? , understand the multi-source troubleshooting of dust.

Surface evaluation also has method and condition requirements

Surface evaluation also requires clear methods and conditions. Different methods may give different results, and you should confirm when comparing:

• Evaluation method (wipe, stick or optical);

• Sampling area and location;

• Evaluation limits and judgment rules;

• The time interval after cleaning.

When methods are not unified, the comparability of superficial evaluation results is limited. Specific testing requirements should correspond to project procedures and acceptance conditions.

Contact possible reasons based on time records

When determining the source of pollution, the following should be recorded:

• when and how it was last cleaned;

• air particle trends;

• where and when surface deposits occur;

• Records of personnel, material and equipment operations.

Correlating this information can distinguish whether it is a problem of continuous input, instantaneous introduction or cleaning method. For particle changes after personnel enter, please refer to How to locate the cause of increased particle number after personnel enter?。

Different processing directions

Directions for dealing with excessive air particles usually include checking filters, airflow paths, return air conditions and pollution sources.

Directions for dealing with surface dust may include:

• Check cleaning methods and tools;

• Check contact and lead-in paths;

• Adjust materials and tool management;

• Check settling rate and cleaning cycles.

If one treats surface deposits solely in terms of air problems, sources of contact and entrainment may be ignored. When there is dust on the surface of the equipment but the air is qualified, the cleanliness of the cover and boundary management should be checked instead of directly determining that the filter has failed.

Project judgment example

There is dust on the outer cover of a piece of equipment, but the air test in the protected area passes. The investigation found that dust accumulation mainly comes from the residue of wiping materials and contact with tools. Adjustment methods: Change cleaning materials, adjust tool placement, and increase the frequency of surface cleaning. After adjustment, the dust on the surface is reduced, and the air test remains qualified.

In another project, air particles continued to be high, and there were also deposits on the surface. Investigation revealed that the filter seal bypass allowed unfiltered air to enter. Adjustment method: After repairing the seal, air particles will decrease and surface deposition will also decrease.

These two situations indicate that surface dust accumulation and excessive air particles reflect different problems and need to be evaluated and dealt with separately.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

Surface dust accumulation and air particles exceed the standard, and the corresponding investigation directions are different. Aili Industrial has collaborative capabilities in fans, motors, filters, control systems and complete machine assembly links. It can cooperate to check filter sealing, air supply status, air flow path and surface cleaning conditions during operation inspections, helping to distinguish whether pollution comes from air input, contact introduction or cleaning methods, rather than judging based on just one indicator. 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。