When checking the condition of a coating booth, people often look at the fan.

Is the fan rotating?
Can you hear the exhaust operating?
Is air coming out?
Is a filter installed?

These checks are, of course, important.
However, what really needs checking in a coating booth is closer to the actual work.

It is whether paint mist is being extracted correctly at the position where the operator actually performs coating.

A rotating fan is of little use if extraction is ineffective at the working position.
Even with a high exhaust air volume, mist returning toward the operator creates problems for both quality and the working environment.
Even if the booth specifications are adequate, the workpiece or the operator’s standing position may disrupt the airflow.

A coating booth is more than just exhaust equipment.
It is essential equipment supporting coating quality, operator safety, odor control, and environmental performance.

That is why checking a booth requires observing the actual airflow at the working position, as well as its equipment specifications.

1. A Running Booth Does Not Necessarily Mean Effective Extraction

When the coating booth fan is rotating, the booth appears normal at first glance.

You can hear the exhaust.
Air is flowing.
Filters are installed.
The exhaust duct is connected.

However, these observations alone do not establish that the booth is working correctly.

What matters is the direction in which paint mist flows at the location where the operator is spraying.

Under normal conditions, paint mist flows toward the booth extraction rather than returning toward the operator.
However, disrupted airflow can cause mist to return toward the operator.
Mist can also linger behind or below the workpiece.

In this situation, mist redeposits on the coated surface, causing dirt inclusions, surface roughness, and a gritty finish.
At the same time, the operator is more exposed to mist and odors.

A booth must be assessed by whether extraction is effective at the working position, rather than simply whether it is running.

2. Ineffective Extraction at the Working Position Increases Quality Defects

When booth extraction is poor, paint mist remains in the surrounding space.

If this mist returns to the coated surface, it affects the appearance of the coating film.

The following defects are likely to occur.

• Dirt inclusions
• Rough finish
• Roughness
• Uneven gloss
• Dirt pickup
• Roughness of the coating film surface
• Uneven color
• Redeposition of mist before drying

Disrupted booth airflow is a major problem, particularly for products with demanding appearance requirements.

Operators may try to respond by adjusting the paint or gun settings.
However, if booth airflow is the cause, changing only the paint or work method will not resolve the underlying problem.

When examining coating defects, always check booth airflow as well as the paint, thinner, gun, and operator.

3. The Operator’s Position Can Also Disrupt Airflow

Booth airflow is not determined by equipment alone.

The operator’s standing position and movements also affect airflow.

For example, an operator standing too directly in front of the extraction face may block the airflow with their body.
When coating a large workpiece, the workpiece itself can act as a wall and impede mist flow toward the extraction.

If the operator sprays at an angle from outside the booth, mist may also flow out of the booth more readily.

Booth airflow therefore must not be measured only with the booth empty.

Place the actual workpiece in the booth.
Observe from the operator’s actual standing position.
Reproduce the actual coating posture.
Check the actual gun direction.

You need to observe how mist flows under these conditions.

4. Workpiece Shape Changes How Mist Is Extracted

Even in the same booth, airflow changes with the shape of the workpiece being coated.

Flat-panel products.
Box-shaped products.
Frame-shaped products.
Products with deep recesses.
Large products with broad surfaces.
Many small parts arranged together.

Mist flow changes when workpiece shape changes.

Large workpieces obstruct airflow.
Mist may linger deep inside recessed workpieces.
Arranging many small parts together can disrupt the air between them.
Closely packed fixtures and hangers create areas that extraction cannot reach effectively.

Booth airflow therefore needs to be checked with workpieces prone to defects, as well as representative workpieces.

Before concluding that the booth has no problems, clarify which product, position, and coating posture were used for the check.

5. Insufficient Supply Air Can Cause Mist to Return

When booth extraction is poor, people tend to suspect only the exhaust fan.

However, the cause may be on the supply air side.

For an exhaust fan to discharge air outside, an equivalent amount of fresh air must enter the room.
Insufficient supply air makes airflow inside the booth or coating room unstable.

Insufficient supply air causes problems such as the following.

• Vortices form inside the booth
• Mist returns toward the operator
• Dust from outside enters through gaps
• Doors become difficult to open
• The air-conditioning balance is disrupted
• Odors and dust from other processes flow into the coating room

Increasing exhaust alone will not stabilize booth performance if the balance with supply air is poor.

Checking booth airflow requires assessing exhaust and supply air together.

6. Clogged Filters Weaken Extraction at the Working Position

Clogged filters are a very common cause of poor booth airflow.

A clogged filter restricts the passage of air.
As a result, extraction at the working position becomes weaker even while the fan is running.

Clogged filters cause the following problems.

• Lower air velocity at the working position
• Returning mist
• Contamination inside the booth
• Torn filters
• Increased fan load
• Higher electricity costs
• Deposits in ducts
• Increased odors

Filter condition can be difficult to judge by appearance alone.

A filter may be clogged internally even when its surface does not look very dirty.
Even if an operator feels that extraction has become weaker recently, replacement may be delayed unless measurements are taken.

Managing filter differential pressure is therefore effective.
Differential pressure indicates how much resistance the filter creates between its upstream and downstream sides.

Measuring differential pressure makes it easier to decide when to replace a filter using numbers rather than impressions.

7. Measure Air Velocity at the Working Position

Measurement location matters when measuring booth air velocity.

Measuring only part of the booth opening does not reveal conditions at the working position.
Measurements near the fan also differ from those where the operator actually performs coating.

The actual working position is what needs checking.

• Where the operator stands
• In front of the workpiece
• Above the workpiece
• Below the workpiece
• The left and right edges of the booth
• Locations where mist tends to remain
• Positions where defects tend to occur

Air velocity varies by location.
It may be sufficient in the center but inadequate at the left or right edges.
Extraction may be effective above the workpiece while mist accumulates below it.

Measurements must be taken at multiple points.

Results also differ between an empty booth and a booth containing a workpiece.
It is important to measure under conditions close to those of production.

8. Use a Smoke Test to Observe Airflow

Taking measurements with an anemometer is important.
However, numbers alone can sometimes make the airflow pattern difficult to understand.

A smoke test is useful in this situation.

A smoke test uses smoke to make airflow visible.
Smoke is generated, and its direction of movement inside the booth is observed.

A smoke test can check the following.

• Whether mist flows toward the extraction
• Whether it returns toward the operator
• Whether vortices form inside the booth
• Whether it lingers behind the workpiece
• Whether flow differs between the left and right sides
• Whether supply air causes crossflow
• Whether outdoor air entering through doors or windows affects the flow

A smoke test is also easy for shop-floor personnel to understand.

Airflow is invisible.
Using smoke, however, allows everyone on the shop floor to observe the same phenomenon and share an understanding of the problem.

This is extremely important in improvement activities.

9. Mist Flow Also Affects Operator Safety

Ineffective extraction at the working position affects operator safety as well as quality.

When paint mist and odors return toward the operator, the operator is more likely to inhale them.
Even when protective equipment is used, poor booth airflow worsens the working environment.

Coating work is inherently demanding.

Odors.
Mist.
Heat.
Protective equipment.
Standing work.
Maintaining the same posture.
Detailed appearance inspection.

With these existing demands, poor booth extraction further increases operator fatigue and discomfort.

Improving booth airflow improves quality and also shows care for operators.

10. Disrupted Booth Airflow Also Affects Odor Control

People often think of increasing exhaust volume when considering odor control.

However, odor problems are also related to airflow at the working position.

Stagnant air inside the booth leaves odors near the operator.
A poor supply/exhaust balance can also carry odors to other areas of the factory.

Increasing exhaust fan output will not resolve the underlying problem if odor sources remain inside the booth.

Odor control requires the following checks.

• Whether mist or odors return toward the operator
• Whether they linger inside the booth
• Whether deposits have accumulated in the exhaust path
• Whether circulation water or sludge produces odors in a wet booth
• Whether insufficient supply air allows odors to spread through the factory

Odors must be assessed in terms of airflow, water, sludge, and cleanliness, as well as exhaust.

11. Common Booth Airflow Challenges in Vietnamese Factories

Vietnamese factories are prone to the following booth airflow challenges.

The booth is considered problem-free if the fan is rotating.
Air velocity is not measured at the working position.
Filter replacement criteria are not defined.
Exhaust is increased while supply air remains insufficient.
The operator’s standing position obstructs airflow.
Mist accumulation caused by workpiece shape is not assessed.
Smoke tests are not conducted.
Inadequate cleaning inside the booth disrupts airflow.
Deposits in ducts and exhaust outlets are not checked.
Odor control is considered only in terms of fan capacity.

Under these conditions, the booth’s actual problems remain hidden.

What is needed is to verify airflow on the shop floor, rather than simply examine equipment specifications.

12. Basic Items to Check When Assessing Booth Airflow

The following items provide a practical approach to checking coating booth airflow.

1. Air velocity at the working position

Measure at the position where the operator actually performs coating.

2. Mist flow

Check that mist flows toward the extraction during spraying.

3. Smoke test

Use smoke to check airflow, stagnation, and reverse flow.

4. Supply air conditions

Check that supply air is sufficient and that there are no crosswinds or turbulence.

5. Filter condition

Check clogging, tears, replacement intervals, and differential pressure.

6. Workpiece arrangement

Check whether the workpiece obstructs airflow or mist lingers behind it.

7. Operator position

Check whether the operator’s body or movements obstruct airflow.

8. Cleanliness inside the booth

Check whether paint residue, dust, or contamination affects airflow or quality.

9. Exhaust duct

Check internal duct deposits, blockages, bends, and resistance.

10. Odors

Check whether odors return toward the operator or into the factory.

These checks allow booth problems to be understood more accurately.

13. The Value of Checking Booth Airflow According to CoatureVietnam

CoatureVietnam does not regard a coating booth as merely exhaust equipment.

A coating booth supports coating quality, operator safety, odor control, and environmental performance.

Fan specification values alone are not enough to determine whether the booth is truly functioning.

Is extraction effective at the working position?
Is mist returning?
Is mist lingering behind the workpiece?
Are supply and exhaust air balanced?
Are operators exposed to mist and odors?

These points need to be checked.

This connects with CoatureVietnam’s valued principle,
“Coating the Future with Science and Care.”

Science means measuring and observing air velocity, differential pressure, airflow, and mist movement, then identifying the causes.
Care means creating an environment where operators can coat safely and consistently without being troubled by mist or odors.

Summary

In a coating booth, a rotating fan alone is not enough.
A high air volume alone is not enough either.

What matters is whether extraction is truly effective at the position where the operator actually performs coating.

Air velocity at the working position.
Mist flow.
Smoke testing.
The balance between supply and exhaust air.
Filter clogging.
Workpiece shape.
The operator’s standing position.
Cleaning inside the booth.
Exhaust ducts.
Odor movement.

Checking these factors together reveals the booth’s true condition.

Improving booth airflow does more than reduce quality defects.
It also protects operator safety, reduces odors, and makes coating operations a better place to work.

CoatureVietnam checks coating booth airflow on the shop floor and proposes improvements that address quality, safety, and the environment together.