Odors are a common subject of consultation in coating operations.

“The coating booth smells strongly.”
“Operators are noticing odors.”
“A thinner smell is spreading through the factory.”
“Neighbors or other departments have raised concerns about the smell.”
“Would increasing exhaust fan output help?”

In these cases, increasing exhaust is often the first option considered.
Indeed, inadequate exhaust allows odors to remain in the booth or factory.

However, coating booth odors cannot always be solved by exhaust alone.

Every odor has a source.
Odors from paint and thinner.
Odors from booth circulation water.
Odors from decomposing sludge.
Odors from paint residue and tar deposited in exhaust ducts.
Odors from cleaning operations or inadequate cleaning.
Odors returning from the curing oven.

Increasing exhaust alone without identifying these sources will not resolve the underlying problem.

When controlling coating booth odors,
identify where the odors originate before extracting them.
This is important.

1. Problems Remain When Odor Control Relies Only on Exhaust

When odors are present, it is natural to want to increase exhaust fan output.

However, relying only on exhaust can leave the following problems unresolved.

• Odors inside the booth decrease somewhat, but are discharged outside
• Electricity costs increase
• Supply air becomes insufficient, disrupting the air balance in the factory
• Dust from outside enters the coating room more easily
• The odor sources remain
• Odors do not improve where the operator stands
• Odors from booth circulation water and sludge do not improve

Exhaust is a means of moving odors.
It does not, however, reduce their generation itself.

Odor control should first reduce sources, then prevent stagnation through airflow, and then treat exhaust as necessary. This sequence is important.

2. There May Be More Than 1 Odor Source

Multiple causes contribute to coating booth odors.

Typical sources are as follows.

Paint and thinner

Solvent-based paints and thinners contain components that evaporate readily.
Odors are generated during coating, mixing, cleaning, and before drying.

Booth circulation water

Wet booths use water to collect paint mist.
Poor management of circulation water produces odors.

Paint sludge

Oversprayed paint solidifies in the water and becomes sludge.
Leaving sludge unattended causes decomposition odors and strong smells.

Exhaust ducts

Paint residue, mist, oil, and tar deposited inside ducts may generate odors.

Inadequate cleaning

Odors remain when booth floors, walls, filter surroundings, exhaust openings, mixing areas, and cleaning areas are dirty.

Curing oven exhaust

Odors generated during baking or drying may be noticed depending on the exhaust path and airflow inside the factory.

Odor control requires checking these sources separately.
Treating the issue simply as “the coating booth smells” can lead to misidentifying the cause.

3. Circulation Water and Sludge Management Are Important in Wet Booths

In wet booths, a major source of odors may be on the water side.

A wet booth uses water to collect paint mist.
Its circulation water therefore contains a mixture of paint components, resins, pigments, solvents, booth treatment chemicals, and fine sludge.

Odors develop if this water is not managed properly.

Examples include the following conditions.

• Sludge has accumulated for a long time
• Circulation water is dirty
• Treatment chemicals are unsuitable
• pH is not controlled
• Excessive foaming occurs
• Decomposition is progressing
• Water passages are blocked
• Sludge collection is infrequent

Increasing exhaust alone under these conditions leaves the odor sources in place.

To control odors in a wet booth, check circulation water and sludge before examining the exhaust fan.

4. Prompt Sludge Removal Is Important

Paint sludge is a typical form of contamination generated inside a booth.

Leaving sludge unattended worsens water quality.
Paint components may dissolve into the water, increasing odors and the load on wastewater treatment.

The key to sludge management is to remove it consistently and as early as possible.

The longer sludge remains in the water, the greater the odors, contamination, and cleaning burden.
Sludge accumulating in water passages or around pumps also impairs circulation water flow.

Check the following items in sludge management.

• Sludge collection frequency
• Sludge flotation and settling characteristics
• Compatibility with the chemicals used
• Water pH
• Foaming
• Decomposition odors
• Blockages in pumps and water passages
• Disposal method
• Cleaning intervals

Odor control may start with water management, as well as air management.

5. Paint and Thinner Selection Also Affects Odors

Equipment is not the only cause of odors.
The paint and thinner being used also have a major influence.

For solvent-based paints, odor intensity varies with thinner type, dilution amount, drying speed, and volatility.

For example, a high proportion of readily volatile solvents increases odors immediately after coating.
Using cleaning thinner in open containers spreads odors throughout the work area.
Poor ventilation in the mixing area produces odors outside the coating booth as well.

The following changes can also be considered for odor control.

• Switching to a low-odor thinner
• Switching to a low-VOC paint
• Switching to a high-solids paint
• Converting to waterborne paint
• Converting to powder coating
• Improving cleaning methods
• Improving local exhaust in the mixing area
• Managing container lids

However, changing the paint or thinner also affects quality and drying conditions.
Decisions must therefore consider coating film performance, workability, drying behavior, and equipment compatibility, as well as odors.

6. Poor Booth Airflow Allows Odors to Linger

Odors are influenced by airflow as well as their sources.

Poor airflow inside the booth leaves odors near the operator.
Odors may also spread outside the booth and be noticed elsewhere in the factory.

Causes of poor airflow include the following.

• Insufficient exhaust
• Insufficient supply air
• Clogged filters
• Duct resistance
• Workpieces obstructing airflow
• The operator’s standing position disrupting airflow
• Accumulated contamination inside the booth
• Incoming crosswinds
• The effects of doors and openings in the factory

The place where an odor is noticed is not necessarily its source.
This is because airflow carries odors.

Odor control therefore requires checking how air flows, as well as where smells are present.

7. Deposits in Exhaust Ducts Can Also Cause Odors

Coating booth exhaust ducts become dirty over time.

Paint mist.
Dust.
Oil.
Tar.
Moisture.
Sludge-like deposits.

These deposits inside ducts can generate odors.
They can also increase duct resistance and reduce exhaust air volume.

Leaving duct deposits unattended causes the following problems.

• Odors persist
• Exhaust capacity decreases
• The fan is subjected to additional load
• Duct cleaning becomes difficult
• Fire risk increases
• Odor complaints arise from outside the factory

It is also important to check deposits inside ducts before replacing an exhaust fan.

The cause of booth odors cannot be identified without examining the entire exhaust path.

8. Odor Control Also Prevents External Complaints

Coating booth odors are not only an internal factory problem.

When discharged outside with exhaust, odors may become an issue for neighboring factories, industrial parks, local residents, or customer audits.

Environmental, safety, and occupational hygiene requirements are increasing, particularly among Japanese manufacturers and other foreign-owned companies.
Although odors can be difficult to manage numerically, they readily lead to complaints.

Increasing exhaust may reduce odors inside the factory.
However, discharging those odors outside can lead to external complaints.

Odor control must consider both the working environment inside the factory and effects outside it.

9. VOC Control and Odor Control Are Related, but Not Identical

VOC stands for volatile organic compounds.
Some of the organic solvents contained in paint and thinner evaporate into the air as VOCs.

VOC control is important for environmental regulations and emissions management.
Odor control, on the other hand, addresses smells perceived by people.

A large amount of VOCs does not necessarily produce a strong odor.
Conversely, some components smell strongly even in small quantities.

VOC control and odor control are therefore related, but are not exactly the same.

Odor control needs to address both of the following.

• Reducing the amount of VOCs
• Reducing odors perceived by people

A combination of measures must be considered, including paint changes, exhaust improvements, odor treatment equipment, enclosure of work areas, local exhaust, and sludge management.

10. The Basic Sequence for Odor Control

Coating booth odor control is easier to organize when considered in the following sequence.

1. Identify the sources

Identify where odors originate, such as paint, thinner, booth water, sludge, ducts, cleaning areas, or curing ovens.

2. Reduce generation

Consider low-odor materials, low-VOC paints, improved cleaning methods, container management, and early sludge collection.

3. Prevent stagnation

Check booth airflow, the supply/exhaust balance, extraction at the working position, and mixing area ventilation.

4. Remove contamination

Clean the booth and ducts, replace circulation water, and remove sludge.

5. Treat exhaust as necessary

Consider activated carbon adsorption, combustion treatment, catalytic treatment, or scrubbers.

Skipping this sequence and immediately installing only exhaust treatment equipment may limit its effectiveness.

11. Common Odor Control Challenges in Vietnamese Factories

Vietnamese factories are prone to the following odor control challenges.

Increasing exhaust fan output is assumed to solve the problem.
Odors from booth circulation water are not checked.
Sludge is collected infrequently.
Thinner containers are left open.
Ventilation during cleaning operations is insufficient.
There is no exhaust duct cleaning history.
The location of odor generation is not distinguished from the location where it is perceived.
The external effects of exhaust are not checked.
VOC control and odor control are confused.
Odors are not evaluated when changing paints.

Odors readily become a source of complaints on the shop floor, while their causes are often spread across several sources.
It is therefore necessary to assess sources and airflow separately, rather than rely only on impressions.

12. Basic Items to Check for Odor Control

The following items provide a practical framework for checking coating booth odors.

1. Where odors are perceived

Check locations separately, including inside the booth, the operator’s position, mixing areas, cleaning areas, factory aisles, and outdoors.

2. When odors are perceived

Identify the timing, such as during coating, mixing, cleaning, or drying, after a shutdown, or first thing in the morning.

3. Materials used

Check paint, thinner, cleaning solvents, and booth treatment chemicals.

4. Booth circulation water

Check water contamination, pH, foaming, sludge, and decomposition odors.

5. Sludge management

Check collection frequency, treatment methods, and storage conditions.

6. Airflow

Check whether odors linger at the working position.

7. Exhaust path

Check duct deposits, exhaust outlet location, and external effects.

8. Cleanliness

Check inside the booth, floors, walls, filter surroundings, mixing areas, and cleaning areas.

9. External effects

Check effects on neighbors, the industrial park, and customer audits.

10. Verification after improvement

After taking action, check operators’ perceptions, odor locations, material consumption, and the cleaning burden.

13. The Value of Odor Control According to CoatureVietnam

CoatureVietnam does not regard odor control as merely an exhaust equipment issue.

Odor control protects operator safety and comfort.
Odor control protects coating quality.
Odor control reduces environmental risks.
Odor control protects confidence in the factory.

Strong odors increase the burden on operators.
Odors discharged outside may become a problem for neighbors or during customer audits.
Odorous booth water or sludge also affects equipment management and wastewater treatment.

Odor control must therefore consider paint, thinner, water, sludge, cleaning, airflow, and exhaust treatment together, as well as exhaust itself.

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

Science means identifying odor sources separately and organizing the conditions of materials, water, air, and equipment.
Care means creating coating operations where operators can work with confidence without being troubled by odors.

Summary

Coating booth odors sometimes cannot be solved by exhaust alone.

Even if exhaust fan output is increased, odors continue if their sources remain.
Even if odors inside the factory decrease, they may be discharged outside.

The first important step in odor control is to identify the sources.

Paint and thinner.
Cleaning solvents.
Booth circulation water.
Paint sludge.
Exhaust ducts.
Cleanliness.
Curing oven exhaust.
The supply/exhaust balance.

The true causes of odors cannot be understood without considering these factors together.

Controlling coating booth odors improves the working environment, improves quality, and addresses environmental concerns.

CoatureVietnam sees odors as an indication of how the overall coating process is managed, as well as a smell problem, and proposes improvements suited to each operation.