IEC 60079-10-2 Explained: Classification of Areas – Combustible Dust Atmospheres

When people think about explosion hazards, they often imagine flammable gases and vapors. However, combustible dust can be equally dangerous and has been responsible for some of the most devastating industrial explosions in history.

Dust explosions have occurred in grain elevators, sugar processing plants, pharmaceutical facilities, coal handling systems, and numerous food processing industries around the world.

To establish a systematic approach for evaluating these hazards, the industry relies on IEC 60079-10-2 – Explosive Atmospheres – Part 10-2: Classification of Areas – Combustible Dust Atmospheres.

This standard provides the methodology used to identify and classify areas where combustible dust clouds or dust layers may create explosive atmospheres and establishes the basis for determining Zone 20, Zone 21, and Zone 22 areas.

Proper hazardous area classification is essential because it directly influences equipment selection, installation practices, and risk management strategies throughout the facility.

This article explains what IEC 60079-10-2 is, why it is important, and the major concepts that engineers should understand when performing combustible dust hazardous area classification studies.

Quick Answer

What Is IEC 60079-10-2?

IEC 60079-10-2 is the international standard that governs the classification of areas where combustible dust atmospheres may be present.

The standard provides guidance for evaluating:

• Sources of dust release.
• Dust cloud formation.
• Dust layer accumulation.
• Cleaning and housekeeping practices.
• Extent of hazardous areas.
• Zone classification.

Its objective is to identify areas where explosive dust atmospheres may occur so that suitable protective measures and explosion-protected equipment can be selected.

Why Is IEC 60079-10-2 Important?

Combustible dust hazards are often underestimated because dust may appear harmless during normal operations.

However, when fine combustible particles become suspended in air and encounter an ignition source, a violent explosion can occur.

Incorrect classification may result in:

• Installation of unsuitable equipment.
• Inadequate ignition protection.
• Increased explosion risks.
• Regulatory non-compliance.
• Unnecessary project costs.
• Unsafe operating conditions.

Because hazardous area classification directly influences equipment selection and plant design, proper classification is one of the most important aspects of combustible dust safety.

Who Uses IEC 60079-10-2?

The standard is widely used by professionals involved in facilities that process, transport, or store combustible dust.

Typical users include:

• Process engineers.
• Electrical engineers.
• Instrumentation engineers.
• Hazardous area specialists.
• EPC contractors.
• Facility operators.
• Dust explosion consultants.
• Regulatory authorities.

The results of hazardous area classification studies are normally documented on hazardous area drawings and become a key input for equipment selection and installation design.

What Is a Combustible Dust Atmosphere?

A combustible dust atmosphere exists when combustible dust is dispersed in air under atmospheric conditions in concentrations capable of propagating combustion after ignition.

Examples of combustible dust materials include:

• Grain dust.
• Flour dust.
• Sugar dust.
• Wood dust.
• Coal dust.
• Aluminum dust.
• Plastic powder.
• Pharmaceutical powders.

Many materials that are not normally considered flammable can become highly explosive when finely divided and dispersed in air.

What Is a Hazardous Dust Area?

A hazardous dust area is an area in which combustible dust in the form of a cloud or dust layer may create an explosive atmosphere requiring special precautions regarding the selection, installation, and use of equipment.

The classification depends on several factors, including:

• The likelihood of dust cloud formation.
• The duration of dust presence.
• The characteristics of the dust.
• Dust release sources.
• Dust accumulation.
• Housekeeping practices.
• Ventilation conditions.

IEC 60079-10-2 provides the methodology for evaluating these factors and determining the appropriate hazardous area classification.

Scope of IEC 60079-10-2

IEC 60079-10-2 specifies the principles and methodology used to classify areas where combustible dust atmospheres may occur.

The standard provides guidance for determining:

• Whether a hazardous dust area exists.
• The probability of combustible dust clouds occurring.
• The likelihood of dust layer accumulation.
• The extent of hazardous areas.
• The appropriate zone classification.

The standard applies to facilities handling combustible dust, fibers, and flyings, including:

• Grain storage terminals.
• Flour mills.
• Sugar processing plants.
• Woodworking facilities.
• Coal handling systems.
• Food processing plants.
• Pharmaceutical manufacturing facilities.
• Metal powder processing facilities.

However, IEC 60079-10-2 does not establish equipment design requirements. Instead, it provides the classification methodology that supports equipment selection and installation standards.

Major Concepts of IEC 60079-10-2

Although the standard contains extensive technical guidance, combustible dust classification generally revolves around several key concepts:

• Sources of dust release.
• Dust cloud formation.
• Dust layers.
• Housekeeping practices.
• Extent of hazardous areas.
• Zone classification.

Understanding these concepts is essential because they form the basis of every combustible dust hazardous area study.

What Is a Source of Dust Release?

A source of dust release is any location where combustible dust can escape into the surrounding atmosphere and potentially form a dust cloud.

Examples include:

• Conveyor transfer points.
• Bagging stations.
• Dust collectors.
• Bucket elevators.
• Screw conveyors.
• Mixers and blenders.
• Hoppers and silos.
• Grinding and milling equipment.

Identifying all potential dust release sources is one of the first steps in performing a hazardous area classification study.

Dust Clouds and Dust Layers

Unlike gas classification, combustible dust classification must consider both suspended dust clouds and accumulated dust layers.

A dust cloud can form an explosive atmosphere when fine combustible particles become dispersed in air.

Dust layers also present significant hazards because they may:

• Become dispersed and form explosive clouds.
• Create smoldering ignition sources.
• Cause equipment overheating.
• Contribute to secondary explosions.

The presence of dust layers is one of the most important differences between IEC 60079-10-1 and IEC 60079-10-2.

The Importance of Housekeeping

Good housekeeping plays a major role in combustible dust hazard management.

Poor housekeeping can allow dust to accumulate on:

• Floors.
• Cable trays.
• Equipment surfaces.
• Structural steel.
• Lighting fixtures.
• Ventilation ducts.

Accumulated dust can later become airborne and create conditions for a devastating secondary explosion.

For this reason, housekeeping practices are specifically considered during hazardous area classification studies.

How Are Dust Zones Determined?

IEC 60079-10-2 establishes three hazardous area classifications for combustible dust atmospheres.

Zone	Description
Zone 20	Area in which a combustible dust cloud is present continuously, frequently, or for long periods.
Zone 21	Area in which a combustible dust cloud is likely to occur occasionally during normal operation.
Zone 22	Area in which a combustible dust cloud is not likely to occur during normal operation and, if it occurs, exists only for a short period.

The determination of these zones requires engineering judgment and a detailed understanding of the process and operating conditions.

Examples of Typical Dust Zone Classifications

Although every facility must be evaluated individually, typical examples may include:

• Inside a dust collector – Zone 20.
• Area around bag filling equipment – Zone 21.
• Areas adjacent to enclosed conveyors – Zone 22.
• Inside silos and hoppers – Zone 20.
• Areas near bucket elevator discharge points – Zone 21.

The actual classification may vary depending on dust release frequency, process conditions, and housekeeping effectiveness.

Extent of Hazardous Areas

Combustible dust hazardous areas rarely extend indefinitely from the release source.

The extent of the hazardous area depends on several factors, including:

• Quantity of dust released.
• Particle size.
• Dust characteristics.
• Air movement.
• Ventilation conditions.
• Building geometry.
• Cleaning frequency.
• Process operating conditions.

Determining the extent of dust hazardous areas often requires engineering judgment supported by process knowledge and industry guidance documents.

Primary and Secondary Dust Explosions

One of the most dangerous aspects of combustible dust hazards is the potential for secondary explosions.

A small initial dust explosion may disturb accumulated dust layers and disperse large quantities of combustible dust into the air.

This newly suspended dust can then ignite and produce a much larger and more destructive secondary explosion.

For this reason, dust accumulation and housekeeping practices play a critical role in hazardous area classification and overall explosion risk management.

Advantages of IEC 60079-10-2

IEC 60079-10-2 provides a systematic and internationally recognized methodology for evaluating combustible dust hazards and determining where special precautions are necessary.

Without a structured classification approach, facilities handling combustible dust may underestimate explosion risks and install unsuitable equipment in hazardous locations.

Key advantages of IEC 60079-10-2 include:

• Provides a standardized methodology for dust hazardous area classification.
• Supports proper selection of Ex equipment for dust atmospheres.
• Improves process safety and risk management.
• Addresses both dust clouds and dust layers.
• Promotes consistency between projects and facilities.
• Encourages good housekeeping practices.
• Supports compliance with international standards and regulations.
• Provides the basis for installation, inspection, and maintenance programs.

For many industries, combustible dust classification forms a critical part of their overall explosion protection strategy.

Limitations of IEC 60079-10-2

Although IEC 60079-10-2 provides comprehensive guidance, combustible dust hazards can be difficult to evaluate because many variables influence the formation of explosive atmospheres.

Some limitations include:

• Requires detailed knowledge of dust characteristics.
• The extent of hazardous areas may be difficult to determine.
• Changes in housekeeping practices can affect classification.
• Operating conditions may vary over time.
• Additional testing and industry guidance may be required.
• Engineering judgment plays a significant role in classification decisions.

For these reasons, hazardous area classification studies should always be performed by competent personnel with experience in combustible dust hazards.

Relationship Between Dust Presence and Zone Classification

The classification of combustible dust hazardous areas depends primarily on the frequency and duration of dust cloud formation.

The following general relationship often applies:

Frequency of Dust Cloud Presence	Typical Zone
Continuous, frequent, or long periods	Zone 20
Occasional during normal operation	Zone 21
Infrequent and short duration	Zone 22

However, the final classification also depends on factors such as dust release characteristics, ventilation, and housekeeping effectiveness.

Examples of Industries Affected by Combustible Dust Hazards

Combustible dust hazards exist in a surprisingly wide range of industries.

Examples include:

• Grain storage and handling facilities.
• Flour mills.
• Sugar processing plants.
• Woodworking facilities.
• Coal-fired power plants.
• Food processing plants.
• Pharmaceutical manufacturing facilities.
• Metal powder production facilities.
• Textile manufacturing facilities.
• Chemical processing plants.

Many organizations do not initially recognize that their products or by-products can create explosive dust atmospheres.

Indoor Versus Outdoor Dust Hazards

The location of equipment can significantly affect combustible dust hazards.

Indoor facilities often present greater risks because:

• Dust can accumulate over long periods.
• Ventilation may be limited.
• Dust layers can remain undisturbed.
• Secondary explosions are more likely.

Outdoor installations generally benefit from natural ventilation and weather conditions that may reduce dust accumulation.

However, outdoor dust hazards should never be ignored because dust clouds and accumulations can still occur under certain operating conditions.

Common Mistakes During Dust Hazardous Area Classification

Experience throughout the industry has shown that several classification mistakes occur repeatedly.

Examples include:

• Assuming dust is not combustible without testing.
• Ignoring dust layer accumulation.
• Overlooking hidden dust deposits.
• Underestimating the importance of housekeeping.
• Applying gas classification principles directly to dust hazards.
• Failing to reassess classification after process modifications.
• Ignoring secondary explosion risks.
• Using generic classification drawings without verification.

Many of these deficiencies can result in inappropriate equipment selection and significantly increase explosion risks.

Relationship Between IEC 60079-10-2 and Other Standards

IEC 60079-10-2 forms part of the broader hazardous area engineering framework and should be used together with several other IEC 60079 standards.

Standard	Purpose
IEC 60079-10-1	Classification of explosive gas atmospheres.
IEC 60079-10-2	Classification of combustible dust atmospheres.
IEC 60079-31	Protection by enclosure for dust atmospheres.
IEC 60079-14	Selection and installation of electrical equipment.
IEC 60079-17	Inspection and maintenance of installations.

Together, these standards provide a complete framework for managing explosion risks associated with combustible dust atmospheres.

Why Engineers Should Understand IEC 60079-10-2

Combustible dust explosions can be extremely destructive, yet dust hazards are often less understood than gas hazards.

A basic understanding of IEC 60079-10-2 helps engineers:

• Recognize combustible dust hazards.
• Interpret dust hazardous area drawings.
• Select suitable Ex equipment.
• Improve housekeeping strategies.
• Identify secondary explosion risks.
• Reduce classification errors.
• Improve process safety management.

Because combustible dust hazards exist in many industries that are not traditionally associated with explosion risks, IEC 60079-10-2 remains one of the most important standards for engineers involved in industrial safety and hazardous area management.

Frequently Asked Questions (FAQ)

What is IEC 60079-10-2?

IEC 60079-10-2 is the international standard that specifies the principles and methodology for classifying areas where combustible dust atmospheres may occur. It provides guidance for determining Zone 20, Zone 21, and Zone 22 hazardous areas.

What is the purpose of combustible dust hazardous area classification?

The purpose of hazardous area classification is to identify locations where combustible dust clouds or dust accumulations may create explosion hazards so that suitable protective measures and explosion-protected equipment can be selected.

What is the difference between Zone 20, Zone 21, and Zone 22?

Zone 20 is an area where a combustible dust cloud is present continuously, frequently, or for long periods. Zone 21 is an area where a combustible dust cloud is likely to occur occasionally during normal operation. Zone 22 is an area where a combustible dust cloud is not likely during normal operation and, if it occurs, exists only for a short period.

Why are dust layers important?

Dust layers can become dangerous because they may ignite, create overheating conditions, or become dispersed into the air and form explosive dust clouds that can lead to secondary explosions.

Does IEC 60079-10-2 apply to all types of dust?

No. The standard applies only to combustible dusts capable of forming explosive atmospheres. Non-combustible dusts generally do not require classification under IEC 60079-10-2.

Can dust explosions occur outside traditional industrial facilities?

Yes. Combustible dust hazards exist in many industries, including food processing, agriculture, woodworking, pharmaceutical manufacturing, and metal processing facilities.

Conclusion

IEC 60079-10-2 is one of the most important standards within the IEC 60079 series because it establishes the methodology used to identify and classify areas where combustible dust atmospheres may occur.

The standard provides a systematic approach for evaluating dust release sources, dust cloud formation, dust layer accumulation, housekeeping practices, and the extent of hazardous areas, ultimately leading to the determination of Zone 20, Zone 21, and Zone 22 classifications.

Because combustible dust explosions can be extremely destructive and often occur in industries that do not traditionally consider themselves hazardous, a proper understanding of IEC 60079-10-2 is essential for engineers, consultants, EPC contractors, and facility operators.

Accurate hazardous area classification helps reduce ignition risks, improve process safety, and ensure that explosion-protected equipment is selected and installed appropriately throughout the entire facility lifecycle.

Technical Review

References

• IEC 60079-10-2 – Explosive Atmospheres – Part 10-2: Classification of Areas – Combustible Dust Atmospheres.
• IEC 60079-10-1 – Explosive Atmospheres – Part 10-1: Classification of Areas – Explosive Gas Atmospheres.
• IEC 60079-31 – Explosive Atmospheres – Equipment Dust Ignition Protection by Enclosure "t".
• IEC 60079-14 – Explosive Atmospheres – Electrical Installations Design, Selection and Erection.
• IECEx System – International Certification System for Equipment Used in Explosive Atmospheres.
• International Electrotechnical Commission (IEC).
• EN IEC 60079-10-2 – Classification of Areas – Combustible Dust Atmospheres.