Hazardous Electrical Area Classification

A Hazardous Area Classification (HAC) study is an essential analysis aimed at reducing the chances of igniting flammable materials. This study focuses on identifying sources of gases, vapors, and combustible dust, and implementing ignition control designs. HAC is a type of hazard and risk assessment specifically addressing the probability of explosive atmospheres (flammable dust/air mixtures) in certain areas. The classification is conducted following either the NFPA standard’s two Division system or the ATEX standard’s three Zone system.

Upon completing the HAC, steps are taken to manage and control potential ignition sources effectively. This includes enforcing stringent regulations on possible ignition sources in areas with a high likelihood of explosive atmospheres, thereby substantially lowering the risk of explosions in these classified zones.

The primary motivation for conducting HAC has traditionally been to ensure that electrical systems do not present an ignition hazard in facilities dealing with flammable or combustible materials. In North America, the HAC is mandated under the National Electrical Code (NEC), while in Europe, it adheres to the ATEX standards. However, to achieve an acceptable safety level within a plant, it’s crucial to regulate non-electrical ignition sources with the same rigor as electrical sources.

A hazardous area extent and classification study involves due consideration and documentation of the following:

  • The flammable materials that may be present;
  • The physical properties and characteristics of each of the flammable materials;
  • The source of potential releases and how they can form explosive atmospheres;
  • Prevailing operating temperatures and pressures;
  • Presence, degree and availability of ventilation (forced and natural);
  • Dispersion of released vapors to below flammable limits;
  • The probability of each release scenario.

The following explains the significance of Class, Group, Division and Ignition Temperature.

Class is used to provide a general definition of the physical characteristics of the combustible fuel. The three classes are:

  1. Class I: Gasses, vapors, and liquids that can be present in explosive or ignitable mixtures.
  2. Class II: Combustible dust that can be present in amounts that could produce explosive mixtures or dust of an electrically conductive nature.
  3. Class III – Fibers or flying that is easily ignitable but is not apt to be suspended in the air in such amounts to produce ignitable mixtures.

Group designations are used to selectively divide a class into categories of material by relatively similar combustion characteristics. Groups are designed by the letters A through G. Groups A through D, are Groups for Class I, and E through G are Groups for Class II materials.

Group Hazardous Material in Surrounding Atmosphere
Group A Acetylene
Group B Hydrogen, fuel and combustible process gases containing more than 30% hydrogen by volume or gases of equivalent hazard such as butadiene, ethylene oxide, propylene oxide, and acrolein.
Group C Ethyl ether and ethylene or gases of equivalent hazard.
Group D Gasoline, acetone, ammonia, benzene, butane, cyclopropane, ethanol, hexane, methanol, methane, natural gas, naphtha, propane or gases of equivalent hazard.
Group E Metal conductive dusts, including aluminium, magnesium and their commercial alloys or other combustible dust whose particle size, abrasiveness and conductivity present similar hazards in connection with electrical equipment.
Group F Carbonaceous dust, coal-black, charcoal, coal or coke dust that has more than 8% total entrapped volatiles or dust that has been sensitized by other material, so they present an explosion hazard.
Group G Flour, sugar, starch, grain, wood, and plastic dust and chemicals

The decision to classify an area as hazardous should be based on the probability that a combustible mixture could be present. Two division classifications are used to specify the likelihood of a flammable atmosphere being present. It is important to understand that it is always preferable to prevent the formation of combustible atmospheres (combustible dust clouds) and dust layers than to have an area classified as hazardous and not to control combustible dust clouds.

Once it is decided that an area should be classified, the next step should be to determine the likelihood of the hazard occurring: Is the area Division 1 or Division 2?  The division defines the probability of hazardous material being present in an ignitable concentration in the surrounding atmosphere.

Two European Directives, the ATEX Equipment Directive 94/9/EC (ATEX 95) and the ATEX Workplace Directive 1999/92/EC (ATEX 137) address safety in hazardous areas where there is a danger from potentially explosive materials – the ATEX Directives relate equally to places where combustible dusts or flammable gases or solvents may be present

A combustible liquid and gases zone hazardous (classified) location is subdivided into Zone 0, Zone 1, and Zone 2 while a combustible dust zone hazardous (classified) location is further subdivided into either Zone 20, Zone 21, or Zone 22, in which combustible dust is or might be present in the air or in layers, in quantities sufficient to produce explosive or ignitable mixtures.

European & IEC Classification Definition of Zone or Division North American Classification
  •  Zone0 (gasses)
  •  Zone20 (gasses)
An area in which an explosivemixture is continuously present or present
for long periods
  • Class I Division 1 (gases)
  • Class II Division 1 (dusts)
  • Zone1 (gases)
  •  Zone 21(dusts)
An area in which an explosive mixture is likely to occur in normal
  • Class I Division 1 (gases)
  • Class II Division 1 (dusts)
  • Zone2 (gases)
  •  Zone 22(dusts)
An area in which an explosive mixture is not likely to occur in normal
operation and if it occurs it will exist only for a short time
  • Class I Division 2 (gases)
  • Class II Division 1 (dusts)
  • Class III Division 1 (fibres)
  • Class III Division 2 (fibres)

Regulatory Compliance and Standards for HAC

In the US, hazardous area classifications are governed by NFPA 70, National Electrical Code (NEC). The NEC provides requirements for electrical installations, including those in hazardous locations, in the United States.

  • NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, provides guidelines for classifying hazardous locations where flammable gases and solvents are present.
  • NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, provides guidelines for classifying hazardous locations where combustible dusts and fibers are present.

The following international standards are used to define hazardous area classification zones, or their equivalent:

  • EN 1127-1; Explosive atmosphere – Explosion prevention and protection. Part 1: Basic concepts and methodology
  • EN 60079-10; Electrical apparatus for explosive gas atmospheres. Part 10: Classification of potentially explosive atmospheres

EN 50281-3; Electrical apparatus for use in the presence of combustible dust. Part 3: Classification of areas where dusts are or may be present.

Hazardous Area Classification (HAC) Assessment

Implementing Hazardous Area Classification (HAC) in industrial settings within the USA for process safety involves a structured approach to ensure the safe handling of hazardous materials. Here are the key steps:

Hazard Identification: Identify potential sources of flammable gases, vapors, or combustible dust within the facility. This includes all materials and processes that could create an explosive atmosphere.

Gathering Data: Collect information on the properties of hazardous materials, including flammability ranges, ignition temperatures, and potential release scenarios.

Risk Assessment: Conduct a risk assessment to evaluate the likelihood and potential impact of an explosive atmosphere. This involves analyzing the frequency and duration of the presence of hazardous substances.

Area Classification: Classify areas into specific zones based on the risk assessment. In the USA, this typically follows the National Electric Code (NEC) guidelines, classifying areas as Class I (gases and vapors), Class II (dust), or Class III (fibers and flyings).

Selection of Suitable Equipment: Choose equipment and protective systems certified for use in the classified zones. This includes electrical equipment and any machinery that could act as an ignition source.

Control and Mitigation Measures: Implement control measures to prevent the release of hazardous substances and mitigate risks. This may include ventilation, process containment, and grounding and bonding to prevent static build-up.

Documentation and Mapping: Document the classification process and create detailed maps of the classified zones. This information should be readily accessible for reference and training purposes.

Training and Awareness: Educate employees about the risks associated with hazardous areas and the safety protocols in place. Ensure they understand the importance of following these guidelines.

Regular Review and Updates: Periodically review the HAC to reflect any changes in processes, materials, or relevant safety standards. Regular audits help maintain compliance and safety.

Compliance with Standards: Ensure adherence to relevant safety standards and regulations, such as OSHA guidelines and the NEC, which are critical in the USA.

Why Perform Hazardous Area Classification

Performing Hazardous Area Classification is an essential practice for ensuring safety in environments where explosive or flammable substances are handled. This classification involves analyzing areas of a facility to determine the presence and extent of hazardous conditions, typically categorized into zones based on the likelihood of an explosive atmosphere. By clearly identifying these areas, industries can implement appropriate safety measures, such as selecting suitable equipment and controls that are designed to operate safely in these conditions. This not only helps in preventing accidents like fires or explosions but also ensures compliance with safety regulations and standards. Hazardous Area Classification is fundamental for risk management, guiding the design, operation, and maintenance of facilities in a way that prioritizes the safety of personnel and the integrity of operations in the face of potentially hazardous environments.

Why Work with Prime Process Safety Center

  • Expertise in Hazard Identification: Our team specializes in accurately identifying and classifying hazardous areas, ensuring comprehensive risk assessment in environments with flammable substances.
  • Customized Classification Approach: We tailor our Hazardous Area Classification to the specific nature of your operations, considering the unique characteristics of the materials you handle.
  • Up-to-Date with Codes and Standards: Our methodology is aligned with the latest industry guidelines, codes, and standards, ensuring your facility adheres to current best practices and regulatory requirements.
  • Practical Safety Solutions: We provide not just assessments but also practical and effective safety solutions, advising on suitable equipment and safety measures for classified hazardous areas.
  • Mitigation of Explosion and Fire Risks: Our classification service is pivotal in reducing the risks of fires and explosions, thereby enhancing the overall safety of your facility.
  • In-Depth Risk Analysis: We conduct thorough evaluations of potential ignition sources and the properties of hazardous materials, providing a detailed understanding of the risks present.
  • Regulatory Compliance Assurance: Our service ensures that your facility remains compliant with safety regulations, protecting you from potential legal and financial penalties.
  • Long-Term Operational Safety: By identifying and classifying hazardous areas, we help you maintain long-term operational safety and avoid costly accidents and downtime.
  • Comprehensive Documentation: We provide detailed documentation of our findings and recommendations, supporting your safety management and compliance efforts.
  • Ongoing Support and Guidance: Our commitment extends beyond the initial assessment, offering ongoing support and guidance to keep your facility safe and compliant.


1. What is Hazardous Area Classification?

It’s the process of analyzing and classifying areas in industrial settings where flammable gases, vapors, mists, or dusts could create an explosive or fire hazard.

2. Why is Hazardous Area Classification important in industries?

It’s crucial for ensuring the safe selection and installation of equipment, reducing the risk of ignition in areas with potentially explosive atmospheres, and ensuring compliance with safety regulations.

3. What industries typically require Hazardous Area Classification?

Industries like oil and gas, chemical manufacturing, pharmaceuticals, food processing, and any others where flammable materials are processed or stored.

4. How are hazardous areas classified?

Areas are classified based on the type, concentration, and likelihood of the presence of hazardous substances, typically into Zones (for gases and vapors) or Divisions (for dusts).

5. What standards are used for Hazardous Area Classification?

The most common standards include the National Electrical Code (NEC) in the US, the International Electrotechnical Commission (IEC) standards, and the European ATEX directives.

6. What is the difference between Zone and Division classification systems?

The Zone system, used internationally, categorizes areas into Zones 0, 1, and 2 for gases and 20, 21, and 22 for dusts, while the Division system, used mainly in North America, classifies areas into Division 1 and 2.

7. Who should perform Hazardous Area Classification?

Qualified professionals with expertise in process safety and knowledge of applicable standards should conduct these classifications.

8. What factors are considered during Hazardous Area Classification?

Factors include the type of hazardous materials present, their physical and chemical properties, operational processes, environmental conditions, and facility layout.

9. How does Hazardous Area Classification impact equipment selection?

It determines the type of explosion-proof or intrinsically safe equipment that should be used in different areas to prevent ignition of hazardous atmospheres.

10. Is Hazardous Area Classification a one-time requirement?

No, it should be reviewed and updated regularly, especially when there are changes in processes, materials, or facility layout, to ensure ongoing safety compliance.

11. What are some Potential Ignition Sources and Controls to be Considered in Hazardous Area Classification?

  • Flames;
  • Direct-fired space and process heating;
  • Use of cigarettes/matches etc;
  • Cutting and welding flames;
  • Hot surfaces;
  • Heated process vessels such as dryers and furnaces;
  • Hot process vessels;
  • Space heating equipment;
  • Mechanical machinery;
  • Electrical equipment and lights
  • Spontaneous heating;
  • Friction heating or sparks;
  • Impact sparks;
  • Sparks from electrical equipment;
  • Stray currents from electrical equipment
  • Electrostatic discharge sparks:
  • Lightning strikes.
  • Electromagnetic radiation of different wavelengths

12. In what way can ignition sources effectively controlled in all hazardous areas ?

  • Using electrical equipment and instrumentation classified for the area in which it is located. New mechanical equipment will need to be selected in the same way.
  • Grounding of all plant/ equipment.
  • Elimination of surfaces above auto-ignition temperatures of flammable materials being handled/stored
  • Provision of lightning protection
  • Correct selection of vehicles/internal combustion engines that have to work in the zoned areas (see Technical Measures Document on Permit to Work Systems);
  • Correct selection of equipment to avoid high intensity electromagnetic radiation sources, e.g. limitations on the power input to fibre optic systems, avoidance of high intensity lasers or sources of infrared radiation
  • Prohibition of smoking/use of matches/lighters
  • Controls over the use of normal vehicles
  • Controls over activities that create intermittent hazardous areas, e.g. tanker loading/unloading
  • Control of maintenance activities that may cause sparks/hot surfaces/naked flames through a Permit to Work System
  • Precautions to control the risk from pyrophoric scale, usually associated with formation of ferrous sulphide inside process equipment

13. What are some best practices for hazardous area classification?

  • Follow established engineering practices such as NFPA, API, NEC, IEC and PIP etc.
  • Ensure that hazardous area requirements are established before purchasing equipment.
  • Ensure that hazardous area classification layouts reflect the current status of the facility.
  • Review and update layouts before each modification.
  • Ensure that the addition of new equipment does not impact existing equipment / facility and if so, take corrective action.
  • Ensure that the area classification “cloud does not encroach roads, walkways, occupied buildings, welding / fabrication yards etc.
  • Perform a thorough review when introducing new sources of release in an existing facility.
  • Ensure equipment installed in the classified area is rated for service conditions.
  • Follow the manufacturer’s installation manual, applicable codes and standards.
  • Maintain proper documentation.

14. What are some precautions to be taken in hazardous areas?

Precautions include compliance with classifications (according to NEC), training and awareness programs, prevention of ignition sources, regular maintenance and inspection, proper ventilation, use of appropriate Personal Protective Equipment (PPE), and implementation of an emergency response plan and permit-to-work system.

15. What main safety measures to take for Class I, Class II, and Class III locations?

Safety measures vary for each class. For Class I locations, use explosion-proof equipment and proper ventilation to handle flammable gases or vapors. Class II locations require dust-tight equipment and dust control to manage combustible dust hazards. In Class III locations, protect against ignitable fibers with proper enclosures and handling protocols.

16. What is explosion-proof Protection and intrinsically safe protection?

Explosion-proof protection is a type of protection that involves using an enclosure capable of withstanding an explosive gas or vapor within it. The enclosure also prevents the ignition of an explosive gas or vapor surrounding it. This type of protection operates at an external temperature that ensures the surrounding explosive atmosphere will not be ignited.

Intrinsically safe protection ensures that electrical equipment, under normal or abnormal conditions, is incapable of releasing sufficient electrical or thermal energy to cause ignition of a specific hazardous atmospheric mixture in its most easily ignitable concentration.