Understanding the hazardous locations classification system

Understanding hazardous classified locations, a critical aspect of industrial safety, is important to ensure the well-being of workers and the integrity of operations.

By Herbert Post November 30, 2023
Courtesy: CFE Media and Technology

Plant safety and PPE insights

  • Regulatory compliance with NFPA 70 (NEC) and OSHA 29 CFR is vital for electrical safety in hazardous locations, minimizing fire and explosion risks.
  • Understanding the classification system (Classes, Divisions, and Groups) is crucial for implementing effective safety measures and equipment in hazardous locations, ensuring personnel and asset protection.

Hazardous classified locations, a critical aspect of industrial safety, pose significant risks to personnel and assets. These specialized areas contain materials that, due to their nature, can lead to fires, explosions, or other hazardous incidents. Understanding these locations is important to ensure the well-being of workers and the integrity of operations.

Hazardous locations regulatory standards and codes

When it comes to hazardous locations, adherence to stringent regulatory standards and codes is imperative to ensure the safety of personnel and facilities. Two key regulatory entities play a crucial role in this context.

National Fire Protection Association (NFPA) 70 National Electric Code. NFPA 70, commonly known as the National Electric Code (NEC), sets the guidelines and requirements for safe electrical installations in hazardous areas. It provides comprehensive guidance on electrical equipment selection, wiring methods, grounding, and bonding to prevent potential ignition sources.

The NEC’s classification system categorizes hazardous locations based on classes, divisions, and groups, that when combined help assess the hazardous conditions of a specific area. Articles 500 to 503 of the NEC detail the requirements for electrical equipment and wiring for all classes and divisions. Compliance with NFPA 70 is vital for maintaining electrical safety and minimizing the likelihood of fire and explosion hazards.

OSHA 29 CFR. The Occupational Safety and Health Administration (OSHA) issues the Code of Federal Regulations (CFR), specifically Section 1910.307, which focuses on electrical equipment used in hazardous classified locations. OSHA 29 CFR mandates measures such as enclosure requirements, ventilation, and maintenance practices to mitigate hazards in the workplace. According to the standard, it is required that all equipment used in a hazardous location be marked correctly with the class and group, as well as the temperature range for which it is approved.

Hazardous locations classification system

The hazardous locations classification system is a vital framework used to assess and designate the level of risk in specific areas with the presence of potentially dangerous substances. The system is divided into three main components: Classes, Divisions, and Groups, each tailored to address distinct hazardous scenarios.


Class I: Locations with potential flammable gases or vapors

Class I pertains to environments where flammable gases or vapors may be present, creating an atmosphere prone to ignition. Implementing explosion-proof equipment and other safety measures is crucial to prevent potential hazards in these areas.

Class II: Locations with combustible dust

Class II involves areas where combustible dust particles can become suspended in the air, creating the risk of explosions. Proper dust control and ventilation are essential to safeguard workers and equipment in these environments.

Class III: Locations with easily ignitable fibers

Class III locations are characterized by the presence of easily ignitable fibers, such as cotton, wool, or other similar materials, in sufficient quantities to create a potential fire hazard. These fibers have the capacity to ignite rapidly and can propagate flames quickly if exposed to an ignition source. Class III hazardous areas are less common compared to Class I and Class II locations. Due to the specific nature of the materials involved, electrical equipment used in Class III locations needs to be designed to prevent the entrance of fibers and be dust-tight to ensure safety.

Proper equipment selection and adherence to safety guidelines are essential to mitigate the risks associated with easily ignitable fibers and maintain a secure working environment.

Divisions (For classes I, II and III)

  • Division 1: Hazardous areas may contain ignitable concentrations of hazards during normal operation or due to frequent maintenance, repair work or equipment failure.

  • Division 2: Ignitable concentrations of hazards can also be present in hazardous locations under abnormal operation conditions.

Groups (Applicable to Class I and Class II)

Class I Groups

  • Group A: Atmospheres with Acetylene

  • Group B: Atmospheres with Hydrogen, Butadiene, Ethylene Oxide, Propylene Oxide, Acrolein, and similar gases or vapors

  • Group C: Ethylene, Cyclopropane and Ethyl Ether

  • Group D: Acetone, Ammonia, Benzene, Butane, Ethanol, Gasoline, Hexane, Methane, Methanol, Methane, Naphtha, Natural Gas, Propane and Toluene

Class II Groups

  • Group E: Atmospheres with combustible metal dust such as Aluminum, Commercial Alloys, and Magnesium

  • Group F: Atmospheres with carbonaceous dust such as Carbon Black, Charcoal, Coal, and Coke Dusts

  • Group G: Atmospheres with non-conductive dust and other combustible dusts such as flour, grain, plastic, wood and chemicals.

In hazardous locations, understanding this classification system is paramount to implementing appropriate safety measures, equipment, and protocols. Proper categorization aids in determining the level of risk and identifying suitable strategies to mitigate potential dangers, ensuring the well-being of personnel and safeguarding valuable assets.

Proper classification best practices

Proper classification best practices are crucial for ensuring safety in hazardous locations. Three essential aspects play a pivotal role in maintaining a secure environment:

Selection of appropriate equipment and PPE

Selecting suitable equipment and personal protective equipment (PPE) is paramount in hazardous locations. Employing explosion-proof, intrinsically safe, or non-incendive equipment, based on the classification, prevents potential ignition sources. Equipping personnel with the right PPE, such as flame-resistant clothing and respirators, enhances their protection against hazards.

Preventing potential explosions and fires

Mitigating the risk of explosions and fires requires proactive measures. Implementing rigorous housekeeping practices, such as controlling dust or vapor accumulation, significantly reduces ignition possibilities. Regular equipment inspections, maintenance with proper lockout tagout, and repair are vital to ensure their integrity and prevent malfunction-induced hazards.

Training, education for hazardous area personnel

Proper training and education are instrumental in hazard awareness and response. Hazardous area personnel must undergo comprehensive training on area classification, emergency procedures, and the proper use of equipment and PPE. Regular safety drills enhance preparedness for potential incidents, fostering a culture of vigilance and adherence to protocols.

TradeSafe is a CFE Media and Technology content partner.

Original content can be found at TradeSafe.

Author Bio: Herbert Post is VP of health and safety at TradeSafe. He has spent the last 13 years facilitating best practices and teaching updated regulations.