An explosive atmosphere refers to a mixture of air and hazardous substances in the form of gases, vapors, mists, or dusts, which can ignite under specific conditions. When this mixture comes into contact with a source of ignition, such as a spark, high surface temperature, or electrical fault, it can cause an explosion or fire. 

Oxygen (usually from the air). 

Class/Division System used in North America, mainly governed by the National Electrical Code (NEC) in the U.S. and the Canadian Electrical Code (CEC) in Canada. The NEC and CEC define the standards for electrical installations in hazardous locations. The Class/Division system categorizes environments based on the type and likelihood of hazardous materials being present, ensuring that the appropriate safety measures are taken to prevent explosions or fires. 

These classifications are divided into classes, divisions, groups, designed to address the varying types and risks of hazardous materials present in different environments. Although the system can seem complex, it’s essential to understand these ratings as they directly impact the safety and suitability of the technology used in your workplace. 

 
Classes 
Classes define the type of hazardous material present in the environment. 
  
Class 1: Locations where flammable gases, vapors, or liquids may be present. 
Examples: Oil refineries, chemical plants, gas processing facilities. 
  
Class 2: Locations where combustible dust may be present. 
Examples: Grain elevators, flour mills, coal handling plants. 
  
Class 3: Locations where combustible fibers or flyings may be present (but not likely to be suspended in air in ignitable concentrations). 
 
 
Divisions 
Divisions define the likelihood of the hazardous material being present. 
  
Division 1 (D1): Hazardous substances are present under normal operating conditions or frequently during maintenance or repair. 
Example: A chemical plant where flammable vapors are regularly present. 
 
Division 2 (D2): Hazardous substances are present only under abnormal conditions, such as equipment failure, leaks, or maintenance. 
Example: A gas storage facility where gases may only escape due to a valve failure. 

 
Groups 
Groups categorize the specific types of gases, vapors, or dusts based on their ignition properties (explosiveness and combustibility). 
  
For Class 1 (Gases, Vapors): 

• Group A: Acetylene (highly explosive and volatile). 
• Group B: Hydrogen or gases with similar properties (e.g., butadiene, ethylene oxide). 
• Group C: Ethylene or gases with similar explosive characteristics. 
• Group D: Methane, propane, butane, gasoline, and similar gases (less volatile than Group A, B, or C). 

 
For Class 2 (Dusts): 

• Group E: Combustible metal dusts (e.g., aluminum, magnesium). 
• Group F: Carbonaceous dusts (e.g., coal, charcoal). 

• Group G: Combustible dusts from grain, flour, plastics, chemicals (e.g., grain dust, flour dust). 
  
  

Summary of Classes, Divisions, and Groups 

Class	Division 1 (D1)	Division 2 (D2)	Group Examples
Class 1 (Gases)	Flammable gases or vapors present under normal conditions.	Gases or vapors only present during abnormal conditions.	A (Acetylene), B (Hydrogen), C (Ethylene), D (Propane, Methane)
Class 2 (Dusts)	Combustible dust is present under normal conditions.	Dust is present only under abnormal conditions.	E (Metal Dusts), F (Coal Dust), G (Grain, Flour)
Class 3 (Fibers)	Combustible fibers are present under normal conditions.	Fibers or flyings present under abnormal conditions.	Not divided into specific groups.

 

What is C1D2?  

In short, Class 1 Division 2 (C1D2) refers to hazardous environments where flammable gases, vapors, or liquids are present only under abnormal conditions, such as equipment malfunctions or leaks. While these substances are typically absent during normal operations, equipment used in these locations must be designed to prevent ignition in the event of accidental exposure. 

• Explosive Atmosphere Likelihood: The presence of flammable gases or vapors in C1D2 areas is infrequent and only occurs during abnormal conditions such as equipment leaks or accidental releases. 
• Normal Operation: During normal operation, no hazardous atmosphere should be present. However, equipment must be capable of preventing ignition if a hazardous substance is released unexpectedly. 

 

ATEX Directive Overview 

The ATEX directive (short for Atmosphères Explosibles) is a European regulation designed to ensure safety in environments where there is a risk of explosions due to the presence of flammable gases, vapors, mists, or dusts. The directive covers both: 

• ATEX 99/92/EC (also known as the ATEX Workplace Directive), which governs the safety of workers in explosive atmospheres. 
• ATEX 2014/34/EU (also known as the ATEX Equipment Directive), which governs the design and certification of equipment used in explosive atmospheres.
  
  

ATEX divides hazardous locations into Zones, based on the likelihood of an explosive atmosphere forming: 

For Gases, Vapors, and Mists: 

• Zone 0: An area where an explosive atmosphere is present continuously or for long periods (more than 1,000 hours per year). 
• Zone 1: An area where an explosive atmosphere is likely to occur during normal operations (between 10 and 1,000 hours per year). 
• Zone 2: An area where an explosive atmosphere is unlikely to occur during normal operation, and if it does, it will be infrequent and last for a short time (less than 10 hours per year). 

For Dusts: 

• Zone 20: Explosive dust is present continuously or for long periods. 
• Zone 21: Explosive dust is likely to occur occasionally during normal operations. 
• Zone 22: Explosive dust is unlikely to occur during normal operation and will persist only for short periods. 

 

What is ATEX Zone 2? 

Zone 2 is considered one of the least hazardous of the three zones. While it’s possible for an explosive atmosphere to form in Zone 2, it happens infrequently and only under abnormal conditions like equipment leaks or failures. 

• Explosive Atmosphere Likelihood: Flammable gases or vapors are only expected to be present for short durations and not under normal operating conditions. 
• Equipment Requirements: Equipment used in Zone 2 must be designed to prevent ignition, but the standards are less stringent compared to those required for Zones 0 and 1. For instance, non-sparking equipment or equipment with low surface temperatures is often used. ATEX-certified equipment is labeled with the marking for Zone 2, ensuring that it is safe for use in such environments. 
• Typical Industries: Zone 2 environments are common in industries such as oil and gas refineries, chemical processing plants, pharmaceutical manufacturing, and food processing facilities, where occasional leaks or emissions of flammable substances can occur.