Class 1 Division 2 and ATEX Zone 2: A Comprehensive Overview

 

What is a Hazardous Location? 
A hazardous location is any area where the presence of dangerous substances, such as flammable gases, vapors, or combustible dust, poses a potential risk of explosion or fire. The risk in these locations arises when these substances mix with air to form an ignitable mixture. 
 
What is an Explosive Atmosphere? 
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. 
 
Key Components of an Explosive Atmosphere 
 
Oxygen (usually from the air). 
Supports combustion by reacting with flammable substances. Usually supplied by the air (around 21% oxygen). Without oxygen, combustion cannot occur. 
 
Fuel (Flammable Substances) 
The combustible material that ignites when mixed with oxygen. Can be gases (e.g., methane, propane), vapors, mists, or dusts. It needs to be present in specific concentrations (between LEL and UEL) to form an explosive mixture. 
 
Ignition Source  
The trigger that initiates combustion. Common sources include electrical sparks, hot surfaces, static electricity, and open flames. Without an ignition source, the fuel-oxygen mixture won't ignite. 
 
 
Class/Division System Overview 
 
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. 
 
Classes and Divisions Classification 
 
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). 
 Examples: Textile mills, woodworking facilities.
 
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 Zones Classification 
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. 

 
Comparison Between Class 1 Division 2 (C1D2) and ATEX Zone 2 

Feature	C1D2 (Class 1 Division 2)	ATEX Zone 2
Geographical Scope	North America (U.S. and Canada)	Europe (European Union, under ATEX directive)
Classification System	Class/Division System	Zone System
Likelihood of Hazard	Flammable gases or vapors present only under abnormal conditions (e.g., leaks, equipment failure)	Explosive atmosphere unlikely during normal operations, present only under abnormal conditions (e.g., brief malfunctions)
Regulatory Framework	Governed by NEC (National Electrical Code) and CEC (Canadian Electrical Code)	Governed by ATEX Directive 2014/34/EU
Equipment Requirements	Must avoid ignition sources (sparks, overheating). Explosion-proof not always required, but equipment must prevent ignition.	Category 3 equipment required; designed to prevent ignition in case of accidental exposure to explosive atmospheres.
Common Industries	Oil and gas, chemical processing, pharmaceuticals, fuel storage (North America)	Oil and gas, chemical plants, refineries, pharmaceuticals (Europe)
Certification Bodies	UL (Underwriters Laboratories), CSA (Canadian Standards Association)	Requires ATEX certification (equipment marked with ATEX)

FAQs

What is a C1D2 area?
A Class 1 Division 2 (C1D2) area is a hazardous location where flammable gases, vapors, or liquids are present only under abnormal conditions, such as equipment malfunctions or leaks.

Is C1D2 explosion proof?
Not necessarily. Equipment in C1D2 areas doesn’t always need to be explosion-proof, but it must prevent ignition in case of accidental exposure to flammable substances.

Is Class 1 Div 2 the same as Zone 2?
Not exactly, but they are similar. C1D2 (North America) and ATEX Zone 2 (Europe) both refer to areas where hazardous materials are present under abnormal conditions, but they follow different classification systems.

What are Zone 1 and Zone 2 hazardous areas?
Zone 1 is an area where explosive atmospheres are likely to occur during normal operations. Zone 2 is where explosive atmospheres are unlikely but could occur briefly under abnormal conditions.

Is ATEX Zone 2 intrinsically safe?
Equipment in Zone 2 can be intrinsically safe, but not all equipment is. Intrinsically safe equipment limits energy so it cannot ignite a flammable atmosphere, but other protection methods can be used as well.

What is the USA equivalent to ATEX?
The USA equivalent to ATEX is the Class/Division system, governed by the NEC (National Electrical Code), with UL (Underwriters Laboratories) providing certification.

What is the difference between Division 1 and Division 2?
Division 1 refers to areas where hazardous materials are present under normal operations, while Division 2 refers to areas where these materials are only present under abnormal conditions.

What are ATEX Zones based on?
ATEX Zones are based on the likelihood and duration of the presence of explosive atmospheres in the area.

Can ATEX Zone 2 equipment be used in C1D2 areas?
Sometimes, but equipment must meet both ATEX and C1D2 standards, as they are regulated by different codes and certification bodies.

Why is it important to use C1D2 or Zone 2 certified equipment?
Certified equipment ensures safety by preventing potential ignition of flammable substances, which reduces the risk of explosions and ensures compliance with safety regulations.