ATEX: Selecting Equipment for Explosive Atmospheres

• It is important to take special precaution when using equipment, instrumentation, and when operating in areas that pose a risk of explosion.
• ATEX Directives define the types of safety ratings that are necessary to protect people and equipment in potentially explosive areas.
• Potentially explosive gases, liquids, and dust all pose different risks, so it’s important to understand the exact requirements when operating in these areas.

The nature of many industrial processes means an explosive gas, vapor, or dust atmosphere might be present. This may be as a by-product of the process or as an inherent process hazard. Either way, operators must take the necessary precautions to ensure that a fire or explosion does not take place. Furthermore, special safety is necessary in areas that can lead to an explosive atmosphere, which is where ATEX Directives come into play.

Components of an Explosive Atmosphere

The explosion triangle shows the three components which would allow a fire or explosion to take place:

• fuel sources
• ignition or heat source
• oxygen or other oxidizing agent

Fuel Sources

Fuel sources from industrial processes are typical split into two types:

• “Gas” includes vapor and mists. Typical gas fuel sources can include ammonia, methane, hydrogen, propane, ethane and butane. These are often found in chemical and petrochemical processes.
• “Dust” includes fibers and flyings. Typically, dust fuel sources can include dust layers and clouds. These are often formed from metal processing, food & beverage production, pharmaceutical manufacturing, paper and wood processing.

Ignition Sources

Potential sources of ignition are wide reaching. For example, they can include sparks from cutting and welding equipment, hot surfaces, friction, impact sparks, electrostatic discharge, lightning, and many more.

Oxygen

Consideration should be given to not only oxygen in the air, but also oxidizing agents such as chlorine.

Explosion Protection

Operators can prevent a fire or explosion by effectively removing one of the legs of the triangle. The concept of explosion protection is to do just this. Operators can achieve this by either removing or restricting the presence of oxygen, fuel, or potential sources of ignition. Therefore, through careful consideration of the process environment, process design, and by employing equipment suitable for the protection methods chosen, risks can be reduced or eliminated.

What is the ATEX Directive?

The term ATEX comes from the French term “ATmosphères EXplosibles”. There are two European Union ATEX directives. Initially, there’s the “equipment directive” which is for manufacturers of equipment for use in potentially explosive atmospheres (ATEX 114) 2014/34/EU. Secondly, there’s the “workplace directive” for the health and safety of workers at risk from explosive atmospheres: (ATEX 137) 1999/92/EC. The IEC 60079 series of standards, which also form the basis of the EU 2014/34/EU (ATEX) directive give detailed guidance on:

• evaluation and classification of hazardous areas within a plant
• selection and implementation of relevant equipment explosion protection methods

We offer a wide range of Intrinsic Safe products with ATEX barriers and other hazardous area certified products.

What is ATEX Zone Classification?

The ATEX 1999/92/EC workplace directive sets out the minimum requirements for improving the health and safety of workers potentially at risk from explosive atmospheres. Moreover, compliance with this directive includes a requirement to fully assess and document all potential explosion risks, including:

• flammable / explosive material characteristics
• source and grades of potential release (continuous, primary, secondary)
• ventilation and dispersion

Overall, this information is useful to characterize the areas of a plant into zones by the likelihood and frequency of an explosive atmosphere being present.

ATEX Zones vs Class/Div

Although the zone system relies on IEC standards and has wide international adoption, there are some national regulations that employ alternative methods; for example: the North American regulations relating to construction and operation of electrical systems.

The US National Electrical Code (NEC) and the Canadian Electrical Code (CEC) have alternative definitions for hazardous areas. Moreover, they use a Class and Division format to differentiate them.

It’s important to note that as the NEC/CEC regulations evolve the zone model has increasing acceptance.

What are ATEX Equipment Groups and Categories?

The ATEX equipment directive 2014/34/EU applies to electrical and/or mechanical equipment. Generally, this applies for use on the surface / above ground, below ground, and on offshore installations. Specifically, this directive covers:

• all equipment for use in potentially explosive atmospheres, and which are capable of causing an explosion through their own potential sources of ignition
• protective systems for use in potentially explosive atmospheres
• components, or any item essential to the safe functioning of equipment and protective systems, but with no autonomous function

Manufacturers are responsible for ensuring all relevant products have a conformity assessment in relation to the specific product type.

Equipment Groups

Equipment and products which fall within the scope of this directive divide into two groups:

Group I

Mining Industry
: applies to underground equipment in mines and any surface machinery with exposure to risk of firedamp and/or combustible dust emissions

Group II

Non-Mining Industry: applies to equipment for use in, for example, the process industry where explosive atmosphere potential from gases, vapors, mists, or air/dust mixtures are likely to occur

Equipment Categories

Each equipment group further divides into categories that depend on the level of protection available.

Group I Categories:

• M1: equipment in this category are for mining use and require to remain functional in the presence of an explosive atmosphere
• M2: equipment in this category are for mining use but will de-energize in the event of an explosive atmosphere

Group II Categories:

• Equipment Category 1: Equipment in this category is for use in Zone 0 areas (gases) or Zone 20 (dusts). Furthermore, this equipment must have a very high level of inherent protection. It must provide protection, even in the event of expected and rare faults. Additionally, a guarantee of safety is necessary in the case of two independent faults occurring.

• Equipment Category 2: Equipment in this category is for use in Zone 0 areas (gases) or Zone 20 (dusts). This equipment must have a very high level of inherent protection. It must provide protection, even in the event of expected and rare faults. In addition, a guarantee of safety is necessary in the case of two independent faults occurring.

• Equipment Category 3: 
Equipment in this category is for use in Zone 2 (gases) or Zone 22 (dusts). Equipment must provide necessary protection during normal operation.

ATEX Protection Methods

Various explosion protection methods can be useful depending on the nature of the hazard and on the specific process. Referencing relevant sections of the IEC 60079 series of standards and specification gives full requirements for each type of protection method. The tables below summarize the common protection methods for both gas and dust. Moreover, they show which zones they are applicable for, the method of protection, and the relevant IEC 60079 reference.

Protection Types – Gas

Protection Types – Dust