Safety in industrial plants is of crucial importance, especially in areas with potentially explosive atmospheres. EX zones are special areas where there is an increased risk of explosions. Correct handling of these zones is essential to prevent accidents and ensure the safety of people and equipment. In this guide, you will learn everything you need to know about EX zones, their classification and the relevant ATEX directives.
The ATEX directives (ATmosphères EXplosibles) are the most important regulations for protection against explosive atmospheres in Europe. They set requirements for materials, equipment and work processes to ensure safety in EX zones.
In this guide, you will learn everything you need to know about EX zones, their classification and the relevant ATEX directives in order to optimize your work in potentially explosive atmospheres.
Requirements for explosions
Before we turn to EX zones, it is important to understand what conditions are required for explosions. An explosion can only occur under certain conditions. The following elements must be present at the same time:
- Flammable substances that can form an explosive atmosphere with air
- Air or oxygen
- Ignition source
A explosive atmosphere occurs when air or oxygen mixes with flammable gases, vapors, mists or dusts - under normal atmospheric conditions. If such a mixture is ignited, the combustion spreads to all unburned material.
An area that is potentially at risk is considered potentially explosive if an explosive atmosphere can occur there. For an explosion to occur, the concentration of the flammable substance in the air must be within certain values, which are referred to as the "explosion range". This range varies greatly depending on the flammable substance in question.
The limits of the explosion range are defined by the lower explosion limit and the upper explosion limit. An explosion can only occur if the concentration of the flammable material is within these two limits. For example, an explosive atmosphere can occur inside a partially filled petrol tank, whereas a completely filled tank poses no risk as the upper concentration limit is exceeded here.
In commercial and industrial applications, various ignition ignition sources can occur, including
- Hot surfaces: These include, for example, radiators, hotplates, boilers and overheated machine parts.
- Flames and hot gases: Typical ignition sources include Bunsen burners, candles, matches and open heating systems with flames.
- Mechanically generated sparks: These are caused by friction or impact - for example when a hammer hits metal or when grinding materials.
- Electrical installations: Opening and closing electrical circuits, such as electric motors, can lead to ignition sources.
- Static electricity: These are discharge sparks that occur when charged parts are discharged by contact due to different voltage levels.
What are EX zones?
EX zones are specific areas in which an explosive atmosphere can occur and which therefore require special safety precautions. In order to regulate the use of electrical equipment in these zones, electrical equipment designed for use in potentially explosive atmospheres is divided into two main equipment groups:
- Group I: This includes electrical equipment used in underground areas where there is a risk of firedamp.
- Group II: This group refers to electrical equipment used in all other potentially explosive atmospheres. Within this group there is a further subdivision into three categories depending on the specific hazards.
Appliances in appliance group II are additionally marked with a letter indicating the state of the atmosphere:
- G - for areas in which explosive gas, vapor, mist or air mixtures are present
- D - for areas in which dust can form an explosive atmosphere with air
Equipment groups are used to classify electrical equipment according to the risk they pose in potentially explosive atmospheres. While the equipment groups define the type and safety precautions of the equipment, EX zones are specific areas in which such hazards can occur.
EX zones are classified based on the probability and duration of the occurrence of an explosive atmosphere, for example EX Zone 0, EX Zone 1 and EX Zone 2. These zones provide detailed information on how and where certain devices may be used and therefore play a decisive role in the safe handling of electrical equipment in explosive environments.
The main difference between EX areas and normal areas lies in the probability of ignition. There is a higher risk in EX areas, whereas in normal areas the risk of explosion is non-existent or greatly minimized.
Overview of the different EX zones
EX zones are classified based on the probability and duration of the occurrence of an explosive atmosphere. They are typically divided into the following zones:
- EX Zone 0: Areas in which an explosive atmosphere is present continuously or for long periods of time.
- EX Zone 1: Areas in which an explosive atmosphere occasionally occurs.
- EX Zone 2: Areas in which an explosive atmosphere occurs only rarely or for a short time.
In addition, there are zones that are specifically designed for dust-forming environments:
- EX Zone 20: Areas in which an explosive dust atmosphere is present continuously or for long periods of time.
- EX Zone 21: Areas in which an explosive dust atmosphere occasionally occurs.
- EX Zone 22: Areas in which an explosive dust atmosphere occurs only rarely or for a short time.
These zones provide detailed information on how and where certain devices may be used and therefore play a decisive role in the safe handling of electrical equipment in explosive environments.
The classification of the EX zones is decisive for the safety systems used in these areas. The ATEX Directive 1999/92/EC stipulates that every company must draw up an explosion protection document as part of the explosion protection document in which potentially explosive atmospheres are divided into zones.
While EX Zone 0 has extremely strict safety requirements, in EX Zone 1 has high requirements, albeit somewhat less stringent. In EX Zone 2 the requirements are less rigid, as the risk of an explosive atmosphere is low here.
Similar rules apply to the dust-forming zones: EX Zone 20 and EX Zone 21 require high to moderate safety standards, while in EX Zone 22 less stringent requirements apply, as an explosive dust atmosphere rarely occurs.
It is important to note that the terms "frequently", "occasionally" and "rarely" do not have clear definitions. The relevant standards lack concrete figures. However, the following has become established in specialist circles:
- "Frequently" refers to more than 50 percent of the operating time.
- "Occasional" describes situations that may occur at irregular intervals, such as venting or sampling, and usually corresponds to 1 to 10 percent of the operating time.
In practice, you should assign the higher EX zone in case of doubt.
