Potentially explosive atmospheres, also known as Ex zones, pose a significant risk in various industrial working environments. These areas are characterized by the presence of flammable substances such as gases, dusts or liquids and can develop hazardous explosive mixtures. Operators of such working environments must comply with various legal obligations. These differ depending on the classification of the Ex zones, based on the frequency and duration of explosive atmospheres.

Safety in hazardous areas is of great importance, as it not only protects the working environment, but also ensures the health and safety of employees and the environment.

Ex-zone definition

Potentially explosive atmospheres, known as Ex zones or ATEX zones, are specific working environments or locations where there is a risk of an explosive atmosphere occurring. These explosive atmospheres can arise due to the presence of flammable substances. Ex zones cover various phases of industrial processes, from the storage of raw materials to internal logistical processes and process engineering steps such as separating, drying, crushing, dosing and packaging.

The operators of a process gas or switching system in work areas where there is a risk of explosion have legal obligations to ensure safety:

1. Labeling of Ex zones: The Ex zones must be clearly marked to draw the attention of employees and visitors to the explosion hazard.
2. Avoidance of ignition sources: It is crucial to prevent or minimize potential ignition sources in Ex zones to reduce the risk of explosion.
3. Measures to prevent explosions: Operators must take suitable measures to prevent a possible explosion or to limit its effects.
4. Documentation of explosion protection: An explosion protection document must be created and maintained containing all relevant protective measures and safety precautions.

In which areas is there a risk of explosion?

Explosive substances are ubiquitous in certain industries. This is particularly the case in areas where oil and gas are extracted and processed, but also in mining, the chemical industry and electrical engineering, for example. However, explosive substances can also occur in high concentrations and in different pressure ratios in less typical areas, such as warehouses or intralogistics.

Regardless of the industry, special precautions should always be taken to minimize the risk of explosions. In hazardous areas, it is crucial to carefully identify and control anything that could potentially create or contribute to an explosive atmosphere.

Why is this so important? On the one hand, it is about ensuring the safety of employees and visitors. On the other hand, protecting the environment and the immediate surroundings of the company plays a decisive role. Alongside fire protection, explosion protection is therefore a central component of any operational safety concept. The first step should always be a careful risk assessment to identify potentially explosive areas and their boundaries within the company. This essentially includes all storage, production and conveying sites where explosive gas or explosive dust is present, can arise or is used in a targeted manner. Examples of this are hazardous material storage facilities or the use of chemicals or gas-powered machinery.

Ex zone classification – gases, dusts and their explosion hazard

Potentially explosive atmospheres in industrial plants are divided into different zones in Germany, but also worldwide, according to the frequency and duration of the occurrence of explosive atmospheres. This classification is crucial for determining safety measures. There are a total of six Ex zones, whereby a distinction is made between gas, vapors and mists on the one hand and dusts on the other.

Ex Zone 2 and 22: Rare and short-term risk

In Ex zone 2, there is only a rare and short-term risk of an explosive atmosphere during normal operation. “Rarely” is often defined in practice as occurring once a year. A “short time” means that the risk of explosion exists for less than 30 minutes per year. The same conditions apply in Zone 22, but for explosive dust clouds.

Ex zones 1 and 21: Occasional risk

Ex zone 1 is an area in which an explosive atmosphere may occasionally occur under normal conditions. “Occasionally” means that the explosive atmosphere is present for less than 50% of the operating time, but for longer than a total of 30 minutes per year. These periods also apply to zones 21, which refer to combustible dusts.

Ex zones 0 and 20: Frequent risk

In Ex zone 0, a hazardous explosive atmosphere is frequently present during normal operation. “Frequently” means that it occurs during more than 50 % of the operating time. In practice, this category almost exclusively includes pipes and containers filled with corresponding gases, vapors or liquids. The risk of a dust explosion has its equivalent in Ex Zone 20.

Strict safety measures and explosion-protected devices must be used in Ex zones, especially in the vicinity of containers with explosive contents or in areas with explosive mists. The clear classifications of the individual zones serve to ensure safety in potentially explosive environments and provide the basis for protective measures and regulations that are appropriate to the hazardous situation.

Explosion protection and fire protection are connected

Explosion protection concerns areas in which explosive atmospheres can occur, e.g. when processing flammable substances. This has an impact on escape routes and requires structural measures such as fire-resistant structures and fire safety precautions. Explosion protection and fire protection officers work together and their tasks include the ongoing review of the explosion protection document. An explosion protection document is a written record that summarizes all relevant information and measures to prevent explosions in hazardous areas. This document can be used to demonstrate compliance with the current safety standards for potentially explosive atmospheres.

In industries where flammable substances are present, preventive measures are crucial to avoid accidents and damage. This includes the assessment of fire and explosion hazards and flammable materials, the marking of hazardous areas, measures to avoid ignition sources, alarm and rescue plans, fire extinguisher provision, training, the appointment of fire safety officers and protective measures for work in hazardous areas.

In connection with explosion hazards, the creation of an explosion protection document and the division into Ex zones are of great importance. All protective measures and the entire procedure relating to explosion protection in hazardous areas should be reviewed regularly.

Explosion protection: Safety parameters

Depending on the area and system, some safety-related parameters play a decisive role in explosion protection. These values are necessary in order to plan and implement explosion protection measures.

Important safety-related parameters include

1. Explosion limits: These describe the mixing ratios between flammable substances and oxygen at which an explosion is possible.
2. Minimum ignition energy: This is the amount of energy required to ignite the ignitable mixture of a substance in a specific oxidizer.
3. Minimum ignition pressure: The minimum pressure required to ignite the ignitable mixture of a substance in a specific oxidizer.
4. Maximum gap width (MESG): This value is determined in a standardized procedure and specifies the maximum gap width in a container that prevents an explosion from being triggered by the gap.
5. Explosion points: These indicate the conditions under which an explosive gas-oxygen-inert gas mixture can explode.
6. Flash point: The lowest temperature value at which a liquid substance can be ignited in the presence of an ignition source.

For gases, these values are often shown in a triangular diagram that identifies different areas for explosive mixtures. In the case of dusts, the particle size, the dust density in the air, the maximum pressure build-up over time, the maximum explosion overpressure and the minimum ignition energy are important criteria for the effects of a dust explosion. Ignition sources such as hot surfaces, static electricity and mechanically generated sparks must be taken into account and avoided.

Ex zones national and international

Explosion protection for devices and switchgear is defined internationally by the IEC 60079 series of standards. This series of standards, which also forms the basis for EU Directive 2014/34/EU (ATEX), covers aspects such as the types of ignition protection for electrical equipment and the classification of potentially explosive atmospheres in different zones. However, national regulations may deviate from these international standards.

Electrical installations in North America are a striking example of this. In the USA, the relevant regulations are set out in the National Electrical Code (NEC), while in Canada they can be found in the Canadian Electrical Code (CEC). A decisive difference often lies in the definition and zoning of potentially explosive atmospheres.

In the North American “Division” system, for example, only two probabilities are defined for the occurrence of ignitable mixtures:

• Division 1: In this category, ignitable gases, vapors or dust particles occur either continuously or intermittently during normal operation. These divisions correspond approximately to zones 1 and 0.
• Division 2: Here, the probability of ignitable mixtures occurring during normal operation is low. This can be compared with zone 2.

Requirements for explosion protection in accordance with ATEX directives

The ATEX Directives 2014/34/EU and 99/92/EC, also known as Articles 114 and 137, have enshrined explosion protection, or explosion protection for short, in European law. These directives specify which requirements devices must meet in order to be considered explosion-proof and which work areas are permitted in environments with an explosive atmosphere.

Manufacturers of explosion-protected devices must label them uniformly and define the permissible area of application by means of a device category. Users or companies are in turn obliged to classify their potentially explosive atmospheres into explosion protection zones depending on the type of hazard (D for dust, G for gas) and the presence of flammable substances.

Device groups in explosion protection according to ATEX

Safety in potentially explosive atmospheres is not only about the classification of these areas, but also about the classification of the devices used in them. This categorization is the result of a risk assessment in which manufacturers of equipment with potential ignition sources must set the protective measures in relation to the probability of the occurrence of potentially explosive atmospheres.

For marked standard systems, it is possible to test a specific device sample as long as no deviations from this sample are made. For all other equipment, however, a certified test is required, either by a notified body or an appropriately trained service technician. According to Directive 2014/34/EU (ATEX), equipment is divided into the following groups and categories:

1. Equipment group I: This group relates to potentially explosive atmospheres underground where there is a risk from firedamp and/or dust. There are categories M1 and M2:
   • The M1 category indicates a very high level of safety.
   • Category M2 indicates a high level of safety. The devices switch off as soon as an atmosphere is potentially explosive.
2. Equipment group II: These are potentially explosive areas above ground in which the hazard arises from liquids or a cloud of flammable gases. This group is subdivided into equipment categories 1, 2 and 3:
   • Device category 1 stands for a very high level of safety. The degree of protection is very high, even in the event of rare faults and in the event of two independent faults.
   • Device category 2 means a high level of safety. The degree of protection is high if faults are expected and in the event of a fault.
   • Device category 3 offers an increased level of safety. The degree of protection is normal in normal operation.
3. Equipment group III: This group includes potentially explosive areas above ground where there is a risk from finely dispersed dust.

Serafima: Your full-service partner for more protection in the industry

At Serafima, we understand the importance of Ex zones for the safety and efficiency of industrial processes and offer industry-independent, globally reliable solutions. Whether you need industrial and safe centrifugal or axial fans, spare parts or comprehensive advice, our team is here to help. With more than 20 years of experience in providing customized solutions for process gas systems in the chemical, petrochemical and steel industries, we are your manufacturer-independent full-service partner. Place your trust in our expertise – together we will ensure your success.

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