ATEX, Appareils destines a etre utilises en ATmospheres EXplosibles, refers to possible hazardous environment where an explosive mixture of air and explosive material may be present in a room, a part of a room or a restricted indoor or outdoor space.
The ATEX Directive 99/92/EC classifies explosive atmospheres into area classes. This classification is applied to atmospheres where a combination of dusts, aerosols, vapors, gases, and air may form an explosive mixture. Areas where this standard must be applied are, for example, oil refineries, paint shops, biogas power plants and peat processing plants. Design aims to classify areas into groups and area classes, each of which has its own rules for applying protection methods and precautions.This is referred to as drawing up an explosion protection document, prepared according to Directive 99/92/EC. Area classification aims to save lives using cost-efficient and reasonable risk management principles. Directive 99/92/EC can be found in website: http://ec.europa.eu/
Directive 94/9/EC refers to equipment and protection systems intended to be used in explosive atmospheres. Generally this Directive is referred to as: the ATEX Equipment Directive. Its purpose is to create a harmonized set of norms to unify the legislation of the member states. Directive 94/9/EC can be found in website: http://ec.europa.eu/
This Directive is applied to all equipment and components intended to be used in areas where explosive liquids, gases, or dusts are present. For example, the following equipment is classified as primary ATEX equipment:
Electrical and mechanical equipment, protection systems, safety and control systems, and the components of equipment protection systems.The Directive does not apply to medical equipment, household gas equipment or facilities for storing explosives. International standard IEC 60079-0 and the CENELEC EN 60079-0 standard contain more detailed specifications for equipment and requirements.The common goal is to provide a set of instructions to ensure that devices sold meet essential safety requirements.
The main principle in making the safety classification is to prevent the formation of an Ex atmosphere. This is done by eliminating sources of ignition and by minimizing the consequences of possible explosions (94/9/ EC). The most important thing is to take all safety requirements into account. These may include all sources of ignition, faults, and potentially incorrect uses. The safety specifications also include safety, maintenance, and protection instructions and related markings.The previous guidelines primarily contained instructions on managing the current situation.
An explosion is a sudden increase in volume and a release of energy in a harmful manner.
Usually it involves the generation of high temperatures and the release of gases. An explosion causes pressure waves. Explosions are categorized as deflagrations if these waves are subsonic and detonations if they are supersonic (shock waves). A third type is a thermal explosion, which occurs with the rapid conversion of a highly exothermic reaction accompanied by a temperature rise. The disastrous property of an explosion comes with a rise in pressure and often with a high dose of heat radiation from the fireball, both occurring in a very short period of time. In ATEX areas, causes of explosion must be eliminated or minimized.
To generate the sudden chemical reaction of an oxygen and flammable substance compound, the mixture must be in an explosion range to release a high-energy explosion. Flammable substances normally occur in the form of a dust, mist, gas, or vapor. Normally an explosion occurs only if the three main factors react in a convenient mixture.
1. Flammable material
3. Ignition source
Flammable materials can be flammable gases, flammable liquids, and flammable solids. Of these, a flammable liquid can occur as a form of mist and also as a vapor. Some of the substances may need only very little energy to react. Normally gases and vapors are the most flammable. In flammable materials, solids can be in the form of dust, fiber, or flock. The reaction of flammable solids causes a rapid temperature rise and high pressure. Normally solids need more energy to react than gases but the energy of the reaction causes heavy explosions.
The ignition of an explosion can be started by several sources:
• Hot surfaces
• Flames and hot gases
• Mechanically generated sparks
• Electrical installations
• Equalizing currents
• Static electricity
• Electromagnetic waves
• Optical radiation
• Ionizing radiation
• Adiabatic compression and shock waves
• Exothermal reactions
Ensto recognizes this by taking all due caution to minimize the risk of ignition caused by materials or by the design of an enclosure.The structure must be designed to eliminate all electro-static charges. Generally charges are formed when two materials with different charges come into contact with each other. A larger contact area or greater distance between the surfaces of the materials touching each other increases the likelihood of a charge. Danger of an increasing charge in material increases when the resistivity of the other material decreases.
If the material has a charge, an electro-static discharge may occur. A charge can be discharged in many ways, but the most common ways are spark discharges and brush discharges. Both of these can cause a dangerous ignition, because the energy released can ignite gases and vapors. A spark discharge occurs when the charge between two conductors in different potentials increases to a sufficient level. In a brush discharge, energy is released when a charged object is approached by a round conductive object.
These charges can be eliminated effectively by using potential equalisation or grounding. Potential equalisation refers to the connection of two conductive objects to each other. Grounding refers to the connection of a conductive object to the ground potential.
The specification contains three explosion groups. These groups are based on the measured ignition capabilities of gases and vapors at a certain temperature. The classification is split into sections I and II, and groups designated A, B, and C. For example, group A contains common alcohols with a low flash temperature and group C contains gaseous hydrogen with a relatively high flash temperature.
Dust atmospheres, in accordance with IEC 60079-10-2 and IEC 60079-31, are classified in different zones. IEC 60079 gives guidance on how to identify and classify the areas where hazards from dust can occur. The area classification method evaluates the material’s properties, emission sources, dust layers and formation probability of an explosive dust-air mixture.
An area where combustible dust, as a cloud, is present continuously or frequently during normal operation. Areas, such as the inside parts of equipment, e.g. mixers, silos, filters, mills, transfer pipes, closed conveyors.
An area where combustible dust, as a cloud, is likely to occur during normal operation. Areas, such as filling and emptying areas and places where dust accumulates and the probability for formation of an air-dust mixture is high.
An area where combustible dust clouds may occur infrequently and persist for only short periods. Areas such as storage facilities of closed packages, outlet sides of air filters, surroundings of rarely opened equipment. And if the probability
for formation of an air-dust mixture is high in abnormal conditions.
Gas atmospheres are classified as follows according to IEC 60079-10-1 and IEC 60079-7.
An area where an explosive mixture of air and flammable gas, vapor, or particles is present continuously, for long periods, or frequently.
An area where the occasional occurrence of an explosive mixture of air and flammable gas, vapor, or particles is likely.
An area where the occasional occurrence of an explosive mixture of air and flammable gas, vapor, or particles is not likely but rare and only short-term.
The Atex equipment groups and their classifications are divided into two groups and normal industrial use in accordance with 94/9/EC Equipment group II is divided into three categories by the equipment directive. Equipment in higher categories can be used in lower categories, but equipment in equipment group II cannot be used in equipment group I spaces. Equipment in equipment group I is intended for use in underground parts of mines.
Equipment category 1
Design and structure of the equipment ensure an extremely high level of safety when the operating conditions specified by the manufacturer are observed. The equipment must be able to ensure sufficient level of safety even in rare fault situations. The equipment must ensure two protection methods independent of each other and safety must be maintained even when two faults are present simultaneously. Equipment in this class is intended to be used in Zones 0 and 20 and Ga and Da.
Equipment category 2
Design and structure of the equipment ensure a high level of safety when the operating conditions specified by the manufacturer are observed. The equipment must be able to ensure a sufficient level of safety during repeated error situations and normal equipment fault situations. Equipment in this class is intended to be used in Zones 1 and 21 and Gb and Db.
Equipment category 3
Design and structure of the equipment ensure a normal level of safety when the operating conditions specified by the manufacturer are observed. The equipment must be able to ensure a sufficient level of safety during normal operation. Often the manufacturer’s declaration of conformity is sufficient and third-party approval is not required. Equipment in this class is intended to be used in Zones 2 and 22, and Gc and Dc.
IEC 60079-14 specifies an alternative way to describe zones. EPL uses risk evaluation in equipment selection and, when compared to CENELEC described above, is a better way to mark area classifications. It must also be noted that EPL aims for a uniform risk evaluation, not country-specific models.
Temperature groups or flammability groups refer to temperatures which the equipment or protective structure surface must not reach under any conditions. This temperature limit prevents the gas or vapor flash temperature from being reached. The temperature group and highest allowable surface temperature are usually determined by combined testing of the protective structure and the component.
Temperature classification of gas atmospheres
Types of protection
Ex d protection type refers to a protection type, which withstands the explosion pressure. The protection type must be in accordance with standard IEC/EN 60079-1, which makes it suitable for Zones 1 and 2.
Ex e protection type refers to an increased safety protection type. The protection type must be in accordance with standard IEC/EN 60079-7, making it suitable for Zones 1 and 2. Only intrinsically safe Ex approved components are allowed to be installed inside the enclosure. Suitability of this structure for the area class must be ensured through electrical design and technical solutions so that the equipment does not produce sparks and cannot overheat exceeding the temperature limits.
Ex i protection type refers to an intrinsically safe protection type. The protection type must be in accordance with standard IEC/EN 60079-11, making it suitable for area classes 0, 1, and 2. The equipment’s electrical circuit energy must be below the dangerous minimum ignition energy (MIE) even in fault situations. In this case the power is restricted before it is transferred to the Ex area. Sparks are not generated even in short-circuit situations. An accurate specification for Ex i enclosures or markings does not exist, but Ensto recommends the use of Ex e enclosures and light-blue color coding of cables, cable glands, and equipment inside the enclosure. It is recommended that Ex i enclosures are visually different from normal enclosures. Additionally the circuits should be color-coded and visually different from other electrical circuits.
Ex t protection type refers to a dust-proof enclosure.The protection type must be in accordance with standard IEC/EN 60079-31, making it suitable for area classes 0, 1, and 2. Spark-generating components, such as relays and switches, can be installed inside the enclosure. These components do not need to be approved for Ex areas.
Marking and documentation requirements of the ATEX Equipment Directive provide the user with information on the product’s properties.