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ATEX

 

Definition

ATEX is the common term for the European directives on explosion protection and is derived from the French term ‘ATmosphères EXplosibles’. In the EU context, ATEX primarily comprises two directives: Directive 2014/34/EU on equipment and protective systems intended for use in potentially explosive atmospheres, and Directive 1999/92/EC on health and safety at work and the obligations of operators in potentially explosive work areas.

For operators of mixing plants, ATEX means that equipment and protective systems must be approved for the relevant zone classification and selected appropriately if flammable dusts, vapours or gases may be generated during the mixing process.

 

Why ATEX is important in mixing technology

When mixing powders or bulk materials, an explosive atmosphere may form if fine particles come into contact with air or oxygen in sufficient concentrations. Such an atmosphere can be ignited by an ignition source; typical ignition sources include electrostatic discharges, hot surfaces and mechanical sparks.

This is particularly relevant for products such as:

  • Sugar, flour, starch, milk powder
  • active pharmaceutical ingredients
  • Pigments and additives
  • Metal powders such as aluminium or magnesium

  • chemical intermediates

     

Zone classification

The ATEX zone classification describes the likelihood of an explosive atmosphere occurring.

 

  Gas atmospheres

  • Zone 0: explosive atmosphere present continuously or for long periods
  • Zone 1: An explosive atmosphere is likely during normal operation

  • Zone 2: An explosive atmosphere is unlikely during normal operation and, if it does occur, it will only be for a short time

     

  Dusty atmospheres

  • Zone 20: An explosive dust atmosphere is present continuously or frequently, typically inside plant facilities
  • Zone 21: An explosive dust atmosphere is occasionally present during normal operation

  • Zone 22: An explosive dust atmosphere is unlikely during normal operation and, if it does occur, will only be of short duration

     

    Equipment categories and labelling

  • ATEX equipment is classified into a category depending on the zone in which it is used.
  • Category 1: very high level of protection, suitable for the most demanding requirements
  • Category 2: high level of protection
  • Category 3: standard level of protection for areas at lower risk
  • An example of a marking is CE Ex II 1/2 D c T4:
  • II – Equipment group outside the mining sector
  • 1/2 D – Category for dusty atmospheres
  • c – structural safety

  • T4 – maximum surface temperature of 135 °C

     

    Key design features of ATEX-compliant mixers

  • ATEX-compliant mixers are designed to prevent ignition sources or to limit their effects.
  • Earthing and equipotential bonding for the dissipation of electrostatic charges
  • low-spark or spark-free materials and precision manufacturing
  • Monitoring of bearings, seals and drives to limit hot surfaces
  • sealed housing design to minimise dust escape
  • Prevention of dead spaces where dust deposits could build up
  • Explosion pressure relief via rupture discs or suitable dampers
  • Pressure-surge-resistant design or explosion decoupling, if required by the process

  • ATEX-certified components such as motors, sensors, valves and switches

     

    Additional protective measures

  • Depending on the product and process, additional measures may be required:
  • Inerting with nitrogen or another inert gas
  • Oxygen monitoring
  • Explosion Protection Document and Ignition Hazard Assessment
  • Selection of suitable surface temperature classes
  • Tuning the system to dust characteristics such as minimum ignition energy or the Kst value

  • If flammable liquids, solvents or vapours are introduced into the powder, a hybrid mixture is formed. Its ignition sensitivity is significantly higher than that of the dust alone and must be assessed separately.

     

    Benefits for operators

  • An ATEX-compliant design supports:
  • Legal certainty in planning, operation and documentation
  • Personal protection for employees
  • Equipment protection and a reduced risk of production downtime
  • Insurance and auditability

  • Seamless integration into hygienic or process engineering system designs

     

    Practical application in mixed media

  • In the food, pharmaceutical, chemical and metal powder processing industries, ATEX requirements are often taken into account as early as the planning stage.
  • In the food industry, a configuration where Zone 20 is on the inside and Zone 22 is on the outside is a common scenario.
  • In the pharmaceutical industry, ATEX requirements are often imposed in addition to hygienic design and GMP guidelines.
  • In the chemical industry and in the plastics sector, a combination of ATEX-compliant design and inerting is often advisable.
  • In the case of metal powders, a particularly stringent safety strategy is often required due to their high sensitivity to ignition.

ATEX is not an optional feature, but rather a legal requirement in many applications for equipment, protective systems and work areas where there is a risk of explosion.