Ex basics

Explosion protection as a sub-field of safety engineering deals with protection against the risk of explosion and its effects. For plant operators, this means that all protective measures for integrated explosion protection must be carried out according to a specified sequence.

Primary explosion protection

Primary explosion protection is understood to mean protective measures to prevent an explosion by preventing an explosive atmosphere in hazardous quantities and by hazardous dust deposits.

Possible protective measures are:

  • Modification of process methods

  • Substitution of flammable substances

  • Removal of oxygen (inerting)

  • Artificial ventilation

  • Closed systems

  • Concentration limitation

Secondary explosion protection

Secondary explosion protection involves the use of types of protection to prevent ignition sources. After all the possibilities of "primary explosion protection" have been exhausted, there may still be areas where a hazardous explosive atmosphere occurs. This is where "secondary explosion protection" comes into play. It deals with compliance with the building regulations and the ignition protection types of explosion-protected electrical and non-electrical equipment, such as the measuring devices from KROHNE.

Tertiary explosion protection 

Tertiary explosion protection includes design measures that limit the propagation of an explosion that has already occurred to a safe level by stopping or limiting it. 

Possible design measures are:

  • Explosion-proof construction

  • Explosion relief

  • Explosion suppression

  • Flameproof devices

Differentiation of the Ex zones

As a basis for which protective measures are to be taken, potentially explosive atmospheres are divided into zones according to their explosion risk. Assignment to Ex zones depends on where and to what extent an explosion risk exists. The boundary conditions are therefore defined according to their frequency and duration:

  • Potentially explosive gas atmospheres Zone 0, 1 and 2

  • Dust explosion hazard areas Zone 20, 21 and 22

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In the assessment of explosion hazards, the actual frequency of occurrence of one or the other operating condition is regularly discussed. This is because there is no fixed definition of the terms "constant", "occasional" and "infrequent" used in zoning.  

As a guide, normal operation is the operation of "intended use" according to DIN EN 60079-10. In TRGS 722, "operational disturbances" are included in normal operation:  

Constantly: Temporally predominant (> 50 % of the operating time according to TRGS 722). 

Occasional: May occur at irregular intervals (< 1 % to 10 % of operating time); e.g. venting or sampling. 

Infrequent: Occurs only due to malfunctions (< 1 to 10 h/a); e.g. flanges, connections, fittings, emergency depressurisations. 

EPL: Equipment Protection Level According to IEC 60079-0, equipment is classified into three different protection levels.

The letters "G" and "D" determine whether the equipment is suitable for the gas Ex area (G) or for the dust Ex area.