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Topics

Explosion Protection for Humans and Machines

The topic of explosion protection originated in mining. Mixtures of methane and air that arise in coal mining and are explosive in a certain ratio were handled with controlled explosions until the second half of the century. But how does it work now?

Flaring off firedamp is no longer necessary due to a number of technical achievements and protection regulations. However, the topic of explosion protection has not lost its importance despite all this. It is now widespread not only in mining, but also in other industries, because explosive materials are also present there. Common examples include the chemical industry, during the production of crude oil or natural gas and in the food industry.

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Economical system operation
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An Explosive Mixture

Combined with oxygen, these substances create a “dangerous explosive atmosphere.” If hot surface or an electrical ignition spark occur, this quickly leads to a situation that must be prevented under all circumstances. This is because such an event has the potential to directly harm many people, not to mention the impacts on the environment or the production systems. Therefore, appropriate member states’ directives and the legislation based on it have now become well-established in Europe: the ATEX directives (Atmosphere explosible). These include the 1999/92/EC for plant operators and the 2014/34/EU (previously 94/9/EC) for equipment manufacturers. The most important equivalents of Europe’s ATEX on the American market are the appropriate articles for the “Hazardous classified locations” (HazLoc) of the NEC and CEC and the EAC Ex. Other important regulations include the EAC conformity process (Eurasian Conformity) for Russia, Kazakhstan and Belarus, which replaces the old GOST import processes and is very similar to the ATEX and CE.

Explosion Protection

A distinction is generally made between primary, secondary and tertiary explosion protection. The measures of the primary explosion protection are aimed at preventing or restricting the generation of explosive atmospheres. Secondary explosion protection measures are used to prevent the ignition of explosive atmospheres – i.e. to prevent potential ignition sources. The measures of tertiary explosion protection are used to mitigate impacts of an explosion, bringing them to near-harmless levels. As part of an hazard assessment, which must be performed by each plant operator, the operator must ask if – as part of the primary explosion protection – it is possible to replace potentially explosive material to prevent an explosion in the first place. If this is not possible, then the plant operator is asked to classify the plant depending on the hazard and to mark the access. The zone model is the most used method worldwide and is specified in 1999/92/EC. A classification into “Divisions” is often found in the U.S. and Canada.

Ex Zones

The zone model classifies plant areas based on hazards present into Zones 0, 1 and 2 for gas atmospheres and 20, 21 and 22 for dusty atmospheres. As part of risk analysis, the plant operator must assess how often and for how long explosive atmospheres can occur in the different areas of a plant. Accordingly, the operator must divide her/his plant into these Zones. Zone 0 and Zone 20 are in this case the most dangerous ones (Fig.: Zone Description Table). Example: The Zone classification for a tank that is filled with liquid crude oil and includes a pressure switch might look as shown in our illustration.

Device Selection

All devices that will be used in Europe for explosive atmospheres in Zones 0 and 1 or 20 and 21 must be certified by a recognized body and must include a mark that is listed in the type test certification. This identification mark includes the required information for usage in explosive areas. It provides information about the equipment group and the category. With respect to the equipment group, operating resources are divided into two groups: devices for use in mines susceptible to firedamp (I) in categories M1 and M2, and devices for all other applications (II) in the categories 1, 2 and 3, with the appendix G for gas and D for dust. The category indicates the Zone in which the equipment can be used. In addition, the identification marking includes information about the type of protection, the gas or dust group and the temperature class if the device was tested in accordance with a standard. Several options generally exist to prevent an explosion. These were carefully developed during the last decades and taken into account in the respective standards. Different types of protection were defined for electrical equipment. However, certain types of protection are not appropriate for all zones. The Ex n type of protection, for example, can only be used in Zone 2. The Ex i type of protection (intrinsic safety), in contrast, is approved for equipment up to Zone 0. We are selecting intrinsic safety for our example. It is one of the most favored and widely used types of protection.