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4. DKE

DKE German Commission for Electrical, Electronic & Information Technologies of DIN and VDE

Overview

Flexible intermediate bulk containers (FIBC) are used worldwide in large numbers for the storage and transport of granulates and powders. They are mainly made of polypropylene tapes. This material is known for its high electrical insulation properties. When the charged bulk material is filled into the FIBC, electrostatic charges accumulate. A conical bulk is formed, whereby the particles, which are predominantly charged in the same direction, attempt to repel each other as a result of Coulomb forces. The increasing charge density results in ionization of the surrounding air, and the ions thus formed transport the charge to the inside of the container wall. If the container has been made conductive through appropriate measures and is earthed, then the charges can flow off from the container wall. In an insulating container, on the other hand, the product charges will accumulate on the container wall. If an earthed electrode approaches, such as the hand of an employee, for example, there is a so-called brush discharge which is not only perceived as a weak electric shock but can also ignite combustible gas and vapour/air mixtures present there. In order to avoid electrostatic ignition hazards in potentially explosive atmospheres, FIBCs shall be used that meet the requirements for different conditions of use. They are divided into the types A, B, C and D. It should be noted that inflammable charges can be generated not only during filling, but also during emptying. Type A does not meet any electrostatic requirements. Type B consists of insulating material whose breakdown voltage is so low that no propagating brush discharges can occur. It may be used in areas where there is a risk of explosion due to dust, but not in areas where there is a risk of explosion due to gases or vapours. Type C has a conductive or dissipative structure and can be used in all potentially explosive atmospheres provided that it is earthed during filling and emptying. Type D is made of insulating material, has no earthing devices and limits charges to a safe level according to the corona discharge principle. However, there are limitations with regard to the minimum ignition energy and the charge current strength, as well as the requirement for earthing of conductive parts in its environment. To evaluate the electrostatic properties of FIBC, the IEC 61340-4-4 standard test procedure was developed and first published in 2005. It was replaced in 2012 by the revised second edition, which was mainly revised in the following points: Introduction of a mandatory classification for FIBC into the four types A, B, C and D and addition of guidance on the safe use of FIBC in relation to hazardous areas and zones as defined in IEC 60079-10-1 and IEC 60079-1.0-2. Measurements of resistance to earth point and breakdown voltage should only be performed at low humidity. The FIBC marking requirements have been changed to make them clearer and thus easier for the end user to understand. Classifications, performance requirements and instructions for internal liners in conjunction with FIBC complete the instructions for safe use. An added informative Annex now provides guidance on test procedures, quality control and monitoring. As proposed in this standard Amendment 1 to the last complete revision, which was not published until 2012, is mainly intended to clarify the text at selected points and to make the standard easier to understand. The responsible committee is DKE/K 185 "Elektrostatik" ("Electrostatics") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.

Document: references other documents

Document: referenced in other documents

Responsible national committee

DKE/K 185 - Elektrostatik