DKE German Commission for Electrical, Electronic & Information Technologies of DIN and VDE
DIN EN 61340-4-4
; VDE 0300-4-4:2012-09
Electrostatics - Part 4-4: Standard test methods for specific applications - Electrostatic classification of flexible intermediate bulk containers (FIBC) (IEC 61340-4-4:2012); German version EN 61340-4-4:2012
Elektrostatik - Teil 4-4: Standard-Prüfverfahren für spezielle Anwendungen - Einordnung flexibler Schüttgutbehälter (FIBC) in elektrostatischer Hinsicht (IEC 61340-4-4:2012); Deutsche Fassung EN 61340-4-4:2012
Overview
Flexible intermediate bulk containers (FIBC) are used worldwide in great quantity for the storage and transportation of powdered and granular material. Typically, they are constructed from woven polypropylene fabrics. This material is known for its high insulation capability. During filling of the charged bulk, electrostatic charge can build up in the FIBC. A conical pile is created; during the process particles primarily with the same charge try to repel one another due to Coulomb forces. Increasing charge density leads to ionization of the ambient air and the ions formed that way transport the charge to the inside of the container wall. Provided the container has been made conductive and divertible by means of corresponding measures and is grounded, the charges can flow off from the container wall. However, on an insulating container the product charges will accumulate on the container wall. If a grounded electrode approaches, for example, the hand of an employee, this leads to a so-called brush discharge, which can not only be perceived as a low electric shock, but which can also ignite flammable gas and vapour/air mixtures. For prevention of electrostatic ignition risks in explosive atmospheres, FIBC corresponding with the requirements shall be used for various operating conditions. They are classified into the types A, B, C and D. It shall be taken into account that inflammable charges can occur not only during filling, but also during emptying. - Type A does not meet any requirements with respect to electrostatics. - Type B consists of isolating material, the breakdown voltage of which is so low that no propagating brush discharge can occur. It can be used in areas which are explosive due to dusts, but not where there is danger of explosion due to gases and vapours. - Type C has a conductive or divertible structure and can be used in all explosive atmospheres provided that it is grounded during filling and emptying. - Type D consists of insulating material, has no earthing equipment and limits charges to a safe level in accordance with the corona discharge principle. However, there are limitations with regard to minimum ignition energy and charging current as well as the demand for grounding of conductive parts in its environment. For evaluation of the electrostatic properties of FIBC, the standard test method IEC 61340-4-4 has been developed and was published for the first time in 2005. It has been replaced with this second edition which has mainly been revised in the following points: - mandatory classification for FIBC into the four types A, B, C and D. - Instructions for the safe use of FIBC in relation to hazardous areas as they are specified in IEC 60079-10-1 and IEC 60079-10-2 have been added. - Resistance measurements to the groundable point as well as breakdown voltage shall only be carried out at low humidity. - The requirements for the marking of FIBCs have been modified in order to ensure uniqueness and, as a result, easier understanding for the end user. - Classifications, performance requirements and instructions for inner liners in connection with FIBCs complete the instructions for safe use. - An added informative annex provides instructions for test methods, quality control and monitoring. The responsible committee is K 185 "Elektrostatik" (AK 185.0.7 "Elektrostatische Sicherheit von Schüttgutbehältern") ("Electrostatics" ("Electrostatic safety of intermediate bulk containers")) of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.
