Preventing electrostatic hazards of flexible intermediate bulk containers

Flexible intermediate bulk containers (FIBCs) are used in industry in large numbers for the storage and transport of granules and powders worldwide. They are mostly constructed from polypropylene fabric, a material well known for its high electrostatic chargeability. Concerning electrostatic ignition hazards, precautions are required in fire and explosion endangered areas during filling and emptying processes. There is no risk of ignition when using FIBCs constructed from fabric containing interconnected conducting threads or ribbons provided all conducting components are grounded. However, in very rare cases a bag may not be properly grounded. Here corona discharge could be a remedy. This paper investigates why corona discharge works insufficiently when the whole bag is equipped with thin metal fibers which are not interconnected and form corona points, improving more or less static dissipation. It has been shown that undirected corona discharge into the vicinity of the bag is much less effective than when an established path to ground is provided for the corona current. The optimum place for the latter was found to be at the loops of the FIBC