Incendivity of sparks from surfaces of electrostatically charged liquids

Abstract

Hydrocarbon liquids prone to electrostatic charging may accumulate a considerable charge in the liquid of a tank being filled eventually leading to a spark in the possibly flammable atmosphere of the tank. As an important step in the assessment of the hazard, this paper studies the discharges between an earthed metal electrode and the surface of a charged liquid in particular with respect to the incendivity of the occurring sparks in a propane/air atmosphere which may be taken as representative of the tank atmosphere containing hydrocarbon vapour. Using a variety of spherical electrodes with diameters ranging from 10 mm to 40 mm as well as ellipsoidal electrodes of 50/25 mm and 30/15 mm dia. ignition could be obtained when the charge transfer in the sparks was raised to approximately the same level of the order of 0.1 μC. To achieve this it was necessary to charge the liquid surface to a potential of 58 kV for spherical and 62 kV for ellipsoidal electrodes. Based on these results and making some allowance for a safety margin it is advocated that a surface potential exceeding ca. 40 kV should be regarded as potentially hazardous in tank filling operations.