Proc. 2012 Joint Electrostatics Conference 1 Comparison of charge neutralisations of conductors and insulators with corona ionisers A. Ohsawa National Institute of Occupational Safety and Health, Japan (JNIOSH) 1-4-6 Umezono, Kiyose, Tokyo 204-0024, Japan phone: (81) 42 491 4512; fax: (81) 42 491 7846 e-mail: ohsawa@s.jniosh.go.jp Abstract—This paper reports a numerical investigation of phenomena of charge neutral- isations of insulators and conductors with the use of a balanced DC or AC ioniser using 2-D cylindrical electrohydrodynamic modelling. The purpose of this study was to examine the dif- ference between the phenomena of the charge neutralisations of conductive and insulating ob- jects on the basis of the motion of ions and to discuss the validity of the standard test method using a conductive plate with regard to its performance and proper applications. We found that the macroscopic ion behaviours with conductive and insulating plates are very similar; however, the early-stage phenomena of the insulator charge neutralisation are complicated and significantly different from the conductor ones, which indicates that the evaluation by the stan- dard test may lead to potential problems in practical applications. In addition, the results of simulations demonstrated that, in the insulator charge neutralisation, ionisers themselves can cause latent hazards during neutralisation, such as a relatively high surface potential for highly electrostatic-sensitive devices and a bipolar surface charge distribution potentially leading to propagating brush discharges, while such situations could not be observed in the conductor neutralisation. We propose proper use of ionisers and the standard test to avoid such hazards. I. I NTRODUCTION The electric field resulting from static charge on insulating materials yields electrostatic forces and sometimes initiates electrostatic discharges that can lead to problems and ac- cidents in industry. For example, electrostatic forces attract particulate contaminants or cause materials to stick in undesirable ways; in addition, electrostatic discharges, includ- ing those from isolated conductive materials by induction, sometimes result in malfunction of electronic equipment, damage to electronic devices, or occasional fires and explosions. Controlling static charge, therefore, is important to prevent such electrostatic hazards in in- dustry. Charge neutralisation is one of the methods to control the static charge, and corona ionisers are very widely used because of their simplicity.