The subject of this manual is safe practice for avoiding electrostatic discharge hazards in the manufacturing and processing of chemical and plastic powders. It is written with the practicing engineer and plant technician in mind. Practical information to enhance the process safety is provided in straightforward terms. The manual describes the basic phenomena of powder electrostatics, giving special emphasis to polymer powders. The identified types of electrostatic discharges are discussed and explanations of the conditions that favor or inhibit each type are given. A number of industrial incidents where ESD-induced dust ignitions occurred are reviewed, with the authors contributing their own views on causes and preventive measures. The important quantitative measures of electrostatic hazards are identified, along with the methods needed to perform meaningful measurements. Concrete recommendations, based on the authors' experience, are provided in the form of a list of "Do's" and "Don'ts" applicable in the plant environment. Finally, appendices provide a wealth of useful background data plus an informative "Q and A" section covering practical engineering issues. This manual will be extremely useful to chemical plant engineers, operating and maintenance personnel, safety engineers, processing plant engineers, design engineers, and consultants, as well as persons in the chemical, pharmaceutical, plastic, and food handling industries.
Table of Contents
INTRODUCTION. Ignition Probabilities. ELECTROSTATICS IN PLASTIC POWDER PROCESSING. Charge Generation and Separation. Charge Dissipation. Electrostatic Discharge. MEASUREMENTS. Intrinsic Powder Property Measurements. Extrinsic Parameter Measurements. Closure. OTHER ISSUES. ESD-Induced Minimum Ignition Conditions. Particle Size Adjustment. Charge Dissipation. Level Indicators. Dense-Phase Pneumatic Transport. Corona-Induced Degradation. Use of Conductive Fibers in Filter Bags and Liners. EXAMPLES OF DUST EXPLOSIONS. Incident at GE Plant in Mt. Vernon (1966). Incident Reported by Maurer, et al. Union Carbide Incident (1987). United Biscuits Incident. Another Ignition Due to a Propagating Brush Discharge. Examples of Mixed Powder and Flammable Liquids. Closure. DO'S AND DON'TS FOR ABATEMENT OF ELECTROSTATIC HAZARDS IN DUSTS. ANNOTATED BIBLIOGRAPHY. APPENDICES. Powder Charging. Electrostatic Ignition of Powders. Useful Electrostatic Modeling Data. Nomograph for Capacitive Discharge Risk Assessment. Some Questions and Answers About ESD Ignition Hazards in Polymer Powders. Ignition Hazards of Representative Dusts as Indicated by Their Minimum Ignition Energies.