(141b) Electrostatic Hazards during Pneumatic Conveying of Combustible Dusts in Flexible Hoses

Authors: 
Stern, M., Exponent, Inc.
Dee, S., Exponent
Ibarreta, A. F., Exponent, Inc.
Ogle, R., Exponent, Inc.
Myers, T. J., Exponent, Inc.
Pneumatic conveying of combustible dusts is a widely practiced method for transporting powders within facilities handling, using, or generating powders. Because of the tendency of dusts to cause charge separation with the walls of the pipe, hose, or tube, electrostatic hazards are inherent to these processes. Due to the practical challenges of using only rigid pipe, flexible hoses are often employed in these systems. Many flexible hoses are constructed with rubber or plastic materials and may include a conductive spiral winding for structural support, electrical bonding, or both. Depending on the construction of these hoses and the application, sufficient accumulation of charge can lead to propagating brush discharges, which may be capable of igniting a combustible dust. Case studies of installations that have led to, or could have led to, incendive electrostatic discharges will be discussed and examined. Finally, we will consider the current industry standards, test methods, and analysis techniques available to designers, operators, and investigators for evaluating the safety of these products.