Evaluating Self-Heating and Ignition Hazards in Combustible Dust Handling Equipment

Many types of organic combustible dusts may pose a hazard of self-heating to the point of smoldering and even flaming  ignition during processing, storage and handling.  Company, industry, and national standards provide guidelines for mitigating this likelihood; however, fire and explosion incidents still occur.  This paper aims to provide the reader with a tutorial on self-heating hazards associated with organic combustible dusts and will use case studies to demonstrate lessons learned. For example, one case study will discuss the investigation of a serious burn injury caused when workers attempted to clear a combustible solid blockage from a cyclone separator downstream of a rotating drum dryer while the unit was still running. The paper will discuss the cause of the fire to point out how the hazard potential was known at the facility but not appreciated by the workers or front line managers. The facility had a frequent history of clearing such jams in the equipment without mishap; however, the safety precautions slowly degraded over time. Oftentimes, unintended accumulations of combustible material including deposits in ductwork, equipment blockages, and idle equipment lead to isolated smoldering combustion events. If the smoldering material is liberated, for example by restarting equipment, clearing the blockage, or just structural collapse of the deposit, a larger fire or even a dust explosion may occur. The lessons learned from past incidents can be used to demonstrate the hazards of these materials and to improve safety through design, operation, and maintenance of combustible dust handling systems.