Dust Explosions - The Nature of the Problem and Practical Measures for Its Control

 Vahid Ebadat, Ph.D.

Chilworth Technology, Inc.

113 Campus Drive

Princeton, New Jersey 08540

Tel: 609 799 4449

Fax: 609 799 5559

Email: safety-usa@chilworthglobal.com

Website: www.chilworth.com

Many powders will burn slowly or with difficulty as a layer on a surface, but can explode if dispersed as a cloud.  In fact, the vast majority of powders can form explosible dust clouds if the particle size is small and moisture content is low.  The concentration of dust in the cloud is important.  The density of an explosible dust cloud resembles a dense fog.  Although such concentrations are not normally expected to be present within processing buildings, explosible dust clouds are regularly formed inside the material handling/processing equipment, i.e. when bins are being filled, powders are being transferred, or dust is being collected in a dust collector.

The particle size of the dust is a property which influences the explosibility of the dust cloud.  Powders include pellets, granules, and dust particles. The finer the particles, the greater the surface area per unit mass and thus, the more explosible a given dust is likely to be.  When the cloud is composed of a series of particle sizes ranging from fine to coarse, the fines play a prominent part in the ignition and the explosion propagation.  The presence of dusts should therefore be anticipated in the process stream, regardless of the starting particle size of the material.

The moisture content of a product will also affect the explosion risk.  A dry dust contains less than 5% moisture. Dry dusts of a small particle size will be more easily ignited and produce more violent explosions.  Moisture within or on the particle surface reduces both the flame propagation ease and rate.

This presentation will enable the participants to utilize methods for quantifying hazards and will estimate the hazardous properties of combustible dusts.  Thus, this course will provide the attendees with the ability to screen the materials that they handle, to aid in determining the precautions that should be taken in handling, processing, and storing combustible powders.  This will include sensitivity to various types of ignition hazards – such as electrical arcs and electrostatic discharges – and the severity of combustion incidents – such as explosions and flash-fires.

The content of the course is addressed to members of technical staff – engineers, chemists, research and development personnel, and others – who need to understand the hazardous properties and hazardous consequences of dust combustion.  Attendees can expect to leave this course with knowledge that will assist them in participating in Process Hazard Analyses, Pre-startup Safety Reviews, and Incident Investigations.  Also, they will be better-equipped to respond to questions concerning the equipment and environment in which combustible dusts are handled.

Vahid Ebadat, Ph.D., M.Inst.P, MIEE, C.Eng., C.Phys. is the CEO of Chilworth Technology, Inc. Dr. Ebadat has worked extensively as a process and operational hazards consultant for the chemical, pharmaceutical and food industries. He is a regular speaker at training courses on gas and vapor flammability, dust explosions, and controlling electrostatic hazards. He is a member of NFPA 77 Technical Committee on Static Electricity, NFPA 654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particular Solids and ASTM E27 Committee on Hazard Potential of Chemicals. Dr. Ebadat's research has culminated in the publication of numerous technical papers and articles.