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, moisture content is low, and the dust cloud concentration (measured in g/m3) is above the Minimum Explosible Concentration (MEC). 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 size of the dust particle is a property which influences the explosibility of the dust cloud. The finer the particles, the greater the surface area per unit mass and thus, the more explosible a given dust is likely to be. In other words, the ease of ignition and the severity of the resulting explosion increases with a decrease in particle size. The moisture content of a product will also affect the explosion risk. A sufficient amount of moisture within or on the particle surface reduces both the ease and the rate of flame propagation. Dry dusts of a small particle size will be more easily ignited and produce more violent explosions.
A systematic approach to identifying dust cloud explosion hazards and taking measures to ensure safety against their consequences generally involves:
- Understanding of the explosion characteristics of the dust(s)
- Identification of locations where combustible dust cloud atmospheres could be present
- Identification of potential ignition sources that could be present under normal and abnormal conditions
- Proper process and facility design to eliminate and/or minimize the occurrence of dust explosions and protect people and facilities against their consequences
- Adequate maintenance of facilities to prevent ignition sources and minimize dust release
This presentation will discuss a well-tried approach to identify, assess, and eliminate/control dust explosion hazards in facilities. This presentation will also 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.
This presentation will also include the “Dust Hazard Assessment (DHA)” requirements of the New National Fire Protection Association (NFPA) 652: Standard on Fundamentals of Combustible Dusts.
Attendees can expect to leave this presentation better-equipped to respond to questions concerning the equipment and environment in which combustible dusts are handled and how to meet the requirements of the new NFPA 652.