Combustible dust is a term used to classify any of a wide variety of finely ground organic or metallic materials. It’s generated as a byproduct of various industrial processes across numerous industries including the food, textile, plastics, and power generation industries.
According to OSHA, combustible dust can act as fuel for a fire in the presence of oxygen and an ignition source. Moreover, if the combustible dust is sufficiently dispersed in the air and held within a confined space, an explosion can occur. Under the proper conditions, even materials that are not flammable when in larger pieces, such as aluminum and iron, may be explosive as a fine dust.
A great example of this can be seen in the explosion of a General Mills factory in 1878. The explosion blew the roof off of the mill, engulfed multiple city blocks in flames and was described as a “night of horror” by a local reporter. The culprit of this massive explosion? Flour. Flour from the milling process had begun to build in clouds within the factory and eventually ignited in a deadly explosion.
Combustible dust classification
One way OSHA classifies combustible dust is according to the strength of the explosion of which it can produce. Dust explosion classes range from St 0 to St 3 with St 3 representing the most hazardous materials:
- St 0 (no explosion) includes silica
- St 1 (weak explosion) includes powdered milk, sugar, and charcoal
- St 2 (strong explosion) includes cellulose and wood flour
- St 3 (very strong explosion) includes aluminum and magnesium
Additionally, OSHA has defined a number of hazardous location classifications. Class II locations are locations where combustible dust is present in various hazardous concentrations. This class is further divided into two divisions: Division I, which includes areas where combustible dust is present in the air under normal operating conditions in hazardous concentrations; and Division II, which includes areas where combustible dust is not generally suspended in the air in hazardous concentrations, but could accumulate over time.
Methods for reducing and combating combustible dust
Because combustible dust is often created as a byproduct of a process, it can accumulate within pieces of equipment or on work surfaces over time. Therefore, it is possible for the conditions necessary for a fire or explosion to arise with little to no warning. There are a variety of preventative measures that can be implemented in any industrial process to reduce the likelihood of dangerous situations due to combustible dust.
Dust inspections
For a fire or explosion to occur, there must be a fuel source. However, due to the nature of combustible dust production, it may not always be evident that there is a fuel source present. For this reason, it is imperative to perform regularly scheduled dust inspections and implement housekeeping procedures. A dust inspection involves looking for dust residues in both open and hidden areas. If dust residues are present, they should be cleaned in a way that prevents dust clouds from forming (as the dispersion of combustible dust in the air is one of the conditions necessary for an explosion).
Dust collection systems
Dust collection systems typically include a vacuum unit for air filtration and are designed to be part of the air quality management system of a process. General Kinematics offers completely enclosed equipment that compliment these systems, for varying industries that contain material particles which can lead to an explosion, minimizing maintenance and cleaning for otherwise dust laden areas.
Smoking, sparks, and open-flame controls
In addition to fuel, an ignition source is needed for a fire or explosion to take place. To prevent ignition, open flames and sparks (including areas of mechanical friction) should be kept away from any areas known to produce combustible dust. Additionally, measures should be taken to ensure all employees never smoke in areas that may contain combustible dust. GK equipment is designed with few moving parts and an elegant two-mass design that requires minimal electrical power to operate. To learn more about the custom equipment solutions General Kinematics has to offer, call our expert engineers.
