Combustible dust has long posed a serious hazard in industrial production environments. For many companies, incorporating preventive strategies is essential to hinder the accumulation of combustible dust in manufacturing plants and facilities before deflagration, flash fires, or dangerous explosions occur. At risk are employees, personnel, and visitors, but also loss of property—equipment and machinery, and even the facility itself.
What is Considered Combustible Dust?
Combustible dust is a byproduct of dry material production processes such as sifting, mixing, cutting, grinding, sanding, and so forth. As a result of these processes, the fine particulate matter becomes suspended in the air or through other oxidizing mediums. Foods, grains, and agricultural facilities, chemical, fertilizer, and pharmaceutical plants, furniture factories and woodworking facilities, paper mills, textile manufacturing, metal processing plants, coal-fired plants, recycling facilities, and wastewater treatment plants are the type of production environments that commonly generate finely ground organic and inorganic materials during processing. The material may be metallic or nonmetallic, or both, as either can hold combustible properties that, with the right combination of air or other gases, can deflagrate, catch fire, and explode.
Dust collection required to mitigate the risks and hazards from combustible particulate matter is complicated and begins with the right dust collector system. The “right” dust collector would be a system designed to filter the particulate matter generated, following OSHA guidelines and, principally, NFPA (National Fire Protection Association) codes and standards, and also, when applicable, meeting ATEX and FM international standards. In other words, each dust collection and explosion prevention solution should be designed according to what makes sense for a particular plant, with consideration to the specific application and process conditions.
An effective dust collection system is one that significantly mitigates, if not eliminates, dust deflagration hazards. When implementing or designing a collection system it is recommended to follow standards established by NFPA. The breadth and depth of the research into safety standards are exhaustive. It is common for NFPA worded standards to be incorporated into the codes and regulations of federal or state OSHA agencies, which are mandatory.
NFPA has numerous standards to aid engineers in the design of specific dust collection systems and to ensure compliance with such important standards as:
- NFPA-652-2019: Standard on the Fundamentals of Combustible Dust
- NFPA-654-2020: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
- NFPA-68-2018: Standard on Explosion Protection by Deflagration Venting
- NFPA-69-2019: Standard on Explosion Prevention Systems
- NFPA-61-2017: Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities
- NFPA-484-2019: Standard for Combustible Metals
- NFPA-664-2017: Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities
- NFPA-70-2017: National Electrical Code (NEC)
Filtering Combustible Dust with a Dust Collector System
Knowing how to filter combustible dust with the right dust collection system requires a high degree of expertise. There are either wet or dry collection systems available. Choose a design team with proven experience. Choosing a wet or dry collection solution depends on the specific application. Either systems utilized depend on the physical properties of the material dust—its particle size, concentrations, ignition potential, and so forth. Look to the Kst and Pmax values of the material dust to determine its explosive potential, with the higher Kst value indicating the potential for a more severe explosion.
Wet Collections Require Scrubbers
Scrubbers are dust collectors designed for wet collection systems. They collect and suppress explosive dust, and then neutralize inherent explosive properties to eliminate and reduce the threat of explosion. Wet collection systems are best for abrasive dust applications that may otherwise tear, shred, and damage dry filter media. Design features offer continuous collection and removal of airborne dust particles. Airflow contacts the particulates with water, limiting its explosion potential and then transferring the matter into the water stream for separation and filtering. On the downside, wet collection systems require fresh water and generate wastewater which must be treated.
Dry Dust Collection Systems
Dry combustible dust collection systems have a twofold design feature to hinder the accumulation of combustible dust in the workplace. First, they are designed to prevent explosions. However, if one does occur, the system is able to contain and minimize the impact of the explosion or direct a deflagration away from personnel to prevent injury. Dry collectors are equipped with fire suppression components and mechanical instruments such as explosion vents, spark detection sensors, spark arrestors, backdraft dampers, flame retardant filters, spark resistant fans, explosion-proof motors, smoke detectors, and emergency sprinkler systems. On the downside, though they are an effective system, the design features can add significant costs to the unit.
Contact the Dust Collector Experts at CPE Filters
Filtering dust from production environments provides a safe and healthy workplace; because combustible dust can present risks of explosion and fire, each risk should be managed separately. The selection of a wet or dry collection system will in large part be determined by the physical properties of the dust generated at the facility. To install the “right” dust collection system and help develop a control strategy with custom design features that comply with published standards, contact the experts at CPE Filters for advice and recommendations.