In this explosive series, we turn our attention to a potentially deadly hazard prevalent in, but not limited to, manufacturing and processing industries: combustible dust. The series explains what combustible dust is, how the risks are quantified, what a dust hazard analysis entails, and how to mitigate the hazard and protect workers. We hope this information can be used to minimize the risk of a combustible dust flash fire or explosion in your facility.
In Part 2 of this series, we learned that NFPA 652, Standard on the Fundamentals of Combustible Dust, provides basic principles and requirements regarding identifying and managing flash fire and explosion hazards due to combustible dust. NFPA 652 requires owners to conduct a Dust Hazard Analysis (DHA) where combustible dusts are present to identify hazards and implement the necessary safeguards. After reviewing the basics of a DHA in Part 2, we’ll now focus on the types of corrective actions that can be implemented once gaps in safeguards or processes have been identified. The National Fire Protection Association (NFPA) and OSHA are the best sources for information pending the completion of a consolidated standard.
Chapters 8 and 9 of the 2019 edition of NFPA 652, Standard on the Fundamentals of Combustible Dust, provides instructions on hazard management, including methods to mitigate and prevent combustible dust flash fire and explosion hazards. Section 9.2 pertains to building design and provides guidance on protection features, including:
Section 9.3 of NFPA 652 specifies that all components of enclosed systems that handle combustible particulate solids must be designed to prevent the escape of dust. Dust should be controlled and contained at its source, and if this is not possible, dust collection methods must be employed. Specific requirements for several types of industrial dust collection systems used in pneumatic conveying systems are spelled out in this section, including dust collection systems and centralized vacuum cleaning systems.
Requirements for air-material separators (AMS), air-moving devices (AMD) – such as fans and blowers, and duct systems are also specified. NFPA 91, Standard for Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Particulate Solids, is referenced as the governing standard for AMDs and duct systems.
Section 9.3.9 specifies requirements for bulk storage enclosures such as bins, tanks, hoppers, and silos. Generally, fixed bulk storage enclosures should be located outside of buildings if an explosion hazard exists. Interior surfaces must be designed to facilitate cleaning and minimize combustible dust accumulation.
The remainder of NFPA 652 Chapter 9 specifies equipment design criteria for other industrial systems, including pressure protection systems, material feeding devices, enclosed conveyors, and process equipment, such as mixers, blenders, and dryers.
Section 9.4 of NFPA 652 examines the various potential ignition sources that must be controlled in an environment containing combustible dust, including (but not limited to):
Dust control measures are covered in section 9.6 of NFPA 652, which begins by requiring continuous suction or other methods to control combustible dust emissions from normal operations. Other methods to control dust include liquid dust suppression methods and fans to limit dust accumulation in elevated areas difficult to access for housekeeping. Additional housekeeping methods are covered in section 8.4, including:
It’s important to also comply with other applicable NFPA standards, such as NFPA 654, NFPA 61, NFPA 484, NFPA 664, and NFPA 655, containing additional dust control requirements for specific industries such as manufacturing, agriculture, food processing, combustible metals, wood processing, and others.
Finally, OSHA recommends cleaning dust at regular intervals, using cleaning methods that do not generate dust clouds. Additionally, companies should develop and implement a hazardous dust inspection, testing, housekeeping, and control program. This program should be in writing with established frequency and methods.
Stay tuned for Part 4 of this series, where we’ll examine the implementation of management systems, such as procedures and training to address combustible dust hazards, as well as the use of PPE and flame resistant garments as a last line of defense to protect workers from catastrophic injury.
Make sure you have all the facts about the potential dangers of flash fires or explosions due to combustible dust. Access all posts in this series which explains what combustible dust is, how the risks are quantified, what a dust hazard analysis entails, and how to mitigate the hazard and protect workers.