Dust collection systems are used in many industries to capture airborne dust generated during operations. By removing dust particles, they maintain clean air in working environments to ensure the safety of employees, equipment, and goods. Some dust particles generated from chemicals, textiles, wood, and other sources can be combustible under specific conditions and concentrations (See Figure 1). Ironically, many explosions happen in dust collectors that don't operate in compliance with National Fire Protection Association (NFPA) guidelines.
Figure 1: The dust explosion pentagon shows all five elements that must be present in an industrial facility simultaneously to cause a combustible dust explosion. Monitoring Dust
As dust collectors hold a significant amount of suspended combustible dust in one confined space, they are the most common location for a combustible dust explosion. According to the 2022 Combustible Dust Incident Report, dust collectors were the primary source of combustible dust incidents in 2022. During this year, seven dust collector explosions and four fires caused 15 injuries and 5 fatalities. One of these occurred at an aerospace parts manufacturer in Niles, Ohio on October 18, 2022. When titanium dust was removed from a unit, the dust ignited, burning two contractors.
To mitigate combustible dust hazards, dust collectors must follow NFPA standards that are enforced by the Occupational Safety and Health Administration (OSHA). In addition to upholding NFPA provisions, the OSHA Combustible Dust National Emphasis Program inspects facilities that generate or handle combustible dusts that pose a fire hazard when suspended in air. While OSHA does not have its standard that regulates dust collection systems, it has housekeeping standards that limit the accumulation of dust associated with dust collector explosions.
So, how do you ensure your dust collector system is safe and designed according to NFPA standards?
First, it is important to understand which NFPA standards are involved with combustible dust issues. While the NFPA has several documents that relate to combustible dust, facility managers should start with NFPA 654: The Standard for the Prevention of Fire and Dust Explosions for the Manufacturing, Processing and Handling of Combustible Particulate Solids. It provides best engineering practices to protect facilities from combustible dust explosions including standards on how to design a safe dust collection system.
Depending on the specific type of potential hazard, NFPA 654 refers to other standards for explosion venting and prevention including:
A pending new NFPA 660 Combustible Dust Code will consolidate six existing standards (including 61, 484, 652, 654, 664 and 665) to resolve conflicts between requirements and serve as a single source of all combustible dust fundamental and industry-specific standards, providing best practices to protect facilities from dust-related fires and explosions. Once approved it will be enforced in late 2024 or early 2025.
Within its standards, NPFA has incorporated performance-based options as an alternative to prescriptive methods. Companies have the flexibility to take a performance-based approach as long as equipment designs meet NFPA requirements, satisfy Life Safety Goals, and are backed by third-party testing. The facility manager must ensure that equipment is installed, operated, and maintained within the tested limitations of the design.
Before installing a new dust collection system or starting a new manufacturing process, facilities must determine if dusts are combustible. Equipment, processes, environment, and product changes can affect dust characteristics. Identifying dust properties will determine the correct filter, housing size, ductwork system, dust discharge configuration, and the need for explosion protection components in filtering specific types of dust.
An accredited testing laboratory with equipment and methods compliant with NFPA requirements can determine dust particle traits such as size and shape, gravity effects, moisture level, and abrasiveness. If the dust is identified as combustible, further testing will determine the dust's explosive index (Kst value) and its maximum pressure in a contained explosion (Pmax). Any dust with a Kst value greater than zero also requires a dust hazard analysis to determine and correctly size system requirements such as explosion venting or suppression systems.
Explosibility testing also helps determine whether a wet or dry dust collection system is more applicable to the application. Dry dust collectors use dry media such as filter cartridges to capture industrial dusts while wet dust collectors filter dust by impingement with water droplets.
By removing combustible dust particles without contacting oxygen, web scrubbers better control the hazard. However, metal dusts react to water and can produce gas. As dry dust collectors pose a higher risk of a combustible explosion, they require additional explosion-protection equipment to meet NFPA standards. However, they can scale to very large airflows, filtrate very small particles, and manage heavy dust flows. A wet scrubber requires additional systems to handle larger airflows. Heavy dust loading also increases water consumption and the need for treatment. NFPA 484 specifies requirements for wet scrubbers and dry collectors.
With so many options and requirements, designing a safe dust collection system can be a huge and complex undertaking. Camfil compliance experts can ensure your equipment meets all standards pertinent to your specific situation. Many suppliers do not understand NFPA rules or the differences in configurations for specific dust collection. Some state NFPA rules out of content and make recommendations to pass insurance auditors without being fully compliant by recommending a partial system with the need for future add-ons.
After reviewing the type of dust for removal, Camfil makes recommendations using its knowledge of NPFA standards. An on-site visit is conducted to take measurements and determine a Camfil system configuration specific to a facility. Compliance experts also review NFPA standards with in-house personnel, recommend specific dust collectors, and outline ancillary equipment requirements that could include ductwork protection, active explosion suppression systems, and venting.
A well-designed dust collection system is imperative to protect staff and the workplace from the potential of explosions and fires while maintaining OSHA compliance by following NFPA requirements. It also can pay for itself in energy and maintenance savings, costing far less to operate than a unit with a low initial price. With the guidance of third-party compliance experts such as Camfil, you can mitigate combustible dust hazards associated with dust collectors that follow the latest industry standards.
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