In 2006, the U.S. Chemical Safety Board (CSB) conducted a study demonstrating that government enforcement officials and facility personnel alike were generally unaware of the hazards of dust, leading to failure of identification of fire, flash fire, and explosion hazards in the workplace. This study cited 281 dust incidents that occurred at U.S. businesses between 1980 and 2005, resulting in 119 deaths and 718 injuries and convincing the CSB that many of these incidents could have been prevented or consequences mitigated if the facility personnel had conformed their workplaces to relevant National Fire Protection Association (NFPA) standards. As a result of the 2006 study, the CSB suggested that the Occupational Health and Safety Administration (OSHA) develop a federal standard to address combustible dust hazards in workplace environments. Figures 1 and 2 demonstrate the distribution of combustible dust incidents by industry and by material as a result of the 2006 CSB study.
According to OSHA and NFPA standards, a combustible dust is a combustible particulate solid that presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle size, shape or chemical composition. Combustible dusts are often either organic or metal dusts that are finely ground into very small (generally <500 μm) particles, fibers, fines, chips, chunks, flakes, or a small mixture of these forms. The hazards of combustible dust are associated with a wide array of materials, industries, and processes. Materials that may form combustible dust include, but are not limited to, those listed in Figure 3.
Following numerous dust-related catastrophic accidents and as a result of the CSB 2006 combustible dust study, OSHA published the Combustible Dust National Emphasis Program (NEP)2 on October 18, 2007. The purpose of the Combustible Dust NEP was to provide guidance for inspecting facilities that generate or handle combustible dusts. Then, in 2008, a dust explosion occurred at the Imperial Sugar refinery in Port Wentworth, Georgia, resulting in 14 fatalities and 40 injuries. As a result, OSHA reissued its Combustible Dust NEP, raising concerns about dust to the top of the list for inspectors, and increasing enforcement activities throughout the country.
In October 2009, OSHA published an advance notice of proposed rulemaking (ANPR)3, requesting comments on issues related to the hazards of combustible dust in the workplace. The ANPR requested data and comments on a variety of topics, including hazard recognition, hazard assessment, training, and numerous other safety topics related to preventing, mitigating, and responding to combustible dust hazards. In July 2017, however, under the Trump administration, several worker safety rulemakings were withdrawn, including efforts to regulate worker exposure to combustible dust.
Still, OSHA inspectors have authority to issue citations under various regulations for facilities handling combustible dust, such as the housekeeping regulations in 29 CFR 1910.22 as well as Section 5(a)(1) of the OSH Act (the General Duty Clause). The General Duty Clause gives OSHA inspectors the authority to issue citations for a wide range of deflagration, explosion, or other fire hazards that may be caused by combustible dust. The Combustible Dust NEP encourages inspectors to consult relevant NFPA standards for evidence of feasible means of abatement, including NFPA 652, Standard of the Fundamentals of Combustible Dust, which was originally published in 2016.
NFPA 652 requires all facilities that manufacture, process, blend, repackage, generate, or handle combustible dusts or combustible particulate solids, to comply with the appropriate industry-specific standards when required, such as NFPA 61 for the agricultural and food processing industry and NFPA 484 for combustible metals, metal powders, and metal dusts. NFPA 652 was developed due to inconsistent requirements between various industry sector standards, establishing a relationship and hierarchy between NFPA 652 and any other NFPA combustible dust standards, and simplifying OSHA compliance and enforcement.
NFPA 652 Overview & Requirements
NFPA 652 was created to promote and define combustible dusts hazard analysis, awareness, management, and mitigation. The original NFPA 652 standard also defined the new term, Dust Hazard Analysis, or DHA, as a systematic review to identify and evaluate the potential fire, flash fire, or explosion hazards associated with the presence of one or more combustible particulate solids in a process or facility. Historically, revised NFPA standards only applied to new facilities or existing facilities when modified. However, due to the history of accidents and OSHA input, NFPA made some of the requirements in the revised NFPA standards, including the DHA, apply retroactively to existing facilities that have not been modified.
The general requirements include the following steps:
- Test dust for combustibility and explosibility.
- Conduct a DHA.
- Implement measures to prevent and mitigate hazards.
- Develop management systems and train site personnel.
Combustibility and Explosibility Testing
NFPA 652 allows the determination of combustibility or explosibility to be based on either historical facility data or published data deemed representative of the current materials and process conditions or based on an analysis of representative samples. The combustibility and explosibility testing is used to determine appropriate solutions to several important safety questions, including each dust's ignition sensitivity and explosion severity in order to support the DHA and hazard prevention and mitigation strategies.
Dust Hazard Analysis
Each facility handling combustible dust is required to complete a DHA, and the DHA must be conducted or led by a qualified person. During a DHA, a team of assessors conducts a systematic review of relevant portions of a facility to identify and evaluate the potential fire, flash fire, or explosion hazards associated with the presence of one or more combustible particulate solids in a process or facility.
NFPA 652 states the following regarding items to be considered in a DHA:
- Identification and evaluation of the process or facility areas where fire, flash fire and explosion hazards exist;
- Where such hazards exist, identification and evaluation of specific fire and deflagration scenarios shall include the following:
- Identification of safe operating ranges;
- Identification of the safeguards that are in place to manage fire, deflagration, and explosion events; and
- Recommendations of additional safeguards where warranted, including a plan for implementation.
The DHA is one of the requirements that is retroactive. While it applies to both new and existing facilities, existing facilities have three years to comply with the requirement to conduct a DHA. The changes in the 2019 edition of NFPA 652 include an extension of the deadline to September 7, 2020 for completion of DHAs.
Prevention and Mitigation Measures
After a dust has been determined to be explosible or combustible, facility management must develop a plan to address the hazards of the dusts onsite. This can be completed through a performance-based design for mitigating or preventing combustible dust hazards, which gives facilities flexibility for compliance with the standard as an alternative to prescriptive requirements. NFPA 652 also outlines prescriptive requirements for hazard management mitigation and prevention, which are summarized in Table 1.
When managed correctly, facilities can use a performance-based design option to establish the level of protection needed, usually when a prescriptive solution is found to be infeasible or impractical. However, use of the performance-based design option requires that the facility maintain sufficient documentation, including documentation that supports the validity, accuracy, relevance, and precision of the proposed methods.
Management Systems, Training and Hazard Communication
No combustible dust program is complete without implementing effective management systems and training site personnel on the hazards of combustible dust, which apply retroactively to both new and existing facilities. The management systems referred to in Table 1 are written facility procedures, training, and other documentation that address fire and explosion hazards.
2019 Standard Updates
OSHA and industry continue to recognize combustible dusts as a major cause of many fires and explosions throughout the world. Since the original standard was published, a number of updates have been made to NFPA 652, including the 2019 edition of the standard which includes several noteworthy changes.
- An extension of the deadline to September 7, 2020 for completion of DHAs;
- The introduction of a DHA revalidation requirement; and
- A reorganization of the standards' sections related to management systems and hazard mitigation and prevention.
While some efforts to regulate combustible dust were rescinded in July 2017, OSHA inspectors remain focused on combustible dust enforcement through the NEP and have the authority to reference relevant NFPA standards when appropriate and necessary. The consensus standard, NFPA 652, is intended to provide accumulated guidance regarding the determination of dust combustibility and explosibility and the pertinent practices and equipment needed to prevent and mitigate catastrophic fires and explosions at industrial facilities. Management systems and associated training also play a critical role in continuing to control dust fire and explosion risks.
Essentially, personnel at facilities handling dust should be addressing several key considerations:
- Have all dusts been evaluated to determine combustibility and explosibility?
- Have all potential combustible dust hazards been evaluated using a DHA?
- Have all recommendations from the DHA been implemented as appropriate?
- Have management systems been developed to address dust hazards onsite?
- Has the facility implemented an effective housekeeping program to minimize dust accumulation?
- Are all employees effectively trained on the management systems and hazards associated with handling dusts onsite?
For questions or guidance regarding combustible dust, the requirements of relevant NFPA standards, or OSHA enforcement, please contact Linden Terpstra at firstname.lastname@example.org or Josh Haar, PE at email@example.com.
1 U.S. Chemical Safety and Hazard Investigation Board, “Investigation Report: Combustible Dust Hazard Study”, Report No. 2006-H-1 (November 2006).
2 Directive Number CPL 03-00-008.
3 Proposed Rule, Federal Register No. 74:54333-54347, Publication Date 10/21/2009.