by Judith Lesslie, CFSE, CSP
Those who work in high hazard industries are familiar with the OSHA Process Safety Management (PSM) and EPA Risk Management Plan (RMP) requirements for routine process hazard analyses. Potentially less well known is the variety of additional guidance for specific chemical hazards, such as combustible dusts. Guidance available for assessing the risk of combustible dust incidents is available via OSHA guidance, a national emphasis program (NEP), technical manuals, and interpretation letters; and industry standards for the fundamentals of and prevention of dust explosions.
This blog will provide a general overview of combustible dust hazards, including serious past incidents, and provide information on some of the relevant guidance for those who are interested in more information. Future blogs on the subject of combustible dusts will review relevant dust properties, signs that a dust hazard may be present in a process, common ignition sources and safeguards, and potential dust hazard assessment (DHA) methods.
This is a potentially dangerous miss in a variety of manufacturing processes. Why? Because combustible dust explosions are highly credible when processes are not properly safeguarded, with the potential to result in catastrophic events, including loss of lives, serious disabling injuries, environmental damage, and major commercial costs from equipment and building damage and loss of production. Ignition sources range from various types of sparks generated by movement of dust, including via insulated, non-grounded or plastic storage containers; mechanical sparks such as from malfunctioning blowers or “tramp metal” present in the dust-handling process; electrical sparks from equipment malfunctions; and hot surfaces exceeding the auto-ignition temperature of the dust, as may occur with equipment malfunctions or maximum rate/exothermic reaction onset temperatures from product layer buildup.
The US Chemical Safety Board (CSB) identified nearly 300 combustible dust incidents between 1980 and 2005, collectively involving 120 deaths, 718 injuries, and major damage to facilities. There are also more recent events. For example, there was a major sugar dust explosion and fire in 2008 at a Georgia sugar mill that resulted in 14 deaths and many serious injuries; and other recent serious incidents in industries as diverse as HHC and non-HHC chemical processes, food waste recycling, wastewater sludge handling, coal dust handling, metal-handling, paper mills, wood chipping and sawmills, and grain handling.
Combustible dust explosions have generated substantial regulatory and industry standards activity in recent years resulting in a set of requirements and guidance documents that put users in a much better position to identify, understand and control their combustible dust hazards. Some of the major sources of information include:
OSHA Hazard Communication Guidance for Combustible Dusts (OSHA 3371-08), 2009
OSHA Technical Manual – Section IV, Chapter 6, Combustible Dusts, Directive TED-01-00-015, effective date 2/10/2020
OSHA Combustible Dust National Emphasis Program (Reissued) (OSHA CPL 03-00-008), 2008
NFPA 652, Standard on the Fundamentals of Combustible Dust (2019). This document provides combustible dust technical basics, general requirements, hazard identification and other topics; and it directs users to industry/commodity-specific guidance documents, including:
NFPA 61, Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities, 2020
NFPA 484, Combustible Metals, 2022N
FPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, 2020
NFPA 664, Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities, 2020
NFPA 68 Standard on Explosion Protection by Deflagration Venting, 2018
NFPA 69 Standard on Explosion Prevention Systems, 2019
NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, 2021
FM Global Safety Data pamphlet FM 7-76, Prevention and mitigation of combustible dust explosion and Fire, interim revision 2020
Do you handle potentially combustible dusts at your site? It is difficult to adequately control a hazard that is not well-understood. Even if you have a good-quality PHA, it may not delve deeply enough into the combustible dust topic in accordance with NFPA 652.
NFPA 652 states that existing processes and compartments (e.g., building compartments) shall have a completed Dust Hazard Assessment (DHA) by September 7, 2020 (parag. 22.214.171.124) and that the DHA shall be reviewed and updated at least every five years (parag. 7.1.4). Are you in compliance? Are you positive your site is managing its combustible dust risks in all phases of operation well enough to prevent a serious explosion?
While this standard is not legally binding at this time, OSHA inspectors have been encouraged to use NFPA standards to identify dust safety issues; and the General Duty clause requires employers to provide a workplace “…free from recognized hazards…”. Lack of a DHA or a poor quality DHA places sites at risk of an OSHA violation under the General Duty Clause.
If you have not previously taken a deep dive into the properties and hazards of your particular dust(s) and completed a DHA at your site, now would be a good time to do so. If you do not have the right expertise in your staff to assess dust hazards, consider selecting a process safety consultancy with deep experience and expertise to assist you. Their range of experience enables assessors to share the general and specific methods proven to minimize dust explosion hazards across industry. This independence from the site and company has the best probability of a careful assessment with fresh eyes on the relevant critical systems and leads to more efficient compliance with the necessary standards.
Stay tuned for more. Future blogs on the subject of combustible dusts will review important dust testing needs and properties, signs that a dust hazard may be present in a process, common ignition sources and safeguards, and potential dust hazard assessment (DHA) methods.