Combustible dust: Small particles, big hazard

In 2010, a combustible dust explosion and fire at the AL Solutions metal recycling facility in West Virginia killed three workers and injured a contractor.

At the facility, a metal blender used for processing the metal zirconium was malfunctioning, and a spark likely ignited zirconium powder inside the blender, according to a Chemical Safety Board investigation. A burning metal dust cloud formed when a flash fire pushed metal dust particles from the blender. The cloud caused another explosion in the plant when it set off more combustible dust in the building, leading to the deaths.

The incident illustrates the tragedy that can occur from combustible dust – small particles that can be explosive in certain conditions.

CSB has been urging OSHA to promulgate a general industry standard for combustible dust since 2006, when a CSB study found that 281 dust-related incidents from 1980 to 2005 killed 119 workers and injured 718. CSB has labeled the standard as the first issue in its “Most Wanted Chemical Safety Improvement” program.

OSHA published an advance notice of proposed rulemaking in 2009 and conducted stakeholder meetings. In its most recent regulatory agenda, the agency labeled the standard as being in the pre-rule stage. The next action is to assemble hearings under the Small Business Regulatory Enforcement Fairness Act, which currently is scheduled for August 2016. Whether that leads to a proposed rule remains to be seen.

NFPA guidance

In the meantime, employers can use other guidance. The National Fire Protection Association released a comprehensive combustible dust standard, known as NFPA 652, in September 2015.

“NFPA does a great job of getting subject matter experts together to create these standards,” CSB investigator Mark Wingard said. But “at the end of the day, it’s ultimately a voluntary standard. Some companies are going to follow it, and some companies aren’t. If you really want to capture all the people who have this risk and hazard in their workplace, you really need to turn it into something not voluntary [but] mandated. The CSB has identified one of the best ways to do this is for OSHA to do a rule on it.”

NFPA 652 outlines the general requirements for controlling combustible dust hazards and refers to NFPA’s five industry- or commodity-specific standards when applicable:

• NFPA 61: Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities
• NFPA 484: Standard for Combustible Metals
• NFPA 654: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
• NFPA 655: Standard for the Prevention of Sulfur Fires and Explosions
• NFPA 664: Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities

Guy Colonna, NFPA division manager of industrial and chemical engineering, said NFPA 652 aims to ensure “fundamental requirements are addressed consistently across industries, processes and dust types.” Colonna said fundamental pieces of industry-specific standards were incorporated into the new standard, allowing the other standards to concentrate on their “unique hazards” in the industry.

“Whether that’s the owner/operator of a facility, engineer, designer, equipment installer, fire marshal or insurance inspector – whoever are the hazard evaluators and protectors of the dust system – it focuses their attention on those key aspects of the hazard assessment for all the elements that contribute to the dust explosion pentagon, and makes sure those are dealt with at a fundamental level before you get into the specific types of safeguards that then may be unique and therefore require you to go to one of those other industry-specific documents,” Colonna said.

The standard’s general requirements state that a facility owner or operator is accountable for the following when the potential for combustible dust is present:

1. Detect the “combustibility and explosibility hazards of materials.”
2. Identify and evaluate fire, flash fire and explosion hazards.
3. Manage the hazards.
4. Train affected individuals about the hazards.

In case of confusion among the various standards, NFPA 652’s conflict section strives to provide clarity on which standard to follow when guidance differs.

Dust hazard analysis

Existing facilities are recommended to complete the analysis to identify and evaluate hazards within three years after the standard was published. The analysis asks owners and operators of facilities to identify hazards and needed protective measures and plan implementation of safeguards.

“The concern is if there’s no timetable it would never get done,” Colonna said. “The committee [that developed NFPA 652] is sensitive – they’re not proposing a shutdown and redesign of every industrial facility where solids are handling and dust could be present. They’re starting with saying: ‘Do the DHA. See what it tells you.’”

Ultimately, NFPA hopes employers can be proactive rather than simply responding to disastrous incidents. They also can take credit for previous safeguarding.

“Giving an infinite time for completion of a hazard analysis suggests those industries are going to prefer to be reactive instead of proactive,” Colonna said. “None of these industries have had a problem reacting once there’s been a major incident. Not doing the hazard analysis, not identifying which segments of the facility might have a problem, they’re basically saying, ‘As long as I continue to have no problems, everything must be OK.’ That’s a dangerous logic to follow.”

The new voluntary standard will help companies be safer, and it offers both “prescriptive requirements” and a “performance-based design option” for managing hazards, said Vahid Ebadat, chief technical officer of Princeton, NJ-based safety services provider Chilworth Technology and CEO of Chilworth Asia Pacific.

The traditional prescriptive approach specifies which steps to take to meet the goal, while the performance-based approach begins with the goal and allows the flexibility of devising whatever method results in the desired outcome with the corrective measures.

“Those [companies] who have had the chance to review and understand [the standard’s] requirements seem to have a positive opinion, since it provides the performance-based option, if the prescriptive approach proves to be impractical,” Ebadat said.

Moving forward

If OSHA promulgates a general standard for combustible dust, NFPA hopes that the agency would consider the NFPA standards as part of that regulatory process, Colonna said.

OSHA notes that it has previously addressed aspects of this risk by publishing a safety bulletin in 2005 on preventing and limiting combustible dust fires and explosions, implementing a National Emphasis Program in 2008, and releasing several other guidance resources.

The Chemical Safety Board wants more.

“We continue to try to work with them to press upon the importance of adhering to our recommendations and making sure they update their Hazard Communication Standard to make it more clear what dust explosion hazards are, putting out guidance documents and making sure they’re blanketing broader industry coverage because it does affect a broad variety of industries,” CSB Chairman Vanessa Sutherland said.

Awareness is crucial. Wingard said CSB has identified several common themes connected to combustible dust incidents: The potential hazard of fine dust is underappreciated or unknown, and facilities do not properly clean up dust through housekeeping. OSHA guidance notes that materials in large form that do not burn – such as aluminum – can be “explosible” as dust.

Sutherland said employers can take three actions to protect against the hazard:

• Review CSB materials, including a safety video and investigation reports.
• Review and adopt NFPA standards.
• Pay greater attention to worker training and facility housekeeping.

“Their internal practices are focused on minimizing the amount of accumulated dust, making sure workers are getting the training they need for housekeeping to minimize the dust and make sure it’s less of a hazard, [and] also workers are kept up to date on new practices and consensus standards through NFPA,” Sutherland said. “They can do all of these absent an OSHA rule. It’s just unfortunate it might breed inconsistency among industries and companies."