Dusting Up on Risk & Regulation

A perfect storm of conditions can result in an explosion or fire at a biomass-using facility, events that are often preventable.
By Anna Simet | January 26, 2016

When West Pharmaceutical Services’ plant in Kingston, North Carolina, exploded in 2003, resulting in six deaths, dozens of injuries, and complete destruction of the facility, it was ultimately concluded that the accident was preventable. Not simply in that the design of the suspended ceiling and operation of the facility didn’t take into account the hazards of combustible dust, but that some employees knew about the dust, but were unaware of the risk. According to the U.S. Chemical Safety Board report, while dust removal and good housekeeping were priorities at the facility, dust accumulated above the ceiling over time, going unrecognized as a serious hazard—even though maintenance workers were aware of the dust, they lacked an effective understanding of the danger.

Dust explosions resulting in injuries, fatalities and facility destruction are not uncommon at grain elevators, woodworking facilities, fossil fuel power generation plants, various food industry sectors involving materials such as sugar, flour, tobacco and more, as well biomass facilities that utilize pulverized or ground wood material to make energy or wood pellets.

Owners, operators and all employees of plants at risk for combustible dust incidents should be educated on the risks. A great teaching tool to use for that purpose is the explosion pentagon, says Tim Cullina, P.E., senior consulting engineer at Fauske and Associates, a process safety engineering company. For a dust explosion to occur, five conditions must be met: a fuel source (combustible dust), an oxidizer (oxygen in air), an ignition source such as a spark, dispersion of the dust and confinement of the dust cloud.

Cullina, who teaches a class on the basics of combustible dust, says that it’s also important to understand that removing of the dust and confinement of the dust cloud. doesn’t safeguard a facility against an event—it may still be susceptible to deflagration. “You’re not going to explode, but if you take away the confinement and still have a dust cloud, oxygen and ignition, it can be just as damaging. Deflagration only needs four of those items—I refer to it as the deflagration diamond.

Apart from employee education, understanding the role of various regulatory agencies—OSHA, fire marshals, building departments and the National Fire Protection Association have in enforcing codes and safety requirements is crucial, according to Cullina.

Sorting Out Authority
NFPA, which is made up of volunteers who sit on technical committees to provide expertise for the development of codes and standards designed to minimize the risk and of fires and explosions, OSHA, insurance companies and the local permitting authorities may all recommend or require different things, Cullina points out. “What is really going to protect your people and your facility? In each case, it's about education, and how much each authority having jurisdiction (AHJ) understands about combustible dust and risk assessment.”

Going back 15 years, many of the AHJs were not aware of combustible dust hazards, according to Cullina. For example, in one jurisdiction, it was against code to install an indoor bucket elevator. “The builder requested a variance from this requirement, and the building department granted it without conditions,” Cullina says. “The permitting authority was unaware of the risks of using a bucket elevator indoors to transfer combustible particulate. If this had been an agricultural facility, an OSHA standard would have mandated additional ignition control requirements, but in this case, that OSHA standard did not apply. The local insurance broker issued a policy without inspection. Even if there was an inspection, there is no guarantee that the insurance inspector would have been aware of the risk from combustible dust. The NFPA standards for combustible dust have been in place for many years. But the owner, the permitting authority, and the insurance company were not aware of these standards.”

NFPA is not an enforcement or an inspection agency, Cullina points out—it has no power, nor does it police or enforce compliance with the contents of NFPA documents. “That job is left to the local jurisdictions that adopt the NFPA documents as code,” he explains. “Most commonly, fire protection requirements are enforced through fire marshal inspections.  They’ll have a list of things they’re looking for to make sure that at a minimum, you’ve addressed them, and they may or may not include some of the specifics of NFPA. But usually, they’re more generic, like certain plumbing requirements, which are common and understood. The combustible dust standards haven’t been, but they are more so now because a lot more attention has been brought to bear on it.”

In some cases, the local authority might be aware of combustible dust issues and have made the requirements, and other cases they haven’t trained themselves to look for it.  “The fire marshal is the only entity in the process with authority to bring things to a screeching halt. If they see something wrong, they can shut you down,” Cullina says. “OSHA doesn’t have that authority.” 

Local jurisdictions may or may not make certain NFPA standards laws—for example, NFPA 664, which applies to woody biomass. “They may or may not make you put in the explosion vent, or a suppression system,” Cullina points out. “They may or may not be sensitive to checking whether you’re completely grounded so that you won’t create a static spark. From OSHA’s point of view, the very existence of this standard lets us know this is a problem and that you should know about it if you’re in this business. Even if they don’t have a standard specifically for your individual piece of equipment or operation, you do have the general duty clause which says you’ll provide a safe workplace.”

Therefore, OSHA can use NFPA standards as evidence of knowledge that the industry has a standard, and remedies for hazards. “It’s an onion—there are these different layers, we have to talk about all these different aspects to get a broad picture [of requirements].”

The key component to all of these codes, designs and specification is to have someone in the design, engineering and operations with clear evidence of capability and relevant experience with combustible dust to ensure that the systems not only comply with the NFPA codes and standards, but also to provide on-going support for any modification to existing operations, according to Justin Price, project engineer at Evergreen Engineering.

Risk at New, Existing Facilities
“Some typical examples of fires and failure can be seen across the wood products industry, all are symptomatic and provide us with great lessons we can learn to protect the lives of our employees,” Price says. “We see many fires started from material building up on motors and bearing or other mechanical components. Once the wood builds up on these components, it acts like an insulator and retains the heat. The heat then is cause for the event. This can happen quickly, and is many times in places that are difficult to reach and therefore often overlooked in the housekeeping task.”

 Other times, it is simply poor design, in that the bearing is inaccessible. “Alternatively, pressure relief systems are not in place,” Price says. “Even to the extent that process interlocks are not applied.”

 When we are designing a new facility, the key to compliance and best method of mitigating risk is hiring the right engineering/designer who has the experience. “For existing operations, we find it very helpful to begin with a standard combustible dust checklist that is available through OSHA,” Price says. “From that checklist, you can determine the biggest risk factors to consider as you move to the next step, which is to perform the combustible dust assessment.  The combustible dust assessment will identify the hazards and mitigation that should be installed for each.”

An ideal design eliminates the ignition sources, operates well-above or well-below the flammable limits, or provides an inert atmosphere, according to Price. In these designs, there is no effect or mitigation of the dispersion, confinement or fuel on the dust explosion pentagon. “This means that the fuel and dust will be present in the system, and a performance-based design option will need to be incorporated into the overall mitigation plans,” Price says. “There are no ideal designs, so one must take care to protect the failure with the detection devices, extinguishing or suppression systems.”

Price says typical design flaws his firm sees include poor design in bin venting, detection and suppression systems in the pneumatic systems, and for the material handling, poor designs in the chutes and transitions of the conveyors. Another area of concern is that although many portions of biomass and pellet plants’ raw material will fall outside the moisture content requirements of NFPA (greater than 25 percent) for deflagration protection, the designs do not consider what happens when the material collects in corners, pockets and other areas of the equipment and dries, Price points out. “When the material dries and a bearing failure occurs, fires are very common.”

Fires and failure are not unusual across the wood products industry in general, and while unfortunate, there is a silver lining—they provide the rest of the industry with great lessons and takeaways to protect the lives of employees. 

In Price’s opinion, the key to risk mitigation at biomass and pellet mill operations is to draw on the years of experience in the engineered wood products, sawmills and composite panel products operations, as they experience many of the same issues. “This isn’t to say the wood product industry has it figured out, but more so to say that they have some great processes in place for the hazard identification and equipment to help with the mitigation techniques,” he says.

Cullina points out that just because a facility might be meeting its AHJ requirements, it doesn’t mean the facility is safe.  “There’s a spectrum when you talk about “right” or “wrong,” and that’s where you introduce the concept of risk assessment and risk management,” Cullina says. “The right and wrong is whether you did what the code says, and that’s much easier to enforce. You may be aware of the requirements, but are you aware of ducts or other types of transport systems inside your plant and what’s going on inside them?”

For existing facilities, undergoing a combustible dust audit, or risk assessment, can determine whether the facility is up to code, identify safety issues, ensure employees are aware of and trained to deal with and avoid hazardous scenarios, as well as determine an appropriate risk mitigation plan.

Walk Through an Audit
A combustible dust audit begins with a site visit to the facility by Fauske’s or Evergreen’s audit team to review and evaluate several elements of the facility that affect the wood dust mitigation and control program. Prior to the visit, Evergreen will request background information from the facility to assess current mitigation and control plans as well as other relevant safety programs. 

The general process and procedures of the audit include document reviews, facility inspections and employee interviews that are intended to provide a representative assessment of employee knowledge of the facility’s wood dust control program and the hazards associated with combustible wood dust. “The audit will encompass all aspects of the facility’s wood dust control program. Safety committee meeting minutes will be reviewed, along with crew safety meeting minutes to evaluate whether hazards are being addressed and acted upon,” Price says. Maintenance records, management bulletins, and safety notices will be reviewed to ensure good communication is happening between the committees, management, and employees.

During the on-site audit review, the audit team will complete various general and focused inspections to help assess the facility’s activities and conditions to determine the effectiveness of the program’s achievement. “Should there be specific observations of hazardous systems during the audit, we will focus their inspection on these particular systems,” Price says.

At the conclusion of the audit, a closing meeting will be held with client’s project team to provide an overview of the audit findings. “Any critical dust conditions identified will be brought to their attention. If high-risk conditions are found, they will be brought to the senior management team immediately,” Price says.

Within a month of the closing audit meeting, the audit team will provide a final written report, including a series of recommendations to help the facility improve the level of compliance going forward.

Boiling It Down
Proactive risk mitigation, and knowing your facility, its fuel and unique risks—and training all employees to share in that knowledge—could prevent disaster, Cullina emphasizes. “Dust collectors are a really common component in biomass facilities. Do you know how much risk you have of that dust being ignited in that dust collector? Is there a chance your dust collector could explode? When you have a baghouse, you’ve got four of the five explosion pentagon elements already. All you need is the ignition source, and you’ve met all of the requirements to create that explosion. It would be a very good idea to ensure that your baghouse is appropriately grounded so that you’re not going to create static spark that might in turn ignite the dust.”

There is no excuse for not knowing that a facility has combustible dust, according to Cullina, and there are many lists available that identify combustible dusts. “But to make it even simpler, if your powder or dust is organic, then it is combustible,” he says, adding that it is every facility’s responsibility to understand the particular dust it has, especially when creating a protection system against it. “This is really important when making calculations, to decide, for example, how big the vent has to be,” he says. “You should be using data from the dust that’s used in the plant at that point. Take a sample and have it analyzed so that you know the combustible dust characteristics and can appropriately design the relief valve and the explosion vent. A lot of people don’t have the individual data to do that. You’ve got to test your own dust, you need to know what your risk is, and that’s part of your risk assessment, to make effective risk management decisions.”

Cullina points back to West Pharmaceutical Services, noting that the facility was very clean and well-kept, meeting codes and regulation. “But, unknown to them, their process was creating very small, fine particles of dust. The maintenance guys, they knew the dust was up there, but it didn’t mean anything to them—they hadn’t been trained on it. People think only operators need to know [about risks], but all employees need to understand this risk—if dust is accumulating somewhere, it needs to be cleaned up.”

NFPA Codes Relevant to Biomass Industry
• NFPA 68: Guide for Venting of Deflagrations
• NFPA 69: Explosion Prevention Systems
• NFPA 77: Static Electricity
• NFPA 91: Exhaust Systems for Air Conveying of Materials
• NFPA 650: Pneumatic Conveying Systems for Handling Combustible Materials
• NFPA 652: Standard on the Fundamentals of Combustible Dust
• NFPA 654: Standard for the Prevention of Fire and Dust Explosions from the 
Manufacturing, Processing, and Handling of Combustible Dust
• NFPA 664: Standard for the Prevention of Fire and Explosion in Wood
Processing and Woodworking Facilities

SOURCE: Evergreen Engineering


Anna Simet
Managing Editor, Biomass Magazine