Snowball Effect of Process Safety Practices with Applications in Dust Hazards

Process safety goes beyond implementing engineered and administrative controls—it begins with building a safety culture anchored in transparent communication across all facility operations. Often, seemingly minor details can signal underlying risks that may lead to a hazardous incident. These early indicators are sometimes overlooked by dedicated safety personnel alone, underscoring the importance of open communication among operators, maintenance teams, supervisors, and management.

This article highlights key data points that can serve as early warnings for potential hazards—and outlines practical approaches for gathering this information through a collaborative, safety-focused culture. To provide deeper context, we also examine a case study involving a combustible dust event, illustrating how strong communication and data collection can drive safer outcomes.

Leading Indicators for a Robust Safety Program

The data available about a process is very important when developing and monitoring the safety of a process. In a presentation given at the 2024 CCPS meeting, Angela Summers from SIS-TECH Solutions [1], discussed the process safety indicators that the American Petroleum Institute identifies in API 754 [2]. These internal indicators can be applied to any industry, not just petroleum. When properly recorded and collected, these indicators can reveal areas that might need attention to prevent future accidents. The data collection for these indicators can be difficult and requires cooperation from different areas within a company, but there are methods that can aid in the effectiveness of these conversations. 

As shown in Figure 1, the top Tiers, 1 and 2, are lagging indicators that are often used for nationwide public reporting, while Tiers 3 and 4 are leading indicators that are used for internal use. API provides guiding principles for these indicators, including the crucial goal that “indicators should drive process safety performance improvement and learning.”

Proactive safety programs focus on understanding and addressing Tier 3 and Tier 4 indicators. These indicators can help to predict where potential issue could arise.  They are seemingly little things that could provide important information. Tier 4 includes work orders, bypass use, and test deferrals. Work orders can reveal a lot about how a piece of equipment is operating. How many work orders were filed in the past year? Was the problem adequately fixed? Is it a repeating issue? More than one failure per year with the same piece of equipment is indicative of a problem that needs to be addressed. Another indicator is the number of times controls are bypassed. Bypassing controls on a piece of equipment takes away the engineered controls that were put in place to ensure safe operation of the equipment. This lowers the level of risk protection put in place. The third indicator is test deferrals. Tests are done to ensure up-to-date, relevant data from which to analyze the process. Test deferrals result in old, potentially irrelevant data being use. Tests can be deferred for several reasons. Scheduling issues and resource availability may be common reasons for testing deferrals, but these often indicate that testing is “low priority.” Safety indicators being overlooked or under-prioritized indicate a management system that does not fully understand or care about the hazards in their facility.

Tier 3 requires a little more effort regarding data collection and analysis. The first indicator looks at demands on current safeguards, asking questions like: How often are the safeguards needed? How well do the safeguards hold up over time? Safeguards are meant to “prevent against incident," but they should not have to be used frequently. This otherwise points to abnormal operation of the process equipment which generally leads to high risk of accident and subpar operation quality. Another indicator to consider is the “failures on test.” This means monitoring test records and safeguard failures and using that data to determine a failure rate.

Interpreting and utilizing this kind of data may be difficult if there are not well-kept and accessible records. Having a lack of data is not uncommon. These records require effort from employees across the facility, so it can be difficult to prioritize. The paper, “Improving Process Safety Culture through Behavioral Based Process Safety,” by David Heller, et. al. [3], presents various ways to start discussions with employees throughout a facility to learn more about the potential hazards and how to prevent them, therefore facilitating data collection.

Regular talks with hourly operation and maintenance staff reinforce trust between different positions and leads to more collaboration and effective communication. “Gemba walks” are encouraged to observe the process and find ways to make it safer. The word Gemba, originating from the Japanese word “the real place,” is often known as “the place where value is added” [4]. Gemba walks involve walking through the process in a facility, talking to those doing the work, and learning more about how the process is done. These walks are meant to gather information and interact with workers. Though often with the intention of improving the process overall, Gemba walks can reveal many things relating to safety. Good questions to ask could be: What risks do you look for? What mistakes have happened or what could happen? Who do you communicate with regularly? What kind of pressure do you deal with? These types of questions can be asked of operators, managers, or engineers. They all can offer insight into the process that might not be considered, and it might be a good way to look for those Tier 4 indicators mentioned earlier. 

In summary, the API indicators are meant to “provide useful information for driving improvement” and identify the underlying cause of major hazards [1]. The leading indicators, Tiers 3 and 4, are helpful to find those underlying issues and preemptively address potential hazards. The information covered by Tiers 3 and 4 is not always easy to collect, so fostering a safety culture that promotes open communication within a company aids in collection of these indicators. 

Leading Indicators to Address Combustible Dust Hazards

The API indicators and Safety Culture practices can be applied in a variety of industries including addressing combustible dust hazards, a common hazard found in all kinds of manufacturing. Combustible dust hazards have been put in the spotlight due the OSHA Combustible Dust National Emphasis Program (NEP). A Dust Hazard Analysis (DHA) is a systematic review outlined in NFPA 652: Standard on the Fundamentals of Combustible Dust [5] that is meant to address combustible dust hazards within a facility. A DHA can help identify leading indicators and develop a safer process.

One of the API 754 Tier 4 leading indicators is test deferrals. This could mean postponing testing protection equipment, or other maintenance activities that are meant to be done at a scheduled time. Part of a Dust Hazard Analysis is testing materials that may have changed. DHAs are meant to be done every 5 years to account for any process changes that may have been made without considering combustible dust hazards. Often, facilities do not have a Management of Change program that is sensitive to combustible dust. They sometimes fail to consider combustible dust as a hazardous material and do not give DHAs the proper attention in the recommended timeframe.  Correct testing data can be very important for a facility. Collecting, reviewing, and applying these parameters aids in the prevention or mitigation of explosions. Table 1 summarizes typical testing done for combustible dust.

(Adapted from Amyotte & Eckhoff [2010] [6])

The second portion of this table contains testing parameters that are useful for determining what conditions are needed for a combustible dust event and the likelihood of those conditions being met. Combustible dust explosions are often explained using the dust pentagon, shown in Figure 2. Starting with the fire triangle, a fire needs fuel (the dust), oxygen, and an ignition source. The addition of dispersion creates a flash fire, and the addition of confinement creates an explosion. If one of these five is missing, an explosion cannot occur. Removing one of the three components of the fire triangle prevents any event from happening. First, the MEC addresses the fuel aspect of the fire. The cloud must be sufficiently dense to provide enough fuel, and the MEC can define that limiting concentration. Second, the LOC addresses the oxygen component. Sometimes inerting systems can be used to reduce the oxygen below concentrations needed for a fire. Lastly, the ignition can come from many different sources, which is why there are so many tests and data parameters (MIE, MIT, LIT) that can be used to determine possible ignition sources. 

Case Study:  Fatal Combustible Dust Explosions at Didion Milling Inc.

The deadly Didion Milling incident in 2017 [7] was the result of many issues that could have possibly been prevented using the Tiers 3 and 4 indicators and a greater emphasis on a strong safety culture within the company. The incident started with a smoldering nest in the bran process equipment, which initiated the primary explosion. This explosion propagated throughout the process equipment, resulting in a secondary explosion. After the second explosion, a fireball was released from the facilities largest dust collector. A series of explosions spread throughout the building while a deflagration was traveling back through process equipment. These events tragically resulted in the deaths of 5 employees and injuries to the other 14 employees in the facility. Multiple buildings were completely destroyed and others severely damaged.

The CSB investigation [7] revealed issues related to management of change, incident investigation, emergency preparedness, and a lack of understanding of the material hazards, along with several other issues. Firstly, much of the equipment was not considered hazardous despite containing combustible dust. Proper calculations and considerations of the MEC would have revealed that this equipment could present a deflagration hazard and needed explosion protection and isolation. The CSB investigation report states:

"Didion’s dust collector calculations were incorrect and that the Dry Grit Filter did contain an explosive dust concentration on the night of the incident, as evidenced by the Dry Grit Filter explosion. Had Didion acted upon this hazard, the incident consequences could have been reduced." p.173 [7].

Isolation and proper explosion protection would have prevented the propagation of the deflagration flame front throughout the process equipment. This would have prevented the incident from becoming as large and damaging as it was. This is an example of Tier 4 information not being collected and utilized correctly. There was also a reoccurring pattern of inadequate airflow within the ductwork which resulted in smoldering from accumulated product. Regular checks for adequate airflow are a recommended practice for combustible dust handling processes. This is a type of Tier 4 indicator that could have been used to prevent smoldering within the equipment. 

The facility had several incidences of fires in the past 5 years that had been reported and investigated, but action items were not made or were not followed up on. This is an example of Tier 2 indicators not being properly utilized. Didion failed to learn from their past incidents and allowed the occurrence of fires within the facility to become normalized. Their lack of engineering controls like explosion protection, adequate airflow, and isolation between process equipment meant there was an over-reliance on administrative controls, like procedures, housekeeping, and personal protective equipment. 

Due to the lack of knowledge within the leadership of Didion, hazards were not well-communicated, and administrative controls were also inadequate to prevent a combustible dust event from occurring. This demonstrates a poor safety culture and lack of quality communication within the company. There were reoccurring hazards that workers were aware of, as well as findings from audits and inspections by external parties. These events were not taken seriously by Didion leadership, so no actions were taken to address the hazardous conditions. 

Conclusion

Preventing hazards in a facility requires attention not only to major systems and controls, but also to the small, often-overlooked details that can have a significant impact. Leading indicators—such as trends in work orders or the frequency of test deferrals—can reveal areas in need of increased focus. Effectively capturing and using this information is essential. Achieving this requires collaboration and open communication among all personnel, ensuring everyone is aware of potential risks and understands the factors that could elevate hazard levels. Prioritizing safety measures and taking timely action are key to avoiding catastrophic incidents.

References

1. Summers, A., & Bukowski, J. (2024, March 25). Can Your Maintenance Data Records Support API 754 Metrics? Global Congress on Process Safety. https://aiche.confex.com/aiche/s24/meetingapp.cgi/Paper/679271
2. API. (2021) Recommended Practice 754 Fact Sheet, Process Safety Indicators for the Refining and Petrochemical Industries, https://www.api.org/-/media/files/oil-and-natural-gas/refining/process%20safety/rp-754-fact-sheet.pdf
3. Heller, D. (2024, March 26). Improving Process Safety Culture through Behavioral Based Process Safety [Review of Improving Process Safety Culture through Behavioral Based Process Safety]. https://aiche.confex.com/aiche/s24/meetingapp.cgi/Paper/679592
4. Six Sigma Daily. (2018). What is a Gemba Walk and why is it important? Sixsigmadaily.com. https://www.sixsigmadaily.com/what-is-a-gemba-walk/
5. National Fire Protection Association (2019). NFPA 652: Standard on the Fundamentals of Combustible Dust 
6. Amyotte, P., & Eckhoff, R. K. (2010). Dust explosion causation, prevention and mitigation: An overview. Journal of Chemical Health and Safety/Journal of Chemical Health & Safety, 17(1), 15–28. https://doi.org/10.1016/j.jchas.2009.05.002
7. U.S. Chemical Safety and Hazard Investigation Board (2023). Fatal Combustible Dust Explosions at Didion Milling Inc. [Review of Fatal Combustible Dust Explosions at Didion Milling Inc.] CSB Investigation Report, No. 2017-07-I-WI.