Ignition Source Elimination as a Primary Basis of Safety: Can You Rely on It?

Dust explosions continue to pose a significant hazard in industries handling bulk powders. In 2022 alone, the US saw 26 dust explosions and 79 powder fires, resulting in fatalities, injuries, and production losses.¹ Traditionally, National Fire Protection Association (NFPA) standards such as NFPA 652² have guided industries in managing dust fire and explosion risks. These standards emphasize explosion protection measures such as explosion relief venting, suppression, and isolation, while also promoting explosion prevention strategies like controlling ignition sources and eliminating explosible dust cloud atmospheres. In practice however, explosion prevention strategies, particularly control of ignition sources, are often considered as a secondary basis of safety, meaning that explosion protection and isolation would still be recommended as the primary basis of safety. However, explosion protection and isolation measures can sometimes be both challenging and expensive.

     
A lesser-explored alternative is to focus more and rely on ignition source elimination as a primary safety approach. Although ignition source elimination is a widely applied strategy, it is rarely the primary or the sole defense (basis of safety) due to the complexity of identifying and controlling/eliminating every credible ignition source. This article examines the feasibility of using ignition source elimination as a primary basis of safety*, offering a potentially practical and perhaps cost-effective alternative to traditional explosion protection and isolation systems without compromising safety.

* A primary basis of safety refers to the most fundamental or critical method used to control and prevent hazardous events in industrial processes. It is the main approach or system implemented to mitigate risk and ensure safety.

Current Industry Practices: Risk & Cost

Explosion Protection & Isolation Systems

The bulk powder handling industry relies heavily on explosion protection and isolation systems, including explosion relief venting, suppression, and fast acting valves, to mitigate the aftermath of explosions, thus providing protection to people, plant and the environment. While extremely effective, consideration of these systems can present challenges, including:

It should be noted that there are many situations where explosion protection and isolation would still be required as the primary basis of safety along with the management of explosible atmospheres and ignition sources.

Control of Flammable/Explosible Atmospheres

In addition to explosion protection and isolation systems, some industries attempt to prevent explosions by controlling/ reducing dust cloud concentrations (fuel control) or using an inert gas such as nitrogen or carbon dioxide (oxidant control) to reduce the oxygen needed for the combustion process to occur. However, keeping dust cloud concentrations below the Minimum Explosible Concentration (MEC), at all times, may not be possible due to the nature of some dust handling, processing, and transfer operations. Inert gas systems are challenging to implement, often requiring the existing plant to be re-engineered and sealed, along with the need for continual supply and monitoring of oxygen levels and potential risks of asphyxiation.

     
Nevertheless, attempts should be made to control explosible dust cloud formations and the accumulation of hazardous levels of dust on various surfaces in process buildings by effective dust release management and regular housekeeping.

Ignition Source Control as a Primary Basis of Safety

While identifying and controlling ignition sources is recognized as an essential part of any process safety strategy, most industries hesitate to use it as their primary basis of safety approach. This caution stems from the challenge of reliably identifying and managing all credible ignition sources in complex environments. However, the benefit of eliminating credible ignition sources is clear: no ignition means no explosion, no flash fire, and no fire.

     
As we can all appreciate, several critical factors must be addressed so that ignition source control can be used as the primary basis of safety:

* Accurate Powder “Ignition Sensitivity” Data: Depending on the nature of the powder handling, processing, transfer, and packaging operations, this may include knowing the minimum ignition energy (MIE), minimum auto-ignition temperature of the dust cloud (MAIT), layer ignition temperatures (LIT), and onset temperature for self-heating for each powder handled – and possibly more. Any “ignition sensitivity” test must be performed on a representative sample of the powder/dust as it may be present in the facility and process. For some tests one might use the fines fraction (particle size less than 75 µm and moisture content less than 5%) for testing for a more conservative approach.

* Hazard Identification: A thorough hazard identification process is necessary to recognize and locate all credible ignition sources that might be present during normal and or foreseeable abnormal conditions. This is likely to be undertaken as a part of, or as an extension, to a Dust Hazards Analysis (DHA). For each identified ignition source, an assessment of the maximum “igniting power”/ignition energy that could be generated is required – to compare with the associated powder/dust ignition sensitivity characteristics. This often necessitates specialist input, particularly for complex ignition sources like static electricity, mechanical sparks, or heat/thermal sources. Note: “igniting power” is sometimes referred to as “incendivity”.

* Safety Management Systems: A structured robust program for managing the identified ignition sources is needed. This includes safety systems (e.g., bonding & grounding, process & surface temperature controls & monitors), equipment maintenance, and strict procedures for hot work. Also, changes other than replacement in kind should trigger a Management of Change (MOC) exercise.

* Training: Operators must be trained to recognize and manage potential ignition sources and their early warning signs³, with a strong emphasis on safety culture.

Practical Applications of Ignition Source Elimination

Despite the challenges, some industrial operations already rely on ignition source control as their primary basis of safety, often without formal acknowledgment. Common examples include:

* Manual Drum Filling: The dust clouds generated during powder bulking in drum filling operations may easily exceed the MEC somewhere, even if local dust extraction is present – perhaps due to powder surges or ineffective dust extraction. And these processes frequently lack (for obvious practical reasons) explosion protection systems.

* FIBC Filling: During the filling of Flexible Intermediate Bulk Containers (FIBCs), dust clouds inside the bags present an explosion risk. However, FIBCs rarely incorporate explosion protection measures.

* Manual Powder Handling: Processes such as weighing, dispensing, and manual powder transfers to equipment/vessels similarly rely on ignition source elimination without additional explosion protection.  In fact, almost anytime we have manual powder handling and processing operations and processes the primary basis of safety is avoidance of credible ignition sources.  Exceptions perhaps include when the powder quantity is too small to give rise to an explosible dust cloud of any significant size.

In these cases, ignition source control is effectively the primary basis of safety, highlighting its existing use in industry.

Expanding the Use of Ignition Source Elimination

Given that some operations already rely on ignition source elimination as their primary safety strategy, the question arises: can this technique be applied more widely and more formally? The key is in conducting detailed dust hazard analyses and using the technique for simpler operations.  This includes:

Every application should be analyzed based on the particular hazard and be subject to an assessment as outlined in section 2 of this article. By way of example, let’s consider a ribbon blender. Making sure there can be no ignition source inside the blender means making sure that no ignition source can enter and that none can arise on the inside. Laboratory tests should be selected and performed to determine the sensitivity to ignition of the powders to be blended; mechanical spark risk (dust cloud minimum auto-ignition temperature), risk of ignition of accumulated powder layer on hot surfaces (layer ignition temperature), and static electricity spark ignition energy (minimum ignition energy). Inside the blender, if bearings are external, if there is no internal electrical equipment and if potential impact/rubbing speeds of moving parts against casing, for example, are low (say, less than 1m/s) then it might be possible to base safety on avoidance of ignition sources. External ignition sources are process dependent (what is upstream), and a tight safety management system needs to be in place and fully functioning to avoid the introduction of extrinsic sources of ignition.

     
By managing potential ignition sources like friction sparks or static electricity, and ensuring electrical equipment is appropriately rated, it may be possible to safely eliminate the need for traditional explosion protection systems in some applications.

Costs & Benefits of Ignition Source Elimination

Although explosion protection and isolation systems are a critical safety component of many powder handling and processing facilities, they can be costly and require ongoing maintenance, especially when retrofitted to older plant. By contrast, ignition source elimination, when properly implemented, might offer significant cost savings. Not only can it reduce the need for expensive added systems, but also simplify plant operations by eliminating the need for complex technical solutions that carry an associated risk of failure during emergencies.

     
Industries might benefit from considering ignition source elimination as a primary basis of safety for straightforward process plant, provided they have a thorough understanding of the explosion properties of their powders, perform an expert dust hazards analysis (DHA), and lay down a robust safety management system.

Conclusion

Ignition source identification and control is often overlooked as a primary basis of safety in combustible dust hazard management. One prevailing reason for this amongst some practitioners might be the lack of confidence in being able to identify all credible ignition sources that might be present under both normal and foreseeable upset conditions. However, avoidance of ignition sources as a primary basis of safety holds potential for simplifying safety strategies and reducing costs, especially in straightforward processes. By accurately identifying hazards, understanding powder “ignition sensitivity” characteristics, and rigorously managing safety systems, many powder handling and processing operations already successfully rely on this approach, and could probably do so more widely in others. 

Obviously, where the primary basis of safety is avoidance of credible ignition sources, there would still be a need for effective housekeeping and local exhaust ventilation as secondary bases of safety so that potential fuel source is eliminated or minimized.

In situations where despite identifying and controlling ignition sources, the risk of a dust cloud explosion is still deemed to be intolerable, explosion protection and isolation may need to be considered as the primary basis of safety. Ultimately, a balanced and well-assessed approach to combustible dust hazard control, that integrates ignition source elimination, where appropriate, supported by explosion protection when needed, offers a flexible, potentially cost-effective path to maintaining plant safety.

     
Paul Cartwright, BSc, D.Phil., CPhys. is co-founder and chairman of Stonehouse Process Safety Inc. He has worked in the process industries for more than 40 years, primarily in the field of process safety. For more information, call 609-455-0001, email [email protected], or visit www.stonehousesafety.com.

References

1. Dust Safety Science, 2022 Combustible Dust Incident Report

2. NFPA 652, 2019: Standard on the Fundamentals of Combustible Dusts

3. Ebadat V, Cartwright P. Electrostatic hazards: identifying the early warning signs to reduce explosion risk. Process Safety Progress 2024; 43(1): 27-33.