When explosive atmospheres are discussed in industry, the immediate image is usually that of flammable gases or solvent vapours. However, there is an equally serious and far less visible risk: combustible dust in suspension. A cloud of flour, powdered sugar, or a pharmaceutical excipient can, under certain conditions, generate an explosion with devastating consequences.
This article explores the principal industrial sectors in which combustible dusts create ATEX-classified hazardous areas, explains the technical parameters that determine the level of risk, and outlines the obligations imposed by current legislation—particularly EN 17348:2022—on those who operate, manage, or contract services within such installations.
Why Dust Can Be as Dangerous as Gas
A solid dust particle does not burn on its own. The danger arises when the dust is dispersed into the air at sufficient concentrations. In this state, the surface area exposed to oxygen increases exponentially, and the resulting mixture can be ignited by a very small amount of energy—sometimes as little as an ordinary electrostatic discharge or the friction generated by a metal tool.
- KSt (bar·m/s): Explosion severity index. It measures the maximum rate of pressure rise during a dust explosion. The higher the KSt value, the more violent the deflagration and the greater the potential destructive force of the explosion.
The technical parameters that determine the risk level of a combustible dust are:
- Pmax (bar): Maximum explosion pressure. It represents the highest pressure reached during a dust explosion under standard test conditions and is a key parameter for designing explosion protection and containment systems.
- MIE (mJ): Minimum Ignition Energy. This is the minimum amount of energy required to ignite a combustible dust cloud. The lower the MIE, the more sensitive the dust is to weak ignition sources such as electrostatic discharges, mechanical sparks, or friction.
- MEC (g/m³): Minimum Explosible Concentration. This is the lowest concentration of combustible dust suspended in air that can support an explosion. Below this threshold, there is no explosion risk; above it, an explosive atmosphere may exist if an ignition source is present.
- MIT (°C): Minimum Ignition Temperature of a dust cloud. This is the lowest temperature at which a combustible dust cloud will ignite when exposed to a hot environment or surface under specified test conditions. It is a critical parameter for determining the maximum permissible surface temperatures of equipment operating in ATEX-classified areas.
ATEX regulations classify combustible dusts into three categories according to their KSt value: St 1 (KSt ≤ 200), St 2 (KSt 200–300), and St 3 (KSt > 300). Most commonly encountered industrial dusts fall within the St 1 or St 2 categories; however, this does not make them harmless. They still require appropriate hazardous area classification (zoning), risk assessment, and the implementation of suitable explosion prevention and protection measures.
Food Industry: The Sector with the Largest Exposure to Risk
The food industry is probably the sector with the highest number of facilities that generate ATEX-classified areas due to combustible dust, largely because it routinely handles raw materials in the form of powders or fine granulates with significant explosive potential.
Flour and Cereal-Based Products
Wheat flour typically has a KSt value of 50–100 bar·m/s and a Minimum Ignition Energy (MIE) below 100 mJ. In flour mills and industrial bakery facilities, storage silos, pneumatic conveying systems, mixers, and baghouse filters commonly constitute permanent Zone 20 or Zone 21 hazardous areas. The cleaning and maintenance of this equipment therefore require the use of certified ATEX vacuum extraction systems.
Sugar
Powdered sugar is one of the most explosive industrial dusts in terms of KSt, with values that can exceed 150 bar·m/s. Its Minimum Ignition Temperature (MIT) of the dust cloud is relatively low (approximately 350°C), making it particularly sensitive to frictional heating and hot surfaces. Sugar refineries, confectionery manufacturing plants, and icing sugar packaging facilities routinely operate with Zone 20 hazardous areas inside process equipment such as silos, conveyors, mills, and dust collection systems.
Cocoa and Chocolate
Cocoa powder typically exhibits KSt values in the range of 75–150 bar·m/s. Cocoa processing plants and chocolate manufacturing facilities often contain extensive Zone 21 hazardous areas, particularly around grinding, sieving, conveying, and packaging operations. In addition, the natural fat content of cocoa can lead to deposits forming on equipment and surrounding surfaces. As these deposits dry out, they can break down into fine combustible dust, further increasing the risk of dust cloud formation and explosion.
Starch and Starch Derivatives
Corn starch can reach KSt values exceeding 200 bar·m/s, placing it within the St 2 explosibility class, and it also exhibits a very low Minimum Ignition Energy (MIE). For this reason, it is commonly used as a reference material in dust explosibility testing. Starch production facilities, manufacturers of starch-based adhesives, and paper mills that use starch in their processes all fall squarely within this risk category and typically require comprehensive ATEX zoning and dust explosion protection measures.
Milk Powder and Whey Powder
Dairy powders—including skimmed milk powder, whey powder, and whey protein concentrates (WPC/WPI)—typically exhibit KSt values within the St 1 to St 2 range and a relatively low Minimum Ignition Energy (MIE), with the risk often exacerbated by their fat content. Spray drying towers, widely used in dairy processing, are classified internally as permanent Zone 20 hazardous areas due to the continuous presence of combustible dust. Historically, incidents involving milk drying facilities have been among the most common causes of dust explosions in the European food industry, highlighting the critical importance of ATEX-compliant design, dust control, and cleaning procedures.
Spices and Flavourings
Certain ground spices—such as black pepper, paprika, and cinnamon—exhibit significant explosive characteristics when handled in powdered form. Their fine particle size, low Minimum Ignition Energy (MIE), and high flammability make spice grinding, blending, and packaging facilities particularly susceptible to combustible dust hazards. As a result, these installations are typically subject to ATEX hazardous area classification requirements, with appropriate explosion prevention and protection measures required throughout the process.
Pharmaceutical Industry: Maximum Requirements in Controlled Environments
The pharmaceutical industry handles powders with extremely fine particle sizes—many of them micronised—within environments that must simultaneously comply with ATEX requirements and Good Manufacturing Practice (GMP) standards. This dual obligation makes the management of hazardous classified areas particularly complex, as explosion protection measures must be implemented without compromising product quality, contamination control, traceability, or regulatory compliance.
Active Pharmaceutical Ingredients (APIs)
Many active pharmaceutical ingredients in powdered form are combustible. Their typically very fine particle size (D50 below 10 μm for micronised products) makes them particularly hazardous, often resulting in extremely low Minimum Ignition Energies (MIEs)—sometimes below 1 mJ. This means that even a trivial electrostatic discharge may be sufficient to cause ignition. As a result, weighing booths, blending lines, and capsule filling equipment are commonly classified as Zone 21 hazardous areas within pharmaceutical manufacturing facilities.
Powdered Excipients
Lactose, microcrystalline cellulose (MCC), polyvinylpyrrolidone (PVP), mannitol, pharmaceutical-grade corn starch, and many other excipients commonly used in pharmaceutical formulations are combustible when in powdered form. Lactose, for example, can exhibit KSt values in the range of 80–120 bar·m/s and a Minimum Ignition Energy (MIE) below 100 mJ. Consequently, the handling, weighing, blending, and transfer of these materials frequently give rise to ATEX-classified hazardous areas that require appropriate explosion prevention and protection measures.
Pigments and Coating Colourants
Tablet coating processes often use powdered pigments and colourants—such as titanium dioxide, iron oxides, and aluminium-based pigments—which, under certain conditions, can generate combustible dust atmospheres. During the handling, weighing, transfer, and preparation of coating suspensions, these materials may create ATEX-classified hazardous areas, particularly in powder dispensing and formulation preparation zones. Appropriate dust containment, extraction systems, and electrostatic control measures are therefore essential to minimise ignition risks
Additional Risk: Interaction with Solvents
In processes that combine combustible dusts with organic solvents—such as wet granulation or coating operations using alcohol-based solutions—there may be a simultaneous risk of explosive atmospheres arising from both flammable gases/vapours (Zones 1 and 2) and combustible dusts (Zones 20, 21 and 22). The classification of these hazardous areas, together with the selection of equipment intended for use within them, must take this dual hazard into account, ensuring compliance with the requirements applicable to both dust and gas/vapour explosive atmospheres.
Other Industries Exposed to Combustible Dust Risks
Compound Feed and Animal Nutrition
Compound feed manufacturing plants handle raw materials such as soybean meal, fish meal, vitamin additives, and ground cereals, all of which can generate combustible dust clouds during processing. These materials frequently create extensive Zone 21 hazardous areas throughout conveying, mixing, and packaging systems.
Although often overlooked in ATEX literature, the compound feed industry presents a significant real-world explosion risk. The combination of combustible organic dusts, high-throughput production processes, and extensive material handling systems has resulted in a noteworthy accident record, making it a sector where ATEX compliance and dust explosion prevention measures are particularly important.
Wood Processing and Biomass Industry
Wood dust typically exhibits KSt values in the range of 80–120 bar·m/s, making it a combustible dust capable of generating explosive atmospheres when dispersed in air. Facilities such as MDF plants, particleboard manufacturers, shipyards, sawmills, and biomass pellet production plants are therefore required to comply with ATEX regulations, particularly in relation to their wood dust extraction, filtration, conveying, and collection systems.
Powder Metallurgy and Metal Processing Industries
Aluminium, magnesium, titanium, and other metals in fine powder form are exceptionally explosive—some exhibiting KSt values exceeding 300 bar·m/s (St 3)—and have very low Minimum Ignition Energies (MIEs). Powder metallurgy plants, foundries carrying out sanding and polishing operations, and additive manufacturing facilities (metal 3D printing) commonly operate with Zone 20 hazardous areas within their metal powder handling equipment.
What the Regulations Require: EN 17348:2022 and Its Impact on Vacuum Cleaning Operations
The European standard EN 17348:2022, which came into force in March 2023, establishes the technical requirements that industrial vacuum cleaning systems used in explosive atmospheres containing combustible dust must meet. Its introduction represents a significant shift in approach: it is no longer sufficient for a vacuum cleaner simply to carry an ATEX marking.
The requirements that the standard imposes on the complete system include:
- Filtration capable of effectively retaining fine particles, including the submicron fraction commonly present in pharmaceutical powders.
- Control of electrostatic charge and documented earthing of all conductive components.
- Construction materials designed to prevent spark generation.
- Protection against the hazardous accumulation of combustible dust within internal components.
- System design tailored to the specific characteristics of the dust being handled, including its KSt, Pmax, MIE, and MEC values.
- Validation of the complete system by qualified personnel
- Compliant technical documentation, including operating manuals, ATEX certificates, inspection records, and maintenance logs.
Failure to comply with EN 17348:2022 may result in the loss of insurance coverage, as well as civil or criminal liability in the event of an accident. It may also lead to enforcement actions and penalties imposed by labour inspectorates or industrial regulatory authorities.
How Lagupres Operates in Facilities Handling Combustible Dust
At Lagupres, we have more than 25 years of experience carrying out work in industrial environments where explosive atmospheres are present. Our technical capabilities extend from risk assessment through to service execution, including:
- Analysis of the dust type and determination of its explosibility parameters
- Classification of ATEX hazardous areas throughout the facility, including Zone 20, Zone 21, and Zone 22 environments.
- Design of the vacuum extraction system in accordance with EN 17348:2022 for the specific dust involved.
- Execution of the service using certified equipment and personnel qualified to work in explosive atmospheres.
- Preparation of the Explosion Protection Document (EPD), or collaboration with the client’s technical team in its development and maintenance.
- Training for operators and maintenance technicians on the safe use of vacuum cleaning and extraction systems in explosive atmospheres.
- Preventive and corrective maintenance supported by comprehensive documentation and record-keeping
If your facility handles any of the dusts described in this article and you have questions regarding the classification of your hazardous areas or the compliance of your vacuum cleaning and extraction system, please contact us for a no-obligation consultation.