Assessment of Increased Fire Risks Due to the Use of Alternative Fuels in the Cement Sector

In the cement sector, the use of Alternative Derived Fuels (ADF) is rapidly expanding in line with goals to reduce energy costs and carbon emissions. However, this transformation introduces more complex fire and explosion risks compared to traditional fuel systems. This article provides a technical analysis of the fire risks associated with ADF use during storage, transportation, and combustion processes, and evaluates fire safety measures within the framework of relevant international standards (NFPA, ATEX, EN). The focus is particularly on the correct design and applicability of foam extinguishing systems and the integration of early detection technologies. Fire prevention strategies are discussed in the context of operational continuity and facility safety. In conclusion, the importance of a risk-based fire management approach is emphasized to ensure that safety is not compromised while pursuing sustainable production goals.

Keywords: Cement sector, ADF, fire safety, foam extinguishing systems, NFPA 11, ATEX, explosion risk, alternative fuels, thermal camera, dust explosion

Fatıma TEKİN

Oyak Çimento - Risk and Compliance Executive

In recent years, the cement sector has been seeking alternatives to fossil fuels in order to reduce energy costs and lower carbon emissions. Alternative Derived Fuels (ADF), also known as Refuse-Derived Fuels (RDF), are high-calorific-value fuels produced by processing industrial and municipal waste. The use of ADF helps reduce energy expenses, which account for approximately 30–40% of the sector’s operational costs, while also contributing to a lower carbon footprint. For example, in 2020, about 12 million tons of waste were used as ADF in cement plants across Europe, preventing the emission of 21.2 million tons of CO₂. Additionally, burning waste such as end-of-life tires and plastics at high temperatures in cement kilns allows for safe disposal without leaving behind hazardous residues However, the shift toward ADF as a fossil fuel substitute introduces new safety responsibilities. These fuels, with their high calorific value and heterogeneous composition, can pose unexpected fire and explosion risks during storage and usage. For instance, storing high-energy waste materials generates significant amounts of flammable dust, which can place considerable strain on fire detection systems; similarly, stockpiling used tires creates a large fire load, prompting insurance companies to require special fire protection measures. Therefore, cement plants transitioning to ADF must revisit their facility-wide risk assessments and develop comprehensive safety strategies that account for the nature of these new fuels. In the following sections of this article, the risks introduced by ADF in terms of storage conditions, transport systems, and fire safety systems, along with the necessary technical precautions, will be examined.

Storage Conditions

The safe use of Alternative Derived Fuels (ADF) begins with the establishment of proper storage conditions. Unlike conventional coal storage facilities, ADF storage areas contain materials with highly diverse physical and chemical properties. These fuel piles may include a mix of paper, plastic, fabric scraps, and even biologically-based waste, exhibiting heterogeneous and unpredictable behavior. In particular, the decomposition of organic waste by microorganisms can lead to spontaneous heating over time within stored fuel piles. According to research, RDF (Refuse Derived Fuel) types produced from municipal waste can gradually heat up at ambient temperatures and may reach around 75°C, the threshold for spontaneous ignition. Numerous incidents have been reported in the literature where waste fuel piles caught fire spontaneously at such temperatures. Therefore, temperature control, ventilation, and pile management are critical in ADF storage areas. It is considered good practice to limit the size of fuel piles, prevent the formation of hot spots through regular turning or layering, and closely monitor moisture levels. High moisture can trigger biological activity that accelerates heating and also lower the calorific value of the fuel, negatively affecting the combustion process.

Early warning and fire prevention systems must be fully operational in ADF storage areas. Storage sites should be monitored 24/7 using heat sensors, smoke detectors, and even infrared cameras strategically placed to detect temperature increases or smoke within the piles. Indeed, in many modern facilities, infrared thermal cameras installed on the ceilings and walls of storage hangars can identify abnormal heat build-up (hotspots) within waste piles before any flames develop.

Figure 1. Combined use of IR camera-based temperature monitoring and automatic extinguishing system in an RDF storage area.

The effectiveness of such systems depends on their ability to detect reliably even in dusty environments. For example, cement facilities that use waste-derived fuels can cool down potential fire-prone areas before smoke is released by combining infrared thermal monitoring with automatic sprinkler systems in their storage areas. In addition to ventilation and detection systems, appropriate types of fire extinguishing equipment should also be readily available on-site. Since ADF storage areas are typically large enclosed hangars, fixed-pipe fire sprinklers or monitor-based extinguishing systems are generally installed in these locations.

Figure 2. Example of monitor-based foam extinguishing systems in an RDF storage area.

Automatic fire sprinklers designed specifically for the storage environment are triggered by signals from detection systems and provide cooling before ignition occurs. Within storage areas where fire department access may be limited, firewalls and fire curtains can be used to create compartments, preventing a potential fire from simultaneously affecting the entire fuel stock and adjacent facility sections. Finally, training facility staff on dust cleaning in the storage area and regularly removing accumulations of combustible dust throughout the depot can significantly reduce both fire and explosion risks.

With these precautions in place, a high level of safety can be achieved during RDF storage. Indeed, many facilities have taken measures against such risks by equipping their storage areas with smoke detectors, infrared cameras, and automatic extinguishing systems. However, safely storing the fuel alone is not sufficient—equal care must be taken during the transportation of RDF and even during its feeding into the combustion process.

Transportation Systems

The journey of stored RDF (Refuse-Derived Fuel) from storage to kiln feeding is a phase that is just as critical for safety as storage itself. Typically, RDF is transferred from bunkers to conveyor belts, and from there to a dosing unit that feeds the rotary kiln. These transportation systems inherently include mechanically moving parts and exposed areas where the fuel is in contact with the environment. Whether using belt conveyors, screw conveyors, or pneumatic conveying lines, risks such as fuel spillage, friction-induced heating, or equipment malfunctions can arise. One notable hazard involves fine particulate material spilled from RDF along belt conveyors, which can accumulate as dust and form explosive dust clouds when mixed with air. If this dust cloud encounters an ignition source, such as a spark or hot surface, a dust explosion may occur. Unfortunately, past experiences with coal systems have shown that cement plant transport and grinding equipment often lack adequate fire and explosion protection. This shortfall was overlooked for years due to the relatively low frequency of coal dust incidents. However, transitioning to RDF—with its diverse composition—could result in more severe consequences if similar negligence persists. For example, RDF dust with high plastic content may exhibit very different explosion characteristics compared to coal dust. In such cases, routine equipment faults like static electricity buildup, bearing overheating, or belt slippage could easily trigger a major explosion.

To minimize these risks, a principle of enclosed and controlled transport should be adopted. In many modern cement plants, RDF is transported using pipe conveyors or enclosed screw conveyors that are insulated from weather conditions and ignition sources. These systems ensure smooth material flow and help contain dust buildup. Nevertheless, even in fully enclosed systems, protective equipment such as pressure relief panels and explosion suppression systems should be installed to mitigate damage in the event of an explosion. At high-risk points like grinders or ground RDF silos, zoning according to the ATEX Directive (e.g., Zone 21, Zone 22) is crucial, along with selecting explosion-proof (Ex-proof) electrical equipment to eliminate ignition sources. Installing spark detectors and heat sensors along transport lines is another key element of an early warning system. For example, temperature sensors embedded in conveyor belts can detect overheating due to bearing failure and stop the belt before a fire breaks out. Similarly, if spilled material beneath the belt ignites due to friction, smoke detectors can trigger an alarm. Fire compartmentalization should also be considered in system design: installing fire dampers at the start and end points of conveyors can prevent a fire in one area from spreading along the entire line. Fires on long conveyor systems transporting flammable materials can quickly spread to production equipment and endanger the entire facility. Therefore, an integrated fire detection and suppression system must be implemented throughout the entire RDF transport route. In conclusion, the safe transfer of RDF from storage to kiln must be secured with appropriate engineering controls (dust management, spark prevention) and active protection systems (detectors, extinguishers). Even with the right infrastructure, the human factor must not be overlooked—operators and maintenance personnel should be trained to detect early signs of irregularities (unusual noise, smell, vibration, etc.) and supported with clear procedures.

Fire Safety Systems

In response to the increased fire risks associated with RDF (Refuse-Derived Fuel) use, the most critical line of defense is the facility-wide fire safety system. A multi-layered safety network must be established by integrating appropriate detection and suppression equipment into each stage of storage and transportation. Early detection is particularly vital to enable intervention before a fire grows out of control. In addition to smoke and heat detectors in storage areas, sensors should be installed at critical points such as conveyor transfer zones and grinders. This allows conditions like spark formation or material overheating to be addressed before they escalate into full-blown fires. Since keeping RDF away from ignition sources alone does not guarantee absolute safety, automatic fire suppression systems must remain constantly operational. Conventional water sprinkler systems are one of the primary methods for cooling large areas and controlling fires. However, due to the specific characteristics of RDF fires, foam-based suppression systems are often more critical in certain scenarios. When high-calorific waste burns, it can generate thick black smoke and a dense layer of flammable gases. In such cases, cooling with water alone may not be sufficient. Foam-based suppression systems mix water with a foam concentrate at specific ratios to create a foam solution that is dispersed over the fire. The foam layer acts like a blanket, covering the flammable material and cutting off its contact with oxygen, thereby smothering the flames while simultaneously cooling the surface. This method is especially effective in suppressing fires in deep waste piles or in liquid-derived waste fuels (such as waste oils), where the foam leaves a film layer that prevents re-ignition—something water alone cannot achieve. For this reason, foam nozzles should be strategically installed in RDF storage and feeding areas as an integral part of the overall fire safety plan.

The critical role of foam suppression systems lies in their ability to quickly control RDF-related fires—if they are correctly designed and operated. However, technical errors and negligence in these systems can not only fail to provide the expected protection but may also worsen the situation. For example, if the foam concentrate and water are mixed in the wrong ratio, the resulting foam may lack the necessary density and stability, preventing it from fully covering the flames and extinguishing the fire. Similarly, mistakes in calculating the coverage area of foam sprinklers can result in parts of the fuel pile not being wetted by foam. Inadequate nozzle placement or an insufficient number of sprinkler heads may allow fires to grow undetected in blind spots of the storage area. Moreover, without regular maintenance, foam concentrate may degrade, and pipelines may become clogged or blocked with residue, rendering the system non-functional. In emergency situations, equipment failures such as non-working pumps or stuck valves have previously led to tragic outcomes in industrial facilities. In summary, effective foam suppression system design must include accurate hydraulic calculations, proper selection of foam concentrate (e.g., synthetic, Class A, AR-AFFF, or protein-based, depending on fuel type), and regular testing and maintenance. If these aspects are neglected, the system may fail to operate when most needed, turning a small ignition event into a major fire or explosion disaster. Therefore, in cement plants utilizing RDF, foam suppression systems must comply with relevant standards (e.g., NFPA 11, EN 13565), be routinely tested and inspected by qualified teams, and be supported by backup plans for potential failure scenarios.

Conclusion

The use of alternative derived fuels (RDF) in the cement industry offers significant benefits in terms of sustainability and efficiency, but it also introduces new responsibilities that must be addressed from a risk management perspective. Even in traditional coal systems, fire and explosion risks have not been fully addressed for years; when working with RDF, these risks reach levels that allow no room for negligence. Therefore, cement plant management must view RDF use as a strategic transformation and redefine not only operational goals but also occupational health and safety objectives. Industry experts point to the transition to alternative fuels as a critical opportunity to improve existing fire and explosion protection infrastructure. In this process, technical expertise and employee awareness will be decisive for a successful transformation.

To ensure safe production with RDF, comprehensive risk-focused measures must be implemented. First, a proactive safety culture should be established across the facility, promoting the identification and mitigation of risks before they occur. In this context, the integration of advanced early warning systems (e.g., infrared thermal cameras, optical flame detectors) and regular functionality testing of existing detection networks is essential. Second, the improvement of fire suppression systems must be prioritized. Appropriate types of sprinklers and foam nozzles should be installed in RDF storage areas and transport lines, with hydraulic capacity and backup units designed for worst-case scenarios. Third, explosion risk management must not be overlooked. In accordance with ATEX directives, all equipment must be reviewed, and systems such as pressure relief panels, explosion suppression mechanisms, and inerting applications must be implemented to guard against dust explosions. Finally, the human element must be aligned with this technical transformation through training and drills. Personnel must receive thorough education on RDF characteristics, fire load, emergency procedures, and response techniques. Regular fire and explosion drills will ensure prompt and appropriate responses in the event of an incident.

In summary, while RDF use is becoming an inevitable trend in the cement industry, managing this transformation safely is both possible and necessary. Technical and organizational measures supported by a well-designed risk management plan can reduce RDF-related fire and explosion risks to acceptable levels. In this way, plants can achieve their sustainability goals without compromising safety. From both a legal compliance and corporate social responsibility perspective, every investment made to ensure the safe use of RDF is crucial to preventing major accidents and maintaining uninterrupted production. When this balance is achieved, the cement industry will not only contribute to environmental benefits by turning waste into energy but also effectively protect its workers and facilities.

Kaynaklar:

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4.       Orglmeister Infrarot-Systeme GmbH. Fire Avoidance in Cement Plants: Early IR Detection in Alternative Fuel Storage Areas.

5.       Gajewska, J. et al. (2019). Self-Heating and Spontaneous Combustion Hazards of Refuse-Derived Fuels. Materials, 12(3).

6.       Grosskopf, V. (2020). The Coal Mill Safety Interview: An In-Depth Look at Explosion and Fire Protection in the Cement Industry. Dust Safety Science.

7.       National Fire Protection Association (NFPA). (2021). NFPA 11: Standard for Low-, Medium-, and High-Expansion Foam.

8.       National Fire Protection Association (NFPA). (2022). NFPA 68: Standard on Explosion Protection by Deflagration Venting.

9.       National Fire Protection Association (NFPA). (2022). NFPA 69: Standard on Explosion Prevention Systems.

10.   European Union. (2014). Directive 2014/34/EU on the Harmonization of the Laws of the Member States Relating to Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres (ATEX).

11.   European Committee for Standardization (CEN). (2009). EN 13565-2: Fixed Firefighting Systems – Foam Systems – Part 2: Design, Construction and Maintenance.

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