Bucket Elevator Safety: Identify, Prevent, and Protect
According to technical studies, about 50% of explosions in solids handling facilities originate in bucket elevators.
This article will help you:
- Identify the specific risks associated with this equipment.
- Prevent the formation of hazardous atmospheres and minimize the chances of ignition.
- Protect your facilities through certified solutions, complying with ATEX regulations and international technical standards.
Bucket elevators are essential equipment in the vertical transport of bulk solids in sectors such as animal feed, agri-food, chemical or sugar, among others. Its closed design, the accumulation of fine dust and the multiple moving mechanical elements favour the formation of explosive atmospheres and the appearance of ignition sources, making the elevator a critical point from the point of view of industrial safety.
Why are bucket elevators a critical focus of explosion risk?
The coincidence of three key factors makes this equipment one of the most vulnerable points against dust explosions:
- Presence of combustible dust: Thin, dry materials transported by the elevator, such as feed, starches or chemicals, have a high explosive potential. Minimal dust accumulation is enough to create a dangerous mixture with air
- Formation of explosive atmospheres: The accumulation of dust or the presence of suspended dust combined with internal turbulence and lack of effective suction systems, can lead to explosive atmospheres inside the equipment.
- Internal ignition sources: The mechanical operation of the equipment can generate heat, friction, and sparks. If these sources are not eliminated or controlled, the risk of ignition increases considerably. Poor maintenance intensifies these risks.
Common hotspots where ignition sources can occur include:
- Friction or misalignment of the band, generating heat and incandescent particles.
- Overheating of bearings, due to wear or lack of maintenance.
- Jamming, foreign bodies or belt slippage on pulleys.
- Tape break with metal buckets, capable of generating sparks.
- Electrostatic discharges, between components not properly grounded.
The combination of these ignition sources with an explosive atmosphere can trigger an explosion inside the elevator, with the risk of propagation to other connected equipment.
Explosion Prevention and Protection Measures
Once the causes that make the bucket elevator a critical source of risk have been identified, it is essential to act on the elements that make up this risk: combustible dust, the explosive atmosphere and the sources of ignition. When it is not possible to guarantee the simultaneous absence of these three factors, facilities must incorporate measures that allow any possible explosion scenario to be anticipated, controlled and mitigated.
Prevention Measures
Prevention is the first line of defense against the risk of dust explosion in bucket elevators. Act on the factors that favour the formation of explosive atmospheres and/or on the possible sources of ignition, allowing to significantly reduce the probability of a deflagration during the operation of the equipment.
The most common measures for the prevention of explosive atmosphere:
- Dust collection systems on the foot and head of the equipment.
- Regular cleaning of the equipment.
Among the measures to act on possible sources of ignition:
- Correct grounding and equipotentiality, use of an antistatic material band when the Minimum Energy of Ignition of the product is low (EMI < 10 mJ).
- Installation of magnets or grids to prevent the entry of foreign bodies.
- Monitoring of ignition sources: temperature in bearings, belt misalignment, speed, jamming.
In addition, a rigorous preventative maintenance program combined with an ongoing industrial cleaning strategy is critical to keeping risk under control. These practices prevent the deterioration of key components and ensure the proper functioning of all prevention systems.
Protection Measures
When the risk cannot be completely eliminated, protective measures are applied. These solutions are designed to limit the destructive effects of an explosion, preventing its spread and reducing material and personal damage.
Common protection measures in bucket elevators include:
- Explosion Venting: Installation of panels that release pressure and flames to safe areas.
- Flameless Venting: It confines the flames in a mesh envelope, allowing the escape of combustion gases without emitting flame.
- Explosion Suppression: Use of extinguishing agents that suppress the explosion in its initial phase, avoiding the increase in pressure.
- Explosion isolation: non-return valves, rotary valves, worm screws or chemical barriers that prevent propagation to adjacent equipment.
The choice of protective measures must be based on a rigorous technical analysis, adapted to the specific operating conditions of each lift. Applicable regulations recommend the combined use of protection and insulation systems, selected based on the type of product, the design of the equipment and its location within the plant.
One of the most widespread solutions is the explosion venting system, using panels or doors installed in strategic areas (usually the head and foot of the elevator). These devices allow the pressure and flame generated during a deflagration to be released in a controlled manner, avoiding structural damage. However, when the elevator is located indoors, the use of conventional venting can pose a new risk, as discharging the explosion into a confined space can lead to severe consequences.
In these cases, it is preferable to use flameless venting systems, which integrate a metal mesh to cool and contain the flame, allowing its safe installation indoors without spreading fire to the environment.
When superior protection is required, or the system design does not allow venting, explosion suppression is the most effective option. These systems detect the deflagration in milliseconds and activate pressurized bottles with extinguishing agent (such as baking soda), suffocating the explosion before it fully develops.
Suppression, in addition, can play a critical role as insulation when installed in elevator inlet or outlet ducts. In this way, it acts as a chemical barrier that prevents the spread of the flame to other interconnected equipment, such as silos or cyclones. This point is especially sensitive on elevator legs, where a pressure wave could be amplified and cause severe damage.
Most common combinations according to the type of process:
- Venting + mechanical or chemical isolation, in equipment located outdoors.
- Suppression + chemical isolation, when the elevator is indoors or handling products with low EMI value.
- Flameless venting + chemical barriers, in critical processes where the emission of flame or incandescent particles is not allowed.
Regulations and Applied Certifications
- ATEX Directive 2014/34/EU
- UNE-CEN/TR 16829:2016
- NFPA 61, 68, and 69
- UNE-EN ISO 80079-36:2017
Case Study: Installation of Protective Equipment in Bucket Elevators
Within the framework of the safety adaptation project in the food industry facility dedicated to the manufacture of sugar, the integral protection of two interior bucket elevators responsible for the vertical transport of raw sugar was carried out. Both elevators, double-barreled, presented a significant risk due to dust accumulation and the absence of active explosion protection systems.
Initial diagnosis
Following a risk assessment (ATEX), the need to implement advanced explosion protection systems was identified with the aim of reducing mechanical and explosion risks due to the combustible nature of sugar dust and the presence of favorable conditions for possible ignition (frictional heat sources, dust accumulation, continuous mechanical movement).
During the technical evaluation , the following risks were identified:
- Classification of Zone 20 interior, with cleaning procedures in place, localized aspiration and correct grounding.
- High risk of explosion due to dust accumulation inside the elevator.
- Lack of temperature monitoring in bearings and critical areas.
- Exposed moving parts without adequate protections.
- Absence of explosion suppression and isolation systems.
According to Directive 1999/92/EC, when preventive measures are not sufficient to eliminate the risk, it is mandatory to incorporate specific protection systems.
Implemented solutions
A combined strategy of suppression and chemical isolation was chosen, designed to act in milliseconds in the event of an incipient explosion and prevent its spread within the system.
- Additional mechanical protections:
- Folding metal covers and perimeter locks with safety interlock.
- Automatic inhibition of operation if the guards are open.
- Continuous monitoring and control:
- Temperature probes in bearings (with alarm at 75 °C).
- Belt speed and misalignment sensors.
- Full integration into the plant SCADA system.
- Explosion Suppression System:
- 6 kg suppression and insulation bottles distributed in the head and foot of the elevator.
- Pressure and optical detectors certified for use in Zone 20.
- Centralized line controller.
- Complementary insulation system:
- 6 kg suppression and insulation bottles distributed on elevator rods.
- Chemical barriers in suction, discharge and loading ducts.
Results
After the implementation of the system, tangible improvements were obtained in safety and operation:
- Elimination of entrapment risks and exposure to moving elements.
- Reduction >80% of dust accumulation in critical areas of the elevator.
- High traceability of faults thanks to real-time monitoring.
- High reaction speed to critical events (detection + suppression < 20 ms).
- Elimination of the risk of spread to silos and logistics areas.
- Verified compliance with ATEX regulations.
- Start of predictive maintenance plan based on real operational data
