Operators and staff must be aware of the very specific fire hazards posed by the application and process and have a plan in place to avoid a crisis

Greater material volumes and faster belt speeds increase the chances of fires due to higher operating temperatures, increased dust, more static energy and greater friction between moving and stationary components. The consequences of a fire on a high-speed conveyor are existential, i.e., if proper measures for prevention or suppression are not taken, there is a chance of substantial destruction. Flames can be conveyed throughout the facility quickly, putting the entire operation and everyone in it in jeopardy. Beyond the obvious workplace safety issues, recovery from the insurance, production loss and legal ramifications could take years.

Conveyor fires are very hard to fight if not caught right away, leading to a system-wide shutdown. The infrastructure can be long, transferring from one belt to the next, spreading a fire through a variety of enclosures and structures and potentially discharging onto large storage piles of fuel. In addition, the conveyor structure is often elevated or inclined/declined over an extended length, making access for firefighting difficult. With tons of fuel, widespread distribution and limited access, at times the only option is to wait until the fire burns itself out.

An example of a quickly spreading conveyor fire happened at a metal recycling facility in Indianapolis in 2021. A conveyor belt caught fire and transported the flames to a storage facility with 80,000 tons of oily metal scrap that immediately burst into flames. Large amounts of fuel along with high winds meant it took five fire departments — including crews from the main Indianapolis Fire Department and the nearby Indianapolis Speedway — 13 hours to contain the flames. The plant suffered significant losses.²

From a workplace safety perspective, besides the burn hazard, a major threat during a conveyor fire is the gases released as a byproduct of combustion, such as carbon monoxide (CO). Proximity to a burning conveyor belt can expose workers to CO poisoning and toxic gases, such as hydrogen cyanide (HCN) and sulfur dioxide (SO₂), oxygen depletion, convective and radiant heat, and irritants such as smoke particulates.

Most industrial processes involve large machinery and potentially combustible materials, but belt fires can be caused by a number of circumstances. Due to hotter weather, conveyor fires often happen during summer.³ However, this is only a contributing factor and operators should be aware of the triggers. Conveyor fires generally have three common elements: heat sources, fuel sources and oxidizing agents.

Heat from friction is estimated to be the cause of about 30% of belting fires.³ Seizures or failures in bearings are common, causing rolling components to freeze. As the belt slides over them, the friction raises the temperature of the belt. This type of frictional heat can also happen when the belt contacts the system structure or components, or if brakes are left partially deployed.

Material accumulation can pose a friction hazard, as well. Accumulated buildup on the return side of the belt or the pulley face can lead to slippage, causing friction-generated heat energy. Also, spillage under the structure at the loading or discharge zones can pile to the level of the belt, causing it to slide across the top of the piled material rather than on the rollers. Friction heat created by the belt dragging over piles of spilled material can lead to smoldering fires or “hot spots” in the spillage piles. Hot spots can also be common in processing some materials, such as clinker or slag.

High temperatures found near the conveyor can heat the nearby belt, and sparks from maintenance involving cutting or welding can contribute to the hazard, as well. Grinding gears or tramp metal hitting structures can spark, leading to hot spots or triggering combustion. Electrical fires, short circuits or exposed electrical equipment are also potential sources. Perhaps the most common electrical source is static discharges, caused by friction.

Conveyors carry potential fuel for a belt fire, either in the cargo load or in the form of combustible dust emissions. However, the belt itself can become fuel, igniting elastomers, adhesives, carcass and covers. Pulley materials such as lagging and coatings can also ignite.

In addition, fuel sources can be present in the environment around the belt, such as containers of flammable liquids (lubricants, solvents, portable equipment fuels, de-icing chemicals, etc.), along with oily rags or small spills. Clearing the area around the belt inside and outside is important, because trash and debris from maintenance can ignite, along with nearby vegetation.

Fire can’t live without air. Unfortunately, neither can we. There isn’t much we can do about oxygen, but operators should be aware of potentially flammable or combustible fumes or gasses emitted by processing and maintenance chemicals. Operators who use forced air ventilation also need to be aware of the air flow direction, so that any potential hotspots or open flames in the area around the conveyor aren’t exacerbated by increased airflow.

Fire requires heat, fuel and an oxidizing agent (usually oxygen in the ambient air). For an explosion to initiate, there must be the elements of the fire triangle plus dispersion of combustible dust or liquid, or flammable gas within a confined space.

Many explosions start as localized flash fires caused by the ignition of a distributed fuel and oxidizing agent in an open area or large enclosure. Often, a flash fire will cause a significant dispersion of combustible dust, creating conditions for a secondary ignition that may result in an explosion or spreading of the localized fire.⁴ Many common bulk materials that seem inert may be easily ignited in dust form or give off flammable or combustible vapors when heated. Some materials, such as brown coal, can spontaneously ignite.

Bulk material handling, by its nature, is a dusty business, and many raw materials from biomass to mining tailings can generate combustible dusts. Clouds of dust can be highly combustible and potentially explosive if sparked, which results in catastrophic damage instantaneously.

Preventing combustion begins with a good dust mitigation plan. The facility should have a housekeeping policy in place to prevent the accumulation of fugitive dust. Ensure that the sealing system on a conveyor is properly maintained in order to prevent particle emissions that can lead to a catastrophic event.

Keep an enclosed conveyor as sealed as possible to prevent particle emissions to help prevent a catastrophic cascading effect. Dust layering, on bearings for example, can prevent heat from dissipating, causing elevated temperatures. This could ignite the settled dust, leading to fire spreading to the conveyor, and potentially resulting in the explosion of airborne dust. To make matters worse, the primary explosion will likely cause more dust to become airborne, resulting in even more severe secondary explosions.

Contain dust using enclosures, proper skirting and dust curtains in the loading zone.

Suppress dust using water sprayers with surfactant additives within the transfer area.

Collect dust using air cleaners, dust bags and a regular cleaning schedule.

Install a fire protection system.

Install explosion mitigation devices, such as vents, suppression or explosion isolation.

Monitor belt speed and pulley misalignment. A slowing or drifting belt can be indicators of a friction hazard.

Monitor bearing temperatures.

If the application emits fumes or vapors, install appropriate hazardous duty ventilation and gas sensing equipment.

Most countries have general workplace safety regulations defining fire hazards, such as the ones found in the U.S. Occupational Safety and Health Administration (OSHA) standards.⁵

Further regulations can be set by local ordinances and permits or industry-specific regulatory bodies, including the Mining Safety and Health Administration (MSHA). Industry best practices, set by organizations like the Conveyor Equipment Manufacturers Association (CEMA), should also be followed. Not all strategies are appropriate for all situations, but workplace safety should always be the number one goal.

A “production first” design approach can have catastrophic consequences both for staff and operations. This extends from the design of the area around the conveyor down to the conveyor components themselves. Construction materials, roadways, paint, and surface coatings at loading and transfer points should be fire-resistant or retardant. Facilities should have access, infrastructure and procedures in place for quick fire response.

Designing the environment around conveyors requires understanding the needs of the specific systems and applications involved. Enclosed conveyors mitigate spillage but can facilitate the containment and concentration levels necessary for dust explosions. When designing the area around the conveyor, consider proper ventilation and the addition of heat sensors for activation of deluge systems to replace fusible deluge sprinkler heads. Near the points where the conveyor enters and exits the process or building, install CO sensors to detect potential hazards (hot spots, smoldering material, toxic fumes, etc.).

When constructing the conveyor, conduct a specific fire safety risk analysis for the initial design. For rebuilds, retrofits or upgrades, assess conveyor arrangements, location, components or changes in bulk material specifications outside the original material provisions.

Make sure the entire system is grounded and that there is control over the accumulation of static charges. Utilize anti-static and fire-retardant conveyor belting with a surface resistance not to exceed 300 megaohms and pair it with anti-static lagging on the pulleys. Consider non-combustible enclosures around critical points, including where the conveyor passes through openings in any buildings. Perhaps most importantly, ensure the conveyor design is of sufficient capacity to carry the maximum expected load without spillage.

Provide adequate access for inspection, maintenance and cleaning in the design. Chute and structural clearances should allow for some belt mistracking to avoid friction contact between the belt and the structure. Install or program sequential stoppage of equipment feeding or receiving bulk materials to stop the conveyor when safety devices are actuated within the process.

Use only pulleys and idlers manufactured to appropriate standards for the application. Fluids in hydraulic systems and grease in idler bearings should be specified as fire-resistant or retardant. Use hazardous duty-rated motors, sensors and electrical equipment when combustible dust or flammable fumes or gases are likely.

Smoke and gas detectors at critical locations.

Belt tracking devices where the belt enters the head, takeup and tail pulleys.

Belt misalignment detectors.

Belt rip (tear) detection devices at the loading point and at a safe run-down distance from the delivery end.

A belt-slip detector on every drive pulley and tail pulley arranged to alarm and stop the conveyor if the belt slips. Best practice is to calibrate the alarm to when the speed is reduced by 10% and shut down if the speed is reduced by 20%.

Heat detectors and/or hot spot extinguishers with bulk materials that tend to be hot or combustible.

Heat-detecting fiber optic sensors along the conveyor run.

Plugged chute detection alerts to minimize material accumulation as an ignition source.

Temperature monitoring devices on bearings, as close to the outer race as possible.

Metal detectors or magnets to identify or remove tramp metal.

According to OSHA, “When there is a delay or setback during an incident, the risk of injury rises for facility workers as well as for emergency responders. Everyone is safer when facility and emergency personnel share information and develop safe procedures to handle incidents involving combustible dusts.”⁶

Firefighting is best left to trained employees for first response and professionals for fighting major fires. To reduce the impact of a fire event, train staff on the indicators, have a clear and simple response procedure, conduct periodic response drills and schedule independent risk management reviews.

Specialized techniques may be required to extinguish a conveyor fire in the presence of combustible dusts. If combustible particles are present, high power water jets can send accumulated dust into suspension — leading to a subsequent explosion — and special water application techniques may be necessary.

Due to the development of fire-retardant equipment and stricter regulations, conveyor fires are relatively rare. However, these measures were developed to prevent the tragic events of the past. Fewer incidents can lead to reduced awareness over time, which could result in complacency and greater risk.

Like the conveyor fire in Indianapolis, a billowing blaze can be seen for miles and can potentially destroy a company that the community trusts and depends on. But just having fire-retardant equipment isn’t enough. Operators and staff must be aware of the very specific fire hazards posed by the application and process and have a plan in place to avoid a crisis. It benefits the workplace, the staff, the community and the bottom line.

¹ United Nations Environment Programme (UNEP), International Resource Panel, and Stefan Bringezu et al., Assessing Global Resource Use: A Systems Approach to Resource Efficiency and Pollution Reduction, pg. 10 (Nairobi: UNEP, 2017). www.resourcepanel.org/sites/default/files/documents/document/
media/assessing_global_resource_use_amended_130318.pdf.

² Mack, Justin L., Firefighters battle large industrial fire on Indianapolis’ southwest side, IndyStart. Indianapolis, IN. May 23, 2021. www.indystar.com/story/news/local/indianapolis/2021/05/23/fire-indianapolis-wayne-town-ship-alpine-truck-salvage/5233619001/.

³ European Commission, Fernandez, Marta, Rodriguez, Angel et al. Research Fund for Coal and Steel, Early Detection and Fighting of Fires in Belt Conveyor, EUR 25346 2013.

⁴ Triangles, Squares and Pentagons – The Anatomy of a Combustible Dust Hazard By Chris Cloney Mar 26, 2018, Explosion Fundamentals. www.mydustexplosionresearch.com/.

⁵ Occupational Safety and Health Administration (OSHA), Fire Safety Standards. U.S. Department of Labor. June, 2021. www.osha.gov/fire-safety/standards.

⁶ Occupational Safety and Health Administration (OSHA), Fire-fighting Precautions at Facilities with Combustible Dust, U.S. Department of Labor OSHA 3644-04 2013. www.osha.gov/sites/default/files/publications/OSHA_3644.pdf.

R. Todd Swinderman, president emeritus, Martin Engineering. He has authored dozens of articles and papers, presenting at conferences and customer facilities around the world and holding more than 140 active patents. He also served as president of the Conveyor Equipment Manufacturers’ Association (CEMA). Swinderman retired from Martin Engineering to establish his own engineering firm, currently serving the company as an independent consultant.