Identifying And Preventing the Causes of Conveyor Fires

March 3, 2024|Conveyors & Sortation, Material Handling, Safety

Clean conveyor systems, ongoing maintenance, good fire-fighting capabilities and awareness of hazards can prevent conveyor fires.

By: Dan Marshall and R. Todd Swinderman, Contributors

Bulk handling facilities with extensive conveyor networks are at particular risk of large-scale fire events. The size and speed of modern conveyors can spread fires over great distances in a very short time. Conveyor fires are typically difficult to fight as the belt can easily ignite itself, and if not spotted in time, burning material can even be transferred from one conveyor to another. The belt path often runs through a variety of enclosed structures and inclined conveyors can develop a flue-like effect that intensifies the air flow, feeding the blaze.

In underground applications, the danger is far more acute. Statistical data[1] from conveyor belt research reveals that up to 70% of fires in underground coal mines occur in excavations equipped with belt conveyors. With enough friction and heat, many conveyor belt constructions are capable of self-sustained fire propagation whether they are made from natural materials, synthetics or a combination of the two. Once ignited, they tend to produce a thick, black smoke resembling a tire fire, which is often a far worse risk to personnel than the flames themselves. Smoke and heat can quickly travel through shafts, limiting visibility, access and escape, and it can take days to completely extinguish.

CAUSES OF BELT FIRES

Although heat caused by friction is the principal trigger of conveyor fires, there can be several underlying causes. Seized components such as rollers, brakes or bearings are a common source, often exacerbated by fugitive material that acts as an abrasive. It has been estimated that frictional and static ignitions may account for up to 40 percent of all belt fires.

Other causes are less predictable, such as overheated motors, electrical fires, incidental ignition of surrounding spillage and foreign material entering the cargo stream producing sparks. These sudden ignitions can be spontaneous and, in some cases, leave little trace as to the trigger for the fire.

To create a fire there must be three elements: oxygen, heat and fuel (aka, “the fire triangle”). One factor that makes conveyor fires so hazardous is that the belt itself can be the fuel. According to a study of belt fires conducted by the National Institute for Occupational Safety and Health[2] (NIOSH), any of the standard neoprene, PVC, chloroprene and BELT-approved SBR belts can ignite.

In fact, a 3-year research project (Edaffic[3]) concluded that although some belts were hard to extinguish and burned completely while others ignited quickly and went out on their own (self-extinguishing), there is no non-flammable belt, particularly when accompanied by combustible material.

BELT TESTING FOR FRICTION

What leads to friction can often be sourced back to either the discharge zone or the loading zone, or both. Dust emissions of any kind (combustible or non-combustible) tend to foul rolling components, leading to failure of the seals and contamination in the bearings and causing rollers to seize. Continuous frictional contact with a seized idler or the roller face can exceed safe operational temperatures resulting in extreme wear on the belt, degrading the main fire-retardant layer and exposing the heat-sensitive materials found in the belt’s inner construction.

Tests have been developed to study the resistance of conveyor belts to ignition, glowing or sparking when under intense friction conditions. The “Drum Friction Test” uses a sample of conveyor belt suitably mounted around a drum that rotates at a specified speed and belt tension.

The test measures different tensions for a given time period until the belt breaks. Although the sample may remain intact depending on the test standard, testers must specify the maximum temperature the drum reaches during the testing. For example, testers for coal mine applications set the maximum drum temperature to approximately 325 degrees Celsius, or 617 degrees Fahrenheit, which is below the ignition temperature of coal dust. However, some standards allow drum temperatures up to 400 degrees Celsius, or 725 degrees Fahrenheit, for non-flammable cargos.

CONTROLLING FUGITIVE MATERIAL

Dust control is extremely important when handling combustible substances. Examples include:

Coal: Carbon-based, highly-flammable material that burns at high heat, with dust that is easily ignited by a spark.
Petroleum coke (petcoke): Carbon-rich derivative of oil processing, used as a coal alternative for power generation, among other applications. In dense concentrations, the dust is combustible with a high-energy spark.
Cellulose: A naturally occurring polymer found in wood, paper and grains; dust readily ignites.

CONSIDERATIONS FOR CONVEYOR FIRE PREVENTION

Often, the return on investment (ROI) for preventative equipment isn’t recognized until managers are inspecting burnt rubble. Safety-minded operators understand that equipment like belt cleaners and impact cradles, when properly designed, can just as easily help prevent fires than cause them.

Impact cradles and support cradles help reduce fugitive material by providing a stable belt surface that facilitates effective sealing.

Transfer chute design is a critical element of fugitive material control, with sufficient settling zones and confinement. External wear liners paired with improved skirt seal designs mitigate fugitive spillage and dust emissions and protect rolling equipment from fouling and seizure. The decrease in spillage mitigates the collection of potential fuel.

Modern belt trackers with troughed idlers or gripping return idlers are so sensitive that they correct the belt path immediately, reducing friction fires and spillage.

A heavy-duty belt cleaner system featuring modern primary and secondary cleaners increases the volume of discharge and limits the amount of carryback and fugitive dust.

CONCLUSION

It is incumbent upon employers to protect workers from one of the most potentially hazardous pieces of mechanical equipment at any facility: conveyors. Knowing the risks of fire, facilitating periodic inspections, and striving to implement the steps and equipment needed for a safer workplace should be the goal of every operation. Experience has shown that clean conveyor systems, good fire-fighting capabilities and ongoing maintenance form the best defense against fire. WMHS

Daniel Marshall is Process Engineer, Martin Engineering. Dan has developed multiple belt conveyor products and is an expert in dust suppression. He co-authored Martin’s FOUNDATIONS™ The Practical Resource for Cleaner, Safer, and More Productive Dust & Material Control, Fourth Edition, widely used as one of the main learning textbooks for conveyor operation and maintenance.

Todd Swinderman is President Emeritus of and consultant to Martin Engineering, having also served as V.P. and General Manager, CEO and Chief Technology Officer at the company. Todd has authored dozens of articles and papers and has presented at conferences and customer facilities around the world. He holds 140+ active patents.

Martin Engineering is a global innovator in the bulk material handling industry. The company’s series of Foundations books is an internationally-recognized resource for safety, maintenance and operations training. Martin Engineering products, sales, service and training are available from 17 factory-owned facilities worldwide. For more information, contact info@martin-eng.com, visit www.martin-eng.com, or call (800) 544-2947.

[1] http://tinyurl.com/3243558t

[2] http://tinyurl.com/2f33amwr

[3] http://tinyurl.com/ye5d5d84