Conveyor Fires: Causes and Prevention
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 (NIOSH),1 any of the standard neoprene, PVC, chloroprene, or BELT-approved SBR belts can ignite (see Fig. 1). Though some belts were self-extinguishing, the conclusion is that there is no non-flammable belt, particularly when accompanied by a combustible material.2 Conveyor fires can happen anywhere, at any time (Fig. 2).
FACTS ON FRICTION
Inadequate belt cleaning in the discharge zone can lead to dust and carryback on the return side of the belt, causing a fouled tail pulley to run under a stalled belt, which creates tremendous heat.
Dust emissions of any kind (combustible or noncombustible) originating from the loading or discharge zones can also cause friction. These dust emissions tend to foul rolling components, leading to failure of the seals and then contamination in the bearings, eventually causing the roller to seize (Fig. 3). A rolling component can also stall if impact or cargo weight causes the bearings to collapse.
Continuous frictional contact with a seized idler or the roller face can cause a loaded belt to exceed safe operational temperatures. It can also potentially result 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.
CONTROLLING FUGITIVE MATERIAL
Control of fugitive material and regular cleaning of spillage are imperative. Without proper belt cleaning, chute sealing, and belt tracking, spillage that collects around the loading/discharge areas and along the belt path can damage moving components, restrict access by fire crews and potentially act as fuel.
Dust control is extremely important when handling combustible substances. It is recommended that, instead of only taking into account the fire triangle, operators consider the “Dust Explosion Pentagon.” Figure 4 illustrates the five components.
Examples of highly combustible materials include:
- Coal—Carbon-based, highly flammable material that burns at high heat, with dust that is easily ignited by a spark.
- Petroleum coke (petcoke)—A 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 highenergy spark.
- Cellulose—A naturally occurring polymer found in wood, paper, and grains; its dust readily ignites.
Significant amounts of dust can collect on the walls of the loading zone chute. If a foreign metal object is accidentally introduced into the enclosed area, a spark can potentially create an explosion. Additionally, common maintenance within the chute—such as removal of the wear liner using a cutting torch—often requires confined space entry by workers. If the inside of the chute is not adequately cleaned, this task could pose a serious hazard.
THINK LIKE AN INSPECTOR
When examining conveyor equipment, one should approach the task with the same critical mindset as an inspector from OSHA, MSHA, or the local fire department. Safety professionals recommend a holistic view of the system and the combustibility of the material. When making a conveyor fire risk assessment, also consider:
- Spillage levels and cleaning schedules.
- The conveyor’s proximity to workstations.
- How the conveyor design (enclosures, narrow walkways, etc.) could create a hazard for employees.
- Safe storage of flammable liquids.
- Compliant signage.
With conveyor systems, the potential return on investment (ROI) for prevention equipment often isn’t recognized until managers are inspecting burnt rubble and negotiating with insurance adjusters. However, safety-minded operators understand that the same equipment they would implement for increased efficiency, such as belt cleaners and impact cradles, can also help prevent fires.
- Impact cradles and support cradles help reduce fugitive material by providing a flat, stable belt surface that facilitates effective sealing.
- Transfer chute design is a critical element of fugitive material control, with sufficient settling zones and confinement. New raised chute designs also allow for external wear liners that eliminate the need for confined space entry or torch removal. When paired with improved skirt seal designs, fugitive spillage and dust emissions are drastically reduced.
- Modern belt trackers detect mis-tracking and correct the belt path immediately using troughed idlers or gripping return idlers.
- A heavy-duty belt cleaner system featuring modern primary and secondary cleaners with an effective tensioner increases the volume of discharge and limits the amount of carryback and fugitive dust. Along with limiting spillage, tail pulley health is improved and there is less fouling of rolling components.
A global leader in conveyor accessories, Martin Engineering is dedicated to conveyor safety by educating the bulk handling industry on the hazards of conveyor fires. Its Foundations™ Learning Center is the largest comprehensive free conveyor training archive on the web, providing detailed insight into the causes and prevention of deadly fires.
CLEANER IS SAFER
Operators should regularly contain airborne dust at transfer points and remove accumulation. Damaged rollers must be replaced promptly. Conveyor belt alignment is also an essential prerequisite to belt safety. Mills should consider using flame-resistant grease and other lubricants. Fire detection and suppression systems must be tested in accordance with regulatory standards.
Experience has shown that clean conveyor systems and ongoing maintenance form the best defense against fire.