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OEM warns of conveyor belt dangers

Recognising the hazards is a key step toward preventing conveyor-related injuries, according to Martin Engineering.

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Cleanup brings workers within close proximity of a moving conveyor
Cleanup brings workers within close proximity of a moving conveyor

The US-based company has issued an advisory warning that a conveyor presents enough danger zones that the entire system should be considered a hazard.

 

“In bulk materials handling applications, a conveyor is typically a massive, complex and extremely powerful system. It’s usually constructed of rubber belting, set on rolling idlers, wrapped around large steel drums at each end and driven by a high-torque motor,” the company said.

 

“In most applications, a conveyor belt moves at a relatively constant speed, commonly running somewhere between 0.5m and 10m per second [≈100 to 2,000 fpm]. An Olympic sprinter has a reaction time of about 0.18 seconds when poised at the starting line and totally focused on the race. If this athlete becomes tangled in a conveyor belt travelling 1.5m per second [≈300 fpm], the person would be carried 0.27m [≈10.6 inches] before even realising what has happened.

 

Martin said that a ‘regular’ worker would likely require a longer time to react. “For simplicity’s sake, we can assume it would be twice the athlete’s reaction time, so the worker would be pulled twice as far, introducing the potential to strike many more components or to be pulled farther and harder into the first one.

 

“In addition, most conveyors are engineered with the ability to start remotely. The system may go from dormant to active at any time at the push of a button, and that ability can suddenly catch a worker unaware, leading to serious injury or death.”

 

Dan Marshall, a Martin Engineering process engineer, observed: “When a conveyor belt is moving, there will usually be more tension on the carrying side. If the conveyor is merely stopped and de-energised, that tension may remain in the belt in the form of stored energy.”

 

Marshall noted that a system under tension will always try to approach equilibrium – that is, it will try to release the energy. This release will likely come in the form of a pulley slip, which occurs when the belt slides around the head pulley to equalise the tension.

 

The distance the belt will move is proportional to the amount of tension stored and the belt’s modulus (elasticity), possibly several feet. If a worker is on the belt or close enough to be pulled in during this sudden release of energy, injuries or death can occur.

 

“There’s a simple rule of thumb regarding conveyors: If it’s moving, don’t touch it,” said Marshall. “The most common way to prevent inadvertent contact is with suitable guarding that renders the moving components inaccessible.”

 

For maintenance or repairs, procedures for lockout/tagout/blockout/test-out should always be followed when working on a stationary conveyor, and systems should be equipped with anti-rollback devices (also known as backstops) on the head pulley.

 

Many of the moving parts on a conveyor belt system are rotating components. These parts include idlers, drive shafts, couplings, pulleys and speed sensors. Items rotating at a high speed pose the risk of entanglement or entrapment.

 

“All moving machine parts should be guarded with adequately constructed, properly installed, functioning and well-maintained guards,” said Marshall.

 

There are many pinch points on a conveyor, components that the belt actually touches or comes near, including the drive pulleys, snub pulleys, idlers, stringer, chute walls and deflectors. If a worker’s limb travels with a conveyor belt, it will meet one of these components. The limb, as well as its attached worker, will become trapped between the belt and the obstruction.

 

The same thing can happen with a tool, which can pull a worker into the entrapment faster than the person can let go. “Effective fixed guards should be absolute in their protection; workers should not be able to reach around, under, through or over the barrier separating them from moving components,” added Marshall.

 

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