It is common knowledge that drive systems must be de-energized prior to performing work on or around belt conveyors. This includes lock-out and tag-out of the conveyor's drive components. These procedures should be done for any related equipment that might feed material to or from the belt conveyor. This other equipment may include other conveyors, feeders, crushers and slide gates. In addition, restrict access to any load points that may be serviced by mobile equipment.

However, what is not common knowledge is that even if the belt conveyor is properly locked-out and tagged-out there is a potential for accidents or fatalities.

During a belt conveyor's normal operation, the belt is usually under considerable tension. The belt is stretched just like a rubber band. The amount of tension in the belt is based on factors such as length and width of the belt, size of the drive, amount of conveyed material and the weight of the gravity take-up. There are places along the conveyor system where the tensions are considerably higher than other areas. The arrangement of the drive system determines where the tensions are high and where they are low.

This is a concept that all employees required to work around the conveyor belt must understand. Learning this must be included in the safety training along with lock-out and tag-out procedures. Yet, most of the time it is not included. Only after someone is killed or injured do we understand the need for this type of training.

The first thing to decide is which employees need this safety training. Those who should be training include:

• cleanup personnel,
• maintenance personnel,
• conveyor belt inspectors,
• foreman responsible for belt conveyors,
• sales personnel that walk belt conveyors,
• conveyor operators,
• engineers who design conveyors,
• planning and scheduling personnel, and
• safety personnel.

It is critical to educate the employees on where the tensions are located based on the conveyor-drive configuration. Most belt conveyors have the drive located at the discharge or head end of the belt conveyor. On these systems, the highest tensions are located at the point where the belt is against the drive pulley. Directly behind the drive pulley the belt tensions are considerably lower (see figure 1).

On a head-driven conveyor, the tension on the belt is highest just before the belt leaves the drive pulley, which in this case is the head end. The lowest tension areas of the belt are located on the return side of the belt.

When the driven pulley is located at the tail end of the conveyor, the lowest tension areas of the belt then move to the upper side of the belt system (see figure 2). The highest tension area of the belt is still just before where the belt leaves the drive pulley.

The same principles hold true when the drive is located in the center of the belt. Again, the highest tensions are located just before the belt leaves the drive pulley (see figure 3). After the belt leaves the driven pulley, the belt tensions drop drastically. As the belt travels toward the driven pulley again, the tensions increase until it passes through the driven pulley and relaxes.

So, why do we care about these tensions? Even if a belt has been properly locked-out and tagged-out, these tensions may be present when the conveyor belt is shut down. For instance, if an inclined belt has an emergency shutdown with material on the belt, the weight of the material will cause the belt to roll backward, risking injury to the unwary employee. Properly installed brakes and backstops may help the roll-back situation. However, if employees are required to be on the conveyor or near pinch points on the conveyor, the belt must be physically restrained from moving under its own power. This is called blocking the conveyor belt. Do not rely on the backstops or brakes to prevent the belt from moving on its own. Lifting the gravity take-up may or may not release these tensions. Do not rely on this method.

Other potential hazards may not be so obvious. There have been instances when the belt is empty, and it has moved due to the internal tensions by the belt stretch. Blocked chutes, material trapped at load zones, material under the belt, or bad bearings may stall the belt enough to cause considerable belt tensions. It is extremely important that the list of employees described above be properly trained on where the tensions are low and where they are high. Many times our youngest, least-experienced employee is assigned the task of cleaning up around belt conveyors with little or no knowledge of the dangers the belt conveyor may have.

Martin Engineering recommends continuing the practice of lock out and tag out, but there are instances when the belt conveyor must be restrained from moving under its own power. A pre-job analysis should be performed prior to assigning employees to work around belt conveyors. This will determine if a block-out procedure is required.

Once the determination has been made that a block-out procedure is required, how can this be accomplished? Belt clamps, chains and come-alongs (ratchet lever hoists) can be used to physically restrain the belt by securing it to a substantial member of the conveyor's structure. Keep in mind that the belt may move in either direction based on the conditions present at the time of the work. Also keep in mind that these conditions can and do change as the work progresses.

Although a belt conveyor is locked-out and tagged-out, the risk of injury around belt conveyors is high. Physically restraining the belt during certain conditions will protect employees from the risk of injury or death.

Larry Goldbeck is manager of conveyor technology for Martin Engineering, and the originator and lead instructor for the company's workshop on operations and maintenance of clean and safe belt conveyors.

Pre-Job Analysis for Block-out

This pre-job analysis should ask:

• Will any work be performed in pinch-point areas? This includes all pulleys, all troughing rolls, return rolls, drive components, belt cleaners, and sealing systems along the load zone.
• Will the belt need to be cut? The weight of the belt alone can make the belt travel forward or backwards.
• Will several crews be working on the belt system at the same time? If so will the work performed by one crew affect the safety of another crew working someplace else along or around the belt?
• Have all personnel being assigned the task been properly trained on the potential stored energy that may exist in the belt system?
• Have all personnel been properly trained in the correct blocking procedures to prevent the belt from traveling under its own power?
• Is the correct blocking equipment available?