Wear your seatbelt. Get an annual physical. Add to that good advice: Keep the plates in place on your shredder.

It is not just catastrophic accidents that cause trouble. Simply using improper posture when positioning an 80-pound screen can create problems. Most shredder manufacturers engineer to minimize the potential for injury. Unfortunately, human error can override even the best engineered system.

“Frequent safety training of the personnel working near or with the shredders is very important,” says Andreas Schwarz, president of Lindner America LLC, Raleigh, North Carolina. “This training should include the proper operation and procedures, but also the risks associated with handling the material that is being processed.”

The most common problem with safety is that operator positions tend to have a high turnover, and new operators are often just trained by other operators and not by factory technicians,” Schwarz continues. “This tends to dilute the knowledge level, hence, important information is lost.”

Terri Ward of SSI Shredding Systems Inc., Wilsonville, Oregon, says operator maintenance training is completed during the startup of the equipment. “Specific training regarding the safety features is explicitly carried out and includes lockout training to identify and secure all forms of energy and retained energy,” she says. “A comprehensive operation and maintenance manual addresses safety throughout the life of the shredder.”

Lack of space around the machine and poorly trained staff are common issues with shredder operations, says Dale Walker, technical engineer with Weima America Inc., Fort Mill, South Carolina.

Other shredder manufacturers like Mike LaGoe, director of project management for Vecoplan LLC, Archdale, North Carolina, says common sense is not a given. “You would assume it is observed but it’s not always,” he says.

LaGoe heads up the design, development and commissioning of Vecoplan systems that produce alternative fuel feedstock from waste and biomass. As an example, he says one should never try to clear a jam without the machine properly locked out.

Another no-no he says, “Never have a machine in a position that an operator can be above the height of the hopper.” LaGoe has seen people who wanted to put a shredder in front of a loading dock. “This would allow for the possibility of someone walking by to fall in,” he warns.

NONCATISTROPHIC DANGERS

While first thoughts of industrial accidents might turn to serious injuries, it is the minor injuries that create both insurance claims and days off from work.

Requiring operators to wear steel-toed boots is a good basic rule. If an unprotected operator drops a knife holder onto his foot, this slip could cause severe foot damage.

“Wearing proper protection gear to prevent cuts and eye injury is important,” Schwarz says. Depending on the material stream, respiration protection also might be necessary.

Cut hands and broken knuckles can occur on basic maintenance. When removing cutters, operators often turn the wrench in the direction of the rotor. When the bolt breaks free, the operator’s hand makes contact with an adjacent cutter.

Alternative fuel should not contain hazardous materials, but if it is municipal solid waste (MSW) based, it can contain biohazards such as used syringes or other medical related waste. For this reason, it is important to presort waste before it goes into a shredder.

“Highly flammable or explosive materials should never go into a shredder,” Schwarz says. “The shredder cannot avoid any materials from getting into it. This responsibility falls to the equipment in front of the shredder or the operator feeding it.”

Since it can never be 100 percent certain that a flammable substance will not get into a shredder, a fast, reliable and effective fire extinguishing system should be part of the operation. This can prevent a major fire and keep a fire from spreading to another part of the facility.

As far as Ward is concerned, “Safety starts with selecting the right shredding technology for the material or application and then properly maintaining the equipment.” She says low-speed, high-torque shredding technology is often safer than higher speed technology given its lower impact, less friction and dust and lower heat generation. These factors, she says “combine to reduce the opportunity for sparking, fire, explosion or material flying out of a hopper.”

Schwarz points to ergonomics to promote a safer environment. Lindner has a maintenance door that can be hydraulically opened. This allows the operator to stand right in front of the rotor for simple knife change.

Screens also need to be replaced on a regular basis, Schwarz says. “Lindner engineered a screen cradle that is lowered hydraulically so that the operator can pull the heavy screens out of the machine at hip level,” he says. “The patented screen system we have only requires the operator to tighten two screws per screen right in front of the operator. There is no need to crawl under the shredder to remove screens,” Schwarz says.

This keeps the operator out of the shredding material, which is waste and could contain hazardous materials—both biological and chemical. Maintenance and screen doors are electrically interlocked so that they cannot be opened while the rotor is turning or is under power.

Vecoplan’s dual-shaft shredders have two maintenance control boxes, located on each side of the shredder. They will only operate the rotor on their respective sides. “This gives the operator line of sight so they can be sure that there is no one near the rotor when they turn it,” LaGoe says. “It will also only work when the door on the other side is closed and the pressure lock is engaged.”

This ensures that there is no one in the machine on the other side that an operator would not be able to see.

Regular visits by technicians also are recommended. Schwarz suggests an annual visit by a factory technician—not only to help keep the machines in good shape, but also to help keep proper maintenance and safety procedures in place.

“Maintenance intervals and cleaning are crucial for a long shredder life and optimal, high output operation,” Walker agrees. Every application is different. Therefore, suggested schedules are created individually and noted in the machine manual. Typical maintenance topics are rotating/changing cutting knives and counter knives; hydraulic oil change; components check and so on.

Regular maintenance is vital because a shredder has lots of wear parts—not just its knives. “If a part is worn to the point that it should be replaced, it must be done. If that does not happen, it will wear to the point where it cannot be replaced anymore,” Schwarz says.

ENGINEERED SAFETY

There are multiple safety devices and practices that manufacturers use to insure the safe operation of their shredder systems. For example, Henry Gilliland, electrical engineer with Vecoplan LLC, points to the company’s radio-frequency identification (RFID) keyed locking door switches on the shredder rotor maintenance doors. These are designed to prevent tampering and unsafe operation of the equipment.

“On our V-ECO shredders we have designed a Safety Category 3, PLd safety control system,” Gilliland says. This control system uses a programmable safety relay to implement a cross monitored, dual-channel, redundant circuit. “Our goal is to reach the highest level of functional safety possible while still remaining an economical option for our customers,” he adds.

LaGoe notes that Velcoplan’s hoppers are designed with a minimum height of 40 inches to prevent fall-in. Access doors have limit switches that will stop the machine if opened.

“Every safety and operating training is based on the specific characteristics of the material being shredded,” Walker says. Its systems have an inspection flap/screen basket that can only be opened by pressing two buttons at the same time. That assures that no hands are on or inside the machine. The same concept applies with the manual rotor control.

Two security brackets secure the open inspection flap/screen basket from accidental closing. Emergency switch-offs are located at the machine and control cabinet. And the ram is secured during maintenance to prevent any movement.

Since wear depends on the material that is being processed, a shredder should be checked once a day to make sure everything is within normal parameters.

“Daily checking of wear items is a lot more reliable than using a fixed amount of operating hours as a guideline,” Schwarz says.

In waste-to-energy (WTE) operations, wear is rarely consistent. “If parts are not changed at the appropriate time, it will definitely affect the bottom line and will, without a doubt, increase the operating expense,” he adds.

Another possible issue? Drives might overheat when the drive system is poorly cooled. Weima generally offers air or water cooling. Vecoplan provides liquid cooled rotors where the application requires. Its temperature sensors will shut down an overheating system.

“A system that has overheated should be locked out and inspected prior to restarting,” LaGoe says. Often overheating is due to the rotor becoming wrapped with material.

Lindner’s shredders are designed not to overheat, but they can certainly jam. The company uses a torque-limiting clutch to stop the rotors in case of a jam. This not only prevents damage to the shredder, but also minimizes damage to the knives, according to the company.

All an operator has to do is open the maintenance door a few inches and pull out the trapped material. Since the door opens to the inside of the shredder, almost no material falls out of the machine, according to Lindner. This design eliminates the need to empty the entire shredder and deal with major cleanup.

LaGoe notes that keeping hazardous or unexpected materials out of the shredder is the responsibility of the operator feeding the system. “We also provide classification equipment downstream of the shredder,” he says. This includes waste screens, windsifters, eddy currents, magnetic separation and NIR (near infrared). So, he says, feedstock should not really impact safety.

Lock out/tag out (LOTO) should always be adhered to say manufacturers. A common safety error is trying to clean out a rotor when the machine is not locked out.

Vecoplan’s dual-shaft shredders have two maintenance boxes located on each side of the shredder. The shredders are equipped with safety control systems.

Weima shredders come with one main electrical switch. “With it you are able to switch off all components instantly,” Walker says.

“We recommend the standard and most up to date, code compliant procedures be used with our equipment,” Gilliland says. “All of our controls panels are capable of being locked out using standard LOTO pad locks.”

During the commissioning of Vecoplan equipment, each customer is walked through the proper LOTO of the machine, he adds.

“No maintenance or cleaning should be done on the equipment until the machine has been properly locked out and tagged out,” Gilliland emphasizes.

“The best thing that an operator can do for safety is having and following an approved lock out tag out procedure,” LaGoe says. “Employee training is key.”

On Vecoplan equipment, the control panel has a main breaker that powers the starters. “This breaker should be placed in the off position and all personnel doing work on the shredder should have a lock with their name on it on the breaker or in a gang box that has the key to the breaker lock,” LaGoe advises.

Of course what happens to the shredded material after it leaves the primary shredder also should not be ignored.

“I believe the most common mistake fuel processors make is focusing too much on the perceived safety hazards associated with shredding and not enough on what happens with material as it travels through downstream equipment and eventually into storage bunkers or stockpiles,” SSI’s Ward says. “A small piece of residual metal can create a spark in a secondary shredder that joins a large stockpile of engineered fuel that sits and smolders overnight.”

She adds, “Fire detection and suppression shouldn’t be left to shredder suppliers alone. A comprehensive, facility-wide system that covers the entire processing line and storage area is a wise investment to protect both personnel and property.”

While maintenance and cleaning is important important for the life of the equipment and productivity, more importantly, an accident can not only ruin a worker’s day, it can negatively affect an entire operation.

The author is a contributing editor to Renewable Energy from Waste based in the Cleveland area.