March/April 1994
To the dismay of auto shredder operators, explosions do happen, but there are ways to minimize their frequency and impact. Here, equipment manufacturers and operators offer some such ideas.
By Sarah Hart Winchester
Sarah Hart Winchester is a Duluth, Ga.-based writer.
Pop, Pop, BOOM!
The sound of the exploding automobile shredder reverberates like thunder throughout the scrap plant and into neighboring areas. Flames lick the sky, smoke fills the air, and sirens wail in the distance--a sign that the fire department is on its way.
Such potentially dangerous scenarios are far from uncommon. In fact, most shredder operators average one shredder explosion per month, according to industry sources. Fortunately, these explosions usually do not harm employees or equipment, or even cause significant downtime. “Over the past five to seven years, shredder explosions have become more of a nuisance problem than a question of serious danger,” says Gunn Phillips, sales director for Lindemann Recycling Equipment Inc. (Charlotte, N.C.).
Still, even minor explosions can become a sticky publicity problem, particularly if nearby businesses or residences are affected by the noise. What may seem to the recycler like an undesirable but fairly routine part of doing business may actually be perceived by outsiders as something close to a crisis. "The scare factor is significant, especially in densely populated areas," says Dan Smith, a manager at Yorke Doliner and Co. (Ansin, Fla.). "People don't like to hear explosions."
Practicing Prevention
While shredder explosions may be inevitable, manufacturers have worked to lessen their severity through machines with such design features as explosion panels, carefully placed vents, and rugged palls. Shredder operators, meanwhile, can take steps on their own to prevent explosions and reduce the impact of those that do occur.
One of the most critical of those steps, experts agree, is a preshredding inspection program designed to keep potential explosion culprits in the scrap stream out of the shredder. "We have a rigid preshredding inspection procedure involving four people," says Bob Wilson, president of Shredders Inc. (Birmingham, Ala.). "They're instructed to pop every hood and pop every trunk, because it's usually something left in a car that will cause an explosion." The number-one cause of explosions, in fact, is gas tanks left inflattened automobiles, but undetonated air bags, sealed propane tanks, cans of paint and paint thinner, and even dry toner remaining in a copy machine are named as problems too. "There is no shredder explosion that is not precipitated by flammable or explosive material going into the machine," explains Scott Newell, president of Newell Industries Inc. (San Antonio).
Operators add that the success of any inspection program relies on management. If management makes the prevention of shredder explosions a priority, and conveys its commitment to workers, the inspection program is much more likely to be a success, they say. It’s also beneficial to put an emphasis on educating customers about unacceptable materials. "We give people handouts reminding them of our specifications and of what we take and don't take," notes Wilson. "We also have lots of signs posted in the area."
Another apparent key to preventing explosions is to anticipate when they're most likely to occur so certain precautions can he taken. "Most explosions seem to occur the first thing in the morning," notes Dennis Schreck, district manager of Universal Engineering (Cedar Rapids, Iowa.). The shredders are typically opened at night for maintenance, he explains, adding, "When they're closed again, a lot of dust is knocked loose and it floats around in the shredder." The best way to cut down on morning shredder explosions, says Schreck, is to flood the machine with water during the first five to 10 minutes of operation to eliminate the dust.
In addition, one manufacturer believes that the speed at which a shredder is operated can help reduce the number of explosions. According to Jim Schwartz, vice president of engineering for Texas Shredder Inc. (San Antonio), running the shredder slowly may reduce the chance of an explosion, as a slower shredder operating speed generates less heat and consequently less friction. "The less friction, the less chance there is for an explosion," says Schwartz. "Whether a shredder is dry/damp or wet, I'd recommend running it as slowly as possible." He notes, however, that this may require purchasing a motor that can operate at slower speeds, but advises customers not to make that significant investment until it’s time to replace the motor anyway.
While Schwartz asserts that many European operators have been employing this slow-down strategy to prevent explosions for the past 25 years, there are skeptics in the United States. "No matter how slowly you run the shredder, you will still have friction and beat," observes Smith.
Wet Down Your Shredder?
It may also be possible to minimize explosions by selecting equipment based on the wet shredder vs. dry shredder debate. But first a clarification: Most shredders in the United States are dry or dry/damp shredders, though the terminology can be misleading as most dry or dry/damp shredders use some water. Manufacturers estimate that wet shredders account for only 20 to 30 percent of shredders in use here.
Many scrap recyclers believe that wet shredders experience fewer explosions, for the simple reason that the water inside the equipment creates an environment less hospitable to friction, heat, and fire. "We have two wets and one dry, and you get away with a multitude of sins in the wet shredder you don't get away with in the dry," maintains a Midwestern-based shredder industry source. "The introduction of water prevents and minimizes explosions, and we have fewer in the wet than we do in the dry."
Detractors say wet shredder systems can be more expensive to install because they may require a special foundation or additional structures. They also fault wet shredders for creating muddy conditions, requiring a dewatering press or some other method for drying the fluff, and creating a heavier residue-thus raising disposal costs in communities that charge by weight rather than by volume.
In the end, however, most operators say, choosing between a wet and a dry shredder really comes down to personal preference. "It's almost a matter of do you prefer a Ford or a Chevrolet," remarks Wilson. "It's kind of like the old 'less filling/tastes great' ad," laughs another operator. "There are testimonials to both sides."
Recovering From Explosions
Since it's more of a question of when, rather than if, a shredder will explode, an organized recovery plan can be just as important as prevention measures.
"Our first and foremost action after an explosion is to make sure our personnel are OK," offers Smith. "Then we make sure the machine is shut down, and we place any residue that's in the processing system into a separate area to make sure it's not smoldering." The company sprays water on the residue if necessary.
If any of the scrap in the shredder is on fire, Newell advises continuing to operate the shredder while fighting the fire until the scrap is shredded and the fire extinguished. "If there's a fire in the shredder, the last thing you want to do is burn up your conveyer belt," adds Schreck. "The general rule of thumb is to keep shredding, if possible, and flood the shredder with water." That means keeping fire-fighting equipment on hand. "We recommend having water available on the first transfer conveyer," Schwartz advises. By doing so, operators rarely need to call the fire department, they say, and shredder makers agree. "There's no need to call the fire department," says Schwartz, "unless it is a very severe explosion and there is danger of fire to ancillary equipment or the surrounding structure." Luckily, Newell adds, fires caused by shredder explosions generally don't spread far from the shredder, and they don't last long.
Once any emergencies are dealt with, manufacturers and operators stress, recovery should proceed by discussing the explosion with plant employees and using the experience to help cut down on future explosions. One operations manager explains his company's strategy in these regards: "We do an investigation after an explosion, asking our employees what we were running at the time of the explosion, what color the smoke was, and if they smelled anything. After one of our larger explosions, we thought we smelled sulphur, and we believe we shredded something with gunpowder. Another one was a propane explosion." Further discussions with the crew emphasize the severity of explosions and encourage interaction on how everyone in the plant can work together to prevent future explosions. "After an explosion, we tell our employees that inspection is 99.9 percent of prevention," he says, "and they're interested because they're the ones at risk."
Tactful Fingerpointing
After recyclers have identified the cause of an explosion, it's useful to link it to a specific supplier, if possible, in order to prevent future problems. "One part of inspecting the scrap closely is knowing which supplier's cars you're shredding at any given time," says Schwartz. "As much as possible, you should keep the cars segregated and color-code them with paint so you're certain you're shredding a certain supplier's cars."
Linking a specific supplier to scrap that exploded is not only a way for recyclers to negotiate a lower price for the scrap, but also allows them to discuss ways to ensure the quality and consistency of any scrap purchased in the future.
The most challenging aspect of negotiating with suppliers, says a shredder operator, is in striking the tight balance. If recyclers don't take a firm stance with suppliers that carelessly sell them scrap containing volatile substances such as gas tanks, paint thinner, and propane, they will experience a great number of explosions. On the other hand, taking a hard-line approach can damage or even sever an important business relationship, and the supplier will simply sell to a competitor.
Still, despite the difficulties involved in asking suppliers to accept responsibility for explosive loads of scrap, it makes sense to get serious with the source of frequent explosions, regardless of the potential impact on the business relationship. "If you put a problem into your shredder," says Schreck, “you're going to get a problem out."
In fact, while shredder operators may find these problems inevitable on occasion, industry experts stress the importance of taking such positive steps toward prevention and recovery. Through careful preshredding inspection and responsible postexplosion procedures, shredder operators can ensure the safety of their workers and the longevity of their equipment.
Shredder Safety Tips
For many people, the first thing that comes to mind when discussing shredder safety is preventing shredder explosions. Although explosions are the most vivid and attention-grabbing potential hazard in the plant, it’s the more commonplace safety issues that generally pose a greater threat. “I’m unaware of anyone being injured in a shredder explosion,” says Newell, “but I’m aware of far too many people being injured on conveyors.”
So here are some tips experienced operators and manufacturers offer for avoiding shredder accidents:
Turn the shredder as well as its auxiliary equipment off before servicing or cleaning. “The area of most concern in a shredding system is the conveyor,” Schwartz maintains. “There are more people injured there than anywhere else.” As an example, he notes, workers may attempt to save time by cleaning out the pinch points on the conveyors while the system is running. If their clothing gets caught on the pinch points, they can be severely injured.”
Develop a no-access zone around the shredder when it’s in operation. “When the shredder is running, the area should be off-limits,” Schreck stresses. “I’ve seen some customers build 10- or 12-foot rubber curtain walls to keep people out during operation.”
Be sure that workers understand how to use the shredder’s safety features, such as the electrical lockout that prevents workers from starting the shredder accidentally during maintenance and repair and emergency stop controls that can override the main controls. Also, the experts advise, install emergency controls near workers’ areas and post signs indicating their location.
Install guards on various points of the shredder to protect operators from any flying metal. “It’s important to keep the manufacturer’s safety shield in place and in good condition,” advises Schwartz. “Every time the feed rolls are raised, some scrap can get out of the shredder, and there’s an opportunity for metal to come shooting out.” In addition, in areas where conveyors are placed over walkways, cover the underside of the conveyor to prevent material from injuring workers below.
Keep the explosion panels in good working order. “Since the explosion flaps are like big rubber doors, they can burn, and it’s important they be replaced,” says Schreck. “Sometimes workers in a hurry will replace the rubber flaps with metal or plywood, but that’s a mistake.”
Ensure that operators never climb in or under the shredder while it is running.
Forbid employees from attempting to repair the shredder on their own.•
To the dismay of auto shredder operators, explosions do happen, but there are ways to minimize their frequency and impact. Here, equipment manufacturers and operators offer some such ideas.