Some unsettling facts directly related to the new issues: • Most product damage occurs in the MTZ – the area from the loading dock drive approach into and across the shipping/receiving area. As a lift truck enters a trailer, fragile loads can be damaged due to dock shock and trailer drop. • The cost of damaged products or unsaleables is a major expense – and can actually exceed profits. Nearly 9 percent of all profit dollars are lost to damaged product, according to one report*. Dock shock and trailer drop are contributing to the problem. • The cost for repairs to a single dock seal as a result of trailer movement caused by trailer drop can be as high as $2,000. • A first-time back injury can cost as much as $10,000 when drugs, doctor visits and physical therapy are factored into the ailment. A Ohio State University report says the cost of severe back injuries that occur when a person is hurt over and over again can cost as much as $300,000. Dock shock is a source of vibration, which is known to pose a serious health risk – particularly to the spinal area. • Food Distributors International, the Food Marketing Institute, and Grocery Manufacturers of America: Unsaleable Products: 2000 Industry Benchmark Report

Joe Manone

If you think your loading dock is operating at peak efficiency and making progress toward a good safety record, it’s now time to re-think. Here’s why: two emerging dock issues – dock shock and trailer drop – threaten to adversely affect the profitability and safety of virtually any food manufacturing operation with a dock.      

Dock shock & trailer drop defined

Dock shock and trailer drop are terms coined by Rite-Hite to describe unsafe situations that occur during the process of unloading and loading semi-trailer trucks.
        Dock shock describes jarring that occurs when a lift truck (stand-up walkie or forklift) crosses between the warehouse floor and the trailer bed due to the bumps and gaps that exist on traditional dock levelers.
        Trailer drop describes vertical trailer bed movement or “drop” that occurs with the weight of lift trucks traveling in and out trailers due to trailer suspension systems. Trailer drop causes lift truck operators to experience significant jolts, which can lead to chronic back and neck injuries.
        Rite-Hite began to research the issues in 2001 when companies in the food industry, as well as others, expressed concerns about product damage and damage to dock equipment. Customers were also concerned about the adverse affects that jarring and jolting have on the health of forklift drivers.        

Jarring and jolting observed

At virtually any traditional loading dock configuration, lift truck operators encounter significant jarring and jolting as they transfer materials within a facility’s shipping/receiving/staging area and move in and out of trailers. This area is often referred to as the Material Transfer Zone (MTZ).
        As the company studied the issue it became clear that no single culprit is responsible for jarring and jolting, which is one of the primary reasons why the problem has gone unchecked. Instead, the dynamics of lift trucks (both forklifts and stand-up walkies) and their interaction with semi-trailer trucks are a key factor.
        This realization dictated the need to further analyze how dock levelers and vehicle restraints influence the situation. Dock levelers serve as a bridge between the dock floor and a semi-trailer. Vehicle restraints are devices that latch onto a trailer’s Rear-Impact Guard (RIG) to keep them from separating from the dock during loading/unloading. The restraints help to prevent a variety of catastrophic accidents.
        Research showed that a lift truck experiences significant jarring as it encounters bumps and gaps found on standard dock levelers during the loading and unloading process. Subsequent analyses showed conclusively that dock shock serves as a significant source of vibration.
        Similarly, research demonstrated that trailer beds move vertically, or “drop,” due to the weight of lift trucks traveling in and out of unstable trailers. Trailer drop is often severe when trailers with air-ride suspension systems are involved because the systems float up and down to maintain a consistent trailer height when loaded or unloaded. The situation causes lift truck operators to experience significant jolts.        

Problems created

Key problems observed are that jarring and jolting damage forklift loads, as well as dock equipment. Other problems are health-related.
        As a lift truck enters a trailer, fragile loads can be damaged, or fall off the pallet if not properly secured. Driving forklifts over steeply inclined levelers and bumpy terrain and into unstabilized trailers also accelerates wear on brakes, tires, transmission, steering axle and other components.
        The situation is also hard on dock levelers, seals, shelters and bumpers. Rite-Hite estimates the cost for repairs to a single dock seal as a result of trailer movement can be as high as $2,000. Productivity is also hampered because lift trucks need to slow down to avoid problems created by dock shock and trailer drop.
        On the safety front, further study showed that jarring and jolting within the MTZ is an issue that is closely tied to occupational vibration. There are two types of occupational vibration: segmental, such as hand-arm, and Whole-Body Vibration (WBV), which is transmitted to entire body through supporting surfaces, such as the legs when standing and the neck, lower back and buttocks when sitting.
        WBV exists in many environments. At the loading dock, WBV exposure has often been associated with forklifts. According to documented reports, back disorders are more prevalent and more severe in forklift operators exposed to WBV versus non-exposed operators.
        It’s also important to note that problems with vibration have not gone unchecked. The International Organization for Standardization (ISO) has issued various guidelines for vibration exposure levels. ISO2631/1, for example, outlines acceptable vibration standards. The European community has also taken notice. In 2002, the European Parliament and the Council of the European Union issued Directive 2002/44/EC to provide minimum health and safety requirements regarding the exposure of workers to the risk arising from vibration.
        Problems with lift truck jolting and jarring at the dock have also caught the attention of key industry organizations. The Occupational Health Clinics for Ontario Workers Inc. recommends that employees minimize the undulations of the surface over which lift trucks must travel as a way to reduce the effects of WBV. At the same time, the National Institute of Occupational Safety and Health (NIOSH) reports that shock (jarring and jolting) causes 36 percent of all head, neck, and back injuries associated with mobile equipment operators.        

Loading dock equipment: a contributing factor

For years, the forklift industry has worked to address problems associated with WBV. Just some of the forklift innovations designed to minimize vibration include pneumatic tires, contoured and pivoting seats, vibration-dampening engines, anti-vibration seats, and advanced seat-suspension systems and seat cushions. However, many studies indicate that loading dock equipment – not just forklifts – contribute to WBV and chronic injuries at the loading dock.
        Key factors often cited as being problematic within the MTZ are the warehouse floor surface, as well as undulations and sudden, unexpected movements or loads. Published reports show that the amount of vibration transmitted to lift truck operators is primarily a factor of how smooth the driving surface is.
        Leading researchers have also suggested that sudden changes in elevation, such as when entering/exiting a rail car, results in harmful high impact loads. These same reports suggest that special attention be paid to the design of entry points into trailers. Additionally, researchers recommend that bridges used to span the space between the dock and the trailer (or a rail car) be designed to minimize any shock, especially if the height of the dock is higher/lower than the floor of the trailer.
        The severity of dock shock and trailer drop varies from dock to dock yet there’s little doubt that dock shock and/or trailer drop exist at any facility that operates loading docks and lift truck equipment.        

Taking appropriate steps

The first step toward protection against dock shock and trailer drop is to realize the issues are relatively commonplace. It’s also worth noting important safety statistics. Namely, the National Safety Council recently reports that one-fourth of all U.S. workplace illnesses and injuries are back related. The American Society of Orthopedic Surgeons, meanwhile, reports that back injuries are the most costly medical condition in America. All told, it’s estimated that back injuries cost U.S. companies billions annually.
        Careful analysis of loading dock equipment is also recommended. A properly chosen system can help prevent dock shock and trailer drop. To address dock shock, some levelers feature a specially designed rear hinge to create a smooth transition between the warehouse floor and the leveler. These same levelers also use a re-designed crown on the front of the leveler to smooth out the transition from the leveler to the truck bed.
             A new category of vehicle restraints is also available to specifically address trailer drop. The restraint supports the rear of the trailer during the loading and unloading process, which minimizes both vertical and horizontal trailer movement.
        Another worthwhile consideration is to have a trained loading dock equipment representative inspect your dock situation to assess the severity of dock shock and trailer drop and the risk involved.

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Rite-Hite Corp., 8900 N. Arbon Dr., Milwaukee, WI 53223.

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