Just-in-time logistics, steady product flow management and the never-ending drive for maximum efficiency have intensified the attention given to loading dock design. A multitude of fluctuating variables must be considered when coordinating dock heights and door sizes, as well as selecting the proper loading dock equipment.
Productivity and Efficiency
A dock area should be flexible enough to accommodate any vehicle. When determining proper loading dock height, decide which vehicles will be serviced at the facility most frequently and then make sure a majority of the docks accommodate this height. The most common dock height is between 48 to 52 inches. Vehicle beds may range from 30 to 62 inches in height.
The height differential between the loading dock and the trailer bed is an important consideration. It helps to guarantee smooth product transfer from vehicle to building and vice versa. There are three basic ways to accommodate the height differential: dock levelers, truck levelers and elevating docks.
The dock leveler accommodates differences between the loading dock height and the truck/trailer bed height. Longer dock levelers will accommodate greater height differences. The longer deck reduces the angle of incline/decline that occurs when the dock leveler is positioned. Figure 1 shows a typical installation of a hydraulic dock leveler. Improper applications and use of dock levelers where there is a severe grade difference can lead to damage and premature failure of both the dock levelers and the material handling equipment in use, such as forklift trucks. Customized dock levelers can be made to suit unique applications and offset the height difference.
Tailgate trucks are the most difficult to accommodate at a standard loading dock. Before loading/unloading, the tailgate must be lowered. Then, it may be impossible to back the trailer close enough to the dock before impacting the dock wall. (Note: Some powered tailgates retract below the truck. These trucks can be positioned and serviced at normal dock areas.) The solution to this situation is to use a self-supporting pit design (Figure 2). The dock leveler pit is poured three-sided, open to grade level. The open pit design also facilitates the easy removal of debris buildup from under the leveler.
When efficiency must be maintained at all docks, installation of a truck leveler is recommended. This allows the operator to adjust the height of the trailer. Two standard designs are available: pit-mounted or surface-mounted. Once the trailer bed is positioned at the loading dock floor height, the truck leveler can be cycled, and loading/unloading can be carried out safely and efficiently. Truck levelers can also be equipped with deck-mounted vehicle restraints for increased safety. In addition, electric activation allows safety interlock features to other loading dock equipment.
Surface-mounted truck levelers allow up to 30 inches above level positioning. They are mounted on a concrete base in front of the dock face and can be relocated to another dock area if necessary. Side-mount hydraulic cylinders or mechanical screws can be used to position the deck assembly. The length of the truck leveler and the mounting position are essential factors to consider. Improper consideration can cause unsafe loading conditions or damage the loading dock equipment.
When non-hydraulic or sustained load positioning applications are required, screw-style actuation is available (for surface and pit-mount units). Pit-mounted units offer the greatest flexibility by accommodating height variations above and below the dock. They are also well suited for applications with close door spacing, since the cylinders or screws are mounted in the pit, directly under the deck assembly. Figure 3 shows a pit-mount truck leveler in combination with a dock leveler.
A simple and flexible means of accommodating vehicle height variations is the installation of a hydraulic elevating dock (Figure 4). Elevating docks can be in virtually any size and capacity. They can service trucks at any height and offer access to ground level for fork trucks. Pit-mounted elevating docks are capable of height adjustments between zero inches and 60 inches. The only disadvantage is they must cycle up and down every trip into and out of the trailer. Greater efficiency can be achieved by using an elevating dock wide enough to allow side-by-side pallet loading.
Many elevating docks are set into a three-sided pit, recessed into the dock wall. They can also be mounted at the face of the dock, but may be an unwanted obstruction. Elevating docks are also available in a low-profile design to facilitate ground-to-truck loading/unloading without the need of a pit. This is particularly beneficial when dealing with a hand pallet truck and low-volume product movement.
Elevating docks must be raised and lowered for each product transfer from dock to trailer; consequently, they are less efficient than dock levelers.
Aiding in Climate Control
Dock seals or shelters can be installed to maintain the internal climate of the facility, as well as protect against product damage. Benefits include:
1. Efficiency: Seals and shelters improve the loading dock environment. Worker morale and productivity are related directly to the workplace environment and its safety.
2. Return on Investment: A seal/shelter can pay for itself in months with the cost savings it generates in energy retention.
3. Merchandise Protection: Protects products against damaging heat, cold, rain, snow and wind. Minimizes vermin entry.
4. Safety: Eliminates rain, ice and snow from loading areas, improving dock safety.
5. Energy Savings: Reduces heating and cooling costs by maintaining interior temperature control.
6. Security: Helps eliminate pilferage goods and unauthorized entry into loading/unloading areas.
7. Increased Storage Capabilities: Positioned trailers at loading docks can become secure, temperature-controlled extensions of the facility.
Dock shelters are applicable to virtually any size door,  but are generally installed on doors from nine feet by nine feet to 12 feet by 12 feet.
A Safe Workplace
Warehousing and distribution are rated among the most hazardous of all industries. A single accident can total as much as one million dollars in insurance, downtime and liability costs. Several styles of loading dock safety systems are readily available. They are designed to accommodate various dock configurations to minimize unscheduled truck departure, trailer theft, collapsing landing gear, trailer creep and dock leveler free fall. Incorporating one or a combination of the following devices will reduce the potential of a loading dock accident.
Vehicle restraints are designed to hold the trailer in place by locking onto the trailer�s rear impact guard, commonly referred to as the ICC (Interstate Commerce Commission) bumper. The ICC bumper extends down from the rear of the truck/trailer. This prevents premature vehicle departure. A two-way communication system is usually part of a vehicle restraint installation. In January 1998, an updated Federal Motor Vehicle Safety Standard came into effect establishing standards for the strength and position of ICC bumpers on new semitrailers.
A two-way, high visibility communication light system indicates to the operator that a truck is in position and tells the driver loading/unloading is still in progress. The high visibility traffic-style indicator light mounts to the exterior wall along with the warning signs. They are positioned so the truck driver can see them easily and clearly. The light system should be interlocked to a vehicle restraint for increased safety.
The hook restraint is one of the most effective forms of a vehicle restraint safety system. It can locate and hold almost any truck trailer, providing it has an ICC bumper. It is also the best method of theft protection for vehicles positioned at the loading dock. A two-way communication system is incorporated with the hook restraint.
The manual wheel chock is the oldest form of safety device to guard against premature truck departure and trailer creep. Wheel chocks are tapered blocks usually with a length of chain attached. Wheel chocks are placed in front of the vehicle wheels once the vehicle is positioned. Installation of powered wheel chocks assures vehicles are safely held in position even if they do not have an ICC bumper. The wheel chocks are normally embedded in the approach area of the dock and do not create an obstruction of any kind. Some styles will mount above surface level. When a vehicle is positioned, the chock is activated. It is powered toward the dock until it makes contact with the vehicle wheels and then stops. This prevents premature vehicle departure and trailer creep. A two-way communication system is incorporated with the wheel chock.
For facilities that service vehicles without ICC bumpers, powered wheel chocks with a two-way communication system should be considered. However, there are many disadvantages to using manual wheel chocks including: personnel may find them inconvenient and not use them; if the chocks are stolen, the trailer cannot be secured; manual positioning of chocks can take a lot of time/labor; and wheel chocks may not hold the vehicle in slippery conditions.
Another type of device, hydraulic dock levelers are downward biased by design. When the trailer pulls away, the leveler deck and lip assembly will lower to the lowest operating position below the dock surface. By equipping the leveler with �Auto Return,� the unit will return automatically to the stored position after the truck departs. This automatically eliminates the potential of a recess that can be present if the leveler is below the dock surface.
A safety barrier can be installed at virtually any loading bay door. Safety barriers protect against accidental injury and damage due to fork trucks going over the edge of the loading dock or impacting the overhead door.
As stated previously, every loading dock is characterized by its own special requirements. Consultation with a qualified loading dock or material handling supplier will help you identify which solutions best meet your requirements.
Phil Corvetti is vice president of Pentalift Equipment Corporation. You can request a copy of Pentalift�s Loading Dock Design Guide by contacting Phil at 519-763-3625 ext. 250, faxing 519-763-2894 or e-mailing dockdesign@pentalift.com.