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A loading dock or loading bay is an area of a building where goods vehicles (usually road or rail) are loaded and unloaded. They are commonly found on commercial and industrial buildings, and warehouses in particular.
Loading docks may be exterior, flush with the building envelope, or fully enclosed. They are part of a facility's service or utility infrastructure, typically providing direct access to staging areas, storage rooms, and freight elevators.[1]
- 5Components of Loading Docks
- 5.2Loading Dock Accessories
Basics[edit]
Loading Dock Design Standards
In order to facilitate material handling, loading docks may be equipped with the following:
- Bumpers – protect the dock from truck damage, may also be used as a guide by the truck driver when backing up.
- Dock leveler – a height-adjustable platform used as a bridge between dock and truck, can be operated via mechanical (spring), hydraulic, or air powered systems.
- Dock lift – serves same function as a leveler but operates similar to a scissor lift to allow for greater height adjustments.
- Dock seals or dock shelters – compressible foam blocks against which the truck presses when parked; seals are used at exterior truck bays in colder climates where this will provide protection from the weather.
- Truck or vehicle restraint system – a strong metal hook mounted to the base of the dock which will hook to the frame or bumper of a trailer and prevents it from rolling away during loading operations, can be operated via manual, hydraulic, or electrical systems; this system can replace or work in conjunction with wheel chocks.
- Dock light – a movable articulating light mounted inside the dock used to provide lighting inside the truck during loading operations.
- Indicator lights that show truck drivers when to back in or pull out.
- Loading dock software – provides a method for tracking and reporting on the loading dock activity.
- Side Shift, the truck dock is equipped with a side shift facility to enable accurate aligning of the roller deck with the truck. This facility includes two hydraulic cylinder assemblies, one at the front and one at the rear end of the dock and enables a left/right movement.
Warehouses that handle palletized freight use a dock leveler, so items can be easily loaded and unloaded using power moving equipment (e.g. a forklift). When a truck backs into such a loading dock, the bumpers on the loading dock and the bumpers on the trailer come into contact but may leave a gap; also, the warehouse floor and the trailer deck may not be horizontally aligned. In North America, the most common dock height is 48–52 inches (120–130 cm), though heights of up to 55 inches (140 cm) occur as well.[1] A dock leveler bridges the gap between a truck and a warehouse to safely accommodate a forklift.
Where it is not practical to install permanent concrete loading docks, or for temporary situations, then it is common to use a mobile version of the loading dock, often called a yard ramp.
Dangers[edit]
There can be very serious accidents on loading bays. One example is trailer creep (also known as trailer walk, or dock walk), which occurs when the lateral and vertical forces exerted each time a forklift truck enters and exits the trailer cause the trailer to slowly move away from the dock, resulting in separation from the dock leveler. Factors that affect trailer creep are the weight and speed of the lift truck and load, the gradient of the ground the trailer is parked on, the condition of the suspension, tire air pressures, the type of transition being used (dock levelers, dock boards), and whether the trailer has been disconnected or if it is still connected to the tractor. Trailer creep is often prevented by a vehicle restraint system.
Separation of a vehicle from the loading dock also occurs when a driver prematurely pulls away while the truck is still being loaded/unloaded. This issue is usually caused through a driver not correctly observing traffic lighting signals on a loading bay which prohibit the movement of the trailer. It is also important to ensure that drivers are adequately trained on the safe system of work they are expected to follow.
Loading zone[edit]
In different parts of the world, a section of a public or private road may be allocated for loading goods or persons, at specific or at all times. There are parking signs and/or road markings to warn motorists of parking regulations. These areas are known as loading zones or loading bays in many jurisdictions. They are generally monitored by parking inspectors, and vehicles found to be violating the rules can be towed or fined.[2][3]
Typical warehouse exterior showing loading docks
An interior loading dock at the New Research Building, Harvard Medical School
A reinforced concrete loading dock under construction
Safety[edit]
There are many ways to prevent an accident at a loading dock. Different forms of safety preparation include dock lights, back-up lights, trailer restraints, wheel chocks, Heavy Duty Rising Roller Barrier, safety gates and safety netting. There are many online courses for safety training, and it is very important to regularly audit equipment, making sure that it is correctly assembled and in good working order.
Components of Loading Docks[edit]
Loading Dock Levelers[edit]
A loading dock leveler is a piece of equipment which is typically mounted to the exterior dock face or recessed into a pit at a loading dock. Commonly referred to as “bridging the gap”, a dock leveler allows for the movement of industrial vehicles (e.g. Forklifts, Pallet-Jacks) between a building and a transport vehicle. Because of the different heights and sizes of many freight and semi-trucks, a dock leveler is an all-encompassing fixed solution[buzzword] to fit varying transports, capacities and budgets.
Basic Dock Leveler Components
Although there are many different types of dock levelers for,[4] many share common components:
- Dock: Area of a warehouse or building where loading/unloading of transport vehicles takes place
- Dock Pit: Recessed opening in the building’s floor which accommodates the pit-style dock leveler. Pits are commonly lined along the edges with reinforcing steel angles that are embedded in concrete
- Shim: Steel plates used to help level pit-mounted dock levelers. Shims may be placed under the frame structure and welded in place to provide a structural load path to the foundation of the building
- Frame: Supporting structure of a dock leveler
- Deck: The deck assembly is the most visual aspect of the loading dock leveler. Driven and walked over often, most decks have an anti-skid surface such as a tread plate to provide traction at the various working angles. The deck assembly pivots at the back end furthest from the transport vehicle (or, more commonly, the dock door opening)
- Lip: The lip assembly is pivotally attached to the deck assembly at the end closest to the transport. Often stored when the leveler is not in use, or sometimes used as barrier protection for an industrial vehicle, the lip pivots from a vertical stored position onto the bed of the transport vehicle’s floor. Lips are operated either manually, by pull chain, or hydraulically with an electric pump driving a piston to lift the plate and move the lip
- Toe Guard: Protective shield mounted flush to the side of a dock assembly in order to prevent toe and foot injuries while dock leveler is above dock
- Activation System: Providing the motive power of the dock leveler, these systems can be mechanical (springs) pneumatic (air bladders) or hydraulic. They may or may not require external power interfaces, depending on the type of leveler.
- Bumpers: Help to prevent the transport vehicle from contacting and damaging the exterior of the building, dock leveler or vehicle restraint. Commonly made from rubber, they range in size, projection and are based on vehicles serviced among other factors.
Applications of Dock Levelers
As the needs of consumers in the loading dock area have changed, so have the kinds of levelers and their applications. Although some feature special designs, many fall into the following categories:
- The most common type of dock leveler is the Pit Leveler which is found in a recessed concrete opening in a building’s concrete floor at the dock door. There are three major sub-categories:
- Mechanical Pit Levelers are the most common of Pit Levelers. It utilizes a mechanical spring system to raise the leveler and is commonly “upward biased” which means the spring is tending to force the leveler deck to rise up all of the time and a restraining device is preventing such motion. Although requiring no electrical power supply and being the least expensive up front, the mechanical pit leveler tends to be the most expensive to service and to maintain over their life.
- Air Pit Levelers employ a pneumatic bag system in order to raise and lower the leveler deck. It also requires an electrical power source, either at the dock or adjacent. Generally, Air Pit Levelers are moderately more expensive than mechanical levelers but with reduced service and maintenance requirements comparatively.
- Hydraulic Pit Leveler is one of the most versatile of the pit style levelers. Raised and lowered by a hydraulic cylinder, the hydraulic pit leveler comes in many configurations with various electrical phasing and sources. This pit leveler option gives the most flexibility with lower service and maintenance costs.
Additional Types of Dock Levelers
- A vertical leveler is a dock leveler that is stored in a vertical position, allowing you to store the leveler completely inside the building and close the dock door onto concrete floor instead of across the leveler. Vertical levelers provide optimal environmental control and are often used in food service applications or areas where wash down is a concern. They are typically pit or shelf-mounted and hydraulically operated.
- Rail Dock Levelers are a variation of the vertical leveler used to service rail cars. While some rail dock levelers are mounted in a pit, most are mounted on a sliding rail which allows them to move horizontally along the rail track either hydraulically or manually. Pit mounted are ideal for larger rail door openings and provide lower service and maintenance costs while rail mounted units can be moved to align with more narrow rail car opening. Rail Dock Levelers are typically hydraulically operated.
- An economical alternative to Pit and Vertical Levelers is an Edge of Dock (EOD) Leveler, which is usually mechanically operated but may also be pneumatically or hydraulically operated. Often found mounted on the exterior wall of a building with an integral bumper set, or pit mounted in certain applications, the Edge of Dock has a limited vertical operating range. It is geared toward operations where the transport vehicle bed is at, or near, the floor level of the building. This is commonly referred to as “dock level.” Edge of Dock Levelers may be considered an upgrade from portable dock boards as they are fixed to the dock and have some form of lift assistance.
- Top of Dock (TOD) Leveler is a version of an Edge of Dock Leveler which is typically mounted to the floor surface and the leading edge of the dock face of the building. Requiring minimal or no concrete to work, the working range of the Top of Dock Levelers is intended to provide primarily above-dock working range.
Alternatives to Dock Levelers
A flexible less-expensive alternative to a Loading Dock Leveler is a Dock Plate or Dock Board. Often more portable and not fixed to a dock or transport vehicle, dock plates and dock boards and metal ramps which help bridge the gap between dock and truck. Dock Plates are commonly made out of aluminum and suited for lighter loads, such as handcars or dollies. Dock Boards are generally made out of steel and suited for heavier loads such as motorized equipment or electric pallet jacks.
Dock Leveler Safety Requirements
[5] OSHA Walking-Working Surfaces standard, which includes below guidelines:
- 29 CFR 1910.30(a)(1) Portable and powered dock boards shall be strong enough to carry the load imposed on them
- 29 CFR 1910.30(a)(2) Portable dock boards shall be secured in position, either by being anchored or equipped with devices which prevent their slipping
- 29 CFR 1910.30(a)(3) Powered dock boards shall be designed and constructed in accordance with Commercial Standard CS202-56 (1961) 'Industrial Lifts and Hinged Loading Ramps' published by the U.S. Department of Commerce, which is incorporated by reference as specified in Sec. 1910.6.
- 29 CFR 1910.30(a)(4) Handholds, or other effective means, shall be provided on portable dockboards to permit safe handling
- 29 CFR 1910.30(a)(5) Positive protection shall be provided to prevent railroad cars from being moved while dockboards or bridge plates are in position
- 29 CFR 1910.178(k)(4) Positive protection shall be provided to prevent railroad cars from being moved while dockboards or bridge plates are in position.
Loading Dock Accessories[edit]
Loading dock accessories are components that can be added to a loading dock to improve communication, enhance safety, preserve energy, and more. These components can consist of lights, seals, barriers, signs, and protective units. Loading Dock Accessories can be added during the initial installation of loading dock equipment, or anytime thereafter.
Types of Loading Dock Accessories[edit]
Slots At A Loading Dock Drive
Loading dock accessories can be categorized into the following groups:
· Dock Lights
· Communication Lights
· Signage
· Safety Barriers
· Energy Saving Solutions[buzzword]
· Protective Solutions[buzzword]
Dock Lights
Loading Dock Lights, also known simply as “dock lights,” shine into freight trailers when loading or unloading cargo on the loading dock of a warehouse. They create a safer work environment and reduce accidental product damage by lighting the interior length of the trailer with a spot light bright enough to reach the back of the trailer. A dock light is composed of two parts: a light head and an arm. The light head is attached to the arm, which is jointed in one or two segments, and allows a range of motion for the light head to enter the trailer. In order to pull the light into place when needed, or collapsed it when not in use, the arm mounts on to a wall near the dock door opening. Dock lights come in multiple variations to fit specific material handling needs, their configurations range from long lasting heavy-duty to light weight and economical.
Communication Lights
Loading dock communication lights are traffic style lights housed together in a fixture with one red and one green light module. The lights are designed to alert truck drivers and loading dock personnel to the status of docking trucks at a loading dock. They are usually used as a set of two fixtures that visually “communicate” what is happening to the drivers outside and the personnel inside who cannot see each other. The two lights are attached on the loading dock wall both inside and outside of the dock door and are connected to each other electronically. The paired units are used as opposing stop-go signals.
When a truck is parked securely in the loading dock bay, the light they see on the outside of the building is red, indicating the truck should not move. While the light is red on the outside of the building, the inside light is green, indicating to warehouse personnel that it is safe to enter the trailer of the truck for the loading and unloading of cargo. When the work of the dock personnel is complete, the inside light is switched to red, communicating that it is no longer safe to enter the back of the trailer. This action simultaneously changes the light on the outside to turn green, indicating that it is safe for the truck to pull away.
Signage
Short phrases or instructions are made into metal or vinyl signage and can be used in conjunction with loading dock communication lights to clarify the visual meaning of the light. These signs are placed near the lights for the best visibility. Signs that are placed inside the warehouse are meant for loading dock personnel to read, while signs that are placed outside of the warehouse are meant for truck driversOftentimes outside signs are also written in reverse for drivers to read in their rear view mirrors.
Safety Barriers
As required by OSHA 1910.26,[6] elevated work platforms, such as a loading dock with an open or uninstalled overhead door, should have some form of a safety barrier in place to prevent pedestrians or forklift trucks from falling off the edge. Safety barriers can come in a variety of forms.
Leveler barrier lips can be installed on most pit-style loading dock levelers. When the leveler is stored, an extension of the lip is positioned several inches above the platform and acts as a wall to prevent forklifts from driving over the edge.
A chain, rail, or gate can also be equipped to the dock door opening to prevent pedestrians from falling off the edge of the platform. These can remain in place until a truck trailer is safely in position and dock personnel are ready to load/unload the trailer. These types of safety barriers can also help prevent forklift trucks from accidentally hitting the overhead door when closed.
Energy Saving Solutions
Outside air can infiltrate a facility through the openings around a loading dock. This can be from the dock leveler, dock pit, or edges of the overhead door. Energy Saving Solutions can be added to help preserve the interior atmosphere of the facility and keep energy costs down.
Energy saving solutions[buzzword] can be various types of seals, made of foam, rubber, brush, tape, or magnets. These seals can be applied to openings around the dock leveler, inside the dock pit, or to the bottom of an overhead door.
Protective Solutions
Protective Solutions[buzzword] are loading dock accessories designed to prevent damage to the overhead door, door track, dock control boxes, or other dock equipment.
When the overhead door at a loading dock is closed, protective solutions[buzzword] such as gates, rails, or metal arms can be installed in front of the door to prevent forklift trucks from coming in contact with the door. Metal guards can also be placed around the door track.
For loading dock control boxes, metal stanchions or concrete bollards can be positioned in various locations around the controllers, protecting them from forklift damage.
References[edit]
- ^ abSophia Greenbaum. 'Whole Building Design Guide: Loading Dock'. National Institute of Building Sciences. Retrieved 2008-02-26.
- ^[1]Archived November 11, 2013, at the Wayback Machine
- ^[2]Archived February 28, 2014, at the Wayback Machine
- ^various applications
- ^29 CFR 1910.30(a)
- ^'1910.26 - Dockboards. | Occupational Safety and Health Administration'. www.osha.gov. Retrieved 2019-07-23.
External links[edit]
- Media related to Loading bays at Wikimedia Commons