In a car or truck, the front wheels steer the vehicle. However, a forklift has the steering wheels in the rear end of the forklift so it can swing in a circle around the front wheels that support most of the load. This allows the forklift to rotate the load into the correct position.
The operator must check that there is room for the rear end to swing when making turns. This clearance can be maintained in your workplace by permanently marking aisles with painted lines or arranging storage racks in a way that creates obvious aisles for travel. However, these marked aisles will only be effective if you keep them clear of stored materials, which can gradually encroach as space is needed.
A forklift is not as responsive as a car when turning the steering wheel. Rear steering makes it difficult to stop a forklift quickly or swerve and still maintain control. As a result, it is important not to drive a forklift fast or round corners quickly.
A backrest extension on the forks prevents part of the load from falling rearward toward the operator. This is required when loads are lifted high and the type of load would allow all or part of it to fall to the rear under conditions such as acceleration, sudden stops or driving on an uneven surface.
An overhead guard prevents an object on the forks or on a high rack from falling onto the operator while picking or placing a load at elevation. Overhead guards are required on all forklifts that can lift a load above the operator unless conditions such as clearances would not allow the forklift to be used.
The guard is designed to be effective in deflecting small packages. They are not designed to withstand the impact from a full load.
The masts on newer forklifts are designed for traveling so that operators have a better view through the center in the direction of travel. The image to the right demonstrates improvements in forklift mast design.
Operator restraints will hold you in the seat if you strike an object or if the forklift overturns. Since 1992, forklift manufacturers have been required to equip new forklifts with operator restraints such as seat belts. Many forklift manufacturers offer restraint systems that can be retrofitted on older forklifts.
Failure to wear a seat belt can result in the operator being thrown outside the protective cage in the event of an overturn. If your forklift has a restraint, such as a seat belt or a lap bar, you must use it.
A forklift works on four very important principles that must be understood by all operators:
The Fulcrum Principle states that a forklift has two weights (load, counterweight), each located on the end of a beam which is balanced on a fulcrum, similar to a playground seesaw. A load is located on the forks and is balanced by the weight of the forklift with counterweight. The forks are supported by a fulcrum point located along the axle of the front wheels.
Operators must also understand the Stability Triangle. All forklifts have a stability triangle with the three sides of the triangle as shown in the illustration to the right. The sides of the triangle are formed by the center of each front wheel and the center of the rear wheel or at the center of the axle if there are two rear wheels.
Just imagine you're riding a tricycle. A tricycle is nothing more than a triangle on wheels. If you peddle around a corner too fast and shift your center of gravity outside the stability triangle, you'll tip over sideways. If you shift your center of gravity over the rear wheels, you are less likely to flip over backwards.
The Center of Gravity (CG) is the point at which the weight on both sides of the fulcrum is equal. The load on the forks is counterbalanced by the weight of the forklift body. Counterweight is built into it. The vehicle-load combination CG must be located inside of the stability triangle to prevent the forklift from tipping forward, falling sideways or dropping its load.
A moment is calculated in inch-pounds. It equals the distance (in inches) x weight (in pounds) from a fulcrum to each end of the beam.
There are two important moment calculations that determine the stability of the forklift load.
The forklift moment is the distance from the fulcrum at the center of the front wheel to the center of gravity (CG) of the unloaded forklift multiplied by (x) the capacity rating of the forklift.
Forklift moment = distance from fulcrum to CG x capacity of forklift.
The load moment is the distance from the fulcrum to the forklift CG of the load multiplied by (x) the weight of the load in pounds.
Load moment = distance from fulcrum to load CG x capacity of forklift.
Whether a forklift will safely carry a load or tip over can be determined by comparing the forklift moment and the load moment. To be safe, the load moment must be less than the forklift moment.
Forklifts have a capacity plate to tell the user what loads are safe to lift. If the plate says the capacity is 30,000 pounds or less then that capacity is rated for a load with a center of gravity 24” from the face of the forks. Most pallets are 48” x 48” and have a 24” CG if the weight of the load is evenly distributed. If the forklift capacity is greater than 30,000 pounds then the label will rate the load at a 36” or 48” center of gravity since larger forklifts usually lift physically larger loads.
Let’s take a look at an example that illustrates what we've been discussing. An evenly distributed 48" wide load on the forks has a center of gravity that is 24” from the face of the forks.
If the load weighs 4,000 pounds then the load moment will be (24" x 4,000 lb.) = 96,000 inch-pounds.
Using the example and capacity plate in the previous section, a forklift rated at 5,000 pounds at 24 inches would safely lift a load with a moment of up to (24" X 5,000 lb.) = 120,000 inch-pounds.
In this case, the load above would be safe to lift.
Forklift Moment = (24" X 5,000 LBS) = 120,000 inch-pounds
Load Moment= (24" X 4,000 LBS) = 96,000 inch-pounds
The load is safe to lift because load moment is less than forklift moment.
Let’s say the same 4,000 pound load was 66" wide, the load moment would then be 132,000 inch-pounds (33” X 4,000 lb.). Would the load be safe?
Forklift Moment = (24" X 5,000 LBS) = 120,000 inch-pounds
Load Moment= (33" X 4,000 LBS) = 132,000 inch-poundsIn this example, the load moment is greater than forklift moment, so the load is too heavy for the forklift and it would tip forward.
As the load is raised, it becomes possible for the forklift to fall to the side as well as tip forward because the combined CG might move outside the stability triangle. The operator must consider the CG of the forklift and load together.
The combined CG can move outside the stability triangle if:
These actions will have the following effects:
If you drive a forklift on an incline, you must keep the load on the uphill side. Otherwise, you may have no weight on the wheels that steer and can lose control. The load could also fall off or cause the forklift to tip.
Operator procedures that reduce the risk of overturn, collision or loss of the load use the following procedures:
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