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Course 725 - Powered Industrial Truck Safety

Safety guides and audits to make your job as a safety professional easier

How a Forklift Works

Driving a Forklift: Different than Driving a Car

forklift driving

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.

1. A forklift has the steering wheels _____ so it can rotate the load into the correct position.

a. in the front end of the forklift
b. in the rear end of the forklift
c. locked by special mechanisms
d. in opposition to each other

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safety
design
Left: "Old design"
Right: "New design"
seat belts
Seat belts save lives!

Forklift Safety Measures

A backrest extension on the forks prevents part of the load from falling rearward into 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.

Overhead Guard

An overhead guard prevents an object on the forks or on a high rack from falling down 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.

Mast

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

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.

2. Which forklift component prevents part of the load from falling rearward into the operator?

a. Backrest extension
b. Overhead guards
c. Forklift masts
d. Operator restraint

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Principles of Lifting Loads

A forklift works on four very important principles that must be understood by all operators:

gsg image stability
Fulcrum Principle
  1. Fulcrum Principle
  2. Stability Triangle
  3. Center of Gravity
  4. Moment

Fulcrum Principle

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.

Stability Triangle

gsg image stability
Stability Triangle

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.

Center of Gravity (CG)

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.

3. Which of the following principles states that a forklift has two weights (load, forklift counterweight), which are balanced in a way similar to a playground seesaw?

a. Moment
b. Center of Gravity
c. Stability Triangle
d. Fulcrum Principle

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Load Composition

gsg image moment
4500 pounds loaded properly (top) will exceed the rated capacity of 4500 pounds if the box is positioned lengthwise (bottom).

The stated capacity of a forklift only applies to the load center indicated on the data plate. If the load is not centered at the specified position, the forklift's capacity will be reduced. Loads come in all shapes and sizes, not just symmetrical boxes. The load size, position, and weight distribution critically affect the forklift's capacity and the stability of the truck. Consider the following factors before engaging a load:

  • Weight, Size, and Position
  • Safe Load Capacity
  • Maximum Load Moment
  • Balance
  • Stability

Weight, Size, and Position

Load weight, weight distribution, size, shape, and position are key factors affecting the stability of the forklift. Forklifts are designed to carry a capacity load at a standard load center, commonly 24 inches. This means that the forklift’s capacity was determined as if the load were a cube whose weight is evenly distributed (i.e., whose center of gravity is exactly in the center of the cube) and which is resting on a standard pallet having dimensions of 48 inches by 48 inches.

load
This forklift has a capacity of 5,000 lbs at a 24 in. load center and 173 in. fork height. (see diagram).

With this standard load, the horizontal distance from the center of the load to the vertical part of the forks would be 24 inches. Of course, most loads are not perfectly shaped cubes having their center of gravity exactly in the middle of the cube. If it is irregularly shaped, has unbalanced weight distribution, or is not centered on the forks, the rated capacity may be reduced.

Capacity Plates

Forklifts have a capacity data plate to tell the user what loads are safe to lift. The data plate will indicate the maximum lifting capacity of the machine to the full extension height of the mast and a specified load center for a given configuration. 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 inches 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.

4. Most pallets are _____ if the weight of the load is evenly distributed.

a. 36" x 36" and have a 18" CG
b. 36" x 48" and have a 28" CG
c. 48" x 48" and have a 24" CG
d. 48" x 48" and have a 36" CG

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Safe Load Capacity

load
This forklift can carry 5,000 pounds at a 24 inches load center, but only 3,333 pounds at a 36 inches load center.

The forklift's capacity to safely lift a load without tipping is based on the forklift's rated capacity, the load center distance, and other factors.

You can use field calculations to estimate the forklift's reduced lifting capacity if manufacturer's instructions are not available. This calculation method will not produce exact load reduction figures, so use this method only as a guideline. The forklift manufacturer is the source of more precise information.

Assume a situation where a forklift truck that has a 5,000 pound capacity at a 24-inch load center needs to move a load whose center is 36 inches from the front face of the forks in the horizontal direction. The first thing to recognize is that the actual load center distance of 36 inches exceeds the standard load center distance of 24 inches on which the 5000 pound capacity is based, so the safe load capacity is actually less than 5000 pounds.

To estimate the truck's safe load capacity with a load that has a 36-inch load center, take the standard load center (24 inches) and divide it by the actual load center (36 inches), and then multiply the result by the forklift's stated capacity to get the new approximate safe load capacity:

(24 in/36 in) x 5,000 lb = 3,333 lb (approximate safe load capacity at maximum fork height)

Other Factors Affecting Capacity

There are many factors that affect the lifting capacity of a forklift. If any of the factors are changed, particularly the attachments on the forklift carriage or the load center, check the capacity data plate for accuracy to ensure safe load handling.

See the

Summary of factors that affect the lifting capacity of a forklift to safely lift a load include:

  • Make or Manufacturer
  • Model
  • Power Source
  • Battery Weight
  • Tire Type
  • Tire Size
  • Mast Lift Height
  • Mast Carriage Type
  • Attachments
  • Load Center of Gravity (CG or LC)

5. The forklift's capacity to safely lift a load is based on _____.

a. forklift center of gravity and rated capacity
b. load moment, center of gravity and the load center
c. rated capacity, load center distance, and other factors
d. manufacturer's recommendations and nature of the ground

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Raising the Load Can Create Instability

gsg photo stability
As the load is raised, it becomes possible for the forklift to fall to the side.

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.

  • This combined CG moves forward as the forklift is loaded.
  • The combined CG also moves as the load is moved and as the forklift travels over surfaces that are rough or inclined.

The combined CG can move outside the stability triangle if:

  • The load is picked up on the tip of the forks.
  • The load is tilted forward.
  • The load is tilted too far back when raised.
  • gsg image Load CD
    If the load CG moves outside the Safety Triangle, the forklift may tip forward.
  • The load is wide.
  • Forklift movement causes the center of gravity to shift.

These actions will have the following effects:

  • Tilting the load forward moves the combined CG toward the front axle.
  • Tilting the load back moves the combined CG toward the rear axle.
  • Driving across an inclined surface moves the combined CG toward the downhill side of the triangle.
  • Driving across rough or uneven surfaces moves the combined CG toward the rut or low side of the triangle.
  • Turning moves the combined CG toward the side now facing the original direction of travel.

6. What happens to the combined center of gravity (CG) when a forklift is driven across an inclined surface?

a. The CG does not move on the stability triangle
b. The CG moves toward the downhill side of the stability triangle
c. The CG moves toward the uphill side of the stability triangle
d. The CG moves toward the center of the stability triangle

Next Section

Driving on an Incline

gsg image stability
Keep the load uphill to maintain control of the forklift.
Click to Enlarge

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:

  • Make sure the load is stable and safely arranged on the forks.
  • Do not tilt the forks forward except when picking up or depositing a load.
  • Tilt the load backward only enough to stabilize the load.
  • Keep the load low just above the pavement with forks tilted back when traveling.
  • Cross railroad tracks diagonally when possible.
  • Enter elevators squarely.
  • Keep the load uphill when going up or down an incline.
  • Drive at a speed that will allow you to stop safely within the stability triangle.
  • Slow down on wet or slippery surfaces.
  • Slow down to make turns.
  • Avoid driving over loose objects or on surfaces with ruts and holes.

7. Keep the load _____ with forks tilted back when traveling.

a. low, just above the pavement
b. high over the traveling surface
c. raised to the mid point on the masts
d. raised at least 24 inches above the pavement

Check your Work

Read the material in each section to find the correct answer to each quiz question. After answering all the questions, click on the "Check Quiz Answers" button to grade your quiz and see your score. You will receive a message if you forgot to answer one of the questions. After clicking the button, the questions you missed will be listed below. You can correct any missed questions and check your answers again.

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