Skip Navigation

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.

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 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.

Overhead Guard

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.

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.

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.

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 can safely lift 5,000 lbs. 173 in. high with a center of gravity 24 horizontal inches from the front face of the forks.

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 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.

Safe Load Capacity

load
Improperly distributed loads may tip the forklift if the operator exceeds the stated capacity of the truck. This forklift can carry 4,000 pounds at a 24 inches load center, but only 2,666 pounds at a 36 inches load center.

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 handle 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 at a 36-inch load center, take the rated load center and divide it by the actual load center. Then multiply this number by the stated capacity to get the new approximate safe load capacity:

24 in/36 in x 5,000 lb = 2,666 lb (approximate safe load capacity)

Maximum Load Moment

The maximum Load Moment is the product of the object's weight multiplied by the object’s distance from the fulcrum, which is a fixed point that acts as the pivot point. On a sit-down counterbalanced forklift, the fulcrum or pivot point is the axle of the front wheels. It is this product, or Load Moment, which determines how much overturning force is being applied to the forklift.

Load Moment = Weight X Distance

Because the overturning force depends on both the weight of the load and the load’s distance from the pivot point, a forklift’s capacity is always stated in terms of both: the load’s weight and its load center distance.

For example, if a forklift’s capacity as stated on its data plate is "3,000 pounds at a 24 inch load center," this means that the Load Moment cannot safely exceed 72,000 inch-pounds (24-in. x 3,000 lb = 72,000 inch-pounds.)

If the load center distance for the actual load is greater than the standard 24 inches, the only way to keep the Load Moment from exceeding 72,000 inch-pounds is to reduce weight of the load. The easiest way to determine the maximum load when the load center distance is greater than the distance stated on the data plate is to divide the maximum Load Moment by the actual load center distance. For example:

If a load is 60 inches long (30-inch load center) then the maximum that this load can weigh is:

72,000 inch-pounds / 30 in-load center = 2,400 pounds

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.

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.

Instructions

Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

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

2. Which of the following is the point at which the weight on both sides of the fulcrum is equal?

3. Which of the following equals the distance from the fulcrum to the CG of the load multiplied by (x) the weight of the load in pounds?

4. The forklift combined center of gravity (CG) will not move out of the stability triangle if _____.

5. Turning moves the combined center of gravity (CG) _____.


Have a great day!

Important! You will receive an "error" message unless all questions are answered.