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What You Need to Know About Forklift Stability

What You Need to Know About Forklift Safety



"If you can drive a car, you can drive a forklift" is one of the most dangerous pieces of advice ever given to novice forklift drivers. Aside from having a steering wheel, brakes and an accelerator in common, they are 2 completely different vehicles. Most importantly, forklifts are far less stable than cars and any forklift training program should include full instructions about forklift stability. This is what you need to know about forklift stability.


The Forklift Stability Triangle

One big difference between cars and forklifts is that cars are supported by 4 points of stability while powered industrial trucks (even those with 4 wheels) have only 3 stability points. Understanding the "stability triangle" is the first key to understanding how to safely operate a forklift.

forklift stability triangle

The fact that lift trucks carry their loads on forks in front of the tires is another reason why operating forklifts is nothing like driving a car. In the diagram above, notice how the center of gravity shifts from the middle of the carriage to the front axle when carrying a maximum load. Also note that the maximum load is "theoretical."  "Theoretically," all forklift operators would carry loads as specified in their manufacturer's manual. Forklifts are designed to carry evenly balanced, neatly stacked pallets placed at the rear of the forks as close to the mast as possible. Only if this is done can they safely carry a maximum load as specified in the manual and on their data plates. The diagram below shows how drastically load positioning on the forks can affect forklift stability.

forklift stability when carrying a load


If the lift truck is carrying a 4'X4' pallet at the rear of the forks, it can carry a maximum specified load (in this case, 4000 lbs.). Placing a 6' container on the forks shifts the weight 12" forward and reduces the load limit to just 2,666 lbs. The same weight displacement occurs when using attachments such as forklift fork extensions and forklift boom attachments. This is why OSHA regulations state that forklift attachments that can affect balance must have manufacturer's or a qualified engineer's approval and a data plate that states the maximum load the lift truck can carry when using the attachment.

Another factor that influences a forklift's center of balance is the height at which a load is being carried. The illustration below shows that an unloaded forklift's center of gravity (or balance point) is between the wheels and near the ground. As the load is lifted, the balance point moves upwards and outwards. This is why carrying loads close to the ground is vitally important. A load carried at height dramatically reduces a forklift's stability both longitudinally (forward and backwards) and laterally (sideways).

forklift stability at height

 

When it is necessary to drive a forklift on a sloping surface (such as a ramp), the load should be at a higher level than the carriage to avoid tipping forward. When driving up or down a gradient when carrying a load, travel in reverse. If the lift truck is not carrying a load, it is safer to drive forward because the counterbalance is at the rear of the vehicle.

operating a forklift safely on ramps

Forklifts are least stable laterally and roughly half of forklift fatalities occur when forklifts tip over sideways. The reasons why this happens are usually because:

  • The operator turns too sharply at too high a speed.
  • The operator attempts to turn on a sloping surface. This makes the forklift tilt sideways.
  • A load is off balance.

The danger of tipping sideways increases if the load is being carried at height instead of near the ground.


How to Operate a Loaded Forklift Safely


In order to operate a loaded forklift safely:

  1. Never exceed the carrying capacity of the forklift.
  2. Carry a balanced load at the rear of the forks.
  3. Carry the load with the mast tilted backwards.
  4. Carry the load as low to the ground as possible.
  5. Accelerate and brake smoothly.
  6. Turn slowly and smoothly.
  7. Never turn on a sloping surface.

Note: This article is for your information only and is not intended to replace OSHA approved forklift training materials. The illustrations and much of the information in this article comes from OSHA's Powered Industrial Trucks Load Composition page. More extensive information is available there.

Further Reading:

What You Need to Know about Forklift Load Capacities
Forklift Stability Basics
Forklift Accessories - It's a Matter of Balance
Determining Your Forklift Carrying Capacity