622 Forklift Competent Person

Principles of Lifting Loads

Moment and Stability

Moment is the product of the object's weight times the distance from a fixed point (usually the fulcrum). In the case of a forklift, the distance is measured from the point at which the truck will tip over to the object's line of action.

The line between the base of the front wheels is the forward tipping axis.

The distance is always measured perpendicular to the line of action. The weight of the forklift behind the front wheels creates a stabilizing forklift moment, while the load carried in front of the wheels creates an opposing load moment. Increasing either the weight of the load or its distance from the forward tipping axis increases the load moment.

Forward Stability

OSHA 1910.178 Appendix A explains that, for forward stability, the forklift moment must be equal to or greater than the load moment. If the load moment slightly exceeds the forklift moment, the rear wheels may lose contact with the floor, resulting in loss of steering control. If the load moment greatly exceeds the forklift moment, the forklift can tip forward.

The physical relationship can be expressed as:

Forklift moment = forklift weight × distance from forklift CG to forward tipping axis

Load moment = load weight × distance from forward tipping axis to load CG

Note: These formulas help explain why load weight and load position affect forklift stability. Operators, however, do not normally calculate these physical moments before handling a load.

Lateral Stability

OSHA 1910.178 Appendix A explains that, for lateral stability, the combined center of gravity (CG) of the forklift and load must remain within the lateral boundaries of the stability triangle. If the combined CG moves outside a lateral boundary, the forklift can tip sideways. Factors that can cause the combined CG to shift toward or beyond a lateral stability boundary include turning too sharply, traveling too fast while turning, operating on uneven or sloped surfaces, and carrying a load with an elevated or laterally offset CG.

The physical relationship can be expressed as:

Lateral stability is maintained when the line of action through the combined CG remains within the applicable lateral stability boundaries.

Lateral stability decreases as the combined CG moves closer to a lateral stability boundary.

Note: These relationships help explain why load position, load height, turns, slopes, and uneven surfaces can affect lateral stability. Operators do not normally calculate lateral stability before handling a load. Instead, they should operate the forklift according to the manufacturer's instructions, capacity information, and safe operating procedures.

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