This explainer is for anyone studying for forklift operator certification. OSHA's powered industrial truck standard, 29 CFR 1910.178, lists "Vehicle capacity" and "Vehicle stability" among the truck-related topics of initial operator training in paragraph (l)(3)(i) (except in topics the employer can demonstrate are not applicable to safe operation of the truck in its workplace, as (l)(3) states), and "Composition of loads to be carried and load stability" among the workplace-related topics in (l)(3)(ii). The standard ends with Appendix A, "Stability of Powered Industrial Trucks", which explains what those words mean. This explainer reads that appendix as it stands in the eCFR. It does not describe a rule change.
Is Appendix A a requirement?
No. Its heading calls it a "Non-mandatory Appendix to Paragraph (l) of This Section", and 1910.178(l)(8) states: "Appendix A to this section provides non-mandatory guidance to assist employers in implementing this paragraph (l). This appendix does not add to, alter, or reduce the requirements of this section." The requirements themselves are in the paragraphs of 1910.178, for example (o)(2): "Only loads within the rated capacity of the truck shall be handled."
What do load center, moment and line of action mean?
Appendix A-1 gives definitions "to explain the principle of stability". Three of them carry most of the explanation:
- "Load center is the horizontal distance from the load's edge (or the fork's or other attachment's vertical face) to the line of action through the load's center of gravity."
- "Line of action is an imaginary vertical line through an object's center of gravity."
- "Moment is the product of the object's weight times the distance from a fixed point (usually the fulcrum)." For a powered industrial truck, the appendix says, the distance is measured from the point at which the truck will tip over to the object's line of action, always perpendicular to the line of action.
The same list defines the fulcrum as "the truck's axis of rotation when it tips over", longitudinal stability as "the truck's resistance to overturning forward or rearward" and lateral stability as "a truck's resistance to overturning sideways". A-2.1 names the factors that contribute to stability: "the vehicle's wheelbase, track, and height; the load's weight distribution; and the vehicle's counterweight location (if the vehicle is so equipped)."
What is the stability triangle?
A-4.1 explains that "Almost all counterbalanced powered industrial trucks have a three-point suspension system, that is, the vehicle is supported at three points. This is true even if the vehicle has four wheels." The steer axle is attached by a pivot pin in the axle's center, and "When the points are connected with imaginary lines, this three-point support forms a triangle called the stability triangle."
A-4.2 then explains: "When the vehicle's line of action, or load center, falls within the stability triangle, the vehicle is stable and will not tip over. However, when the vehicle's line of action or the vehicle/load combination falls outside the stability triangle, the vehicle is unstable and may tip over." The appendix refers to two figures for this; they are not reproduced here.
Why does a forklift tip forward?
A-3.1 explains the principle with a see-saw, and A-3.2 applies it to "The longitudinal stability of a counterbalanced powered industrial truck": if the load's weight times its distance from the front wheels is less than the vehicle's moment, "the system is balanced and will not tip forward". A-5.1 says the axis of rotation when a truck tips forward "is the front wheels' points of contact with the pavement", and that "if the load moment slightly exceeds the vehicle-moment, the truck will begin to tip forward, thereby causing the rear to lose contact with the floor or ground and resulting in loss of steering control. If the load-moment greatly exceeds the vehicle moment, the truck will tip forward."
How is the rated load center used to work out a safe load?
A-5.2 explains that "the truck manufacturer normally rates the truck at a maximum load at a given distance from the front face of the forks." It adds that trucks with a capacity of 30,000 pounds or less "are normally rated at a given load weight at a 24-inch load center", and larger trucks "at a 36- or 48-inch load center". Its advice to operators: "the operator should always check the data plate to determine the maximum allowable weight at the rated load center."
For unusual loads, such as loads longer than 48 inches or with an offset center of gravity, A-5.3 says "a maximum allowable load-moment should be calculated and used to determine whether a load can be safely handled", and gives this example: "if an operator is operating a 3000 pound capacity truck (with a 24-inch load center), the maximum allowable load-moment is 72,000 inch-pounds (3,000 times 24). If a load is 60 inches long (30-inch load center), then the maximum that this load can weigh is 2,400 pounds (72,000 divided by 30)."
What affects sideways (lateral) stability?
A-6.1 says lateral stability depends on where the line of action of the combined truck and load center of gravity falls relative to the stability triangle; when the truck is not loaded, "the truck's center of gravity location is the only factor to be considered". A-6.2 lists the factors: "the load's placement on the truck, the height of the load above the surface on which the vehicle is operating, and the vehicle's degree of lean."
Does movement change the picture?
Yes. A-7.1 says the weight transfer and shift in the center of gravity caused when the machine is "moving, braking, cornering, lifting, tilting, and lowering loads, etc., are important stability considerations." For a maximum load, A-7.2 suggests "the load should be carried at the lowest position possible, the truck should be accelerated slowly and evenly, and the forks should be tilted forward cautiously", and adds that "no precise rules can be formulated to cover all of these eventualities."
Where to practice
The training topics in 1910.178(l) are quoted in our forklift operator training study guide, and the load handling rules in 1910.178(o) are in the traveling and loading study guide and its practice test. goraedu does not train, evaluate or certify operators: under 1910.178(l) the employer must make sure each operator is trained and evaluated and must certify that they were.