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Design Stability Testing for Forklifts

November 15, 2021

Forklifts or powered industrial trucks are used to move materials in many different industries. They can raise, lower, or move large heavy objects. These lift trucks are often used to move pallets full of crates or boxes as well. Before choosing any forklift for sale in Illinois, there are many considerations regarding design, stability, and safety, not to mention the proper function and installation of lift truck parts.

The Occupational Safety and Health Administration (OSHA) oversees the standards related to forklift operation and safety. It recognizes different types of trucks, each with different hazards to operators. Falling loads are more of a risk with a sit-down, counterbalanced high-lift rider truck. Tip over of a forklift is a danger. On the other hand, hand trucks don’t lift loads as high, but workers must be careful of lifts falling between the trailer and dock.

Stability is mainly affected by weight distribution, the truck’s weight, truck speed, wheelbase, wheel tread, the type of suspension, and tire and mast deflection under load. One can calculate stability values using data for similar types of trucks, but tilting platform tests verify a specific truck design is ready for production. However, manufacturers and users can adapt these tests to their requirements; so, for example, the vehicles acquired from forklift distributors can be accurately assessed.

OSHA Guidelines

Forklifts fall into different categories. In fact, OSHA recognizes seven different classes. Classes I through III include those with electric motors and span:

  • Class I: Electrically operated rider trucks
  • Class II: Electrically operated narrow aisle trucks
  • Class III: Electrically operated hand trucks or hand/rider vehicles

Other lift trucks are driven via an internal combustion engine, like a typical motor vehicle:

  • Class IV: Trucks with solid/cushion forklift tires
  • Class V: Lift trucks with pneumatic tires

The remaining two categories include:

  • Class VI: Tractors with electric and internal combustion engines
  • Class VII: Forklifts able to navigate rough terrain

Design stability is a concern for all of them. The typical forklift has a frame, power source, a hydraulically operated mast, and forks for lifting. The load backrest prevents loads from shifting backward, while an overhead guard protects operators should a load fall. In addition, each truck has a counterweight, which provides stability when lifting heavy objects.

Stability triangle is perhaps the most important factor in forklift design. Every lift truck has three points of contact. For a four-wheel truck, these include the two front wheels and the middle of the rear axle. Its counterpart in a three-wheel forklift is the rear steer wheel. The stability triangle is a concern, with the shifting weight of gravity when cargo is lifted.

Importance of Load Capacity

For any given forklift, one must know the maximum loading capacity to safely operate it. Operators with forklift jobs in Chicago must know this. Considering the truck’s center of mass, it’s possible to calculate whether the mass center would be out of the safety zone. OSHA explains the load capacity calculation, which any worker can do in the field.

Using the calculation described here, one can determine the safe load capacity by dividing the rated load center by the load center; this value is then multiplied by the stated capacity to arrive at a safe load weight capacity.

OSHA Standards

Some of the safety standards outlined by the administration include:

  • All trucks should have a label stating a nationally recognized testing laboratory has approved them.
  • Manufacturers must approve any modifications/additions that change a truck’s capacity and operational parameters before it is operated.
  • If front-end attachments are added post-factory, trucks should be marked with the approximate weight after modifications (at a maximum elevation with a laterally centered load).

Capacity is, therefore, a major safety factor, but OSHA also dictates the use of approved trucks in the presence of combustible atmospheres. There are 11 different designations for industrial trucks that identify which can be safely operated given the presence of ignitable compounds. These are outlined in the Occupational Safety and Health Standards for powered industrial trucks.

Other safety guidelines include:

  • Inspecting the vehicle for damage before each shift begins.
  • Reporting the damage and removing the truck from service until it is fixed.
  • Removing any truck from service that emits exhaust sparks or flames.
  • Decommissioning any truck that exceeds normal operating temperatures, until the overheating condition is resolved.
  • Not operating a truck with a fuel leak until it is repaired.
  • Engaging the brakes before dismounting the vehicle.
  • During refueling or recharging, ensuring there is proper ventilation and there is no smoke and checking there’s a fire extinguisher close by.
  • Determining the truck’s load capacity and center of gravity before operating it.

For more about requirements, recommended practices, operational inspections, removal from service, and maintenance, see this OSHA forklift fact sheet.

System of Active Stability (SAS): A Key Innovation in Toyota Forklift Safety

Lift truck tip-overs account for many of the injuries and fatalities involving these vehicles. Toyota engineers have developed the SAS to address the risks of side tipping and reduce the number of lift truck accidents. It does so by sensing instability and reacting to it before operators know anything is wrong, so tip-overs, falling cargo, and injuries can be avoided.

The stability enhancement system uses sensors to monitor a truck’s operations. It measures lateral (side-to-side) and longitudinal (front-to-back) instability. The SAS uses two systems—the Active Control Rear Stabilizer and Active Mast Function Controller. Designed to prevent forward tipping, the controller automatically restricts mast angle and speed, with a calculation of load height and weight, based on instability detected.

Various sensors monitor operations and factors that lead to instability (tracking load height/weight, travel speed, and yaw rate). When a computer detects an abnormality, it reacts, and SAS locks a hydraulic cylinder located on the truck’s rear axle. This changes the shape of the vehicle’s stability footprint—from triangular to rectangular—reducing the chances of lateral overturn.

Forward Tilt Angle Control: Senses load weight and mass height. If the angle becomes too great, operator control is overridden, preventing the truck from tilting forward.

Rear Tilt Speed Control: The same sensors are used to reduce the tilt speed of the mast. Therefore, the truck is less likely to tilt backward or spill cargo. An automatic fork leveling feature is included, as well, and adds safety when working with highly stacked loads.

Design Stability for Other Warehouse Vehicles

The design specifications of other types of equipment need to be considered as well. For example, pallet jacks each have rated weight capacities and dimensions. Those with adjustable forks require operators to consider the size of the load and center of gravity, as with a forklift.

Likewise, operating scissor lifts requires considering various parameters, such as weight, dimensions, and performance of the equipment. There are also scissor lifts under forklift operator cabins to provide a lifting mechanism. Both types of vehicles undergo design stability testing, including those via computer. Stress analysis is conducted using mesh elements, so the minimum and maximum strain, displacement, and stress can be calculated during part design.

Design stability is, therefore, often assessed and obtained via 3D modeling, using CAD software.

Forklift Training

Design stability testing is crucial, but lift trucks are only as safe as how they’re operated. On this front, forklift training is needed to ensure operators know how to handle the vehicle in all situations.

OSHA pallet jack regulations are similar to those of forklifts because both are covered under the category of powered industrial trucks. The training standard covers not just forklifts and pallet trucks, but also vehicles such as high lift, rider, straddle, reach rider, and motorized hand trucks, among others. Per OSHA guidelines, any employee must be trained to operate the specific powered industrial truck. However, the administration does not provide training; it writes standards and guidelines for employers to train truck operators.

The latest standard requires companies to ensure operators are physically able to drive a powered truck. The Americans with Disabilities Act limits how employers can impose physical qualifications on workers. Nonetheless, medical qualification requirements are permitted if the health or safety of others is a concern and reasonable efforts can’t be made to accommodate someone.

Importantly, separate operator training must be provided for each type of vehicle used. Even if a different type of attachment is added, the worker must receive instruction on safe use prior to operating the truck. Employee training must cover all operating instructions, precautions, and warnings that a vehicle’s operator’s manual includes, including operator restraint systems.

OSHA training requirements dictate forklift operators receive:

  • Formal instruction: Courses include lectures, discussions, and written materials, as well as videos and interactive computer learning materials.
  • Practical training: The trainer must provide demonstrations; the trainee is required to conduct exercises using the vehicle.
  • Evaluations: The trainee must conform to OSHA performance expectations for the safe operation of the vehicle.

Regardless of the type of truck, the operator is expected to be familiar with the operating instructions, controls and instrumentation, and engine and motor operation. Various operational parameters must be covered. However, it’s not only the truck that training should address. Workplace-related topics such as surface conditions, load composition, stacking and unstacking, pedestrian traffic, and hazardous locations are required topics. So are operating in narrow aisles, on ramps/sloped surfaces, and in environments where poor ventilation exists.

Passing the OSHA forklift test is essential to becoming an operator. However, it’s not the only training operators will experience in their careers. The agency also requires:

  • Refresher training: Ensures operators can use a forklift per its design specifications if they’ve been observed operating a vehicle unsafely. Refresher training is also required if operators have been in accidents or near-misses or have had evaluations showing they don’t operate trucks safely. Assignment to a different type of truck or changes in workplace conditions with safety considerations warrants additional training as well.
  • Certification: The operator’s name, date of training, evaluation date, and trainer’s or evaluator’s name must be included on training documentation.
  • Developing a training program: OSHA doesn’t offer a training program specifically, though employer-developed programs are expected to follow its standard. Guidelines can be found as part of the Compliance Assistance for the Powered Industrial Truck Operator Training Standards. However, the agency highlights hazard identification, supervision, operating procedures and policies, maintenance and repair procedures, facility design, and operational training and safety. It also encourages the careful selection of truck design, types, attachments, and modifications.

Forklift Design and Selection

The specifications of the forklift will tell you the weight capacity and operational parameters, such as lift speed, gradability, right angle stack, and travel speed. Some Toyota forklifts are rated to lift 12,000 pounds or more, and electric pallet jacks and stackers can approach capacities of 6,000 pounds. For even greater loads, Toyota Empty Container Handlers can transport loads of nearly 20,000 pounds. A hand pallet jack has a lower capacity but is still capable of handling 5,500-pound loads.

The choice versus the types of loads encountered is critical for all lift truck jobs. When vetting a new or used forklift, Chicago warehouses and other facilities have relied on Atlas Toyota Material Handling. Not only do we offer many types and categories of industrial lift vehicles, we offer many options for certification courses. The Toyota factory-certified-technician courses are offered at our Elk Grove Village and Bedford Park, IL locations, on an as-needed basis.

For information on each forklift for sale in Illinois and registration for training classes, browse our website or call 877-438-2719.


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