Are you familiar with the National Institute of Occupational Safety and Health (NIOSH) lifting equation? The lifting equation provides valuable guidelines for performing and evaluating two-handed manual lifting tasks in the workplace. It defines the recommended weight limit as the weight of a load that can be lifted by a healthy worker repetitively over an extended period of time (such as an 8-hour shift) without risk of developing musculoskeletal trauma injuries such as lower back pain.
Under ideal conditions, the maximum weight that the average healthy worker can safely lift with two hands is 51 pounds. Of course, in the real world, conditions are never ideal, and the physical ability of each individual worker will also limit maximum lifting weights.
NIOSH identifies a number of lifting conditions that must be taken into account in computing the recommended manual weight limit for a particular task, including:
- Horizontal and vertical location of the load. The optimal horizontal and vertical lifting position is directly in front of the worker, close to the torso, and between the knees and shoulders, with optimal height being hip height.
- Distance the load must be moved. Obviously, shorter distances place less strain on workers.
- Balance of the load. An asymmetrical load places unequal stress on the worker’s body, requiring greater effort to balance the load during transport. The more symmetrically balanced a load, the easier it will be for a worker to carry.
- Frequency of the lift. The more repetitions required, the greater the cumulative stress placed on the worker’s body. The amount of time between repetitions is also important. The shorter the time between repetitions, the greater the risk of muscle damage.
- Hand coupling available. Designated handholds assist with lifting, balancing and controlling an object as it is manually transported. When handholds are not provided, additional strain is placed on muscles during lifting and carrying.
- Length of time over which lifting will occur. In addition to the number of lifts and amount of time between each lift, the total length of time over which lifting must be performed will also affect worker performance. Repetitive lifting through the course of an 8-hour shift will be create greater risk of injury than lifting for two hours alternated with other activities.
It is important to take these conditions into consideration when determining the recommended weight limit for manual lifting tasks in your workplace. However, given the wide range of variations in both worker physical capabilities and workplace conditions can be realized by utilizing powered carts to move equipment and materials previously handled manually. By replacing manual tasks with powered material handling equipment, companies can realize considerable savings in both production efficiency and lift-related worker injuries. Contact the ergonomic experts at DJ Products for more information.