Background
One-third to one-half of all occupational illnesses or injuries involves overexertion. Workers in jobs with more demanding lifting requirements, such as hospital patient care, warehouse work or certain manufacturing jobs report an even higher incidence of strains and sprains. The National Institute for Occupations Safety and Health (NIOSH) has estimated that over 30 percent of the workplace and a generally older workforce increase the risk of injuries due to manual material handling in this more physically vulnerable population. Certain job tasks, the amount of overtime worked and other personal factors can place an employee at risk for injury.

Manual material handling (MMH) is defined as the unaided moving of objects, often combined with twisting and awkward postures and contributing to musculoskeletal disorders. Traumatic occurrences (slips, trips, falls, and blows to the body.) cause the other bodily injuries, pain and disability. Typically, not one specific occurrence but rather the awkward body positions, repetition, force and duration associated with movement lead to back, neck and other problems (Cumulative Trauma Disorders).

Most low back problems are due to muscle strains and sprains.Most low back pain is acute in nature and employees return to work within a few weeks. However, studies show employees who have experienced back pain are up to four times more susceptible to a recurrence in the future. Low back impairment reduces the ability to function effectively on the job, impacting individual and company performance and productivity. It is important to realize low back pain may or may not involve low back impairment and therefore may not qualify as a disability requiring comprensation.

Because of the biochemical structure of the back, lifting even relativly light loads can produce high pressure within the spinal discs. Handling less than 40 pounds does not usually produce severe sprain or strain. However, some studies have found that even lifting 35 pounds close to the body may be hazardous for some people. The incidence and severity of injuries increase with increasing weight, size of the object and the frequency of lift. Injuries to the shoulder, elbows and wrists, as well as the back become a concern.

A study at Ohio State University (Marras 2005) reported that forward bending is a significant risk factor. Employees who bend more than 45-degrees on a consistent basis have about a 20 to 50 times increased risk for spinal displacement (1 c-m shift between vertebrae and discs)

Tools such as NIOSH lifting Formula can be used to calculate the recommended weight limit for single and multiple lifts. The formula takes into account factors such as weight of the object, distance of the object from the center of the body, start and end-point of the lift, amount of body twist, frequency and duration, and quality of the hand grasp. If all of these factors were perfect, the maximum recommended weight limit is 51 pounds. Any changes in the above-mentioned factors reduce the 51-pound figure. This figure gives a starting point for reducing stress. Any changes to the workstation or job task can then be factored in to change the allowable weights at the workstation.

This document focuses on approaches to reducing the incidence of chronic types of injuries for employees.

Systematic Review
A systems approach is used to reduce the total amount of required MMH and minimize the hazards associated with these activities during the planning and construction phases by creating a unified material handling system. This approach could involve:

Mechanizing and automating handling operations, including use of robots
Increasing the quantity, size or weight of unit loads and then handling them with powered equipment
Using gravity to move material
Standardizing handling methods
Reducing the weight of handling equipment, like substituting lighter plastic materials for heavier metals in carts
Minimizing reaches above the shoulder and below the knee

Process redesign
Process redesign should be done to improve handling tasks physically, thus making tasks more acceptable for a larger percentage of the workforce. It is estimated that up to two-thirds of material handling injuries can be prevented if the task were designed to be within the physical capacities of 75 percent of the workforce.

General principles for such redesign include:

Reducing the size and/or weight of the load
Reducing the distances the load must be lifted or carried
For warehouse and picking operations, placing the heaviest and most frequently picked items in the middle racks in order to minimize awkward and enhance productivity.
Designing workstations to allow materials to be slid rather than lifted.
Using a lifting jack that lifts materials to conveyor height will reduce stressful lifts from floor to conveyor
Providing handles on objects to be lifted.
Providing ergonomically designed tools to make efficient and safe usage of applied with the hand
Considering job rotation for those involved in constant manual material handling tasks.

The Following items should be addressed in task redesign:

Reducing the size and/or weight of the load
Reducing the distances the load must be lifted or carried
For warehouse and picking operations, placing the heaviest and most frequently picked items in the middle racks in order to minimize awkward postures and enhance productivity.
Designing workstations to allow materials to be slid rather than lifted
Providing handles on objects to be lifted
Providing ergonomically designed tools to make efficient and safe usage of force applied with the hand
Considering job rotation for those involved in constant manual material handling tasks

The following items should be addressed in task redesign:

Handles should be provided for units weighting more than 10 pounds. Bulky objects weighting more than 40 pounds should have handles for two-person lifting.
Handles of equipment and material containers should be designed to accommodate a power (cylindrical) or oblique (thumb extended) grasp. Without a handle, a pinch grip that is only 25 percent as powerful as a power grasp is used. The pinch grip can be associated with carpal tunnel other wrist disorders and should be avoided.
Handles should be textured to reduce slippage. They should be designed to minimize the force of the fingers and hands and provide adequate clearance of at least one inch should exist around the hands and gloves, where they will be worn, to allow the wrist to be in its most natural and strongest position.

Where trays are used, the following design and usage guidelines should be observed:

To reduce the load on the spinal column and upper extremities, tray width (front to back) should be reduced to 14 inches or less, with a maximum acceptable width of 20 inches.
Tray length impacts the shoulder muscle. Minimizing length ensures the weight is carried by the stronger biceps instead of the weaker shoulder muscles. Recommended length is 19 inches, never to exceed 24 inches.
Improve tray stability by loading it uniformly, using dividers or baffles and sizing it for the particular material.
Shipping boxes are among the most frequently handled items in the industry.

Recommended dimensions are 20 inches long by 14 inches wide, by 6 Inches deep.

The following dimensions should not be exceeded for an unaided lift of 40 pounds at 30 inches: 30 inches long, 20 inches wide, 19 inches deep or high.

Handholds should be provided where weight exceeds 40 pounds and for cases moved constantly onto pallets.

Handcart selection should include consideration of the following:

Loads of less than 500 pounds
Tasks occurring less than 200 times per day
Distances of less than 100 feet
Being pushed rather than pulled to take advantage of the body’s strength
The operator’s pushing or pulling from the swivel end
Handles being placed to straddle the load center of gravity
Handle Height of 36 to 44 inches.
Unloading product to shelves a level no lower than 20 and 45 inches above the floor
Braking systems being used where ramps must be negotiated
Frequent ramp usage; carts carrying more than 500 pounds

Worker selection and Training
Employee selection through a health history questionnaire and clinical examination using back x-rays has been used, but it is not currently considered predictive of injury. X-rays carry radiation exposure risks that must also be considered. For the physical examination to be of preventative value, a job analysis detailing the physical requirements of each essential job function must be available to the doctor prior to an individual’s examination. Strength testing also lacks total reliability as a predictive indicator of injury risk due to flaws in the assumptions that must be made to develop strength test models. These models usually deal with the single most difficult lift rather than repetitive lifting of lower weight objects. They assume that lifting techniques are consistent among individuals and injury occurs because of the most difficult lift, which may not always be true. Care should be taken to comply with the current Americans with Disabilities ACT (ADA) regulations.

Strength testing programs should meet the following criteria:

They should be safe to administer
They must provide reliable quantitative data
They should be related to specific job requirements
They should be practical

Training programs on safe lifting are widespread but have not succeeded in greatly reducing the back injury rate. Training integrated into the actual work situations is like to be more effective than training that relies solely on classroom instruction, videos or slides. Continual reinforcement training by the direct supervisor has been shown to be the most productive.

Training should focus on making the employee aware of the dangers of careless and unskilled lifting and teaching the employee how to avoid stresses on the body. Curricula should deal with fitness, the effects of lifting on the body, the biomechanics of lifting, stretching/warm up activities, developing handling skills, avoiding unexpected occurrences and usage of handling aids.

Source:Zurich