Preventing Back Injury in Manual Materials Handling

About three of every four Canadians whose job includes manual materials handling (MMH - lifting, carrying, pushing and pulling, etc.) suffer pain due to back injury at some time. Although back injuries are preventable, they continue to occur in the workplace at a high rate.

Major causes of back injury are the weight of the load lifted, the range of the lift, the location of the load in relation to the body, the size and shape of the load, and the number of lifts performed. Excessive bending and twisting increases the risk for back injury.

How often the worker performs MMH tasks, and for how long, are extremely important factors. Frequently repeated and long-lasting tasks are the most tiring and therefore the most likely to induce back injury.

For most workers, lifting loads over 20 kilograms results in an increased number and severity of back injuries. While weight of the load is the most obvious factor, it is not the only one determining risk of the injury. The location of the load is also important. A load lifted far from the body imposes more stress on the back than the same load lifted close to the body. A bulky object is harder to lift than a compact one of the same weight because it cannot be brought close to the body. A bulky object also forces an awkward and potentially unbalanced position. The preferred range for lifting is between knee and waist height. Lifting above and below this range is more hazardous.

The following are some helpful, preventive tips extracted from the Canadian Centre for Occupational Health and Safety's OSH Answers Web service.

Decrease or eliminate MMH demands

Wherever possible, heavy MMH tasks should be either eliminated, or performed by powered or mechanical handling systems, as long as the worker is properly trained in the safe use of this equipment. Lifting and carrying can be easier and safer if aided by lift tables, conveyors, yokes or trucks. Gravity dumps and chutes can help in disposing of materials.

When mechanical aids cannot help, there are several other ways to decrease the MMH demands on the body. Here are some examples:

• Decrease the weight of handled objects to acceptable limits.
• Reduce the weight by assigning two people to lift the load or by splitting the load into two or more containers. Using light plastic containers also decreases the weight of the load.
• Change the type of MMH movement. For example, lowering objects causes less strain than lifting. Pulling objects is easier than carrying. Pushing is less demanding than pulling.
• Change work area layouts. Reducing the horizontal and vertical distances of lifting substantially lowers MMH demands.
• Reducing the travel distances for carrying, pushing or pulling also decreases work demands.
• Assign more time for repetitive handling tasks. This reduces the frequency of handling and allows for more work/rest periods.
• Alternate heavy tasks with lighter ones to reduce the build-up of fatigue.

Reduce stressful body movements such as bending and twisting.

• Keep all materials at a work level that is adjusted to the worker's body size.
• Eliminate deep shelves to avoid bending.
• Ensure sufficient space for the entire body to turn.
• Locate objects within easy reach.
• Ensure clear and easy access to the load.
• Use slings and hooks to move loads without handles.
• Balance contents of containers.
• Use rigid containers.
• Change the shape of the load so that it can be handled close to the body.

Improve the work environment

The design of the work environment is an important element of back injury prevention.

• Keep the temperature of the working area between 18ºC and 21ºC when practical.
• Ensure an adequate work/rest schedule. In extreme cases that require heavy MMH in temperatures above 30ºC, rest periods or light work load tasks may account for up to 75 percent of the work time.
• Wear clothing designed to decrease the heat absorption by the body and to increase evaporation. This is particularly important for people required to work in a hot environment.
• Use proper protective clothing for work in a cold environment. This is essential to protect the worker from hypothermia and to preserve the dexterity needed for safe work.
• Illuminate the work area for MMH tasks that require precise placement at the level of 200 lux.
• Use task lights or other additional light sources for tasks requiring fine visual discrimination.
• Use angular lighting and colour contrast to improve depth perception. This helps the worker where MMH involves climbing stairs or moving in passageways.

For outdoor tasks, the temperature conditions including the humidex (in hot weather) or wind-chill factor (in cold weather) have to be monitored very closely.

• Reduce MMH tasks by half when the temperature exceeds 28ºC.
• Stop MMH when the temperature exceeds 40ºC.
• Restrict MMH to the minimum possible when wind-chill drops below -25ºC.
• Stop MMH when wind-chill drops to -35ºC.

General lifting rules

• Prepare to lift by warming up the muscles.
• Stand close to the load, facing the way you intend to move.
• Use a wide stance to gain balance.
• Ensure a good grip on the load.
• Straddle the load.
• Bend the hips and knees.
• Keep the back straight.
• Keep arms straight.
• Tighten abdominal muscles.
• Tuck chin into the chest.
• Initiate the lift with body weight.
• Lift the load close to the body.
• Lift smoothly without jerking.
• Avoid twisting and side bending while lifting.
• Do not lift if you are not convinced that you can handle the load safely.

It is also important that workers take advantage of rest periods to relax tired muscles and that they report discomfort experienced during work to help identify hazards and correct working conditions BEFORE injury can occur.

Another cause of back injury is that workers sometimes undertake physically demanding tasks they are not ready for. Muscles, tendons and ligaments are not prepared to meet the physical stress of MMH tasks when they are not "warmed up". They are more likely to pull, tear or cramp when stretched or contracted suddenly under such conditions, and can lead to more serious and permanent injury if physically stressful work is continued. It is equally important that the worker be mentally prepared for the task. Accidents happen when fatigue, stress or distractions are involved, especially when the worker is not accustomed to handling heavy or awkward loads.

CCOHS has prepared OSH Answers on Back Injury Prevention

        http://www.ccohs.ca/oshanswers/ergonomics/inj_prev.html

and on Manual Materials handling (lifting)

        http://www.ccohs.ca/oshanswers/ergonomics/hlth_haz.html