How can we prevent back injury resulting from MMH?
To prevent occupational back injuries, it is essential to identify the factors of MMH that make the worker more susceptible to injury or that directly contribute to injury.
When efforts to prevent injuries from MMH focus on only one risk factor, they do not significantly reduce the injury rate. A more successful approach such as the one offered by ergonomics combines knowledge of engineering, environment, and human capabilities and limitations. The following aspects should be considered:
- organization of work flow
- job design/redesign (including environment)
- pre-placement procedures, where necessary
- training
How does job design/redesign reduce the risk for back injury due to MMH?
The design or redesign of jobs involving MMH should be approached in the following stages:
- eliminate heavy MMH
- decrease MMH demands
- reduce stressful body movements
- pace of work and rest breaks
- improve environmental conditions
How can we decrease MMH demands?
Where possible, use mechanical aids. The next step is to decrease the manual material handling demands. There are several ways to achieve this:
- 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. 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.
How can we reduce stressful body movements in MMH?
It is important that the design of MMH allows the worker to do tasks without excessive bending and twisting. These body motions are particularly dangerous and can cause back injury even when not combined with handling loads.
- Provide 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 that there is a 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 the load can be handled close to the body.
How do we set up a proper work pace, and a beneficial ratio of work to rest breaks, to reduce the risk for back pain due to MMH?
Pace of work, particularly when externally imposed, may significantly contribute to the worker discomfort, and consequently to the onset of musculoskeletal injuries, including low back injuries. As a rule, pressure to work at a certain pace coming from management creates the mental need to work in a hurry. This in turn creates tension not only in the mind but also in the body. Tensed muscles are much more prone to injury, leading to WMSD.
Very recent research on the causes of back injury shows that workers at high risk for back pain (for example, those who lift for a living or where lifting is significant part of their job) need more frequent and longer breaks. Even a moderate pace of lifting (not necessarily at the maximum lifting limit) if maintained for a prolonged time without breaks, rapidly decreases workers’ lifting ability by speeding up their fatigue. It also means that in the second half of the working day, the risk for contracting low back injury (and, for that matter, any other musculoskeletal injury) is higher. And because of this it would be wise to assign heavier tasks at the beginning of the working day rather than at the end (but after the worker is “warmed up”).
It would be ideal if workers could work at their own pace and have some freedom to take a rest break when they start feeling the effects of fatigue. However, this might be impractical. It seems reasonable to incorporate two additional 15-minute breaks, mid-morning and mid-afternoon, in addition to the 30-minute lunch break, If that schedule is still not feasible, shorter but more frequent breaks can do as well.
It is also important that novices whose jobs involve lifting and MMH be given time to adjust by allowing them more breaks.
Improve the environment to reduce the risk for injury due to MMH?
The design of the work environment is an important element of back injuries prevention.
- Keep the temperature of the working area between 18°C and 21°C when practical.
- In extreme cases that require heavy MMH in temperatures above 30°C, rest periods or light work load tasks may account for 75 percent of the work time.
- Wear properly designed clothing to decrease the heat absorption by the body and to increase evaporation. This is particularly important for people required to work in high temperature environment.
- Encourage using proper protective clothing for people working in a cold environment. This is essential to protect the worker from hypothermia and to preserve dexterity needed for safe work.
- Illuminate the work area for MMH tasks at the level of 200 lux.
- Use task lights or other additional light sources to improve the ability to see clearly where MMH requires 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.
When the MMH tasks are done outdoors, 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 28°C.
- Stop MMH when the temperature exceeds 40°C.
- Restrict MMH to the minimum possible when wind-chill drops below -25°C.
- Stop MMH when wind-chill drops to -35°C.
Does training reduce back injuries?
There is little evidence to indicate that training alone reduces the number of MMH injuries. When combined with work design, training is an important element in the prevention of injuries. Proper training also shows the worker how to actively contribute to the prevention of injuries. A good training program should:
- make the worker aware of the hazards of MMH
- demonstrate ways of avoiding unnecessary stress
- teach the worker to handle materials safely
Instruction on how to lift “properly” is the most controversial issue concerning training in MMH. There is no single correct way to lift because lifting can always be done in several ways. Because of this, on-site, task specific training is essential. In fact, it is sometimes safer to allow the worker to use common sense acquired by experience rather than to force new bio mechanically correct procedures. But there are some 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.
- 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; this prevents fatigue from building up
- report discomforts experienced during work; this may help to identify hazards and correct working conditions.
Finally, there is an aspect of training that cannot be overlooked if training is to be part of an effective prevention program.
Workers should be educated that muscles, tendons and ligaments are not prepared to meet the physical stress of handling tasks when they are not “warmed up.” They are more likely to pull, tear or cramp when stretched or contracted suddenly under such conditions. This, painful enough by itself, can lead to more serious and permanent injury if physically stressful work is continued. Warming up and mental readiness for physically demanding tasks are important for any kind of MMH, but particularly for occasional tasks where the worker is not accustomed to handling loads. Workers are more likely to have “ready-to-go” attitude for the task ahead when they understand that other preventive measures are also tried.