SECONDARY RISK FACTORS
People who work outdoors – on construction sites, doing avalanche surveys, or work on loading docks – face additional risk of injury aggravated by cold. Cold temperatures produce a reduction in the hands ability to feel (tissue sensitivity), function (dexterity) and grip strength. It also makes muscles and joints stiffer, and increases reaction time. As a consequence, workers must use greater force to grip and hold hand tools, which increases the risk of an MSI.
The effects of cold temperatures can be made worse by:
- Not dressing appropriately for the environment and activity e.g. for physically active work, wear layers of clothing that can be removed as the worker warms up. For less active work, more layers may be needed.
- Not keeping the head covered to retain body heat and not keeping the feet warm and dry.
- Lifting or forceful exertion when chilled; stiff joints and muscles increase the risk of injury.
Vibration affects tendons, muscles, joints and nerves. Vibration to a specific body part can decrease sensitivity and result in unnecessary increases in muscle contraction, which may lead to injury or fatigue of that part. Localized vibration from machines and hand tools can damage the nerves and blood vessels of the hands and arms. Whole-body vibration, experienced by people who operate heavy equipment such as truck and bus drivers, increases the risk of lower back pain and damage to the spinal discs. The body’s response depends on the duration, frequency and extent of the vibration.
The effects of vibration can be made worse by:
- Machines and power tools that are not maintained. Well-maintained equipment minimizes vibration.
- Not limiting exposure to vibration by failing to implement work practices and administrative controls such as task rotation and rest breaks.
- Not wearing appropriate personal protection equipment where required e.g. vibration dampening gloves.
- Simultaneous exposure to cold temperatures.
Appropriate lighting and elimination of glare in the work area allows for adequate depth perception and contrast by the worker(s) when handling material such as when lifting and carrying objects. Improper lighting can be a contributing factor to a musculoskeletal injury. For example, poor lighting could cause the worker to misjudge weight and object shape resulting in inappropriate or poor lifting techniques.
The effects of illumination can be made worse by:
- Lighting is not maintained e.g. replacing burned out bulbs.
- Lighting in the work area was not designed for the type of work tasks being performed.
Characteristics of the organization of work
Work recovery cycles and task variability:
The objective of planned work recovery cycles and task variability is to avoid the onset of fatigue of specifi c muscles or body parts, which can put workers at an increased risk of injury.
Work recovery cycles and task variably can include rotating jobs, performing tasks with different physical or mental demands, or a rest break. The need for recovery cycles and task
variability depends on:
- the nature of the task,
- worker characteristics, and
- environmental conditions.
Fatigue increases the risk of injury. Risk of injury depends largely on the ratio of work period to work recovery cycles/task variably, that is, the recovery time compared to exertion. Risk control for work
recovery cycles and task variably:
The demands of physical handling should be well below the normal exhaustion level for the worker. When developing work recovery cycles and task variability for a specifi ed task consider work rate, load weights and whether tasks involve vigorous or minor exertions.
To vary physical demands, consider alternating physical task with non-physical tasks, or long cycle tasks with shorter ones, or to a task where the demands on specifi c muscle and body parts are sufficiently different. Ideally,workers should be given the flexibly to vary type of tasks they perform.
Review the adequacy of work recovery cycles and task variability whenever there are changes in any
of these factors:
- The requirements of a task
- Environmental conditions
- The work process
- Physical capacity of workers
Individual workers vary in the rates at which they perform the same task. Some individuals need longer periods to recover from physical work to prevent injury.
The more critical or physically demanding the task, the more desirable it is to let the worker set the pace, where possible. Just as important, where possible, is to avoid sudden increase in workload.
Planning the work rate will also involve consideration of work recovery cycles/task variability and staffing schedules.
Risk Factors can overlap:
More than one risk factor can be present in a task. The more risk factors in the task, the greater the
risk of injury. For example:
A worker bends forward from the waist to lift a box from the floor. The bending is an awkward posture (work posture) linked to the location of the box (out of proper lifting/bending* range?) on the floor (layout of the workplace). The box is wrapped with twine, which the worker grabs to lift the box (contact stress). If the worker repeatedly lifts boxes from the floor (repetition), or does similar lifting tasks all day (long duration, organization of work tasks), the risk of MSI is further increased.
Eliminating or Minimizing Risk Factors:
After identifying and assessing risk factors, the next step is to determine which control measures
should be implemented, and which ones eliminate or minimize the risk of MSI. Ask the following questions when considering control measures:
- Can exposure to the risk factor be eliminated?
- How can the intensity/magnitude of the job duty be reduced?
- Can frequency of the job function be reduced?
- Can duration be reduced?
Control measures for eliminating or minimizing risk factors:
- Engineering Controls
- Administrative Controls
- Personal Protective Equipment (PPE) Controls
The purpose of engineering controls is to design (or change by redesign) physical aspects of the workplace or tools to reduce or eliminate employee exposure to ergonomic risk factors. Engineering controls are preferred over other control methods. They are relatively permanent and benefit anyone performing the job – not just the individual who experienced an MSI.
Some examples are: adjusting work heights, minimizing reach distances, changing the layout of workstations, using adjustable or angled tools or equipment and the use of carts and other conveyors.
Administrative control functions include determining appropriate policy, procedures, education and training activities that affect the individual worker and the work environment. These actions are intended to reduce the workers’ exposure to MSI risks. This can be accomplished by reducing the duration of exposure and/or slowing the onset of fatigue and discomfort. For example, by ensuring that repetitive or demanding tasks incorporate opportunities for rest or recovery breaks (e.g. allow brief pauses to relax muscles; change work tasks; change postures or techniques).
To be effective, administration controls require:
- support by management,
- education and training,
- employee awareness of risk factors, and
- monitoring to ensure effectiveness of program and compliance of WCB requirements.
Personal Protective Equipment
Personal protective equipment may only be used as a substitute for reducing MSI risk factors where
engineering and administrative controls are not practicable. For example, workers may wear vibration-dampening gloves while using a chain saw or wear knee pads while working on their knees to install flooring.
MANUAL MATERIAL HANDLING:
Manual handling (i.e. lifting, carrying, pushing and pulling) of heavy, bulky, and/or irregularly shaped objects during work tasks) can lead to possible musculoskeletal injures. Under these circumstances a worker is more susceptible to injury as these type of tasks often require using awkward body postures, which can place considerable physical demands on the body, especially the back. The following information lists potential causes of MSI where such tasks are performed, as well as, examples of ways to prevent injuries (control measures) while performing these tasks.
Manual material handling examples:
- manually loading and unloading material from vehicles, boxes or pallets
- manually moving materials in warehouses, offices or outdoor work locations
- stocking shelves, etc.
This section on material handling is divided into the following categories:
- Extended reaching
- Working heights
Lifting of heavy, bulky, and/or irregularly shaped items can increase the risk of MSI’s. Lifting too
heavy a load puts unnecessary strain on the body, particularly the back.Proper lifting techniques play an important role in ensuring no injuries occur while performing these tasks (e.g. hold object close to the body and lift with the legs not the back). It is important that lifting be performed between the shoulder and knuckles height.
Knuckle height is when the arms are straight down in front of the worker, the height above the floor where the knuckles of the hands are located is the lowest height a worker should be lifting from or bending down to. Lifting and handling materials above shoulder level or below knuckle level (particularly while bending or twisting) adds unnecessary stress to the spine and back muscles.
In some cases lifting may have to be performed from the floor level. Where a mechanical lift is
unavailable and the material does not allow for the proper use of body mechanics, workers must be trained in proper lifting procedures (e.g. seek assistance from a co-worker).
- Restrict lifting to between knuckle and shoulder height.
- Minimize frequency of lift.
- Where possible separate the material into more manageable loads.
- Don’t put a load(s) on the fl oor if it needs to be manually lifted again later.
- When moving an item, test its weight before lifting.
- Don’t overestimate your ability to handle heavy items.
- Get as close as possible to loads and get a firm grip before lifting.
- Position yourself so that you are facing your load.
- Avoid reaching, twisting and bending.
- Be sure of your footing before performing the lift.
- Where feasible, provide lifting aids (lift tables, mechanical or powered assists, hoists, etc.) to move heavy or bulky loads.
- Ask for assistance if in doubt.
- Establish safe lifting work procedures and ensure workers are trained in them.
Depending on the distance an object is carried,it’s weight and size, there may be unnecessary strain placed on the body for long duration’s, which can attribute to an increase of MSI. It is important to be aware that the weight that can be safely carried by hand is less than the amount that can be safely lifted. This is due to the fact that carrying involves holding the object for a longer period in combination of having to physically move it. The longer the holding time (i.e.distance of travel while carrying object) the less weight that can be carried; the limiting factor is fatigue of the grip and shoulder muscles.
The grade of the floor is also a factor – carrying uphill or downhill increases the strain on the body, especially on stairways.
Eliminate the need to carry by:
- Using a cart, dolly, or pallet jack.
- Using a conveyor.
- Rearranging the work place.
- Providing slides or tables between workstations.
If elimination of carrying is not feasible:
Reduce the weight by:
- Reducing the size of the object.
- Using lighter material for the object.
- Reducing the capacity of the container.
- Reducing the weight of the container itself.
- If unable to reduce the weight, ask for assistance to move the object.
Reduce the distance material is carried by:
- Moving the operation closer to the previous or following operation.
- Using conveyors or rollers.
- Changing the layout of the workplace.
Note: If carrying can not be eliminated, provide proper handles on object to ensure a good grip and proper positioning of object when carried by worker(s).
Extended reaching occurs when workers are required to reach to heights or distances outside of the range from knuckle to shoulder height, and more than about 18 inches from the front of the body. This can require bending, twisting, stretching, and holding the arms up high or other awkward postures. In such postures, the weight of objects (and even of the body itself) creates greater stress on muscles and tissues due to the “lever effect”. Extended reaching can cause musculoskeletal injuries to the neck and shoulders.
- Adjust work stations, fi xtures, parts, tools, etc. to put the most-used items within easy reach.
- Keep workplaces clear of obstructions which increase reaching.
- Use platforms, step stools or other such aids to reach locations above shoulder height.
- Support or counter balance tools that are used above chest level.
- Limit or avoid reaching to full arms length for or with loads, or exerting force with the arm extended.
- Provide turntables, to allow easy access from all side.
Poor working heights in combination with any of the following can increase the risk of MSI:
- duration of work,
- high forces,
- static loading, and
If the work area is raised too high,the shoulders and arms must frequently be lifted upto compensate, which may lead to cramping and fatigue in the neck and shoulders.
If work heights are too low, the back and neck must be bent forward which can lead to neck and back pain or discomfort.
Ideally the height of work surfaces or the height of the worker’s position should be adjustable to
allow the employee to work from an appropriate neutral position at all times.
Work at an appropriate height by using:
- False bottom bins and lift tables to change the product height and reduce the need to bend or stoop.
- Adjustable working platforms, stools, and ladders to allow for neutral positions of the limbs, neck and torso.
- Tilt tables (e.g. drafting tables) to bring work closer.
- Extended handles on tools.
Reduce the demand on the body by:
Limiting the period of time required to perform an operation that is overhead, to the side, or down low. This can be accomplished by changing tasks frequently (e.g. paper work that may be normally completed at the end of the shift could be done in intervals through out the day to allow the body to recover).
The right work angle keeps the shoulder in a more comfortable position.
The greater the force required to push or pull an object, the greater the risk of developing an MSI.
In general, pushing a load is preferable to pulling a load. While pulling a load, arm and shoulder extension and abduction (working behind the mid-line of the body) and twisting may create an MSI risk factor.
Posture is a key factor in limiting how much force can be exerted in pushing and pulling. With extended reaches, or other awkward postures, less force can be exerted. On the other hand, by leaning into a push or away from a pull, the operator can apply more force. For example, pushing a heavy hand truck down a long corridor is usually possible because the large muscles of the legs and trunk can be used. Moving the same hand truck in a tight space where upright posture must be maintained is more difficult because the smaller arm muscles must be used to maneuver it.
Push or pull force is affected by:
- Body weight.
- Height of the work (height of handles).
- Distance of force application from body, or amount of trunk flexion/extension.
- The amount of friction between the worker’s shoes and the floor.
- How long the force must be applied.
- The distance the object must be moved.
- The availability of a brace or structure for the worker to push against.
- The texture of the floor surface e.g. carpet, smooth, slippery.
- Debris on surface areas.
Eliminate the need to push or pull by using:
- Conveyor system.
- Fork lift.
- Slide, chute, etc.
- Powered carts instead of hand carts.
Reduce the force by:
- Reducing the weight or size of the load.
- Using wheels and casters.
- Improving the size, composition, tread,maintenance and swivel properties of wheels on carts.
- Using ramps.
- Regular maintenance of equipment and floor surfaces e.g. lubrication of equipment; keep floor surfaces clean and clear of debris.
- Redesigning the work area to minimize how far items need to be moved.
- Installing automatic doors.
- Making friction work for the worker– minimize the friction on the object (i.e. don’t push on carpets) and maximize traction for the worker by wearing appropriate shoes.
- Providing well-designed handles in appropriate locations.