Industrial ERG

CHAPTER 11 INDUSTRIAL WORKSTATION DESIGN

LEARNING OBJECTIVE

Students will be able to recognize the best work surface height for a given task and identify the basic principles behind seated, standing, and leaning workstations. They will be able to identify common workstation solutions and how to apply work space envelopes.

Most all workers perform their tasks at some sort of workstation. Whether the worker is a truck driver in a vehicle, an office worker at a desk, or a healthcare worker in a hospital, they work at some sort of workstation. This chapter discusses specific industrial types of workstations that involve assembly repair and fabrication types of tasks (Ostrom, 1994).

INTRODUCTION

A workstation is a location where a person performs one or more tasks that are required as part of his/her job. The design of the workstation can have a profound impact on the person's ability to safely and effectively perform the required tasks. Reach capability, body size, muscle strength, and visual capabilities are just a few of the factors that should be considered in workstation design. The design guidelines to be discussed in this section include the following:

1.

 Accommodate people with a range of body sizes or anthropometric dimensions.

2.

 Permit several working positions/postures to promote better blood flow and muscle movement.

3.

 Design workstations from the working point of the hands. People work with their hands so we want their working height to be relative to their hand height.

4.

 Place tools, controls, and materials between the shoulder and waist height, where they have the greatest mechanical advantage.

5.

 Provide higher work surfaces should be provided for precision work, and lower work surfaces for heavy work.

6.

 Round or pad work surface edges should be rounded or padded to reduce compressive forces.

7.

 Provide well-designed chairs in order to support the worker.

As each of the design guidelines is discussed, keep in mind that some of these principles may not be applicable to designs for individuals with special needs. Different tasks may also require different design guidelines, such as a shorter bus driver who may need a brake pedal extension.

GENERAL WORKSTATION GUIDELINES

Workstations should be designed to accommodate the anthropometric characteristics of a range of workers. In general, a well-designed workstation should be able to accommodate 90–95% of a worker population. This helps to ensure that workers can perform their job tasks comfortably and in a safe manner. There are several different sources of data that can assist with ergonomic design of the workplace.

Anthropometric tables contain data on human body dimensions and can be extremely useful in designing a work environment. When designing a new workstation, you should first identify the target audience, determine the appropriate anthropometric measurements, and ideally, create a mock-up for trial.

Figure 11.1  is an example of a height-adjustable table with a hand crank. This is an example of how you can accommodate workers with a range of body dimensions.

Figure 11.1  Hand crank workstation (Photo with permission from Pro-Line)

For operations where highly repetitive actions are required, where existing tools are not optimal, and where the workplace cannot be adjusted, a specially designed tool should be considered. Examples of special purpose tools include the following:

· Spring-loaded scissors that prevent irritation of the backs and sides of the fingers caused by opening conventional shears

· Bent pliers to maintain the wrist in a neutral posture

· Adjustable position (straight to pistol) screwdriver for multiple uses that encourages the use of neutral postures (Refer to the Hand Tool Section for more information on tools and neutral postures).

Situations when special tool designs are not recommended include the following:

· If the tool is used for a short part of a multitask cycle and thus becomes an extra tool to pick up and set down frequently.

· If the operation is not a continuous one and occurs only occasionally in the work shift

· If the workspace around the operator is limited, and there is no place to set tools between uses (Eastman-Kodak, 2003).

MOCK-UP OR FITTED TRIALS

The following illustrates the advantages of using a mock-up before actually purchasing equipment. In this example, aircraft access doors were being repaired. The workers were bending over into awkward, stressful postures when working on the access doors. One of the workers created a fixture for holding the access doors, which would allow them to rotate 180°.  Figure 11.2  is the original design developed by a worker. As you can see, the heavy-duty locking pin and open support structure allowed almost 180° of rotation. The large diameter casters created low push forces, even when the door was attached to the fixture.

Figure 11.2  Original fixture

Navy Hazard Abatement funding was used to improve and mass produce these fixtures. Prior to mass production of the fixture, a prototype (mock-up) was fabricated and put into use by the workers. The first prototype ( Figure 11.3 ) was inferior to the one made by the workers, and needed improvements were identified during this trial use. The wheels were too small, which required high forces to move the fixture and access door. The locking mechanism was unstable, and the support structure actually reduced the amount of rotation. A great amount of information was gained from creating and testing the mock-up that helped in designing the final product ( Figure 11.4 ).

Figure 11.3  Prototype fixture

Figure 11.4  Final fixture

The final fixture design, shown on the left, permits 180° of rotation, and is height adjustable and has a heavy-duty locking pin and large diameter casters to reduce push/pull forces.

The original fixture design was built in-house; we borrowed the design and expanded on it. A great amount of worker pride was shown by using the original design. The new fixture can be shared with other activities, and they save 3–5 days of labor per door now.

GENERAL WORKSTATION GUIDELINES PERMIT SEVERAL WORKING POSITIONS/POSTURES

One of the tenets of biomechanics is that static loading of muscles and joints is something that should be avoided. Static loading is considered a potential risk factor for WMSD development. To avoid static loading, it is recommended that workers be allowed to periodically change their working posture. When changing posture, the individual utilizes different muscle groups, increases blood flow, and allows the muscles to rest.

There are many possible postures for working. Each has benefits and disadvantages to be considered. We will discuss a few of them in detail:

· Sitting

· Reclined

· Standing

· Sit/stand

· Leaning.

Each of the postures a worker uses should be equally safe and free from ergonomic stresses. One approach for permitting different working postures is to allow the worker to both sit and stand while performing job tasks.

Seated Posture

Seated workstations are very common, but there are guidelines to follow when determining if a workstation should be seated. A seated workstation is not appropriate when working with heavy items, repetitive extended reaching, or heavy forces.

Sitting is preferred in the following situations:

· All repeatedly used items are easily located within the seated workspace (i.e., “reach envelope” shown in Figure 11.5)

· The items being handled do not require the hands to work more than 6 in. above the work surface on average.

· No large forces are required (heavy objects greater than approximately 10 lb). Using mechanical assists, such as a counterbalance, may eliminate or reduce large forces.

· Fine assembly or writing tasks are done for a majority of the shift (e.g., precision work or visual inspection).

Figure 11.5  Horizontal reach envelope

Note: Workers should not handle more than 10 lb from a seated position.

If the workstation is a seated workstation, they need to provide the following:

· All tools, parts, and controls to be within easy reach.

· Appropriate height work surface for the individual/task, height adjustable preferred. Figures 11.6 and 11.7 illustrate adjustable work benches.

· Chair providing good support

· Foot support if necessary (solutions for this will be shown later in this module)

· Part/task should be oriented toward the employee.

· Padded work surface edge, to reduce compression

· Allow clearance for head, thighs, and knees.

· If feasible, alternate between sitting and standing, or leaning.

Figure 11.6  Adjustable workbench (Photo with permission from Pro-Line)

Figure 11.7  Manual adjustable workbench (Photo with permission from Pro-Line)

Provide Well-Designed Chairs

Providing a well-designed, ergonomic chair can be extremely important in designing or choosing a safe and comfortable workstation. Many manufacturers market their chairs as being “ergonomic”. What makes a chair ergonomic? With regard to vendors and chair manufacturers, the term “ergonomic” is often overused. In order to select a good ergonomic chair, a few issues need to be considered:

· How many hours does a typical user spend in a chair? (24-h chairs are more durable than 8-h chairs)

· Is the user population extremely tall, short, or heavy?

· Is the work surface adjustable?

· What is the height of the work surface?

The duration of time a user spends in a chair will affect the type of cushion and padding that the chair may need, as well as the degree of adjustability required. For example, if a chair is only used briefly for a few minutes a day, then a very simple and rudimentary chair may suffice. However, a chair that a worker uses for an entire work shift should provide the full range of adjustable features.

If the user population is extremely tall, short, or heavy persons, a standard ergonomic chair may not meet the workers' needs. There are special chairs designed for tall, short, or heavy persons that should be chosen in these circumstances.

If the work surface height is adjustable, the chair height should also be adjustable.

If the work surface height is made for standing, a regular ergonomic chair will probably not adjust high enough. For standing and sit/stand workstations, a prop stool or an elevated chair with a foot rest may be more appropriate. Figures 11.8–11.10 show a variety of ergonomic chairs.

Figure 11.8  Traditional ergonomic chair (Photo with permission from IzzyPlus-www.izzyplus.com)

Figure 11.9  Saddle style of chair (Photo with permission from IzzyPlus-www.izzyplus.com)

Figure 11.10  Reversible chair (Photo with permission from IzzyPlus-www.izzyplus.com)

Solutions for Workers Who Are Required to Sit

Awkward neck/back angles are common issues for seated tasks and compression on the forearms/elbows is also common.

Figures 11.11 and 11.12 show a before and after example of a seated workstation. The before photo shows a worker with neck and back bent forward to see her work and compression from the edge of the desk on her elbows. In the second photo you can see task lighting, the work piece in a fixture which angles it toward the worker, and a padded forearm rest to reduce compression.

Figure 11.11  Worker in awkward posture

Figure 11.12  Worker illustrates good posture

It is common for workers to rest their elbows on the surface of a table or work bench to stabilize the hands and rest the shoulders. However, the tissues of the forearm can be placed under pressure where work surfaces have sharp edges. These edges can dig into the forearm, causing discomfort and potential nerve damage. These pressures can be alleviated by using pads and rounded corners on working surfaces.

General Workstation Guidelines – Design From the Working Point of the Hands Working Envelope keep everything within easy reach. An ergonomically designed workstation should keep most of a worker's tasks within a certain maximum distance (referred to as a “working envelope”). The working envelope for a specific worker is defined by the sweep radius of the arms, with the hands in a grasping or reaching position. In general, forward reaches more than 20 in. (50 cm) in from the body when standing, or 15 in. (38 cm) in from the body when sitting, should be avoided. An occasional reach beyond this range is permissible, since the momentary effect on the shoulders and back is transient; however, frequent reaching of this type can quickly become fatiguing.

The primary seated work envelope is 14–18 in. where the most frequently used items should be kept. The secondary reach zone for occasional reaches is 22–26 in. Two-handed reaches are generally shorter than one-handed reaches.

Figure 11.5  shows the horizontal reach envelope and  Figure 11.13  shows the vertical reach envelope (Grandjean & Kroemer, 1997)

Figure 11.13  Vertical reach envelope

Figure 11.14  shows how a chair that allows backward sitting can provide postural support to a worker.

Figure 11.14  Alternative seated posture

1. Laboratories Common Issues We see a lot of seated workstations in laboratories and the solutions are similar for different work environments. Figure 11.15 shows a woman using a microscope with her back severely bent and compressive force on her arms.

Figure 11.15  Poor posture

Other common laboratory problems include a lack of knee space, pipette use, eye strain, and fatigue and extensive standing.

2. Laboratories Common Solutions

A few simple solutions for laboratory use include the following:

· Tilting, padded forearm supports

· Ample storage space to allow unencumbered access to tools

· Risers or adjustable work surface

· Mats and foot rests

· Adjustable chair with foot ring

· Shorter tubes, electric pipettes, multipipettes

· Sit/stand work stations

· Video microscope – with a screen instead of eye tubes.

Figure 11.16 illustrates the posture when provided a chair with back support, a padded surface for the arms, and a device to bring the work closer to the individual so they are not leaning forward in an awkward posture.

Figure 11.16  Good back support

GENERAL WORKSTATION GUIDELINES PERMIT SEVERAL WORKING POSITIONS/POSTURES

People do not usually prefer to work standing, they feel it is tiring. The truth is that standing produces the least amount of stress on the spine-intervertebral disc between the third and fourth vertebrae. Even standing bent over is less stressful to the spine than sitting in a poor posture, especially if the seats are not supportive.

Note: Laying down produces ∼75% less disc pressure than standing at ease.

Reclined Posture

When employees are working overhead (such as aircraft mechanics), a recliner allows them to get closer to their work and reduces the static loading associated with holding their arms, neck, and back off the ground. Figure 11.17 shows the use of a creeper to avoid static loading in an awkward posture for an aircraft mechanic.

Figure 11.17  Industrial creeper

Standing Workstations

Standing workstations are appropriate when the task deals with heavy objects and/or frequent extended reaches, or the worker has to move around a lot. Standing gives us greater mobility, our reaching capacity is greater and it is faster for us to walk to another area since they don't have to get up out of a chair.

Standing is also preferred if the workplace or workstation does not have knee clearances for seated operation, or downward forces must be exerted, such as in wrapping and packing operations. If feasible, provide a sit/stand or lean chair and ensure there is suitable seating available for breaks and meals.

Venous pooling increases the heart rate as the heart tries to maintain constant cardiac output. Walking actually helps the heart by providing a “milking action” in the leg muscles that aids in moving the blood from the legs back to the heart. Venous pooling causes swelling of the legs (edema) and varicose veins in addition to increasing the load on the heart.

The veins are the body's blood storage location. If the legs do not move, the blood from the heart tends to come down the legs but not go back up; this is called venous pooling (Konz et al., 1990). Venous pooling is caused by standing with no leg movement. This type of inactive standing causes more discomfort than active standing, where the individual walks 2–4 min every 15 min (Mital, 1989). Shoes that are worn unequally may also present a problem. Worn shoes require the wearer to stand on a curved surface rather than a flat surface. Figure 11.18 shows attributes of a good standing workstation.

Figure 11.18  Attributes of a good standing workstation

There are many ways to make standing more comfortable for a worker. One can provide a support to lean against.

Figure 11.18 shows a foot rail. Foot rails should be at least 1 in. in diameter, 6 in. off ground. Foot rails allow the user to shift their weight from 1 ft to another and relieve pressure. This is the same concept behind foot rails in bars – if the patrons are more comfortable, they are more likely to stay.

Hard floors should be avoided or covered with padding in areas where standing is required. Plastic, cork tile, wood, and carpet are preferable to concrete or metal grating. However, these types of flooring are not always practical for an entire work area. In these cases, individuals may modify their standing area with carpet, rubber mats, old rugs, or wooden platforms.

Figures 11.6 and 11.7 show there should be adjustable height work surface (hand crank and pneumatic) platforms that can be stacked to create steps or taller platforms and a height-adjustable platform.

When selecting a work surface consider the following criteria:

· If the work surface is used by multiple users during different shifts, strongly consider making the work surface user adjustable.

· If the user of work surfaces changes regularly (for instance, work surfaces in locations that have a high turnover rate or office buildings where people change offices regularly) consider user-adjustable work surfaces. If user-adjustable work surfaces are not an alternative, the work surface should be maintenance adjustable.

· If adjustability of the work surface is not feasible, consider adjusting the height of the individual with platforms or person lifts as shown in Figure 11.19.

· When no adjustability is possible, ensure that the “working height” is at or just below the elbow rest height of the 50th percentile of the typical population that works at that particular job (This should be used as the last alternative and is not recommended).

Figure 11.19  Height-adjustable platform

Leaning Workstations

Leaning is preferred in the following situations (commonly referred to as sit/stand workstations):

· Repetitive operations are done with frequent reaches

· more than 16 in. forward and/or

· more than 6 in. above the work surface

· Multiple tasks are performed, some best-done sitting and others best done standing.

· Employee has to travel away from work area.

· There is not enough room or adjustability to alternate sitting and standing.

Lean chairs support two-thirds, of the user's body weight while maintaining upright posture. The semisitting posture relieves stress on the spine and the muscles and increases circulation in the lower extremities by providing relief from prolonged standing. This also allows the user to easily get up.

Standing Work Height

Figure 11.20 shows the recommended work heights for standing workstations. These heights are based on whether the work to be performed is considered light, medium, or heavy. The rule of thumb is that the work station should be lower for heavier work.

Figure 11.20  Standing work height guidelines

Whether the workstation is designed to be standing, sitting, or a sit/stand workstation, the vertical reach envelope of the individual needs to be considered.  Figure 11.21  shows the vertical reach envelopes that need to be considered.

1. General Workstation Guidelines

· Present parts upright and forward facing.

· Avoid extended reaches or twisting.

· Allow for several equally safe postures/positions.

· Conserve momentum and use gravity.

· Alternate arms (or legs) for repetitive work – consider “mirror image” assembly lines.

· Use two hands for power.

· Avoid static loads.

· Design for a small woman's reach; a large man's fit.

· Encourage neutral postures.

· Utilize large muscles for force, small muscles for precision.

· Provide adjustable seating with supportive backrest and arm supports as necessary.

· Ensure the feet are supported and proper illumination provided.

Figure 11.21  Vertical reach envelopes

Table 11.1  provides a summary of the criteria that should be applied when deciding whether to design a workstation to be sitting, standing, or sit/stand.

Table 11.1  Criteria for Designing a Workstation

Parameters	Standing Workstation	Sit–Stand/Leaning Workstation	Sit to Stand Workstation	Sitting Workstation	Special Considerations
Heavy load and/or with high forces – greater than 10 lb	Work surface height 6–16 in. below elbow height	Not recommended	Not recommended	Not recommended	Provide a place for short breaks. A lean station or a chair
Intermittent work with moderately high forces – 2–10 lb	Work surface height 4–6 in. below elbow height	Work surface height 4–6 in. below elbow height	Not recommended	Not recommended	Provide a place for short breaks. A lean station or a chair
Extended reach envelope	If variable tasks are required	If variable tasks are required	If moderately fine work is required and/or forces are less than 10 lb while sitting	If fine or precise work is required and/or forces are less than 2 lb	Ensure worker can reach items required without attaining awkward postures
Variable work surface heights	If forces greater than 10 lb are required. Work surface height 6–16 in. below elbow height	If moderately high forces are required – 2–10 lb	If moderately fine work is required and/or forces are less than 10 lb while sitting	If work can be performed at approximately elbow height and forces are less than 2 lb	Ensure worker does not attain sustained awkward postures
Repetitive movements	If forces greater than 10 lb are required. Work surface height 6–16 in. below elbow height	If moderately high forces are required – 2–10 lb	If moderately fine work is required and/or forces are less than 10 lb while sitting	If work can be performed at approximately elbow height and forces are less than 2 lb	Ensure worker has adequate recovery time from repetitious movements
Repetitive tasks requiring moderately high visual attention – production inspection	If extended reaches are required	If worker can remain in the leaning posture and perform all tasks required	If moderately fine work is required and/or forces are less than 10lb while sitting	If work can be performed at approximately elbow height and forces are less than 2 lb	Ensure adequate illumination and worker has adequate time from repetitious movements
Precise work and/or requiring demanding visual attention	Not recommended	Not recommended	Not recommended	Work surface height 2–4 in. above elbow height	Ensure adequate illumination and worker has adequate recovery time from visually demanding tasks

KEY POINTS

Summary of seated workstation design guidelines

If a job does not require a great deal of physical strength and can be done in a limited space, then the work should be done in a sitting position.

Note: Sitting all day is not good for the body, especially for the back. Therefore, there should be some variety in the job tasks performed so a worker is not required to do sitting work only. A good chair is essential for sitting work. The chair should allow the worker to change the general working positions easily.

The following are some ergonomic guidelines for seated work:

· The worker needs to be able to reach the entire work area without stretching or twisting unnecessarily.

· A good sitting position means that the individual is sitting straight in front of and close to the work.

· The work table and the chair should be designed so that the work surface is approximately at the same level as the elbows.

· The back should be straight and the shoulders relaxed.

· If possible, there should be some form of adjustable support for the elbows, forearms, or hands.

Summary of standing workstation design guidelines

1. Standing for long periods of time to perform a job should be avoided whenever possible. Long periods of standing work can cause back pain, leg swelling, problems with blood circulation, sore feet, and tired muscles. Here are some guidelines to follow when standing work cannot be avoided:

· The worker needs to be able to reach the entire work area without stretching or twisting unnecessarily.

· A good sitting position means that the individual is sitting straight in front of and close to the work.

· The work table and the chair should be designed so that the work surface is approximately at the same level as the elbows.

· The back should be straight and the shoulders relaxed.

· If possible, there should be some form of adjustable support for the elbows, forearms, or hands.

· If a job must be done in a standing position, a chair or stool should be provided for the worker, and he or she should be able to sit down at regular intervals.

· Workers should be able to work with their upper arms at their sides and without excessive bending or twisting of the back.

· The work surface should be adjustable for workers of different heights and for different job tasks.

· If the work surface is not adjustable, then provide a pedestal to raise the work surface for taller workers. For shorter workers, provide a platform to raise their working height.

· A footrest should be provided to help reduce the strain on the back and to allow the worker to change positions. Shifting weight from time to time reduces the strain on the legs and back.

· There should be a mat on the floor so the worker does not have to stand on a hard surface. A concrete or metal floor can be covered to absorb shock. The floor should be clean, level, and not slippery.

· Workers should wear shoes with arch support and low heels when performing standing work.

· There should be adequate space and knee room to allow the worker to change body position while working.

· The worker should not have to reach to do the job tasks. Therefore, the work should be performed 8–12 in. (20–30 cm) in front of the body.

REVIEW QUESTIONS

1. List those items that are important when considering setting up a new workstation.

2. A workstation should be setup from___________________________.

3. What is one thing that can be done to reduce the amount of stress on a worker's back who is in a seated workstation?

4. Why is alternating from one posture to another so important?

5. When setting up a workstation the items that are used seldom should be placed ___________?

6. Why would a seated workstation be selected over a standing workstation?

7. Conversely, why would a standing workstation be selected over a seated workstation?

8. What is the ergonomic risk factor associated with a sharp edge on a workbench?

9. Why an Irish bar? Lol why not an Italian bar?

10. A generator has to be repaired. There are multiple areas on the generator that have to be adjusted. How could one set up a workstation so that all these access points can be worked on?

REFERENCES

1. Eastman-Kodak. (2003). Kodak's Ergonomic Design for People at Work. Eastman Kodak Company.

2. Grandjean, E., and Kroemer, K. (1997). Fitting the Task to the Human. A Textbook of Occupational Ergonomics 5th edn. CRC Press.

3. Konz, S., Bandla, V., Rys, M., and Sambasvian, J., Eds. (1990). Standing on Concrete Versus Floor Mats. Advances in Ergonomics and Safety II. Taylor and Francis, pp. 991–998.

4. Mital, A. (1989). Footprints. In S. Konz, & S. Subramanian, Advances in Ergonomics and Safety I. Taylor and Francis, pp. 203–205.

5. Ostrom, L. (1994). Creating the Ergonomically Sound Work place. Jossey-Bass.

ADDITIONAL SOURCE

1. Konz, S., Bandla, V., Rys, M., and Sambasvian, J., Standing on Concrete vs Floor Mats, In Advances in Industrial Ergonomics and Safety II, B. Das (ed.) London: Taylor and Francis, pp. 991-998 1990.