Industrial Ergonomics

I am looking for specific examples of Worksite Modification done on assembly lines. I have been looking in some of the literature and am unable to find specific examples of Worksite Mods. Can you help?

The best set of examples of worksite modifications for assembly lines is to be found in the book which we helped to prepare for the UK Health and Safety Executive. It is called A Pain in Your Workplace: Ergonomics problems and solutions (ISBN 0 7176 0668 6). It contains about 70 case studies of ergonomics improvements that have been made to assembly lines (many automotive and food lines) as well as other industrial and office settings. The book costs £10.95 and can be purchased from:

HSE Books
PO Box 1999
Sudbury, Suffolk
CO10 6FS
ENGLAND

Other good titles include:

• Case studies in Ergonomics Practice by H G Maule and J S Weiner (eds) London: Taylor and Francis 1981 (ISBN 85066 208 7)



• Making the Job Easier: An Ergonomics Ideas Book National Safety Council; Chicago IL: NSC 1988

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Where can I find information on ergonomics in aerospace primarily relating to electrical wiring assembly?

Although I am more familiar with the assembly of automotive wiring harnesses rather than aerospace harnesses, the ergonomics issues are similar between the two. In general, the two main problems are:

• Anthropometry
  Often the assembler must reach to the top or bottom of a near-vertical wiring board, which can cause problems for especially tall or short staff. This is best addressed through placing the height of the board so the vertical 'window' over which they must work is centred around the user's elbow height and goes no higher than their shoulder height. Obviously height adjustability of the board is the best way to achieve this.



• Repetitive tape wrapping actions
  Usually the bundles of wires must be wrapped by a tape which holds them together neatly. Manually wrapping the wires usually involves repetitive flipping of the tape roll by one hand whilst the other pulls and holds the wires together. This can present risks of upper limb disorders to the wrists and hands.

Since you are based in the US, I would recommend that you contact our associates The Joyce Institute who have conducted extensive training and consulting work in both aerospace and automotive wire assembly. They may be contacted by phone on (206) 441 6745 or 1-800 645 6045.
CR

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I'm revamping an upholstery operation. In doing so, I'm searching for ergonomically designed sewing machine stations, hand tools i.e., scissors, cutters, etc. What equipment resources are available (catalogues)? Are there case studies available relative to the sewing industry?

An interesting statistic: the prevalence of neck problems in occupational groups is 98% for sewing machinists!

In terms of tools, scissors should be spring loaded, self opening and designed to sit in the palm of the hand for stronger power grip cutting action.

References that may be of use:

• McCormack et al (1990)
  Prevalence of tendinitis and related disorders of the upper extremity in a manufacturing workforce. J. Rheumatol. 17 (7), pp 958-64.



• Guangyan et al (1995)
  Factors affecting posture for machine sewing tasks: the need for changes in sewing machine design. Applied Ergonomics, 26, No 1.

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I was taking a look at your biomechanical package for calculating the disc compression forces in the lumbrosacral joint of the spine. How was the value actually calculated?

The equation is based on the NIOSH guide:
National Institute for Occupational Safety and Health (1983) A work practices guide for manual lifting. Technical report No. 81-122. Cincinnati, Ohio: US Department of Health and Human Services (NIOSH) (Available from the American Industrial Hygiene Association, Akron, Ohio).

See also Don Chaffin (1985) Manual Materials Handling Limits. Chapter 20 in "Industrial Ergonomics: A Practitioner's Guide" (edited by David Alexander and Babur Mustafa Pulat). Published by Industrial Engineering and Management Press, Institute of Industrial Engineers, Norcross, Georgia, USA.
CR

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I am involved with a design project which involves the design of an ergonomic torch. The torch is currently a search light with a organic body design. The main problem is where the handle is being used as a natural counter weight in the hand. Can you provide a range of guidelines that would be appropriate to enable it to be sold to a mass market?

The following are some basic guidelines from the literature on handtool design. Good references include Bodyspace by Stephen Pheasant, Ergonomic Design for People at Work by Eastman Kodak, Occupational Biomechanics by Chaffin and Andersson and a Taylor & Francis book called The Worker at Work. I think it is important that the centre of gravity is close to the hand - it sounds like that is an issue in your question. Some guidelines follow:

• Weight A hand-held device should require minimal grip force to hold and use. To control a tool or device, people should not have to use grip forces which may be near their maximum grip capacity. Since finger muscles are small and individual muscle groups are relatively weak, even small forces may exceed a persons maximum grip capacity. Therefore the weight of a tool or device should be kept low. For power tools held in one hand and used repetitively, a common guideline is that tools heavier than 0.5 to 1 kg are excessive and should be supported by a counter- balancing system.



• Distribution of weight The centre of gravity of a tool or device should be located close to the hand to reduce fatigue and be aligned with the axis of the grip. Heavy or unbalanced devices tire the muscles very quickly, particularly if the arm is extended. Handles should be located close to a devices centre of gravity to reduce the tendency of the device to slip out of the hand or bend the wrist in the ulnar direction (towards the little finger).



• Texture and materials The surface of a hand-held device should maximise texture to provide tactile feedback and minimise slippage in the hand, without introducing abrasion to the hand surface. Highly polished and smooth surfaces for the area to be gripped by the hand should be avoided. A readily identifiable texture also provides an input to the sensory nervous system to assist in maintaining the grip. A proper material will also help reduce thermal conductivity so it does not feel cold to the touch.



• Grip architecture / shape In general, the form of the product should complement the anatomical nature of the hand and its biomechanical properties. The device should be designed to map the natural topology (shape) of the hand by filling the palms natural folds and encouraging a more relaxed posture for the fingers. It should encourage a power or oblique grip on the device, with maximal surface contact with the hand. If an appropriate handle shape is not used, the person may add to the biomechanical stress by bending the wrist into awkward postures. If possible, the handle should accommodate a variety of hand postures, all of which are safe and comfortable.


Handles and grips should generally be designed for a power grip on which more force may be generated. Compared to the other grip types, power grips are less fatiguing because they require a lower percentage of the persons total gripping strength to maintain control. In order to allow a power grip, the handle should allow fingers to wrap around the surface for at least 270 degrees. Pinch grips should be avoided because the muscle groups involved are usually not used to their greatest mechanical advantage, which accelerates the onset of fatigue. The pinch grip requires large muscle and tendon forces relative to the grip force produced.


• Size For females, handle diameters for a power grip should range between 22 and 36 mm. The grip diameter of 36 mm allows the maximum power grip strength to be applied, and the grip force at 45 mm is 95 per cent of that at 36 mm. These data are based on cylindrical measurement devices where a power grip can be applied. For males, all the recommended limits should be increased by 10% to 12%.


Enclosed (D-shaped) handles should be designed to accommodate the hand as it supports a load and moves through several heights and distances in front of the body. A handle design that forces the wrist away from its strongest (neutral) position will limit the amount of weight that can be handled comfortably. These types of handles should also be located at or above the line passing through the centre of gravity of the load.


• Wrist postures A hand-held device should encourage use in a naturally comfortable hand and wrist posture. It should encourage and support use with minimal flexion, extension, ulnar or radial deviation since these postures have been shown to increase the pressure within the carpal tunnel of the wrist. Furthermore, the ability to apply gripping forces decreases when the wrist deviates from the neutral position.



• The shape should conform to the natural holding position of the hand, and handles should be angled to reflect the axis of the grasp. Normally this is about 78 degrees from the horizontal when the axis of the device function is horizontal, as it would be for a device such as the Telxon 1124.



• Handle length The force bearing area of a device or tool should span the breadth of the palm, which for the 95th percentile male would be a length of at least 100 mm. This dimension is also relevant to enclosed (D-shaped) handles.



• Exposure to hand trauma Hand-held devices should be shaped to minimise direct pressure against the sensitive inner palm. All potential sharp edges should be smoothly curved off. Continued pressure from the edges of devices gives rise to discomfort, and eventually damage to the hand of the user. All exterior edges of a tool which are not part of the functional operation and which meet an angle of 135 degrees or less should be rounded off with a radius of at least 0.8 mm (1/32 in). All corners formed by the intersection of three or more surfaces of which two form an angle of 135 degrees or less should be rounded to at least 1.6 mm (1/16 in).



• Tactile and visual cues - A hand-held device should offer visual and tactile cues for the finger location which optimise comfort and control.

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I am responsible for market research within the area "hearing protection equipment" at a Swedish manufacturer. I am interested in all types of research/statistics within this area: the number of employees per country (Scandinavia, Europe, US, Australia, Japan, HongKong etc) covered by law to use hearing protection. I am also interested in market research reports containing information regarding market size, market shares, major trends etc. Do you know if any institute in any country has made anything like this?

I believe that you may find some relevant information on the UK situation is available from the Health and Safety Executive. I have seen a number of publications from HSE on hearing protection - often in connection with the UK's Noise at Work Regulations. Also HSE publish data on the cost of injuries and this may contain information of interest to you. For example, in 'The costs to the British Economy of work accidents and work related ill health' (1994) they say 76000 days were lost due to deafness and 121500 people reported work related deafness and ear conditions.
AC

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Are there any suggestions for correct postures/positions for photographers? Colleagues of mine who develop their own black and white film/pictures complain of constant back pain from stooping over the sinks, enlargers, etc. Some stand for hours at a time in the same place. Are there any remedies to prevent such pains? Do you see any other possible precautions that can be taken in the photography studio (ergonomically)?

As you say, working in a stooped posture can quickly bring about back and shoulder pains. The key to avoiding this is to get the working height right. Ideally, for standing work, the work surface should allow the person to stand absolutely upright, with their head/neck no more than 20 degrees from the vertical. A good working height allows the hands to be at about elbow height (with arms/shoulders relaxed) and I would recommend that your colleagues try to adapt the heights of the equipment etc. so that they can work at elbow height with their backs straight. Of course with sinks, its often the bottom of the sink that needs to be considered, rather than the level of the work surface around it. Any equipment that places other constraints on posture may also need to be considered - for instance, anything that has eyepieces, or requires close examination during use should be placed so that the user can still stand upright. Good lighting, where possible, also promotes better posture by avoiding "stooping to see".

Pains can also be prevented by taking short frequent breaks from the work. Breaks should include a change of posture and some "moving about" to give the muscles a rest. Take a short walk if possible.

Finally, to avoid the aches that result from standing up in one place for a long time - have you considered a "sit/stand" work station? This should still be at a height suitable for standing use, but a "prop"- style stool can allow the person to lean back when they wish, relieving the pressure on the legs and giving a change of posture. In addition, anti-fatigue matting is available commercially and can make prolonged standing more comfortable (it provides a cushioned surface for standing).
AB

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What is the maximum weight a person should lift at any job?

This question is too vague and therefore can not be answered.

It is overly simplistic to think of lifting safety in terms of weight - that's why the UK Manual Handling regulations call into account four factors : load, task, environment, individual capability.

Just think of the variety of people, lifting rates, start / end of lift, characteristics of the load, hot/ cold working environments etc and I think you'll agree!

Tools like the NIOSH lifting equation give a good balance between the factors as does biomechanical modelling but you also must know when they are appropriate to use.

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I am a designer in the medical industry and could use some help in designing for patient comfort. What kind of software is available for ergonomic issues? Anthropometric data and Human Factors?

There is quite a lot of software available for conducting ergonomics analysis. I'll point you to some of my favourites.

You enquired about anthropometry, and I think the best one is Peoplesize by a UK company called Open Ergonomics (tel +44 01509 218 333). It is easy to use and compiles a wide range of anthropometric measurements for different ages and different populations (US, UK, German, Japanese)

For Biomechanical analysis (e.g. of low back problems from lifting etc) try the University of Michigan 3D Static Strength Prediction Program Call. 313 936 0435, or email This e-mail address is being protected from spam bots, you need JavaScript enabled to view it .

A few modelling packages are also available for helping in design and comparing humans to 3d models. A well-known one is SAMMIE from the Nottingham University in the UK, and another is called JACK. I don't have any more contact details for these two at hand, but I am sure they can be found on the web. Another one I have used recently is called Mannequin Pro, and it requires far less computing power than the others (it can run on an ordinary PC) although it is a bit strange in its interface.

There are others, including one by Liberty Mutual / Liberty Risk Services called Computask I believe - again more information can be found on their website.
CR