Friday, February 17, 2012

Principles of Human Effort Engineering

Principles of Motion Economy

Use of the Human Body

1. The two hands should begin as well as complete their motions at the same time.

2. The two hands should not be idle at the same time except during rest periods.

3. Motions of the arms should be made in opposite and symmetrical directions and should be made simultaneously.

4. Hand and body motions should be confined to the lowest classification with which it is possible to perform the work satisfactorily.

5. Momentum should be employed to assist the worker wherever possible, and it should be reduced to a minimum if it must be overcome by muscular effort.

6. Smooth continuous motion of the hands are preferable to straight line motions involving sudden and sharp changes in direction.

7. Ballistic movements are faster, easier and more accurate than restricted (fixation) or controlled movements.

8. Work should be arranged to permit an easy and natural rhythm wherever possible.

9. Eye fixations should be as few and as close together as possible.

Arrangement of the workplace

10. There should be a definite and fixed place for all tools and materials.

11. Tools, materials and controls should be located close to the point of use.

12. Gravity feed bins and containers should be used to deliver material close to the point of use.

13. Drop deliveries should be used wherever possible.

14. Materials and tools should be located to permit the best sequence of motions.

15. Provisions should be made for adequate conditions for seeing. Good illumination is the first requirement for satisfactory visual perception.

16. The height of the work place and the chair should preferably arranged so that alternate sitting and standing at work are easily possible.

17. A chair of the type and height to permit good posture should be provided for every worker.

Design of tools and equipment

18. The hands should be relieved of all work that can be done more advantageously by a jig, a fixture, or a foot-operated device.

19. Two or more tools should be combined wherever possible.

20. Tools and materials should be prepositioned whenever possible.

21. Where each finger performs some specific movement, such as in typewriting, the load should be distributed in accordance with the inherent capacities of the fingers.

22. Levers, hand wheels and other controls should be located in such positions that the operator can manipulate them with the least change in body position and with the greatest speed and ease.


Ralph M. Barnes, Motion and Time Study Measurment of Work, John Wiley & Sons, New York, 1980

Principles of Ergonomics

1. Work in neutral postures
2. Reduce excessive forces
3. Keep everything in easy reach
4. Work at proper heights
5. Reduce excessive motions
6. Minimize fatigue and static load
7. Minimize pressure points
8. Provide clearance
9. Move exercise and stretch
10. Maintain a comfortable environment

Good explanation with illustrations is available in

Principles of Fatigue

Fatigue refers to the issues that arise from excessive working time or poorly designed shift patterns. It is generally considered to be a decline in mental and/or physical performance that results from prolonged exertion, sleep loss and/or disruption of the internal clock. It is also related to workload, in that workers are more easily fatigued if their work is machine-paced, complex or monotonous.

Fatigue results in slower reactions, reduced ability to process information, memory lapses, absent-mindedness, decreased awareness, lack of attention, underestimation of risk, reduced coordination etc. Fatigue can lead to errors and accidents, ill-health and injury, and reduced productivity. It is often a root cause of major accidents

Key principles in fatigue

1.Fatigue needs to be managed, like any other hazard.
2.It is important not to underestimate the risks of fatigue. For example, the incidence of accidents and injuries has been found to be higher on night shifts, after a succession of shifts, when shifts are long and when there are inadequate breaks.
3.The legal duty is on employers to manage risks from fatigue, irrespective of any individual’s willingness to work extra hours or preference for certain shift patterns for social reasons. Compliance with the Working Time Regulations alone is insufficient to manage the risks of fatigue.
4.Changes to working hours need to be risk assessed. The key considerations should be the principles contained in HSE’s guidance. Risk assessment may include the use of tools such as HSE’s ‘fatigue risk index’.
5.Employees should be consulted on working hours and shift patterns. However, note that employees may prefer certain shift patterns that are unhealthy and likely to cause fatigue.
6.Develop a policy that specifically addresses and sets limits on working hours, overtime and shift-swapping, and which guards against fatigue.
7.Implement the policy and make arrangements to monitor and enforce it. This may include developing a robust system of recording working hours, overtime, shift-swapping and on-call working.
8.Problems with overtime and shift-swapping may indicate inadequate resource allocation and staffing levels[1].
9.There are many different shift work-schedules and each schedule has different features. This sheer diversity of work and workplaces means that there is no single optimal shift system that suits everyone. However, a planned and systematic approach to assessing and managing the risks of shift work can improve the health and safety of workers.
10.There are a number of key risk factors in shift schedule design, which must be considered when assessing and managing the risks of shift work. These are the workload, the work activity, shift timing and duration, direction of rotation and the number and length of breaks during and between shifts. Other features of the workplace environment such as the physical environment, management issues and employee welfare can also contribute to the risks associated with shift work.
11.Sleep disturbances can lead to a ‘sleep debt’ and fatigue. Night workers are particularly at risk of fatigue because their day sleep is often lighter, shorter and more easily disturbed because of daytime noise and a natural reluctance to sleep during daylight.

( Source:    )

Principles of Equity in Compensation

In Equity Theory Towards a General Theory of Social Interaction (The Academic Press, 1976), J. Stacy Adams proposed that an employee continuously monitors his or her inputs and outputs on the job, and perceives an equitable situation when the ratio of his or her inputs and outputs are equal, to those of other employees. If this ratio is not equal, the employee may feel angry (as a result of not being paid enough) or guilty (as a result of being paid too much). Either feeling could result in dissatisfaction or discomfort.

(  Pay equity: Iinternal and external considerations  )

Principles of Differences in Productivity or Output of a person

It is empirically observed by IEs that in a group of workers there can be difference of 100% in output between the top performing worker and the lowest performance workers.

Related Materials

Human Factors Engineering Considerations in Safety - Principles and Practices

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