work-space design

1. WORK-SPACE DESIGN 1

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3. 3 INTRODUCTION Many of the tools, facilities and workplaces are found to be not suitable to human use because of their design features. Examples include: uncomfortable chairs, low or high sinks in toilets and kitchens, clothes, repairing tools and equipments. These examples are the results of failure to design equipment and facilities to fit the physical dimensions of the people who will use them. This chapter will focus on how things can be designed to fit the physical dimensions of people.

4. 4 ANTHROPOMETRY It deals with the measurement of the dimensions and other physical characteristics of the body such as the volumes, center of gravity and masses of body segments. Body dimensions are fundamental to a wider range of design problems. Body measurements could be static or dynamic (functional). Engineering anthropometry is concerned with the application of both types of data to the design of the things people use.

5. 5 Static Dimensions Taken when the body is in a fixed (static) position. They consist of skeletal dimensions (between the centers of joints) or contour dimensions (skin-surface dimensions such as head circumference). Many dimensions can be measured (NASA Anthropometric source book contains 973 measurements from 91 worldwide surveys). Many of the dimensions have specific applications (helmets, gloves, etc.). But many body features dimensions also have general utility. See figure 13-1 and table 13-1. (Also see the figures in BODYSPACE).

6. 6 What does a 5th percentile or 95th percentile mean? The answer is that the percentile refers to the percent of the population that have a dimension below the stated dimension. How can we calculate any percentile value? Use the Formula: X(p)=m + sz You will also need to use the z-values table. Body dimensions vary as a function of age, sex, and for different ethnic populations (see figure 13-2). Stature and related dimensions generally increase until the late teens or early twenties. They then remain relatively constant and then decline when entering into old age.

7. 7 Figure 13-3a illustrates the differences between the dimensions due to sex difference and figure 13-3b illustrates the differences due ethnic reasons. Differences in dimensions between people working in different occupations are also common (occupational differences).

8. 8 Dynamic (functional) Dimensions Taken while the body is engaged in some physical activity. In most physical activities, the individual body members function in concert (many members are moved and the relative position is affected).

9. 9 General discussion about static and dynamic dimensions Static anthropometric data exists more than dynamic anthropometric data even though dynamic data are more representative of actual human activities. Although there is no clear way of converting static data to dynamic, the following recommendations may be helpful:

10. 10 Reduce heights (stature, eye, shoulder, hip) by 3 percent. Elbow height: no change, or increase by 5 percent if elevated at work. Knee or popliteal height, sitting: no change, except with high-heel shoes. Forward and lateral reaches: decrease by 30 percent for convenience, increase by 20 percent for extensive shoulder and trunk motions.

11. 11 USE OF ANTHROPOMETRIC DATA The data should be representative of the population that would use the item designed. If designing for general purposes, the features must accommodate a broad range of people. But when items are designed for specific groups, the data used should be specific for such groups.

12. 12 PRINCIPLES IN THE APPLICATION OF ANTHROPOMETRIC DATA Three general principles: Designing for extreme individuals: All should be accommodated. Sometimes, a single design dimension is a limiting factor that might restrict the use of the facility for some people. This factor can dictate either a maximum or a minimum value of the dimension in question.

13. 13 Designing for the maximum population value is the strategy used if a given maximum (high) value of some design feature should accommodate all (almost) people. Examples: heights of doorways, strength of supporting devices such as ropes. Designing for the minimum population value is the strategy used if a given minimum value (low) of some design feature should accommodate all (almost) people. Examples: The distance of a control button from the operator, the force required to operate the control.

14. 14 Designing for adjustable range: Some features of equipment or facilities can be designed so that they can be adjusted to the individuals who use them. Examples: automobile seats, office chairs, desk heights. The practice is to provide for adjustments (of the relevant dimensions) to cover the range from the 5th percentile female to the 95th percentile male of the population. What will be the percent of the population covered if the above mentioned range is used?

15. 15 Designing for an adjustable range is the preferred method of design. But sadly, it is not always possible. Designing for the average: The cheapest and most quick method. But does an average person exist? A person who is average on one or few dimensions will surely not be average on many dimension. This is because there is no perfect correlation between the dimensions.

16. 16 Designing for the average is common and often is acceptable in situations involving non critical work where it is not appropriate to design for the extreme and also where adjustability is impractical. Example: A checkout counter at a supermarket is built for the average customer.

17. 17 SUGGESTIONS FOR USING ANTHROPOMETRIC DATA IN DESIGN Specify the body dimensions that are important in the design. Define the population to use the facility or equipment. This will establish the dimensional range that needs to be considered. Determine what principle should be applied (average, extreme, or adjustable).

18. 18 Determine the percentage of population to be accommodated. Locate the appropriate anthropometric tables to be used and extract the relevant values. Add the appropriate allowances (clothing, shoes etc�). Build a full-scale mock-up of the equipment or facility and have representative people of large and small user (of the population) try it.

19. 19 POSTURE CONSIDERATION Posture is defined as the relative orientation of the parts of the body in space. It is determined by the connection (relationship) between the dimensions of the body and the dimensions of the workspace. The connection may be physical (seat, worktop) or visual (location of displays and tools). If the dimensional match is inappropriate, the short-term and long-term consequences of the well-being of the person may be severe.

20. 20 To maintain a certain posture over a period of time, the muscles must be used to counteract the external and internal forces acting on the body. A varied working posture (dynamic) is better than a fixed (static) working posture. Simple guidelines for better posture are offered in Pheasant�s book (page62 & 63).