Document bBnQgyX87KryKyymqaQDQob81

70 BOSS A. MC FARLAND value of one dimension, the corresponding range of values for a second dimension can be determined. The use of such tables can sometimes help to avoid thp un necessary consideration of some of the many individual body measurements that might be pertinent to the design of a piece of equipment. In general, stature correlates reasonably well with body heights and lengths, and weight j with breadths, depths, and circumferences.18 A person of the 5th or of the 95th percen tile in height and weight will tend to approximate (but not necessarily duplicate) the 5th or 95th percentiles in his other measurements. Thus, if the height and weight of a group are known, and these measurements are easily taken, approxi mations of some of their other body dimensions may be obtained by referring to correlation tables for this group or even for roughly comparable groups. These have been worked out extensively for the military population by Newman and White. However, it cannot be too strongly emphasized that the correlations are not high enough to permit precise individual prediction, but only group predic tion. With intergroup comparisons there is an added factor of error. For these reasons measurements of the dimension involved are always preferable in situa tions where any degree of precision is required. j 8. Dynamic Body Measurements l So far the discussion of anthropometric measurements has centered around the-static-dimensions-of-the..human-body--AlthQUgh_thcse_dim.ej3fiionsj&Le;ielEz ful in solving many problems of human sizing in equipment operation) it is evident that a man never operates his machine in the rigid nude positions in which his measurements are taken. For this reason additional material on the dimensions of the human body under dynamic conditions is necessary. Tp take the most'obvious case, clothing can and does alter a man's weight and dimensions considerably. For example, if precise values of weight are required, it is necessary to add allowances for the type of clothing worn while working and for the-weight of pocket contents. For men, street clothing may weigh 4 to 8 pounds. While the total increases in the example cited may amount to only about 5 per cent of the nude weight, the specification of a precise reference weight may be important for . -dRRign-pv)Tpose.y,-ior-example,-iLan-engineer..adds-a^per.c.en,tage.safety factor to. the strength of a structure based upon a nude referencerrw'eigKt that safety! factor would obviously be less than intended. The percentage difference might not be great but situations can be readily visualized where such differences may be of practical-importance, .for.example, when establishing limitations for the] num ber of people occupying an elevator or a vehicle; in conservation of critical rnaterials; or in transport equipment where weight penalties must be reduced to a minimum.2 In addition to increasing weight, clothing increases body dimensions, and in " R. A. McFarland, A. Damon, and H. W. Stoudt, The Application of Human Body Size Data to Vehicular Design. Special Publication 142, Soc. Automotive Engrs., 1955. fit JVi'1Vf.$* ;B y' &j HUMAN ENGINEERING AND INDUSTRIAL SAFETY 71 (Stases restricts the range and distance of movement as well, as in functional aji^^&slb-.With light summer clothing such changes may be negligible, while winter clothing the differences may be considerable. Other appliesdifferences for clothed and unclothed dimensions might be signifi- ^l^6tild be calculation of area of contact from anthropometric descriptions of ejlniiids-and feet, as well as clearance-between hand controls, and clearance .iBj|||||||s(or foot-operated controls. fii'Ogreater generalimportance, however, in the over-all concept of dynamic Jappis the fact that variations in certain body measurements can influence WS5e?8 ability to perform those movements or actions required for the ^i&ftpTafpjon of his mechanical equipment. For example, the location of a con- ~'||||||Iarge man might well be grossly inadequate for a much smaller opera^^Slcases such as this, one of two courses of action may be taken. Either (I) .u^ontrbi must be relocated so as to be equally accessible to both the largest and 3jlcst;men,t or, if this is not feasible, (8) adjustability must be built in at one uui'of'Jtrie'[machine dimension, either at the control itself or at the seat or stand(ir^^gSnhe operator.18 nSdnsidering the whole problem of the functional human dimensions per- ^mftp>i|he-- safe design of mechanical equipment, it becomes apparent that |B^ic*!ta needed, in addition to the statio body dimensions in the working .jpfe&l^lpof three types: (1) the eye level of individuals in the working posioi ffi^i)^iei-maximum-arm-reaches,-in- various- -vertical- and -horizontal planes, fn|be attained without altering position, and the extension of these reaches JllPfJfiy further movements of the trunk or body; (3) the leg reaches that |||f|ihed without altering position.16 ^^prnah-Seated Eye Level. This is a basic measurement of considerable fffirfnrtS^in.the design of working areas of industrial equipment. The eye posi- B p^||erator will determine, in part, how much' of his surroundings he > Se6' and ^ow we^ b will be able to see it. Many working areas ^^^^^Ipfzone in which the operator's eyes will be able to supply him with ^^MMssa^-yisual information most efficiently. The -disadvantages of an eye IS8l^igb^|ft^oo high are obvious in the case of vehicular equipment, for ex- " ^^i^oonditions-existrthe' designer must-see^that-the- spatial-relallc|f'''or^lng area are redesigned so as to permit optimum visibility, done, however, unless he first knows at what height above a ^T^atll^erthe operator's eyes will be located. Although it tnJght geem that 5^pqia'hej^)iti3E0.uld..he-aJairly, straightforward.static .anthropometric, meas- has a pro equipment. [. occupational groups have been directly measured for normal ' "R. M. Thomson, and J. Orlansky, "Layout of Workplaces," in Joint Services Guide to Equipment Design, Wright-Patterson Air Force Base, Ohio, jSM-j!* i.'fl r&K