Document OE3Vyez1VR2q0jep8DZan0DdX

72 ROSS A. MC FARLAND sitting eye height. One is a group of commercial truck and bus drivers who aver aged 29.36 inches in this dimension.11 See Table 2 for the distribution of the series. In the other series 100 male employees of the Civil Aeronautics Adminis tration averaged 29.66 inches with a standard deviation of 1.24 inches. In an other male series of 4,000 AAF flying personnel on which sitting eye height, erect, was taken, the average was 31.47 inches with a S.D. of 1.27 inches.13 For this series, however, a correction factor may be subtracted to adjust for the probable slump in normal sitting eye height. This factor, or difference, between erect and normal seated posture, has been variously determined as follows: (a) two studies at Wright Field showed an average of 1.2 inches;20 (6) 360 commercial truck and bus drivers averaged 1.8 inches;11 (c) 131 civilian pilots showed an average of-2.25 inches.21 In general, those with smaller sitting heights will have a smaller than average slump -while those with large sitting heights will be above average in slump. For women, only two small series of erect sitting eye height are available; 443 female pilots averaged 30.0 inches, while 151 nurses averaged. 29.3 inches.17 No direct information on slump is available, but it might be tentatively assumed that the average would be slightly less than those observed for males. b. Arm Reaches. One limiting factor in establishing the dimensions of any working area, including the location of controls, tools, and materials, is the func tional arm reach of the operator. It might seem that the static body measure ment of anterior arm reach could be used.as an indication of the maximum bound aries of the working area for the location of hand controIsrHoweverTIhis dfmension defines only the very limited reach area directly in front of the shoulder.Reach to a vertical plane in front of the worker falls off rapidly as the arms are moved to the sides or up and down. Moreover, there is no completely satisfactory , way of predicting functional arm reach from anterior arm length or any other ,| single static dimension because of the numerous other variables involved, such as individual differences in sitting heights, shoulder breadths, and variations in | the biomechanics of movement at the shoulder. Owing to these difficulties most .jij j of the research in this field has been directed toward the study of specific installs-: tions for specific populations rather than toward more generally applicable descriptions of biomechanics and human abilities. Thisius^not.idifficult .to undetgj stand since the humanvbodjTTs so complexThat-a_T_o_rm.i.c..f.eE..S.blleff1iinumFertof kdescrips,sa tions would, be required in order to provide , inforraaiior^?'torbWeiWution of-'#'|f significant percentage of industrial situations. It is necessary to develop orderly < summaries of the degree of movement, the precision of movement, and the force; Of movementtoTthe' component"parts of the body-with-and^withouttsupplementary body support and with various degrees of flexion, extension, rotation, adduction; and abduction. " D. I. Pfttt, Cockpit dimensions in relation to human body size, TSEALS-69SSSTT, | ATSC, USAAF, April 29,1945. "B. G. King and J. J. Swearingen, Some biological factors in the design of civil aircraft, J. Aviation Med., 19, 414-419 (1948). SESa^j-' tirmRfi^ i feTA > J si HUMAN ENGINEERING AND INDUSTRIAL SAFETY 73 JygPhgreasiest type of functional arm-reach data to obtain is that concerned 1S3uVi,t;'righly a single horizontal or vertical plane. On horizontal surfaces two "reach" Sjforop';?.! may be defined. First, there is a normal reach zone in which work can be jjffjjr^irtost easily without the use of the upper arm. Second, there is a maximum q-fc^ii'lAz.iivgithat extends to the points of maximum arm reach. In general, of course, ^'T^Kpsiftoo1s, or materials that must be handled often or accurately should be ^.liT^redl^ithin the normal reach zone. Secondary items or controls, used only*1 ally, may be located beyond the normal reach zone but within maximum dtW:t ^ shows a drawing of the dimensions of these normal and maximum for m'4?leK,h,nd Normil lor X rMulmum for < riaW hind fa! gif W - rffiffitthunro'S, The normal and maximum working areas on a horizontal surface as determined 17 -i;cyr.cnts made on 30 males. The areas are shown for the.right and left hands working 33 ^or hands working together. (Reprinted with permission from Ralph .f;.s,;TVor/c Methods Manual, 1944, John Wiley and Sons, Inc.) a-- constructed by Barnes. The zones, he believes, should be api^^1^^^^fef;bpu.t_95._.peiu-cent.--of..the....adult ..working--population..,.Eor._some i r j, (iipational groups, or for segments of the general population larger Jie'^ese dimensions could be increased. It will be -noticed that the eao^ ann are semicircular in shape. Work requiring two hands ^^sQl'gi'ip.eated. within the overlapping areas of the right and leftjiands.22 reach to a vertical plane in front of the operator will lie &1^shoulder. As the arms are moved to the right and left, or from this point, decreasing portions of the vertical plane will fall A Work Methods Manual. Wiley, New York, 1944. See also P. C: Squires, normal work area, XJ. S. Naval Medical Research Laboratory, Report No. 276, gBglMiConn, 1956. '