Document jB5Q1JKy65mLaxKQKjaRNGn5N

78 ROSS A. MC FARLAND HUMAN ENGINEERING AND INDUSTRIAL SAFETY 79 adjustability of the dimension between the foot controls and the seated position of the worker. Although there is the possibility of making the controls themselves adjust able, it has generally been found easier and more satisfactory to have a range of front-to-back adjustability in the seat. The amount of adjustability will depend upon the range of leg length of the population operating the machine. To give a \ V STEERING POST SEAT REFERENCE POINT TOE PAN X. 8TEERIN0 ' POST PIVOT FLOOR _L -FIXED REFERENCE POINT Figure 6. Schematic diagram of a mock-up' truck cab designed to determine the various adjustments and arrangements required by a population of a given range in body size. A similar mock-up could be designed for almost any kind of equipment or working area. (From Kephart and Dunlap") concrete example,.it. was found that 6*/ inches o^. ad|Ustabifityj;w.as|co.mpletely ;;;l adequate for 90 per cent of all commercial bus and truck drivers.26 With other populations, as where small women are using the same equipment as large men, the range_would be greater. This engineering problem oocutb only when the seat . is a fixed part of the working area, as in vehicular equipment; where the seat is a movable stool or chair, a wide range of positions is usually feasible, and the problem can be solved much more simply. d. Seating Dimensions. In those industrial tasks that require or permit a seated position, the most efficient and comfortable design of seats and chairs is essential. This necessitates the use of a special group of body measurements, many of gare basically static in nature, such as seat breadth. However, additional ^including clothing increments, room for changing of positions, and body S^ces during the operation of controls, require a partially dynamic treatment fMfelem. The location, dimensions, and adjustability of the seat should be with reference to the arrangements and location of the tools, materials, - ' s. and displays used by the person. In addition, the seat must afford the maximum comfort, consistent with efficiency, in order to reduce fatigue, lcujnal, comfortable seat design can do much to add to the efficiency and il'yiciisjob performance. g^|gsITf[Seat designs, equally as much as in other aspects of equipment design, the that is to use the equipment must be measured directly. For this 1*TM a|j.is difficult to make specific recommendations applicable to industry in |iitW?T'rro'- giv__e___a__n__e__x__t_r_e_m___e_ e,,,,x_a_m___p_ile__,__s__o_m___e__orf itLhe._s_e. ajt :d__i_m__e_n__s_:io__n__s__a__n__d3 llo_ca1ti:o__ns_ jtp for female factory workers would be most unsatisfactory for a substan- of the size range of commercial truck drivers. What will be l^.,,J~^...t,,;...Med here are the pertinent body dimensions and design principles relevant fii^K&'Afi^irllonstruction. Some specific figures will be given, based on data drawn pyjjMj^'o;m.dijferent segments of the population. The dimensions and characteristics that must be considered include the breadth, depth, height, slope, and jPf j|he seat and back rest. Kbreadth. This dimension is one of the easiest to establish and can be lllg lie seat breadth of the individual as measured across the buttocks when eped position. In a study of the seating problem in industry, Garner has SSjggjjcthe breadth need be only 16 to 17 inches.27'28 These may be accept- jldnimum figures, but if changes of seated position are occasionally possible Spe,. and if all but the very broadest of male workers are to be included, a |SdJ19 inches will be more satisfactory. H||depth. The most important single consideration in seat depth (length) Ifratei parts of the hip bones that bear the weight of the seated body (the ^ j|aerosities) should be properly supported. A depth of as little as 8 to 10 ^ ` _. 1 be sufficient for this purpose, a requirement fulfilled by almost all yjw^&i^lutt jiakjeats. If the seat depth is excessive, workers with shorter legs will find 0f seat cutting .into the baok of-the, call,,and wjll be unable to >if jjjj^nee satisfactorily unless they shift their buttocks forward' on the seat. ^ other hand, long-legged workers will have inadequate .thigh support if M^|tefia.tds':tQ0 short. The upper limit for this dimension can be^^ennined.from >**^g^jb&!ijil'gh- length of the smallest segment of the population to be.accommodated, from tBe back of the calf to the plane of the back' while in'the seated "^^g^ltip^phe. 5th percentile of a large series of the general population was 17.0 dimension (males 17.4, females 16.8).12 A seat depth greater than Garner, Posture in its relation to industrial fatigue, Med. J. and Record,. 138, ^SsSS3'.5'J,.,lt. Gamer, Fatigue in its relation to accident prevention, Ind. Med., 6, 66f>-668 (1937).