Document baj3MeBV4byDkyZL3BMJM81BZ

( 106 EOSS A. MC FARLAND any desired direction 'by shifting the position of a foot. It is necessary, therefore that a satisfactory area be provided for him to carry out compensatory shifts oi his trunk or foot. If operations must be conducted from the standing position anc involve such movements as manual adjustments with extended.arm reach, or the removal of one foot from the ground to operate controls, suitable hand or foot reste should be provided. These furnish not only an additional point of postural support but also eliminate unnecessary energy requirements that would otherwise be needed for support of the extended extremity. The lack of a stable platform of operations will force the worker to divide hie attention between maintaining his posture against unusual disorienting forces anc operating his machine. Further, the additional energy utilized for maintaining balance is nonproductive. In consequence, unstable or slfppery footing, inadequati seating, and poor body support all adversely influence control operation, reduci efficiency, contribute to muscular and perhaps mental fatigue, and greatly increasi the opportunity for injury. h. Emergency Controls. An emergency control is generally operated by ,thi worker making the error or having the accident. Hence, it should be placed so tha* it can be operated by other members of the body than the one likely to become caught or injured in the apparatus. Whether the safety stop should be operated b; hand or foot or by either is dependent on the task and on certain other factordi:| involved in rapid control operation. Hand-operated controls have some advantages :;! -in-that-the-reaction-time-of-the-hands4sJess..than_that-of..the-feet,,MQreo.v.er,.iLihs operator is standing, he may have to shift his weight from one foot to the other. in||| order to manipulate a foot control, thereby adding time to the operation. If the emergency control is to be operated by the hand, it should be positioned ! within easy reach by either hand when the operator is at or near the normal work#! place or hear.the area where the injury is likely to occur. The same, of course, is| true for. aioot-operated control. The control should not have to be used accurately^ and should require only a small amount of force. Since speed of operation is^prob=fl ably the most important factor in determining the success of an emergency control?^ any arrangement that can only be operated by one particular limb (such as the:! right foot) is likely to be unsuccessful.2 -41 ----j~^q^^nnfan|s^JHuman-engmeering-data-Eelating4-tQiAhei^design...of....lo6^ controls are less <pgmplete ithamthe conaparable:data.,on.vhand;.c.ontro,lkwln ,geheja;la hqweveri the:problems encountered in the design, of foot controls are relatively les|l| complex.ii:FiiqntStosb.hck.'Seat adjustability can establish satisfactory access to foqtraj controls for people of varying leg lengths, as mentioned above under "Seating Dimensions." The lateral location of pedals frequently can be more critical, howjj| ever, especially in vehicular or other types of equipment where frequent use oft|i several pedals is essential both to the operation of the machine and to the safetyi| of the operator. When foot controls are crowded, many operational difficulties arei* often present, especially with heavier footgear, such as the unintentional applica-Si tion of one pedal while attempting to depress the other, or undue delay in remov9,|i HUMAN ENGINEERING AND INDUSTRIAL SAFETY 107 -.TEST7 |^^S;Iug`'thq;f,oot from one pedal in order to avoid striking the edge or underside of a ecbiiid 'p.edal. The optimum lateral spacing will vary widely depending on the size j^^^|^S',type of shoes or bo.ots normally used on the job. Clearances should not be m^3lullsessari1y large, however, especially between pedals to be used in rapid rj^iucncej.since this may increase application time. 2yk$ne|,gf the aims of foot-pedal design is to lower the energy demands on the ^^fej^erl't'drliThis can be accomplished in part by a lever-arm ratio requiring rela- amounts of work. The machine layout may sometimes place the leg E^S{#Amfa|i^al positions or may require the driver to make complex compensatory ots in order to move the foot from one pedal to another, thus resulting ^mll^ry fatiSue- For this reason there should be no structural interference ^^viuj'-thelmovement of the leg or legs during operation of the controls. In order to A^yoK-Uiihiiecessary leg motion, the height of a foot pedal in the rest position should jJwMSpjl^ixjJppd 10 inches above the floor, 8 inches being preferable. In all cases there ^^lrgraMp a, reasonably large contact area between the sole of the foot and the J^^^i^npder to prevent slippage, and for pressure of long duration, contact with ^^Aliyjwljaillfoot is desirable.88 However, since the arch of the foot can exert a greater aw8[Wtei)ihe toe, the foot should be applied to the pedal so that the distance from " pedal axis is about 4 inches.89 This fact is confirmed by the research 'Snd Weddell, who state that maximum force with minimum fatigue is jhen the bones of the lower leg are in a direct line with the pedal axis. iof contact is toward the front of the heel. It was found, in addition, that im leg position, of those tested, for exerting maximum pressure without |yith the thigh horizontal and the knee at a 45 angle from the vertical. ;h is elevated from the seat a greater pressure can be exerted. Should (ty.be desirable and feasible in the pedal stalk itself, there are some data Ijthat about 8V2 inches of adjustability will be necessary in order to ate persons (males) of different body size.90 ..Iwrtbfa&fcSa*1 ffc,.', S. Standardisation 0/ Equipment sSfcr'i. ||he major factors that may cause a worker-to deviate from the best a job is the variable nature of the controls and equipment pro- thTiffflffidff&r ig calleTupon"to employ'different type o{ device in order to effect a given end. The arrangement of -i" p- `Koch, Fiissbediente Arbeitsmachinen und Ermudung, ArbettsseAvf4,:<3,. 5M9 (1941). lakgyy-M- jifeUer, Die gunstige Anordung im sitzen betatigter Fuszhebel, "^rbeiUphynologU, and G. M. Weddell, The pressure which can be exerted by the foot of a the Ieg * variou* Positions, R. N. P. 44/188, Royal, Naval Personnel Med. Research Council, Cambridge University, England, 1944. Psychological requirements in aviation equipment design. J. Aviation Me'd.. (P 1i'ltt8' Psychology and aircraft design. Mech. Eng., 69, No. 2, 135 (1947).