Document 4v87zqGKgKmJm1Vz3GaejNaOa

108 BOSS A. MC FARLANB the controls, the manner in which they are operated, and their "feel" may differ significantly from one model to another. Even though the different models are equally effective in performing a given operation, the difference becomes important because it introduces novelty into a situation where uniformity is needed. In many industrial tasks, it is essential that the worker devote his whole attention to the result and not to the means. A good example is the operation of a motor vehicle through heavy traffic. Here the operator should be devoting his attention to his surrounds and to making judgments relative to distances, directions, and speeds, and not to the manner in which his controls are to be operated. To be truly effective, equipment, insofar as possible, should be amenable to automatic operation. It should provide the opportunity for the utilization of habitual modes of action. This does not imply that the worker should never change his response as any change in the situation may require. Rather, the fundamental motions he employs should be so stabilized that in moments of stress and decision he should be able to devote himself to solving the problems so suddenly presented and not to the types of movements he is to make. When the worker is called upon to utilize different models of equipment, he must pause and consider the manner in which the particular equipment operates and is thus unable to give his entire, attention to the larger problem confronting him. Furthermore, when the worker is confronted with different equipment from time to time, he may never be able to develop appropriate habitual responses because of the constant change. With standardized-equipment.-thejiEorker..can-devote his entire attention to the situation ' confronting him and thereby can anticipate and deal more effectively with what-, ever hazardous circumstances develop.2 IV. Design of the Working Area in Relation to Environmental Variables The way in which a worker carries out his job is influenced to a large extent 1 by a group of physical variables consisting of temperature, humidity, noise, vibra-;i tion, and so forth, and any other features especially characteristic of the working J environment. The optimum integration of the man with the machine cannot be.jw achieved, in a human engineering sense, unless these physical variables are taken into account in the initial design, or the redesign, of the worker's machines andra equipment, as. wiiras'TFeWhble~brKisrimiiiediBte''working-areat93~Many-of-ttn^H variables pertihent' to this discussion are given detailed treatment in special chAffigp ters of this voiume and hence will be treated here only briefly in regard to certain ' selected aspects. Mubiroftheresearch in human tolerances to physical variables.has.been based upon physiological hazards to man or upon sensory stimulation. However, another important kind of tolerance to consider is what may be called a performance:! tolerance where some definable impairment in performance serves as a criterion} . " R. A. McFarland, Human Factors in Air Transportation--Occupational Health and j Safety. McGraw-Hill, New York, 1953. HUMAN ENGINEEKING AND INDUSTRIAL SAFETY 109 might be the level of sound intensity at which a worker's co-ordina^Ktfefion^ecomes measurably impaired; a specific feature of a man's behavior is thus 'w^^cfafcpned rather than only possible damage to his ear, ^ftfgifeuch tolerances are very significant for industrial safety because they refer K^jjTconditions in which an employee's performance may be below par and errors prevalent. This point of view takes account of those factors, such as sjlpjWnation,' sound, and temperature, which may have adverse effects upon an ^^^Sbr's performance and which may be controlled through human engineering An increased error rate is often one result of exceeding an operator's ^.Spc'nqrmance tolerances for one. or more of these variables. Although there are $5j$m;in'y jstudies of the effects of environmental variables upon behavior, much of ^as D0* been gathered and systematized an no tn -- PHYSIOLOGICALLY HARMFUL ZONE -ft- DISCOMFORT ZONE \COMFORT I ZONE 7<0 <30- 30-70% LUXURY ZONE no4' o* if? DECELERATION '0 * "/,,c` . / "a JtTrTF.-rt physical variables of the environment and their influence, on comfort, djsSfcgjfaSywUi. These figures were prepared specifically with reference to the operators Mts3l{-co,nmeroial vehiles, but could be applied in a general way to some other fisnrn such as this can, of course, give only approximate yalues since lfetM"':,,ffi?ljnterdependent with one or more additional factors. (After McFarland") - f'