I NDUSTRIAL S TUDIES ON F ATIGUE

12.6 I NDUSTRIAL S TUDIES ON F ATIGUE

United States Public Health Service conducted a study on 889 interstate truck drivers in three cities—Baltimore, Nashville and Chicago to find out the relationship between working hour and fatigue. This is one of the most valuable studies in the field of industrial psychology. The objectives of this study were:

To determine if various period of truck driving would produce demonstrable and significant psycho physiological changes;

To investigate the nature of these changes; and

To discover whether a characteristic pattern of psycho physiological

Industrial Psychology

The sixteen factors which were considered as contributing to fatigue in truck drivers were:

1. Performance of a skilled operation requiring a high degree of alertness and attention.

2. Nervous strain due to driving under adverse conditions.

3. Muscular exertion in loading and unloading and in the repair and maintenance of vehicles.

4. General irregularity of habit as a result of long distance hauls.

5. Failure to obtain satisfactory rest or sleep during rest periods or when off duty.

6. Physical condition.

7. Constant use of the eyes, frequently under unfavourable conditions such as glare, etc.

8. Social factors in the environment or occupational tradition possibly promoted by enforced absence from home.

9. Monotony inducing sleepiness.

10. The consumption of coffee and alcohol.

11. Exposure to all types of weather conditions.

12. Exposure to toxic fumes and gases.

13. Economic insecurity, that is, fear of losing one’s job especially in the case of older men.

14. Noises

15. Vibration

16. Sedentary occupation—the effect of posture. Crowden (1932) 5 classify muscular work in industry into three general types:

(i) Heavy muscular work that is too strenuous for a steady, continues rate of work to be maintained. Examples of this type of work are loading trucks, building roads and possibly mining coal.

(ii) Moderate heavy work that is continuous and which the rate of expenditure of effort is much lower than in the first type and is somewhat balanced by the rate of recovery. Examples of this type of work include machines tending and many other kinds of factory work.

(iii) In this type muscular work in the industry is light, speed work which involves a relatively small expenditure of energy but which often require a postural stain that cause unnecessary fatigue. Example is office work.

Crowden found that in a 50 yard borrow run the worker expends approximately 8% of his energy in raising and lowering the handles, 22% in attaining a wheeling speed and in stopping, and the remaining 70% in the run itself. This study shows the tremendous inefficiencies that would

Industrial Fatigue

result from interfering with the run once it is stared. While studying the energy cost of moderately heavy work, Bedale (1924) found that carrying a load with a yoke as a milk-maid does is the most economical method from the point of view of expenditure of bodily energy. Any method of carrying weights which requires postural strain and displacement of the body when walking is more costly.

Crowden holds the view that light speed work involves little expenditure of energy, but that there may be considerable fatigue because of the cramped or uncomfortable position maintained by the worker.

According to Blum & Naylor, the men who had been driving prior to being tested performed less efficiently on the average than those who had not driven on tests of the functions like (i) aiming, (ii) resistance to glare and (iii) speed of eye movement.

The data on these tests, however, do not differentiate consistently between drivers who worked from 1 to 10 hours and those who worked over

10 hours. In items 1–7 this difference does occur. The heart rate decreased slightly with hours of driving. The average white cell count was higher in men who had driven since sleeping than in men who had not drivers since sleeping. No relationship was found between hours of driving and ability to estimate the size of known objects, differentiate white cell counts, hemoglobin content of the blood, acidity of the urine, specific gravity of urine, visual acuity and the total base and potassium concentration of blood serum.