Human Capabilities & Work Physiology II

Transcription

1 Human Capabilities & Work Physiology II Vision Circadian rhythms Musculoskeletal system Recognition of Work Environment Hazards: Introduction to Industrial Hygiene and Ergonomics Visual Capabilities We depend primarily on vision to gather information about the state of the world outside our own bodies! 1

2 We Read instructions Look up information in books Respond to traffic signs Use maps to navigate Refer to dials and meters to understand speed, temperature, etc Vision Rays are REFRACTED by lens Lens focuses light rays on retina Retina converts light to signal 2

3 The Visual System CORNEA: protects eyes, performs 70% of focusing required to produce image on the retina LENS: focuses light rays on retina IRIS: controls the amount of light admitted VITREOUS HUMOR: maintains eye shape, refractive properties The Visual System FOVEA: area of greatest sensitivity RETINA: converts light to signal ~120 Million Rods White, Black, Grey ~10 Million Cones Colors OPTIC NERVE: transmits signal to brain 3

4 Visual Capacities Visual acuity: ability to detect small details and to discriminate small objects (resolving capacity of the eye) Contrast sensitivity: ability of the eye to perceive a small difference in luminance (this is how we can appreciate different grades of shading and brightness) Visual Capacities Speed of perception: time interval that elapses between the appearance of a visual signal and its conscious perception in the brain (e.g. could be improved with better lighting and luminance) 4

5 Best Vision is achieved when: Image is focused on fovea Lighting is adequate Target is in direction of gaze Target is fixed Contrast is adequate Target Detection & Recognizition Size Shape Color Brightness Contrast Illumination Motion Clarity Time to view Visual defects 5

6 Visual Fatigue Excessive stress on any of the functions of the eye Loss of productivity Lowering of quality More mistakes Increased accident rate Visual complaints Bad lighting is the cause of 5% of all industrial accidents Circadian Rhythms Night work/shift work 6

7 Our Biological Clock Ergotropic phase: The human organism is geared to performance Trophotropic phase: The human organism occupied with recuperation and replacement of energy Circadian Rhythm Latin circa (About) di (Day), about a day Night/day cycle It resets on a daily basis so that it has a cycle time of exactly 24 hr in normal people It is important because of shift work About 20% of workers in the US are shift workers of some sort 7

8 Circadian variation as measured by body temperature Alertness ratings are often related to these circadian variations! Average hours of sleep by shift workers 8

9 Occupational problems among shift workers who periodically work at night 9

10 Night/Shift Work Ergonomics is faced with the problem of planning work schedules in such a way that night/shift work does as little harm as possible to health and social life (Kroemer & Grandjean, 1997) Night/Shift Work Some schemes: Weekly rotating 5 day schedule Weekly rotating 7 day schedule Rapid rotation 7 day schedule Factors: # of Shifts, 8 or 12 hrs shifts? 10

11 Night/Shift Work Short-term effects Occur because of a mismatch between the demands of the work and the state of the worker s circadian rhythm Poor quality sleep Need to maintain alertness during work Fatigue Night/Shift Work Long-term effects Higher risk of cardiovascular disease Gastrointestinal ailments Emotional and social problems Our society is not only daytimeoriented but also weekend-oriented! 11

12 Recommendations If Night/Shift work is unavoidable Night/shift workers should not be engaged when they are below 25 years old over 50 Workers should not be employed on night work if they: Have a tendency towards ailments of the stomach and intestine, Are emotionally unstable Prone to sleeplessness Recommendations If Night/Shift work is unavoidable Short-term rotations are better than long-term ones Continuous night work without rotation should be avoided Whether one, two or three nights are worked in a row, they should be followed immediately by at least 24 hr of rest Every shift should include one longer break for a hot meal, to ensure adequate nourishment 12

13 MUSCULOSKELETAL SYSTEM The human body is able to move because it has a widely distributed system of muscles! Musculoskeletal System Muscles make up approximately 40% of the total body weight The human body: 600 muscles Most activities are carried out by fewer than 80 pairs 13

14 Musculoskeletal System Muscle fibers: a muscle has several hundred thousand fibers Muscular contraction: ability of the muscle to shorten to about half its normal resting length Muscle metabolism: energy for muscle action comes from the food we eat and digest Carbohydrates = primary source of muscle energy Muscular efforts DYNAMIC EFFORT: MOTION Characterized by an alternation of contraction and extension Tension and relaxation Muscle length changes often rhythmically Blood flows through the muscle A dynamic effort can be carried out for a very long time without time for recovery 14

15 Muscular efforts STATIC EFFORT: POSTURE Characterized by a prolonged state of contraction (tension) of the muscles Muscle does not change its length Blood no longer flows through the muscle Muscle does not receive oxygen A static muscular effort cannot be carried out for extended periods Muscular efforts STATIC vs. DYNAMIC There is no sharp line between static and dynamic muscular effort. Often one particular task is partly static and partly dynamic 15

16 Static Muscular effort A static muscular effort leads to: A higher energy consumption Raised heart rate Longer rest periods needed There are static components in almost every form of physical work Jobs which involve bending the back forward or sideways Holding things in the hands Manipulations which require the arms to be held stretched our or raised above shoulder height 16

17 There are static components in almost every form of physical work (cont.) Putting the weight on one leg while the other works a pedal Standing in one place for long periods Raising the shoulder for long periods Muscular Efforts 17

18 Static vs. Dynamic Muscular Efforts: What do you see? Static vs. Dynamic Muscular Efforts: What do you see? 18

19 Static vs. Dynamic Muscular Efforts: What do you see? Static vs. Dynamic Muscular Efforts: What do you see? 19