## Human Factors

What color is the Anthropometry book?
Beige
What year was the Anthropometry book made?
1978
Human Factors Engineering Definition
Study of interaction between people and their work
What is Human Factors Engineering?
measurement, analysis, evaluation, and design of systems involving human-machine/tools/equipment-task-environment interaction for the purpose of enhancing performance, safety and health
Four Components In Workforce
1) Human
2) Machine/Tools/Equipment
4) Environment Interaction
Human Factors Engineering (American) =
Ergonomics (European)
In America, Physical Work is Considered
Ergonomics
In America, Mental Work is Considered
Human Factors
Discipline Based On
Human Capacity>Job(Work) Demands
(90-95% of Population)
Benefits of HFE
1) Increased productivity and production
2) Reduced injury and accident rates
3) Increased efficiency & reliability
4) Enhanced maintainability
5) Increased worker morale and job satisfaction
Must be able to understand the
Human Capacity
Who created an article about “Help! My Computer is Killing Me”?
National Enquirer
What test would you perform using three or more variables/groups?
F-Test
Analysis of Variance
Statistical method used to test differences between two or more means
T-Test
Compares mean of two samples
If you wanted to compare height alone, what procedure do you use?
Simple Linear Regression
If you wanted to compare height, weight, and arm length, what procedure do you use?
Multiple Linear Regression
If you wanted to compare the performance of sophomore, juniors, and seniors, what performance do you use?
Analysis of Variance
Reliability
consistency, little variation
Validity
Valid measure of what it needs to be measured
What is it called when you tighten with a screwdriver?
Supination
What is it called when you loosen with a screwdriver?
Pronation
When leaning forward,…
the weight of the upper body and muscle pull produce a pressure in the lumbar spine similar to the pressure produced on the ground by the weight of a ladder and pull of a rope.
(there is tremendous amount of pressure in the muscles)
What causes the back strain?
Compression
Flexion
movement that closes the angle at a joint
Extension
movement that opens the angle at a joint
(T/F) You cannot extend body part unless you have started with a flex position
True
Abduction
movement away from body the body mid-line
Hyper-extension
Extend beyond anatomical position
Palmar Flexion
Hand Flexion
Dorsi Flexion
Hand Extension
Ulnar Deviation
move toward the ulna bone
(Ulna is on the pinkie side)
(Radius is on the thumb side)
Anthropometry
study of human body dimensions
Name of the book NASA Published
Anthropometric Source Book
Volume I: Anthropometry for Designers
Sagittal Plane
Splits body into left and right
Coronal/Frontal Plane
Front and Back of the Body
Transverse Plane
Up and Lower Body
Factors that affect body size
1) Age
2) Sex
3) Ethnicity and nationality
4) Nutritional status and general health
5) Type of Occupation
Factors that add to natural size
1) Clothing
2) Body Position
3) Restraints
Principles of Design
1) Design for extremes
3) Design for the average
Design for extremes
when a design for the very small (large) person also fits the very large (small) person
when a fixed extreme design cannot accommodate the other extreme
Design for the average
When the other two designs are not feasible
Two types of lower back injuries
1) Suddenly
2) Accumulative effect time
RWL
Required Weight Limit
Stress is also called the
stressor
When stress is called the stressor
strain is called the stress
Stress
condition that has adverse effect on the body
Strain
reaction to stress
U-Shape Curve
some optimal stress that you perform at its maximum
Variable Classifications
1) Physiological
2) Biomechanical
4) Environmental
5) Mental
6) Psychological
7) Psychosocial
Physiological
source (vision, hearing)
how you performing the work
Mental
processing information
Psychological
affects the way you behave
Psychosocial
interaction between yourself and other people and how you react
Primary sources of job stress
1) work demands
2) work design
3) workplace and workspace designs
4)physical environmental design
5) Psychosocial factors
Joints
Permit movement, posture, strength, support, shape, protection for organ.
Are pivots to the motion.
Muscles
Generate forces for movement and posture.
Made up of elastic protein fibers and connective tissues.
Can stretch and contract.
Tendons
connective tissue strands that connect muscles to bones. Transmit muscle forces to bones.
Cannot really expand/contract.
Tendon Sheath
fluid-filled protective covering over tendon near a bony projection (joint) or tough connective tissue to protect tendon from wear and tear
Ligaments
protein cords that bind the bones at a joint.
Bursa
fluid-filled sac over certain joints that protect tendons from wear and tear
Types of muscles
smooth, cardiac and skeletal
Tendinitis
inflammation of the tendons.
May be caused by excessive muscular forces or repetitive forces
Tenosynovitis
inflammation of the tendon sheath.
Excessive gripping and squeezing of hand tools.
Bursitis
inflammation of the bursa
Prime mover
effects actual movements
Antagonist
-acts by relaxing and enabling p.m. to work
– capable of preventing the movement by contraction
Fixator
provides stable base by steadying a part of body from which other muscles perform
Synergist
controls position of immediate joints such that in passing over several joints, it may exert power in moving distal joint
In lab, you do not test beyond what percentage?
75%
What is the capacity that you should not exceed in an 8-hour job?
1/3
Metabolism
conversion of foods into mechanical work and heat
ATP
Aerobic Metabolism
With enough oxygen in the cells ATP can be regenerated continuously
Anaerobic Metabolism
When Oxygen is deficient in the body ATP is regenerated with the help of creatine phosphate
inefficient and produces lactic acid which poisons the muscles
Food is converted into
ATP
PWC
Physical Work Capacity
VO2 Max
Maximal Oxygen Uptake
Physical Work Capacity
maximal rate at which the body can use oxygen at sea level under specified conditions
PWC is also called
VO2 Max
HRMax=
220-Age
O2 vs HR is
Approximately Linear
Interpolate to 200 to get VO2 Max/PWC
PWC is measured in
liters/min
1 liter/min=
4.83 kcal/min
Job energy on 8-hr job
< 1/3 worker PWC
Job energy on 1-hr job
< 1/2 worker PWC
HR TWA
time weighted average heart rate
HR TWA for women
< 110 beats/min
HR TWA for men
< 120 beats/min
TWA HR=
(sum of read heart rate*hours worked at that rate)/Time worked
Acts as pivot when bend, forward, backward, side ways when lifting
L5/S1
L5/S1
The 5th level diskof the lumbar spine and 1st level disk of the sacro.
Accounts for the most back injuries
L4/L5
Accounts for the second most back injuries
Effect of lifting
degeneration and herniation of L5/S1 and L4/L5 spinal discs
Factors affecting lifting ability
2) Personal
3) Environmental
4) Management
5) Psychosocial
Classification of lifts
Squat
Stoop
Free style
Squat
Trunk upright and knees sharply flexed.
Better for heavier lifting objects.
Stoop
Trunk flexed at hip and knees fairly straight.
Better for light and medium lifting objects.
Biomechanical
Limits
Compressive forces over 6400 N at the L5/S1 disc is considered dangerous.
3400-6400 N compression is considered a range within which the injury is likely to occur.
Below 3400 N is considered safe.
3 Force Components
Compression
Shear
Torsion
Metabolic Limit for 8-hr job
9.5 kcal/min
NIOSH
National Institute for Occupational Safety and Health
OSHA
Variables that are in the NOISH equation
H
V
H
horizontal distance from ankles to c.m. of load
V
height of c.m. above floor at start of lift
LI
Lifting index
LI=
L/RWL
When LI is ____, it is at great risk of injury?
> 3
Applications of Biomechanics
Determine upper limits of loads (weights) that a person can handle (lift, lower, etc.).

Determine maximal muscular forces that can be exerted for a certain task or by a certain muscle group.

Determine amount of compression or shearing forces in joints from tasks.

Muscle force
compare force required to lift, say, to the weight being lifted
Compare muscle force during task to
muscle force capacity
What kinds of sensory/environmental factors have significant effects on work efficiency and health?
1. Thermal
2. Visual stimuli
3. Auditory
4. Olfactory
What biomechanical attributes of a worker affect his/her job performance and health?
1. Physical size
2. Limitation of movement
3. Muscle strength
What kinds of worker behavioral or performance problems can be caused by poor work design?
1. Heavy turn over
2. Labor unrest
3. Job dissatisfaction
4. Absenteeism
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