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Human Factors
Undergraduate 3

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What is anthropometry? List some examples of anthropometric data.
  • Anthropometry- is the study and measurement of human body dimensions.
  •  Anthropometric data are used to develop design guidelines for heights, clearances, grips, and reaches of workplaces and equipment for the purpose of accommodating the body dimensions of the potential work force. 
  • Anthropometric data are also applied in the design of consumer products such as clothes, automobiles, bicycles, furniture, hand tools, etc.

• Descriptive statistics of anthropometry:

 Know how to calculate statue for a selected population percentile.

 Know how to estimate the link-length or landmark of interest using the Drillis and 

Contini (1966) Figure.

  • Age: Stature increases to age 20-25 and starts to decrease after age 35-40. Women shrink more than men do.

  • Gender: On average, adult female dimensions are about 92% of adult male values. However, 12-year-old girls are, on average, taller and heavier than boys with the same age.
• What are the six steps for use of anthropometric data in design?
  1. Determine the intended users.
  2. Determine the relevant body dimensions.
  3. Determine the percentage of the population to be accommodated.
  4. Determine the percentile value of the selected anthropometric dimension (5%, 95%, or some other). Examples: design a stool to accommodate the 95th percentile of male body weight. That should include most people. Design a tray to be carried by workers to be light enough for the 5th percentile of women.
  5. Make necessary modifications to the data to take in to consideration clothing, gloves, and headwear.
  6. Use mock-ups or simulators to test the design.
  • Design for the extremes (safety)
  • Design for adjustable range (seats and steering wheels of cars, office chairs)
  • Design for the average as a last resort (checkout counters)
• General principles for workstation design: Clearance, Reach, and Adjustability
  • Clearance requirements - consider the largest users (95th percentile male)
  • Reach requirements - consider the smallest users (5th percentile female)
  • Adjustability requirements
  • Adjusting the workplace (shape, location, and orientation of the workplace)
  • Adjusting the worker position relative to the workplace (change in seat height, use of platforms or step-up stools)
  • Adjusting the work piece (lift tables, parts bin for easier access)
  • Adjusting the tool (adjustable-length hand tool)

Most researchers consider the normal line of sight to be about _____ degrees below the horizontal plane.

Work surface height for standing: Use _____ height as reference.
elbow height
• The two most prevalent musculoskeletal injuries are _____ and _____.
low back pain and upper-extremity (UE) cumulative trauma disorders. 
  • Basics about the musculoskeletal system
  • The musculoskeletal system consists of bones, muscles, and connective tissues, which include ligaments, tendons, fascia, and cartilage.

  • The main functions of the musculoskeletal system are to support and protect the body and body parts, to maintain posture and produce body movement, and to generate heat and maintain body temperature.
• Bones & joints: Most joints are _____ joints.
Synovial joints
• Connective tissues: Tendons, ligaments, cartilage, and fascia
  • Tendons- are dense fibrous connective tissues that attach muscles to bones and transmit the forces exerted by the muscles to the attached bones.
  • Ligaments- are also dense fibrous tissues, but their function is to connect the articular extremities of bones and help stabilize the articulations of bones at joints.

  • Cartilage- is a translucent elastic tissue that can be found on some articular bony surfaces and in some organs such as the nose and the ear.
  • Fascia- covers body structures and separates them from each other.
• What are three types of muscle contraction?
  • Concentric contraction (isotonic): The muscle shortens while contracting and produces a constant internal muscle force (Arm flexor muscles when an object is lifted upward).

  •  Eccentric contraction: The muscle lengthens while contracting, which occurs when the external force is greater than the internal muscle force (When a person picks up a heavy object and is unable to hold it in the desired position).
  • Isometric contraction: The muscle length remains unchanged during contraction (When a person pauses during lifting and holds the object in a static position).





• NIOSH lifting index: If LI is greater than or equal to 1, such a lifting is hazardous.
• Upper-extremity cumulative trauma disorders (CTDs): Common forms
  • Tendon-related CTD (tendonitis): Inflammation of the tendons
  • Neuritis (nerve pain caused by nerves rubbing against bones): Tingling and numbness
  • Ischemia (obstruction of the blood flow to a body part, e.g. pressure forces from the handle of a hand tool): Tingling and numbness

  • CTDs of the fingers: Caused by vibrating hand tools; can cause numbness, tingling, or pain when the hands are exposed to cold. Examples include white fingers, trigger finger and gamekeeper’s thumb.
  •  CTDs of the hand and wrist (carpal tunnel syndrome): Conventional keyboards bend the wrist and narrow the carpal tunnel.
  •  CTDs of the elbow: Tennis or golfer’s elbow.
• What should be considered for hand-tool design?
  • Bend the tool, not the wrist
  • Shape tool handles to assist grip
  • Provide adequate grip span
  • Provide finger and glove clearance
• What is the primary function for muscles?
  • Primary function: To generate force and produce movement.
• What are the three types of muscle cells (fibers)?

Three types of muscle cells (fibers):

Skeletal muscle: Voluntarily moves limb segments and supports joints

Smooth muscle: Autonomic functions (e.g., digestion of food)

Cardiac muscle: Brings contractions of the heart

• The three major sources of energy include: _____, _____ and _____.

Carbohydrates (glucose),Fat (fatty acids),Protein (amino acids)

• What is the difference between Aerobic and anaerobic metabolisms?

Aerobic metabolism (with oxygen) of carbohydrates

C6H12O6 + 6O2      36 ATP + 6CO2 + Heat

Anaerobic metabolism (without oxygen) of carbohydrates

C6H12O6        2 ATP + 2 Lactic Acid 

• What are the functions for circulatory system and respiratory system, respectively?


  • Transports oxygen and energy carriers (mostly glycogen) to various consumer organs
  • Collects waste products and delivers them to the excretory organs
  • Involved in thermoregulation: Control of body temperature

  • Functions as a gas exchanger:
  • Supplies body with oxygen
  • Removes carbon dioxide
  • Divided into two parts:
  • Upper respiratory system: Nose, pharynx, larynx, and trachea
  • Lower respiratory tubes: Bronchial tubes and alveoli

• The three methods for assessment of energy expenditures at work include:

Oxygen consumption

Heart rate counting

 Subject rating of perceived effort (RPE)

  • Oxygen consumption and heart rate are highly correlated. 
  • The correlation is low at light loads: influenced by psychological events.
  • With heavy work, cardiovascular capacities may be exhausted before metabolic or muscular limits are reached.
• Static work and local muscle fatigue: Rohmert curve

Fatigue: Exponential decrease of max hold time with the increase of %MVC (Rohmert, 1965)


Fatigue causes:

  • Blood closure
  • Occlusion
  • CO2, lactate increase -> H+ increase -> pH decrease 
  • Glycogen decrease
  • Heat increase

Fatigue can be examined using electromyography (EMG).

• What are stressors? List some typical examples.

Influences on information availability and processing that are not inherent in the content of the information itself. 



  • Examples include:
  • Environmental: Noise, vibration, heat, and dim lighting
  • Psychological: Anxiety, fatigue, frustration, and anger
• What are the four major effects of stress?
  • A psychological experience: Usually but not always feelings of frustration or arousal.
  • A change in physiology: e.g., change in heart rate or change in the output of catecholamines, measured in the urine after periods for flying combat maneuvers.
  • Stressors affect the efficiency of information processing, generally by degrading performance.
  • Stressors may have long-term negative consequences for health.  




High-frequency vibration:

  • Can be specific to a part of the body (handheld power saw) or to the whole body (from a vehicle).
  • Remediation for the former involves, tool selection and limiting dose exposure.
  • Whole body vibration makes it difficult for the user to input or control the device because of loss of precision. Written information may be blurred.
  • Remediation: insulating the user and the interface (input device) from the source of vibration (cushioning), using larger fonts.
  • Low-frequency vibration (rocking of a ship) and motion sickness:  Acts as a distracter making it hard to concentrate.  
Thermal Stress
  • Excessive heat or cold degrades performance and causes health problems.
  • Comfort zone: 73°F to 79°F in the summer; 69°F to 75°F in the winter.
  • Humidity: Less humidity is allowed (60%) at the upper temperature limit; more is allowed (85%) at the lower limit
Sources of excessive heat: Furnaces or boilers, outside temperatures, ovens, etc.
Sources of excessive cold: Freezers, outside temperatures, air conditioning
Body temperature is moderated by:
  • Clothing
  • Air movement
  • Physical activity
  • Provide ample amounts of fluids in excessive heat.
  • Protective clothing may cause a loss of manual dexterity.
Air quality
  • Poor ventilation: May not even be aware of carbon monoxide
  • Pollution: e.g., smog 
  • Lack of oxygen (anoxia) at high altitudes and cold can lead to frostbite as the body tries to provide oxygen to the brain and heart.
  • Negative effects on perceptual, motor, and cognitive performance 

• Psychological stressors: Amount of stress is related to the person’s understanding or _____ of the situation.

cognitive appraisal 
• What is optimal level of arousal?

Optimal level of arousal: Performance increases as arousal increases up to a certain point and then subsequently declines as stress-induced arousal increases further.

• Workload Overload: What is TR/TA model?

TR/TA (time required for the task/time available for the task) or time-ratio 

Determined by task analysis (include “think time”)

Allows for spare capacity of about 20%

Ratio can be > 1.0 if time-sharing

• What are the four different types of measurement for mental workload?
  • Primary task measure: Change the nature of the main task and see how performance changes.
  • Second task measure: Give a second task, measure changes in its performance as the primary task is changed in difficulty.
  • Physiological measure: Measure heart rate, eye movement, muscle tension, etc.
  • Subjective assessment: Self-report of users (example: NASA Task Load Index).
• Some basics about fatigue and Sleep Disruption
  • One effect of continuous work overload is fatigue.
  • Fatigue is a stressor that degrades performance and creates problems in maintaining attention. 
  • Fatigue studied in military operations (Desert Storm), long-haul truck drivers, medical workers in hospitals. 
  • Fatigue can also result from long periods of doing little.
Circadian Rhythms: Jet lag and shift work
  • Desynchronization: The circumstances when one tries to work against the natural circadian rhythm of the body.
  • Two implications:
  • Jet lag: Eastbound flight is more disruptive than westbound flight. Remediation includes: Go on the local time immediately (do not nap to catch up). May need to allow an extra day for recovery after a long trip.
  • Shift work: The best plan may be to rotate shifts slowly (every 14-21 days), or to rotate by delaying rather than advancing the shift. 
• List some examples of remediation to sleep disruption
  • Get more sleep
  • Napping (15 minutes with 10 minutes recovery time): Presence of sleep inertia
  • Build up sleep credits
  • Sleep management
  • What does not work: Drugs such as caffeine
• What is the difference between safety and health?
• What is the difference between safety and health?


    • Safety is concerned with injury-causing situations (acute)
    • Health is concerned with disease-causing situations (prolonged)

• Before safety became legislated, workers had to prove the employer’s negligence in not_____, which was not precisely defined.

providing a reasonable amount of care 

Before safety legislation, the three common laws that employers could use to defend  themselves include: _____, _____ and _____.


 • Contributory Negligence  , • Fellow Servant Rule and • Assumption of Risk .


  • Contributory Negligence: The employer was not liable if the employee was injured due to his own negligence.
  • Fellow Servant Rule: The employer was not liable for an injury to an employee that resulted from the negligence of a fellow employee.
  • Assumption of Risk: The employer was not liable because the employee took the job with full knowledge of the risks and hazards involved.


• What is workers’ compensation?
    • The first two laws based on providing compensation to workers for on-the-job injuries for were thrown out as unconstitutional (around 1910). One was in Montana for miners and the other in New York for eight highly hazardous occupations.
    • After a devastating fire (1911) in a shirt factory in New York which killed 146 workers and seriously injured 70 more, the Supreme Court ruled that state workers' compensation laws were constitutional in 1917.
    • Today over 80% of workers are covered by state workers' compensation laws.
    • Workers' comp is a form of insurance paid by the companies.
    • Claims must meet three conditions:

It arose from an accident,

It arose out of the worker's employment, and

It occurred during the course of employment.

  • Workers are not allowed to sue their employers, but may sue a third party.
  • Manufacturers are responsible for faulty equipment (liability).
When was OSHA established? What are OSHA’s responsibilities?

In 1970, OSHA (Occupational Safety and Health Administration) was established as a federal

What are OSHA’s responsibilities?
  • Implements safety programs
  • Sets health and safety standards
  • Conducts inspections
  • Investigates problems
  • Monitors illnesses and injuries
  • Issues citations, assesses penalties, petitions the courts to take action against unsafe employers
  • Provides safety training
  • Maintains a database of health and safety statistics
• The duties of NIOSH include: _____, _____ and _____.
  • Performing research and educational functions,
  • Conducting or reviewing research to identify hazardous types of conditions, and
  • Preparing recommendations for OSHA standards and workplace design or safety applications.
What are the two implications for human factors in product liability?
  • Concept of reasonably foreseeable
  • Tradeoff between risk and benefit (making something safer could make it less efficient)
• List some examples of causal and contributing factors for accidents
What is the definition for human error?
inappropriate human behavior that lowers levels of system effectiveness or safety.
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