Lecture 3 & 4

Question 1

Define (generally) Ergonomics.

Answer 1

• An applied scientific discipline concerned with how humans interact with the tools and equipment they use while performing tasks and other activities.
• Also called “human factors engineering”
• Ergonomics seeks to develop a “fit” between people and the jobs they do.

Question 2

What are the different types of metabolism?

Answer 2

• Basal metabolism - energy used only to sustain the vital circulatory and respiratory functions.
  
  • Basal Metabolic Rate (BMR)
    
    • 20yr old male - 1.0kcal/hr/kg.body weight
    • 20yr old female - 0.9 kcal/hr/kg.body weight
• Activity metabolism - energy associated with physical activity
  
  • Metabolic Rate (AMR): Varies significantly with activity.
• Digestive metabolism - energy used for digestion
  
  • Digestive Metabolic Rate (DMR) is about 10% of (BMR+AMR)
• Total daily metabolic rate:
  
  • TMR_d = BMR_d + AMR_d + DMR_d

Question 3

Question 4

A 30 year old female office worker’s job consists of the following during an eight-hour shift (percentages based on time): 10 percent walking (assume 4.5 km/hr), 25 percent standing, and 65 percent seated. She weighs 57kg. During the time when she is not working, her activities consist of the following: sleeping 8.0 hr; resting(reading, watch tv etc.), 7.0 hr; jogging, 30 min; and standing, 30 min.

What is her total energy expenditure?

Answer 4

Question 5

Capacity of human body to use energy and apply forces depends on what?

Answer 5

• Capacity of cardiovascular and respiratory systems to deliver required fuel and oxygen to muscles and carry away waste products
• Muscle strength and endurance
• Ability to maintain proper heat balance within the body.

Question 6

Draw a graph of work activity vs energy expenditure, what is the recommended mean energy expenditure over 8 hour shift?

Answer 6

Question 7

Draw a graph (energy expenditure/oxygen consumption vs time) and show the areas of oxygen debt and oxygen recovery.

Answer 7

Question 8

A 72 kg. male worker performs a repetitive task with a 12- min work cycle. During each cycle his energy expenditure rate is 7.8 kcal/min for 20% of the time and 5.6 kcal/min for the remaining 80%. On average, what rest break should be allowed at the end of each work cycle.

Answer 8

Question 9

Define muscle endurance.

How long does muscle endurance last?

Answer 9

• Muscle endurance is defined as the capability to maintain an applied force over time.
• After about 8 to 10 minutes, a person can only apply about 25% of maximum static force achieved at beginning of test.

Question 10

What is Anthropometry?

Answer 10

• Empirical science concerned with the physical measurements of the human body, such as height, range of joint movements, and weight.
• Differences in body dimensions exist because:
  
  • Ethnicity and Nationality
  • Heredity
  • Diet
  • Health
  • Sex
  • Age
  • Living conditions

Question 11

What are the different anthropometric design approaches?

Answer 11

• Design for extreme individuals
  
  • If maximum value of design feature should accommodate all people (or vice versa for minimum)
• Design for adjustability
  
  • To acommodate the 5th percentile female to the 95th percentile male.
  • An adjustable range is the preferred method of design, but of course, it is not always possible.
• Design for the average user
  
  • When design for extreme individuals and adjustability are not feasible.
  • Should only be done after careful consideration of the situation and never as an easy way out.
• Design different sizes for different size users
  
  • When the only way to accommodate user population is to make the product in different sizes (e.g., clothing, shoes)

Question 12

Define cognitive ergonomics

Answer 12

Study of the capabilities and limitations of the human brain and sensory system while performing activities that have a significant information processing content.

Question 13

What are some guidelines for sensory reception design?

Answer 13

• Standardization - having similar devices operate in the same way.
• Redundancy - presenting information using more than one sensory mode.
• Stimulus variation - use of variable stimuli rather than stimuli that are constant and continous.
• Graphical displays - information presented graphically usually more effective than same information presented as text.

Question 14

When should information be displayed visually and when should information be displayed auditory?

Answer 14

• When to use visual
  
  • Long message
  • Complex message
  • Referred to later
  • Noisy environment
  • Person remains in one location
• When to use auditory
  
  • Short message
  • Simple message
  • Requires action now
  • Very light or very dark
  • Person expected to move around
  • To attract attention to exceptions.

Question 15

What are the different types of attention?

Answer 15

• Selective attention - Driving
  
  • situation in which a person needs to monitor multiple sources of information in order to perceive irregularities or opportunities
• Focused attention - Making conversation in a noisy bar
  
  • situations in which a person must cope with multiple input channels but focus on only one channel for a sustained period of time.
• Divided attention - Operating several machines at once
  
  • situations in which there are multiple stimuli, but multiple tasks must be performed together
• Sustained attention - Life boat rescue
  
  • situations in which a person must watch for a signal of interest over a relatively long period of time, and it is important to avoid missing the signal.

Question 16

What are factors leading to lack of attention/boredom on the job?

Answer 16

• Short cycle times
• Low requirements for body movements
• Warm environment
• Lack of contact with other workers
• Low motivation
• Low lighting levels in workplace

Question 17

What are the guidelines for memory?

Answer 17

• Minimize demands on working memory:
  
  • minimize the number of alphanumeric items that must be kept in working memory and length of time they must be retained.
• Exploit chunking
  
  • Formulate meaningful sequences out of a string of alphanumeric characters.
  • Use letters rather than numbers
  • limit chunk size to 3 or 4 characters
• Increase frequency and recency of using information stored in long-term memory
  
  • Drills to recall emergency procedures
  • Regular and frequent training sessions
  • Standardized procedures in batch operations
• Use memory aids
  
  • Written instructions for procedures that must be carried out in the correct sequence

Question 18

What are factors that affect the difficulty and speed of response selection and execution?

Answer 18

• Decision complexity
  
  • Mores choices, the more complicated decision process and time to decide.
• Response expectancy
  
  • expected information processed much faster than not expected.
• Compatibility
  
  • response compatibility means that the possible responses should be consistent with one’s expectations
• Trade-off between speed and accuracy
  
  • negative correlation between speed and accuracy in response selection and execution.
• Feedback
  
  • Allows a person to see and/or hear the effect of their actions.

Question 19

What are some guidelines for control design?

Answer 19

• Use coding to make controls easier to distinguish
• Code by:
  
  • Location. e.g., car foot pedals
  • Colour. e.g., emergency stop button
  • Size and shape. e.g., aircraft cockpit controls
  • Labelling (text or icon). e.g., CNC machine tool.

Question 20

Define visual acuity and show how it is calculated.

Answer 20

Question 21

Explain why light is important in the workplace.

Answer 21

• 80% of the information input the human brain comes from visual stimuli.
• Colour discrimination - capability to distinguish colours, approximately 20% of population has some form of colour blindness.
• Adaptation - ability to adapt to changes in light level
  
  • Dark adaptation - from bright to dark environment. (Light adaptation vice versa)

Question 22

Define Luminous flux and luminous intensity.

Answer 22

• Luminous flux - rate at which light energy is emitted in all directions from a light source - Units: lumen (Im)
• Luminous intensity - lumious flux emitted in a given direction
  
  • UnitsL candela (cd). Candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation…
    *

Question 23

Explain illuminance and how it changes with light source distance/angle from surface.

Answer 23

Question 24

What is luminance?

Answer 24

• Luminance (L) - amount of light reflected from a surface
  
  • Units: cd/sq m
• Depends on:
  
  • Illuminance - amount of striking surface (E)
  • Reflectance - depends on color and texture of surface (R)

Question 25

What is the equation to measure contrast?

Answer 25

Question 26

How is sound intensity is measured?

Answer 26

• Sound intensity is measured from the listener’s perspective
• Could be measured as pressure, e.g. N/m² or Pa
• Intensity is measured relative to a reference pressure and converted to logarithmic scale called sound pressure level (SPL) with units of decibel (dB):

Question 27

What are the regulations regard noise?

Answer 27

• The Noise Regulations specify actions at certain levels of noise, when averaged over an 8 hour working day, and also specify exposure to maximum noise.
• For daily exposure average above 80dBA, employers must provide hearing prtection if requested.
• For daily exposure averaging above 85 dBA, employers must provide hearing protection, and make sure it is used.

Question 28

A worker is exposed to two noise sources, one at 80 dBA and the other at 84dBA. Determine:

• the total sound pressure level of the two sources
• the permissible duration of exposure for this sound pressure level, to keep below the daily personal noise exposure level of 85dBA.

Answer 28

Question 29

What are the physiological effects of noise?

Answer 29

• Startle response - due to sudden loud noise
  
  • causes spontaenous muscle contractions, blinking eyes, head-jerk movement.
• Hearing loss (three categories)
  
  • Temporary threshold shift - hearing impairment of short duration
  • Noise-induced permanent threshold shift - results from long term exposure to high noise levels
  • Acoustic trauma - single exposure to high intensity noise can cause temporary or permanent hearing loss.

Question 30

What are techniques used to control noise exposure?

Answer 30

• Administrative controls
  
  • managing the exposure durations for employees working in noisy environments by setting time limits on exposure to noise level.
• Engineering controls
  
  • Noise abetement at three locations
    
    • Source - design quieter machinery insulation, vibration dampin, lubrication, natural cooling instead of fans
    • Receiver - use of ear plugs, helmets
    • Path between source and receiver - enclosures for noisy machines, sound proof doors.