Topic 1: Human Factors & Ergonomics
Essential idea: Designers consider three human factors to ensure products meet ergonomic needs.
1.1a : Anthropometric:
Nature of design:
Design is human centered and, therefore, designers need to ensure that the products they design are the right size for the
user and therefore comfortable to use. Designers have access to data and drawings, which state measurements of human
beings of all ages and sizes. Designers need to consider how users will interact with the product or service. Use and misuse
is an important consideration. (1.5, 1.18, 1.20)
Concept and principles:
• Anthropometric data: static and dynamic data, structural and functional data
• Primary data versus secondary data
• Percentiles and percentile ranges
• Range of sizes versus adjustability
• Clearance, reach and adjustability
Guidance:
• Collecting anthropometric data considering reliability and limitations
• Interpreting percentile tables for user populations
• Design contexts where different percentile ranges are used
Anthropometrics:
Anthropometrics deal with body measurements, particularly those of size, strength, and physical capacity. For
example, making a product fit people’s measurements such as making a mouse curve to fit in all hands.
Define user population
The range of users for a particular product or system.
Outline how large user groups may be defined Consideration has to take into account age,
gender and physical condition.
Describe how a user group sample is based on the factors age, gender and physical condition.
Around World War II, Henry Dreyfuss Associates started to develop
anthropometric guidelines for designers using data gathered from other sources, which are inherently
biased since most are still culled from the military. The primary difference was that this data was being
generated to allow designers to apply human factors information to design CONSUMER Products. (Before
this data was systematically developed, designers used "rule-of-thumb’s like a table height should
be @ 1 meter, which worked fine for designing simpler objects, but not for complex objects like
automobiles).
The charts generated focused on three different sets of numbers, called percentiles. Let's say the adult
population makes up 100%, researchers break down the group into 100 percentile groups with the first
percentile being the smallest and the 100th percentile being the largest. As designers, most of the time, it
suffices to limit ourselves to dealing with the 5th to the 95th percentile, meaning that we would cover
90 out of 100 adults. Dreyfuss charts include the 2.5%, 50%, and 97.5%, covering 95% of the adults.
Since the 1st and 100th percentiles are rare in that they encompass extremes, they are rarely considered.
Henry Dreyfuss designed his charts to be visual aids, so that they could be photo stated to scale and
incorporated into drawings, but as designers, we really never consider the 50th percentile. If a small
person (2.5 or 5 %) can reach the lever in front them, or see over the steering column, anyone in
percentile groups above that can as well. Conversely, if a tall person (95 or 97.5%) can sit in car interior
without hitting their head on the ceiling, anyone smaller can fit in as well. So what we look for are the
extremes in relation to the tasks at hand.
In anthropometrics there is no such thing as a 50th percentile person. You will never meet someone whose
entire anthropometric measurements fits in just one percentile, and this is where reality and statistical
purity collide, especially in product testing, once you have applied the numbers, so don't make
assumptions every person who is 180cm are going to have the same seated height.
Outline the use of the concept of “methods of extremes” to limit sample sizes
Sample users are selected to represent the extremes of the user population plus one or two intermediate
values, for example, evaluating a kitchen layout may use the shortest (2.5thpercentile), the mean (50th
percentile) and the tallest (97.5th percentile).
Percentiles are shown in anthropometry tables and they tell you whether the measurement given in the
tables relates to the 'average' person, or someone who is above or below average in a certain
dimension.
If you look at the heights of a group of adults, you'll probably notice that most of them look about the
same height. A few may be noticeably taller and a few may be noticeably shorter. This 'same height'
will be near the average (called the 'mean' in statistics) and
is
shown in anthropometry tables
as the fiftieth percentile, often written as '50th %ile'. This means that it is the most likely height in a group of
people. If we plotted a graph of the heights (or most other dimensions) of our group of people, it would
look similar to this:
First, notice that the graph is symmetrical – so that 50% of people are of average height or taller, and 50%
are of average height or smaller. The graph tails off to either end, because fewer people are extremely tall
or very short. To the left of the average, there is a point known as the 5th percentile, because 5% of the
people (or 1 person in 20) is shorter than this particular height. The same distance to the right is a point
known as the 95th percentile, where only 1 person in 20 is taller than this height.
So, we also need to know whether we are designing for all potential users or just the ones of above or
below average dimensions. Now, this depends on exactly what it is that we are designing.
For example, if we were designing a doorway using the height, shoulder width, hip width etc., of an
average person, then half the people using the doorway would be taller than the average, and half
would be wider. Since the tallest people are not necessarily the widest, more than half the users would
have to bend down or turn sideways to get through the doorway. Therefore, in this case we would need to
design using dimensions of the widest and tallest people to ensure that everyone could walk through
normally.
Deciding whether to use the 5th, 50th or 95th percentile value depends on what you are designing and
who you are designing it for.
Usually, you will find that if you pick the right percentile, 95% of people will be able to use your design. For
instance, if you were choosing a door height, you would choose the dimension of people's height (often
called 'stature' in anthropometry tables) and pick the 95th percentile value – in other words, you would
design for the taller people. You wouldn't need to worry about the average height people, or the 5th
percentile ones – they would be able to fit through the door anyway.
Here are some examples of other situations - your design project will normally fit into one of these groups:
What is it that you are aiming
for with your design?
Design examples:
Examples of
measurements to
consider:
Easy reach
Vehicle dashboards,
Shelving
x Arm length,
Shoulder height
Smallest user: 5th
percentile
Adequate clearance to avoid
unwanted contact or trapping
Manholes,
Cinema seats
x Shoulder or hip width,
Thigh length
Largest user: 95th
percentile
A good match between the user and
the product
Seats,
Cycle helmets,
Pushchairs
x Knee-floor height,
Head circumference,
Weight
Maximum range: 5th to
95th percentile
A comfortable and safe posture
Lawnmowers,
Monitor positions,
Worksurface heights
x Elbow height, Sitting
eye height, Elbow
height (sitting or
standing?)
Maximum range: 5th to
95th percentile
Easy operation
Screw bottle tops,
Door handles,
Light switches
x Grip strength,
Hand width,
Height
Smallest or weakest user:
5th percentile
To ensure that an item can't be
reached or operated
Machine guarding mesh,
Distance of railings from
hazard
x Finger width
Smallest user: 5th
percentile
Largest user: 95th
percentile
Arm length
Users that your design
should accommodate:
Compare the collection of static anthropometric data with the collection of dynamic anthropometric
data:
Static data is much easier to gather, as people are asked to remain still while
measurements are taken.
Dynamic data involves people carrying out tasks. People carry out tasks in
many different ways.
While static data is more reliable, dynamic data is often more useful.
Describe the instruments used in the collection of anthropometric data
Instrument
Image
Operation
Torso Calipers
This caliper works similar to those used in our
workshops- vernier caliper. These torso
calipers make a direct reading of the
distance between the subject's back and
the front of the subject's abdomen.
Cloth tape
Flexible cloth or ribbon tape measure which
can be moulded round the body.
Sitting height
meter
The Sitting Height Table has a standard type
of ball-bearing mounted, counter-balanced
head block, giving accurate and direct
readings from 320 mm to 1090 mm.
In addition it has a secondary carriage, fitted
with an anti-reverse carriage lock, in order to
compensate for upper leg variations: and an
adjustable foot-rest in order to compensate
for lower leg variations.
Identify an appropriate percentile range for the design of adjustable equipment
Equipment might include car seats, office chairs, desk heights, footrests. The range from 5th percentile
female to 95th percentile male will accommodate 95% of a male and female population because of the
overlap between female and male body dimensions for each dimension.
Multivariate accommodation (fitting in several variables, for example, in a car you need to fit in terms of
sitting height, leg room, arm reach, viewing angles, hip breadth, thigh length) means that accepting 5%
being designed out for each important dimension is not viable, because different people will be designed
out for each variable. People have different proportions. Those designed out because they are too tall
may not be the same as those designed out because their arm reach is too short.
Task: Identify an appropriate percentile range for the design of the adjustable equipment listed below:
x Car seats
x Office chairs
x Economy Aircraft seat
Explain how designers use primary and secondary anthropometric data in solving a design problem
Primary anthropometric data collection
(also called field research) involves the collection of data that does not already exist. This can be
through numerous forms, including questionnaires and telephone interviews amongst others.
Secondary anthropometric data collection
(also known as desk research) involves the summary, collation and/or synthesis of existing data
rather than primary data, where data is collected from, for example, research subjects or
experiments.
1.1b Psychological factors:
Nature of design:
Human beings vary psychologically in complex ways. Any attempt by designers to classify people into groups merely results in
a statement of broad principles that may or may not be relevant to the individual. Design permeates every aspect of human
experience and data pertaining to what cannot be seen such as touch, taste, and smell are often expressions of opinion rather
than checkable fact.
Concepts and principles:
• Psychological factor data
• Human information processing systems
• Effect of environmental factors
• Alertness
• Perception
Guidance:
• Data in relation to light, smell, sound, taste, temperature and texture as qualitative or quantitative (ordinal/interval)
• Methods of collecting psychological factor data
• Representing the human information processing system using flow diagrams
• Applying the human information processing system to a common task
• Evaluating effects and reasons for a breakdown in the human information processing system
• User responses to environmental factors
• How environmental factors induce different levels of alertness
• The importance of optimizing environmental factors to maximize workplace performance
• Assessing the impact of perception in relation to the accuracy and reliability of psychological factor data
Psychological factors:
Psychological factors have more to do with the brain and the body such as smell, light, sound, texture and
temperature.
Temperature
Heating conditions in work and leisure,
comfort zones e.g. supermarket/restaurant
temperatures that are comfortable for the
consumer.
Sound
Supermarkets carefully choose music that is
‘easy listening’ to try to improve the mood of
the consumer while shopping.
Light
Lighting in workplaces, safety. E.g. effects of
florescent. Lighting effect on ambience and
mood e.g. lighting in restaurants – gentle,
calming, stimulating.
Texture
Appreciation of textile qualities and their
applications in design situations. E.g.
smoothness of kitchen work surfaces for
reasons of hygiene, tiles on a factory floor (i.e.
roughened surface to prevent slipping).
Colours
Effects on emotions. e.g. sense of `warmth' and
`coldness' i.e. `warm' red/orange/yellow ‘cool'
violet/green/blue. The use and application of
such knowledge in the designed environment.
e.g. decoration, symbols,
Smell/ Taste
Aroma dispensers to provide an expected smell
(e.g. fresh bread, coffee odors in supermarkets)
or to mask other odors e.g. cigarette smoke in
bars.
Identify the general human factors contributing to accidents
Categories of factors that cause accidents include management (policies, safety education,
decision centralization),
physical environment (noise, temperature, pollutants, trip hazards, signage), equipment design
(controls, visibility, hazards, warnings, guards), the work itself (boredom and repetitiveness, mental
and physical workload, musculoskeletal impacts such as force, pressure and repetition),
social and psychological environment (group rules, morale), and the worker (ability, alertness, age,
fatigue).
Outline the factors that contribute to thermal comfort in office and other working environments
Thermal comfort describes a person’s psychological state of mind and involves a range of
environmental factors: air temperature, the heat radiating from the Sun, fires and other heat sources, air
velocity (still air makes people feel stuffy, moving air increases heat loss), humidity, and personal
factors (clothing and metabolic rate). Hopefully in an office environment where a number of people
work together, the thermal environment satisfies the majority of the people. Thermal comfort is not
measured by air temperature, but by the number of people complaining of thermal discomfort .
Thermal comfort affects morale and productivity.
Thermal comfort is that condition of mind that which expresses satisfaction with the thermal environment.
Thermal environment is those characteristics of the environment which affects a person's heat loss.
In terms of bodily sensations, thermal comfort is a sensation of hot, warm, slightly warmer, neutral,
slightly cooler, cool and cold.
From the physiological point of view, thermal comfort occurs when there is a thermal equilibrium
in the absence of regulatory sweating
between the heat exchange between the human body
and the environment.
Discuss the legislative requirements for temperature in the workplace
Legislation sets minimum and maximum temperatures for different types of workplace, and workers
have the right to refuse to work if such temperatures are not maintained. Legislation bodies use
questionnaire or
surveys to identify potential issues as part of a planned workplace inspection. Questions such as:
x Do you find the atmosphere hot, cold, stuffy or draughty?
x When do you notice these
conditions?
x What effect do these conditions have on your work?
x How do you deal with them?
To assess the risk they conduct a risk assessment to:
x
x
x
Assess the number of people likely to be exposed to the thermal comfort hazards and the duration of
the exposure;
Assess the likelihood of the hazards and consequences identified below; and
Use the risk assessment table to identify the risk rating.
Outline the legislative requirements for decibel levels for working with machinery.
Excessive noise in the workplace can cause workers to lose their hearing and/or to suffer from tinnitus
(permanent ringing in the ears). The level at which employers must provide hearing protection and
hearing protection zones in, for example, the UK is now
85 decibels (daily or weekly average exposure), and the level at which employers must assess the risk to
workers’ health and provide them with information and training is now 80 decibels.
There is also an exposure limit value of 87 decibels, taking account of any reduction in exposure
provided by hearing protection, above which workers must not be exposed.
Describe the methods used for identifying hazards and evaluating risks.
Methods include the following:
x Scenario analysis attempts to identify patterns of behavior that precede accidents. If such behavior
can be identified, then it may be avoided by a redesign of a product.
x Fault tree analysis determines the causes of failures by first identifying the types of injuries that may
occur and concluding with redesign solutions.
x Hazard assessment determines probable causes for injury and indicates ways to eliminate the
hazards.
Fault Tree Analysis of Ladder
Task: Using the Risk Assessment table below- suggest your answers in the blank boxes provided. An
example has been done for you. You could also use this table in your Design Project
Task
Boiling water
using kettle
Risks
Burns &
Electrocution
Cause of risks
x Spillage
x Over-filling
x Electrical contact
with water
Level of risk Action to reduce risk
x Ensure kettle has stable base and is
High
secured
x Water does not exceed highlighted
Max level on Kettle
x Electrical cables are not close to
contact with water
x Electrical cable does not dangle/hang
over
Using Pillar Drill
Listening to your
I-pod
Explain how human factors specialists determine adequate product safety.
Behavioral testing: perform some activity with the product such as unpacking, assembly, operation and
maintenance.
Task: Conceptual testing: evaluate safety instructions and warning messages without exposing people to
hazardous conditions.
1.1c Physiological factors:
Nature of design:
Designers study physical characteristics to optimize the user’s safety, health, comfort and performance.
Concepts and principles:
• Physiological factor data
• Comfort and fatigue
• Biomechanics
Guidance:
• Types of physiological factor data available to designers and how they are collected
• How data related to comfort and fatigue informs design decisions
• The importance of biomechanics to the design of different products considering muscle strength, age, user interface and
torque
Physiological factors:
Physiological factors have more to do with bodily tolerances such as comfort and fatigue. For example, padding
parts in a seat bottom where pressure will be applied for long periods of time.
Outline physiological factors that affect ergonomics.
For example, bodily tolerances such as fatigue and comfort. For example, the controls of a machine may be
designed for correct reach but if in constant use may cause fatigue and inefficiency. A car seat may be
comfortable for short journeys but not for long journeys.
Discuss the influence of perception when collecting data relating to psychological factors.
Quantitative data may be used in a design context relating to psychological factors, but individuals vary in their
reaction to the data.
For example, one person will find a room temperature comfortable while another person will find it
uncomfortable, though the temperature is constant.
Define biomechanics
The research and analysis of the mechanics of living organisms.
Discuss the importance of biomechanics to the design of a given artifact
Factors to consider are muscle strength and age of the user and the handle size, surface texture, and
torque required by the product.
Task: Use the examples below to explain the importance of biomechanical factors to making the design a
success.
Product
Can opener
Valve wheel
Corkscrew
Door handle
Biomechanical
factors
Reason