Department of Cognitive Science

Michael J. Kalsher

Human FactorsPSYC 2200

Engineering Anthropometry and Work Space Design

Anthropometry

• The study and measurement of human body dimensions.

• Derived from Greek words anthropos (“man”) and metron (“measure”).

• Provides fundamental basis and quantitative data for matching the physical dimensions of workplaces and products with body dimensions of intended users.

Anthropometric Data

• help optimize the match between the physical dimensions of products, tools, and workplaces and the body dimensions of individual users.

• are commonly used to design guidelines for heights, clearances, grips, and reaches of workplaces and equipment.

• are sometimes used in the design of various types of consumer products.

Examples

•http://science.dodlive.mil/2011/09/01/us-army-anthropometric-survey-ansur-ii/

•http://www.wsj.com/articles/how-to-find-the-phone-that-fits-your-hand-1395795606

•http://www.allmediascotland.com/media-releases/83909/media-release-safety-training-experts-lead-the-way-to-measure-up/

Major Sources of Human Variability

• Age

• Sex

• Race and Ethnicity

• Occupational Variability

• Generational or Secular Variability

• Transient Diurnal Variability

Human Variability: Age

Body dimensions generally change as a function of age.

-- Stature increases until age 20 or 25 and decreases after age 35 or 40 (affects women more than men).

-- Some other body dimensions (e.g., weight, chest circumference) increase through age 60 before declining.

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Human Variability: Sex

– Adult men, on average, are taller and larger than adult women.

– 12 year old girls are typically taller and heavier than their male counterparts; girls see maximum growth rate between 10-12 yrs of age, whereas boys see maximum growth rate between 13-15 yrs of age.

– On average, adult female dimensions are 92% of corresponding male values, but there is significant variation.

Human Variability: Race and Ethnicity• Both size and proportions vary

greatly between different racial/ethnic populations.

• World’s tallest people are Northern Nilotes of southern Sudan (average 6’ tall), shortest people are the pygmy people of central Africa (average 4.5’ tall).

• Equipment designed to fit 90% of the U.S. male population would fit ~90% of Germans, 80% of Frenchmen, 65% of Italians, 45% of Japanese, 25% of Thai and 10% of Vietnamese.

Human Variability: Occupation• Obvious differences based on the demands of the job, such as

the type and amount of physical activity, or special physical requirements.

• Truck drivers tend to be heavier than average; coal miners have larger torso and arm circumferences.

• Self-evaluation and self-selection play important roles.

Human Variability: Generational or Secular Variability

• Research reveals that the stature of Americans has changed about 1 cm per decade since the early 1920s due largely to improvements in nutrition and living conditions (Annis, 1978).

• Some interesting findings: – Griener & Gordon studied 22 body dimensions in U.S. Army

soldiers. – Found that some dimensions (ex: body weight, shoulder

breadth) still show trend of growth while others do not show considerable change (ex: leg length)

Human Variability: Transient Diurnal Variability

• Body weight varies up to 1kg per day because of changes in body water content.

• Measured height can “shrink” by up to 5cm at the end of the day, due to effects of gravitational force on person’s posture and thickness of spinal disks.

A Changing Population

• On average the American workforce is getting older, bigger, and is comprised of significantly more women.

• Suggests a need for:– updated anthropometric databases and

corresponding changes in the equipment design.– using physical testing as a means of job selection,

but only if physical features can be validly linked to job performance.

Gauging Anthropometric Features: The Normal Distribution

• Used to characterize anthropometric features in a population.

• Mean (measure of central tendency).

• Standard deviation (degree of dispersion in a group of measured scores).

1 = 68%

2 = 95%

3 = 99%

The Importance of Percentiles• A percentile value of an anthropometric dimension

represents the percentage of the population with a body dimension of a certain size or smaller.

• Percentiles help to estimate the percentage of the user population that will be accommodated by a specific design. – A seat surface designed using the 50th percentile value of the hip

breadth of U.S. males, then we can estimate that about 50% of U.S. males (the ones with narrower hips) will have their hips fully supported by the seat, whereas the other 50% (those with wider hips) cannot.

• In a normal distribution, the 50th percentile value is equivalent to the mean of the distribution.

Calculating PercentilesFor normal distributions, percentiles can be calculated by using the formula:

X = M + F x s, where:

• X= percentile value being calculated• M=mean (50th percentile) of the distribution• F= multiplication factor corresponding to the required percentile

(number of s.d.’s to be subtracted from or added to the mean). • s= standard deviation Multiplication Factors for Percentile Calculations

Measurement Tools

a. Anthropometer with straight branches

b. Anthropometer with curved branches,

d. Sliding compassc. Spreading calipers

Measurements and Methods

• Data collection requires standardization of methods– Body dimension must follow standard definitions

• Clearly identifiable body landmarks and fixed points in space are usually used to define the various measurements.

• Person being measured required to adopt a standard (upright, straight) posture specified by a measurer.

Measurements and Methods: Morant Technique

– Uses a set of grids that are usually attached to 2 vertical surfaces meeting at right angles.

– Subject is placed in front of the surfaces and body landmarks are projected onto grids for measurements.

• Filming, videotaping techniques, use of multiple cameras & mirrors, holography and laser techniques.

Measurements and Methods: Photographic Methods

Anthropometric Terminology: Standardizing Measuring Methods

• Height– A straight-line, point-to-point

vertical measurement

• Breadth– A straight-line, point-to-point

horizontal measurement running across the body or segment

• Depth– A straight-line, point-to-point

horizontal measurement running fore-aft the body

• Distance– A straight-line, point-to-point

measurement between body landmarks

• Circumference– A closed measurement

following a body contour

• Curvature– A point-to-point

measurement following a body contour

Anthropometric Terminology: Standardizing Measuring Methods

Nature of Anthropometric Databases

– Time-consuming, and labor-intensive.

– Most surveys carried out with special populations • e.g., military personnel who may not be representative of the non-military

population

– Most recent civilian anthropometric effort studied 2,500 European and 2,500 U.S. civilians mean and women of various weights between 18 and 65 years of age (Civilian American and European Surface Anthropometry Resource, SAE, 2002).

• Used U.S. Air Force’s whole body scanner

– Most people working in this area are generally concerned with designing for the middle 90% of the population (5th to 95th percentiles)

Structural and Functional Data– Structural (static) data measurements are taken

with the body in standard & still positions • Examples: Height, shoulder breadth, width of hand, etc.

– Functional (dynamic) data measurements are obtained when the body adopts various working postures

• Example: area that can be reached by the right hand of a standing person (standing reach envelope).

– Most anthropometric data are static, although work activities can be more accurately represented by dynamic data

Anthropometric Measures: Standing and Sitting

Anthropometric Measures: Hand, Face, and Foot

Static MeasurementsFew tasks require that humans remain rigid and motionless

– Suggestions for converting static to dynamic data• Heights should be reduced by 3%• Elbow height requires no change or an increase of up to 5% if elbow needs

to be elevated for the work• Forward and lateral reach distances should be decreased by 30% if easy

reach is desirable and they can be increased by 20% if shoulder and trunk motions are allowed

• Concerned with human in motion while engaged in some physical activity• Interested in a person’s reach (how far) not just how long the person’s arm is

Dynamic Measurements

Who Cares? Who is going to use this data?

Use of Anthropometric Data in Design

1. Determine the user population. Who will use the product or workplace?

2. Determine the relevant body dimensions.

Which body dimensions are most important for the design problem?

3. Determine the percentage of the population to be accommodated.• Design for extremes• Design for adjustable range• Design for the average

Use of Anthropometric Data in Design

4. Determine the percentile value of the selected anthropometric dimension.

• Which percentile value should be used: 5th, 95th, or some other value? Need to be clear whether designing a lower or upper limit.

5. Make necessary design modification to the data from the anthropometric tables.

• Most anthropometric measures are taken with nude or nearly nude persons. Adjustments need to be made to accommodate real-life situations (e.g., most people at work will be clothed!)

6. Use mock-ups or simulations to test the design.• Critical to include a representative sample of users.

Didn’t use Anthropometric Data

Failed to take into account the average inseam length of males.

General Principles for Work-Space Design

• Goal of human factors is to design systems that reduce human error, increase productivity, and enhance safety and comfort.

• Work-space design is one of the major areas in which human factors professionals can help improve the fit between humans, machines, and the environment

Clearance Requirement of Largest Users• Clearance problems are among the most often

encountered issues in workspace design. – Space between and around equipment – height/width of passageways, dimensions provided for knees,

legs, elbows, head, etc.

• Inadequate clearance may force some workers to adopt awkward posture.– reduces comfort and productivity.

• Clearance dimensions are usually set to accommodate 95% of the population. Upward adjustment should be incorporated to reflect people wearing heavy clothing.

• For female only workplaces, data from the female anthropometric database should be used.

Reach Requirement of Smallest Users

• Reach envelope: the 3-D space in front of a person that can be reached without leaning forward or stretching.

• Objects that need to be reached frequently should be located within the reach area and as close to the body as possible.

• In considering object location, manipulation, and reach, issues of strength and fatigue must also be addressed.

Reach Envelope

Seated female

Standing male

Requirements of Maintenance People• Well-designed workplace should

consider regular functions of people of the work-space as well as the needs and the special requirements of maintenance personnel.

• Maintenance workers frequently need to access areas that do not have to be readily accessed by regular workers.

• Adjustable workplace becomes desirable.

Adjustability Requirements

• Because of conflicting needs of different users, often impossible to have “one size fits all”.

• Desirable to make every effort to make the workplace adjustable if it is feasible.

• Make sure that adjustment mechanisms are easy to use

General Approaches to Workplace Adjustment

1. Adjust the workplace• Shape, location and orientation of workplace• Example: Front surface cutouts allow worker to move

closer to the reach point.

2. Adjust the worker position relative to the workplace• Example: Change in seat height and use of platforms are

some means of achieving vertical adjustability

3. Adjust the work piece• Example: Lift tables can adjust height of workpiece

4. Adjust the tool• Adjustable-length hand tool can allow people with different

length arms to reach objects at different distances• Adjusting the tool to maximize torque or accuracy or

comfort

Visibility and Normal Line of Sight• Ensure that visual displays can be

easily seen and read by workers.

• Requires eyes at proper positions with respect to viewing requirements.

• “Normal” line of sight is the preferred direction of gaze when eyes are at resting condition (approx. 10-15 below the horizontal plane).

• Visual designs should be placed within 15 in radius around the normal line of sight.

Component Arrangement

• Optimum arrangements allow users to access and use components easily and smoothly.

• Careless arrangement can cause confusion and make things more difficult .

• Principles of display layout (see chapter 8) can be applied.

Component Arrangement: Principles of Display Layout

1. Frequency of use principle

2. Importance principle

3. Sequence of use principle

4. Consistency principle

5. Control-display compatibility principle of co-location

6. Clutter-avoidance principle

7. Functional grouping principle

Principles of Display Layout

1. Frequency of use principle– Components used more frequently should be placed in most

convenient locations. Most frequently used displays should be positioned in the primary viewing area.

2. Importance principle– Components most crucial to achievement of system goals

should be located in convenient locations.

3. Sequence of use principle– Components which are used in sequence should be located

next to each other and layout should reflect sequence of operation.

Principles of Display Layout

4. Consistency principle– Components should be laid out with the same component

located in the same spatial locations to minimize memory and search requirements.

– Standardization plays an important role in ensuring that consistency be maintained across broader perspective.

5. Control-display compatibility principle of co-location– Control devices should be close to their associated displays.– Layout of controls should reflect layout of displays to make

visible the control-display relationship.

Principles of Display Layout

6. Clutter-avoidance principle– Adequate space must be provided between

adjacent controls.

7. Functional grouping principle– Components with closely related functions should

be placed close together.– Various groups of related components should be

easily and clearly identifiable.

Component Arrangement: Link Analysis

• Application of design principles requires subjective judgments.

• Qualitative methods such as link analysis and optimization techniques are also available.

– Quantitative and objective method for examining relationships between components, which can be used as a database for optimizing component arrangements

– Link between pair of components represents a relationship between two components and strength of relationship is reflected by link values

The width of a link represents the frequency of Travel between two components. The purpose of the design is to minimize the total travel time across all components. (a) Before reposition of components; (b) After reposition.

Design of Standing & Seated Work Areas

• Standing workplaces– typical in environments where workers make frequent

movements, handle heavy objects or exert larger forces with hands.

– Prolonged standing is strainful, puts excessive load on the body, and may lead to body fluid accumulation in legs.

• Workers should not be required to stand for a long time without taking a break.

• Floor mats and shoes with cushioned soles may increase comfort

• Seated Workplaces– When possible, seated workplace should be used for long-

duration jobs.– Must provide leg/knee clearance area and should provide

adjustable chairs and footrests.– Workers should be allowed to stand up and walk around after a

period of seated work.

Golden Rules for Office Chairs• Should accommodate forward and reclined sitting

positions

• Backrest should have:– an adjustable inclination & should be possible to lock the

inclination at any desired position– a well-formed lumbar pad, which should offer good support to

the lumbar spine between the third vertebra and the sacrum

• The seat surface should measure 400-450mm across and 380-420mm back to front. A slight hollow in the seat, with the front edge turned upwards about 4-6 degrees will prevent buttocks from sliding forward.

Office Chairs

Alternative to Standing/Sitting

Work Surface Height– Nature of task being performed should determine the

correct work surface height.

– Rule of thumb is to design standing work heights at 5-10 cm (2-4”) below elbow level and to design seated working heights at elbow level.

– Precise manipulation requires height above the elbow level.

– Great force application requires a lower height.

– If possible, height should be adjustable to the user.

Work Surface Height

Work Surface Depth

– Take Normal and Max work areas into account in determining depth– Items that must be reached immediately/frequently should be

located within the normal work area and close to the body.

Work Surface Inclination

– Most work surfaces are designed as horizontal surfaces

– Slightly slanted surfaces (15) should be used for reading

– Slanted surfaces improve body posture, involve less trunk movement, require less bending of the neck, and produce less worker fatigue/discomfort

– Users preferred horizontal surfaces for tasks, like writing.

Example of Workspace Design