7. Human Factors and Ergonomics

• Ergonomics is the study of the interactions/interface between humans and machines/processes.

7.1 Ergonomics

• There are a variety of areas for ergonomic analysis

manufacturing: reducing worker stress (physiological) can reduce health problems (lost days), decrease product cost and increase product quality.

consumer: increasing ease of use can increase utility of the product.

• Ergonomics is the basis for many design methods such as DFA

• Ergonomics takes into account,

body proportions


desired function

• Non-ergonomic designs typically lead to personal injuries (and hence lawsuits, etc.)

• Typical ergonomic problems in manufacturing are listed along with possible solutions,

discomfort: uneeded strain on worker (e.g. hunching over)

1. training for proper lifting methods

2. rearrange operation locations and sequence to reduce unnatural motions.

efficiency: unnatural motions slow production

1. training for proper lifting methods

2. rearrange operation locations and sequence to reduce unnatural motions.

cummulative trauma disorders: muscle strain injuries (lifting 30lb packages all day)

1. training for proper lifting methods

2. use special lifting equipment

repetitive stress injuries: repeated motions. For example carpel tunnel syndrome in the wrists.

1. rearrange operation locations and sequence to reduce unnatural motions.

2. use ergonomically redesigned equipment (e.g. computer keyboards)

information overload/confusion: excessive, inappropriate or a lack of detail. (e.g. fighter pilots, airtraffic controllers)

1. redesign displays to be clear with a minimum amount of good information

2. use of color coding and pictures

3. simplify controls to minimum needed

eye strain: fine focus or bad lighting

1. adjust lighting

2. use magnifying lenses

noise: direct hearing or annoyance. (e.g., piercing tones, just too noisy)

1. special hearing protection equipment

2. redesign workspace to reduce noise reverberation

3. redesign equipment to reduce sound emmisions

7.2 Safety

• It is natural for a machine to have hazardous parts/functions/flows.

• If the risk (probability) of coming in contact is high we call this danger

• Typical hazards include,

pinch points


collision with moving objects

falling from heights

slippery surfaces


electric shock



physical strain

• When possible it is best to eliminate hazards. If this is not possible we want to reduce the risk of access (hence danger).

• OSHA (Occupational Safety and Health Administration) regulates workplace procedures.

• Danger can be reduced by,


safeguards (e.g. barriers)

policies and procedures

worker training

special protective equipment (e.g. earplugs)

• Typical additions to machines include,

barrier guards: physical blocks to separate operators and equipment. Interlocks are used to disable the machine when the barrier is open.

passive safety devices: for example seat belts

active safety devices: these include

hand pull-backs

dead-man controls

presence sensing devices

maintenance safety devices: these additions (and procedures) ensure that the machine is still safe, even though the normal safety equipment is disabled.

warnings: large warning signs, buzzers, status lights, etc. are used to promote awareness.

• Note: It is important to place safety considerations at the top of the design priorities. It is so obvious that it is quite often assumed.

7.2.1 Environment

• Environmental considerations are a natural consideration of the design process and can be considered an extension of safety.

• design factors that will impact the environment include,

discharges/waste (gas, liquids, solids) from production processes

energy/fuel utilization in production

aging of the product: decay, inert, toxic, etc.

energy/fuel efficiency in use

• There are a wide variety of laws, agencies and organizations that influence manufacturing and consumer products,

OSHA (Occupational Safety and Health Administration)

EPA (Environment Protection Agency)

NIOSH (National Institute for Occupational Safety & Health)

UL (Underwriters Laboratory)

CSA (Canadian Safety Association)

7.2.2 MIL-STD 882B: System Safety Program Requirements

• This standard addresses the likelihood and acceptability of hazards.

• The basic tables are,





7.3 Human Strength and Proportions

• When designing we can use statistical values of human proportions to set sizes of components, forces, etc.

• These tables are available from a number of sources such as NASA. There is a set of tables in the back of the text book.

7.4 Equipment Interfaces

• When a human interacts with a machine they use controls to begin actions, and displays to monitor status.

• Typical controls include,

switches (push, toggle, touch, etc.)

sliders, knobs

• Typical displays include

indicator lights

audible tones (buzzers, beeps, bells, etc.)

7.5 References

7.1 Ullman, D.G., The Mechanical Design Process, McGraw-Hill, 1997.