Includes designing, installing or checking things for effective human use, and creating environments that are suitable for human living and work. It includes work methods, equipment, facilities, and tools that influence the worker's motivation, fatigue, likelihood of sustaining an occupational injury or illness, and productivity
From MEM30008A Delivery Plan
3. Ergonomic Considerations
- Human capacity: reach, dexterity, strength, repetitiveness, human comfort
- Health effects of human/machine interaction.
Ergononomics is a combination of disciplines. The human factors (anthropometry and biomechanics) come together with the equipment (machine design) and job requirements (task design).
Human Factors: Dimensions, forces, movement, senses (touch, visual, audible etc)
Task Design: Management of time, ease of use, information overload, number of things to do at once.
Machine Design: Hardware to provide function and arrangement, assmbly, servicing, reliability, manufacturability.
For example, the ergonomic analysis for driving a car involves;
Human Factors: Seat size, adjustments, dimensions and reach, grips, pedal force, steering motion.
Task Design: Management of driving time, ease of use, information overload, number of things to do at once.
Machine Design: Mechanical arrangment of pedals, steering wheel, seat adjustments, switches, controls
The following ergonomics topics linked from http://www.ergonomics4schools.com/learningzone.htm
Also see keyword list.
|Aesthetics||Hand Tools||Product Evaluation|
|Computer Systems||Manual Handling||Shiftwork|
|Equipment Layout||Product Design||Work|
General Fields in Ergonomics
Human Computer Interaction
"Human Computer Interaction (HCI) process will affect and /or be affected by other factors such as fatigue, mental workload, stress and anxiety. " (Yili Liu, 2004)
"Biomechanics is the study of characteristics of the body in mechanical terms."
(Karl Kroemer, 2001)
"Occupational biomechanics is an interdisciplinary science that integrates knowledge and techniques from diverse physical, biological, and engineering disciplines. "(Yili Liu, 2004)
In essence, biomechanics analyzes the human musculoskeletal system as a mechanical system that obeys laws of physics. (Yili Liu, 2004)
"Anthropometry is the study and measurement of human body dimensions."
(Yili Liu, 2004; Karl Kroemer, 2001)
Anthropometric data are used to develop design guidelines for heights, clearances, grips and reaches of workplaces and equipments for the purpose of accommodating the body dimensions of the potential workforce. (Yili Liu, 2004)
Product Design establishes and defines solutions to and pertinent structures for problems in a product not solved before, or new solutions to problems which have previously been solved in a different way. (Dieter)
Occupational Safety and Health
Occupational Safety and Health is a field that takes into consideration health and safety standards, conducts inspections, and investigates problems to take appropriate actions to ensure safety and health of employees. (Goetesch, 2002)
Anthropometry and Percentiles
Anthropometry is the measurement of human dimensions. Biomechanics includes the forces and motions. For the engineer or designer, these can define an acceptable range of values for positions, motions and forces.
For example - how strong is a driver's right leg? This will limit force of a clutch pedal in a car. By comparison, a motorcycle clutch is operated by the fingers, so it must operate on a much lower force and shorter motion. For this reason (and others) a motorcycle uses a multi-plate clutch, and a car typically utilizes a single plate clutch with a much stiffer spring.
Driving environments utilize a lot of anthropometric and biomechanical data - cars, motorcycles, planes, earth moving equipment, forklifts, etc. Not only should the forces be within appropriate limits, but the range of motion, reach, visual and audible indicators, display of information, vibration, temperature, repetition, rest periods ... the list goes on. This influences the design and layout of everything that is touched or read: seats, grips, pedals, steering wheels, switches, indicators, displays, labels, etc.
The favourite topic of just about every ergonomic study; sitting at a computer.
Finding the ideal set of measurements is not everything. The worst thing about sitting at a computer is the lack of movement.
Mobility and task variation are more effective than some magic combination of measurements, but hey, measurements are cheap.
A more detailed anthropometric diagram for automotive driver postion is shown below. This diagram shows 2 extremes of stature - the 99 percentile man and the 1 percentile woman. (Other factors could also be included - such as obesity)
Is this a likely range for automotive design?
Full size image here
The Normal Distribution (Bell Curve, Gaussian Distribution)
Percentiles represent how rare the upper and lower sizes are. According to the Gaussian distribution (assuming of course that the population actually fits the Gaussian profile), a 99 percentile is larger than 99% of the population, whereas a 1 percentile is larger than only 1% of the population (or 99% are larger then them).
In addition, the tall extreme is taken for male data, and the short extreme from female. Children do not need to be accomodated since drivers must be adults.
A standard Gaussian curve is assumed. The vertical axis is the frequency (how many people) and is plotted against the horizontal axis of our measurement (stature).
Assuming a curve for men. The average man is the 50 percentile (by definition), which is also the most common height (by Gaussian curve assumption). To make the diagram useful, we need to know the average (mean) height (5 ft 10"), and the standard deviation (sigma) (3").
μ = 70 inches
σ = 3 inches
The diagram above shows that men have a higher standard deviation than women (greater variety in stature). The average man (70") is about the same height as a 80-90 percentile woman.
Combining these above diagrams we can see where the 1 and 99 percentile dimensions would appear in the stature range.
Musceloskeletal Disorders MSDs
Industrial Ergonomics - Safety
Preventing or reducing occupational illness and injury by making changes to the design of work/workplace.
This video covers industrial safety related to overuse and MSD (Musceloskeletal Disorder) injuries.
There is a lot of risk management information available from all state work safety
authorities. That information will be more comprehensive than this short summary,
and is legally recognised, and its generally free.
What is risk management? It is a procedure for checking for safety problems in a workplace and is required by state occupational health and safety laws in Australia.
Machine supply/ use chain: Going through a risk management procedure might seem like overkill if you are considering a guard as the required safety measure. However, if any injuries occur, your record of this process it is your best defense in court.
The risk management procedure may also bring up some good design ideas. In addition, it may reveal some hazard management options that are superior to relying on a guard alone. Briefly, here is the risk management procedure:
1. Consult - or involve the people who use the machine in your process. Those who use the machine will have interest and practical knowledge to help.
2. Hazard identification – look for any hazardous scenarios, such as exposed moving parts, hot spots etc.
3. Risk Assessment – What’s the hazard, and its likely impact on injury if left unattended? For each hazard consider:
- The likelihood of an injury happening
- The consequence of that injury, and
- How often people are exposed to the hazard
4. Risk Control
The hierarchy of controls is a list of control strategies in priority order shown below. You try the first one, if it is not reasonable or practicable to the situation, then you try the second one, then so on.
The groups in the ‘hierarchy of control’ are
1. Elimination (retire the machine or task)
If not then: → 2. Substitution (upgrade machine, or change the job so it is safer)
If not, then: → 3. Engineering / isolation (guarding, fencing, cut off switches etc)
If not, then: → 4. Administration (workplace rules, systems of work, decals, training)
If not, then: → 5. PPE (Personal Protective Equipment)
Note that using a guard is an Engineering control. However, guarding almost always needs instruction and training of workers – an Administrative control.
5. Review – check if your new control measure is OK, and doesn’t introduce any problems of its own.
6. Record keeping – make notes of your good work against each step of the risk management process, it is your record and may become your best defense in court.
How effective is guarding as a method of risk management?
If you consider the hierarchy of control, guarding is a less effective control than selecting elimination or substitution control, but is better than adopting administrative controls (training etc) or Personal Protective Equipment (PPE).
Note also that some guards require regular checking for effectiveness (if they are a consumable) and some require training (if they are not permanent or interlocked) as part of the hazard control.
The importance of human factors in industrial safety standardsSTAMPING JOURNAL® JUNE 2004 JUNE 8, 2004
BY: GARY HUTTER
Human factors contain elements of psychology, engineering, statistics, and observation. Safety codes and standards often are written based on some aspect of human factors, and it may be critical to have a full understanding of the human factors behind the code or standard before applying the same concept to other equipment.
While the NSC publications provide generous guidance, two aspects they do not address fully are the application and implication of ergonomics and human factors in the design of machine safeguards.
Anthropometry and Physical Barrier Guards
The best way to understand human factors in the design of machine safeguards is to integrate the concepts and findings from textbooks on human factors and equipment design. Four of the philosophical and conceptual issues of human factors in the design of safeguards for metal fabrication and other equipment are explained here.
Anthropometry is the science of measuring the human body in terms of size and capabilities. Both of the NSC publications contain a chart and table of allowable guard opening sizes based on the distance from the guard to the hazard (see Figure 2).
The concept is that a person's hand becomes thicker from the fingertips toward the wrist. Hence, an opening of 0.25 inch, big enough for a small finger, can be used only if the hazard is 1.5 in. beyond the guard, but the hazard must be more than 5.5 in. behind the guard if the guard opening is 0.75 in. While this chart originated before the formation of OSHA, it still is considered by that organization to be a compliance threshold.
The ergonomic principals in conjunction with anthropometry data have an important influence upon the proper design of machine guards. The collection of body measurements as design criteria to improve the functionality, efficiency and safety of a human in a system is called anthropometrics. The ergonomic approach utilizes this information to determine allowable space and equipment size and shape used for the design of work environment.
If barriers are used to protect workers from hazardous machines, reach is limited by the length of the arm, and in the case of opening, by the size of the hands and fingers. In applying the ergonomic principal of fitting the work place to the worker one can use the distance that a worker can reach to determine the height of a guard or the distance of barriers from the machine which they guard. The various distances involved in reaching around, above, and through barriers are important in determining what types of guards should be employed in protecting workers from hazardous equipment (NCDOL, 1998).
For example, generally fingers are unable to pass through openings smaller than 3/8” x 3/8”. Therefore, the distance between a guard with such openings and the hazardous equipment does not need to be great than the maximum length of the longest finger.
Anthropometry also comes into play in the design of respiratory devices that protect workers from airborne contaminants generated by machine operations. While engineering controls such as chemical reformulation and dedicated exhaust systems are considered the first line of defense to limit occupational exposures, employers often supply respirators to workers as well.
Workers must choose from various sizes and shapes to find a respirator that fits properly and provides a good seal around the face. Significant facial hair in the area of contact can cause an improper seal.
A review of both NSC publications shows that physical barrier guards often are designed with openings (or are configured to be opened) to allow for physical and visibility access. It is a human factors concept that visibility access may increase an operator's "mental modeling" of the operation. Having a visual understanding, and thus mental model, of how a process works can help workers avoid failures and injuries.
Most machines and safeguards come with written warnings and instructions. The effects of variations in size, color, and configuration of these signs, signal words, and pictures are debated in Safeguarding Concepts Illustrated (see Figure 3). While some sign/warning standards may vary on these features for different applications, from a human factors perspective, people have a complex ability to decipher written information. ANSI standards Z 535.1 through Z 535.5. provide codified information about signage, including safety signs.
Chapter 7 of the Power Press Safety Manual is dedicated to control features and options. It recommends interlocks on disconnect switches and safety blocks, two-hand trip controls, and the use of "safe distance" in positioning controls, all of which are based on certain aspects of human factors.
Interlocks. Interlock configurations help keep operators from making a mistake and also keep the equipment in a safe condition if the operator does make a mistake. An example of a common interlock is found on modern automobiles—an operator cannot start the car when it is in gear and could unexpectedly move forward.
Interlock features would seem universally desirable, but they are not required on all machine controls. One human factors concept that comes into play with interlocks is the potential for "user dependency" on the interlock. In other words, interlocks that keep a machine in a safe condition when an operator makes a mistake need to be 100 percent reliable, because users will tend to depend on them and may begin performing marginally unsafe acts because they are used to the interlock working and protecting them.
Two-hand Trip Controls. Two-hand trips force an operator to have his or her hands away from the hazard. This generally is desirable, but they could cause a secondary hazard when applied to some types of equipment.
These examples of word perception show that operators may be able to understand the content of difficult-to-see warning signs if they are motivated to read them, and if the warning signs have the necessary information. ANSI standards Z 535.1 through Z 535.5. provide codified information about signage, including safety signs.
Press brakes, for example, have no requirements for two-hand trips because they can cause a counterproductive safety tradeoff. Often the part being worked on needs the support and positioning of the operator's hands. The application of two-hand trips would violate the human factors concept of competing incompatibilities: Do I properly position and support the sheet metal and have my hands near to the point of operation, or do I use two-hand controls and have a problem positioning and supporting the workpiece? Forcing a press brake operator to have his or her hands on the two-hand trips could cause the part to fall or shift, causing other safety hazards.
Safe Distance. Both the ANSI standards and OSHA codes for power presses acknowledge the use of a safe distance to safeguard the point of operation. The concept is that if the controls are located some safe distance from the point of operation, the operator will not be able to move fast enough to reach into the hazard zone at the point of operation. Of course, the speed of the operator's hand and arm movement becomes a critical human factors measurement. The standards are based on a hand speed constant of 63 inches per second. While that is pretty fast, there always is someone out there who moves with unusually high speed.
Obviously, machines that form a point-of-operation hazard at different speeds under different conditions are not compatible with the safe-distance approach to safeguarding. While mechanical power presses have large flywheels and gear-drive mechanisms that keep the operating speed of the ram high and consistent, mixers and belt-driven devices may form the point-of-operation hazard in different time increments, depending on the resistance of the mix and slippage of the belts.
Many of the safeguards shown in Safeguarding Concepts Illustrated and other publications are physical barriers that are similar in shape and construction. Human factors studies have determined that people have certain expectations about the performance of many things that they encounter repeatedly, including safeguards.
We blindly stretch our arm around a corner in the dark at chest height to access a wall light switch; we stumble on stairs if the rise is too shallow or too great; and we instinctively reach for a door knob at the same place on the door because they are all at about the same height. These are some of our consistency expectations.
Workers have consistency expectations about safeguards as well. For example, an operator expects a safeguard to be strong enough to keep the hazard from engaging if the operator falls against the barrier guard, and the guard should prevent broken pieces from flying out.
The operator might even expect a physical barrier safeguard to be strong enough to stand on if he or she needs to access something beyond the guard. While the literature on safety does not suggest that guards be used as steps, a guard located in an area where it can perform as a step most likely will be used as a step, so it must be made strong enough for that purpose or be made in a way that prohibits its use as a step.
Human factors comprise elements of psychology, engineering, statistics, and observation. Safety codes and standards often are written based on some aspect of human factors, and it may be critical to have a full understanding of the human factors behind the code or standard before applying the same concept to other equipment.
Dr. Gary Hutter is president with Meridian Engineering & Technology Inc. Consulting Engineers & Scientists, P.O. Box 598, 4228 Commericial Way, Glenview, IL 60025, 847-297-6538, fax 847-297-6615, MrHutter@earthlink.net,www.MeridianEng.com. He also was a contributor in the redrafted and reissued versions of the NSC publications discussed in this article.
National Safety Council, www.nsc.org
Examples for Guarding in Farm Machinery (Australian Standards)
Not every problem can be solved directly with code (i.e. Australian Standards). In such cases, a risk assessment method is used instead. For example, in the auger guarding problem, the machine guarding code specifies an unworkably large distance for the guard mesh at the head of the auger. The problem needs to be solved with a combination of code and risk assessment.
Ergonomics also includes the design and planning of the work itself - such as the hours of work, type of work, noise and environmental comfort, and even touches on management styles and human interaction.
A major component of work health is 'stress'.
Stress can be good and stress can be bad. Good stress can help you work harder and make your job more challenging and interesting. Bad stress can be like a 'work-caused disease' and make you feel anxious or depressed. It can also lead to physical health problems like headaches, muscular tension and chronic fatigue.
If you're feeling the effects of the bad kind of stress you need to make some changes at work. Talk to your employer or human resources manager and let them know how you feel. Ask if any changes can be made to your working arrangements in order to minimise the stress you're experiencing. You can also contact WorkSafe Victoria or your union.
What causes stress?
Lots of things can cause you to feel stressed at work. High demands at work + low control over them = stress.
Here are some examples:
- You're given too much work to do or there aren’t enough people to share the work
- You haven't received enough training to do your job
- You're working long hours
- You're worried you’re going to lose your job ('job insecurity')
- You're having trouble communicating with someone you work with
- You're being bullied or harassed
How to avoid stress at work
Stress prevention should be tackled by workers and employers together.
Workers can bring their concerns to the attention of their employers, and suggest ways that things could be changed. Employers can make changes to workers' duties and the workplace. In this way stress reduction becomes a mutual undertaking.
Things that can help to reduce work stresses include:
- Creating a safe and healthy work environment
- Consulting about changes to job roles or workplace practices
- Minimising unpaid overtime
- Taking a reasonable amount time between shifts and taking regular rest breaks
- Sharing workloads fairly
What can you do?
As well as thinking of ways to change your behaviour at work, or ways to improve your workplace, there are other ways of staying healthy and avoid stress, like:
- Eating well and regularly, make sure you take your meal breaks and rest breaks
- Exercising (this will help you sleep better and give you more energy)
- Sleeping for at least seven or eight hours each night
- Making time to see family and friends
- Trying some relaxation techniques. (Note: Vic government website suggest "yoga" (Hindu for "union") or "meditation". Alternatives do exist; maybe not favourite hobbies of aging botoxed new-age mystics).
In the book The Psychology of Everyday Things Norman eloquently presents this principle of user-centered system design. This book can be recommended for all engineers, programmers, and designers responsible for the development of new devices. Some of the key aspects of user-interface design that Norman emphasizes are to;
- make things visible,
- provide good mapping,
- create appropriate constraints,
- simplify tasks, and
- design for error
Make Things Visible
A well-designed interface between human and machine conveys to the user the purpose, operational modes, and controlling actions for the device. If the design of the device or system is based on a good conceptual model, its purpose will be readily apparent to the user. Most devices have several operational modes, and the user must be able to determine rapidly and accurately whether the system is in the desired mode and when the mode changes. With most devices, a number of user actions are possible at any given time; with complex systems, the allowable commands often depend on the current operational mode. The user should be able to tell what actions are possible at any given instant and what the consequences of those actions will be. Feedback must be provided after each user action that should be readily understandable, and it should match the user’s intentions.
The user’s understanding of the function and operation of a device is paramount to the effectiveness of the system. The function and operation of many common devices is learned through cultural experience. People also expect certain objects to always function in a particular manner: knobs are for turning, buttons are for pushing, and so on. With other devices, the function can and often should be implied by the device itself. That is, the purpose and operation of a particular control or display should by design be as intuitive as possible for the user; for example, the sturdy horizontal handle on the side of the anesthesia machine is for pulling the device from one location to another. Such intuitive operation may be difficult to attain with complex, microprocessor-controlled multifunction devices. However, when the design requires the user to memorize specialized knowledge to operate the system (e.g., “To see the systolic blood pressure trend plot, I must push a particular sequence of soft buttons in a specific order”), the need for training increases, and the chance of system-induced user error increases, especially under stressful, unusual, or high-workload conditions.
Provide Good Mapping
Mapping is the relationship between an action and a response and may be natural or artificial. Natural mappings are intuitive; artificial mappings must be learned. Artificial mappings that have been learned so well that the relationship between action and effect is recognized at a subconscious or automatic level are called conventional mappings. On an anesthesia machine, squeezing the bag to inflate the lungs is a natural mapping. Turning the oxygen flow control knob counterclockwise to increase gas flow is an artificial mapping. However, because this design follows the conventional mapping of valves, users typically do not have difficulty adjusting the flow of oxygen on the anesthesia machine. Unfortunately, for many medical machines and systems, methods for activating alternate modes of action, adjusting alarm limits, or manipulating data are via artificial, unique, and nonstandard mappings.
Any device has three different stages of mapping: 1) between intentions and the required action; 2) between actions and the resulting effects, and 3) between the information provided about the system and the actual state of the system. Inappropriate mapping at any stage leads to delayed learning and poor user performance. If natural or well-known artificial mappings are not used, the designer should seek preexisting standards or perform tests to ascertain optimal mappings, which should be consistent within a single device or system.
Create Appropriate Constraints
Constraints are limitations on the user’s available options or actions and can be physical, semantic, cultural, or logical. The provision of a control that can be oriented only in specific ways is a physical constraint (e.g., a switch can only be either on or off). With a semantic constraint, the meaning of a particular situation controls the set of possible actions.66 For example, the sounding of an alarm is meant to indicate the need to take some kind of action.
Cultural constraints are a set of allowable actions in social situations: signs, labels, and messages are meant to be read. Natural mappings typically work by logical constraints. When a series of indicator lights are arranged in a row, each with a switch underneath, the logical constraint dictates that the switch underneath a particular indicator light controls, or is associated with, that light. Devices, particularly their human interface components, should contain constraints that facilitate simple, logical, and intuitive operation.
Design for Error
Human performance is prone to error. Slips, or actions that do not go as planned, are a common form of human error arising from interactions with devices.67 Accidentally pushing the wrong button is an example of a slip (see Chapter 23). It is the device designer’s responsibility to anticipate user errors and minimize the risk that these inevitable errors will produce ill effects. Actions with potentially undesirable consequences should be reversible and the device should perhaps require additional user acknowledgment prior to completing the action. The designer also can implement aforcing function, a type of constraint that prevents performance of an action that is clearly undesirable. An example of a forcing function is the oxygen/nitrous oxide interlock mechanism that prevents the delivery of a hypoxic gas mixture.
These principles of good design are not limited to the interface between user and machine.4 A well-designed device is also easy to clean, maintain, and repair, and its documentation is organized and understandable. However, many currently available commercial devices violate these basic design principles. In an ergonomics evaluation of a microprocessor-controlled respiratory gas humidifier, Potter and colleagues68 found that the device had hidden modes of operation, ambiguous alarm messages, inconsistent control actions, and complex resetting sequences. One clinically used respiratory gas analyzer issues arcane alarm messages and has multiple display formats that are difficult to access. Another gas analyzer has a hidden calibration mode that renders it unusable if the sampling tubing is not attached when the unit is initially powered up. We have noted that at least two brands of limb tourniquet controllers have no indicator that the cuff is inflated, although this impression is mistakenly given by a display of “cuff pressure” and a running timer on the front panel.
Crisis situations tend to generate “use errors” that may not occur during less stressful times. For example, during simulated crisis situations, many subjects forgot to coordinate the setting of the bag/ventilator selector switch on the anesthesia machine breathing circuit when switching between controlled and spontaneous ventilation.69 At least some of what, on first glance, appears to be human error often can be traced back to poorly designed interfaces between human and machine.70 Devices often are used inefficiently or incorrectly as a consequence of poor design.68 When the device acts in unexpected ways, the user develops erroneous or inconsistent mental models of its operation.71 This problem can be exacerbated when the user has not received adequate instruction before using the device.
Humans rely heavily on the visual sensory channel for communicating or obtaining information. The cathode ray tube (CRT), printed page, vehicle instrument panel, and line drawing are all examples of visual displays. An early application of ergonomics was the design of instrument displays for military applications.72,73 Research continues on developing and improving visual displays for such diverse areas as the airplane cockpit (Fig. 24-8), the nuclear power plant control room, and the office computerized workstation.74,75 Although a complete description of this work is outside the scope of this chapter, a number of guidelines that have resulted from these studies are presented. Much of the specific information presented stems directly from the general considerations already discussed.
Properties of Visual Displays
Three criteria are fundamental to the performance of a display: visibility, legibility, and readability.8 Visibility refers to the degree to which the individual characters or symbols on a display are detectable against the background, and it depends on display features such as symbol size and background color. Visiblity is also influenced by environmental factors, such as ambient light levels, and by the limitations of human perception, such as color blindness and deficiencies of refractive index. Legibility pertains to the degree to which displayed numerals, characters, and symbols can be differentiated from one another. It is primarily influenced by features of the individual symbols, including size, simplicity of form, and stroke width. Readability is a quality that makes possible the quick and unambiguous interpretation of the information intended to be conveyed. For text displays, this is a function of semantics and letter spacing; for symbol displays, simplicity and organization are important.
The preferred size of display components depends on the viewing distance, ambient illumination, and the importance of the information. The perceived size of a display element is a function of the viewing angle. Numerals and letters on a display should be large enough to be easily legible.8 For visual search tasks, larger characters are required.76Tightly packed letters are preferable when text must be read and comprehended quickly, probably because fewer eye fixations are required.8
Displays of Magnitude
Displays of magnitude can be either numeric or graphic. Digital displays, such as a digital watch or the odometer of a newer car, are numeric. Analog displays, such as the capnogram or the dial of a pressure gauge, are graphic. Dials are classified as either moving pointer on a fixed scale or moving scale with fixed pointers. Each type of display has advantages for particular tasks. Numeric displays require less space and are preferable when a precise numeric value is required, because they minimize errors and reading time. However, numeric displays are difficult to read if the value is changing rapidly. For instance, pilots are better at performing basic flight maneuvers in a simulator with analog displays than in one with digital displays.77 Moving pointers are preferable as indicators of control settings, because they provide the simplest relationship to the control motion. When qualitative information is sufficient—for example, for detecting the direction or rate of change of a value—a graphic display or moving pointer dial is preferred.76 Reading a dial to extract quantitative information takes significantly longer (>400 ms) than does a qualitative reading to affirm that the pointer is in the right general location (125 to 200 ms).78 Graphic displays of recent data are especially useful for trend detection and tracking. When markers are not present for each value, people are able to interpolate, but the time required to obtain the reading is prolonged.8 All characters should be in a vertical orientation because it takes longer to read a dial when the characters are rotated.79
Grouping of Displays
Displays should be grouped for optimal performance. Perceptual studies76 support the grouping of important displays within the central 30 degrees of the visual field. The normal visual field extends up to about 30 degrees vertically and about 80 degrees horizontally. Three areas of attention have been described based on response time to visual stimuli: the stationary field, the eye field, and the head field.80 The stationary fieldoccupies the central 30 degrees and is the area of foveal vision. Within this field, multiple displays can be viewed simultaneously without eye movements. The visual field between 30 and 80 degrees is the eye field—the area of peripheral vision. Even when foveal vision is fixed on a display, information can still be extracted from the periphery. Peripheral vision is especially sensitive to motion and can act reflexively to guide the eye to the target information. Targets within the eye field can be brought into foveal view by eye movements; head movements are not required. The head field lies outside the central 80 degrees, and displays in this area are outside the peripheral visual field. To view displays in this area, the head must be moved under conscious control.
The relative importance of particular displays can be deduced from the frequency of readings during task analysis studies.81 Similarly, link analysis14,82 can identify recurrent sequences of display readings. Optimally, important displays should be located in the most convenient positions, and displays that are commonly viewed in sequence should be arranged adjacent to each other. To perform a task, a number of displays often are interpreted concurrently. When multiple channels of information must be mentally integrated, performance is often improved when the information is grouped. In contrast, when information from multiple channels must be kept distinct—for example, during focused attention on a single channel—grouped presentation may be deleterious.83 Most grouping methods are based on Gestalt theory, which describes the ways in which people identify boundaries and groups. The generally accepted Gestalt laws of grouping includeproximity, similarity, closure, continuity, common region, and connectedness.84 These concepts are illustrated below;
Dials and numeric displays are typically read sequentially, and clustering of displays can encourage parallel processing. However, placing displays close together in space does not guarantee parallel input of information and may interfere with focused attention on a particular display. One way of ensuring some parallel processing is with object displays, in which multiple data elements are represented as attributes of a single object. When a single object is viewed, its multiple attributes—such as color, shape, and size—are perceived in parallel.
In some nuclear reactor control rooms, object (polygon) displays of safety parameter data have replaced banks of separate instrument dials.85 In these displays, eight values are represented by eight spokes that form the axes of an octagon. A similar type of polygon display was incorporated into the Ohmeda Modulus CD anesthesia machine (GE Healthcare, Fig. 24-10). In a laboratory study, the Ohmeda polygon display was superior to a numeric display in a simulated detection task.86 Anesthesia residents detected changes in the values of physiologic variables more quickly and accurately with the polygon display than with a numeric display. However, performance with the polygon display was not much better than that with a histogram display of the same information. The applicability of these findings to the use of graphic displays in the OR during real procedures remains to be determined.
Although object displays might seem implicitly superior to multiple dials, early studies have demonstrated some disadvantages to this approach. Petersen and colleagues87compared object displays with multiple bar graph displays in a task of monitoring for changes in the state of a system. They found that the object display was superior when subjects had to detect whether any parameter was out of tolerance, but that multiple bar graphs were better for detecting the number and identities of the out-of-bound parameters.88 Wickens and Andre89 performed an experiment in which subjects viewed either a bar graph display or an object display of three values for 1.5 seconds. The subject was then asked either to make a judgment on the basis of an integration of the values or to recall a single value. Performance was better on the integration task with the object display, but single values were more accurately recalled with the bar graph display. These findings are consistent with many others that support the principle of proximity compatibility, which states that combined displays are best suited to tasks that require information integration, whereas tasks that require independent information processing will benefit from more separate displays.
Display CodingCoding methods can be used to highlight targets of visual search tasks and to provide similarities for grouping. Common coding methods for display elements include color, alphanumeric symbols, geometric shapes, size, brightness, location, and flash rate.
In a comparison of coding methods between color, numerals, letters, and geometric shapes, color and numeric codes were superior in most tasks. Color is the most effective coding method for search tasks, in which the subject must locate and count items in variable positions on a display. Search times can decrease by as much as 70% with color coding. In a study of color coding to organize instruments on a simulated aircraft display, common color coding of relevant instruments was found to facilitate integration of information, and distinct color coding improved the ability to focus attention on each instrument. Subjects commonly respond to color codes faster than to shape or alphanumeric codes. This may be because color is perceived earlier than other types of visual coding in the sequence of information processing. Another reason that color coding may be advantageous is that short-term memory is better for colors than for shapes or numbers. Color coding may be most effective when the display is unformatted, the symbol density is high, or the operator must search for specified information. Color is less useful for identification tasks in which letters and numbers are preferable. Untrained subjects can reliably discriminate only five to nine colors; however, with training, 24 colors can be reliably discriminated. Color coding is more effective when the chosen colors are consistent with prevailing conventions or accepted standards. In the general population, red indicates danger, and green indicates safety.
One disadvantage of color coding is that it cannot be discriminated by the color-vision impaired. Colored lenses, such as those in the protective goggles worn during laser surgery, also impair color perception and may interfere with tasks. Redundant coding must therefore always be used when selection of the wrong object could have adverse consequences. Alternative or multiple coding methods should be considered when more than six codes must be discriminated on a single display. A number of studies suggest that irrelevant color coding can interfere with cognitive processing of visual information, and the overuse of color for coding purposes also increases the visual clutter of a display. Tools have been developed for the controlled study of the optimal properties of displays.
Note: In the above table, there appears to be an error where "The visual system of the person is overburdened" should appear on the left column under Auditory.
Auditory displays also should take advantage of learned or natural relationships. For instance, the pitch should increase as the value increases. In general, the same signal should designate the same information in all situations. Because the number of recognizable auditory signals may be limited, auditory displays should not provide more information than is necessary. Complex messages may best be transmitted in two stages. The first stage should be an alerting signal to identify the general category of information. The second stage may then transmit more specific information. Auditory displays must be carefully designed to prevent masking of the signal by the noise of the environment.
Extremely loud or abrupt-onset signals should be avoided because they tend to startle the operator. Continuous signals can also be disruptive, and perceptual adaptation may limit their effectiveness. A number of methods may be used to improve the signal/noise ratio. Auditory displays should also take into account the perceptual limitations of the user.
Just as the equipment transmits information to the user through displays, the user transmits information to the device via controls. Different types of controls are preferable for different kinds of tasks.
- Switches or buttons are used to transmit binary, or on/off, information.
- Continuous information is usually conveyed with knobs, cranks, wheels, levers, or pedals.
- Keyboards are frequently used to enter numeric or alphabetic information, and cursor position on computer displays may be controlled with a mouse, joystick, trackball, touch screen, or light pen.
- Touchscreen controls began to be used in the 1990's, and accelerated as smart phones became popular. People were already familiar with touchscreen gestures - such as pressing, dragging, zooming etc, so were comfortable at a touchscreen interface.
The control’s design influences the speed and error rate of user actions. Factors such as control type, control “feel” or resistance, control feedback (visual, audible, and tactile), control placement, and keyboard layout are all important considerations for the equipment designer.
Spatial compatibility deals with the physical arrangement of controls and their associated displays. In general, for optimal performance, each control should be located directly below its corresponding display. When controls are located above the related display, the user’s hand may block the view of the display while adjusting the control. When the controls are grouped apart from the displays, controls and their corresponding displays should be arranged in the same pattern.
Controls should also be arranged to conform with the physical layout of the system; for instance, the throttles on a jet correspond left to right with the spatial relationship of the engines. Spatial conformity also refers to the physical similarity between controls and displays. Thus a round dial is a more appropriate display for a knob, and a linear display is more appropriate for a slide control.
Movement compatibility relates to expectations that people have regarding the relationship between control or display movements and system responses. People’s expectations regarding movement relationships often are based on population or cultural stereotypes. For example, moving a light switch up generally turns a light on in the United States, but the same action turns a light off in the United Kingdom and Australia. It therefore is imperative that the designer consider the population that will be using the device. Some guidelines for direction of control movements are listed below;
Driving on opposite sides of the road is another expectation issue. So in Australia people walk past each other by staying on the left, but the opposite occurs in the US or Europe. (e.g. Some cars converted from right-hand-drive to left-hand-drive may have the turn indicator lever on the wrong side - which is very confusing. The driver will turn on the windscreen wipers every time they want to turn a corner!)
Coding of Controls
Mistaking one critical control for another has led to serious accidents in aviation (i.e., confusing the landing gear and flap controls), ground transportation (i.e., mistaking the accelerator for the brake pedal), and medicine (i.e., flowmeter control errors, syringe swaps). Unambiguous identification of controls can decrease the incidence of such errors. Primary coding methods for controls include type, shape, texture, size, location, color, and labels. As with coding of display elements, the success of the coding method depends on detectability, discriminability, compatibility, meaningfulness, and standardization.
Shape is an effective method for coding of controls. It provides tactile feedback to the user, which is especially useful when the user does not routinely observe the operation of the control. On most keyboards, special keys are of different shapes, and the F and J keys often are identified by raised dots. The Federal Aviation Administration requires unique, standardized shapes for cockpit controls. Besides being easily distinguishable, some of these knobs have symbolic meaning; for example, the landing gear control resembles a wheel, and the flap control is shaped like a wing.
Surface texture is another useful coding dimension. The textured rims of the dime, quarter, and half dollar provide a common example. Smooth, knurled, and fluted knobs can be reliably discriminated, even by the gloved hand. Color coding of controls can be effective if a small number of coding categories exist and if the colors are meaningful, and color can also be used to associate a control with a display. One disadvantage of color coding, however, is that the user must look at the control during use.
The most common way of identifying controls is with labels. The advantage of labels is that large numbers of meaningful codes can be developed. Disadvantages include the time required to read the label, the effects of lighting conditions and label position on legibility, and the possibility of reading errors in stressful situations and with high workloads. Additional coding methods are therefore indicated when poor lighting or stressful conditions are present and when controls are cluttered or positioned out of the line of sight. Text labels are not appropriate for equipment sold in an international market; graphic or iconic labels are better. International standards organizations have attempted to develop universal icons for medical equipment; however, this endeavor has been hampered by the difficulty of developing icons that have clear meaning across multiple languages and cultures.
Stature and adult male dimensions (Note: This diagram is in inches). Larger size here
Stature and adult female dimensions (Note: This diagram is in inches). Larger size here
Head movement and visual range: Larger size here
Hand dimensions (Note: This diagram is in inches). Larger size here
Standing (with shoes) 2.5%ile, 50%ile and 97.5%ile male and female dimensions (Note: This diagram is in inches & mm).
Larger size here
Architectural dimensions needed for various common postures (Note: This diagram is in mm). Larger size here
Architectural dimensions needed for various common postures (Note: This diagram is in mm). Larger size here
Architectural dimensions needed for various common postures (Note: This diagram is in mm). Larger size here
Sitting at a console. Alvin Tilley/Henry Drayfus 1959
Sitting at a console. Alvin Tilley/Henry Drayfus 1959
Hand span (as compared to piano keyboard range) .
|Anthropometry|| The study and measurement of human body dimensions.
(Yili Liu, 2004; Karl Kroemer, 2001)
|Biomechanics||Analyzes the human musculoskeletal system as a mechanical system that obeys laws of physics. (Yili Liu, 2004)|
|Carpal tunnel syndrome||Carpal tunnel. The canal in the wrist bounded by osteofibrous material through which the flexor tendons and the median nerve pass.
Carpal tunnel syndrome. Soreness, tenderness, and weakness of the muscles of the thumb caused by pressure on the median nerve at the point at which it goes through the carpal tunnel of the wrist. TREAT: Surgical relief of tension if conservative therapy fails.
|Duty of care||The legal and general obligation and responsibility expected of a person to protect themselves and others from harm in the workplace|
|Ergonomics||The design of equipment and environment to be safe, comfortable and productive for human use|
|Hazard identification||Recognising the risk of an item or situation that may lead to a potential accident or harm to a person|
|Hazards||An item, condition, event or situation that could lead to a potential accident or harm|
|Manual handling||Using human force to move or support a load (including moving, lifting, putting down, pushing pulling, or carrying)|
|Material Safety Data Sheet (MSDS) or SDS||An information sheet designed by suppliers detailing correct procedures when handling a particular substance or chemical|
|Occupational Health and Safety||Legislation, policies, procedures and activities that aim to protect the health, safety and welfare of all people at the workplace|
|Personal Protective Equipment (PPE)||Equipment and clothing items designed to protect the user from potential hazards or injuries whilst doing a task at work|
|Repetitive Strain Injury
|An injury caused by stress of repeated movements.
Also called Occupational Overuse Injury
|WorkCover||A state authority that manages workplace safety, injuries and incidents and compensation|
|Workers Compensation||Payments required by law for an injury to an employee for compensation for a work related injury|
Larger glossary here: http://www.kneelsit.com/glossary/glossary1.html#H