Ergonomics | A1.1

Students must be able toDescribe how ergonomics is used to improve the design of a product by making a design more efficient, usable, functional, effective and safe.

Ergonomics (also called human factors engineering) is the study of how people interact with the products, systems and environments they use. When designers apply ergonomic thinking, the result is products that are safer, more comfortable and more efficient to use.

The field is built on three interlocking disciplines:

• Anthropometrics - the measurement of human body dimensions. Knowing how large or small a user's body is allows designers to set appropriate dimensions for a chair, a control panel or a doorway.
• Physiology - how the body's systems (muscles, nervous system, cardiovascular system) function, respond and reach their limits. Relevant when designing for force, fatigue, posture or sensory capability.
• Psychology - how the mind perceives and interprets information from the senses. Relevant when designing interfaces, environments, warnings or anything that communicates through sight, sound, smell, taste or touch.

A product designed without ergonomic consideration may still function technically. It will be harder to use, more tiring, riskier or inaccessible to some users. Good ergonomic design removes that mismatch.

A practical way to apply ergonomics is to evaluate a design against the five qualities the IB syllabus identifies. Each describes a different way a product can fail to match the person using it:

Ergonomics applied: six product categories

The five qualities above are abstract until you see them in a real object. The categories below are the ones the course uses most often, and each one solves a different kind of body-to-product mismatch.

• Office chairs. Adjustable seat height lets the user place their feet flat on the floor with the thighs roughly parallel to the ground, which keeps the spine in a neutral position and reduces strain on the lower back. Adjustable lumbar support (support for the inward curve of the lower back) prevents slouching and takes pressure off the spinal discs. Adjustable armrests carry the weight of the arms so the shoulders can stay relaxed rather than raised.



• Keyboards and mice. Wrist supports, split or angled key layouts and carefully placed mouse buttons reduce the awkward wrist angles that cause discomfort during long periods of typing. Less strain also means fewer errors and better productivity.
• Medical devices. These are designed to reduce physical strain on doctors and nurses who use them for hours at a time, because a tired user makes more mistakes. Features that prevent accidental injury, such as needle guards and locking connectors, are part of the same thinking.
• Automotive design. Seats, steering wheels and control panels are all shaped around driver comfort and reach. The clearest recent example is the head-up display (HUD), which projects speed and navigation information onto the windscreen so the driver reads it without looking away from the road. Connecting the HUD to a phone lets the driver deal with calls and messages without taking their hands off the wheel.
• Consumer electronics. Phones, tablets and wearables are sized and weighted so they can be held and operated for long periods without the hand or wrist tiring.
• Kitchen knives. A chef's knife should feel like an extension of the hand. Designers control weight distribution so the knife balances near the handle, giving the user more control and better accuracy. Lightweight, non-slip and textured materials improve grip, which matters most when the hand is wet.

Students must be able toExplain and use static and dynamic anthropometric data to design for different people and discuss how factors such as age, gender, ethnicity and disability affect the anthropometric data.

Anthropometric data is the systematic collection of human body measurements - height, reach, grip diameter, shoulder width, eye height and hundreds of other dimensions. Designers use this data to set critical product dimensions.

The World Health Organisation, in its report Physical status: the use and interpretation of anthropometry (1995), calls anthropometry "the single most universally applicable, inexpensive and non-invasive method available to assess the size, proportions, and composition of the human body". Non-invasive means nothing enters the body: you are measuring a person from the outside, with a tape or a caliper, not with a scan or a blood test. That is why the method is used everywhere from hospitals to furniture factories.

Two types of data are collected:

• Static anthropometrics (also called structural) - measurements taken with the body still: standing height, seated eye height, shoulder breadth, hand length, and distances between joints. This data is easy to collect because the subject is not moving. Used when designing furniture, clothing, vehicle interiors and equipment that must fit a stationary body.
• Dynamic anthropometrics (also called functional) - measurements taken during movement: reach envelope, step length, grip force, reaction time, range of motion. This data is harder to collect, but it is often more useful, because it shows the range and the ease of the movements a user can actually make. Used when designing controls, handles, tools and spaces where the user must move to operate the product.

How the data is collected, and why it is not perfect

Measurements are taken with instruments such as calipers (a sliding measuring tool with two arms that close onto the body), tape measures, height gauges and, increasingly, 3D body scanners. Whatever the instrument, two things matter: it must be sturdy, and it must be calibrated, meaning it has been checked against a known standard so its readings can be trusted.

Some measurements are far more reliable than others. Height and weight are simple and repeatable. Body fat measured with skinfold calipers is much less reliable across a large sample, because the result depends on exactly where and how hard the technician pinches the skin. When you use a data table, it is worth asking how the numbers in it were obtained.

There is one convention that surprises most students. Anthropometric data is meant to describe the nude body, so that measurements from different studies can be compared. In practice, cultural expectations often make that impossible, so investigators measure clothed subjects and then subtract an allowance for the type and thickness of the clothing worn. Designers sometimes have to add an allowance back on, since a user wearing a winter coat or protective equipment occupies more space than the table says.

Factors that change the data

No two bodies are identical. A person tall enough to fit clothing size L may have arms that fit a size S. Designing for a single "standard human" always excludes real users. Anthropometric data must account for variation across:

• Age - children and older adults differ significantly from young adults in reach, grip strength and mobility. Children are also a moving target, because they change size quickly.
• Gender - on average, men are taller and heavier than women, a difference driven largely by hormones. Male bones are generally larger and denser: peak bone mass in men is roughly 50% greater than in women, and women lose bone mass faster as they age, so the gap widens over a lifetime. Women on average carry a higher percentage of body fat, which matters when interpreting health measures such as BMI. Products for a mixed population must accommodate both.
• Ethnicity - body proportions vary across populations, so data collected from one group cannot be applied globally without adjustment. For example, people of African descent tend to have higher bone density and lower fracture rates than people of European descent, and measures such as waist circumference and waist-to-hip ratio differ meaningfully between ethnic groups.
• Disability - users with physical disabilities may have reach ranges, grip capabilities or postures that change every dimension a designer must consider. Conditions affecting mobility, such as cerebral palsy or muscular dystrophy, produce body measurements that standard tables do not describe. Wheelchair users often have different upper-body strength and proportions from non-users, which changes both the reach envelope and the forces a product can ask for. See C1.2 Inclusive Design for how these differences shape design requirements.

Using anthropometric data in practice

A designer identifies which body dimension is critical for the product (seat height, grip width, overhead reach distance), selects the data table for the relevant user population, then determines which end of the distribution to design for. Whether the dimension is about reach or clearance controls the choice of percentile. The rules for that are covered in 1.1.3 Percentiles and 1.1.5 Work Envelopes.

Students must be able toIdentify where the 5th, 50th and 5th–95th percentiles are appropriate for a design scenario.

Anthropometric data for any dimension - such as standing height - follows a normal distribution (also called a Gaussian distribution, or a bell curve). Most people cluster near the middle; fewer people are at the extremes. Percentiles tell you what percentage of the measured population falls at or below a given measurement. Someone in the 70th percentile for a dimension measures the same as, or more than, 70% of the sample.

The statistics behind the curve

A normal distribution is described by just two numbers. The mean is the average value, which sits at the peak of the curve. The standard deviation (written with the Greek letter sigma, σ) measures how spread out the values are around that mean. A small standard deviation gives a tall, narrow curve, meaning most people are close to average. A large one gives a wide, flat curve.

The useful part is that the spread is predictable:

• About 68% of the population falls within one standard deviation of the mean (mean ± 1σ).
• About 95% falls within two standard deviations (mean ± 2σ).

This is why percentile tables work at all. Because the shape of the curve is known, a designer can convert "I want to include 90% of users" into two actual measurements in millimetres, taken from the table at the 5th and 95th percentiles.

A second useful piece of arithmetic concerns mixed populations. Within a single gender, the 5th to 95th percentile range covers 90% of people, because 5% are excluded at each end. In a mixed group that is half male and half female, the same range covers about 95% of people. Only the tallest 5% of men and the smallest 5% of women fall outside it, and since each group is half the sample, that is 2.5% + 2.5% = 5% excluded in total.

Three percentiles are used routinely in design:

• 5th percentile - 5% of the population is at or below this measurement. A 5th percentile adult is among the smallest in the population. When designing for reach - how far a person must stretch to operate something - design for the 5th percentile: if the smallest person can reach it, everyone can.
• 50th percentile - the median value; half the population is above and half below. Rarely the right choice on its own - a product sized only for the median excludes people at both extremes.
• 95th percentile - 95% of the population is at or below this measurement. A 95th percentile adult is among the largest. When designing for clearance - how much space a person needs to fit through or under something - design for the 95th percentile: if the largest person fits, almost everyone fits.

Most products should be designed for the 5th–95th percentile range, covering 90% of the population. The extreme 5% at each end are excluded - a deliberate design compromise when the cost of accommodating them is too high.

Designing for the mean alone looks sensible but usually is not. Very few people sit exactly at the average, so a fixed dimension set at the 50th percentile fits almost nobody properly. The problem gets worse when the user group crosses age or gender boundaries, because there is no single average that describes both halves of the group.

Case study: the crash test dummy

Crash test dummies are the clearest example of a 50th percentile decision with consequences. The timeline below is worth knowing in detail, because it shows how long a bad assumption can survive once it is built into testing equipment.

• Sierra Sam (1949). The first widely used dummy was built for the aviation industry, not for cars, and represented a 95th percentile male: heavier and taller than 95% of men. It was used to test ejection seats, aviation helmets and pilot restraints.



• Hybrid I (1971). General Motors redesigned Sierra Samredesigned Sierra Sam into a dummy modelled on the 50th percentile male, using average male height, mass and proportion. Vehicle safety features such as seatbelt geometry and airbag placement were tuned around this body.
• The 1980s. The first female crash test dummy appeared, more than a decade later. It was essentially a scaled-down version of the male dummy, so it captured a smaller body but not the actual anatomical differences between male and female bodies.
• 2022. Swedish researchers developed the first dummy genuinely modelled on female anatomy, designed to capture the injuries women are most likely to sustain rather than simply shrinking a male model.



• THOR 5th ATD. A modern, biofidelic (built to behave like real human tissue) Anthropomorphic Test Device representing a 5th percentile female, designed around female physiology rather than adapted from a male baseline.

Because female anthropometric data was not collected or used for decades, safety features were effectively optimised for a male body, and studies later showed women were significantly more likely to be injured in crashes. The case illustrates the real harm that follows when designers fail to represent the full range of users in their data.

A second example shows the same principle without the tragedy. Computer furniture for primary school children has to cover a very wide 5th to 95th percentile range, across both genders and across several years of rapid growth. Get it right and the furniture encourages good posture, reduces fatigue and prevents long-term back problems. Get it wrong, and a child spends six years at a desk that does not fit them.

A useful heuristic when selecting a percentile: ask whether the dimension involves a person reaching towards something or fitting into something.

Students must be able toExplain the reasons why designers choose adjustability and/or range of sizes for a product, and identify products that use one or both strategies.

Because no single fixed dimension suits the full 5th–95th percentile range, designers have two core strategies for accommodating different body sizes:

Strategy 1 - Adjustability
The product has components that can be moved, extended or set by the user to suit their own body. Examples:

• An office chair with adjustable seat height, lumbar support and armrests allows a 5th percentile small user and a 95th percentile tall user to both sit comfortably at the same workstation.
• A car's steering column and seat position both adjust, accommodating drivers across a wide height range.
• A bicycle saddle slides up and down its post to match the rider's leg length.

Adjustability is preferred when users share a product and need it to fit their specific body. Its main cost is added mechanical complexity and the need for users to correctly set it up.

Strategy 2 - Range of sizes
The product is manufactured in multiple fixed sizes. Users select the size closest to their body. Examples:

• Clothing sold in XS, S, M, L and XL.
• Crash test dummies: the Hybrid III family includes a 50th percentile male, a 5th percentile female and three child dummies; five sizes to cover a wider population range.
• Bicycle helmets offered in S, M and L to fit different head circumferences.

A range of sizes is appropriate when adjustability is mechanically impractical, too costly, or when the product is consumed or worn and cannot be shared. Some products use both strategies - adjustable components within each size - to maximise fit. Clothing is the everyday example: garments are sold in fixed sizes, but drawstrings, elastic bands, belts and adjustable straps let the wearer fine-tune the fit within the size they bought.

Widening the percentile range a product covers is sometimes called design for more types. It is a trade-off rather than a free improvement. Each extra bit of range costs money, adds mechanism or adds stock-keeping complexity, and the cost climbs steeply once you go beyond the 5th to 95th band. Users outside that band usually have to look for a customised solution instead.

Students must be able toExplain the importance of workspace envelopes, adjustability, reach and range of sizes clearance in relation to percentiles and how they are used when designing products.

When designing a workspace, whether it is a cockpit, a kitchen or a production line, a designer needs to map more than body size. They also have to map the space in which the body moves and operates. Three related concepts define that space:

Work envelope (workspace envelope) - the three-dimensional space that a person can comfortably reach and operate within from a fixed position. Imagine a sphere of reachable space around a seated operator. All critical controls must fall within this envelope; otherwise the user must stretch, lean or shift in ways that increase fatigue and error rate. The size of the work envelope changes with body size, so it must be defined using percentile data.

Reach - the maximum distance a person can extend their arm to contact or operate something. Reach is a 5th percentile design concern: if the smallest user can reach every control, everyone can. Place the most frequently used controls in the nearest zone of the work envelope.

Clearance - the minimum space needed to fit part of the body without obstruction: head clearance in a doorway, knee clearance under a desk, shoulder width in a corridor. Clearance is a 95th percentile concern: design so the largest user fits through or into the space, and everyone else will too.

Applying these correctly means using different percentiles for different problems: reach calls for 5th percentile data; clearance calls for 95th percentile data. A single percentile cannot solve both simultaneously. This is one reason adjustable workstations exist.

Why one percentile is never enough: multivariate variation

The usual rule for adjustability is to cover from the 5th percentile female to the 95th percentile male. That sounds like it guarantees 95% coverage, and it would, if human bodies were always in the same proportion. They are not. A tall person can have short arms; a short person can have proportionally long arms. Being 50th percentile for height tells you almost nothing about someone's shoulder width or seated eye height.

Multivariate analysis is the statistical method used to handle several body dimensions at once instead of one at a time. The uncomfortable finding it produces is this: when a product depends on several dimensions together, designing each one to the 5th–95th range still leaves more than 5% of people excluded on at least one dimension. Someone who fits the seat depth may not fit the armrest width.

Designers accept this rather than solve it, because the cost of accommodating every possible combination of dimensions rises very steeply and is rarely justified. What they can do is identify which dimension actually limits the design. In a workstation, that limiting factor is usually arm reach, which is why the reach envelope is defined as a three-dimensional space rather than a single distance.

Where the data comes from

Reliable data is essential before you can define a reach envelope for a broad population. Four sources are commonly used:

• Anthropometric tables - published percentile data for a defined population.
• Dynamic measurement - measuring real users while they move, which captures reach and range of motion that static tables miss.
• Software simulation - digital human models placed into a CAD model of the workspace, so reach and clearance can be tested before anything is built.
• Video analysis - traditionally measurements were taken by hand, but recorded video has proved an effective way to capture how people actually move through a task.

Every one of these can be distorted by clothing, which adds bulk and restricts movement. A reach envelope measured in a t-shirt does not describe the same worker in a padded jacket, gloves and a helmet.

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Students must be able toExplain limiting aspects of user capabilities, including users' visual accuracy, colour perception, strengths, fatigue, muscle control and hearing thresholds.

Physiology is the study of how the body's systems function, respond and break down under use. For designers, the relevant question is: what are the limits of what the human body can do, and how does the product stay within those limits?

Visual accuracy and colour perception. The eye can only see fine detail at the very centre of the visual field, in a small area of the retina called the fovea. Everything outside that centre is peripheral vision, which detects movement well but detail poorly. Approximately 8% of males have some form of colour vision deficiency, meaning they cannot reliably tell certain colours apart. Designs that rely on colour alone to carry critical information (red = danger, green = safe) exclude these users. Good design treats colour as one channel among several, so that shape, symbol and position repeat the same message for anyone who cannot see the colour difference.

Muscle strength and fatigue. The force a person can exert (gripping, lifting, pushing) varies widely by age, gender, hand size and physical condition. Biomechanics is the study of the mechanical laws governing movement in living bodies: levers, joints and load paths. Designing a product that requires excessive force can cause injury over time. A rubber jar opener with a serrated strip works by increasing friction and mechanical advantage, allowing the same torque to be produced with far less hand force. This reduces fatigue and injury risk for users with reduced grip strength.

Muscle control. Fine motor control (precise finger and hand movements) decreases with age, fatigue, cold and certain medical conditions. Products requiring precise input, with small buttons or fine-tuned controls, can exclude users with reduced motor control.

Hearing thresholds. Human hearing is most sensitive in the 1,000–4,000 Hz range. High-frequency hearing loss is common with age. Auditory warnings must be designed to reach users with reduced hearing and must not be masked by background noise in the environment where the product is used.

Every design contains a biomechanical assumption

Whenever a designer specifies a control, they are quietly assuming something about the user's body. That a finger can press this button hard enough. That a wrist can twist this switch. That a hand can turn the handle of a can opener or a corkscrew. Those assumptions come from anthropometric data describing the population's strength, dexterity and fine motor control, and they are only as good as the population the data was taken from.

Several common conditions break the assumption. Age-related muscle weakness, arthritis (painful inflammation and stiffness of the joints), Parkinson's disease (a nervous system disorder causing tremor and slowed movement) and multiple sclerosis (damage to the nerves, causing weakness and loss of coordination) all reduce the force and precision a user can produce. Designers respond either by adapting the original design or by developing adaptive technologies, which are devices that amplify what the user's body can do rather than replacing it.

Packaging is where this fails most often. Older consumers regularly report difficulty with jar lids, soft drink bottle tops, ring pulls and child-resistant screw caps. Reduced grip strength and arthritis turn a task the designer never thought about into a daily obstacle. Better packaging, or a grip aid that supplies mechanical advantage, solves it cheaply.

A different biomechanical problem appears when equipment adds load to the body. Protective helmets are worn in many jobs and sports, and the neck muscles must resist that extra weight for hours. It becomes serious in military and search-and-rescue work, where night vision goggles or a head-mounted display are attached to the front of the helmet. The added mass sits forward of the neck joint, so it acts on a longer lever arm and multiplies the strain.

Biomechanics in sporting equipment

Sport is the clearest showcase for biomechanics, because equipment is refined to improve performance, reduce fatigue or prevent injury. Products are usually developed for elite athletes first, then mass-produced for everyone else.

• Tennis racquets and golf clubs use more responsive materials, so more of the energy the athlete puts in is returned to the ball rather than absorbed by the frame or the arm.
• Competitive swimsuits are engineered to create less drag through the water.
• Javelins include damping technology that absorbs the vibration set up when force is applied sideways during the initial throw.

Biomechanical engineers work on far more ordinary products too, from backpacks to child safety harnesses, and they use the same analysis to investigate how a product is used, misused or found difficult. Applied across the whole population, including children, older adults and people with disabilities, this work becomes design for inclusion.

Designing around the limits of sight

Because vision carries most of the information a user receives, visual design has to be unambiguous: the right information, in the right place, at the moment it is needed, with nothing distracting around it. Designers are responsible for asking how the information will actually be used. A door that opens in only one direction should say push or pull, because nothing in the shape of a flat plate tells the user which is which.

Colour does several jobs at once, and it is worth separating them:

• Appeal. Bright, saturated colours make a product stand out on a shelf; neutral colours suggest elegance and restraint.
• Legibility. High contrast between text and background makes information readable, whether on packaging or a phone screen. Contrast checking tools let a designer test this numerically instead of guessing.
• Inclusion. Choosing colour combinations that remain distinguishable to users with colour vision deficiency is a basic inclusive design move, and it costs nothing at the design stage.
• Brand identity. Consistent brand colours build recognition, and specific colours carry learned associations: gold, silver and black are widely read as signalling luxury and exclusivity.
• Context and safety. Camouflage patterns let clothing and equipment disappear into an environment. The opposite choice, high-visibility orange on lifeboats and life vests, makes equipment as easy to find as possible. Both are colour decisions driven by how the eye works rather than by taste.

Designing around the limits of hearing

Hearing is used deliberately in design for four main purposes:

• Safety. Volume limiters, built into headphones as either software or hardware, cap output at a level considered safe. Separate limits are often set for children and adults, because long listening sessions at high volume permanently damage hearing.
• Privacy. Soundproofing is applied to offices, bedrooms and studios to stop noise entering a space, leaving it, or both.
• Alarms. The pitch, pattern and intensity of an alarm are engineered so the signal carries through the environment and reaches as many people as possible. Police and ambulance sirens, fire alarms and smoke alarms are all tuned to be heard and understood quickly.
• Environments. Acoustic treatment of walls, floors and ceilings absorbs echo and reverberation. Without it, speech becomes hard to follow and music loses definition, whatever the quality of the sound source.

Thermal comfort

A person's experience of a given temperature depends on air temperature, humidity, air movement, radiant heat, clothing insulation, metabolic rate and individual physiology. Two people in the same room at the same thermostat setting may experience it very differently, depending on their clothing, activity level, body composition and acclimatisation. A single fixed temperature cannot satisfy all occupants of a shared space. Designers and facilities managers address this with zoned temperature controls, personal desk fans or heaters, and flexible dress codes. The underlying logic is the same as designing products in a range of sizes: no single fixed setting works for everyone, so the environment must allow for variation.

Students must be able toDiscuss how human senses (smell, sound, touch, taste and vision) are used to influence the design and development of products.

Psychology, in the context of ergonomics, focuses on how the mind receives and interprets information from the environment through all five senses. Products communicate through sensory channels whether their designers intend it or not. Understanding how the brain processes sensory input allows designers to communicate more clearly, create safer products and shape user experience.

Sight (vision). The most information-dense sense. Designers control colour, shape, size, contrast and motion to direct attention and communicate meaning. Orange is used for life rings, life vests and rescue equipment because it is the most easily detected colour against the sea surface and in low-light conditions. The choice is grounded in visual psychology. Text contrast ratios must meet accessibility standards to remain readable for users with reduced vision.

Space and visual boundaries also carry psychological weight. High partitions in an office create a sense of personal territory and acoustic privacy. Lowering them increases visual connection and openness but reduces defensible space, the zone a person perceives as their own and feels in control of. The term was coined by John Calhoun in the 1940s, and the amount of personal space an individual needs varies with culture and upbringing rather than being fixed. Designers balance these competing effects when planning shared environments such as open-plan offices and libraries.

Hearing (sound). Auditory signals carry urgency: a car horn, a fire alarm, a hospital monitor. The tone, pitch, rhythm and volume of a sound communicate different levels of emergency. A warning tone that blends with background noise fails its purpose. Sound design must account for the acoustic environment where the product is used.

Touch (haptic feedback). Textured surfaces, vibrations and physical resistance communicate information without requiring vision or sound. Tactile paving (the raised, bumped tiles at pedestrian crossings) signals a safe crossing point to visually impaired users by touch alone. Digital devices use haptic feedback to confirm input, guide navigation and signal alerts without requiring the user to look at a screen or hear a sound. See the concept introduction below for a full explanation.

Smell (olfaction). Natural gas is odourless; a sulphur compound is added to give it a distinctive smell because the brain responds rapidly to unfamiliar odours. Safety design sometimes uses smell as a warning channel when visual or auditory channels may be missed.

Taste. Less commonly a design consideration, but relevant in food products, medical devices (pill coatings designed to prevent accidental ingestion) and child safety (bitter coatings on hazardous household products).

Psychological data in product design: the mobile phone

Phones are a good example because the technology inside two competing models is often nearly identical. What differs is everything the user senses: colour, shape, material, surface finish, the weight in the hand, the way the screen lights up. Manufacturers vary these deliberately to appeal to different consumer groups. It is not only functions and services that sell a phone. Physical design choices aimed at a buyer's psychological needs, such as wanting to appear serious, playful, expensive or discreet, do a large share of the work.

Environmental psychology and the office

Environmental psychology studies the relationship between an environment and the people inside it. For an indoor office, five factors are usually assessed together:

• Lighting - access to natural light and a view outside, plus adjustable task lighting so individuals can set the level that suits their eyes and their current task.
• Acoustics - quiet spaces that protect concentration by removing distraction and interruption.
• Air quality - usually handled by air conditioning, which controls ventilation, air movement and humidity and can filter pollutants. It introduces its own problems, though: draughts, uneven temperatures and fan noise.
• Temperature - see the thermal comfort discussion in 1.1.6. Radiant temperature has the strongest effect on people, because the body absorbs heat directly from warm surfaces. Sustained high temperatures lead to heat stress and eventually heat exhaustion.
• Worker density - how many people occupy a given area, and whether the space can be adapted and personalised to suit different working styles.

There is a widely used benchmark for judging the result. When about 80% of the occupants report feeling comfortable, the space is considered to have achieved "reasonable comfort". The figure is deliberately not 100%, because individual responses vary too much for that to be achievable. Note also that air temperature on its own is not a valid measure of comfort: all five factors above contribute.

Open-plan offices exist mainly to raise worker density and free up unrestricted space, by removing interior walls or shrinking partitions. The gains are real. Communication barriers drop, the space feels larger, and air and daylight move more freely. So do the costs: more noise transfer, less personal privacy and more visual distraction. The usual compromise is to use carefully placed low barriers to create defensible space within an open layout, so employees can still customise a small area and feel a degree of comfort, safety and control.

To measure any of this rather than guess at it, office designers can use the Physical Work Environment Satisfaction Questionnaire (PWESQ). It surveys staff on the environmental factors listed above alongside physical demands and work systems, and it turns a subjective argument about whether an office "feels bad" into data a designer can act on.

Key Concept

Haptic Feedback

Haptic feedback is the use of vibration, force or texture to send information to a user through the sense of touch. The word "haptic" comes from the Greek haptikos, meaning "able to touch." Designers use it as a communication channel when visual or auditory feedback is unavailable, insufficient or would disturb others.

You already know haptic feedback

• Smartphone notifications and silent confirmations. A phone vibrates to signal an incoming call, confirm a button press in silent mode, or alert you to a message. Without haptic feedback, pressing a touchscreen button gives no physical signal that the input was registered, leading to repeated presses or missed inputs.
• Game controllers. A controller rumbles when a car hits a wall, a character takes damage, or a weapon fires. The PlayStation DualSense goes further: it can simulate surface textures by varying the vibration pattern as a character moves across different virtual materials.
• MacBook trackpad. The trackpad on modern MacBooks does not physically move. A component called the Taptic Engine generates a precisely timed vibration that your finger interprets as a click. Place the trackpad on a table (preventing your hand from resting on the laptop body) and press: there is no movement at all. The "click" exists entirely as haptic feedback.
• Lane departure warnings. Some cars vibrate the steering wheel when the vehicle drifts across a lane marking, delivering the alert through the driver's hands rather than through the eyes or ears. This is especially useful when the driver may have missed a visual warning.

When discussing haptic feedback in an IB context, consider both what it enables (confirmation without sound, navigation for visually impaired users, physical immersion in gaming) and its limits (the sensation is lost if the device rests on a surface rather than in the hand; not all users have full tactile sensitivity; cultural expectations around vibration vary).