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9 Detail about human abilities and the consequences of impairment

9.1 General

9.1.1 The needs and abilities of people change as they advance from childhood to old age and the abilities of individuals in any particular age group vary substantially. It is important to recognize that functional and cognitive limitations vary from comparatively minor impairment to more extreme forms.

9.1.2 This clause, to be used in conjunction with clause 8, provides the tools for identifying and addressing the needs of older persons and persons with disabilities in standardization work.

9.1.3 A brief definition and description of each ability used in the Tables have been given along with information on the effects of ageing and the practical implications of impairment. Examples have been given, where appropriate, of hazards from which older persons and persons with disabilities are more at risk because of their functional limitations.

9.2 Sensory abilities

9.2.1 Seeing

9.2.1.1 Description

Seeing relates to sensing the presence of light and sensing the form, size, shape and colour of visual stimuli.

9.2.1.2 Effects of ageing

The incidence and severity of visual impairment increase with age. Changes in the physical structure of the eye affect several aspects of visual functions, including:

9.2.1.3 Design considerations

People with no useful vision depend mainly on tactile and acoustic input. The majority of people with difficulties seeing have some vision, and therefore use visual stimuli such as size, luminance and colour contrast. Typically, the simpler an image and the clearer its definition, the easier it is to see and read.

9.2.1.4 Risks and hazards

People with a visual impairment are at an increased risk from, for example:

9.2.2 Hearing

9.2.2.1 Description

Hearing functions relate to sensing the presence of sounds and discriminating the location, pitch, loudness, quality and comprehension of sounds. Hearing loss can range from a mild reduction in hearing to profound deafness.

9.2.2.2 Effects of ageing

The majority of people with hearing loss are older people. As people age, they tend to lose the ability to detect higher frequency sounds. Many older people use a hearing aid.

9.2.2.3 Design considerations

With or without a hearing aid, the level, frequency and clarity of any sound is important. Prelingually deaf people may have difficulty understanding written and spoken language.

9.2.2.4 Risks and hazards

People with a hearing loss are at an increased risk if spoken announcements and warnings are not loud or intelligible enough for them, or if frequencies are too high to detect.

9.2.3 Touch

9.2.3.1 Description

Touch functions relate to sensing surfaces and their texture or quality. There will be reliance on other stimuli, particularly visual and auditory.

9.2.3.2 Effects of ageing

As people age, they lose sensitivity and can no longer rely on touch and pain to give early feedback on temperature or injury.

9.2.3.3 Design considerations

People with artificial hands or who lack touch sensation may not be able to use tactile screens or similar types of control devices.

9.2.3.4 Risks and hazards

People with hypersensitive touch will be hurt by stimuli which might cause only discomfort to other people — for example, by sharp points and edges, and very hot/cold surfaces. These stimuli are also more likely to harm people with limited sensitivity, who might remain in contact with them for too long.

9.2.4 Taste/smell

9.2.4.1 Description

Taste and smell are separate senses but have been grouped together in the Tables because of their similar practical implications. Taste relates to sensing four basic qualities, through receptors on the tongue: bitter, sweet, sour and salty. Smell relates to the use of receptors in the nose to sense odours and smells. The two senses of taste and smell are used together to identify the range of flavours which can normally be distinguished.

9.2.4.2 Effects of ageing

The ability to detect odours decreases as people get older.

9.2.4.3 Risks and hazards

Impairment of the sense of taste or smellreduces the body’s defence against toxic materials. For example, people may not be able to detect when food has deteriorated or be alerted to hazards such as smoke.

9.2.5 Balance

9.2.5.1 Description

The ability to maintain balance and avoid falling is dependent on a complex system, which involves the brain coordinating visual stimuli, feedback from the balance mechanism in the ear and movement of the limbs. Continuous control of balance is required during virtually all types of activities.

9.2.5.2 Effects of ageing

The incidence of balance impairments, and thus falls, increases with age. Age-related attention deficits and visual impairment can reduce the ability to avoid hazards and to react to loss of balance.

9.2.5.3 Risks and hazards

Slips, trips or other unexpected disturbances to balance require rapid responses in joint rotations and limb movements and can place extraordinary demands on the balance control system. Even very small edges and protrusions can cause tripping. Older persons are more vulnerable to injury from falls as bones break more easily and consequent complications may be life-threatening. Balance impairment can lead to an increased fear of falling. People in wheelchairs, powered scooters and walkers may have balance limitations, and injuries can severely affect their independence.

9.3 Physical abilities

9.3.1 Dexterity

9.3.1.1 Description

Dexterity relates to activities of hand and arm use, particularly coordinated actions of handling objects, picking them up, manipulating and releasing them, using one hand, fingers and more specifically, thumbs.

9.3.1.2 Design considerations

Dexterity impairment includes an inability to bring thumbs and fingers close together or an inability to separate them very far. Complex operations, such as push and turn, which require sustained pressure and twisting of the wrist, may be painful or impossible. These have implications for the size, shape and location of controls. People with involuntary movement have problems with tasks that require precision, such as opening packaging and dealing with fastenings.

9.3.1.3 Risks and hazards

People with limited dexterity may endanger themselves, for example by inadvertently activating controls, or failing to withdraw a hand quickly from a hazard, such as a flame.

9.3.2 Manipulation

9.3.2.1 Description

Manipulation relates to activities of carrying, moving and manipulating objects. It includes actions using legs, feet, arms and hands — reaching, lifting, putting down, pulling, pushing, kicking, grasping, releasing, turning, throwing and catching.

9.3.2.2 Effects of ageing

Manipulation can be impaired by an inability to use both hands (or feet) when carrying out an activity. It is also affected when joint movement, particularly of the hands or arms, is restricted. Speed of manipulation also declines in old age as a result of slower reaction time and slower movement.

9.3.2.3 Risks and hazards

Individuals with impaired manipulation may risk injury through inadvertently dislodging a device during use. Product design needs to minimize the hazards and consequences of unintended actions.

9.3.3 Movement

9.3.3.1 Description

Movement relates to activities of maintaining and changing the body position and transferring oneself from one area to another using legs, feet, arms and hands.

9.3.3.2 Effects of ageing

Many impairments in movement are experienced in older age which can result in difficulties in daily living, such as dressing, sitting down and getting up again. Examples include:

9.3.3.3 Design considerations

Some people with movement difficulties are assisted by equipment such as wheelchairs or walking aids; others may require personal help. In both cases, extra space is needed around them to allow for approach and manoeuvring.

9.3.3.4 Risks and hazards

People with impaired movement are particularly at risk during emergency evacuation of vehicles or buildings.

9.3.4 Srength and endurance

9.3.4.1 Description

Strength relates to the force generated by the contraction of a muscle, or muscle group, when carrying out an activity. Strength can be the force exerted with a specific part of the body in a specific action (e.g. pushing) or applied to a specific object (e.g. opening bottle tops). Activities include pulling, lifting, pressing, gripping, pinching and twisting.

Strength also depends on endurance, the capacity to sustain force. This can be related to heart and lung function. Limited strength is common to many physically disabling conditions and is a common reason for being unable to operate equipment.

9.3.4.2 Effects of ageing

Reductions in muscle power and stamina are common in older age resulting in impairment of strength. Impairment of grip strength can make it difficult or painful to operate an appliance against resistance or torque. Limitations of stamina will cause fatigue when use of a product requires prolonged activity. Control of passive movement (i.e. when an external force such as gravity causes the motion) can be impaired resulting in difficulties, e.g. lowering a heavy object to the ground or sitting down on a chair.

9.3.5 Voice

9.3.5.1 Description

Voice relates to the sound produced by the vocal organs, usually as speech. Speech impairments may influence speech in a general way, or only certain aspects of it such as articulation, volume, fluency, speed, melody and rhythm.

9.3.5.2 Design considerations

The principal consequence of speech impairmentis the barrier to communication and social interaction. Alternative forms of communication, such as sign language, or devices such as speech amplification, speech synthesis, or use of facsimile or keyboards, may assist.

9.4 Cognitive abilities

9.4.1 General

9.4.1.1 Cognition is the understanding, integrating and processing of information. The information includes abstraction and organization of ideas and time-management.

9.4.1.2 People with a cognitive impairment may have trouble learning new things, making generalizations and associations, and expressing themselves through spoken and written language. These impairments can produce anxiety, loneliness, depression, delusions, obsessions and compulsions. Such disorders may result in reduced ability to concentrate on a task.

9.4.2 Intellect

9.4.2.1 Description

Intellect is the capacity to know, understand and reason.

9.4.2.2 Effects of ageing

As people get older they may have more difficulty concentrating and in continuing to pay attention to a task. Changes in the sleep/wake rhythm may mean older persons are sleepy and thus less alert during the day. Conditions such as dementia and Alzheimer's disease, which are more predominant among older persons, lead to progressive intellectual decline, confusion and disorientation.

9.4.2.3 Design considerations

Impairment leads to perception problems, which include difficulty taking in, attending to, and discriminating sensory information. Difficulties in problem-solving include recognizing the problem, identifying, choosing and implementing solutions, and evaluating the outcome.

9.4.3 Memory

9.4.3.1 Description

Memory relates to specific mental functions of registering and storing information and retrieving it as needed.

9.4.3.2 Effects of ageing

Failing memory affects people’s ability to recall and learn things and may also lead to people being confused. Short-term or long-term memory can be affected. Short-term memory is more important for product use. People can forget what they should be doing before they complete a task.

9.4.3.3 Risks and hazards

Memory impairment can lead to a hazard if an uncompleted task results in a dangerous situation such as the gas supply turned on but not ignited. Design needs to ensure that systems are "fail-safe".

9.4.4 Language/literacy

9.4.4.1 Description

Language and literacy are the specific mental functions of recognising and using signs, symbols and other components of a language.

9.4.4.2 Effects of ageing

Ageing sometimes affects a person’s language ability, for example as the result of a stroke. When people have a stroke, their language ability may be affected. They may be able to think in the same manner but be unable to express their thoughts in words. Language impairment may cause difficulty in any, some or all of comprehension or expression of written or spoken language. People of all ages with dyslexia have difficulties in reading and writing.

9.4.4.3 Risks and hazards

People with a language impairment may be put at risk if they are unable to comprehend written warnings or significant instructions.

9.5 Allergies

9.5.1 Description

9.5.1.1 An allergy is an immunological reaction to a substance which may be serious and, in some circumstances, life-threatening. Allergies are also disabling when the need to avoid contact with an allergen (the substance to which their body is hypersensitive), imposes limitations on an individual’s activities. In view of the implications for products, particularly labelling and warnings, information is provided on this topic.

9.5.1.2 Types of allergens that cause allergic reactions include pollens, dust particles, mould spores, food, latex rubber, insect venom and certain medicines. Many products and devices unnecessarily contain substances, such as nickel, which cause allergic responses.

9.5.1.3 Allergic reactions can range from mild and annoying to sudden and life-threatening. An example of sudden reaction is swollen throat and acute difficulties in breathing for people allergic to a certain foodstuff.

9.5.2 Contact allergies

Contact allergies are caused by allergens that enter the body through the skin. They are particularly contained in powders, lotions, perfumes, scented products, cosmetics, household chemicals, some metals or latex, and may be found in many household, building and electrical appliances. Contact allergy is prevalent among about 15 % of the population and is often life-long.

9.5.3 Food allergies

A food allergy is a reaction or intolerance to one or more foodstuffs. A great number of foods can cause allergic reactions, the most common being milk, wheat, soy, egg, peanuts and fish. Food colours, preservatives and additives are also a major cause of allergy.

9.5.4 Respiratory allergies

9.5.4.1 Airborne allergens cover those that are inhaled, such as dust, pollen, mites, moulds and animal detritus. The most typical respiratory allergy is asthma, which results in constriction of the respiratory channels and breathlessness.

9.5.4.2 For the purposes of this Guide, this clause includes chemical sensitivities, i.e. reactions to chemicals in the human environment. These allergy-like reactions may result from exposure to a wide variety of synthetic and natural substances, such as those found in paints, carpeting, building materials, plastics, perfumes, cigarette smoke and plants.

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