These models, briefly described as an elderly person, a person with one-sided disabilities, and a person in a wheelchair, were chosen to represent a wide range of physical characteristics that can make buildings difficult to use. The Elderly A number of characteristics associated with old age create difficulties in building use. Many elderly people suffer from rheumatic conditions and stiff joints, which limit their hand grasping and manipulation ability. They are unable to move their limbs to extreme positions such as for reaching up, down or twisting round. Reduced muscular strength and energy increase this problem and can preclude activities requiring even moderate strength or activities sustained over long periods of time.
Many situations are hazardous for elderly people because of their reduced physical ability.
Leaking gas or smoke may not be detected, slight differences in floor level may not be seen, pots and pans may be easily spilled, and warning signals may go unheard. Some elderly people are particularly susceptible to falls and stumblings because of poor vision and balance as well as reduced strength and ability to react quickly. For an older person the consequences of a fall are quite serious because bones tend to be more brittle and therefore more subject to breaks. Elderly people may experience difficulty in moving from one place to another or in standing for long periods of time. Quite often the hands are used for extra balance while walking and the more stable posture of sitting is preferred.