The National Safety Council reports more than 10,000 stair deaths per year in the entire United States and a much greater number of people get injured because of such accidents. The following paper discusses various aspects of stair safety in terms of its overall design and the designs of its individual elements.
A stair is a composition of one or more riser elements in combination with the treads to achieve a desired elevation. A riser can be defined as a vertical distance between two horizontal surfaces of adjacent treads. A tread could be understood as a distance measured horizontally between the vertical planes of the foremost projection of adjacent treads at a right angle to the tread's leading edge. For assuring safety, it becomes imperative to check that uniformity is maintained in these sizes of the riser and treads. Dimensional uniformity in the widths of treads and the heights of riser is one of the most important safety factors in the stair design. On account of the psychometric calculations of the user, a mere difference of a quarter inch between adjacent riser height can cause and accident. The elderly people are more prone to such accidents as compared to the young users. Therefore the stairs that are not dimensionally uniform are significant hazards.
Treads that are less than 9 inches wide result in the greatest number of missteps. Research indicates that riser heights between 6-8 inches and tread widths of 10 to 13 inches are most comfortable and fit most people's preferences. As per specification in building code, a maximum difference of 9.5 mm is permissible between the sizes of the largest and the smallest tread and the greatest riser height shall not exceed the smallest by more than 3/8 of an inch (9.5 mm). In case of the winders, treads should have a minimum depth of 10 inches at a distance of 12 inches from the smaller side. Optimal stair dimensions are 7.2 inch riser heights with either an 11 or 12 inch tread width.
Providing a handrail assures greater safety to the stairs even if it is protected from both the sides with walls. The use of handrail prevents the loss of balance while using the stair. The absence of handrail is a major factor in stair accident. The human factors design handbook, 1992 suggests the rail height to be around 34 inches (there are varying data on the specified height where the handrail should be installed), and it should be seen that the rail has an appropriate size and section that could facilitate proper grip. The handrail should be maintained regularly and it should be checked that it is properly anchored to the surface.
The handrail should be continuous throughout the entire flight and should not break anywhere in between. At the end, it should terminate in a newel post or should be treated to fix in an adjacent wall but should not be left untreated and open. When anchored against the wall, the rails should have a minimum space of one and a half inches with the wall to provide space for the knuckles during the grip. The stairs that are open from the sides should be installed with guards in combination with the handrail to provide lateral support. The guards should be placed close enough to each other that disallow the passage of a four inches sphere.
While proposing an architectural design, stairs with one or two steps should be avoided