- ARE STAIRS DANGEROUS?
Stairs that are poorly designed may be so inherently dangerous that the risk
of using them is unacceptably high. In 1990 in the United States, an estimated
998,000 people received hospital treatment for injuries resulting from
stair accidents, and 45,948 were hospitalized, based upon figures compiled
by the National Electronic Injury Surveillance System.
Much research has been undertaken to understand the design features that
contribute to stair safety. This research has been reflected in many updates
to the building codes, and federal legislation that has been adopted as part
of the Americans with Disabilities Act (ADA).
- STAIRWAY DESIGN IS GOVERNED BY BLDG. CODES AND THE ADA:
Since safety for persons using stairways is at stake, the construction of
stairways is governed by building codes. Under California Law, this is the
Uniform Building Code and Title 24 of the California Administrative Code
("State Building Code"). Title 24 addresses the State of California response
to the requirements imposed by the ADA at the federal level to provide for
accessibility to buildings for the disabled.
- WHY DO PEOPLE FALL ON STAIRS?
People fall on stairs because of several known factors acting singly or in
concert. These factors result from the way the stair is designed, some from
the way it is constructed or maintained, some from the environment in which
the stair is set, and some from the way people use stairs.
To understand stair falls, we must consider normal human gait and then examine
the factors that may act to disrupt it while using a stairway. Also, descending
stairs demands a gait quite different from ascent. Serious falls incurred
during descent far out number those in ascent. This is especially
true since the consequences of falling down a stairway are so much more serious.
The following stair design defects are the most common in giving rise to
injuries:
- Treads that are too narrow.
- Risers that are too high or too low
- Dimensional irregularity of the rise and run of the steps.
- Inadequate handrails, including the inability to grasp the handrail.
- Slippery tread material, especially at the nosing of the steps.
- Inadequate illumination.
- Confusing, patterns on the . tread, - making the nosing of the steps
hard to distinguish.
- Distracting surroundings such as mirrors, confusing lighting, shadow,
and other factors causing the stairway user to be distracted.
In addition to the above design defects, the following stair maintenance
issues frequently give rise to injuries.
- Water, snow, ice or other foreign substances on the treads.
- Loose, worn or improperly installed floor covering on the treads.
- Absent or broken handrails.
- Lighting improperly maintained.
Frequently, design and maintenance defects interact in giving rise to stair
accidents. For example, the absence of slip resistant treads acting in combination
with dew, rain or other contaminants can give rise to slip and fall accidents.
Tread design must consider the environmental factors that the stairway will
be subjected to.
The design of the nosing of the tread is especially critical. This is where
the foot will make primary contact, especially during descent. The ADA allows
a maximum radius of the nosing of Ih inch. Large radius nosing are
dangerous, especially under 'Wet conditions. Grooving of the nosing, especially,
when using ceranu'c tile or stone, can be effective in dealing with wet conditions.
- CODE REQUIREMENTS FOR STAIRWAY DESIGN
- RISE AND RUN GEOMETRY AND THE 7-11 RULE:
One of the most important safety aspects of a stairway is the rise and
run geometry. The Uniform Building Code (UBC) requires a maximum riser
height of 7 inches, and a minimum riser height of 4 inches. The UBC
also requires a minimum tread run of it inches. See exhibit A.
The above rise and run requirements became effective for the 1985 edition
of the UBC. The former figures for rise and run of 7 th inches
and 10 inches, respectively, had been in the UBC since the first edition
in 1927.
Research in recent years has established that these old rules were woefully
inadequate, as evidenced by the enormous number of accidents and deaths
attributed to improper stairway geometry. Studies revealed that riser
heights should be lower than standard practice, and that the tread run
should be greater than standard practice. The combination of lower riser
height and greater tread run provides the proper geometry to enable the
user to accomplish the proper gait and balance necessary to safely traverse
the stairway.
Although the tread run can be increased beyond the minimum of 11 inches
without degrading stair safety, a limit is reached where substantially
increasing the tread run becomes incompatible with the human gait, and
accident frequency increases. In particular, the 11 inch minimum is dictated
by.foot length and is necessary to accommodate the ball of the foot contacting
the nosing.
Consistent with the importance of the tread dimension, the method of
measurement of the tread is expressly stated as the distance measured
horizontally between vertical planes passing through the foremost projections
of adjacent treads. Tread dimension is measured in this manner because
any tread surface underneath the overhang of a sloping riser, or the
nosing on the tread above is not available to the user, especially while
descending the stairway.
- VARIATION OF RISERS, TREADS IS LIMITED TO 3/8 INCHES:
The maximum variation allowed by the UBC between the highest and lowest
risers, and between the widest and the narrowest treads is limited to
3/8 inch. This is the maximum variation allowed over the entire flight
of stairs, and is not a variation between successive treads, or a tolerance
for individual steps. Namely, all riser heights over the entire flight
of stairs.are to be compared, and none are to exceed 3/8 inch. Likewise,
all tread runs over the entire flight of stairs are to be compared, and
none are to exceed 3/8 inch. It must be recognized that this is a much
more stringent requirement than a tolerance for individual rise and runs.
This variation is not intended to be used as a design tolerance, but
it does recognize that construction practices make it difficult to get
exactly identical riser heights and tread dimensions in constructing
a stairway in the field.
This uniformity of risers and treads in any flight of stairs is a very
important safety factor. Research has shown that these values are necessary
so as not to interfere with the rhythm and gait of the stair user.
It is important to note that the stairway design must anticipate the
thickness of the final surface of the stairway and landings. For example,
use of ceramic tile over concrete must consider the measurement-of riser
heights after the stairway and landing finish surfaces have been installed.
- HANDRAILS ARE REQUIRED ON BOTH SIDES OF A STAIRWAY:
The UBC requires that stairways have handrails on each side, and every
stairway required to be more than 88 inches wide must have intermediate
handralls, spaced approximately equally across the width of the stairway.
The UBC allows a single handrail in some limiting situations such as
for single family dwellings. However, prudent design practice dictates
the use of handrails on both sides. First of all, a handrail is the most
important safety feature to provide balance to the user and protect against
falls from missteps. Secondly, the UBC was developed as a minimum requirement.
Thirdly, it is important that a handrail be provided on the right hand
side while descending the stairway, especially for right handed individuals
for ease of grasping, and to permit use of the dominant hand to prevent
falls. Additionally, the Consumer Product Safety Commission (CPSC) has
strongly endorsed the need for handrails on both sides of stairway, especially
for older people.
- HANDRAIL HEIGHT AND LENGTH REQUIREMENTS:
The UBC requires that the top of the handrails be placed not less than
34 inches nor more than 38 inches measured vertically above the leading
edge of treads. prior to the 1991 UBC$ the height of handrails had traditionally
been established within a range of not less that 30 inches and not more
than 34 inches. More recent research has shown that handrails are more
readily reached by users if they are located in a range higher than has
previously used.
Handrails must be continuous over the full length of the flight of stairs,
and must extend 12 inches beyond the top and bottom risers. The emphasis
on handrail continuity is to assure that the stair user will be provided
with support and assistance throughout the entire flight.
These handrail height and length requirements are depleted in Exhibit
B.
- CROSS SECTIONAL HANDGRIP REQUIREMENTS FOR HANDRAILS:
To be truly effective, handrails must be easy to grasp. The UBC requires
that the handrail must not be less than 1-1/4 inches nor more
than 2 inches in cross sectional dimension, or the shape shall provide
an equivalent gripping surface.
However, the ADA and Title 24 limits the cross section to not less than
1-1/4 inches nor more than 1-1/2 inches. Therefore, the handrail cross
sectional dimensions should comply with this more restrictive limitation
to comply with accessibility for the disabled. Furthermore, the handgrip
portion of handrails is required to have a smooth surface with no sharp
corners.
It should be noted that the maximum allowed cross section of 1-1/2 inches
imposed by the ADA is in recognition of the importance of being able
to grasp and hold onto the handrail, especially by older people and the
disabled.
Exhibit C is. presented to illustrate acceptable handrail details, in
conformity 'with the above described ADA and Title 24 requirements.
Many persons are incapable of exerting sufficient finger pressure, especially
for rectangular handrails, or on a handrail having a large cross-sectional
dimension. For example, a handrail that is commonly used consisting of
a 2 by 4 fastened to the -wall, or to the top of the railing is prohibited
from use by the above requirements. For the shapes depicted in Exhibit
C, it is possible for people to actually wrap their fingers around the
handrail and, thereby, obtain better gripping power and support in case
of a misstep or fall.
In addition, as illustrated in Exhibit C, it is necessary to provide
a clear space of at least 1-1/2 inches between the handrail and any abutting
structure or wall to allow proper grasping while traversing the stairway.
- STAIRWAY REQUIREMENTS IMPOSED BY TITLE 24 OF THE CALIFORNIA ADMINISTRATIVE
CODE AND ADA -- FOR DISABLED ACCESS:
- COLOR CODING OF STEPS:
The approach and the lower tread of each stair shall be marked by a strip
of clearly contrasting color at least 2" and not more than 4" wide placed
parallel to and not more that 1" from the nose of the step or landing
to alert the visually impaired. The strip shall be of material that is
at least as slip resistant as the other treads of the stairway.
- OUTSIDE STAIRWAY TREAD MARKING:
Where stairways occur outside a building, the upper approach and all
treads shall be marked by a strip of clearly contrasting color at least
2" and no more than 4" wide and placed parallel to and not more than
I" from the nose of the step or landing to alert the visually impaired.
The strip shall be of material that is at least as slip-resistant as
the other treads of the stair. A painted strip shall be acceptable.
- SLIP-R.ESISTANT TREADS:
All tread surfaces shall be slip-resistant. Treads shall have smooth,
rounded, or chamfered exposed edges, and no abrupt edges at the nosing
(lower front edge).
- PROJECTION OF NOSING IS LIMITED:
The nosing shall not project more than 1-1/2" past the face of the riser
below.
- CLOSED RISERS ARE REQUIRED:
Open risers are not permitted.
Exhibit D is presented to identify the types of stairs, and especially
nosing geometry, that is necessary to comply with ADA requirements.
- CONCLUSIONS:
Those who design, build, or maintain stairs have a duty to ensure that
the finished product is not defective. Use of the stairway should not
present an unreasonable risk of harm to the user. Any violation of a
code requirement would constitute negligence per se Therefore, one who
designs or constructs a stairway must exercise a corresponding duty of
care in the particulars of that design.
Some of the duties owed are set out in the building codes and safety
standards as described above. However, these are only minimum requirements.
Such factors as illumination, selection and color of stairway surface
materials, minimizing surrounding distractions to stairway users -- such
as avoiding mirrors and bright lights - in the design of the stairway
are within the sound discretion of the designer.
Compliance with the above described design requirements will substantially
reduce the risk of injury to stair users.
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