«Effect of Handrail Shape on Graspability by Donald O. Dusenberry, Howard Simpson, and Steven J. DelloRusso Simpson Gumpertz & Heger Inc. Accepted for ...»
Authors’ Pre-print Manuscript
Effect of Handrail Shape on Graspability
Donald O. Dusenberry, Howard Simpson, and Steven J. DelloRusso
Simpson Gumpertz & Heger Inc.
Accepted for Publication in Applied Ergonomics
Amsterdam, The Netherlands
Anticipated publication: early 2009
Effect of Handrail Shape on Graspability
Donald O. Dusenberry, Howard Simpson, ScD, and Steven J. DelloRusso
Simpson Gumpertz & Heger Inc.
41 Seyon Street, Building 1, Suite 500 Waltham, MA 02453 Telephone: 781-907-9000
ABSTRACTThis paper summarizes research performed to evaluate the impact of handrail profile dimensions on graspability. It reports on research performed to determine the forces that stairway users exert on handrails when they fall, tests demonstrating the forces persons with various hand sizes can exert on handrails with different profiles, and comparisons of the probability of loss of grip by stairway users when they attempt to arrest a fall by grasping a handrail. The recommendations based on this work include specific definitions of the shapes of handrails that are deemed to be sufficiently graspable to constitute functional handrails.
Keywords: handrail graspability, stairway falls, handrail profiles, handrail research
-1- Statistics aside, a stair handrail should be designed to serve at least four important functions. First, it should provide a guidance surface (i.e., a source of haptic sensory cues) for the user, along which the user can slide his/her hand while moving up or down the stair. Second, it should serve the user as an object against which forces may be applied as a means for enhancing his/her postural stability while using the stair. Third, the handrail must provide something to grab to arrest or mitigate a fall. Fourth, for individuals who experience difficulty ascending stairs, it should provide a means for the user to help pull himself/herself up the stairs.
The first of the above-named functions is relatively undemanding, requiring only a continuous, firm surface - preferably without interruptions such as balustrade or brackets - on which the user’s hand can slide. The last three functions require, among other features, a handrail cross-section that will allow the user to pull, at various angles, with enough force (“graspability”) to support a significant portion of his/her weight. The most demanding scenario is the third, for which the grasp on the handrail must be sufficient to mitigate the effects of a fall.
In addition to allowing users to develop adequate pulling forces, the grasping surface must be uninterrupted along the length of the handrail, be sufficiently distant from adjacent walls to allow for free grasping action, and be of appropriate height.
The research described herein addresses the performance of handrail shape as it relates to the last two of the four functions described above. The results also are applicable to the evaluation of the ability of handrails to aid in the maintenance of postural stability.
PAST HANDRAIL RESEARCHFor the handrail designer, there are various functional issues that need to be addressed. Intuitively, the greatest force demand on a handrail occurs during a fall. For users already grasping the
the scenarios by which the victim reaches out, grabs the handrail, and arrests his/her fall? For what angles and magnitudes of pull relative to the axis of the handrail should the cross-section be designed? What cross-sectional shapes will enhance the ability of the user to utilize his/her maximum potential pull strength? What shapes will enhance the aesthetic or architectural qualities of the stairway while simultaneously satisfying the functional issues? The answers to these questions are not easy to obtain, and the difficulty is compounded by the consideration that they must be valid for almost the entire user population: whether young or old, small or large, weak or strong, infirm or healthy.
Several researchers have studied the hand and the influence of a number of factors on its ability to develop grasping forces. Wrist and arm position have been shown to influence peak grip forces (Hazelton, et al., 1975; Berme, et al., 1977; Pryce, 1980; Mathiowentz, et al., 1985; Amis, 1987;
Savage, 1988; Chao, et al., 1989; Balogun, et al., 1991; Lee and Rim, 1991; O’Driscoll, et al., 1992;
Su, et al., 1994; Lamoreaux and Hoffer, 1995; Halpern and Fernandez, 1996; Keng, et al., 1996;
Richards, 1997; Werremeyer and Cole, 1997; De Smet, et al., 1998; LaStayo and Hartzel, 1999;
Lee and Zhang, 2004). These references and others (Cochran and Riley, 1986; Cochran, et al.,
2007) address the influence of aspects of the shape and size of the grasped object on grasping force.
In addition, age, gender, physical training, and infirmities have been shown to be determinants for grip strength (Mundale, 1970; Hall, 1981; Steinfeld, 1986; Desrosiers, et al., 1995; Gorski, 2005;
Stairway usage has been studied (Miller and Esmay, 1961; Chaffin, et al., 1976; Archea, et al., 1979; Hay and Barkow, 1985; Templer, 1985; Templer, et al., 1985; McFadyen and Winter, 1988;
Pauls, 1991a; Pauls, 1991b; Templer, 1992; Cohen, 2000; Cohen and Cohen, 2001; Ellis, 2001; Di
concerning stair geometry, including handrail position and cross-section. Elderly persons as a subgroup also have been studied (Hill, et al., 2000a; Hill, et al., 2000b; Startzell, 2000; Wolfinbarger and Shehab, 2000), including evaluation of the role of the handrail in the maintenance of stability (Ishihara, 2002; Whittlesey, 2003). The information presented in these papers primarily is observational.
Some researchers have considered the efficacy of the handrail grasping action and the visuospatial implications of grasping and stepping activities (Maki, et al., 1998; Winges, et al., 2003).
While these prior studies and others have contributed to the understanding of stairway usage and relevant matters related to effective grips on handrails, none has attempted to establish a relationship between the various dimensions of a milled handrail cross-sectional configuration and handrail effectiveness as a grasping surface for stairway use. The only relevant published data prior to the research reported herein was developed at the University of Toronto (Maki, et al., 1984, Maki, et al., 1985a, Maki, 1985b). That research considered handrail texture and user preference, among other factors. Regarding forces that test subjects could exert on stairway handrails, that research tested, for the stabilization function only, a variety of round, square, and rectangular shapes and one milled (decorative) handrail. Test subjects were asked to push or pull on handrails while braced, standing erect on a mock stair. Based on that study, Maki recommended oval handrails (one such shape, with height of 50 mm (2.0 in.) and width of 37 mm (1.5 in.) was tested) and circular handrails with 38 mm (1.5 in.) diameter for young subjects, and circular handrails with 38 mm (1.5 in.) or 44 mm (1.7 in.) diameter or square handrails with rounded corners with 29 mm (1.1 in.) height and width for elderly subjects.
The Maki 1985 research was not intended to determine the forces that people actually exert on handrails during a fall. Rather, the research tested the ability of the test subjects to push or pull on
typical stairway use or during the complex process of falls when inertial effects affect the applied forces, and subjects’ posture tends to be crouched, off balance, and kinematic. Maki’s tests did not consider body-handrail proximity, nor did they model the directions and magnitudes of the forces exerted on handrails during falls. Further, those tests were not designed to evaluate the variety of handrail shapes that are in common use.
RESEARCH DESCRIBED HEREINThe studies described herein were conducted to study fall kinematics, the forces exerted by fall victims on handrails during falls, the nature of the grasp response, the effect of specific handrail characteristics on graspability, and the probability of defined user types in the population maintaining a grasp on specific handrail shapes during a fall.
To assess the function of handrails of various shapes when the applied forces are the largest, the authors replicated conditions during falls. Among the parameters investigated while developing test protocols were the actual forces exerted on handrails during falls and events involving loss of balance, and the position and posture of fall victims when they apply the maximum forces to the handrail.
To achieve fidelity in the graspability studies, these conditions were replicated to the greatest extent practicable. (As discussed below, fall victims do not exert the greatest forces on handrails when standing erect; the greatest forces occur when victims have fallen forward, rotated around an axis running between their foot on a step and hand on the handrail, with arm outstretched to their side.
Hence, test subjects’ arms were extended horizontally during grasp force tests to simulate this posture.).
research on fall kinematics and forces exerted on handrails during falls was performed for the authors at the Centre for Studies in Aging at the University of Toronto.
The ultimate objective of these engineering studies is to arrive at proposed specific language, for adoption by model codes, to define the requirements for functional handrail cross-sections. The various phases of this research have been summarized in papers presented by the authors (Dusenberry, et al., 1996 and Dusenberry, et al., 1999). In addition, Dr. Maki and his colleagues at the University of Toronto published an independent paper (Maki, et al., 1998) on the research that they performed as part of one of the research phases of this project.
The research reported herein includes the following studies:
Tests of subjects induced to fall on stairs to study fall kinematics and to establish forces
Development of specific definitions of shapes that provide appropriate graspability.
This research does not study how stairway users employ available handrails in advance of a fall.
For instance, the authors did not investigate the demographics or usage patterns of handrail users
protocol, subject selection, and analyses were developed to represent the physical characteristics of the adult population with equal consideration to the use of dominant and nondominant hands.
Professor Emeritus Robert W. Mann, a biomechanics expert at the Massachusetts Institute of Technology, and Dr. Alan N. Ertel, an orthopedic surgeon, assisted with the development of the testing protocol at SGH.
Forces Induced on Handrails during Falls and Loss of Balance Events A major goal of this research was to develop an improved understanding of the nature of the stairway fall and handrail grab response phenomena. This was achieved through a test program, conducted at the request of the authors by Dr. Maki at the University of Toronto, involving the recording of the motions and grab responses of subjects during falls and loss of balance on stairs.
Test instrumentation and experimental protocol were developed to identify the influence and relative importance of perturbation magnitude, stance, proximity to the handrail, and initial hand position. The research summarized in this section has been presented in detail elsewhere (Maki, et al., 1996 and Maki, et al., 1998). It is summarized herein because it provides the basis for the author’s analytical studies described later.
These tests used a 51-mm-diameter (2-in. diameter) round handrail made of painted aluminum, mounted 864 mm (34 in.) above the leading edge of the treads of a three-step mock stairway.
Figure 1 illustrates the test configuration. The mock stairway was mounted on a moving platform.
The subjects stood against a vertical backboard mounted to the stairway for support as the platform was accelerated forward to horizontal velocities corresponding to slow, average, and fast descent of stairs. Without warning, the activated stairway was decelerated suddenly to pitch the test subjects forward and down the stairs, which were padded to minimize the potential for injuries. A plastic
this step to regain footing.
The four test subjects were healthy males ranging in age from 20 to 37 years, in weight from 578 N to 890 N (130 lbs to 200 lbs), and in height from 1.7 m to 1.8 m (5 ft-6 in. to 6 ft). Subjects were tested for different standing locations on the stairs, foot positions, velocities, and rates of deceleration, among other variables. Peak platform speeds ranged from 0.25 m/sec to 0.75 m/sec, to represent speeds within two standard deviations of the mean speed that stairway users were observed (Maki, 1998) to traverse stairways. Table 1 summarizes the test program performed on each subject. Data collected included videotapes of the subjects during tests, measurements of human response characteristics, positions of grasp on the handrail, and forces exerted on the handrail.
The forces exerted on the handrail were determined using force plates mounted at the bases of the posts supporting the handrails. Force data were processed and resolved into component forces relative to the main axis of the handrail. To facilitate comparison between individuals of differing size, the force variables were normalized by dividing by body weight.
Stairway accident kinematics were determined from the video data, which also revealed the position of test subjects’ bodies at critical times during the fall and loss of balance sequences.