Skip to main content
NCBI home page
HHS Author Manuscripts logoLink to HHS Author Manuscripts
. Author manuscript; available in PMC: 2018 Nov 1.
Published in final edited form as: Appl Ergon. 2017 Jun 22;65:152–162. doi: 10.1016/j.apergo.2017.06.009

Evaluation of postural instability and impact forces during ingress and egress of scissor lifts at elevations

Christopher S Pan 1, Sharon S Chiou 1, Tsui-Ying Kau 2, Bryan M Wimer 1, Xiaopeng Ning 3, Paul Keane 1
PMCID: PMC5556940  NIHMSID: NIHMS850911  PMID: 28802434

Abstract

Workers are at risk when entering or exiting elevated scissor lifts. In this study, we recorded ground shear forces and postural instability from 22 construction workers while they performed ingress and egress between a scissor lift and an adjacent work surface with varying lift gate opening designs, horizontal and vertical gaps, and sloped work surfaces. From the results of this study, we observed higher peak ground shear forces when using a bar-and-chain opening, with larger horizontal gap, with the lift surface more than 8 inches below the work surface, and having a sloped (26 degrees) work surface. Similar trends were observed for postural instability except the influence of vertical distance was not significant. To reduce slip/trip/fall risk and postural instability of workers while entering or exiting an elevated scissor lift, we suggest scissor lifts be equipped with a gate-type opening to replace the bar-and-chain design. We also suggest the lift surface be placed no more than 0.2 m lower than the work surface and the horizontal gap is as small as possible. Selecting a non-sloped surface to exit or enter a scissor lift is also desirable.

Keywords: scissor lifts, ingress, egress, fall hazard

Introduction

Scissor lifts are commonly found at many construction sites, and when they are used properly they can facilitate completion of many construction tasks. Over the past decade, the use of scissor lifts has increased significantly in industries such as construction, telecommunication, and warehousing and storage. The growing popularity makes scissor lift safety an important issue. The scaffolding industry has long recognized fall hazards associated with work on scissor lifts (Burkart et al., 2004; Heath, 2006; McCann, 2003). A study of the Census of Fatal Occupational Injuries (CFOI) data found that falls from vertical lifts accounted for 44% of vertical-lift deaths, almost all involving scissor lifts (McCann, 2003). A later study conducted by the National Institute for Occupational Safety and Health (NIOSH) confirmed the increasing trend for fatalities associated with falls from scissor lifts and further identified that extensibility factors—the extended height of the lift or the vertical position of the worker—were significant contributing factors to 72% of the scissor lift fatalities (Pan et al., 2007).

Scissor lifts are available that can reach between 6 and 15 m (20 and 50 ft). At such heights, the stability of the lift and worker are of great concern. According to the recent draft version of American National Standards Institute (ANSI) A10.29 (2012), workers may enter and exit scissor lifts at heights greater than 1.8 m (6 ft) when the lift platform surface is adjacent to the elevated surface. The standard further specifies that if the lift platform is adjacent to the elevated surface, there shall not be a vertical gap larger than 0.2 m (8 inches) or a horizontal gap larger than 0.35 m (14 inches) between the lift platform and the adjacent surface. To date, there has been no scientific study on the manner in which the vertical and horizontal gaps were determined and how the distances between the lift platform and the adjacent surface may affect each worker's postural stability. In practice, scissor lifts are sometimes positioned at a vertical distance greater than that recommended by the ANSI standard (0.2 m or 8 inches).

Uneven surfaces could significantly increase the risk of falling, especially during ingress and egress actions. Two types of uneven surfaces are typically considered during the ingress and egress of a scissor lift. One is the difference in elevation between the lift platform and the adjacent work surface; namely, the work surface is either higher or lower than the platform of the scissor lift. The second type of uneven surface is an inclined surface; namely, the adjacent work surface is sloped compared to the platform of the scissor lift. Both conditions introduce significant safety concerns for the use of scissor lifts. First of all, a difference in surface elevations significantly increases the risk of slip and trip (Brauer, 2006). Second, a decided or large difference in surface elevations could significantly increase trunk instability and alter ground impact forces during worker foot contact (landing), which also increases the risk of falling (Fathallah and Cotnam, 1998; Fathallah and Cotnam, 2000). An inclined work surface introduces a higher risk of slipping due to increased ground shear forces and reduced ground compression forces (Zhao et al., 1987). Previous studies have shown that standing on inclined surfaces could reduce standing stability (Bhattacharya et al., 2002/2003; Lin and Nussbaum, 2012; Simeonov et al., 2003, 2009) and may cause changes to body postures and lower extremity biomechanics (Mezzarane and Kohn, 2007; Sasagawa and Ushiyama, 2009). When walking on inclined surfaces, the pattern of walking as well as lower extremity biomechanics will also be altered (in comparison to walking on flat ground) in order to compensate for the increased risk of slip and fall (Leroux et al., 2002; McIntosh et al., 2006). Finally, when performing manual tasks (such as trunk bending and lifting) on inclined surfaces, previous studies have observed altered and unbalanced trunk biomechanical responses (Bhattacharya et al., 2002/2003; Hu et al., 2013, 2016; Jiang et al., 2005), increased magnitude of spinal loading (Shin and Mirka, 2004), and reduced trunk stability (Wade and Davis, 2009) among testing participants. These conclusions are in line with the high incidence rate of fall-related fatal and nonfatal injuries reported from the roofing industry (Wade and Davis, 2005).

Additionally, there is a lack of quantitative data to demonstrate that potential risks may be associated with improper exiting and entering techniques, especially at heights. Measuring sway and other measures of postural instability at heights is difficult (Bain and Marklin, 2012). In fact, this is the first study in the literature to evaluate postural instability, inclined surface effect, and impact force during ingress/egress to an elevated device—a scissor lift. This study also demonstrates how advanced experimental design can be used to develop scientific hypotheses and responds to numerous requests from an industry-wide standard committee (i.e., ANSI A10.29) for methods that involve the safe use of a scissor lift.

The objective of this study was to evaluate the postural instability and impact forces during various methods of exiting and entering scissor lifts at elevation. The first part of the study examined the effects of vertical and horizontal gaps between the lift platform and the adjacent surface on each worker's postural stability. These were evaluated on two types of scissor lift entrance/exit systems. The second part of the study focused on the effect of an inclined landing surface. The hypothesis was that the maximum interaction forces between human participants and landing surfaces resulting from various ingress/egress conditions were different and such differences affect workers' postural stability at elevations and inclined surfaces.

1. Methods

1.1. Participants

Twenty-two male construction workers, mean age of 28.5 ± 10.7 years, who had at least 1 year of experience in working with scissor lifts were recruited from northern West Virginia. Their mean body weight was 82.8 ± 3.3 kg (182.5 ± 7.4 lbs), and mean body height was 1.82 ± 0.08 m (6.0 ± 0.29 ft). All participants underwent a health-history screening before participating in the study to ensure they were free of a history of dizziness, tremor, vestibular disorders, neurological disorders, diabetes, chronic back pain, and falls within the past year resulting in injury with days away from work. Each participant gave informed consent according to the procedures approved by the NIOSH Institutional Review Board.

1.2. Laboratory Setup

A commercially available 5.79 m (19 ft) electric scissor lift (Model SJIIIE 3219, Skyjack, Inc, Ontario, Canada) was used for the study. The SJIIIE 3219 scissor lift platform has a deck extension, a gate for ingress and egress, guardrails around its periphery, as well as toeboards on all sides (Figure 1). This lift platform has a length and a width of approximately 0.73 and 1.6 m (29 and 64 inches), respectively, and a deck to extend overall length to approximately 2.54 m (100 inches). The guardrails, composed of a toprail and a midrail, have a height of 0.99 m (39 inches). The toeboard is about 0.15 m (6 inches) high. This type of scissor lift has a total load-bearing capacity of 249.4 kg (550 lbs). The separate rated load-bearing capacity on the main lift platform and 0.9-m (3-ft) deck are 113.3 and 136.0 kg (250 and 300 lbs), respectively. These specifications conform to ANSI standard A92.6 for Self-Propelled Elevating Work Platforms.

Figure 1. Scissor Lifts.

Figure 1

Open in a new tab

A test structure (Figure 2) was constructed to house measurement devices for capturing force data related to foot pressure from participants stepping from the aerial lift. This structure duplicated conditions found in worksites to be accessed by scissor lifts and served to capture force data typical of that found for workers who routinely step from aerial lifts onto construction or other work surfaces. One side of the test structure was adjacent to the scissor lift while the other side was connected to a mezzanine (2.7 meters or 9 feet height). The participant accessed the mezzanine by climbing stairs at the rear of the test structure, then entered the test structure and the scissor lift. After the testing trials were completed, participants used the mezzanine and stairs to return to the ground floor. Each participant was protected from fall hazards comprehensievly during the testing (e.g., safety net was constructed between the scissor lift and the test structure) (Figure 2).

Figure 2. Experimental Setup.

Figure 2

Open in a new tab

The test structure was 2.4 m (8 ft) tall, constructed of wood (in the shape of rectangular prism), with a top surface area of 1.2 by 2.1 m (4 by 7 ft). It was constructed to house a force plate 0.9 by 0.6 by 0.08 m (35½ by 25⅝ by 3½ inches) level with the work surface. Guardrails were established along the sides of the top of the wood structure and one side of the structure was adjacent to the gate of the scissor lift for access to the lift. A force plate was secured to a lift table that was bolted to the top of the wood structure. The Bishman lift table (Bishamon Lift-2K®; Port Washington, New York) (Figure 2) had a platform surface area of 0.9 by 1.2 m (36 by 48 inches), a capacity of 907 kg (2,000 lbs), and an adjustable height of 0 to 0.76 m (0 to 30 inches). The height of the lift table was adjusted to achieve the desired vertical height for the experiment. A second force plate was placed on the top of the scissor lift platform for measuring the participant's baseline postural stability before exiting the scissor lift. The scissor lift height was set at 3.04 m (10 ft) at all times.

Two three-dimensional Kistler™ force plates (Kistler Group, Winterthur, Switzerland), one on the lift platform and one on the lift table, were used to determine the impact forces and postural instability in each of the experimental conditions (Figure 2). Following standard calibration procedures for the Kistler, a comparison with data collected on the height of both the lift platform and lift table (on the test structure) with the data collected on the ground level was performed, and no significant differences were identified.

1.3. Experimental Conditions and Procedures

The height of the scissor lift was set at 3.04 m (10 ft) for all trials, and two experimental sessions were conducted on two different days. The rationale for testing at the 3.04-m (10-ft) height was that 83% of aerial lift falls, collapses, and tipovers occurred within the height categories of 3.04–5.79 m (10–19 ft) and 6.09–8.83 m (20–29 ft) (Pan et al., 2007).

Two experimental sessions were conducted. In Session 1, participants performed 42 ingress and 42 egress trials while subject to three varying test conditions—lift type, vertical distance, and horizontal distance. Two types of scissor lifts were examined—one with a gate that could be opened for ingress or egress (hereinafter referred to as the “gate” condition) and the other with a bar and a chain on the side of the lift (hereinafter referred to as the “bar and chain” condition) (Figure 3(a)-(b)). Seven different vertical landing positions (distance) were tested: same height as the lift (0 m); 0.1, 0.2, 0.3 m (4, 8, and 12 inches respectively) lower; and 0.1, 0.2, 0.3 m (4, 8, and 12 inches respectively) higher than the lift platform. The horizontal distance from the landing surface was 0.17, 0.35, or 0.53 m (7, 14, or 21 inches respectively) from the lift platform. Both the vertical and horizontal test distances we selected were based on the ANSI A10.29 draft standard (2012) for using aerial platforms in construction.

Figure 3. Two Types of Scissor Lifts.

Figure 3

Open in a new tab

In Session 2, participants were tested for a total of 12 ingress and 12 egress trials while subjected to three varying test conditions—lift type, vertical distance, and slope. The lift types varied between the two configurations (“gate” and “bar and chain”) described in the preceding paragraph. The vertical distance varied among three conditions: the same vertical height (0 m), the lift surface 0.2 m lower than the adjacent work surface (-8 inches), or the lift surface 0.2 m higher than the adjacent work surface (8 inches). The slope of the work surface was varied at either 0 or 26 degrees (∼6/12 pitch). This sloped surface was symmetrically placed with the lower edge facing the scissor lift. The selection of the slope of 6/12 pitch was undertaken because it is the most popular roof slope at which scissor lifts are used. During this session, the horizontal distance between the work surface and the scissor lift was fixed at 0.35 m (14 inches) from the exiting plane, and subjects were required to use a guardrail while exiting and entering the lift. The horizontal distance reflected common working conditions (Kroemer and Grandjean, 1997).

The order of trials for each session was randomized for each participant, with an exception that we did not include the lift type in the randomization order due to the difficulties and time constrains of changing from a “gate” to a “bar and chain” opening.

Each subject's postural stability during the landing phase of each ingress or egress motion was quantified using center of pressure (CP) data registered on a force plate. Postural sway is a normal phenomenon in human beings. As postural sway movement causes the body's CP to approach one's stability boundary, as defined by the outer edges of the base of support, the potential for postural instability increases. In this study, two variables were derived from CP excursions and were used to quantitatively determine each subject's postural stability. The two variables are postural sway distance in medial-lateral (ML) direction and anterior-posterior (AP) direction (Bhattacharya et al., 2002/2003; Chiou et al., 2003; Pan et al., 2009).

The test procedures for egress started with a participant standing quietly on the force plate within the scissor lift. Upon a voice command, the participant then stepped onto the adjacent work surface. The resultant landing forces registered on the force plate located on the landing surface were recorded. The same procedure was followed for the evaluation of ingress motions from the work surface to the scissor lift platform.

1.4. Independent Variables

The independent variables for experiments in Session 1 were task (ingress or egress), lift type (gate or bar and chain), vertical distance (work surface is a vertical distance of -0.3 m [-12 inches], -0.2 m [-8 inches], -0.1 m [-4 inches], 0 m [0 inches], 0.1 m [4 inches], 0.2 m [8 inches], 0.3 m [12 inches] from the lift surface) and horizontal distance (work surface is 0.17 m [7 inches], 0.35 m [14 inches], or 0.53 m [21 inches] away from the lift platform). The independent variables for experiments in Session 2 were task (ingress or egress), lift type (gate or bar and chain), vertical distance (work surface is a vertical distance of -0.2 m [-8 inches], 0 m [0 inches], and 0.2 m [8 inches] from the lift surface), and slope (work surface was either 0 or 26 degrees).

1.5. Dependent Measures

Two groups of dependent variables were examined to evaluate the ingress and egress tasks. The first group included maximum impact forces in medial-lateral (Fx) and anterior-posterior (Fy) directions during landing. The second group of dependent variables characterizes the postural stability during landing phase of ingress and egress motions. The maintenance of postural balance is a complex process that is achieved through the coordination among body segments and between the whole body and the environment. Anterior-posterior (AP) and medial-lateral (ML) sway were used to evaluate postural stability based on the participant's center of pressure excursions determined during the landing phase of ingress and egress motions from the scissor lift. AP and ML sway were defined as the sway distance in the anterior-posterior and medial-lateral direction during the first 30 seconds after landing (Bhattacharya et al., 2002/2003).

2. Statistical Analysis

Statistical Analysis System (SAS) software (SAS Institute Inc., Cary, NC, USA) was used to perform all data analyses. Prior to any statistical testing, the normality assumption was examined using a probability plot. To stabilize variance, data were transformed to their natural logarithm to achieve approximate normality of the statistical distributions when appropriate.

Repeated measures analyses of variance (ANOVAs) were performed using SAS MIXED procedure to evaluate the effect of different experimental conditions on each dependent variable. In this mixed model approach, the fixed effects included four independent variables (task, lift type, vertical distance, and horizontal distance) for Session 1 and four independent variables (task, lift type, vertical distance, and slope) for Session 2; random effects included the correlation within each individual participant.

For each dependent variable, we selected the appropriate covariance model by evaluating models with different covariance structures for each participant. These covariance structures included (1) direct product compound-symmetry, (2) direct product unstructured, and (3) direct product autoregressive. We selected an appropriate model based on Akaike's Information Criterion (AIC), a modified criterion from AIC for use in small samples (AICC), and Schwarz's Bayesian Criterion (SBC) for final analysis using the restricted maximum likelihood method.

Dependent variables that were statistically significant were selected for result interpretation. For multiple comparisons, the Tukey-Kramer (Dunnett, 1980) adjustment was used to determine significant differences among the experimental conditions. The significance level (α) for this study was set at 0.05.

3. Results

3.1. Experiment on Session 1

Repeated measures ANOVAs showed that main effects significantly influenced most dependent variables; changes in horizontal distance did not significantly influence Fy and ML sway, the influences of different vertical distances on AP and ML sway were also not signifcant. More specifically, as shown in Figures 4 and 5, significantly lower peak ground shear forces (Fx and Fy) and sway in both AP and ML directions were observed when using gate opening (vs. bar and chain opening) and during egress (vs. ingress) of the scissor lift. Larger horizontal distance resulted in significantly higher peak Fx and AP sway especially in the 0.53-m [21-inch] gap condition. The lowest ML sway was observed at the 0.35-m [14-inch] condition, but the magnitude of ML sway distance in all three conditions (0.17 m [7 inches], 0.35 m [14 inches], and 0.53 m [21 inches]) were relatively low. Finally, significantly larger peak ground shear forces were observed when the scissor lift was more than 0.2 m [8 inches] lower than the work surface.

Figure 4. Effects of Experimental Conditions on shear ground reaction forces Fx and Fy from session 1.

Figure 4

Open in a new tab

Note: Different letters denote values that are statistically different form one another. Bars indicate the corresponding 95% confidence interval.

Figure 5. Effects of experimental conditions on postural sway from session 1.

Figure 5

Open in a new tab

Note: Different letters denote values that are statistically different form one another. Bars indicate the corresponding 95% confidence interval.

3.2. Experiments in Session 2

Results from Session 2 showed that main effects lift type and slope significantly influenced both peak ground shear forces (Fx and Fy) and sway in both directions. Task significantly influenced Fy and vertical distance significantly influenced peak ground shear force Fx. More specifically, using gate opening (vs. bar and chain opening) and flat work surface (vs. 26-degree sloped work surface) resulted in significantly lower peak Fx, Fy, as well as AP and ML sway (Figures 6 and 7). When the scissor lift was lower than the work surface, significantly higher peak Fx was observed. Finally, exit from the lift generated significantly larger Fy. From Figure 7(e), we can observe a clear interaction effect between task and slope on Fy. This phenomenon was mainly due to the generation of a much higher peak ground shear force in the AP direction when landing on a sloped surface.

Figure 6. Effects of experimental conditions on shear ground reaction forces Fx and Fy from session 2.

Figure 6

Open in a new tab

Note: Different letters denote values that are statistically different form one another. Bars indicate the corresponding 95% confidence interval.

Figure 7. Effects of Experimental Conditions on Postural Instability Experiment 2.

Figure 7

Open in a new tab

Note: Note: Different letters denote values that are statistically different form one another. Bars indicate the corresponding 95% confidence interval.

4. Discussion

The objective of this study was to evaluate the risk of slip and fall and postural instability during various methods of entering and existing scissor lifts at elevation. The results of the Session 1 experiments revealed a greater risk of slip and fall (greater peak ground shear forces Fx and Fy and greater sway in both AP and ML directions) when using a bar and chain opening as compared to a gate opening (Figure 4(a) and Figure 5(a)). During the data collection, it was noted that when subjects performed an egress task from a scissor lift with a bar and chain opening, first they would unhook the chain on the lift then bend at their waist or squat down in order to pass under the top rail (1.07-m [42.5-inch] height). They typically experienced a limited/confined inside space between rails (0.63-m or 25-inch width) while rotating/bending their body toward an open space to exit the lift. To enter a lift with the bar and chain opening, subjects needed to bend their upper body laterally to pass through the top rail while rotating toward the lift platform. These complex body movements resulted from the geometric constraints of the lift and job site environment and caused perturbations to the postural balance system immediately after ingress or egress (Singh et al., 2014; Winter, 1990). The ergonomic recommendations for the dimensions of confined space are to some extent based on anthropometric data, and the above-mentioned workstation design indeed is determined to be potentially hazardous (Bottoms, 1983; Kroemer and Grandjean, 1997). These complex motions associated with using bar and chain openings created non-vertical foot landing postures and, therefore, resulted in larger peak ground shear forces. Entering into the lift also generated much larger ground shear forces and sways as compared to exiting from the lift. We believe such results are mainly due to the unstable nature of the lift surface. When stepping onto the lift surface, a certain degree of sway and wobbling is generated due to the impact. Such ground motion likely generated the observed increase in peak ground shear forces as well as AP and ML sway (Figure 4(b) and Figure 5(b)). When the horizontal gap between the lift and the adjacent structural surface increases, participants demonstrated significantly increased peak ground shear forces in the AP direction (i.e., Fx) and greater sway in the AP direction (Figure 4(c) and Figure 5(c)). When larger horizontal distances present, the participant's landing foot becomes less vertically aligned to the landing surface, which results in larger ground shear forces. Crossing a larger horizontal distance also increased the CP sway in the direction of the motion (i.e., the AP direction). Finally, when the scissor lift surface was more than 0.2 m [8 inches] below the work surface participants demonstrated significantly higher ground shear forces (Figure 4(d)). The larger overall impact force when stepping down onto the scissor lift surface likely generated an increase in ground shear force as well as sway. Some increase of CP sway in both AP and ML directions were also observed when there was a vertical gap between the lift surface and the adjacent work surface; however, such increases were not significant (Figure 5(d)).

In Session 2, we observed smaller peak ground shear forces and CP sways when using a gate opening as compared to a bar and chain opening (Figure 6(a) and Figure 7(a)). In addition, smaller peak ground shear forces and sways were also found when the work surface was flat vs. sloped (Figure 6(c) and Figure 7(c)). Two conditions were tested: one involving no slope and one involving a 26-degree slope. Variable measures of instability and force may have been returned with variable measures of slope, but for the purposes of this project, no slope was contrasted with a decided slope condition. Greater indicators of postural instability—heightened medial-lateral sway and increased anterior-posterior sway—were found to be significantly associated with a sloped landing surface, and it is the finding of this study that sloped surfaces should not be used as landing surfaces (Jones and Hignett, 2007).

Many previous studies investigated sloped and inclined surfaces associated with trunk and whole-body kinematics during manual material handling and gait (Leroux et al., 2002; Shin and Mirka, 2004; Hu et al., 2013, 2016). Tasks involving an upward body motion created greater postural demands on the subjects (Kluzik et al., 2005, 2007; Mezzarane and Kohn, 2007). Entering or exiting onto a lift from a sloped surface placed greater postural demands on the subjects compared to a non-sloped landing surface. This study also identified results that were similar to those studies associated with inclined surfaces: increased the range of motion, elevated the muscle activation level (i.e., increase muscle strength requirement), deployed appropriate postural muscle corrective actions, and caused muscle fatigue in various test conditions (Bhattacharya et al., 2002/2003; McIntosh et al., 2006; McNitt-Gray, 1993; Mezzarane and Kohn, 2007; Yung-Hui and Wei-Hsien, 2005). A previous study on the postural sway following prolonged exposure to an inclined surface (Wade and Davis, 2009) indicated that an individual is less stable directly after performing tasks on an inclined surface and highlighted the importance of optimal work-rest cycles. Several studies on postural stability of roofers suggested there might be an adaptation period associated with working on a sloped surface and more emphasis should be given to workers in the adaption period after exposure to inclined surfaces (Choi and Fredericks, 2008; Hsiao and Simeonov, 2001; Simeonov et al., 2004).

This study demonstrated that ground shear impact forces and postural stability were significantly affected by scissor lift type, horizontal and vertical distances between the lift surface and the work surface, the slope of the work surface, and methods of adjusting the body while entering/exiting the lift. Future studies are needed to examine if the anthropometric size of the subjects affect the ingress/egress strategies and the resultant impact forces and postural instability. Such research could lead to an extension of the design criteria for structural components of the lift that have been demonstrated to significantly influence the human-machine interface. In addition, the body position at landing and performance execution in relation to the requirement of the lift should be further examined. The propensity toward falls as a function of excursions within and beyond the CP could also be examined (Bagchee et al., 1998; Chiou et al., 2003).

ANSI A10.29 draft standard (2012) states that “when transferring to an elevated surface, there should be sufficient vertical clearance to allow for movement of the platform as weight is transferred to or from the aerial lift, and the platform floor should be within 1 foot horizontally of adjacent structure.” This statement in this draft standard was adopted from the regular scaffold standard, which may not be appropriate for aerial lifts (and especially so for scissor lifts). The current ANSI A92.6 Standard (2006) for Self-Propelled Elevating Work Platform [scissor lift] states that “if permitted by the manufacturer, the personnel shall only vacate or enter a raised aerial platform by following the guidelines and instructions provided by the manufacturer.” The results of this study will provide useful quantifiable information for developing safe “entering and exiting procedures at an elevation” for scissor lifts. These study findings can also be applicable for other construction elevated devices, heavy construction vehicles, trucks, mining equipment, and agricultural tractors (Bottoms, 1983; Moore et al., 2009; Pan et al., 2012).

It is inarguable that it is inherently problematic to conduct fall-related research without putting human subjects at risk for fall-related injuries. Common risk hazard exposures, when duplicated in experimental conditions, would require implementation of protective measures from the NIOSH Institutional Review Board (IRB). Any concerns that the IRB might have regarding hazardous exposures to subjects were dealt with through modifications in the experimental design, which was developed to overcome these scientific obstacles and return actionable and useful information, allowing for advanced methods of analysis that would allow the contribution of individual variables to be determined. This study demonstrated that impact forces and postural stability were significantly affected by various entering and exiting methods. Findings from this study will be used to suggest safer work practices to prevent fall injuries from elevations during the use of scissor lifts, and provide input to revise the ongoing ANSI A10.29 standard section in the use of aerial lifts as an elevator (Chiou et al., 2015).

5. Conclusions

In summary, this study quantifies the ground shear forces and stability effects that are found for subjects entering or exiting lifts when the adjacent work surface is sloped, through gates or bar-and-chain openings, and at horizontal and vertical distances from the landing surface. The findings from this research suggest: (1) scissor lifts would have gates in preference to bar and chain openings, (2) the adjacent work surface would be non-sloped, (3) the lift platform surface would be less than 0.2 m (8 inches) lower than the landing surface, and (3) the horizontal distance between a lift platform surface and the adjacent work surface would be less than 0.35 m (14 inches).

Table 1. Maximum Impact Forces and Standard Deviations (S.D.) in Lateral (Fx), Anterior/Posterior (Fy) and Vertical (Fz) Directions, and the Resultant Force (FR) for Various Conditions Tested in Experiment 1.

Condition Max Fx Max Fy AP Sway ML Sway
Mean (SD) Mean (SD) Mean (SD) Mean (SD)
Lift Type
 Gate 217.9 (30.2) 247.9 (29.6) 10.9 (1.2) 7.3 (0.5)
 Bar 296.3 (32.1) 279.4 (39.4) 8.6 (1.4) 9.8 (1.3)
Task
 Ingress 217.9 (28.8) 279.4 (34.6) 10.9 (1.3) 8.7 (0.9)
 Egress 296.3 (35) 268.4 (37.6) 8.6 (1.3) 9.8 (1.1)
Horizontal distance
 7 inches 245.4 (32.1) 279.4 (38.0) 8.6 (1.2) 7.6 (0.9)
 14 inches 296.3 (33.4) 260.3 (35.8) 10.9 (1.4) 9.8 (1.0)
 21 inches 206.9 (30.9) 247.9 (36.5) 8.6 (1.3) 8.7 (1.1)
Vertical distance
 12 inches lower 245.4 (39.9) 279.4 (43.2) 10.0 (1.4) 7.6 (1.2)
 8 inches lower 185.8 (30.7) 268.4 (38.4) 10.9 (1.4) 8.7 (1.0)
 4 inches lower 206.9 (30.2) 200.1 (35.1) 7.8 (1.3) 4.7 (0.6)
 0 inches (flat) 205.7 (28.0) 157.4 (32.5) 7.6 (1.1) 7.5 (0.7)
 4 inches higher 174.7 (28.0) 182.2 (33.4) 8.2 (1.3) 6.2 (1.0)
 8 inches higher 196.9 (30.6) 225.5 (37.2) 8.6 (1.4) 7.6 (1.1)
 12 inches higher 296.3 (32.1) 169.3 (31.6) 7.4 (1.2) 9.8 (1.2)
Open in a new tab

Note: Forces are in Newtons

Table 2. Summary of Repeated Measures ANOVAs by Experimental Conditions Experiment 1.

Tests of Fixed Effects Force Variables Sway Variables
FX FY AP
Sway		 ML
Sway
Lift Type *** *** *** ***
Task *** *** *** ***
Horizontal Distance *** ***
Vertical Distance *** ***
Lift*Task *** *
Lift*Horizontal Distance *
Lift*Vertical Distance *** *
Task*Horizontal Distance * * **
Task*Vertical Distance *** ***
Vertical*Horizontal Distance
Open in a new tab
*

p<0.05

**

p<0.005

***

p<0.0001

Table 3. Maximum Impact Forces and Standard Deviations (S.D.) in Lateral (Fx), Anterior/Posterior (Fy) and sway in the anterior/posterior and mediolateral directions for Various Conditions Tested in Experiment 2.

Condition Max Fx Max Fy AP Sway ML Sway
Mean (SD) Mean (SD) Mean (SD) Mean (SD)
Lift Type
 Gate 183.3 (29.1) 722.3 (188.3) 6.0 (0.7) 3.3 (0.4)
 Bar 239.9 (30.7) 759.2 (195.6) 35.6 (2.8) 17.3 (1.8)
Task
 Ingress 157.9 (25.5) 414.7 (43.4) 35.6 (2.6) 17.3 (1.4)
 Egress 239.9 (36.1) 759.2 (229.5) 9.1 (1.5) 7.4 (1.2)
Vertical distance
 8 inches lower 239.9 (34,3) 759.2 (193.6) 8.2 (1.4) 4.9 (0.8)
 Flat 137.2 (27.4) 720 (186.6) 35.6 (3.1) 17.3 (1.7)
 8 inches higher 180.7 (30.3) 724.7 (197.1) 9.1 (1.3) 7.4 (1.2)
Slope
 0 degrees 183.3 (29.8) 389.1 (44.2) 7.0 (1.2) 7.4 (0.9)
 26 degrees 239.9 (32.4) 759.2 (221.1) 35.6 (2.7) 17.3 (1.6)
Open in a new tab

Note: Forces are in Newtons

Table 4. Summary of Repeated Measures ANOVAs by Experimental Conditions Experiment 2.

Tests of Fixed Effects Force Variables Sway Variables
FX FY AP
Sway		 ML
Sway
Lift type *** *** *** ***
Task ***
Slope * *** ** **
Vertical Distance *
Lift*Task ***
Lift*Slope *
Lift*Vertical Distance **
Task*Slope ***
Task*Vertical Distance *
Slope*Vertical Distance
Open in a new tab
*

p<0.05

**

p<0.005

***

p<0.0001

Acknowledgments

We would like to acknowledge the contributions of SkyJack Inc., which provided the NIOSH researchers with the use of a new scissor lift and other critical technical and design data. The authors are grateful to John Powers, Doug Cantis, and Brad Newbraugh for their valuable assistance with instrumentation and data collection. The authors would like to acknowledge Cathy Rotunda and Caitlin Phalunas for editorial assistance in the preparation of this manuscript.

Footnotes

Publisher's Disclaimer: Disclaimers: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health (NIOSH). Mention of company names or products does not imply endorsement by NIOSH.

References

  1. American National Standards Institute. Self-propelled elevating aerial work platforms. New York, NY: 2006. (ANSI/ASSE A92.6) [Google Scholar]
  2. American National Standards Institute. A draft standard for safe practices for the use of aerial platforms in construction (ANSI/ASSE A10.29) 2012 [Google Scholar]
  3. Bagchee A, Bhattacharya A, Succop PA, Emerich R. Postural stability assessment during task performance. Occup Ergon. 1998;1:41–53. [Google Scholar]
  4. Bain B, Marklin R. An inside step in aerial bucket reduces postural instability during ingress and egress. Proc Hum Factors Ergon Society Annu Meet. 2012;56:1206–1210. [Google Scholar]
  5. Bhattacharya A, Succop P, Kincl L, Lu ML, Bagchee A. Postural stability during task performance on elevated and/or inclined surfaces. Occup Ergon. 2002/2003;3:83–97. [Google Scholar]
  6. Brauer RL. Safety and Health for Engineers. second. John Wiley & Sons, Inc; 2006. [Google Scholar]
  7. Burkart MJ, McCann M, Paine DM. Aerial work platforms, in: Elevated work platforms and scaffolding. McGraw-Hill; New York: 2004. p. 239. [Google Scholar]
  8. Bottoms DJ. Design guidelines for operator entry-exit systems on mobile equipment. Appl Ergon. 1983;14:83–90. doi: 10.1016/0003-6870(83)90153-9. [DOI] [PubMed] [Google Scholar]
  9. Chiou SS, Bhattacharya A, Lai C, Succop PA. Effects of environmental and job-task factors on workers' gait characteristics on slippery surfaces. Occup Ergon. 2003;3:209–223. [Google Scholar]
  10. Chiou SS, Pan CS, Wimer B. National Occupational Injury Research Symposium (NOIRS) Kingwood, WV: 2015. Evaluation of postural stability during various methods of exiting and entering scissor lifts, in: A poster presentation at the 2015. [Google Scholar]
  11. Choi SD, Fredericks TK. Surface slope effects on shingling frequency and postural balance in a simulated roofing task. Ergon. 2008;51:330–344. doi: 10.1080/00140130701652824. [DOI] [PubMed] [Google Scholar]
  12. Dunnett CW. Pairwise multiple comparisons in the homogeneous variance, unequal sample size case. J Am Stat Assoc. 1980;75:789–795. [Google Scholar]
  13. Fathallah FA, Cotnam JP. Impact forces during exit from commercial vehicles. Proc. Hum. Factors & Ergon. Soc Annu Meet. 1998;42:926–930. [Google Scholar]
  14. Fathallah FA, Cotnam JP. Maximum forces sustained during various methods of exiting commercial tractors, trailers and trucks. Appl Ergon. 2000;31:25–33. doi: 10.1016/s0003-6870(99)00020-4. [DOI] [PubMed] [Google Scholar]
  15. Heath FG. Accident waiting to happen. Lift and Access 2006 [Google Scholar]
  16. Hsiao H, Simeonov P. Preventing falls from roofs: a critical review. Ergon. 2001;44:537–561. doi: 10.1080/00140130110034480. [DOI] [PubMed] [Google Scholar]
  17. Hu B, Ning X, Nimbarte AD. The changes of lumbar muscle flexion-relaxation response due to laterally slanted ground surfaces. Ergon. 2013;56:1295–1303. doi: 10.1080/00140139.2013.803161. [DOI] [PubMed] [Google Scholar]
  18. Hu B, Ning X, Dai F, Almuhaidib I. The changes of lumbar muscle flexion-relaxation phenomenon due to antero-posteriorly slanted ground surfaces. Ergon. 2016:1–8. doi: 10.1080/00140139.2015.1124146. [DOI] [PubMed] [Google Scholar]
  19. Jiang Z, Shin G, Freeman J, Reid S, Mirka GA. A study of lifting tasks performed on laterally slanted ground surfaces. Ergon. 2007;48:782–795. doi: 10.1080/00140130500123761. [DOI] [PubMed] [Google Scholar]
  20. Jones A, Hignett S. Safe access/egress systems for emergency ambulances. Emerg Med J. 2007;24:200–205. doi: 10.1136/emj.2006.041707. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Kluzik J, Horak FB, Peterka RJ. Differences in preferred frames for postural orientation shown by after-effects of stance on an inclined surface. Exp Brain Res. 2005;162:474–489. doi: 10.1007/s00221-004-2124-6. [DOI] [PubMed] [Google Scholar]
  22. Kluzik J, Peterka RJ, Horak FB. Adaptation of postural orientation to changes in surface inclination. Exp Brain Res. 2007;178:1–17. doi: 10.1007/s00221-006-0715-0. [DOI] [PubMed] [Google Scholar]
  23. Kroemer KHE, Grandjean E. Fitting the task to the human (5th ed): A Textbook of Occupational Ergonomics. Taylor & Francis Group; Philadelphia, PA: 1997. The design of workstations. [Google Scholar]
  24. Leroux A, Fung J, Barbeau H. Postural adaptation to walking on inclined surfaces: I. normal strategies. Gait and Posture. 2002;15:64–74. doi: 10.1016/s0966-6362(01)00181-3. [DOI] [PubMed] [Google Scholar]
  25. Lin D, Nussbaum MA. Effects of lumbar extensor fatigue and surface inclination on postural control during quiet stance. Appl Ergon. 2012;43:1008–1015. doi: 10.1016/j.apergo.2012.02.003. [DOI] [PubMed] [Google Scholar]
  26. McCann M. Deaths in construction related to personnel lifts, 1992-1999. J Saf Res. 2003;34:507–514. doi: 10.1016/j.jsr.2003.07.001. [DOI] [PubMed] [Google Scholar]
  27. McIntosh AS, Beatty KT, Dwan LN, Vickers DR. Gait dynamics on an inclined walkway. J Biomech. 2006;39:2491–2502. doi: 10.1016/j.jbiomech.2005.07.025. [DOI] [PubMed] [Google Scholar]
  28. McNitt-Gray JL. Kinetics of the lower extremities during drop landings from three heights. J Biomech. 1993;26:1037–1046. doi: 10.1016/s0021-9290(05)80003-x. [DOI] [PubMed] [Google Scholar]
  29. Mezzarane RA, Kohn AF. Control of upright stance over inclined surfaces. Exp Brain Res. 2007;180:377–388. doi: 10.1007/s00221-007-0865-8. [DOI] [PubMed] [Google Scholar]
  30. Moore SM, Porter WL, Dempsey PG. Fall from equipment injuries in U.S. mining: identification of specific research areas for future investigation. J Saf Res. 2009;40:455–460. doi: 10.1016/j.jsr.2009.10.002. [DOI] [PubMed] [Google Scholar]
  31. Pan CS, Hoskin A, McCann M, Lin M, Fearn K, Keane P. Aerial lift fall injuries: A surveillance and evaluation approach for targeting prevention activities. J Saf Res. 2007;38:617–625. doi: 10.1016/j.jsr.2007.08.002. [DOI] [PubMed] [Google Scholar]
  32. Pan CS, Chiou S, Kau T, Bhattacharya A, Ammons D. Effects of foot placement on postural stability of construction workers on stilts. Appl Ergon. 2009;40:781–789. doi: 10.1016/j.apergo.2008.08.003. [DOI] [PubMed] [Google Scholar]
  33. Pan CS, Chiou S, Hsiao H, Keane P. Ergonomic hazards and controls for elevating devices in construction. In: Bhattacharya A, McGlothlin JD, editors. Occupational Ergonomics: Theory and Applications. CRC Press, Taylor & Frances Group; Boca Raton, FL: 2012. pp. 653–693. [Google Scholar]
  34. Sasagawa S, Ushiyama J, Masani K, Kouzaki M, Kanehisa H. Balance control under different passive contributions of the ankle extensors: quiet standing on inclined surfaces. Exp Brain Res. 2009;196:537–544. doi: 10.1007/s00221-009-1876-4. [DOI] [PubMed] [Google Scholar]
  35. Shin G, Mirka G. The effects of a sloped ground surface on trunk kinematics and L5/S1 moment during lift. Ergon. 2004;47:646–659. doi: 10.1080/00140130310001653066. [DOI] [PubMed] [Google Scholar]
  36. Simeonov PI, Hsiao H, Dotson BW, Ammons DE. Control and perception of balance at elevated and sloped surfaces. Hum. Factors. 2003;45:136–147. doi: 10.1518/hfes.45.1.136.27232. [DOI] [PubMed] [Google Scholar]
  37. Simeonov P, Hsiao H, Dotson BW, Ammons DE. Control and perception of balance at elevated and sloped surfaces. Hum Factors. 2004;45:136–147. doi: 10.1518/hfes.45.1.136.27232. [DOI] [PubMed] [Google Scholar]
  38. Simeonov P, Hsiao H, Hendricks S. Effectiveness of vertical visual reference for reducing postural instability on inclined and compliant surfaces at elevation. Appl Ergon. 2009;40:353–361. doi: 10.1016/j.apergo.2008.11.007. [DOI] [PubMed] [Google Scholar]
  39. Singh S, Singh J, Kalra P. Ergonomic evaluation of ingress/egress of vehicle using balance assessment approach. Int J Sci & Eng Res. 2014;5:17–20. [Google Scholar]
  40. Wade C, Davis J. Transitioning sloped surfaces: the effects of roofing work on balance and falls. J Am Soc Saf Eng. 2005:45–50. [Google Scholar]
  41. Wade C, Davis J. Postural sway following prolonged exposure to an inclined surface. Saf Sci. 2009;47:652–658. [Google Scholar]
  42. Winter DA. Biomechanics and Motor Control of Human Movement. second. Ontario, Canada: 1990. [Google Scholar]
  43. Yung-Hui L, Wei-Hsien H. Effects of shoe inserts and heel height on foot pressure, impact force, and perceived comfort during walking. Appl Ergon. 2005;36:355–362. doi: 10.1016/j.apergo.2004.11.001. [DOI] [PubMed] [Google Scholar]
  44. Zhao Y, Upadhyaya SK, Kaminaka MS. Foot-ground forces on sloping ground when lifting. Ergon. 1987;30:1671–1678. doi: 10.1080/00140138708966057. [DOI] [PubMed] [Google Scholar]

RESOURCES