Development of the fall prevention index on the movable scaffold for construction workers

Abstract

BACKGROUND:

Falls are caused by difficulties in maintaining stable posture or center of pressure (COP). Studies on construction-related falls and their prevention are limited

OBJECTIVE:

To propose a fall prevention index (FPI) based on the working environment at height (with or without a handrail) and experience of workers on movable scaffolds.

METHODS:

Thirty participants were enrolled, and their COP distances were measured at the time of falling in the anterior-posterior (AP), mediolateral (ML), and diagonal directions.

RESULTS:

The probability of falling in the diagonal direction is almost zero for workers with more than 20 years of experience and that in the AP direction is almost zero for workers with up to 30 years of experience. There was almost zero probability of falling in the ML direction for workers with >15 years of experience. This index can be used as a tool for predicting the risk of falls, screening workers, and implementing proactive measures to prevent falling accidents on work sites.

CONCLUSIONS:

Preventing falls from movable scaffolds (and height in general) is needed in the construction industry. We propose a fall prevention index based on the working environment (at height, with or without handrail) and experience of workers on movable scaffolds.

Keywords

Center of pressure fall accident construction industry falling limit point

1 Introduction

South Korea’s economic and technological development is due to rapid industrial growth since the early 1970s. However, several industrial accidents have occurred because of a lack of interest in safety-related prevention measures and unclear safety characterizations. In particular, accidents are becoming more diverse as the number of large-scale construction projects has rapidly increased due to the advancement of construction technology [1]. Compared with other industries, construction was identified as a leading cause of work-related deaths in developed and developing countries, and the construction industry is one of the riskiest workplace sectors [2, 3]. In 2017, the Korea Occupational Safety and Health Agency (KOSHA) reported the death toll on construction sites by accident type: 412 from falling from heights and 46 from falling/flying objects [4]. In South Korea, the total number of deaths due to occupational injuries was 554 : 1 in 18–24 age group, 2 in the 25–29 age group, 10 in the 30–34 age group, 20 in the 35–39 age group, 39 in the 40–44 agegroup, 75 in the 45–49 age group, 92 in the 50–54 age group, 117 in the 55–59 age group, and 198 in the 60 and above age group [4].

Movable scaffolds, platform ladders, double scaffolds, and hanging scaffolds are the widely used working platforms on construction sites. Double scaffolds are fixed to the walls of buildings and can be used safely when footholds and safety handrails are installed. Platform ladders are used indoors and are low in height. Hanging scaffolds are utilized in outside jobs on walls of nearly finished buildings. They are considered dangerous because they are hung from two ropes and safety devices are typically installed. Movable scaffolds are built to the required height and easily adjusted to allow workers to move them around.

Accident rates in inexperienced workers increase because they cannot adapt easily to a changing working environment [5]. According to the KOSHA, the industrial accident rate was 10.5% for workers with 2-3 years’ work experience, 18.9% for those with 1-2 years’ experience, and 19.5% for those with less than 1 year of experience [4]. Kaskutas et al. [6, 7] reported a significant difference in the occurrence of death based on workmanship and that the falling accident rate was much higher in inexperienced workers than that in more experienced ones. Lee et al. [8] suggested that falling from high scaffolds occurred in construction workers with careers spanning 3-4 years.

The KOSHA [4] reported that deaths from movable scaffolds represented the highest proportion of falling-related deaths on construction sites (45 of 76). Many falling accidents occurred because of workers’ stress and mental anxiety [9]. Particularly, the height of the work area and absence of safety handrails in movable scaffolds were shown to create anxiety in workers [9]. Not installing movable scaffold safety handrails, not wearing safety gear, and shaking at high scaffolds can be reasons for falling [9]. Even though construction workers believe that they are safe because they had installed handrails, wore safety gear, and fulfilled safety requirements, they are unaware of other physical factors, such as center of pressure (COP) and posture stability. The stability of the movable scaffold decreases with increased height, making it shake more. Maintaining the COP on a movable scaffold is difficult, and the probability of falling increases [8, 9]. Min et al. [9] observed that the length of work experience, installation of safety handrails, and scaffold height influenced the COP movement, back muscle tension, falling risk, and mental anxiety.

Falling can occur because of a person’s difficulty in maintaining a stable posture or COP. Prieto et al. [10] stated that the body continuously changes its COP location to maintain balance, even in the standing position, when the body sways. Winter [11] showed that posture sway was a representational tool to measure posture stability, and Baker et al. [12] measured postural stability by measuring COP with insole pressure. Biswas et al. [13] also revealed that COP movement could be observed in the anterior-posterior (AP) and mediolateral (ML) directions. Azevedo et al. [14] examined the postural imbalances and risk factors for falls in lifting by measuring AP and ML length displacements of the COP.

A review of the studies on fall prevention in projects involving movable scaffolds showed that many researchers [1 , 16] reported that the location of supervisors, installation of safety devices, and safety education can help prevent falls. However, only few studies on fall risk prevention have been actually conducted on operational construction sites. Hence, more research is needed to firmly establish methods for fall prevention by considering the dynamic nature of workers on construction sites. This study proposed an index that can predict the probability of falling by considering the working height, installation of safety handrails, worker’s experience, and COP movement. This index can be used as a tool to predict the risk of fall in screening workers and implementing proactive measures to prevent falling accidents on construction sites.

2 Methods

2.1 Concept of fall prevention index (FPI)

The COP is an important variable when explaining the small posture changes that occur continuously in order to maintain balance, even in the standing position, because body balance is influenced by postural sway [8]. Thus, postural sway occurs when a person is in standing position, and the probability of falling increases as the COP distance increases. This COP movement is expressed as the COP distance and can be measured by using force plate or insole pressure equipment [9]. The COP distance increases when the body’s balancing ability is lowered due to internal or external factors; the person then overturns or falls when this falling limit point is exceeded. FPI is calculated from the COP distance, and the distance is affected by various factors including level of experience, working heights, and availability of a safety handrail. The COP distance is the straight line of the COP displacement in one specific direction (diagonal, AP, or ML). This index can be used to prevent falling from a height when working on scaffold platforms on construction sites. Controlling and maintaining postural balance is important in preventing future falls. Hence, understanding postural balance by measuring COP distance would create awareness and proactive safety education on postural balance.

2.2 Participants

Thirty construction workers with more than 3 years of experience in using scaffold frames in the construction industry participated in this study. Their demographic information is presented in Table 1. The purpose and outline of the experiment were explained to the participants.

Table 1
Participant demographics for FPI test (mean±SD)

Age (year) Height (cm) Weight (kg) Experience (years)

N = 30 23.61±5.46 175.67±8.54 69.55±5.42 4.04±1.25

(male)

Range 21–29 169–180 59.3–72.2 3.5–5.5

	Age (year)	Height (cm)	Weight (kg)	Experience (years)
N = 30	23.61±5.46	175.67±8.54	69.55±5.42	4.04±1.25
(male)
Range	21–29	169–180	59.3–72.2	3.5–5.5

2.3 Apparatus

To measure the change in the COP according to the participant’s movement, a force plate (4060-NC-2000, Bertec Corporation, Columbus, Ohio) was used with a sampling frequency of 1200 Hz (Fig. 1).

Fig.1

Test apparatus (A) force plate, (B) example of test scene.

2.4 Procedures

The participants were instructed to step on the force plate and remain in a stable posture for the zero point adjustment (i.e., apparatus preparation). Next, they were asked to bend forward, backward, to the left, to the right, and diagonally. Each participant’s hands were spread apart as far as possible, and the body’s center point was continuously measured until the instance of falling (steeping out) from the force plate.

2.5 Analysis

The study by Min et al. [9] was utilized to assess the probability of falling. Min et al. [9] reported the COP distance in the AP (anterior means toward the front or chest side of the body; posterior means toward the back), ML (medial means toward the midline of the body; lateral means away from the midline), and diagonal directions with different lengths of work experience, heights (1.8 m and 3.4 m), and presence or absence of safety handrail on movable scaffolds. The COP distance for the diagonal direction was recalculated using Equation (1) [9]: $COP {distance}_{diagonal direction} = \sqrt{X^{2} + Y^{2}} .$ (1)

The mean and standard deviation (SD) of COP distance in each direction were obtained. The falling limit point data were analyzed for normal distribution using Kolmogorov-Smirnov methods and determined to be normal. Then, the estimated COP distances were calculated using the multiple regression analysis by Min et al. [9]. The number of possible falling workers per 10,000 workers on the movable scaffold was calculated using Equation (2): $Z_{i} = [(X_{i} - μ) / α] \times 10, 000$ (2) where

Z_i: probability of falling for each condition (work experience, height, and handrail)

X_i: estimated COP distance in each condition (work experience, height, and handrail)

μ: average of falling limit points in each direction

α: SD of falling limit points in each direction

3 Results

3.1 Falling limit points

The mean and SD of the falling limit points are presented in Table 2. The results showed that workers might fall when the COP moves more than 15.98 cm in the diagonal direction, 6.07 cm in the AP direction, or 12.00 cm in the ML direction.

Table 2
Falling limit points in each direction

Direction Average of COP distance (cm) SD (cm)

Diagonal 15.98 1.84

AP 6.07 1.42

ML 12.00 1.06

Direction	Average of COP distance (cm)	SD (cm)
Diagonal	15.98	1.84
AP	6.07	1.42
ML	12.00	1.06

3.2 Estimated COP distance using multiple regression analysis in each direction

A multiple regression analysis was performed to predict COP distance based on the working environment, including working height, availability of a safety handrail, and level of experience and fall direction (Table 3). The resulting R² value was high in the estimation model of COP distance in all directions. COP distances in the diagonal direction were more influenced more by height (considered heights, 1.8 m and 3.4 m) than by the presence of handrails or workmanship of the movable scaffolds. COP distances in the AP and ML directions were influenced more by height and presence of safety handrails on the movable scaffolds.

Table 3
Coefficients of COP distance in each direction

Direction Unstandardized coefficients Standardized coefficients t p-value R²

B Std. Error Beta

Diagonal Constant 2.213 1.277 1.733 0.058 0.962

Experience –0.227 0.036 –0.619 –6.311 0.003

Height 2.481 0.335 0.725 7.404 0.002

Handrail 1.815 0.569 0.312 3.188 0.033

AP Constant –0.051 0.355 –0.143 0.093 0.964

Experience –0.067 0.010 –0.638 –6.667 0.003

Height 0.660 0.093 0.676 7.091 0.002

Handrail 0.610 0.158 0.368 3.859 0.018

ML Constant 2.263 1.006 2.251 0.088 0.954

Experience –0.160 0.028 –0.609 –5.659 0.005

Height 1.821 0.264 0.740 6.898 0.002

Handrail 1.205 0.449 0.288 2.686 0.055

Direction	Unstandardized coefficients	Standardized coefficients	t	p-value	R²
Diagonal	Constant	2.213	1.277		1.733	0.058	0.962
	Experience	–0.227	0.036	–0.619	–6.311	0.003
	Height	2.481	0.335	0.725	7.404	0.002
	Handrail	1.815	0.569	0.312	3.188	0.033
AP	Constant	–0.051	0.355		–0.143	0.093	0.964
	Experience	–0.067	0.010	–0.638	–6.667	0.003
	Height	0.660	0.093	0.676	7.091	0.002
	Handrail	0.610	0.158	0.368	3.859	0.018
ML	Constant	2.263	1.006		2.251	0.088	0.954
	Experience	–0.160	0.028	–0.609	–5.659	0.005
	Height	1.821	0.264	0.740	6.898	0.002
	Handrail	1.205	0.449	0.288	2.686	0.055

3.3 FPI

A model was developed using multiple regression analysis (Table 3). COP values in AP, ML, and diagonal directions were obtained by assigning random numbers to independent variables in the model, which included length of work experience (1–30 years), height (1.7 m and 3.4 m), and presence or absence of a safety handrail (utilizing the study by Min et al. [9]). Predicted COP values for these variable conditions in the example case in a diagonal direction (1–10 years) are shown in Table 4, along with fall risk probability. All other tables of the results are presented in the appendix. The fall risk values were calculated using predicted COP values and Equation (2). The fall risk value in Table 4 can be interpreted as follows: If a worker has 3 years of work experience and uses a 3.4 m movable scaffold without a handrail, the COP value becomes 13.6 cm (in diagonal direction), and the fall risk probability becomes 967.8 per 10,000 persons.

Table 4
Falling risk index of COP distance in diagonal direction (1-10 years) – example

Work experience (year) Height (m) Handrail (with, without) Estimated COP distance value (cm) Falling risk^* Work experience (year) Height (m) Handrail (with, without) Estimated COP distance value (cm) Falling risk^*

1 1.7 O 8.0 0.1 6 1.7 O 6.9 0.0

1 1.7 X 9.8 4.2 6 1.7 X 8.7 0.4

1 3.4 O 12.2 209.3 6 3.4 O 11.1 40.1

1 3.4 X 14.1 1472.7 6 3.4 X 12.9 479.6

2 1.7 O 7.8 0.0 7 1.7 O 6.6 0.0

2 1.7 X 9.6 2.7 7 1.7 X 8.4 0.2

2 3.4 O 12.0 154.6 7 3.4 O 10.8 27.6

2 3.4 X 13.8 1206.9 7 3.4 X 12.6 368.7

3 1.7 O 7.6 0.0 8 1.7 O 6.4 0.0

3 1.7 X 9.4 1.7 8 1.7 X 8.2 0.1

3 3.4 O 11.8 112.6 8 3.4 O 10.6 18.8

3 3.4 X 13.6 976.8 8 3.4 X 12.4 279.6

4 1.7 O 7.3 0.0 9 1.7 O 6.2 0.0

5 3.4 X 13.1 1.0 10 3.4 X 12.0 0.1

Work experience (year)	Height (m)	Handrail (with, without)	Estimated COP distance value (cm)	Falling risk^*	Work experience (year)	Height (m)	Handrail (with, without)	Estimated COP distance value (cm)	Falling risk^*
1	1.7	O	8.0	0.1	6	1.7	O	6.9	0.0
1	1.7	X	9.8	4.2	6	1.7	X	8.7	0.4
1	3.4	O	12.2	209.3	6	3.4	O	11.1	40.1
1	3.4	X	14.1	1472.7	6	3.4	X	12.9	479.6
2	1.7	O	7.8	0.0	7	1.7	O	6.6	0.0
2	1.7	X	9.6	2.7	7	1.7	X	8.4	0.2
2	3.4	O	12.0	154.6	7	3.4	O	10.8	27.6
2	3.4	X	13.8	1206.9	7	3.4	X	12.6	368.7
3	1.7	O	7.6	0.0	8	1.7	O	6.4	0.0
3	1.7	X	9.4	1.7	8	1.7	X	8.2	0.1
3	3.4	O	11.8	112.6	8	3.4	O	10.6	18.8
3	3.4	X	13.6	976.8	8	3.4	X	12.4	279.6
4	1.7	O	7.3	0.0	9	1.7	O	6.2	0.0
5	3.4	X	13.1	1.0	10	3.4	X	12.0	0.1

^*: Possibility of falling per 10,000 workers on movable scaffold.

Another example is that, if a worker has 26 years of experience and uses a 3.4 m movable scaffold without a handrail, the COP value becomes 8.3 cm in diagonal direction, 1.7 cm in AP direction, and 6.7 cm in ML direction, and the possibility of falling is 0.2 in diagonal direction, 9.75 in AP direction, and virtually zero in ML direction per 10,000 persons. For the same worker (26 years of experience) and movable scaffold (3.4 m) but with a handrail, the COP value becomes 6.5 cm in diagonal direction, 2.1 cm in AP direction, and 5.5 cm in ML direction, and the possibility of falling is virtually zero in diagonal direction, 2.10 in AP direction, and virtually zero in ML direction per 10,000 persons.

In the case of using 1.7 m movable scaffold without a handrail for the worker with 26 years of experience, the COP value becomes 4.1 cm in diagonal direction, 0.5 cm in AP direction, and 3.6 cm in ML direction, and the possibility of falling is virtually zero in diagonal direction, 0.51 in AP direction, and virtually zero in ML direction per 10,000 persons. For the same worker (26 years of experience) and movable scaffold (1.7 m) but with a handrail, the COP value becomes 2.3 cm in diagonal direction, –0.1 cm in AP direction, and 2.4 cm in ML direction, and the possibility of falling is virtually zero in diagonal direction, 0.08 in AP direction, and virtually zero in ML direction per 10,000 persons.

4 Discussion

This study proposed an index that can predict the probability of falling and, thus, help prevent workers from falling on construction sites. Occupational safety and health acts in South Korea require that employers have a responsibility to provide a safe workplace to all workers in industrial settings, guaranteeing their safety [15]. In this respect, in order to reduce the rate of accidents in industrial settings, the FPI suggested in this study can be used to provide a safe and appropriate environment for workers. The COP values in the diagonal, AP, and ML directions can be predicted by applying movable scaffold conditions (with or without handrails) and workers’ length of experience. Accordingly, workers can be placed in an environment with less risk and can be in a better position to demand safety measures, such as wearing a safety gear. Additionally, the probability of falling can be assessed directly during work to provide mental stability to workers. Therefore, site managers and workers at height can use the FPI as a guideline to predict accident rates and prevent falling accidents more efficiently.

For example, the probability of falling in the diagonal direction is virtually zero for workers with more than 20 years of work experience, and that in the AP direction for workers with up to 30 years of work experience is also negligible. It is highly improbable that workers with more than 15 years of work experience would fall in the ML direction. All other tables of the results are presented in the appendix. Although it overestimates the probability of falling, optimism can lead to excessive care among managers and workers on construction sites.

Collectively, these results indicate that the FPI suggested in this study should be used alongside proactive safety education, such as posture balance adjustment, to minimize falling occurrences when assigning inexperienced workers to high places with increased falling risk. Additionally, the shaking of movable scaffolds used in high workplaces should be thoroughly inspected. To ensure safety of workers in scaffolds, supervision should be strengthened, working time and environment should be adjusted [17, 18], and workers should always work in pairs [20]. Meanwhile, proactive measures (including clear instructions on assembling a tower scaffold and engineering controls on selecting components of the scaffold) for the safety of workers on movable scaffolds are necessary [20]. If screening determines that a worker is unfit to work on a movable scaffold, biofeedback exercises are recommended to increase posture stability before the worker returns to the workplace. The nervous system consciously and unconsciously moves the body to maintain a balanced posture [19, 21], and previous studies showed that patients with nerve problems can improve their posture balance through training.

The study limitations are as follows: There were only a few participants, and only COP was measured. Many participants and variable movable scaffold heights would need to be considered in order to more accurately predict FPI. The proposed index cannot be generalized other than the environment mentioned in this study. Studies on posture balance improvement and back pain prevention in workers at height and those on human engineering should be conducted to explore various aspects of accident prevention. This study considered a prefabricated movable scaffold. Hence, there is a possibility of stability issue. We have not investigated the structural rigidity of the scaffolds. Higher scaffolds may be less stable than lower scaffolds due to the changes in the center of mass [9]. A future study should investigate structural stability of scaffolds and its effects on postural stability. Moreover, this study did not validate the proposed FPI. With the author’s knowledge, validation can only be possible by performing a set of experiments on construction sites. A future study should validate the FPI through a set of experiments on construction sites. However, to more accurately predict the possibility of falling per 10,000 persons, various studies need to be conducted by considering the mentioned aspects (structural stability, more participants, various movable scaffolds and heights, etc.)

5 Conclusion

The proposed FPI will assist site managers and workers in predicting the risk of falling, i.e., the possibility of falling per 10,000 workers on a movable scaffold, in screening workers to assign them at a worksite where height is involved and implementing proactive measures to prevent falling accidents. The proposed FPI was calculated using Equation 2, where predicted COP values in all (diagonal, AP, and ML) directions and workers’ length of experience (1–30 years), scaffold height (1.7 m and 3.4 m), and presence or absence of a handrail are considered. Hence, site managers and workers can calculate the risk of falling by entering the necessary details in the FPI. If screening determines that a worker is unfit to work on a movable scaffold (i.e., nonzero in the possibility of falling per 10,000 workers on the movable scaffold), biofeedback exercises are recommended to increase posture stability before the worker returns to the workplace. However, the proposed index cannot be generalized other than the environment mentioned in this study. Although the results overestimate the probability of falling, it can lead to excessive among managers and workers. For instance, the falling risks were all zero for workers with 21–30 years of experience and presence or absence of a handrail in the ML direction. However, in the same condition (21–30 years of work experience, with/without handrail), there is a possibility of fall risks in the AP direction. Hence, site managers and workers who utilize this FPI need to consider falling risk in all directions. The results of this study can contribute to the prevention and scientific understanding of falling accidents. Future research should include more participants and various movable scaffolds and heights. Besides, experiments should be performed to validate the proposed FPI. Additionally, the structural stability of the scaffold and its effects on postural stability need to be studied further.

Conflict of interest

None to report.

Footnotes

The Appendix available in the electronic version of this article: .

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2017R1D1A3B03034037).

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