• Journal of the Korean Society of Safety
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• v.36 no.5
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• pp.36-42
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• 2021

Portable ladders are widely used as ascend and descend pathways and platforms for works at height at residential and industrial sites. In the last 10 years, 267 fatalities and 36,571 accidents related to portable ladders have been reported, suggesting a need to develop countermeasures to prevent such accidents. In this study, an in-depth focus group interview (FGI) was conducted with various stakeholders of portable ladders to survey the current usage and requirements for improving work safety. A new portable ladder called active platform ladder was developed based on the requirements suggested by the FGI. A stability test confirmed that the developed ladder is more stable than conventional ones, suggesting that it can reduce the fall accidents.

• Journal of the Korean Society of Safety
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• v.24 no.6
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• pp.136-143
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• 2009

The injuries as a result of fall accidents is the one of the most common kind of injuries in Korea, especially fall from height is the top most common kind for fatal injuries. Futhermore, the number of fall injuries in manufacturing industry has been steadily increasing from 2000 to 2007. In 2007 the number of fall fatal injuries increased 10.6 % in comparison with the number in 2006. These numbers are 6~17 times higher than those for foreign countries such as the U.K and the USA. So, it is needed to make a study to reduce these numbers for manufacturing industry. To get the goals, we did research as followings. First, this study analyzed statistics by industry, by fall height, by common agent and so on to gain an insight into real aspect of fall injuries. It showed that ladder is the commonly cited agent for manufacturing industry, and 3 risky activities ; the ladder work, the load/unload work, and the maintenance work. Secondly, this study made a survey of manufacturing workers for their understandings of the most 3 risky activities. It showed that 'tendency to work easily' and 'difficulty of applying measures due to inherent working conditions' are main reasons for workers not to implement the preventive measures against the fall accidents. Thirdly, this study tested the slip characteristics of ladder base and lungs. The tests were done based on ANSI standard and KS. In addition to the standard condition, this study performed slip tests in wet and sandy conditions and compared the results with the those of standard condition. It showed that friction coefficient is standard condition > wet condition > sandy condition, and the friction coefficient of ladder for sandy condition is measured to be reduced by 63.9% compared with that for standard condition. Finally, this study developed safety work models for using of portable ladders in consideration of the safety standards of foreign countries such as the U.K, the USA, and the Australia.

• Bulletin of the Korean Mathematical Society
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• v.40 no.4
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• pp.663-669
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• 2003

This paper investigates the tail asymptotic behavior of the severity of ruin (the deficit at ruin) in the renewal model. Under the assumption that the tail probability of the claimsize is dominatedly varying, a uniform asymptotic formula for the tail probability of the deficit at ruin is obtained.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.4
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• pp.241-247
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• 2010

Corrosion of steel embedded in concrete is one of the foremost factors that affect the durability of concrete structures in marine environments. This paper presents an application technique of anode-ladder-system to evaluate corrosion behaviours of marine concrete structure. In order to investigate the behaviours quantitatively, the measurement of potential and current was performed on the concrete elements subjected to the penetration and diffusion of chloride ions. The main variable was the heights from seawater level; namely 3.7, 6.0 and 8.2 m. As a result of the monitoring, it was found that the corrosion characteristics differently behaved with the increasing height. Additionally, through migration test, the relationship between compressive strength of concrete and diffusivity of chloride ions was observed. It is suggested, ultimately, that in order to reduce or mitigate steel corrosion, both appropriate concrete cover depth and high-quality of concrete in early ages should be done.

• Journal of the Ergonomics Society of Korea
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• v.32 no.6
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• pp.549-555
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• 2013

Objective: The purpose of this study was to compare the performance of drilling on the ceiling in three different postures (standing, standing on the ladder and supine on the height adjusted board) and the subjective responses of perceived discomfort after the drilling. Background: Overhead work has been identified as a major occupational risk factor and has been a main research subject. Method: Ten young participants drilled 20 holes at the pre-marked places on the ceiling in three different postures. The drilling duration, resting and drilling heart rate were measured. The levels of perceived discomfort at neck, shoulder, elbow, hand and overall body were asked at the end of each task. Results: The working posture affected the heart rate after the drilling. Perceived discomfort in the neck decreased significantly in supine compared to drilling on the ladder. Conclusion: The results of this study suggest that drilling in supine can be an alternative way to reduce the drilling heart rate and the level of perceived discomfort in the neck without sacrificing the productivity. Application: The results of this study would be considered when drilling on the ceiling is required in construction workers.

• Journal of Drive and Control
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• v.18 no.4
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• pp.19-27
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• 2021

A bunker bed is a type of furniture that efficiently utilizes a narrow indoor space by having a high bed and using the empty space below as a living and storage space. The demand for multi-purpose furniture is increasing due to the recent increase in single-person households and wide-spread shared accommodation. According to the consumer research, one of the major drawbacks of a bunker bed was to get on and off the bed through a ladder or stairs. In order to overcome these problems, it was confirmed that the height adjustment function that can easily adjust the minimum and maximum heights of the bed was necessary. In this study, a height adjustable bunker bed was designed by using a gas spring that generates a repulsive force by the compressed gas inside. The design process consisted of the following three steps: Firstly, the hysteresis characteristics due to a friction and spring constant of a commercial gas spring were confirmed by measuring the repulsive force vs. compressed displacement. Secondly, requirements of the vertical lifting force exerted on the bed against gravity force were derived. Finally, the height-adjustable bed using the four-bar link mechanism was designed with 4 parameters so that the bed weight of 60-70 kgf could be adjusted to 800 mm in height by an affordable initial operation force. The performance was verified through prototype production and the results of vertical displacement and force to move were nearly the same as designed. In addition, an electrically operated height-adjustable bed was also designed with linear actuators and the performance was proved with the prototype.

• Journal of the Ergonomics Society of Korea
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• v.25 no.2
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• pp.107-118
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• 2006

Recently, Korean's 3-D foot data have been extensively collected through 5th national anthropometric survey known as 'Size Korea'. In this study, Korean foot shape was investigated and subsequently classified, based on the existing standard for foot shaping. This study analyzed and categorized Korean foot shapes through the following methods. Although the data used in this study were limited to those of Korean adults, major factors affecting the foot shape were deduced and then categorically grouped by the multivariate statistical analysis. For those whose age ranged from 14 to 70, major factors affecting the foot shape for the male were related to foot breadth, ankle thickness, 1st toe shape, malleolus height, heel to top of the foot length, the ratio between toe-side and heel-side and 5th toe shape. For the female, the ball of foot height was added to the above factors. From the factors extracted, the Korean foot shape was categorized into three groups for the male and four groups for the female. They were the ladder type, the inverted triangle type and the square type. For the female, the triangular type was added to the three types. These findings will serve as useful information for the footwear production industry in Korea.

• Journal of the Korean Institute of Landscape Architecture
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• v.51 no.5
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• pp.1-12
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• 2023

This study evaluated the overturning stability of portable tripod ladders used for high-altitude work such as tree management and pruning work in landscaping construction and management. Portable tripod ladders, which are included in general mobile or portable ladders frequently used in industrial sites, are supported in a triangular support structure, not a 4-point support like common A-type Ladders. In addition, since the working height is more than twice that of a mobile or portable ladder, the possibility of an overturning accident that threatens the safety of workers with a fall accident is high. Therefore, based on the overturning stability test specified in ANSI-ASC A14.7 and EN 131-Part 7, which are related standards for about 130 types of portable tripod ladders sold and used in Korea. An equation to calculate each moment according to working height was derived. Then, each calculated moment was compared to evaluate the safety factor for overturning and stability. As a result of the overturning stability evaluation according to each standard, when the provisions of EN 131-Part 7 were applied, portable tripod ladders with 8 steps in the rear direction and 6 steps or more in the side direction were evaluated as unstable against overturning, but according to ANSI-ASC A14.7 regulations. It was evaluated that the stability against overturning was secured in all directions and number of steps.

• Horticultural Science & Technology
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• v.32 no.4
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• pp.454-462
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• 2014

This study was carried out to determine the effect of tree height on light transmission, spray penetration, tree growth performance, fruit quality attributes, and labor productivity in the slender-spindle system of 'Hongro'/M.9 apple trees. With increasing tree height, the light penetration into the internal parts of the canopy decreased, especially in the lower canopy. Leaf area index (LAI) increased with increasing tree height, thereby leading to a reduction in the extent of spray penetration into the interior of the canopy. With increasing tree height, shoot growth was more vigorous but produced slender shoots in the upper canopy compared to the lower canopy. Although the soluble solid content and coloration of fruit decreased, there was no difference in fruit firmness and acidity. In addition, the number of final fruit set increased, although the production of large fruit (> 305 g) decreased. The increase in tree height also significantly increased the labor required for practices such as thinning of flowers and fruits, pruning, and harvesting. Nevertheless, this problem of increased in labor input in taller trees would was eased by use of a mechanical lift. Utilizing a lift for thinning the flowers of trees 4.5 m in height saved 14.6 min per tree, compared to the use of ladder. Therefore, it is highly considerable that in order to enhance light transmission and fruit coloration, light conditions should be improved in the internal tree canopy of slender-spindle systems.