Introduction
About 350 fatal labor accidents in the construction industry happened in Japan in 2013. The 40% of fatal accidents were due to fall from height. The Safety belt, Harness, is one of the most common falling equipment which has been used all over the world. However body belt has been used in Japan for over 40 years as general falling equipment.
This study was carried out simply drop experiments on Harness and Body belt by using Hybrid-Ⅲ pedestrian model as a human dummy. Fundamental characteristics and impact forces acting on lanyard hook were compared especially at the moment of worker’s fall prevention. An additional drop experiment on energy absorber effect to the worker’s safety at the moment, it was carried out by using harness with shock absorber.
Methodology
Table 1 shows the experimental parameters and conditions used in each test. The experimental parameters are two kinds of safety belts, harness or body belt, and the presence or absence of shock absorber added into the lanyard.
Hybrid-Ⅲpedestrian human dummy was dropped from the assumed eave of the roof using separating devices. The weight of each falling body was 75kg.
The hook of the lanyard connected with safety belts was fixed to the assumed main rope located on the surface of the roof at height of about 1m lower from the gravity. The ropes of the safety belts used in this experiment were all made with nylon and new. They were 1700mm long.
The impact loads acting on the hook of the lanyard were measured with load cell. A high speed camera was also used in the experiments to realize basic characteristics of human dummy posture while falling.
Table 1. Experimental parameters and conditions
Results
Figure 1 shows the posture of Hybrid-Ⅲ pedestrian human dummy attached body belt on the waist with a nylon lanyard at the moment when the fall stopped. The neck and body parts of the HybridⅢ pedestrian model were bent considerably during the falling. From the posture shown in figure1, spinal cord injury at the neck and waist may occur when worker used a body belt with a nylon lanyard in the same falling situation.
Figure 2 shows the posture of Hybrid-Ⅲ pedestrian human dummy attached harness with a nylon lanyard at the moment when the fall stopped. Bending of the body parts did not visually observed in the experiment. However, major neck rotation to the front occurred at the moment.
In contract, bending of the neck and body parts of Hybrid-Ⅲ pedestrian human dummy did not ovserved by using harness with shock absorber device.
Figure 1 Falling posture of human dummy attached body belt.
Figure 2 Falling posture of human dummy attached the harness.
Figure 3 shows the time histories of the impact force acting on the hook of the lanyard on among experiment. The maximum impact force on the harness with nylon lanyard (about 9.5kN, as shown with strait line) was larger than the value of the body belt with nylon lanyard (about 6kN, as shown in a piece of dashed line). Against that, the impact duration of the harness was shorter than that of the body belt.
The maximum impact force was relatively minimized by using harness with shock absorber device (about 4kN, as shown in dotted line).
Figure 3 Impact force on the lanyard due to fall
Discussion
From these results, use of harness without shock absorber device cannot be expected to reduce the maximum impact force and energy at the moment when the fall stopped. Hence, there is some possibility of serious injury due to the large impact force as shown in figure 3.
However, the risk of serious injury inside the body parts might be relatively low as compared with use of body belt without shock absorber, because the falling posture was relatively stable during and at the moment when the fall stopped.
With the body belt without shock absorber, the serious injury risks of head, neck and body parts due to excessive bending could be very high. High speed head acceleration causes head injury such as epidural hematoma and diffuse brain injuries. Also the falling posture might be a handstand posture and the worker’s head might crash directly into some construction equipment or the rigid grand surface. In this case, skull fracture and cerebral contusion also might occur at a high probability. There are nerves controlling diaphragm inside the neck. Diaphragm damage due to the fall might cause out of control of breathing. Strong pressure acting on the back might cause spinal code injuries, which means the victim might have irreversible injury.
Figure 4 shows labor accident statistics data on the main injury parts in victims of fatal falls during 30 years in Japan. This figure shows that head and neck related injury are the major parts due to falling accidents. Therefore, it is important to reduce the risk of head, neck injury for prevention of fatal accidents and physical impediments.
In addition, use of harness with shock absorber device can be expected to reduce the maximum impact force and energy at the moment when the fall stopped. Also, bending of the neck and body parts did not observed in this study. Therefore, use of harness with shock absorber is the best way to reduce serious injury due to fall in the current phase.
Figure 4 Number of fatal falls divided into main injury region
Conclusions
To understand the fundamental safety characteristics of harness and body belt, some drop experiments were carried out. From the results of drop experiments by using human dummy, use of harness with shock absorber is the best way to reduce possibility of serious injuries, such as brain injury, skull fracture, and out of control of victims automatic breathing due to fall in the current phase.
Acknowledgement
This work was partly supported by JSPS KAKENHI Grant Number 23510212.
References
- 1. Ministry of Labor Safety and Health Japan. (2014). Labor accidents reports on casualties disease. (in Japanese)
- 2. Yasumichi HINO. (2012). New prevention methods for falling accidents due to disaster repair works at building construction site. 10th International conference on Occupational Risk Prevention, ORP2012, (CDROM).
Papers relacionados
