| Case Name |
A crane accident by a cargo collapse |
| Pictograph |
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| Location |
A construction site of a wooden house |
| Overview |
On the construction site of a wooden house, a crane operator hoisted sixteen bundles of boards (about 35kg) by a mobile crane. When the operator rotated the crane, the cargo got stuck on a telephone wire and the cargo collapsed. Unfortunately, the collapsed cargo hit a worker and he died. The reasons of the accident are the insufficiency of safety control for workers and the insufficiency of the supervision, the instruction and the consideration of an operation plan. |
| Incident |
On the construction site of a wooden house, a crane operator hoisted sixteen boards (about 35kg) by a mobile crane. When the operator rotated the crane, the cargo got stuck on a telephone wire and the cargo collapsed. Unfortunately, the collapsed cargo hit a worker and he died. |
| Sequence |
* On the construction site of a wooden two-story house, eight workers including 6 carpenters of the main contractor started working from early morning of the accident day with the mobile crane (a truck crane, maximum hoisting weight: 11 tons) of the main contractor.
* Since the site was small, they set outriggers on the local street and a field next to the site under the telephone wire, which is 5.2m high.
* In the afternoon, construction materials including boards were brought and uncharged on the street. At around three o'clock in the afternoon, a site manager ordered the crane operator to move those materials from the street to the site.
* The site manager from the main contractor and the victim from the subcontractor, both of whom had a license for slinging work, slung sixteen bundles of boards (length: 2m, width: 10-15cm, 1 bundles had 15-20 boards, weight: 250kg) with two nylon slings (Length: 5m, diameter: 33mm, both ends eye slings). They slung two points, 30cm from the both ends of bundles, to a crane's hook and the site manager ordered them to hoist them.
* The site manager moved to lay sole plates at the unloading area when the bundles were hoisted, in a horizontal position, as high as the telephone wire.
* When almost all sole plates were laid, the crane operator started to turn the crane over the telephone line. Then, the bundles suddenly fell and hit the head of the victim who was under the bundles.
* A neighbor saw that a part of bundles got stuck on a telephone wire. |
| Cause |
(Human factor)
* Lack of awareness of danger.
Without an order, the crane operator turned the crane to the right above the workers before the other workers had finished to lay the sole plates at the unloading area.
* Conjecture.
The crane operator guessed laying the sole plates would finish soon and the bundles would not fall because the bundles were kept in a horizontal position.
(Equipment factor)
* Equipment flaw.
The bundles fell because the nylon slings were too thick for the bundles to tighten.
(Operation factor)
* Breach of the operation procedure.
When the crane is used, a qualified person must sling and a crane operator must start to turn the crane after receiving the signal from a signaler. In this case, a crane operator started to turn the crane before receiving the signal from a signaler. Next, the loads must be hoisted and moved after the unloading area is decided and prepared. However, in this case, the unloading area was prepared after the bundles were hoisted.
(Management factor)
* Lack of supervision and instruction.
If the manager notices the workers are working under the loads, he must stop the operation and give them a few words of warning. However, the site manager of this case overlooked the dangerous situation.
* Lack of safety education and training.
Due to the lack of the awareness of danger, the crane operator turned the crane without signal and the workers worked under the loads without hesitation. The site manager did not have an ability to give any words of warning when he saw the dangerous situation. The site manager should know the past accidents and confirm the procedures of operations. |
| Countermeasures |
* Before starting the operation, the site manager should make an operation plan, decide signals, delegate someone as a signaler and have an in-depth meeting with all members who will work in the site.
* It also needs the right supervisions and instructions to carry out the above proposals. |
| Knowledge Comment |
(In the crane operation)
* Before starting the operation, The site manager should make an operation plan, decide signals, delegate someone as a signaler and have an in-depth meeting with all members who will work in the site.
* It also needs the right supervisions and instructions to carry out the above proposals. |
| Sequel |
* The reason for the collapse of cargo is often due to the improper sling work.
* In the case of hoisting with a single sling such as the demolition of the short strut, an accident like short strut's unexpected moving often occurs when the final bolt is removed from the short strut.
* The hoisted loads often hit the workers due to the strong wind. |
| Scenario |
| Primary Scenario
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Ignorance of Procedure, Disregard of Procedure, Poor Value Perception, Poor Safety Awareness, Regular Operation, Nonobservance of Procedure, Usage, Operation/Use, Failure, Fracture/Damage, Bodily Harm, Death
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| Number of Deaths |
1 |
| Field |
Civil Engineering
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| Author |
KUNISHIMA, Masahiko (The University of Tokyo)
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