Accident Investigation in the Construction Industry

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Appendix A: Accident investigation

Investigation Report no. 1

Worker dies after being thrown back by concrete pump hose

Summary

A concrete pump truck was pumping concrete into the walkway of a house while the worker held the end hose. The rubber hose was 6m long and had a coupling device attached at the end. The operator of the concrete pump truck saw that the concrete had stopped flowing out of the hose. He pushed the emergency stop button and the pumping stopped. However, compressed air trapped in the supply line behind a blockage forced the blockage to clear suddenly. Concrete burst out of the hose, causing the hose to whip out. The worker holding the hose fell backwards. He struck his head on a piece of scrap lumber and later died of his injuries.

Conclusions

Findings as to the causes

  • The worker who was holding the end hose of the pump truck was thrown backwards when the hose whipped out. Striking his head on a piece of lumber, he suffered fatal injuries.

Findings as to the underlying factors

  • After pumping stopped and the hose was relocated, air got into the pump truck’s delivery system. Once pumping resumed, that air became pressurized, causing an eruption of concrete out of the end hose. As a result the end hose whipped out uncontrollably.
  • The end hose was 20 feet long with a coupling attached at the end of the contrary to the concrete truck pump manufacturer’s instructions. And the hose been about 3.6m long with no coupling as recommended, its whipping action would likely have been less violent when the concrete spewed out.
  • The two workers who were doing the concrete placing had no training associated with blockages. And the operator of the concrete pump truck was unaware of the danger of allowing the boom to drain.
  • Adequate communication among the workers about the hazards associated with concrete pumping operations did not take place.

Investigation Report no. 2

Worker struck by falling wall formwork

Summary

A carpenter on the 30th floor of a high rise building under construction was speaking with his supervisor while standing beside the location where the wall forms were being flown in and erected. The first wall form had just been set and braced. A steelworker was climbing up the walers to access the work platform so that he could help guide the rebar mat into place. The wall form suddenly fell over and the steelworker climbing up was able to jump clear. However, the nearby carpenter was crushed by the protruding work platform attached to the wall formwork and died of his injuries.

Conclusions

Findings as to the causes

  • The wall formwork became unstable and fell over. It was erected and supported on load blocks with an unequal cantilever at the base at each end. There were no structural elements to prevent lateral movement. As a worker climbed up the walers on the wall formwork, it kicked out at the south end load block. The braces were not adequately attached to the wall formwork and therefore were unable to resist the resulting forces to keep the formwork from falling.

Findings to the underlying factors

  • The engineering drawings for the formwork did not include any instruction or details for erecting and supporting the wall form on load blocks. The bracing could not be installed as shown in the engineering drawings. As a result, these sections were constructed without adequate engineering consideration, relying instead on the experience of the carpenters
  • Climbing the walers to access the platform was an unsafe practice and was prohibited by the company’s safe work procedures. Even though workers had been previously observed and reported, the practice continued. The added weight of the worker climbing on the north end of the wall formwork was a contributing factor to the wall falling over.
  • Nailing was ineffective. Each formwork aligner brace was nailed with two nails to the end of a waler. Only one nail for each brace could be considered fully engaged. The ends of the walers had been nailed into a number of times previously and were damaged and cracked. The inadequate bracing connections contributed to the wall form’s instability

Investigation Report no. 3

Walls collapse on street during demolition

Summary

A three-storey building at a street intersection was being demolished. The demolition proceeded until the North West corner with two exterior walls remained. The excavator operator pulled the floor joists to weaker the interconnection between the walls. This dislodged a horizontal beam hidden in cinder blocks in one of the walls. A portion of the cinder block facing north then fell outward onto the street. After cleaning up, the demolition crew began to demolish the free standing wall on the west side. After the excavator reached up and pulled down the top layer of cinder blocks inward into the site, the rest of the wall fell outward onto the street.

Conclusions

Findings as to the causes

During demolition, dislodgment of a hidden horizontal beam caused an unsupported, free- standing cinder block wall to fall outward onto the street. A second wall also collapsed onto the street. There was no temporary bracing to control the fall of the walls so they would fall inward into the demolition site.

Findings as to underlying factors

  • The structural components of the other building were not adequately assessed. There was no comprehensive demolition plan with specific procedures to address the hazards.
  • The demolition contractor began to demolish the building without any advice from a professional engineer regarding the structural capacity of the cinder blocks, the absence of beams and structural supports during the demolition, and the need for shoring and bracing to provide additional support.
  • The prime contractor’s safety system was not adequate to address the identified deficiencies and violations that resulted in this incident. Workers were at risk and the prime contractor failed to ensure safety was coordinated on this site.

Investigation Report no. 4

Excavation collapses killing worker

Summary

A crew of five workers, including the contractor, began installing underground storm sewer pipes on a street. The contractor dumped a bucket of gravel into the excavation. Two workers entered the excavation and spread the gravel at the bottom to make a bed for the pipe. The contractor the lowered a length of pipe and the two workers attached it to the end of the previously installed pipe. The contractor dumped more gravel into the excavation and the workers used shovels and their feet to tamp the gravel around the pipe. One worker left the excavation. About a minute later, the east side wall of the excavation collapsed onto the remaining worker, causing fatal injuries.

Conclusions

Findings as to the causes

  • One side wall of the excavation collapsed. The worker was buried under the loose material and died of asphyxiation.

Findings as to the underlying factors

  • The excavation was not shored or sloped to prevent the side walls from collapsing. Use of an adequate cage would have prevented the wall from collapsing.
  • Site supervision and inspection were in adequate and did not prevent the development of unsafe conditions.
  • The ground was very hard, which led the contractor to believe that the excavation was safe to enter.
  • A previously backfilled sanitary sewer line ran parallel to the excavation. Excessive weight of the loose materials in the sanitary sewer trench may have forced the wall of the excavation to collapse.
  • Vehicle and mobile equipment traffic next to the excavation wall would cause vibrations in the ground. This in turn may have caused the wall of the excavation to crack and collapse.
  • There was no health and safety coordinator at the site to address the hazards of the work site.

Investigation Report no. 5

Worker survives excavator rollover

Summary

A utility hoe operator was pioneering a logging road along a steep slope. The area had been drilled and shot-blasted recently, and the road was being constructed through a prescribed ¾ bench end haul section. The utility hoe operator was stripping the overburden (loose materials created by the blasting) and laying puncheon (small logs and branches) onto the sub-grade to establish a stable platform for the excavator. As the utility hoe operator was travelling back to grab more puncheon, the excavator broke through the previously laid puncheon and slide down a wet bank (40 percent slope). After sliding down 18m, the excavator toppled over a 9m bedrock bluff, landing upside down on a lower bench approximately 45m below the road. The utility hoe operator was pinned in the machine for approximately four hours. He suffered serious injuries.

Conclusions

Findings as to the causes

  • Sandy and soft muddy materials were on top of smooth bedrock. The unstable materials had been made slippery with water draining down the hill.
  • The utility hoe operator did not have adequate experience and training to work as a heading hoe operator.
  • The utility hoe operator did not receive adequate instructions and information about the work in the area.

Findings as to the underlying factors

  • There was poor planning and design for this phase of the road. More field tests to determine the soil conditions were needed and the road marker was not set properly.
  • The charge hand was not was not contracted for his input on whether the utility hoe operator had the necessary experience working on steep slopes.

Investigation Report no. 6

Overhaul ball falls from crane, striking worker

Summary

A conventional crawler-mounted mobile crane was being used to lift and align sheet piles and drive them into the ground. During the final alignment, the crane’s auxiliary hoist brake pedal inadvertently released, dropping the overhaul ball. The overhaul ball struck the top of the sheet pile and then struck a worker who was in a work bucked hooked onto an adjacent sheet pile. The worker in the bucket received fatal injuries.

Conclusions

Findings as to the causes

  • The welder was in the elevated work bucket hooked on the top of an installed sheet pile. He was struck and fatally injured by the falling overhaul ball of the crane’s auxiliary hoist line when the auxiliary hoist brake pedal inadvertently released.

Findings as to the underlying factors

  • The crane operator/foreman had a conflict of job responsibilities. Not only did he have to operate the crane but he also had to coordinate on-site activities outside the crane. This can cause a situation of divided attention.
  • There insufficient feedback mechanisms (audible or visual) to indicate the crane operator/foreman that the brake has not been applied successfully.
  • The pedal force needed to apply the brake exceeded the established standard. The crane operator/foreman may have experienced right leg muscle fatigue at the end of the day. This may have affected his ability to safely operate the brake pedal and latching mechanism.
  • No secondary, positive, drum brake system was available to prevent the overhaul ball from dropping in the event of an inadvertent release of the hoist brake pedal.

Investigation Report no. 7

Worker falls through roof insulation to concrete floor

Summary

Four workers were working on a relatively flat roof of a structural steel building. They were laying down metal roof panels over a layer of blanket insulation that had already been placed across the metal of roof beams. One of the workers fell through the insulation to the concrete floor 5.2m below. The worker died in hospital from his injuries.

Conclusions

Findings as to the causes

  • The worker fell through a layer of insulation and hit the concrete floor 5.2 below. There was no fall protection system in place to stop his fall.

Findings as to the underlying factors

  • Supervisors and workers did not have any written site-specific work procedures for installing roof panels.
  • The employer did not adequately ensure that supervision at the work site complied with the site-safety program requirements. There was no adequate system to ensure that supervisors were trained to perform their safety responsibilities and were carrying them out.

Investigation Report no. 8

Young worker injured when excavation collapses

Summary

A young worker was standing on a section of pipe in an unsloped, unshored trench about 2m deep. He was waiting for another worker to deliver a new section of pipe by excavator. The workers supervisor noticed water at the bottom of the trench, about 2 to 4m from the worker, and told him to get out. The worker stepped off the pipe into the trench to retrieve a laser stick before existing the trench. At that moment, part of the trench wall collapsed, burying the worker almost up to his chest and causing serious injuries.

Conclusions

Findings as to the causes

  • The young worker was injured when the wall of a trench he was standing in collapsed onto him. An engineer concluded that the prime cause of the cave-in was a lack of shoring or sloping.

Findings as to the underlying factors

  • The water in the soil of the trench added hydrostatic pressure to the soil pressure. In addition, the stresses from the spoil piles dumped next to the trench not only pushed down but also pushed out laterally. The unsupported trench cut was unstable and subject to collapse, as the lateral stresses pushed against the face of the trench wall.
  • Vibration from the two excavators that were being used likely contributed to some ground movement.
  • The spoil piles were more than 0.6m deep and close to the edge of the trench excavation, creating lateral stresses on the soil.
  • The construction of the trench required engineering assessment. Engineering advice wasn’t sought out before workers were allowed to enter the excavation.

Appendix B: Articles

South Africa building site collapses, one dead, dozens feared trapped

Tuesday after a soccer pitch-sized section of a shopping mall under construction collapsed near the South African city of Durban, emergency services and police said.

Witness Fiona Mooneal, who lives across a railway line from the construction site, was standing in her kitchen washing up teacups when the three-storey building collapsed as though it had been dynamited.

"It was just after 4.30 (1430 GMT). Suddenly about 200 meters of concrete slab just collapsed all at the same time. The screams of the guys, above all of that mad noise, you could still hear them," she told Reuters.

"It was like when you blow up a building, a bomb. That sound - it was terrible."

It was not yet clear what caused the three-storey building in the town of Tongaat, 30 km (20 miles) north of Durban, to collapse although Deputy Mayor Nomvuzo Shabalala said local authorities had tried to halt construction a month ago.

"There are areas of the law that they did not follow in terms of building of this infrastructure," Shabalala told broadcaster ENCA. "We were not aware that they were continuing building."

If safety regulations are found to have been flouted, the accident could hurt the ruling African National Congress (ANC) as it moves towards an election next year.

Durban and the surrounding province of KwaZulu-Natal are the home of President Jacob Zuma, and the region has enjoyed a construction boom in the last few years, based in part on government investment in infrastructure improvements.

Initial reports suggested as many as 50 workers were trapped under the rubble, although officials later scaled down their estimates.

"There are about 24 people who are at this stage unaccounted for. We're not sure whether they might still be trapped or whether some of them might have gone home," municipal spokesman Thabo Mofokeng told Reuters.

"SO MUCH NOISE"

As darkness fell over the site, scores of rescue workers, sniffer dogs and police, illuminated by powerful arc lights, combed through the broken concrete slabs and twisted lengths of scaffolding, looking for survivors.

"In all my years as a paramedic I have never seen anything like this," said one rescue worker, running to the site carrying oxygen canisters. Others used hydraulic jacks to lift the slabs and grinders to cut through the metal.

"You can't see anything, and you can't hear anything. The generator is making so much noise," another rescue worker said.

Large crowds of onlookers and anxious friends and relatives gathered in the darkness behind a security cordon.

Besides one confirmed death, 29 people, two of them in critical condition, were rushed to nearby hospitals, which initiated full-scale disaster plans, health officials said.

A high death toll could also sour labor relations in the construction sector, which has an otherwise decent safety record due to the strength of South Africa's unions.

"It's mainly broken bones, soft tissue injuries and a bit of shock. But obviously there are a lot of patients that are still trapped on site," said Jenny Meer, manager of the Mediclinic Victoria hospital in Tongaat.

The ANC is expected to win the election expected in April or May next year, although its share of the vote is likely to taper as young post-apartheid South Africans with no knowledge of white-minority rule come of age.

Incidents such as the police killing of 34 strikers at Lonmin's Marikana platinum mine near Rustenburg last year have also fuelled a sense of the ANC neglecting Nelson Mandela's dream of building a more equal, caring society from the ashes of apartheid.

Site accidents in construction industry are caused by various reasons. This paper specially explains the causes of high accident rate in Chong Qing's construction industry, and indicates that there are two major problems contributing to the high construction accident rate, which include problems of management and problems of people. In addition, this paper emphasizes that the four major parties including the government, clients, contractors and individual site staff should take effective measures to reduce the numbers of site accidents. The author believes that the objective to improve safety performance on construction site must be realized through corporate effort of every concerned party.

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