Date of incident: October 2021
Notice of incident number: 2021184390026
Employers: Pile driving company

Incident summary
During the piling installation phase of a 15-storey mixed-use construction project, workers were using a vibratory hammer suspended from a crane to remove a 23.5 m H-beam from a concrete-filled caisson and plant it in the ground nearby. The equipment lost control of the load and the H-beam fell onto the crane cab. The operator was able to escape the cab prior to the impact but sustained injuries in the process.

Investigation conclusions

Cause

• Vibratory hammer’s clamp released H-beam prematurely. The left clamp of the vibratory hammer lost contact with the H-beam it was clamped onto after the H-beam struck a hard object while being driven into the ground by the vibratory hammer. When the clamp lost contact, the H-beam was 1.5 m in the ground, which was not deep enough to keep it standing vertically. As a result, the H-beam fell onto the cab of the crane from which the vibratory hammer was suspended.

Contributing factors

• Hydraulic line failure and lack of replacement part. The segmental casing and the H-beam needed to be removed before the concrete inside the casing solidified. The crew originally intended to remove the segmented casing using the oscillator, a standard piece of equipment for this purpose. A hydraulic line on the oscillator burst, and no replacement part was available on short notice. This resulted in the crew deciding to remove the H-beam from the casing using the vibratory hammer. The employer stated that hydraulic line failures such as this were a rare occurrence, so it was not deemed practicable to have replacement parts on site. In this case there was not sufficient time to obtain the needed part from any local supplier because it was not a stocked item.
• Inadequate risk management. The employer had not identified the hazard of using the vibratory hammer to move the H-beam above ground or mitigated the related risk with adequate controls. The manufacturer’s instructions stated that for safety reasons, the vibratory hammer’s clamp was not to be used to move piles outside of the caissons. The work procedures the workers were following breached this guidance, as the procedures had been made up on the spot to respond to the dynamic challenges that arose when the segmental casing could not be removed from the caisson. The procedures were not specific or complete, and, due in part to time constraints and economic pressure, did not account for all the potential hazards and risks posed by the task of extracting the H-beam and storing it vertically. The hazards of the broken jaw and the hole in the web (see next bullet) were also not identified by the employer.
• Reduced contact between clamp and H-beam web. The fixed jaw side of the caisson clamp was broken, which reduced the contact area by 77%. On the hydraulic cylinder side of the caisson clamp, the contact area with the H-beam web was reduced by the hole in the web. When the clamping cylinder was over the hole, the contact area was reduced by 33%. The force with which the clamp held onto the H-beam was affected by this reduction in contact, but was likely not overly compromised. However, the clamp attachment was not designed for extracting H-beams, so the H-beam had to be positioned off the centreline of the vibratory hammer, which increased the risk of the H-beam being inadvertently released.

Request the full report