Date of incident: April 2020
Notice of incident number: 2020178760013
Employers: Concrete reinforcing firm; bridge construction firm

Incident summary
At a bridge construction site, workers were in the process of wire-tying vertical rebar dowel cages to a purpose-built rebar jig (a template used to position dowel cages needed to create footings for support columns). During the assembly process, the rebar structure collapsed, striking two workers. Both workers sustained serious injuries.

Investigation conclusions

Cause

• Inadequate temporary support. The workers’ employer was in charge of ensuring that adequate temporary support measures were being used during the rebar assembly process. The employer developed a plan that included use of support measures such as guylines and wire rope hoists to temporarily secure the dowel cages during the assembly process. During the assembly process, guylines and wire rope hoists were not installed. This left only the jig being used as a support system to securely hold the dowel cages in place. A WorkSafeBC engineer determined that without cross-bracing such as the guylines and wire rope hoists would have provided, the jig would not have provided adequate lateral support. As a result, the unstable dowel cages collapsed.

Contributing factors

• Inadequately identified and assessed hazards. Some of the hazard assessments required before the rebar assembly work started were not completed, and those that were carried out were inadequate in relation to the stability of the vertical dowel cages. They did not take into account the need for temporary support measures to control the inadvertent movement of the dowel cages during the assembly process. The prime contractor also failed to ensure that hazards were being adequately assessed and addressed by workers throughout the duration of the work activities.
• Failure to follow safe work procedures. The employer had multiple safe work procedures pertaining to the assembly of rebar. The employer had developed a shop drawing, which was also an assembly procedure. A plan was developed to use additional stability control measures during the installation process to address concerns with the shop drawing. Those temporary support measures were not implemented during the installation of the dowel cages.
• Ineffective information and instruction. The employer did not convey to workers proper information and instruction on the rebar dowel cage assembly process with regard to the stability of the structure during installation — specifically that they were required to use guylines and wire rope hoists to secure the dowel cages. The employer’s shop drawing and safe work procedures were not made available to the workers who were performing the work activity.
• Inadequate supervision. Hazards at the site specific to the work process of assembling the rebar dowel cages were not adequately identified, and the established, agreed-upon safe work procedure for ensuring stability control of the dowel cage structure was not followed. The employer did not ensure that temporary support measures were made available and used by the workers. The employer did not make readily available to the workers safe work procedures or all the tools they required, such as guylines and wire rope hoists, and failed to inform and instruct the workers to use the temporary support measures required to secure the dowel cages during the assembly process. The employer’s workers on site were not effectively supervised to ensure that the work was being conducted in accordance with the employer’s instructions related to structural stability. Further, an inspection of the site the day before the incident failed to identify the fact that the agreed-upon temporary support measures had not been installed. After it was reported that the dowel cages were becoming out of plumb vertically, instructions to vacate the hazardous area of the rebar structure were not adhered to.

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