Question 6 of 6: Safety Practices and Regulations — bridge rehabilitation in high traffic

Question 6: Safety Practices and Regulations — bridge rehabilitation in high traffic (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

A bridge rehabilitation in a high-traffic corridor combines almost every hazard class in construction — live traffic, work at height, work over water or over a roadway, hazardous substances released by removing old coatings, confined spaces inside box girders, mobile equipment and lifting — and it does so on a site the public is entitled to drive through. The safety programme must therefore start from the legal structure and work outward to the specific controls, because on a project of this kind the coordination duty is as important as any individual control.

Establish the legal framework first. In British Columbia a multiple-employer workplace must have a prime contractor, designated in writing under section 118 of the Workers Compensation Act, who is responsible for coordinating the health and safety activities of every employer on site. Every other province has an equivalent constructor or principal-contractor concept. A Notice of Project is filed before work begins, a joint health and safety committee is established once the crew exceeds the statutory threshold, and a written exposure control plan is required for each designated substance identified. Everything that follows — the traffic management plan, the fall-protection plan, the rescue plan — is a document the prime contractor owns, keeps current, and enforces against subcontractors.

Traffic is the dominant hazard, and it is controlled by separation before it is controlled by warning. The single most effective measure is positive protection: portable concrete barrier or a barrier-rated system physically separating the work space from the travelled lanes, so that an errant vehicle cannot reach the crew. Where barrier cannot be placed, truck-mounted attenuators and shadow vehicles take its place. The work zone is laid out in the standard sequence of advance warning area, transition taper, longitudinal buffer, work space and termination area, with taper lengths computed from the posted speed and lane width in accordance with the provincial standard — in BC, the Ministry of Transportation and Infrastructure Traffic Management Manual for Work on Roadways, which adopts the same logic as the TAC manual used nationally. Speed is reduced through the zone and enforced, ideally with police presence during lane closures. Traffic control persons must hold current certification, must be positioned where they are visible from the full stopping-sight distance and have an escape route, and must never be used where a barrier or a signal would do the job. Workers wear high-visibility apparel to the required class, and because much of this work is done at night to minimise congestion, the illumination of the work zone, the glare control on the traffic side, and the fatigue management of a night shift all become explicit design items rather than afterthoughts. Public safety is part of the same plan: pedestrian and cyclist routes must be maintained or formally detoured, not simply blocked.

Falls and work over the edge come next. Rehabilitation work happens at the deck edge, under the deck, and on the piers. Guardrails are installed wherever the geometry permits; where it does not, workers are protected by a personal fall-arrest system anchored to an engineered anchor point, with the anchorage, the fall clearance and the swing-fall path all designed rather than assumed. Suspended work platforms, under-bridge inspection units and swing stages require engineered designs, documented inspection before each shift, and an operator trained on that specific unit. A written fall-protection plan is required whenever workers are exposed above the regulatory height and guardrails are not used, and it must include a rescue plan: a worker suspended in a harness must be retrieved within minutes, so the means of rescue has to be on site and rehearsed, not summoned. Where work is over water, lifejackets or personal flotation devices, a rescue boat and a person-overboard procedure are required in addition to fall protection. Openings in the deck are covered and marked, and tools and materials are tethered or contained so that nothing can fall onto traffic or onto workers below — debris netting and containment platforms under the working area serve both purposes.

Hazardous substances are the hazard most often underestimated on a rehabilitation. Older bridges commonly carry lead-based coatings, and abrasive blasting or grinding of the steel releases both lead and respirable crystalline silica. Both are designated substances requiring a written exposure control plan, full containment of the blasting area with negative-pressure ventilation and HEPA filtration, air monitoring, supplied-air or appropriately rated respiratory protection with fit testing, decontamination and washing facilities, hygiene rules prohibiting eating or smoking in the work area, and biological monitoring of blood lead levels for exposed workers. Concrete removal by hydrodemolition or hoe-ram introduces noise well above the 85 dBA exposure limit — a hearing conservation programme with audiometric testing is required, and it should be noted that Canadian regulations use a 3 dB exchange rate, so a doubling of sound energy halves the permissible exposure time. Welding fume, coating solvents, and diesel exhaust in confined areas each need their own controls. Any entry into a box girder, a pier shaft, or a cofferdam is a confined-space entry: hazard assessment, atmospheric testing before and during entry, ventilation, an attendant, a permit and a rescue capability appropriate to the space.

Equipment, lifting and structural integrity round out the technical controls. Cranes and boom trucks working from a shoulder or from the deck require a documented ground-bearing or deck-capacity assessment — a rehabilitation deck may not carry the loads the original design allowed — along with lift plans for critical picks, certified riggers, exclusion zones under suspended loads, and minimum approach distances from any overhead conductors. Temporary works that carry load, including shoring, falsework, needle beams and any staged demolition sequence, must be designed and sealed by a professional engineer and inspected before use, because the rehabilitation temporarily alters the structure's load path and a partially demolished bridge is not the structure the original drawings describe.

Finally, the administrative system that keeps all of this alive. Site-specific orientation for every worker and visitor; daily pre-task planning or toolbox meetings that name the day's hazards and controls; a field-level hazard assessment before each non-routine task; a young or new worker programme; documented competency for every regulated activity from traffic control to crane operation; scheduled inspections with tracked corrective actions; a written emergency response plan that accounts for the difficulty of getting an ambulance to a worker in a live traffic corridor or under a deck; incident and near-miss reporting with investigation of causes rather than of individuals; and visible enforcement, including stop-work authority for every worker. The measure of the programme is not the absence of recorded injuries over a short period, which is largely chance on a project this size, but whether the hazards were identified in advance and controlled as high on the hierarchy of controls as the work allowed — elimination and substitution first, then engineering controls such as barrier and containment, then administrative controls, and personal protective equipment only as the last line.