Question 6 of 6: Safety Practices and Regulations — a multi-lane bridge kept in service during construction

Question 6: Safety Practices and Regulations — a multi-lane bridge kept in service during construction (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 that must carry traffic while it is being rebuilt is one of the most demanding safety problems in civil construction, because it combines the ordinary hazards of heavy construction — height, lifting, heavy plant, concrete, welding — with a continuous stream of moving vehicles a metre or two from the work face, and with the possibility that a construction error will injure the public rather than the workforce. The practices below are organised around that combination. In Canada they are given effect through the provincial occupational health and safety statutes and regulations — the WorkSafeBC OHS Regulation Part 20 (Construction, Excavation and Demolition) and Part 18 (Traffic Control), Ontario's O. Reg. 213/91 under the Occupational Health and Safety Act, and the equivalents elsewhere — together with the internal responsibility system that underpins all of them, the applicable traffic-control manual, and CSA S6, the Canadian Highway Bridge Design Code, for the structural side.

Planning, the prime contractor and the safety management system

The first practice is organisational. A single prime contractor (or, in Ontario, the constructor) must be identified in writing and made responsible for coordinating the safety activities of every employer on site, because a multi-employer workplace with no coordinating mind is where the serious incidents happen. That party establishes and maintains the written health and safety programme, chairs the joint health and safety committee once the workforce reaches the statutory threshold, and holds the pre-job planning meetings at which the traffic-management plan, the erection plan and the emergency plan are agreed with the road authority, police, fire and emergency medical services.

Hazard identification must be systematic rather than reactive: a formal risk assessment for the project as a whole, task-specific job hazard analyses or safe-work procedures for each high-risk operation, and a field-level hazard assessment completed by the crew at the start of every shift, since a bridge deck changes daily. High-risk work is controlled by permit — hot work, confined-space entry into box girders and caissons, lifts over live lanes, work near energised conductors. Every control should be selected by the hierarchy of controls, in which elimination and substitution outrank engineering controls, which outrank administrative controls, which outrank personal protective equipment; on a live bridge the highest-value application of that hierarchy is to eliminate the exposure altogether by closing lanes at night or diverting traffic, rather than to manage it with cones and vests.

Traffic accommodation and worker–traffic separation

This is the hazard that distinguishes the project. A formal traffic management plan, sealed by a professional engineer and approved by the road authority, should set out staging, lane configurations, tapers, speed reductions and detours for every phase. Signing, delineation and taper lengths must follow the governing manual — the Manual of Standard Traffic Signs and Pavement Markings in British Columbia, Ontario Traffic Manual Book 7 in Ontario — with the taper length computed from the posted speed and the lateral shift, not chosen by eye.

The work zone should be separated from live traffic by positive protection wherever the exposure is significant: portable concrete barrier or steel barrier meeting the appropriate MASH test level, rather than cones and drums, with crash-tested end treatments and truck-mounted attenuators shielding the upstream end of mobile operations. Reduced regulatory speed limits with photo-radar or police enforcement, doubled fines in the work zone, and generous advance warning with variable message signs all reduce the closing speed of anything that does enter the zone. Wherever possible the heaviest and most exposed work — girder erection, deck pours, demolition over live lanes — is done under a full closure at night or on a weekend, which is a scheduling decision with a safety purpose.

Workers on foot need their own protections: designated access and egress points that do not require crossing a live lane, a physically separated pedestrian route across the structure, high-visibility apparel to CSA Z96 class 2 or 3 with retroreflective banding for night work, trained and equipped traffic control persons positioned in a location with an escape route, and adequate task lighting for night shifts without glare towards the travelling public. Public and pedestrian protection is the mirror image of the same problem: overhead protection and debris containment where work is above a live lane or footway, closed and signed detours for pedestrians and cyclists, and containment systems for any coating removal or blasting.

Fall protection, structural stability and lifting

Falls remain the leading cause of construction fatalities, and a bridge project is height work throughout. Guardrails on every open edge of the deck are the first choice because they protect passively; where guardrails are impracticable, a personal fall-arrest system with an engineered anchorage of adequate capacity, connected to a horizontal lifeline designed by an engineer, is used, and a written fall-protection plan is required at height in most jurisdictions. Every fall-arrest system needs a workable rescue plan and the means to execute it promptly, because suspension trauma makes a successful arrest into a medical emergency within minutes. Over water, add flotation devices, a rescue boat on station, throw lines, and containment netting.

Structural stability during construction is an engineering control that belongs in the safety discussion because most catastrophic bridge failures happen during erection rather than in service. Falsework, formwork and shoring must be designed and sealed by a professional engineer, inspected before each pour and re-inspected after any load change; erection sequences, temporary bracing and crane pick plans must be engineered, with the partially erected structure checked for wind and for the unbalanced conditions of each stage; and demolition of the existing structure needs its own engineered sequence with a stability analysis at every step. Nothing is loaded until the responsible engineer has confirmed in writing that it may be.

Lifting operations need a documented lift plan with crane capacity charts, ground-bearing and outrigger assessment, exclusion zones under the load, qualified riggers and signallers, and a hard rule that no load passes over live traffic unless the lanes beneath are closed for the duration of the pick. Minimum clearances from energised overhead conductors must be established with the utility and enforced with limit devices and spotters.

Occupational health, plant and site control

The remaining exposures are the ordinary ones of heavy civil work, but they are not less lethal for being familiar. Excavations for abutments and piers must be sloped, benched or shored to an engineered design, with ladder access every 8 m of travel and daily inspection. Confined spaces — box girders, caissons, pier shafts, manholes — require a permit, atmospheric testing, continuous ventilation, an attendant and a rescue capability. Mobile plant needs separated haul routes, backup alarms and cameras, spotters where lines of sight are poor, and a traffic-control plan for the site as distinct from the highway. Energy isolation and lock-out applies to every powered system before maintenance.

Health hazards deserve equal weight: WHMIS 2015 classification, labelling, safety data sheets and worker education for every controlled product on site; silica exposure control for concrete cutting and grinding, with wet methods and on-tool extraction as the primary controls; lead and coatings management if the existing structure is repainted or demolished; noise assessment and hearing conservation using the Canadian 3 dB exchange rate against an 85 dBA eight-hour criterion; welding fume ventilation; and heat and cold stress management for exposed deck work.

Competency, supervision and continuous verification

None of the above survives contact with a real site unless it is trained, supervised and verified. That means orientation for every worker and visitor before first access; certified training for the specific tasks — fall protection, traffic control, confined space, rigging, first aid, WHMIS; toolbox talks at the start of each shift focused on the day's changing hazards; and competent supervision physically present at the work face. Verification is by planned inspections at a stated frequency, third-party audit against the provincial Certificate of Recognition programme, incident and near-miss reporting with genuine root-cause investigation, and a small set of leading indicators — inspections completed, hazards closed out, toolbox talks held — tracked alongside the lagging ones. Emergency preparedness must be specific to this site: rescue from height and from water, extraction from a confined space, a vehicle incursion into the work zone, spill response, and a documented route by which an ambulance can reach any point of a partially closed bridge.

The thread running through all of it is that safety on a live bridge is a design and planning problem before it is a behavioural one. The decisions that matter most — to stage the work so that the heaviest operations happen behind a full closure, to install positive barrier instead of cones, to engineer the falsework properly, to build a pedestrian route that does not cross traffic — are all taken months before anyone puts on a hard hat, and no amount of supervision on the day can compensate for getting them wrong.