Steel, precast and mass timber erection: the hazards

On a cold Monday morning in March, the first column went up at the Prairie Gate Community Centre, a new three-storey building that Tallgrass Construction was putting up on the north side of Winnipeg while its crews finished Cottonwood Place downtown. Ray Lindqvist, who had run the tower crane at Cottonwood Place, now sat in the cab of a 90 t (100 ton) all-terrain crane. Bill Okafor, the erection foreman for Northern Iron Erectors Ltd., watched two connectors, Jess Moreau and Tomas Vega, guide a 9 m (30 ft) column onto its anchor rods. Nora Whitehorse, a first-year apprentice ironworker, held the tag line. Owen Hartley, the Tallgrass safety coordinator, stood back by the gang box with the erection plan open on a tablet. For the next four months, this frame of columns, beams, joists and metal deck would be the most dangerous place on any Tallgrass site.

This course is about putting structures up safely: structural steel, precast concrete, tilt-up panels and mass timber. It follows the Prairie Gate Community Centre from the first column to the last deck sheet. The building has a steel-framed classroom and office wing with composite metal deck floors, a gymnasium with long-span steel joists and tilt-up concrete walls, precast concrete stairs and elevator shaft panels, and a library pavilion built from glued-laminated timber (glulam) columns and beams with cross-laminated timber (CLT) floor and roof panels. Each system brings its own hazards, but all of them share the same three: people fall, loads fall, and partly built structures fall down.

The three ways erection work kills

Erection is the stage of a building's life when it is weakest and when people work highest above the ground with the least around them. The permanent floors, walls and bracing that will one day make the structure stiff and stable are not there yet. Workers walk on beams 150 mm (6 in) wide, stand on decking that has not yet been fastened, and guide multi-tonne loads by hand. Three groups of hazards account for most of the deaths and serious injuries.

• Falls from height. Connectors at the top of columns, decking crews at the leading edge, welders and bolters on beams, and anyone walking on unprotected steel can fall. Falls are the leading cause of death among ironworkers.
• Struck by or crushed by loads. Members swinging from the crane, loads dropped when rigging fails or a hook latch is missing, members that roll or slide off a stack, and tools, bolts and offcuts dropped from above all strike workers below.
• Structural collapse. A partly built frame without its permanent bracing can buckle, tip or fall down, especially in wind, when a column is not anchored properly, when connections are left incomplete, or when too much material is landed in one place.

A fourth group, the health and environmental hazards, matters too: welding fume, noise, cold and heat, ultraviolet light from welding arcs, manual handling of heavy bolts and deck bundles, and fatigue on long shifts. These are covered alongside the tasks that create them in lessons 10 and 11.

What the numbers show

Structural iron and steel work is one of the most dangerous trades in North America. In the United States, the Bureau of Labor Statistics' census of fatal occupational injuries (CFOI) calculates a fatal injury rate for each occupation. For structural iron and steel workers, the rate was 26.3 deaths per 100,000 full-time-equivalent workers in 2019 and 32.5 in 2020, compared with about 3.5 for all US workers. That is roughly eight to ten times the average. Roofers are the only construction trade that has had a consistently higher rate.

Canada does not publish a national fatality rate by trade, and workers' compensation boards group ironworkers with other construction trades. The pattern in provincial investigation reports and safety association bulletins is the same as in the US data: falls from steel, decking and openings; workers struck by suspended loads or by members that shift or fall; and partial collapses during erection. Manitoba's workplace safety and health officers investigate serious incidents on steel erection sites in the same way as on any other construction site, and the Construction Safety Association of Manitoba publishes serious incident summaries that include falls from steel and dropped loads.

The high rates are not a reason to accept the risk. Most erection deaths follow patterns that are well known and preventable: a connector who was not tied off, decking that was not secured, a column with too few anchor rods, a beam released from the crane with only one bolt in, a load swung over workers, a frame left without bracing before a windstorm. The rest of this course works through those patterns one at a time.

Steel, precast and mass timber compared

The three structural systems on the Prairie Gate Community Centre share many hazards, but each has its own character.

Steel frames are assembled from many relatively light pieces, so there are many lifts, many connections and many people working at height for long periods. Precast and tilt-up concrete come in fewer, much heavier pieces, so each lift is high consequence and the work depends on lifting inserts, rigging and braces designed for each piece. Mass timber panels are large and relatively light for their size, so wind can catch them in the air, and the crews installing them work at panel edges with screws and connectors.

The rules that apply

In Manitoba, the Workplace Safety and Health Act and the Workplace Safety and Health Regulation (Man. Reg. 217/2006) apply to erection work as they do to all construction. The regulation does not have a single part devoted to steel erection. Instead, erection work is governed by the general duties of employers, prime contractors and supervisors, by Part 14 (Fall Protection), Part 23 (Cranes and Hoists) and the general duty and engineering provisions of the Workplace Safety and Health Regulation, and by the requirement to follow the design and instructions of the engineer where structures are under construction. The design standards matter too: CSA S16, the Canadian design standard for steel structures, whose erection clause covers erection loads, temporary bracing and erection tolerances, CSA W47.1, under which the Canadian Welding Bureau certifies companies and their welders and, for the library, CSA O86, the Canadian engineering design standard for wood. the National Building Code of Canada (NBC) as adopted in Manitoba decides how the finished building must perform, and the engineer of record's drawings set out what the structure needs before it can stand on its own.

Lesson 2 looks at who is responsible for what under these rules. For now, the point is that erection safety depends on people well away from the steel: the engineer who designs the structure and its temporary bracing, the fabricator who details the connections, the general contractor who prepares the site and coordinates the trades, and the erector who plans and carries out the work.

Who works on and around the frame

Owen listed every group that would work on or near the steel at the Prairie Gate Community Centre.

• Connectors, who work at the top of the frame bolting each member into place as it arrives from the crane. They spend more time at height on narrow steel than anyone else.
• The raising gang: the foreman, connectors, the signal person, the rigger who hooks on the loads on the ground and the tag line handlers.
• Bolting-up and detailing crews, who follow the connectors to install and tighten the remaining bolts.
• Decking crews, who spread and fasten the metal deck that becomes the floor and roof.
• Welders, who make field welds, attach shear studs and install deck fasteners and embedded plates.
• The crane operator, signal person and riggers.
• Precast and tilt-up crews from Plains Precast Ltd., and the mass timber crew from Boreal Timber Structures Ltd..
• Other trades that follow the erector up the building: concrete placers, plumbers, electricians and the curtain wall installers.
• Inspectors and engineers, including Helen Kowal from Morrow Structural Engineering Ltd., the engineer of record, and the special inspector who checks bolts and welds.
• The public walking past the site on the north and east streets.

Some of these people are experts at working on steel. Others, such as an electrician running conduit along a beam after the erectors have gone, may never have worked at height on a frame before. A good erection plan protects both.

How serious is each task?

Owen likes to rank the tasks before the work starts, using likelihood times severity, with an extra weight for how many people are exposed and how long they are exposed.

# Rough risk ranking of erection tasks at the Prairie Gate job (invented scores).
tasks = [
    # task, likelihood 1-5, severity 1-5, people exposed, hours per week at height
    ("Connecting beams at the second floor", 4, 5, 2, 30),
    ("Spreading deck at the leading edge", 4, 5, 3, 20),
    ("Setting tilt-up panels and braces", 2, 5, 5, 12),
    ("Landing deck bundles on joists", 3, 5, 2, 4),
    ("Bolting up from a lift", 2, 4, 2, 25),
    ("Setting CLT roof panels", 3, 5, 3, 10),
]
rows = []
for name, like, sev, people, hours in tasks:
    exposure = 1 + 0.1 * people + hours / 100
    rows.append((round(like * sev * exposure, 1), name))
for score, name in sorted(rows, reverse=True):
    print(f"{score:5.1f}  {name}")

 30.0  Spreading deck at the leading edge
 30.0  Connecting beams at the second floor
 21.0  Setting CLT roof panels
 18.6  Landing deck bundles on joists
 16.2  Setting tilt-up panels and braces
 11.6  Bolting up from a lift

The numbers are invented, but the order matched what Bill Okafor told Owen from twenty years in the trade: connecting and leading-edge decking were the jobs to watch most closely, and the tilt-up panel lifts were the ones where a single mistake could kill several people at once.