Concrete and masonry work: the hazards and who controls them

Concrete and masonry are the bones of most buildings. On Cottonwood Place, the eight-storey mixed-use building that Tallgrass Construction is putting up in Winnipeg, Manitoba, almost everything that holds the building up is concrete: the footings and foundation walls, the underground parking level, the columns, the flat slabs of every floor, the stair and elevator cores, and the block walls of the ground-floor service corridor. Concrete work looks simple from the street. A truck arrives, concrete goes into a form, and a few days later there is a floor. Up close it is one of the most hazardous kinds of construction work, because it combines heavy temporary structures, large loads lifted by crane, pressurized equipment, sharp steel, caustic materials and dust that can scar the lungs.

This course follows the concrete and masonry work at Cottonwood Place from the first formwork drawings to the last block wall. It builds on HSE-370 Construction Site Safety Essentials, which introduced the site, its people and the hazards that injure construction workers most often. This first lesson maps the work, the hazards it creates, the rules that apply and the people who control them.

The work: from drawings to a finished floor

A cast-in-place concrete floor goes through the same cycle at every level, usually in a week or two per floor on a building this size. Each step brings its own hazards.

• Formwork and shoring. Carpenters build the temporary moulds, called forms, that give the concrete its shape, and the shoring that holds the forms up until the concrete can carry itself. On Cottonwood Place, Redline Forming Ltd. uses aluminum beam-and-panel slab forms on adjustable steel shores, and gang forms lifted by the tower crane for the core walls.
• Reinforcing steel. Ironworkers from Ironside Rebar Ltd. place and tie the reinforcing bars, called rebar, that give concrete its tensile strength. Bundles of rebar arrive by truck and are lifted to each floor by crane.
• Embedded services. Electricians and plumbers place conduit, sleeves and boxes in the forms before the pour.
• Placing concrete. Ready-mix trucks from Assiniboine Ready-Mix deliver the concrete, and a boom pump from Tri-City Pumping Ltd. places it in the forms. Smaller pours use a crane and bucket.
• Finishing and curing. Finishers screed, float and trowel the slab, often with ride-on or walk-behind power trowels, and the concrete is kept moist and warm while it gains strength.
• Stripping and reshoring. Once the concrete is strong enough, the forms are stripped and moved up to the next floor, and reshores are installed to share the load of the floors above.
• Cutting and coring. Later, trades saw-cut control joints and core holes for pipes and ducts.

Masonry work runs alongside the concrete frame. Reyes Masonry Ltd. builds concrete block walls around the parking-level stairs and the ground-floor service corridor, including a tall block wall along the west property line beside the occupied office building next door.

What goes wrong

The hazards of concrete and masonry work fall into a few groups. Each later lesson covers one of them in depth.

Collapse of formwork, shoring and walls

The most catastrophic concrete incidents are collapses. Wet concrete is heavy, about 2,400 kg/m³ (150 lb/ft³), and it pushes sideways on wall forms like a liquid. A 200 mm (8 in) slab weighs about 4.7 kPa (98 psf) before anyone adds workers, equipment or the forms themselves. When shoring is undersized, missing, set on soft ground, removed too early or overloaded, a whole floor can come down in seconds, taking workers with it and sometimes dropping onto the floor below. Masonry walls under construction collapse too, usually in wind, because fresh mortar has almost no strength and a tall, unbraced wall acts like a sail. Lessons 2, 3, 4 and 10 cover these hazards.

Struck-by and caught-between

Concrete work involves heavy lifts and moving equipment: bundles of rebar and gang forms on the crane hook, concrete buckets, ready-mix trucks reversing to the pump, pump booms moving overhead, and power trowels spinning at the operator's feet. Workers are struck by loads, crushed between forms and structure, run over by trucks and hit by pump hoses that whip when a blockage clears. Lessons 6, 7 and 9 cover these.

Falls

Formwork crews work at the open edges of slabs and on top of wall forms long before guardrails are permanent. Ironworkers walk on rebar mats. Masons work from scaffolds that are raised as the wall goes up. Falls are a constant hazard, and they overlap with a hazard unique to concrete work: falling onto protruding rebar. Lessons 4, 5 and 11 cover falls in concrete and masonry work.

Impalement and cuts

Vertical rebar sticking up from walls, columns and footings can impale a worker who falls or trips onto it. Even a low dowel can cause a serious injury. Rebar ends, tie wire and form hardware also cause cuts and puncture wounds. Lesson 5 covers impalement protection.

Health hazards

Wet cement is strongly alkaline and causes chemical burns and dermatitis. Cutting, grinding, drilling and chipping concrete and masonry release respirable crystalline silica, which causes silicosis and lung cancer. Concrete work is also loud, heavy and repetitive: lifting block, placing rebar and kneeling on slabs injure backs, shoulders and knees. Lessons 8, 11 and 12 cover these hazards.

The rules that apply

In Manitoba, the Workplace Safety and Health Act sets the general duties of everyone on the site, and the Workplace Safety and Health Regulation (Man. Reg. 217/2006) sets specific requirements. The regulation has requirements for formwork, falsework and reshoring, for concrete equipment such as pumps and buckets, and for work near protruding reinforcing steel, along with the general rules on fall protection, cranes, hazardous products, noise and silica that apply to all construction. It relies on recognized standards for technical detail. The most important for this course is CSA S269.1, the Canadian standard for falsework and formwork, which covers the design, construction, inspection and removal of temporary structures that support concrete. Concrete pumps and placing booms are covered by CSA Z151, the Canadian standard for concrete pumps and placing booms, and masonry construction by CSA A371. Where the regulation requires a professional engineer to design or approve temporary works, that engineer must be licensed in Manitoba.

Who controls the hazards

Concrete and masonry work at Cottonwood Place involves at least six employers on any given pour day: Tallgrass as the prime contractor, the forming contractor, the rebar contractor, the pumping contractor, the ready-mix supplier and the finishing crew, often with the electrical and mechanical trades still working in the forms. Each has a part to play.

• The engineer of record designs the permanent structure and specifies the concrete strength, the reinforcing and, often, the minimum strength before forms can be stripped.
• The formwork engineer designs the formwork, shoring and reshoring, and produces the drawings that show shore spacing, beam sizes, loads and the stripping sequence. The forming contractor hires this engineer.
• The forming contractor builds the forms to the drawings, inspects them and strips them when the strength is confirmed.
• The rebar contractor places and ties the steel, supports vertical bars against collapse and installs impalement protection.
• The pump operator sets up and runs the concrete pump and is responsible for its outriggers, boom and lines.
• The ready-mix driver delivers the concrete and follows the site's traffic plan.
• The masonry contractor builds and braces the block walls and sets up the restricted zone around them.
• Tallgrass as prime contractor coordinates all of them: it schedules the pours, sets the site rules, keeps workers clear of crane and pump zones, and checks that each contractor is doing its part. Superintendent Carla Mendes signs off each pour only after the formwork contractor confirms the forms and shores have been inspected.

A day on a pour

On the morning of the level 3 slab pour, Dev Sandhu, the new general labourer who started on site a month ago, arrives at 6:30. The pump truck is already setting up on the street, with its outriggers on cribbing pads and cones around it. Lena Petrov from the forming crew and her foreman are walking the deck one last time with the shoring drawings, checking that every shore is plumb, every head is snug against its beam and no shore has been knocked out by the trades that worked under the deck yesterday. An ironworker is checking that every vertical column dowel has a cap. Owen Hartley, the safety coordinator, checks that the floor edges have guardrails and that the exclusion zone under the pump boom is taped off.

At 7:00, the pour crew gathers for a pre-task briefing. Carla Mendes covers the pour sequence, the signals between the hose operator and the pump operator, the route the ready-mix trucks will take and where the spotter will stand. She reminds everyone of one rule: nobody goes under the deck while concrete is being placed except the two shoring watchers named on the plan, who are there to look for movement and call a stop. The first truck backs up to the pump at 7:20.

Most pours go exactly like this one. The risks are controlled by planning done days before and a few minutes of checking on the morning. The rest of this course explains why each of those checks matters.

A simple hazard map for a pour day

Tallgrass keeps a simple hazard map for every pour, listing each activity and the controls that must be in place before work starts. Owen uses a short program to print the checklist for the morning briefing and to flag any activity without a named person responsible.

# Pour-day hazard map for the level 3 slab (invented data).
pour = [
    # (activity, main hazard, control, responsible)
    ("Shoring check", "collapse", "walk deck with drawings, sign inspection record", "Redline forming foreman"),
    ("Dowel caps", "impalement", "cap every exposed vertical bar", "Ironside rebar foreman"),
    ("Pump setup", "tip-over, power lines", "outrigger pads, 'line clear' check", "Tri-City pump operator"),
    ("Truck backing", "struck-by", "spotter at pump hopper", "Tallgrass spotter"),
    ("Hose handling", "hose whip", "two-person hose crew, no kinks", "Finishing foreman"),
    ("Under-deck watch", "collapse", "two named shore watchers only", ""),
]
missing = 0
for act, hazard, control, who in pour:
    flag = "" if who else "  <-- NO ONE NAMED"
    missing += not who
    print(f"{act:16} | {hazard:22} | {control}{flag}")
print(f"\nActivities without a responsible person: {missing}")

Shoring check    | collapse               | walk deck with drawings, sign inspection record
Dowel caps       | impalement             | cap every exposed vertical bar
Pump setup       | tip-over, power lines  | outrigger pads, 'line clear' check
Truck backing    | struck-by              | spotter at pump hopper
Hose handling    | hose whip              | two-person hose crew, no kinks
Under-deck watch | collapse               | two named shore watchers only  <-- NO ONE NAMED

Activities without a responsible person: 1

The printout shows one gap: no one is named for the under-deck watch. Owen asks Lena's foreman to name two carpenters before the briefing. A missing name on a list is a small thing, but on pour day it is exactly the kind of gap that lets a shore move without anyone seeing it.