Cranes, hoisting and working near loads

On a building like Cottonwood Place, the tower crane is the centre of the site. It lifts rebar, formwork, concrete buckets, steel, mechanical units and bins of waste, hundreds of times a day, over the heads of workers on every floor. Most workers will never operate or rig for a crane, but nearly every worker will work near one. The hazards for them are a load or part of a load falling, a load swinging into them, being crushed between a load or a counterweight and a structure, and a crane contacting a power line or tipping over. This lesson explains how lifting is organized on a site, the roles of the people involved and the rules every worker follows around cranes, hoists and other lifting equipment. TRD-105 covers rigging and hoisting for the trades in depth, and HSE-374 covers steel erection.

Lifting equipment on a construction site

Cottonwood Place uses several kinds of lifting equipment, each with its own hazards:

• The tower crane stands on a concrete base inside the building footprint and lifts loads up to the top floor and across the whole site. Its operator works in a cab at the top of the mast or by remote control.
• Mobile cranes are brought in for heavy lifts, such as setting the rooftop mechanical units, and for erecting and dismantling the tower crane. They stand on outriggers on mats or cribbing, and their counterweights swing as they rotate.
• Telehandlers, also called rough-terrain forklifts, carry pallets around the laydown area and lift materials onto the lower floors. With a jib or hook attachment, a telehandler becomes a crane and must be used as one.
• The construction hoist, a temporary elevator on the outside of the building, carries workers and materials between floors.
• Small hoists, such as chain hoists and material hoists, lift loads within the floors.

The people involved in a lift

Every lift involves several people, and each has a defined job. Most crane incidents come from confusion about who is responsible for what, or from someone taking on a role they are not trained for.

Crane operators in Manitoba must be trained and hold the certification the provincial rules require for the type of crane they operate, and employers must make sure that riggers and signallers are competent for the work. the Workplace Safety and Health Regulation (Man. Reg. 217/2006) also requires cranes to be inspected and maintained to the manufacturer's requirements and the applicable CSA standards, with a logbook kept for each crane.

Only one person signals the operator at a time, so the operator never receives conflicting instructions. There is one exception: anyone who sees danger can give the emergency stop signal, both arms extended with palms down, moved back and forth, or the emergency stop word over the radio, and the operator stops immediately.

Planning lifts

Every lift is planned, even if the plan is short. For routine lifts, such as bundles of rebar or bins of form material, the plan is part of the daily lift schedule and the rigger's pre-lift check: the load weight, the rigging, the path and the landing area. For lifts that are heavier, more complex or more dangerous, Tallgrass Construction Ltd. requires a written critical lift plan approved before the lift. At Cottonwood Place, a lift is treated as critical if it is more than 75 percent of the crane's rated capacity at that radius, involves two cranes, lifts over the occupied office building or the street, lifts workers, or lifts an unusual load such as a mechanical unit with an uneven centre of gravity.

A critical lift plan names the people involved, describes the load and its weight and centre of gravity, the rigging and its capacity, the crane configuration and its capacity at every radius along the path, the ground conditions and outrigger setup for a mobile crane, the power lines and obstructions, the weather limits, the area to be cleared and barricaded, and the communication method. Everyone involved attends a briefing before the lift.

Rules for workers near cranes

The rules that keep workers safe around a crane come down to staying out of the places where a load or part of the crane could hit or crush them.

• Never stand or walk under a suspended load. Loads are moved so that they do not pass over workers, and workers stay out of the path of a load being moved. If a load must pass over a work area, the area is cleared first.
• Stay out of the swing radius. The counterweight of a mobile crane swings out behind the machine as it rotates and can crush a worker against another object. The swing area is barricaded.
• Use tag lines to control a load, not your hands. A tag line is a rope tied to the load that lets a worker guide and stop its rotation from a safe distance. Workers do not grab or push suspended loads, and they never put themselves between a load and a fixed object.
• Wait until the load is lowered and stable before approaching to land it or unhook it, and do not unhook until the load is blocked or set so it cannot roll or tip.
• Keep the landing area clear, with enough room for the load and for workers to stand clear while it settles.
• Follow the signaller. When the signaller tells workers to clear an area, they clear it.
• Do not ride a load or a hook. Workers are lifted only in an approved personnel basket under a specific plan.

Things that make loads fall or cranes fail

Most crane incidents have causes that can be seen in advance:

• Overloading, from underestimating the weight of a load or lifting at a longer radius than planned. A crane's capacity drops sharply as the radius increases.
• Rigging failures, from damaged slings, the wrong hitch, sharp edges cutting slings, sling angles that are too flat, or loads that are not balanced. Loose material, such as short pieces of pipe or bundles that are not tied, can slip out of the rigging.
• Ground failures under a mobile crane's outriggers, especially on backfill, near excavations or over buried services.
• Wind, which pushes on large loads such as formwork panels and on the crane itself. Each crane has a wind limit from its manufacturer, and large flat loads may have to stop at much lower wind speeds.
• Contact with power lines, covered in lesson 7.
• Two-blocking, when the hook block is pulled into the boom tip and the load line breaks; anti-two-block devices prevent it.

Ray Lindqvist checks the wind speed shown in his cab before every lift of a large panel and at regular intervals through the day. When the wind approaches the limit, he stops lifting large loads first, then all loads, and the crane is left free to turn with the wind, as the manufacturer requires, so the wind cannot push against a locked jib.

The construction hoist

The construction hoist carries workers and materials between floors. It is a machine, not a lift you push a button for and forget. At Cottonwood Place, the hoist is run by a trained hoist operator. Its capacity is posted on the car and is never exceeded. The landing gates on each floor stay closed unless the car is at that floor, and the hoist cannot move with a gate open. Workers do not lean out of the car or reach through the gates, and long materials are secured so they cannot stick out of the car. The hoist is inspected daily by the operator and on a regular schedule by a qualified person, and it is never used as an emergency exit.

Telehandlers and forklifts used for lifting

A telehandler with a boom extended has a lifting capacity that depends on the boom angle and extension, shown on its load chart. Operators must be trained and authorized on the machine they use, wear a seatbelt, keep loads low while travelling, and never travel with the boom raised or extended. When a telehandler is fitted with a hook or jib to lift a suspended load, it is being used as a crane and the crane rules apply: a rigger, a signaller, a clear area and no one under the load.

How close to capacity is the lift?

Before each lift, the rigger and the operator compare the load with the crane's rated capacity at the radius where the load will be picked up and set down. The program below runs that check for a few lifts in the Cottonwood Place schedule, using an invented, simplified load chart, and flags lifts that are critical under the site rule of more than 75 percent of capacity.

# Lift check against a simplified, invented tower crane load chart (tonnes at radius in metres).
chart = {20: 8.0, 30: 5.4, 40: 3.9, 50: 2.9, 60: 2.2}

def capacity(radius):
    # use the chart value for the next larger radius listed (conservative)
    return chart[min(r for r in chart if r >= radius)]

lifts = [  # (description, load in tonnes including rigging, radius in m, over occupied area?)
    ("Rebar bundle to level 5", 2.1, 34, False),
    ("Formwork table, north face", 3.4, 44, False),
    ("Concrete bucket, full", 3.9, 28, False),
    ("Mechanical unit to roof", 2.0, 58, True),
]
for desc, load, radius, occupied in lifts:
    cap = capacity(radius)
    pct = load / cap * 100
    critical = pct > 75 or occupied
    status = "OVER CAPACITY" if pct > 100 else ("CRITICAL LIFT PLAN" if critical else "routine")
    print(f"{desc:28} {load:.1f} t at {radius} m: {pct:5.1f}% of {cap} t -> {status}")

Rebar bundle to level 5      2.1 t at 34 m:  53.8% of 3.9 t -> routine
Formwork table, north face   3.4 t at 44 m: 117.2% of 2.9 t -> OVER CAPACITY
Concrete bucket, full        3.9 t at 28 m:  72.2% of 5.4 t -> routine
Mechanical unit to roof      2.0 t at 58 m:  90.9% of 2.2 t -> CRITICAL LIFT PLAN

The formwork table is over capacity at the planned radius, so it must be picked up closer to the mast or split into smaller pieces. The mechanical unit is within capacity, but it is lifted over the occupied office building and is close to the limit, so it needs a critical lift plan. The rebar bundle and concrete bucket are routine lifts, although the concrete bucket is close to the 75 percent threshold, which is a reminder that the load weight must include the rigging and the bucket, not only the concrete.