Cranes and hoists: types and uses

The word crane covers machines that range from a 500 kg electric chain hoist on a monorail to a crawler crane that can lift more than 1,000 tonnes. They share the same basic job, raising and moving a suspended load, but they fail in different ways and need different controls. A supervisor who can tell a rough terrain crane from an all terrain crane, or a hammerhead tower crane from a luffing jib, can ask better questions about setup, ground, wind and exclusion zones.

This lesson surveys the main families of lifting equipment, what each is used for, the hazards typical of each, and the safety devices you should expect to find. Choosing the right crane for a project is a planning and engineering task covered in CON-250; here the focus is on recognizing equipment and its risks.

Mobile cranes

Mobile cranes travel to the job and set up on outriggers or tracks. They are the most common cranes on construction sites and the type most often involved in overturning incidents, because their stability depends entirely on correct setup and firm ground.

• Telescopic hydraulic cranes have a boom made of nested sections that extend by hydraulic cylinders. Rough terrain cranes have large tires and a single cab and work on unpaved sites. All terrain cranes can travel on highways and work off-road. Truck-mounted cranes and boom trucks combine a crane with a commercial truck chassis.
• Industrial and carry deck cranes are small, manoeuvrable cranes used in plants and refineries. Some can pick and carry a load, which brings special limits on travel speed and ground slope.
• Lattice boom cranes use a boom built from steel sections pinned together. Crawler cranes run on tracks and can travel with a load if the manufacturer allows it. Lattice cranes are assembled on site, which brings the hazards of assembly and disassembly: workers on or under booms, pins under load and heavy components.

Mobile cranes are rated by their maximum capacity at the shortest radius, which can be misleading. A crane described as a 100-tonne machine may lift only a few tonnes at long radius with the boom fully extended. The load chart, covered in Lesson 4, is what matters.

Articulating boom cranes

Articulating or knuckle boom cranes fold like an arm. They are usually mounted behind the cab of a truck and are used to deliver building materials, drywall, steel and equipment. They are compact and versatile, but operators often work from a remote control while standing close to the load, and the boom can move quickly in ways that are hard to predict from the ground. Outrigger setup on sidewalks and residential driveways is a frequent weak point, and their use near overhead lines along streets is a recurring cause of electrocutions.

In Canada, CSA Z150.3 covers articulating boom cranes; in the United States, ASME B30.22 does.

Tower cranes

Tower cranes are fixed to a foundation or a building structure and can lift heavy loads high and at long radius for months or years. Their main hazards come from erection, climbing and dismantling, from wind, and from overlapping work areas when several tower cranes share a site.

• Hammerhead and flat-top tower cranes have a horizontal jib with a trolley that moves the hook in and out. They need clear airspace because the jib and counter-jib sweep a full circle.
• Luffing jib tower cranes raise and lower their jib to change radius. They suit congested city sites where the jib cannot swing over neighbouring properties.
• Self-erecting tower cranes fold for transport and unfold on site. They are common on mid-rise residential projects and need careful ground preparation and ballast.

Tower cranes have overload limiters that prevent the hoist from lifting more than the rated load and moment limiters that stop the trolley from moving out with a load that is too heavy for that radius. They usually carry an anemometer, and the manufacturer sets the wind speeds at which operation must stop and the crane must be left to weathervane, free to rotate with the wind.

Overhead and gantry cranes

Overhead cranes run on rails along fixed runways inside plants, warehouses, steel mills and power stations. A bridge spans the runway and carries a trolley and hoist. Gantry cranes stand on legs that run on rails at floor level, and semi-gantry cranes have one leg on the floor and one end on an elevated runway. Jib cranes swing a horizontal arm from a column or wall, and monorails carry a hoist along a single beam.

Overhead cranes are often run by plant workers from a pendant or wireless remote rather than by a dedicated operator. That convenience is also their main weakness: people who use them occasionally may not inspect them, may side-pull loads or may walk the load over coworkers. Typical incidents involve dropped loads, hands crushed during rigging, loads swinging into people, and maintenance workers on runways struck by moving bridges.

Hoists

A hoist is the lifting mechanism itself: a drum and wire rope, or a sprocket and load chain, driven by an electric motor, compressed air or hand. Hoists are mounted on overhead cranes, monorails and jibs, and are also hung temporarily from beams or lifting points for maintenance work.

• Electric chain hoists and wire rope hoists are used for repeated lifts in plants and for rigging in theatres and arenas.
• Manual chain hoists, also called chain falls, lift by pulling a hand chain.
• Lever hoists, sometimes called come-alongs, lift or pull by working a lever and are used for positioning and tensioning.

A hoist is only as strong as what it hangs from. A 2-tonne chain fall hung from a pipe rack, a roof truss or a beam clamp that was never checked can bring the whole support down. Temporary lifting points need a known rating, from the building's structural drawings, an engineer or a manufactured and marked anchor.

Derricks and hoists for materials and people

Derricks are masts or booms guyed or braced to a structure and operated by a separate hoist. They are less common today but still used for steel erection on tall buildings and in some industrial settings. Material hoists carry materials up a building on a platform that runs on a mast, and personnel hoists, also called construction elevators, carry workers. Riding a material hoist is prohibited, and personnel hoists need their own inspections and interlocks. Lifting people with a crane in a suspended platform is allowed only when no safer method is practical and only with an engineered platform, a trial lift and a written plan.

Other machines used as cranes

Excavators, backhoes, telehandlers, loaders and forklifts are often used to lift suspended loads with a hook or a jib attachment. When they are, they become lifting equipment and the rigging rules apply. The machine must have a rated capacity for the configuration, ideally a lifting chart from the manufacturer, a proper attachment point such as a rated hook on the bucket linkage, and an operator trained in lifting with it.

Ontario's Ministry of Labour has said that excavators and similar machines used to hoist are not cranes for the certificate requirement, but sections 93 to 96, 102, 103, 150(2) and (3), 156, 168 to 172, 175 and 179 of O. Reg. 213/91 still apply. Telehandlers with suspended loads are covered in HSE-218.

Safety devices to look for

Modern cranes carry several devices that protect against the most common failures. They are aids, not substitutes for planning, and none of them should ever be bypassed.

Remote controls and pendants

More cranes and hoists are now operated by wireless remote controls. They let the operator stand where they can see the load, which can improve safety, but they also tempt operators to stand too close to the load or under it. Remotes must have a working emergency stop, must be paired only with the intended crane, and must be stored so that nobody can pick one up and move the wrong crane. Pendants should hang where the operator can stand clear of the load, and their buttons should be clearly labelled with directions that match marks on the crane.