Cranes and Slings
Make sure the load is not too much for the capacity of the crane.
Crane Rated Capacity
One of the most serious hazards that cranes present is collapse of the equipment caused by exceeding the crane's rated capacity. The term "rated capacity" is defined as:
"the maximum working load permitted by the manufacturer under specified working conditions. Such working conditions typically include a specific combination of factors such as equipment
configuration, radii, boom length, and other parameters of use."
The combination of factors that determine rated capacity is set forth in a load chart that must be on the equipment. In general, the load chart states the weight of the load that the
crane can lift at different boom radii. The longer the radius at which the lift occurs, the smaller amount of weight the crane can lift.
Employees must not operate a crane in excess of its rated capacity. Because variable worksite conditions on worksites, such as swinging of the load caused by wind or other factors, the
capacity of the crane may be less than that which exists under ideal conditions.
To comply with the rated capacity, the weight of the load must be known. Before beginning a lift, the operator must determine the load weight by using a reliable means.
Follow all safety measures to prevent accidents.
Safety Measures for Crane Operation
Employers must permit only thoroughly trained and competent workers to operate cranes. Operators should know what they are lifting and what it weighs.
For example, the rated capacity of mobile cranes varies with the length of the boom and the boom radius. When a crane has a telescoping boom, a load may be safe to lift at a short boom length
or a short boom radius, but may overload the crane when the boom is extended and the radius increases.
To reduce the severity of an injury, employers must take the following precautions:
- Equip all cranes which have adjustable booms with boom angle indicators.
- Provide cranes with telescoping booms with some means to determine boom lengths unless the load rating is independent of the boom length.
- Post load rating charts in the cab of cab-operated cranes. (All cranes do not have uniform capacities for the same boom length and radius in all directions around the chassis of the vehicle.)
- Require workers to always check the crane's load chart to ensure the crane will not be overloaded by operating conditions.
- Instruct workers to plan lifts before starting them to ensure they are safe.
- Tell workers to take additional precautions and exercise extra care when operating around power lines.
- Teach workers outriggers on mobile cranes must rest on firm ground, on timbers, or be sufficiently cribbed to spread the weight of the crane and the load over a large enough area.
(Some mobile cranes cannot operate with outriggers in the traveling position.)
- Direct workers to always keep hoisting chains and ropes free of kinks or twists and never wrapped around a load.
- Train workers to attach loads to the load hook by slings, fixtures, and other devices which have the capacity to support the load on the hook.
- Instruct workers to pad sharp edges of loads to prevent cutting slings.
- Teach workers to maintain proper sling angles so slings are not loaded in excess of their capacity.
- Ensure all cranes are inspected frequently by persons thoroughly familiar with the crane, the methods of inspecting the crane, and what can make the crane unserviceable.
Crane activity, the severity of use, and environmental conditions should determine inspection schedules.
- Ensure the critical parts of a crane—such as crane operating mechanisms, hooks, air, or hydraulic system components and other load-carrying components are inspected daily for
any maladjustment, deterioration, leakage, deformation, or other damage.
Keeping Clear of the Load
Be careful to stay clear of the load.
OSHA regulation 1926.1425 seeks to protect
employees against being struck by a moving or falling load.
Safe Hoisting Routes
Where available, hoisting routes that minimize the exposure of employees to hoisted loads must be used, to the extent consistent with public safety.
Stationary Suspended Load
While the operator is not moving a suspended load, no employee may be within the fall zone, except for employees:
- engaged in hooking, unhooking, or guiding the load;
- engaged in the initial attachment of the load to a component or structure; or
- operating a concrete hopper or concrete bucket.
Hooking, Unhooking, or Guiding the Load
When employees in the fall zone are engaged in hooking, unhooking, or guiding the load, or are connecting a load to a component or structure, all of the following criteria must be met:
- The materials being hoisted must be rigged to prevent unintentional displacement.
- Hooks with self-closing latches or their equivalent must be used. Exception: "J" hooks may be used for setting wooden trusses so that a worker need not go onto the truss to open the hook.
- The materials must be rigged by a qualified rigger.
Receiving a Load
Only employees needed to receive a load are permitted to be within the fall zone when a load is being landed.
Operators must be fully attentive while operating the crane.
The operator must not engage in any practice or activity that diverts their attention while engaged in operating the equipment, such as the use of a cell phone (except when
used for signal communications).
Operator Responsibility While the Load is Suspended
The operator must not leave the controls while the load is suspended except where ALL of the following criteria are met:
- The operator remains adjacent to the equipment and is not engaged in any activities that take attention away from his or her duties.
- The load is to be held suspended for a period of time exceeding normal lifting operations.
- The competent person determines that it is safe to do so and implements measures necessary to restrain the boom hoist and telescoping, load, swing, and outrigger or stabilizer functions.
- Barricades or caution lines and notices are erected to prevent all employees from entering the fall zone. No employees are permitted in the fall zone.
The four criteria immediately above do not apply to working gear (such as slings, spreader bars, ladders, and welding machines) where:
- the weight of the working gear is negligible relative to the lifting capacity of the equipment as positioned, and
- the working gear is suspended over an area other than an entrance or exit.
Cranes cannot travel with load if prohibited by manufacturer.
The operator must test the brakes each time a load that is 90% or more of the maximum line pull. The test is handled by lifting the load a few inches and applying the brakes.
In duty cycle and repetitive lifts where each lift is 90% or more of the maximum line pull, this requirement applies to the first lift but not to successive lifts.
Protection Against Rope Detachment
To prevent rope from becoming detached from a drum, neither the load nor the boom must be lowered below the point where less than two full wraps of rope remain on their respective drums.
Traveling with a Load
Traveling with a load is prohibited if the practice is prohibited by the manufacturer. Where it is not prohibited, you must take precautions to prevent hazardous movement of the load
and avoid excessive movement of the load that could overload the crane.
Authority to Stop Operation
OSHA regulation 1926.1418 provides that,
whenever there is a concern about safety, the operator must have the authority to stop and refuse to handle loads until a qualified person has determined
that safety has been assured.
Worker using signals to direct crane operator.
A crane operator often needs a second set of eyes - a signal person - to be able to operate safely. A signal person that uses hand, voice, or audible (bells, whistles, horn, etc.)
signals must be provided:
- when the point of operation, meaning the path the load travels or the area where the load is placed, is not in full view of the operator;
- when the equipment is traveling and the operator's view in the direction of travel is obstructed; or
- when, due to site-specific safety concerns, either the operator or the person handling the load determines that it is necessary.
During operations requiring signals, the ability to transmit signals between the operator and signal person must be maintained. If that ability is interrupted at any time, the operator
must safely stop operations until signal transmission is reestablished and a proper signal is given and understood.
Only one person may give signals to a crane/derrick at a time, though any person may give an emergency stop signal.
Work Area Control
OSHA regulation 1926.1424 is designed to
protect employees who work near a crane from being struck or crushed by the crane's rotating superstructure. To prevent employees from entering an area where
they could be struck/crushed, you must:
- Train each employee assigned to work on or near the equipment in how to recognize struck-by and pinch/crush hazard areas posed by the rotating superstructure.
- Erect and maintain control lines, warning lines, railings, or similar barriers to mark the boundaries of the hazard areas.
- Exception: When you can demonstrate that it is neither feasible to erect such barriers on the ground nor on the equipment, the hazard areas must be clearly marked by a
combination of warning signs (such as "Danger – Swing/Crush Zone") and high visibility markings on the equipment that identify the hazard areas. In addition, you must train each employee to
understand what these markings signify.
Before an employee goes to a location in the hazard area that is out of view of the operator, the employee (or someone instructed by the employee) must ensure the operator is informed
he/she is going to that location.
Where the operator knows an employee went to such a location, the operator must not rotate the superstructure until the operator is informed in accord with
a pre-arranged system of communication the employee is in a safe position.
Sling attached to blade during a hoist to nacelle.
The dominant characteristics of a sling are determined by the components of that sling. For example, the strengths and weaknesses of a wire rope sling are essentially the same as the
strengths and weaknesses of the wire rope of which it is made.
Slings are generally one of the following types:
- Chains. Chains are commonly used because of their strength and ability to adapt to the shape of the load. Care should be taken, however, when using alloy chain
slings because sudden shocks will damage them. Misuse of chain slings could damage the sling, resulting in sling failure and possible injury to an employee.
- Wire Rope. A second type of sling is made of wire rope. Wire rope is composed of individual wires that have been twisted to form strands. Strands are then twisted
to form a wire rope. When wire rope has a fiber core, it is usually more flexible but is less resistant to environmental damage. Conversely, a core that is made of a wire rope strand
tends to have greater strength and is more resistant to heat damage.
- Metal Mesh. Metal mesh slings are widely used in metalworking and in other industries where loads are abrasive, hot, or will tend to cut web slings. Unlike nylon
and wire rope slings, metal mesh slings resist abrasion and cutting. Metal mesh slings grip the load firmly without extensive stretching, easily maintaining balanced loads.
- Fiber Rope and Synthetic Web. Fiber rope and synthetic web slings are used primarily for temporary work, such as construction and painting jobs, and in marine
operations. They also are the best choice for use on expensive loads, highly finished parts, fragile parts, and delicate equipment.
- Fiber Rope Slings. Fiber rope deteriorates on contact with acids and caustics. Fiber ropes slings, therefore, must not be used around these substances unless the
manufacturer recommends them for that use.
- Synthetic Rope and Web Slings. The most commonly used synthetic web slings are made of nylon, polypropylene, and polyester. Because each synthetic material has
unique properties, it should be used according to the manufacturer's instructions, especially when dealing with chemically active environments.
Study the lift before you make it.
Safe Lifting Practices
Slings should be selected based upon the characteristics of the load and the environmental conditions surrounding the lift. Be sure to inspect slings prior to each use and that you
know how to use it safely. There are four primary factors to consider when safely lifting a load. They are:
- the size, weight, and center of gravity of the load;
- the number of legs and the angle the sling makes with the horizontal line;
- the rated capacity of the sling; and
- the history of the care and usage of the sling.
Size, Weight, and Center of Gravity of the Load
The center of gravity of an object is that point at which the entire weight may be considered as concentrated. To make a level lift, the crane hook must be directly above this point.
While slight variations are usually permissible, if the crane hook is too far to one side of the center of gravity, dangerous tilting will result causing unequal stresses in the different
sling legs. This imbalance must be compensated for at once.
Number of Legs and Angle with the Horizontal
As the angle formed by the sling leg and the horizontal line decreases, the rated capacity of the sling also decreases. In other words, the smaller the angle between the sling leg and the
horizontal, the greater the stress on the sling leg and the smaller (lighter) the load the sling can safely support. Larger (heavier) loads can be safely moved if the weight of the load is
distributed among more sling legs.
Rated Capacity of the Sling
The rated capacity of a sling varies depending upon the type of sling, the size of the sling, and the type of hitch. Operators must know the capacity of the sling. Charts or tables that
contain this information generally are available from sling manufacturers. The values given are for new slings. Older slings must be used with additional caution. Under no circumstances shall
a sling's rated capacity be exceeded.
History of Care and Usage
Mishandling and misusing slings are the leading cause of sling-related accidents. Most injuries and accidents, however, can be avoided by becoming familiar with the essentials of proper
sling care and use. Be sure to check this history of the sling to be used and that it has passed inspections.
Care and Use of Slings
Checking a sling attached to a spreader bar.
Proper care and use are essential for maximum service and safety. Slings must be protected with cover saddles, burlap padding, or wood blocking as well as from unsafe lifting procedures
such as overloading to prevent sharp bends and cutting edges. Follow these safe practices when working with slings:
- Before making a lift, check to be certain that the sling is properly secured around the load and that the weight and balance of the load have been accurately determined.
- If the load is on the ground, do not allow the load to drag along the ground. This could damage the sling. If the load is already resting on the sling, ensure that there is no sling
damage prior to making the lift.
- Next, position the hook directly over the load's center of gravity and seat the sling squarely within the hook bowl. This gives the operator maximum lifting efficiency without bending
the hook or overstressing the sling.
- Wire rope slings also are subject to damage resulting from contact with sharp edges of the loads being lifted. These edges can be blocked or padded to minimize damage to the sling.
After the sling is properly attached to the load, there are a number of good lifting techniques that are common to all slings.
- Make sure that the load is not lagged, clamped, or bolted to the floor.
- Guard against shock loading by taking up the slack in the sling slowly. Apply power cautiously to prevent jerking at the beginning of the lift, and slowly accelerate or decelerate.
- Check the tension on the sling. Raise the load a few inches, stop, and check for proper balance and that all items are clear of the path of travel. Never allow anyone to ride on the
hood or load.
- Keep all personnel clear while the load is being raised, moved, or lowered. Crane or hoist operators should watch the load at all times when it is in motion.
- Obey the following "Nevers."
- Never allow more than one person to control a lift or give signals to a crane or hoist operator except to warn of a hazardous situation.
- Never raise the load more than necessary.
- Never leave the load suspended in the air. And never work under a suspended load or allow anyone else to.
Once the lift has been completed, clean the sling, check it for damage, and store it in a clean, dry airy place. It is best to hang it on a rack or wall.
Remember, damaged slings cannot lift as much weight as new or older well-cared for slings. Proper and safe use and storage of slings will increase their service life.
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