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SECTION B15: HOISTING AND RIGGING
SAFETY
Introduction
The ability to safely move materials from one location to another is
a vital part of many activities at Princeton. Hoists are often
used when materials are too heavy or bulky to be safely moved manually.
Because hoists rely upon slings to hold their suspended loads, slings
are the most commonly used materials-handling apparatus.
In part because of the complex nature of the seemingly simple task
of lifting an object, an effective program is necessary to lift and
move heavy loads safely.
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Scope and Application
The Occupational Safety and Health Administration (OSHA) requirements
for hoisting and sling safety are described in this section and apply
to all departments where hoisting techniques are used.
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Program Description
Selection, Use and Inspection of Slings
Workers involved in hoisting and rigging must exercise care when
selecting and using slings. The selection of slings should be
based upon the size and type of the load, and the environmental conditions
of the workplace. Slings should be visually inspected before
each use to ensure their effectiveness. Improper use of hoisting
equipment, including slings, may result in overloading, excessive
speed (e.g., taking up slack with a sudden jerk, shock loading), or
sudden acceleration or deceleration of equipment.
There are generally six types of slings: chain, wire rope, metal
mesh, natural fiber rope, synthetic fiber rope, or synthetic web.
Slings tend to be placed into three groups: chain, wire rope and mesh,
and fiber rope web. Each type has its own particular advantages
and disadvantages. Factors to consider when choosing the best
sling for the job include size, weight, shape, temperature, and sensitivity
of the material being moved, and the environmental conditions under
which the sling will be used. The following guide may be useful
in selecting the appropriate sling:
Chains
Alloy steel chains are strong and able to adapt to the shape of the
load. Care should be taken when using chain slings because sudden
shocks will damage them. This may result in sling failure and
possible injury to workers or damage to the load.
Chain slings must be visually inspected prior to use. During
the inspection, pay particular attention to any stretching, nicks,
gouges, and wear in excess of the allowances made by the manufacturer.
These signs indicate that the sling may be unsafe and must be removed
from service immediately.
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 less
resistant to environmental damage. Conversely, wire rope with
a core that is made of a wire rope strand tends to have greater strength
and is more resistant to heat damage.
When selecting a wire rope sling to give the best service, there
are four characteristics to consider: strength, ability to withstand
fatigue (e.g., to bend without distortion), ability to withstand abrasive
wear, and ability to withstand abuse.
- Strength – Strength of wire
rope is a function of its size (e.g., diameter of the rope), grade,
and construction, and must be sufficient to accommodate the maximum
applied load.
- Fatigue (Bending without Failure)
– Fatigue failure of wire rope is caused by the development of small
cracks during small radius bends. The best means for preventing
fatigue failure of wire rope slings is to use blocking or padding
to increase the bend radius.
- Abrasive Wear – The ability
of wire rope to withstand abrasion is determined by the size and
number of the individual wires used to make up the rope.
Smaller wires bend more readily and offer greater flexibility, but
are less able to withstand abrasion. Larger wires are less
flexible, but withstand abrasion better.
- Abuse – Misuse or abuse of
wire rope slings will result in their failure long before any other
factor. Abuse can lead to serious structural damage, resulting
in kinks or bird caging. (In bird caging, the wire rope strands
are forcibly untwisted and become spread outwards.) To prevent
injuries to workers and prolong the life of the sling, strictly
adhered to safe and proper use of wire rope slings.
Wire rope slings must be visually inspected before use. Slings
with excessive broken wires, severe corrosion, localized wear, damage
to end-fittings (e.g., hooks, rings, links, or collars), or damage
to the rope structure (e.g., kinks, bird caging, distortion) must
be removed from service and discarded.
Fiber Rope and Synthetic Web
Fiber rope and synthetic web slings are used primarily for temporary
work, such as construction or painting, and are the best choice for
use on expensive loads, highly finished or fragile parts, and delicate
equipment.
Fiber rope slings deteriorate on contact with acids and caustics
and, therefore, must not be used around these substances. Fiber
rope slings that exhibit cuts, gouges, worn surface areas, brittle
or discolored fibers, melting, or charring must be discarded.
A buildup of powder-like sawdust on the inside of a fiber rope indicates
excessive internal wear and that the sling is unsafe. Finally,
if the rope fibers separate easily when scratched with a fingernail,
it indicates that the sling has suffered some kind of chemical damage
and should be discarded.
Synthetic web slings are commonly made of nylon, polypropylene, or
polyester and have the following properties in common:
- Strength - Depending
upon their size, synthetic web slings can handle loads of up to
300,000 pounds.
- Convenience and Safety - Synthetic
web slings adjust to the load contour and hold it with a tight,
non-slip grip.
- Load Protection - Unlike other
sling materials, synthetic web is less likely to mar, deface, or
scratch highly polished surfaces.
- Shock Absorbency - Regardless
of the construction material, shock loading (e.g., excessive speed,
rapid acceleration or deceleration) of slings should be minimized.
However, it should be noted that synthetic web slings can absorb
heavy shocks without damage.
- Temperature Resistance –
The lifting capacity of synthetic web is unaffected by temperatures
up to 180 degrees Fahrenheit.
- Economy and Long Life –
Synthetic web slings have a low initial cost and a long service
life. They are unaffected by mildew, rot, or bacteria, resist
some chemical action, and have excellent abrasion resistance.
Synthetic web slings must be inspected before use and should be removed
from service if found to have acid or caustic burns, melting or charring
of any part of the surface, snags, tears, or cuts, broken stitches,
distorted fittings, or wear or elongation beyond the manufacturer’s
specifications.
Safe Lifting Practices
Selection of the sling is only the first step in the rigging process.
The next step is learning how to safely use it to hold and move a
suspended load. There are four primary factors to consider when
lifting a load safely. These are:
- Load Size, Weight, and Center of Gravity
– The center of gravity of an object is that point at which
the entire weight may be considered to be concentrated. To
make a level lift, the hoist hook must be located directly above
this point. If the hook is too far to either side of the center
of gravity, dangerous tilting will result, causing unequal stress
in the sling legs. Load imbalances must be corrected immediately.
- Number of Legs and Angle with the Horizontal
– The smaller the angle between the sling legs and the horizontal,
the greater the stress on the individual sling legs. This
increased stress effectively decreases the weight that can be safely
lifted with any given sling size. Large (heavy) loads can be safely
moved by keeping this angle as large as possible and, when necessary,
distributing the weight of the load among more sling legs.
- Rated Capacity of the Sling –
The rated capacity of a sling varies depending upon the type of
material the sling is made of, the size of the sling, and the type
of hitch. Workers must know the capacity of the sling, and
can obtain this information through charts or tables available through
the manufacturer. The rated capacity of a sling must not be
exceeded, under any circumstances.
- History of Care and Use – Mishandling
and misuse of slings are the leading causes of sling failure.
Following the manufacturer’s recommendations for proper care and
use are essential for maximum sling service life and safety.
Training
Workers involved in hoisting and rigging operations should receive
training in the following:
- Sling and hitch types
- Sling capacity determination
- Equipment inspection, care, and maintenance
- Load weight and center of gravity determination
- Safe lifting techniques
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Roles and Responsibilities
Department
- Identify areas where hoisting and rigging techniques are used.
- Obtain necessary equipment.
- Establish procedures for inspection, care and maintenance of equipment.
- Ensure workers are trained.
Supervisor
- Know when hoisting and rigging techniques are necessary.
- Ensure equipment is properly maintained.
- Ensure workers use safe lifting techniques.
EHS
- Assist in identifying areas where hoisting and rigging techniques
are used.
- Provide worker training.
Individual
- Attend training.
- Know how to perform necessary equipment inspections.
- Know how to maintain equipment.
- Use safe lifting techniques.
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For More Information
Contact an EHS Safety
Engineer at 258-5294.
The following references are available through EHS:
- Sling Safety, U.S. Department of Labor (OSHA 3072)
- Slings, 29 CFR 1910.184
- Rigging Equipment for Material Handling, 29 CFR 1926.251
- Journeyman Rigger’s Reference Card
- W.E. Rossnagel, Handbook of Rigging, McGraw-Hill Book Company,
1964
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