Avoiding unsafe rigging and lifting practices

Electrical Apparatus, Sep 2003 by Nailen, Richard L

No matter what type of work, items must be moved

IF YOU SEARCH THE WEB FOR LIFTING SAFETY, most of the "hits" will deal with avoiding back injuries. Important as that is in the workplace (back pain is said to be the leading cause of disability among American workers below the age of 45; see "How to get relief from lower back pain," EA May 1999), safe crane or hoist usage is also a serious concern. Government regulations and industry standards have much to say about proper selection and use of heavy lifting equipment.

Although many manufacturing operations don't require lifting heavy objects, such work is routine in every electrical apparatus service center.

Overhead bridge cranes do some of the lifting, particularly in the larger shops (see "Getting the proper lift from bridge crane technology," EA March 2000). Most heavy lifting, however, is done by small hoists of capacity from one to five tons. The chain hoist, suspended from a beam-and-column support, is the usual means of handling small motors, shafts, transformers, gearboxes, or switchgear components (Figure 1).

An overlooked hazard

Because they're relatively small, and their use not confined to specially trained operators, lifting devices of this sort can present a serious safety hazard that's all too often neglected. The danger lies in overlooking these essentials to hoisting safety:

* Condition of the lifting equipment.

* The proper attachment of that equipment to the load.

* Operator technique-safe handling of the load.

A load to be lifted is connected to the hoisting mechanism by one or more slings. Four types of sling are in common use. Most small hoists are equipped with chain slings, terminated in hooks (Figure 2). Durable, strong, and easy to handle, such slings are directly usable only for loads having eyes or bollards to which hooks can be attached (Figure 3). For other kinds of load, woven web slings (either with looped ends, or in a continuous loop) are wrapped around a hoisting hook to carry the load (Figure 4). They're the usual choice for lifting shafts or motor/generator rotor assemblies.

Offering the lowest cost per ton lifted, wire rope slings, terminated in either a hook or loop (eye), are the most common type for larger cranes (Figure 5). Less common are wire mesh or chain link slings, especially useful for lifting sharp-edged objects such as steel bars or plates.

Using slings properly involves three key words: "select," "inspect," "correct." Choose the right sling for the job, examine it to be sure it is in safe condition for use, and correctly attach it to the load to be lifted.

OSHA regulations 29 CFR 1910.184 offer extensive guidelines on selection and makeup of slings, such as:

* Hooks, links, or makeshift fasteners "formed from bolts, rods, etc., or other such fasteners," made up on shop premises or a job site, are not to be used.

* Knots shall not be used in lieu of splices.

* Protruding ends of strands or splices are to be covered or blunted.

* An eye splice in wire or manila rope must have at least three full tucks (four in synthetic fiber rope). All splices in rope slings shall be made in accordance with rope manufacturers' recommendations.

* Eyes in wire rope slings shall not be formed by clips or knots.

* Slings shall not be shortened with knots or bolts.

* Nylon web slings shall not be used in the presence of acids; polyester and polypropylene slings shall not be used in the presence of caustics.

A mandatory requirement in those regulations is that "Slings that are damaged or defective shall not be used." Obviously, following such a rule calls for frequent careful inspections. In the same regulation, and again in 29 CFR 1926.251 ("Rigging Equipment"), OSHA prescribes these inspection requirements:

"Each day before being used, the sling and all fastenings and attachments shall be inspected for damage or defect by a competent person designated by the employer. Additional inspections shall be performed during sling use, where service conditions warrant. Damaged or defective slings shall be immediately removed from service."

The OSHA regulations then dictate further "thorough periodic inspection" of alloy steel chain slings, based on the frequency and nature of sling use, but at least "once every 12 months." Such inspections, of which records must be kept, are to search out "wear, defective welds, deformation, and increase in length" (which obviously requires keeping track of measured chain length from one inspection to the next).

In synthetic slings, look for torn stitching, visible red threads from the interior of the fabric, broken or cut fibers, discoloration, and evidence of heat damage. In wire rope slings, causes for concern are security of fittings; rust, broken strands, kinks, and crushing or "bird-caging." "When in doubt, throw it out" is a good rule of thumb.

Inspection history

All slings should have a documented inspection history, and be labeled with a durable tag permanently attached. Remember that the annual inspection interval is a maximum. Hard usage, or the first appearance of trouble at daily inspection, will justify closer surveillance. For any "thorough" inspection, follow the recommendations of ASME B30.16 (see box) and of the hoist or sling manufacturer.