Rigging Defined
Rigging is both a noun – the equipment, and a verb – the action of designing and installing the equipment, in the preparation to move objects.
The word comes from rig, meaning to set up or to prepare, and includes precise work to make sure that this happens safely.
Here are some tips to promote safe rigging.
Determining weight
The capacities of rigging equipment are of little help if you don’t know what the weight of the load is that needs to be rigged and lifted.
In some cases it will be clear that the load is light enough and won’t exceed the capacity of your lifting and rigging equipment. However, there will be cases when you are uncertain whether the load can be lifted safely. This is when you need to establish the weight of the load and compare it to the indicated capacities of the lifting equipment, sling or slings, and rigging hardware.
Hitch based on load type
A rigging hitch is utlised to attach the sling to the load.
There are 3 basic types of hitches:
- Vertical hitch – One end is on the hook, while the other end is attached directly to the load. Use a tagline to prevent load rotation.
- Choker hitch – The sling passes through one end around the load, while the other end is placed on the hook. Load control is limited with only one sling rigged in a choker hitch. A choker hitch will never provide full 360 degree contact. For full contact use a Double Wrap Choke Hitch. The choke point should always be on the sling body, not on the sling eye, fitting, base of the eye or fitting, splice or tag.
- Basket hitch – The sling cradles the load while both eyes are attached overhead. As with the choker hitch, more than one sling may be necessary to help ensure load control.
It is vital that the hitch you choose will be the right one to safely support the load.
Understanding Angles and Tension on slings and hardware
An important thing to recall when working with sling tension is that the lower the angle between the load and the sling, the higher the tension on the sling.
Angles also escalate the tension on hardware. Hardware’s rated capacity decreases when it is pulled from any direction other than vertical.
This is vital information for proper sling and hardware selection and use.
The Right Sling for your load
There are a number of slings to choose from depending on your load. The slings used most often include synthetic web slings, synthetic round slings, wire rope slings, and alloy steel chain slings.
Questions to ask to determine the right sling for your load, are:
- Is the sling compatible with the hinge you are using?
- Does the design and composition of the sling make it sturdy enough to lift the load safely?
- Is the sling in good condition?
- Are the sling and rigging hardware compatible?
- Could the utilised rigging cause the sling to break or be damaged during the lift?
- Will the sling keep the load secure and stable throughout the process?
- Could the sling damage the load it is lifting?
The Right Hardware for the load
Choosing the right hardware for each rigging application is just as crucial as selecting the right slings. Hooks, shackles, eyebolts, and U-bolt wire rope clips are among the most often used rigging hardware in the industry.
While there are a considerable number of hardware types in these categories, the selection process is the same for hooks, shackles and eyebolts. They are rated based on straight, linear tension. Take note that the rated capacity changes when angles are involved, just as it does when using slings.
Inspect the Sling before use
Rigging slings wear out in time and become dangerous when they can no longer safely support their rated capacity. Sling inspections are imperative and should be carried out each time before used.
Any defective sling should be destroyed immediately in line with your company policy. If you find any hint that a part of a sling may be defective, or if you are not sure, take it out of service immediately and follow the procedure for handling defective equipment.
Inspect Rigging before use
Rigging hardware can wear out over time.
It can weaken and fracture from wear, misuse, and/or abuse. It becomes dangerous when it can no longer safely support its rated capacity. Hardware inspections are critical and should be performed before each use.
- Look for identification markings on the hardware. If the identification information is missing or illegible, the hardware is defective.
- Check your hardware carefully for cuts, gouges, corrosion, rust (other than surface rust), and pitting.
- Check each piece for melted areas, welding arc strikes, welding slag or other hot work markings.
- Pay special attention to the area of the hardware that bears most of the weight of the load.
- Carefully check hardware pieces that include pins. If the threads appear damaged or stripped, the pin does not thread/seat properly, or the pin appears stretched or damaged in any way, it is defective.
- Look for bent, twisted, stretched, cracked and broken areas on hardware.
Protect Slings from cuts and tears
Slings should be protected from sharp edges, especially synthetic web slings, which are most susceptible to cuts.
To protect the slings, use padded material interspersed between the sling and the edges. Make sure the material is strong enough to withstand the increased force of the sharp edges against it when the load is lifted.
Determine the loads centre of gravity
The load should be raised directly above the centre of gravity whenever possible.
The centre of gravity will be at the point that your load balances evenly in all directions. It is important to know the centre of gravity to make sure the load being lifted will have stability throughout the procedure.
Pay close attention to detail at Lift time
Leading up to and during the lift, there are details that need special attention. These are:
Testing the Load
When you have finished the rigging of the load, signal the operator to slowly lift it a few inches off the surface so that you can make adjustments when necessary.
- Make sure the sling stays in the right position as it tightens around the load.
- Watch for potential sling and hardware failures.
- Make sure the load is being raised straight up over its centre of gravity so the load will not sway or swing.
- Be aware of possible pinch points and keep your hands and body clear of the load.
- Also, be aware that the load could shift as it is lifted. Position yourself away from the area so that you will not be trapped or crushed if the load does shift. If you detect any issues, or if you are not sure whether the load can be lifted safely, signal the operator to set it back down and re-rig the load before testing it again.
Tag Lines
- Tag lines should be attached to the load to keep it from rotating and swinging out of control during the lift.
- Use the correct number of tag lines and properly trained tag line operators that are needed to control the load safely.
- Make sure that all tag line operators and anyone else in the lift area is wearing a hardhat.
Potential Obstruction
Consider where the load needs to be set down in relation to where it is situated before the lift.
- Look for any interference in the path of the moving load.
- Be vigilant of overhead power lines when watching for obstructions.
- If you see a potential obstruction, check with the operator to ensure that he is aware of it and has chosen a safe path for the load to travel.
Clear the area
- Be sure to clear the areas above and below the path that the load will travel as much as possible right before the lift.
- Ensure workers are aware of the signal given that indicates when a lift is about to commence. The operator can use the equipment’s air horn to make the signal or another type of signal can be established.
Communication with the Operator
- No matter what type of communication has been established between the rigger and the operator, it is a good idea for the rigger and operator to know the standard hand signals for lifting operations. That way if voice communication breaks down, they can still communicate effectively.
- If communication with the operator will be verbal, the rigger and the operator need to know the same standardized set of verbal signals.
- Regardless of what type of communication will take place, make certain that there is only one person who will communicate with the operator and that all other workers involved in the rigging/lifting process know who that person is.
To be able to carry out a quality rigging job, it is clear that your equipment needs to be properly checked regularly and the quality maintained.
If you need a professional team to carry out your rigging, why not take a look at our website and see some of the projects we have carried out.
If you want to get in touch with us, you can call us on +(27) 82 659 3315 or email us at admin@metalprojects.co.za.