Ensuring load security, balance and stability when lifting is crucial for the safety of the equipment, the load itself and most importantly the personnel involved. As with any load handling situations, not paying attention to stability can lead to accidents, injuries or equipment damage.
When using lifting equipment, before the lift takes place, it is essential to ensure that when clear of the ground, the load will adopt the intended attitude and remain securely attached to the lifting appliance without overloading any of the lifting accessories. This means that the load must be both balanced and stable.
In terms of balance, the intention is for a load to remain level when clear of the ground in the majority of lifts. To achieve this, it is first necessary to position the hook of the lifting appliance vertically above the centre of gravity of the load. Once the load is connected, performing a test lift by raising the load a small distance from the ground, will help those carrying out the lift to confirm this, while keeping the risk of the load being unbalanced as low as possible.
The legs of the sling(s) should be distributed as evenly as is practicable according to the lifting points available. The angle at which the individual leg makes with the vertical affects the proportion of the load imposed upon it. All legs should therefore be, so far as is practicable, at a similar angle to provide equal loading. If the load tilts on lifting, the load in the sling legs will become unequal. This effect is particularly significant at small, inclined angles between sling legs.
With rigid loads lifted on two or more lifting points, consideration should be given to how many of the legs will bear the weight. This is because it may be that only two or three will take the majority of the weight, with the remaining legs providing a relatively small ‘balance force’ only. In such cases, larger capacity slings will be required. The use of load sensors will provide a means of monitoring individual leg loadings.
STABILITY
Stability means ‘resistance to toppling’. An object with a narrow base and a high centre of gravity will need less force to topple it than one with a wide base and a low centre of gravity.
As the height of the centre of gravity increases relative to the width of the base, a point will be reached where the object will fall over unless it is supported by external means. At this point, the object is regarded as being unstable and the greater the support required the more unstable it is. A similar situation exists with a suspended load. Forces that risk toppling the load such as wind, acceleration and braking will inevitably be present.
It is essential, therefore, when slinging a load to ensure that it is sufficiently stable to resist these toppling forces. A load will be inherently stable if the lifting sling is attached above the centre of gravity and properly disposed around it. Consult the LEEA COPSULE – Appendix 1.3 for guidance on when the sling is attached below the centre of gravity.
SLING EQUALIZERS
Slingers are increasingly using pulley blocks in the rigging arrangement to improve balance and ensure that the hook is positioned above the centre of gravity (COG). Although this can be beneficial where the COG may be difficult to estimate or when lifting multiple loads with a varying COG, the practice can introduce a number of risks that need to be properly planned and controlled, either by the rigging arrangement itself or through control and safe systems of work during the lifting operation.
Pulley blocks do not have a positive holding mechanism, so as the lifting machine hoists, they will naturally position themselves and the crane hook above the centre of gravity. However, this can only be safe if the position of the COG does not or cannot change during the lifting operation. For example, if during a lifting operation the load should collide or become snagged, the COG will shift. When used with a pulley block this can result in destabilisation, uncontrolled movement and potentially loss of the load. Similarly, lifting dynamics due to horizontal travel can cause the load to tip or swing. Again, this can cause the COG to shift and again cause potential loss of load control.
If considering the use of load equaliser, it is important to properly assess these factors and to reduce the associated risks to an acceptable minimum. This can be achieved through the rigging arrangement or by motion control devices or restraints.
When selecting sling equalisers use only those that have been designed specifically for the task. LEEA only supports the selection and use of equipment designed for the purpose.
If in any doubt with respect to load stability and balance when using pulley systems, LEEA recommends the use of other equipment that has been designed for the purpose, such as sling shortening devices.
As always, ensure that all lifting operations comply with relevant standards and regulations to maintain safety and consult the free to download LEEA COPSULE for guidance on best practice. Adhering to best practices for load security, balance and stability prevents accidents and damage during lifting operations and ensures the safety of personnel and equipment.’
