Mobile crane operations can be a risky task, especially when working with very heavy loads. That is why Lowveld Mobile Crane Hire takes extra safety measures to ensure that nobody gets hurt during a load shifting operation.
Load charts, also called rated capacity charts, identify what a crane is able to lift safely. These charts are kept in the operator's cabin at all times, and will be consulted to ensure that the crane does not get overloaded, with the risk of it toppling over.
The lifting capacity of a crane is limited by:
a. structural strength when the working radius is small; and
b. stability when the working radius is greater.
The load charts on most cranes have a bold line or shaded area dividing the chart into two segments. The divided segments shows the crane operator which capacities are limited by structural strength, and which are limited by stability.
Ratings above the line are based on structural strength, while the ratings below the line are based on the stability of the crane. If a crane is overloaded in the structural area of the load chart, a structural or mechanical component of the crane may fail. However, if the crane is overloaded in the stability area of the load chart, the crane may overturn.
Before starting the operation, the crane operator will examine the ground suface for the following:
a. the presence of water, including when it is mixed with the soil as mud, and where it is present under the surface (e.g. underground springs or streams);
b. the type of ground (e.g. clay, sand, rock or a mixture of these);
c. backfilled ground that was previously an excavation or trench;
d. cavities or penetrations in the ground that have been covered but still exist;
e. When a mobile crane is being set up, the crane operator can only make a decision based on the surface of the ground. Generally, rock provides the most stable supporting surface for a mobile crane. The operator will also avoid operating the crane on one location continiously, as compacting the ground over a period of time may cause the crane to overturn.
Timbers, pads and bog mats
The operator will more than often be using materials to distribute the mass of the mobile crane, and the suspended load to the ground. Lengths of timber (timbers) with rectangular cross sections are the most common form. However, timber and plastic pads are also provided for some cranes. For heavier lifts, bog mats, usually consisting of steel plate, are often used under mobile cranes. Timbers and pads are usually provided under outrigger feet, while bog mats may be used under the tracks of crawler cranes or where larger lifts are carried out.
Cranes on outriggers (or stabilisers)
The use of outriggers on mobile cranes helps to provide greater stability to the crane when lifting loads. Irrespective of the ground conditions, timbers or other means of distributing the load will always be placed under the outriggers. Outriggers are set according to the manufacturer's operating instructions for the specific type of mobile crane. The outriggers will also be used to help level the crane.
Radio equipment with a dedicated radio frequency will be used to optimize communication between the crane operator and dogger. This will prevent injury to people from dropped loads or collision with other plants and structures.
An effective means of communication is particularly important where:
a. the crane operator cannot see the load;
b. the crane operator cannot see the load’s landing area;
c. the crane operator cannot see the path of travel of the load or the crane;
d. the crane operator is not in a position to make an accurate judgement of distance;
e. it is possible for the crane to come into contact with overhead powerlines.
Where radio communication cannot be used, other forms of communication, such as hand signals and bell, buzzer and whistle signals will be used.
Another way to minimise the risk of injury from collision with other mobile plant and vehicles is to increase the visibility of mobile cranes. All vehicles, as well as outrigger beams and stabilizers in Lowveld Mobile Crane Hire's fleet are permanently marked with high visibility hazard striping (i.e. 'zebra striping').
All of Lowveld Mobile Crane Hire's cranes are fitted with counterweights, to ensure stability and prevent the crane from overturning.
Strong winds impose additional loads on a crane and affect the crane’s stability. A maximum permissible wind speed of 10 m/second (36 km/hour) is specified for mobile crane operation by some crane manufacturers. Where wind speeds exceed the maximum figure stated by the crane manufacturer for a specific mobile crane, crane operations will cease until it is safe to continue, and the crane will be placed out of service.
Limiting and Indicating Devices
Limiting and indicating devices have been fitted to all our mobile cranes. The purpose of limiting devices is to stop a specific crane motion before the crane moves out of its limits into an unsafe situation. Indicating devices are used to visually or audibly warn the crane operator that the crane may be approaching its set limits or an unsafe situation.
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