At Chimes Crane Hire, we are committed to the safety of our clients and to the reduction of risk factors that may occur during our operations.
Risks associated with mobile crane operations
Mobile crane operations may present a risk of injury to persons from:
- A. structural failure
- B. crane overturning
- C. contact or collision with other plant and structures and
- D. falling objects.
Structural failure may include the failure of any crane component, such as the boom, jib, hydraulic rams or wire rope. A mobile crane may suffer structural failure if the crane has been overloaded in the structural area of its load chart. Structural failure may occur without warning.
A mobile crane is likely to overturn if the crane has been overloaded in the stability area of its load chart. This may be influenced by a number of factors including:
- A. poor ground conditions such as unstable ground
- B. failure to use or fully extend outriggers or stabilizers
- C. failure to level the crane
- D. high wind conditions
Contact or collision with other plant and structures may occur where sufficient clearances are not maintained between the mobile crane and other plant and structures, such as other cranes, buildings and overhead power-lines.
Falling objects may result from erecting and dismantling activities, and the way loads are secured during lifting operations. Falling objects may present a risk of injury to workers and members of the public.
Load charts, also called rated capacity charts, identify what a crane is able to lift safely. Load charts must be written in English and use metric units. Where the crane has one main load chart, this should be fixed in the operator’s cabin in a clearly visible location. Where the crane has numerous load charts (e.g. for different boom and fly jib configurations), the charts should be kept in a book, folder or envelope in the operator’s cabin.
Lifting should not take place unless the load charts are in the crane cabin. Although the crane’s load moment system may appear to be operating correctly, the load charts must be available to verify that the crane is not being overloaded.
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.
The lifting capacities specified on a load chart must never be exceeded, except during testing of the crane by a competent person under controlled conditions.
On some mobile cranes, there may be numerous load charts for differing boom and counterweight configurations. The load charts may be complex and include numerous conditions that must be complied with to ensure the crane can safely lift a load. Two important factors that are often overlooked when reading load charts are:
- A. The need to subtract the mass of the hook block and lifting slings from the capacity of the crane at the particular radius, unless otherwise noted on the load chart. For example, if the load chart states the crane can lift 20 tonnes at a given radius, but the hook and lifting gear have a combined mass of one tonne, the load to be lifted cannot be greater than 19 tonnes. This issue becomes critical for heavier hook blocks and lifting gear (e.g. spreader beams).
- B. The need to subtract the mass of the fly jib from the capacity of the main hook when lifting from the main hook on the main boom with a fly jib attached to the boom head, unless this is allowed for and noted on the load chart. Capacities of the main boom are generally based on the fly jib being removed. If this issue is ignored, the likelihood of the crane overturning can be very high.
Read the entire guideline document by clicking on the link below.