Going further into the safety standards to follow in the workplace by operators and users of mobile cranes, one might consider a few simple rules that in most cases ensure safe operation without risk to the integrity of individuals near the site of operation. Such simple concepts like: determination of stability of a mobile crane, ground bearing pressure calculation, exclusion zone, earthing/ electrical grounding, wind speed, load test procedure, useful life of the mobile crane, wire rope working conditions, net capacity after “load weight” deduction, etc., are crucial facts to take into consideration even before driving the crane to the job site.
In accordance with ISO 4305:2014, the determination of stability of mobile cranes and the ground bearing pressure calculation, are influenced by several conditions to be taken into consideration, assuming the crane is operating on a firm and level surface (up to 1 % gradient). Such conditions are basically related to the wind speed, the mobile crane weight and its rated capacity, specified by the manufacturer, as well as the inertia forces due to current mobile crane operations (slewing, hoisting, telescoping, etc.). The calculation of the ground bearing pressure and the compliance of the criteria for the mobile crane determination of stability are basic and previous conditions to the mobile crane load test procedure and consequently the safest preliminary steps to avoid any risk of overturning. In this sense, an assessment must be undertaken by the mobile crane operator for best determination of the ground stability, the weight and the capacity of the crane, the maximum bearing pressure under its outriggers, how the wind speed can affect the job there, the load work area and load laydown areas.
The exclusion zone around the mobile crane, lift, slew and travel areas must be established by the rigger/ dogman. A general “rule of thumb” when barricading the mobile crane exclusion zone is to encompass the size of the footprint of the load, plus 1 m outwards for every 2 m of lift height. The idea is to keep persons and other machines away from the vicinity of the lifting operation, especially while loads are raised and traversed off the ground and the wind speed makes the load swing back and forth. Furthermore, heavy weights should not be lifted over people working underneath and should not put any human life under risk, consequently. The load test procedure should always include references to such an useful life preserver, like the mobile crane exclusion zone.
Another important content of the load test procedure should be the existence of either overhead power lines or down shop conductors, around the mobile crane job site. Although an appropriate electrical earthing system shall be fitted to the mobile crane and shall be in use, it would help very much if such power lines can be avoided out of the exclusion zone. If not, the electrical earthing system provides the most direct route to the ground and thus, earthing can be the most useful way to save the operator’s life, in case of any part of the mobile crane, including the wire rope, gets in contact with power cables. It is important to distinguish the mobile crane electrical earthing from mobile crane grounding, which ensures the crane is balanced on uneven ground (determination of stability).
There are many other precautions to be considered but, all those related to the mobile crane components and parts useful life, are critical before leaving to the job site and are most surely not assumed in the load test procedure. All lifting equipment must have a current test date, certified for use and be inspected for damage prior to use by a competent person. Defective equipment must be isolated, tagged and removed from service: Discard any wire rope used on a mobile crane, when the visible number of broken wires in any length of rope diameter exceeds 5% of the total number of wires in the wire rope. Only safest accessories should be taken into consideration e.g., do not use a fibre rope slings if a suitable steel wire rope can be used; use an anemometer to check the wind speed; use always a certified LMI to verify the right weight capacity at any job radius; etc. The mobile crane useful life in accordance with its on road weight and its capacity, is undoubtedly a key point to verify periodically, in order to replace the equipment as soon as minor structural fatigue comes up and its refurbishment is not cost effective.