The following day, under pressure of time, an attempt was made to lift the launcher beam, using four mobile cranes of varying capacity and performance. As anyone who has seen this second operation will appreciate, it provides a striking example of the potential dangers involved in lifting large loads using two or more lifting machines.
Although the New Delhi incident is an extreme example, it is not that uncommon for multiple lifting machines to be needed to lift a single load. Sometimes the weight of the load exceeds that of any single crane or hoist available. In other situations, it is the physical size rather than the weight that poses the problem, or perhaps a combination of the two. There are various possible scenarios, and in this article I will deal with some of those most likely to be encountered.
First, the legal situation. The UK’s Lifting Operations and Lifting Equipment Regulations (LOLER) implement the European Use of Work Equipment Directive. Regulation 8 deals with the organisation of lifting operations and opens with this statement:
“Every employer shall ensure that every lifting operation involving lifting equipment is:
(a) properly planned by a competent person;
(b) appropriately supervised; and
(c) carried out in a safe manner.”
The Approved Code of Practice (ACoP) which accompanies the Regulations states:
“Where two or more items of lifting equipment are used simultaneously to lift a load, where appropriate a written plan should be drawn up and applied to ensure safety.”
This is generally taken to mean that a written plan is always ‘appropriate’ whenever two or more cranes or other lifting machines need to be operated simultaneously to lift and lower the load. However, it generally doesn’t apply where a lifting machine, such as a lever hoist, is used as part of the slinging arrangement for a load suspended from a single lifting machine.
Whether operating within the jurisdiction of LOLER or not, good competent planning is essential, as is effective supervision and careful execution. I have illustrated in earlier articles how accidents often occur as a result of inadequate planning, the plan not being properly followed, or it being revised at short notice and without adequate thought when circumstances unexpectedly change.
Part 1 of BS 7121, the Code of Practice for the Safe Use of Cranes, includes guidance on multiple lifting and addresses the main factors to be considered at the planning stage.
A relatively simple example of a tandem lift is using two overhead cranes in a factory to lift a load in excess of either of them. If the load lends itself to being lifted by a single crane, the best option may be to use a suitable lifting beam suspended between the two cranes to provide a single lifting point. Effectively this is an upside down version of the normal use for a lifting beam which is to connect a single crane to two lifting points on a long load. The weight of the beam has to be taken into account but otherwise it has similar advantages. Provided the two cranes are kept the correct distance apart, their hoist ropes will be kept vertical and their share of the load will not vary.
Ideally the two cranes should be equally matched in terms of capacity, hoist speed and travel speeds. Some variation can be accommodated by this arrangement. For example, if the cranes are not of the same capacity, the position of the single lifting point can be offset from the centre of the beam to share the load in proportion to the SWL of each crane.
Similarly, the hoist speeds need not be matched exactly. If one is faster than the other, the beam will start to tilt. However, provided the design allows for some tilt and the operation is well supervised, the consequence will only be that the faster crane must stop occasionally to allow the slower to catch up. In fact, the facility for the beam to tilt, thereby allowing only one crane to hoist or lower at any particular time, reduces the speed in proportion to the leverage provided by the beam. This is a potential advantage if precise positioning is required.
To some extent the same is true of cross travel movement if the cross travel speeds are not exactly matched. Again, some extra precision can be gained by operating only one crane at a time. However, if the operation requires long travel movement, the speeds need to be matched. For regular operations of this nature involving long travel movement, it may be advantageous to have the facility to mechanically link the two cranes at the appropriate distance apart.
A variation on the single point lifting beam can be used where a long load is unable to support itself. The same arrangement can be used except that the load will be supported by the lifting beam at appropriate intervals along its length.
If the load is strong enough to support itself, then the slinging arrangement can connect each crane to the load independently. The position of the slings may be dictated by the lifting points on the load and thereby determine the share of the load on each crane. In short, there may be a heavy end and a light end to take account of. If the position of the slings is variable, the plan needs to identify where the slings should be placed. Calculations and measurement may suffice for some loads. However, if there is any doubt, load cells should be used to check the loading at the trial lift stage.
Remember also the gantry. This may not be load rated for both cranes loaded to that extent and in close proximity.
In all of these situations, the plan must take account of the possible variations which can occur in the share of the load taken by each crane during the course of the complete lifting operation so as to ensure that neither crane is overloaded.
Load limiters, if fitted, can prevent a crane from lifting a significant overload. However, during a lowering operation, the variation in load share can arise from movement of the other crane and be imposed externally rather than through the hoisting mechanism. A load limiter cannot prevent that. BS 7121-1 recommends that “when all the factors cannot be accurately evaluated, an appropriate down-rating should be applied to all cranes involved.” It goes on to say that “the down-rating might have to be 20% or more.”
The duty rating of the cranes must also be considered. Tandem lifts often have to be done slow enough to maintain adequate coordination between the two cranes. Cranes with a single hoist speed may be too fast, resulting in repeated starts or ‘inching’. Not good for the control panel or motors.
Cranes with dual speed can hoist slower but check the duty rating on slow speed. Some cranes have a much lower duty rating on the slow speed compared to the fast speed. The slow speed is intended only as an intermediate step up to full speed and running at slow speed for more than a few minutes can overheat the motor windings and burn them out.
Coordination of cranes also requires good communication between the person in charge and the crane drivers. In noisy environments, hand signals are generally used to communicate between slinger and crane driver. However, with a tandem lift, there will be at least three and very possibly more people involved. All need to be aware of the instructions from the supervisor, so other methods may be necessary.
Using more than two cranes to lift a load becomes a lot more complex and is not often undertaken in a factory crane context. It is actually quite a rare operation in any crane context and needs excellent planning to ensure the load is properly shared throughout the operation.
The second of the two incidents in New Delhi is a case in point – and a striking example of how not to do it. The beam in question was a rigid load and each crane was attached separately with no means to control the share of load other than each driver’s skill. Unfortunately they allowed the beam to make contact with the telescopic jib of the crane at one end causing the jib to snap, starting a chain reaction. The load was transferred to the next crane and its jib snapped. The crane after was stronger, but toppled over. Only the last crane survived, because that end of the beam was very close to the ground.
If the contact with the jib of the first crane had not occurred, they might have succeeded in lifting the beam. The total crane capacity seems to have been more than adequate. Assuming they were working, the load indicators in the cranes would have alerted the drivers to their share of the load and, with skill, allowed them to avoid overload. But how would they have lowered it? Lowering on any of the cranes would have passed load to the others, risking overload. They would have to lower to shed load back. You can see where that is heading. The plan, such as they had, was inevitably leading to the point of no return and disaster.
The safety of any lifting operation is heavily dependant upon a sound plan properly executed. If anyone needs further convincing, then a search of YouTube using the keywords ‘Aliva84 Capture’ is recommended.
About the author
Derrick Bailes is technical consultant (formerly chief executive) for the Lifting Equipment Engineers Association, 3 Osprey Court, Kingfisher Way, Hinchingbrooke Business Park, Huntingdon, PE29 6FN, tel: +44 (0)1480 432 801, fax: +44 (0)1480 436 314, email: info@leea.co.uk.
