Contributed by Kevin Ball, Group Safety Manager - Smithbridge Group/Universal Cranes; Standards Australia Committee Member
Several of the most high-profile crane accidents of recent times have been those involving multiple cranes (also referred to as tandem lifts). When there are two or more cranes involved in an incident, the impact and outcome of the incident is often magnified. It figures – right? Double the equipment, double the personnel, double the consequences! The complex nature of lifts involving multiple mobile or crawler cranes makes them particularly hazardous.
It’s always important to properly plan any lift, but even more so when there are several cranes involved. Multiple crane lifts are among the most technically complex lifts to plan and execute. As an industry, we generally struggle with multiple crane lifts. The Australian Standards or international equivalents can be difficult to interpret. There is also often a layer of state or local guidelines to meet, which can be at odds with national standards. Guidelines differ between states and countries. Therefore, I must preface this article by saying it will not be possible for me to outline the specific requirements of your local region. I encourage you to do your own research in this regard, but I will attempt to provide some general things to be considered when planning and executing a multi-crane lift.
What is a multi-crane lift?
Put simply, multi-crane lifts are those which involve two or more cranes to support a load either with hooks attached directly to the load by slings, through shackles attached to pad eyes, or directly to an equaliser beam. Upending a vertical vessel using two cranes, one at the top end and a tailing crane on the bottom end is also considered a multi-crane lift.
Note, we are not talking about synchronised lifts here. As outlined in AS 2550.1, clause 1.4.13, a Synchronized motion means “Two or more crane motions under the control of a single command output with bi-directional communication so that the behaviour of one motion causes identical behaviour of the others”, which means they are electrically or mechanically connected – something that overhead and gantry cranes can achieve. However, it is not practical in the mobile crane world. Therefore, we are concentrating on most of the lifts that utilise mobile cranes.
Hazards of multi-crane lifts
We have come across many tragic incidents from all across the world that involved multiple cranes, a few of which are profiled in this issue of Lifting Matters. These incidents reveal critical areas of required understanding when planning a multi-crane lift:
Appropriate load planning for tandem lifts (more on that later)
Real-time information and communication for operators to ensure lift and travel is carried out in unison
Side loads/forces acting on the crane boom or unintended load distribution
Ground preparation and the compounding ground pressures if cranes are close to each other
Appropriate use of lift rigging or equaliser beams
This list is by no means exhaustive but does represent some of the key areas of consideration for tandem lifts.
Lift Planning – developing the Lift Plan
Lifts involving two or more cranes are complex operations requiring considerable skill and planning. As a result, tandem lifts must be planned and carried out under a competent person’s supervision.
As always, multiple lift operations must be preceded by a documented risk assessment that records known hazards and details the relevant controls. In other words, plan the works thoroughly well before the work commences.
The most important thing to note in your lift plan is that tandem lifts require you to make specific calculations about the required capacity of the cranes. You must understand the load share for each crane, the total weight of everything under the boom head (including the hook, rigging, spreader beams, equalising devices etc.) and then add a percentage factor to the total lift load. The percentage depends on the number of cranes involved in the lift, depicted as follows for each crane:
2 cranes – add 20% of the calculated share of the load
3 Cranes – add 33% of the calculated share of the load
4 or more cranes - add 50% of the calculated share of the load
The result of this calculation will provide the required capacities for each crane. In all options above, note the load may not always be even, thus load sharing must be taken into consideration. Alice Edwards from Crane Industry Council of Australia provides more detail on this, and I encourage you to take a look at her information at www.cica.com.au
Some of the other key components of the Lift Plan that must be taken into consideration are:
A site visit to understand the environment, overhead structures, ground conditions, access and site restrictions etc.
The lift study must be completed by competent personnel and include the crane selection criteria
Cranes should be of the same type (i.e. all telescopic mobile cranes). If not, the lift is deemed as a designed lift (see clause 6.27 of AS 2550.1)
The centre of gravity requires special attention, especially for complex structures and loads, when determining crane sizes and load sharing
Load sharing for rigid structures requires special attention, as the weight transfer when lifting or placing a rigid load is critical.
An analysis is required to understand the stiffness – strength of the load to identify the load shift effect if the cranes get out of sync.
Remember the load is everything below the boom head, so all hooks, rigging, spreader beams, load equalising devices etc. are to be included in the load calculations
Cranes must travel in the same direction
The communication method is critical to enable unison in movements – for example, using two-way radios, or when a clear line of sight is possible between all crane drives and the lift caller, then hands signals may suffice
On the Job
Aspects to keep in mind when on the job:
Review the Lift Plan with all people involved in the lift. If there are any changes to the Lift Plan ensure these are documented and all changes are communicated to all members of the lift team
For Australian based work, person(s) involved with any rigging work, hold a High-Risk Intermediate Rigging Licence (RI) as a minimum
Appoint a senior lift supervisor on-site to coordinate the lift who is the sole person in charge of the lift for clear accountability. The senior lift supervisor must hold a RI licence as a minimum.
Make sure the person calling the lift (i.e. in radio communications with all personnel involved in the lift) holds an intermediate rigging qualification as a minimum
Stay committed to your communications plan for the lift. It is critical that this is implemented and maintained as per the Lift Plan
Consider dropping the auxiliary hook around 4m, which then acts as a great plum bob to help you keep your hoist ropes vertical, thus preventing side loading on the boom
Take note of passover load transfers - where the load is lifted from one end of a truck as it moves forward or backwards for the other crane to pick up the other end of the load
Take note of tailing load transfers – where a load is rotated from the vertical to horizontal, or in reverse
Ensure there is only one motion at a time and in the same direction. For example:
a. If pick and carrying, lift the load, then move into position. Don’t do both and make sure all cranes are travelling in same the direction
b. Special note to crawler cranes, make sure the drive sprockets are to the rear of the travel, and the cabs are facing the same way.
c. Special care needs to be exercised when crabbing. If multiple cranes are crabbing, care must be exercised so that all are travelling in the same directions and do not exceed the loads detailed in the Lift Plan.
Perform the lift with extreme care and at low speeds.
Remember anyone can stop the lift. If something is not quite right, stop the lift and consult with the senior lift engineer.
Want to know more?
There are various guidelines and standards applicable to different states within Australia, nationally and internationally. We strongly recommend you research and understand the local applicable guidelines and standards. As an example, Western Australia has its own unique regulations, which are outlined in more detail by a local specialist later in this issue.
Here’s a starting point for guidelines on multi-crane lifts:
Australian Standard AS 2550.1 – Cranes, hoists and winches – Safe use, General Requirements – Section 6.28 Multiple Hoist or Crane Operation
Australian Standard AS 2550.5 - Cranes, hoists and winches – Safe use, Mobile cranes – Section 3 Selection
The Crane Association of New Zealand has published an excellent handbook called the Crane Safety manual and Section 9: Part D covers multi crane lifts in detail.