TT Talk - Costly pickings: the persistent accidental twin-lift problem
Many container terminals will be familiar with the potential problem of lifting two 20' containers from a ship's hold whilst the spreader is in 40' mode. The TT Club has seen many accidents over the years of this nature and advised operators to consider additional procedures or technology to assist in their prevention.The consequences of lifting two 20' containers from a ship's hold whilst the spreader is in 40' mode (which means that only the corner castings at the outside ends of the two containers are attached to the spreader) are almost as varied as the causes, but almost always will be disruptive and expensive to resolve. The TT Club has seen dozens of such incidents; when it raised the issue at the recent ICHCA Expert Panel (IEP) meeting it was immediately recognised as a frequent problem by the broad selection of operational safety experts from around the globe.ConsequencesThe two containers may break loose fully and fall back into the hold, damaging other containers and cargo, perhaps piercing the tank top with the resultant clean-up and potential environmental impact. In one case handled by the Club, declared dangerous goods spewed from one of the containers, seeping into the hold and contaminating foodstuffs in other units. It could as easily have been a flexitank loaded with, say, latex, which would be costly to cleanse. In addition, it is probable that the spreader will be written off and possible damage to hoist cables. It is likely that the ship will claim for damage to the cell guides and demurrage.The direct costs frequently exceed USD250,000 and many have resulted in claims for multiples of this.Even where the crane operator is alerted to the problem and halts the lift, operations will be severely disrupted whilst personnel are lowered into the hold to fit chains to at least the inner corner castings of the containers so that they can be lifted or lowered safely. This operation can be complex and require great ingenuity - one remediation took 42 hours to complete and that led to considerable uninsured cost for the operator, in addition to the ship's demurrage claim.CausesA selection of the causes that have been seen can be summarised as:
- crane operator error in not selecting a twin-lift mode or indeed in trying to lift with a fixed 40' spreader;
- twistlocks not engaged properly;
- difficulty in observing what is being lifted, exacerbated by the depth of the hold and height of gantry cranes for the latest generation of container ships;
- override or disabling of the sensor system, either by the operator or the maintenance department (sometimes without informing the operational staff!);
- the ship's manifest information being incorrect.
MitigationSpreaders designed for twin-lift will almost always have sensors installed to identify the offending gaps between the 20' containers (known as 'TTDS' or Twin Twenty Detection Systems), although a standard single lift 40' spreader may well not have any sensors installed. However, it is recognised that the current sensors are not foolproof. In particular, there are limitations in the sensing capability for open top units and tank containers, which can result in false alerts. Furthermore, there can be problems arising from a number of other factors, including adverse weather, such as snow and high wind. Also, the current sensors can be susceptible to certain colours on containers and reflections. The number of instances where it has transpired that the system has been overridden or disabled veers towards the need for clear and enforced procedures; as has frequently been said, technology should not be seen as replacing considered and applied procedural control.The Club and the ICHCA Expert Panel have raised the matter with the PEMA (Port Equipment Manufacturers Association) Safety Committee; a number of solutions are being investigated further to deal with the inconsistencies of the current sensors or find additional controls. Furthermore, consideration is being given to placing any override mechanism in the crane's machine room, with visual and audible warnings in the operator's cabin, to preclude casual or mistaken disabling of the system. As an alternative, one TT Club case handler mooted the possibility of marking the top of 20' units conspicuously to act as a visual alert to operators - the idea (nicknamed 'George Cross') was passed on to the relevant ISO Technical Committee for consideration.In the meantime, all operators should be alert to the reality that this happens all too frequently and will be costly when it does. Many operators have a policy of ensuring that sensors are installed on all spreaders (both fixed and twin-lift), but it is clear that procedures need to be in place as a safety net since there is not a single root cause except the timely vigilance of human observation and intervention.