The test results indicated that aluminium dross is highly susceptible to a reaction with chlorides when moisture is present. The commodity produces gases when exposed to moisture and the build-up of gasses was considered the most likely cause of the container exploding.
The container was damaged beyond repair, and it is known that some lines and ports are refusing this commodity.
According to the UK Club, at the time the material is tested, before filling the container and shipment, the moisture level is such that the reaction with the commodity does not generate gas at enough rate to meet the UN hazard class 4 criteria. However, the reaction is slow, so after some time there is the possibility of an explosion. This may deform the side panels, but it is also able to ‘pop’ the container where it is joined to the frame.
Such materials are variable in both physical and chemical composition. While there may be evidence that at the time of testing there was not enough moisture to create a reaction which supplies sufficient hydrogen to meet the test criteria, it may not be known how the product has been stored or weather conditions before or at the time of being put in the cargo transport unit.
Because the commodity may be hygroscopic, working with the shippers to limit any time between testing and packing may help in ensuring that representative sampling and testing are improved. It may also be helpful to seek longer test periods for such materials before shipment. If the product meets the Class 4.3 criteria, it should be declared as UN 3170, noting the application of Special Provision 244 regarding ventilation and protection against water ingress throughout the intended journey.
The UK Club suggested that carriers work with shippers on any bookings for recycled aluminium carried in bulk in containers to gain more certainty about pre-shipment controls necessary to avoid excessive moisture content that may lead to a build-up of gasses while transit.