With no British or European standards for skips, they are often made with the base plate extending beyond the end plates, producing a lip. If the tipping hooks snag on this lip instead of the engaging properly with the tipping bar, it is not necessarily visible from the operating position. The problem only becomes apparent when the angle of tipping is reached and the hooks are pushed off the lip. With the skip no longer restrained, it swings out over the back of the lorry. The momentum can lift the front of the lorry off the ground. The potential for the lorry to overbalance is further increased if the stabilisers have not been deployed correctly.
Although there is no established industry standard, the Container Handling Equipment Manufacturers (CHEM) Association has produced a technical standard TS14 "Standard Specification for Skip Containers", which the HSE advises manufacturers to refer to. In section 4.6.3 it states: "There must be no projection of the base plate in the area of the tipping hook engagement with the tipping bar thus preventing inadvertent hooking on the skip."
The HSE advises that skip operators should check all their skips and modify any that have protrusions that hooks could catch on. Driver-operators should perform a visual check to ensure the proper engagement of the hooks on the catch bar during tipping-out, to ensure no hook is just caught on the lip.
New skips should be manufactured without a protrusion that could give rise to false engagement with the tipping hooks, in line with the CHEM association standard TS14.