Safe stacking, storage and securing of containers
This domain tests stack planning and securing. A stack is a structure: every tier transmits load through the corner posts of the boxes below, so height, weight distribution, container condition and wind all matter.
Stacking rules
- Heavier containers go below lighter ones; the bottom tier carries the whole column.
- Align corner castings exactly; a box spanning unsupported space racks and can collapse.
- Never place a 20 ft box on top of a 40 ft box unless the position is designed to support it, and never mix configurations that leave corner castings unsupported.
- Damaged containers, boxes with distorted corner posts or bulging doors do not go into the bottom tier and are not stacked high.
- Stack height is set by the equipment, the pavement design and the terminal's stacking plan, not by what the machine can physically reach.
Securing
Tiers are connected with twistlocks or bridge fittings where the plan requires; base twistlocks secure the bottom tier on trailers or in exposed positions. Empty stacks are particularly vulnerable to wind and need reduced heights or lashing during strong wind and typhoon conditions.
Storage considerations
Segregate dangerous goods according to class and the terminal's DG rules; keep reefer machinery accessible; maintain fire access lanes and hydrant clearance; inspect stacks after impact, after storms and at defined intervals.
Worked example
A planner proposes placing a 32-tonne laden 40 ft box on top of a column of 10-tonne empties. The complaint is not just weight: the column's bottom boxes were never designed for that superimposed load, the centre of gravity is now high, and the stack's wind resistance is worse. The load is re-planned onto a stack with laden boxes below and the mixed stack rejected.
Traps that cost marks
- Assuming the crane can reach a height means the stack is safe at that height.
- Forgetting wind on tall empty stacks, especially before a typhoon.
- Stacking on a bottom box with damaged corner posts because it is out of sight.
- Overlooking fire access and DG segregation when adding rows.