LazyDriver:
Not sure about all tanker work, but I’ve just finished a spell delivering emulsion and these tanks could not be dropped with product on board as the weight would fracture the tank. Something about structural integrity.
I suspect it’s not that they can’t be dropped at all, but that the rough and tumble of constant dropping and swapping when full could ultimately take a toll on the lifetime of the tanker.
If there were genuine structural reasons why a tank couldn’t be decoupled at all when full, there would surely be far stronger safety constraints in place. The dynamic forces on the average British road also surely impose far greater strains on the tanker than the static load of supporting a short overhang.
There are also risks associated with constant dropping and swapping. A trailer can be dropped on its knees. There can be maneouvering bumps. It throws open the job to men who aren’t sufficiently responsible to be trusted to load and unload. It leads to poorly maintained trailers and worn parts, as each tank constantly changes hands.