Final answer:
Danger signs should be placed at a sufficient distance in front and to the rear of a tank truck during offloading in an unsecure area to provide a warning to others.
Step-by-step explanation:
In the context of offloading in an unsecure area, danger signs should be placed at a distance that allows for safe operations. Although there is no specific measurement mentioned, it would be prudent to place danger signs far enough in front and to the rear of the tank truck to provide sufficient warning to other vehicles and pedestrians in the area. This distance should take into consideration the stopping distance of the tank truck, the visibility of the danger signs, and any local regulations or guidelines.