A simple way is to:
1. Place your exploding barrel where you want it. The more the merrier, as one will make the others explode as well.
2. Set the barrels properties to:
Strength = 1
Physics Weight = 100
Physics Friction = 100
leave the rest at default
3. Take an item, such as the battery in sci-fi items, and set it inside the barrel so it can't be seen. Not all the way down on the ground, but midway down the barrel. Give it a name like "trigger".
4. Set the trigger properties to:
Name = trigger
Spawn at Start? = No
Maximum Spawn = 1
Strength = 500
Physics Weight = 6000
Physics Friction = 6000
leave the rest at default
5. Set your Trigger Zone and give it the following properties:
Main = plrinzoneactivateifused.fpi
If Used = trigger
Sound0 =
leave the rest at default
You can fine tune the numbers but basically, the trigger needs to be much stronger than the barrel. You can get creative with a number of barrels in different configurations.
Best.
