How to trigger explosions from a button?

[Col. Whitestone]

In

remnant_skyscraper_03

there is a button that triggers multiple explosions. After examining the prefab and the XML file I can see that the button triggers a sleeper volume, and the sleeper volume has a script that triggers a bunch of burning barrels.
I can see the trigger number on the burning barrels, but how do I assign a trigger number to a burning barrel? I haven't found anything in the Creative Menu that's helpful, and copying the barrel from

remnant_skyscraper_03

into my own prefab only copies the barrel, not the associated trigger.

How is the magic of this "demolition" accomplished?

 

[bdubyah]

Look at the barrels and hold E. You can set triggers on them like you can doors and whatnot.

 

[Col. Whitestone]

I could swear that I did that last night and it didn't work, but now it does. Thanks