Is it possible to stop an effect from playing?

I am trying to create a cool mission where you guide fire tankers on their run. If successful, the tanker will extinguish the flames.

I can pretty much do everything EXCEPT... put out the fires. LOL I don't know if it is possible to stop the effect from running. I don't see any way to make the effect respond to a trigger. I can trigger an explosion or a fire, but I cannot extinguish one.

Any ideas?

Just an update, I tried putting out the fires by using "Explode Unit" thinking that might virtually destroy them, but it did not work.