I see... you're wanting the explosions to appear in random locations as well as at random times?
Hmmmm.....
You'll need to set up a bunch of decal entities (for the "random locations"), script them to play the decal ONCE (and play a sound) when activated... now script a "controller" entity to activate 1 of the random decals at a random time interval. This entity should be always active, too, so either set that property on the entity or use a triggerzone or light for it.
Good luck!
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