Full: Spellcaster lets a big one rip. Nearby opponents are knocked down and poisoned for 3...9 seconds. After 3 seconds, any allies still within the are of effect are also knocked down and poisoned for 3...9 seconds.
"Back blast area clear!" is a call used on modern battlefields to inform allies in the immediate vicinity of the intent to fire a rocket propelled grenade against a tank, since the back blast from such a rocket would be lethal to soldiers standing behind the launcher.
It is also used as a joke among military personnel. One will yell "Back-blast area clear!" before letting loose a loud fart.