Sounds like a land mine to me.
Here is your explode once version...
;Artificial Intelligence Script
;Conjured Land Mine
desc = Land Mine
;Triggers
:state=0,plrwithinzone=1:plraddhealth=-100,sound=gamecore\flak\ww2\bazooka\explode.wav,state=1
;End of Script
..and here is the do it over again and again version...
;Artificial Intelligence Script
;Conjured Land Mine
desc = Land Mine
;Triggers
:state=0,plrwithinzone=1:plraddhealth=-100,sound=gamecore\flak\ww2\bazooka\explode.wav,state=1
:state=1,plrwithinzone=0:state=0
;End of Script