The more complicated way:
add an eventhandler to every unit capable of placing a time bomb, for event "FIRED"
check to see if _this select 4 is "PipeBomb" (test this to get the exact case and spelling), if so, assign a variable to
nearestobject [_this select 0, _this select 4]
then check to see if that variable is in the detonation areas you want. If it isn't forget about it. If it is, wait for the object's position to go to 0,0,0 (=detonated. you only need a getpos _mypipebomb select 0 == 0), then throw a boolean (like area1 = true). Have a trigger when all booleans are true, and you're done. easy.