i think you mean activate the blueprint by collision with box. in the graph of the BP. you will be able to place an event. when the box is entered you get something like an enterbox event. when the event is called you check if it is playing the particle system, if its not playing particle system. then do nothing with the input. but when it is playing particle system. then afflict damage. or better maybe set this up to be done every tick. because the enterbox event will only fire once when the box is entered and once when the box is exited for the exitbox event. there should also be a function of some sort to check if there is something in the collision box. so when you fire the particle system. check if there is something in box. then loop that entire piece so it checks again and again until the particle system is stopped. then you activate the break on the loop so the loop will stop. obviously you will then need loop with break. if i am not much mistaken it is called a while loop with break or for while loop with break or something like that…