I'll probably be illustrated with a cut of sentence where she is talking and then a BOOM. Some thing like,
'We have to go, Mark. Listen to me, the valves have broken free, it's going to ex—"
[BOOM] At that very moment, a resounding explosion shook the ground, tearing their eardrums apart and causing the windows int he house beside them to break and fall to the ground below.
^^Something like that. You could write BOOM in, if you want. That is called onomatopoeia. I don't use it, unless it is a poem, because I think it makes my work look amateurish. Don't know why, just do. Also note that, instead o a dash to illustrate the cut of word, I used a 'longer dash'. <------- I don't know the name of it. This is made by using the Alt code, 0151. Press alt down with it and it appears (use the number pad to the extreme right of your keyboard).
Hope this answers your question.
Edit: I just found out the name. It is called a 'Em dash'. There is also something called an 'En dash' and the well-known hyphen. To learn more, visit the website in the source box.