Metro 2035 Novel: Chapter 10 Question

Tagged with "Spoiler" but let me know if I should censor the text. Anyway, just finished chapter 10 "Red" and I'm a bit confused. Artyom's escaped Okhotny Ryad after the mine he set above the cells was detonated by Dietmer. However, if he was escorted by Red Line soldiers down the passage from Teatralnaya, how or when could he have installed it? And how would he have known where to install it so it would save his ass?

I flicked through the chapter and the one before again but didn't find a set-up to this. Did it miss something?