Ah! You are revealing the plot now Flying Pigs. OK, I'm game & I will speculate ...
maybe he stays inside that room to prevent the horribles escaping. We know he sealed the door preventing anyone entering, thus he heroically sacrifices himself (he's s gonner anyway) for the sake of mankind or maybe, he takes a big breath & sucks them all inside him .... um ... & then sets himself on fire destroying the bugs once & for all or maybe he just so happens to have his chemistry set in there and analyses the little beasties and finds a cure for the contamination