Uh, if they flooded them with nitrogen I don't see why they would hold their breath. It wouldn't really make a difference anyway versus breathing nitrogen, which seems completely normal until you just kind of pass out.
A lot of people don't understand the difference between suffocation and oxygen deprivation, which is why so many people die from going down in holes or silos filled with heavy gasses. People expect to feel *something* if the air is not safe to breath, or they expect a choking sensation, or a suffocation sensation, or some kind of smell, but it doesn't work like that. Since your breathing reflex is triggered by CO2 accumulation, taking breaths of Nitrogen feels just dandy and refreshing as taking breaths of air.