As far as I’m aware NO2 will fill a pit. In the industry I work in NO2 leaks are serious threat because the engines that are worked on are in, what is essentially, a cage that you walk down into. I’ve not experienced it myself but heard from someone who experienced it firsthand as you just start feeling sleepy. I know now that it’s because our bodies are sensitive to asphyxiation from CO2 but not NO2, so as it displaces the oxygen in our lungs you just start getting woozy and tired.

All that being said; I am not an expert. Half this is information from diesel mechanics who work with it and the other half is from random science videos. So take it with a grain of salt.

It’s just heavier??