People panic while normal choking because their blood CO2 is rising and they can’t do anything about it. Being exposed to pure nitrogen doesn’t have that effect, it’s what makes working with nitrogen cannisters so dangerous. If they leak in a confined space and then displace all the normal 21% O2 room air with pure N2 the effect is that workers don’t even notice something is wrong. Instead they just calmly pass out and quickly die. It’s probably the easiest way to go.