It's one little overreach like this that makes it impossible for me to forward this to my microbioligist friend. Any chemical concentration that can kill you is "TOXIC." Air is 80% nitrogen. Flush it with more than that and you'll silently asphyxiate. Many telecom lines are pressurized with nitrogen, too, and if they leak into a small space--and you breathe it--you'll be dead before you know it. Plain old water is toxic too if you drink too much of it!
This could be part of a nefarious plot, but people can easily die from nitrogen poisoning. "The bends" are pretty ugly, too. Also nitrogen induced.
Nitrogen is not a "deadly" gas, and is a part of the air. An extreme over-abundance of nitrogen in one's immediate atmosphere would gradually cause shortness of breath, lightheadedness, and fatigue; conditions a biologist would certainly recognize. Additionally, a nitrogen leak in a laboratory's refrigerator system sufficient to fill the room with nitrogen would set off gas system alarms, and would be so massive as to cause complete failure of the refrigeration system, causing the temperature to rise, also setting off alarms that every one of these systems is equipped with as a standard safety procedure.