The April 2021 issue of Chemical Engineering Progress includes a Process Safety Beacon article (not yet online) called “Recent Nitrogen Fatalities are a Vivid Reminder.” Nitrogen is not in any way toxic, and 79% of what we breathe is nitrogen. Deadly problems arise when the nitrogen displaces oxygen because our bodies cannot detect oxygen-deficient atmospheres.
The urgent need to breathe we feel when we hold our breaths long enough is not due to oxygen depletion but to carbon dioxide accumulation. A person in an oxygen-deficient atmosphere continues to exhale carbon dioxide so these atmospheres give little if any warning of danger. Would-be rescuers also die when they enter confined spaces (hence the need for confined space controls) without air or oxygen supplies.
“Georgia nitrogen deaths: Leak kills six at Gainesville poultry plant” is the incident cited in the Beacon article.
Valero Refinery Asphyxiation Incident
https://www.csb.gov/valero-refinery-asphyxiation-incident/ includes an excellent video. In this case, the victim was close to an opening from which nitrogen was coming out to displace oxygen.
Disclaimer; nothing in this blog constitutes engineering or OH&S advice.