Police across New York City have been warned that "detergent suicides" - which use household cleaners to create poisonous gas - can also kill cops and other first responders, the Daily News reports.
A recent internal order says people who kill themselves in this way often post warning signs, such as "Hydrogen Sulfide Suicide," so relatives and cops know to take precautions before entering the area.
Without a warning, entering the scene could have deadly results for an unsuspecting officer.
The deadly concoction produces hydrogen sulfide, a colorless flammable compound that smells like rotten eggs. It paralyzes the nervous system and kills in only a few breaths.