Mixing bleach and ammonia creates chlorine gas. Chlorine gas is so powerful it was used as a chemical warfare agent in World War I. This stuff can kill you. If it doesn't kill you, it can cause pneumonia and make you extremely sick.
I've responded to victims of chlorine gas twice while working on an ambulance. In both cases, the victim cleaned just one room before becoming overwhelmed by the fumes. Also in both cases, my team and I did not know the reason we were responding and were surprised by the poisonous cloud.
In just a few seconds we were all complaining of coughs, scratchy throats and watery eyes. It felt hard to breathe within a couple of minutes. In both cases, we got the victims out of the houses in a hurry and finished our treatment outside in the fresh air.
Poison control centers nationwide got almost 215,000 calls about cleaning agents in 2006. It was the third most common complaint. This isn't a rare occurance.
Never mix bleach and ammonia. Period. End of story.
It's not always easy to recognize which cleaning products contain bleach or ammonia (there's always so much ethyl-methyl-this-and-that on the labels), so simply follow the rule of thumb to never to mix any cleaning products.
Source:
Bronstein AC, Spyker DA, et al. "2006 Annual Report of the American Association of Poison Control Centers' National Poison Data System (NPDS)." Clin Toxicol (Phila). Dec 2007
Reisz GR, Gammon RS. "Toxic pneumonitis from mixing household cleaners." Chest. Jan 1986
