In a restaurant, chlorine release from use of floor cleaner possibly mixed or contacted with window cleaner that contains ammonia.
https://local12.com/news/local/chemical-blamed-for-deadly-reaction-in-mass-restaurant-common-in-local-eateries
As per information in internet, the following link provides useful information about chemical reaction of bleach with ammonia and other chemicals, in which harmful gases are liberated.
https://www.organic-chemistry.org/chemicals/oxidations/sodiumhypochlorite.shtm